Treatment outcome of dogs with meticillin-resistant and meticillin-susceptible Staphylococcus pseudintermedius pyoderma

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1 Vet Dermatol 2012; 23: 361 e65 DOI: /j x Treatment outcome of dogs with meticillin-resistant and meticillin-susceptible Staphylococcus pseudintermedius pyoderma Jacqueline Bryan*, Linda A. Frank*, Barton W. Rohrbach, Laura J. Burgette*, Christine L. Cain* and David A. Bemis *Departments of Small Animal Clinical Sciences and Biochemical and Diagnostic Services, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA Correspondence: Jacqueline Bryan, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, 2407 River Drive, Knoxville, TN 37996, USA. Background The prevalence of meticillin- and multidrug-resistant Staphylococcus pseudintermedius (MRSP) in canine pyoderma has been increasing in recent years; thus, treatment of these cases has become challenging. Hypothesis Objectives To compare treatment outcome (clinical resolution and treatment duration), adverse effects of medication, and concurrent diseases and medications in dogs with meticillin-susceptible S. pseudintermedius (MSSP) and MRSP pyoderma. Animals Methods Medical records were reviewed retrospectively, and 123 MSSP and 93 MRSP clinical cases between January 2008 and April 2010 were included. Results In MSSP infections, cefalexin and cefpodoxime were the most commonly prescribed antimicrobials, accounting for 43.2 and 34.4% of cases, respectively. In MRSP infections, chloramphenicol and doxycycline were most commonly prescribed, accounting for 52.6 and 14.4% of cases, respectively. Adverse effects were reported in seven MSSP and 31 MRSP cases. The most commonly reported adverse effects were gastrointestinal, prompting antibiotic discontinuation in three MSSP and 20 MRSP cases. Chloramphenicol was associated with the highest incidence of adverse reactions (27 of 51 cases). Of 164 cases with follow up, 43 of 88 MSSP infections and 29 of 76 MRSP infections achieved complete clinical resolution at the first recheck examination. Three MSSP and seven MRSP cases failed to improve or resolve at subsequent visits assessed at 3 4 week intervals. Conclusions and clinical importance Results from this study showed that the majority of pyodermas resolved regardless of meticillin susceptibility. Although some cases of MRSP pyoderma took longer to treat, this is likely to be because of chronicity and not the organism. In addition, adverse effects were frequently associated with chloramphenicol administration. Introduction Staphylococcus pseudintermedius (formerly Staphylococcus intermedius 1,2 ) is regarded as the most frequent bacterial pathogen isolated from pyoderma in dogs. 3,4 It is commonly accepted that pyoderma is usually associated with underlying causes, such as allergies or endocrinopathies, that either disrupt the epidermal barrier and or alter the immune system. Identifying and controlling the underlying cause is critical for effective treatment and prevention of recurrence. 5 7 Meticillin-resistant bacterial infections in nonhuman animals in the USA have recently become more prevalent. 8,9 Meticillin-resistant S. pseudintermedius (MRSP) isolates are characterized by the presence of the meca gene that Accepted 22 December 2011 This study was published as an abstract from the North American Veterinary Dermatology Forum in Veterinary Dermatology 2011; 22: 294. Sources of Funding: This study was funded by the Center of Excellence, University of Tennessee, College of Veterinary Medicine, Knoxville, TN 37996, USA. Conflict of interest: No conflicts of interest have been declared. encodes the production of a low-affinity penicillin binding protein (PBP2a). 1 This altered protein confers resistance to all b-lactam antibiotics, including penicillins, cephalosporins and carbepenems. 9,10 Isolates of MRSP are frequently resistant to multiple classes of antibiotics, including fluoroquinolones, tetracyclines, macrolides and others. 11,12 With the exception of antibiotic usage, 13 risk factors associated with the development of MRSP infections have not been identified. With a recent increase in MRSP associated with canine pyoderma, treatment of these cases has become more challenging. Some isolates of MRSP are susceptible only to chloramphenicol, amikacin and rifampin, with chloramphenicol being the most frequently chosen for antimicrobial treatment Adverse effects from antibiotics occur infrequently but appear to occur more often when treating MRSP which, although unproven, may lead to treatment discontinuation and subsequent failure. The objective of this study was retrospectively to compare treatment outcome, as defined by clinical resolution and treatment duration, and adverse effects of medication observed in dogs with pyoderma caused by meticillinsusceptible S. pseudintermedius (MSSP) and MRSP. ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e

2 Bryan et al. A secondary aim of this study was to assess whether concurrent diseases or medications, at the time of culture, were associated with isolation of MRSP or affected treatment outcome. Materials and methods Selection of cases Results from aerobic culture and susceptibility tests of sterile swabs or tissue samples submitted to the bacteriology and mycology laboratory at the University of Tennessee Veterinary Medical Center (UTVMC) between January 2008 and April 2010 that yielded S. pseudintermedius were obtained. Medical records for these cases were subsequently reviewed retrospectively. Cases were included if they were diagnosed by the UTVMC Dermatology Service with either superficial and or deep pyoderma. Pyoderma was diagnosed in dogs with consistent clinical signs (papules, pustules, crusted papules, epidermal collarettes, nodules, draining tracts) and or cytological evidence. Information acquired and evaluated from the medical record included signalment (age, breed, sex and weight), classification of pyoderma (superficial and or deep), antimicrobial susceptibility of each isolate (including meticillin susceptibility), antimicrobials dispensed, adverse effects of antimicrobial therapy and whether treatment was discontinued, concurrent diseases and medications, outcome of treatment at the first visit and at final evaluation, and number of visits to outcome. The first recheck examination was chosen for consistency because patients did not always return for subsequent visits. Recheck examinations were evaluated at 3 4 week intervals. The outcome at final visit was defined as the last reported recheck evaluation recorded in the medical record in all patients with follow-up evaluations. Outcome of treatment was defined as clinical resolution, improvement or no improvement in clinical signs. Multiple episodes of pyoderma for the same dogs were counted as separate cases as long as the previous pyoderma had been assessed as resolved. Unresolved cases from which MSSP isolates were obtained initially and MRSP isolates were obtained in later episodes of pyoderma were included only as MRSP-infected cases. If cases were receiving antimicrobials prior to obtaining culture results, only the antimicrobials chosen based on in vitro susceptibility test results were included. Multiple antimicrobials for the same episode of pyoderma were included if the antimicrobials chosen were based on in vitro susceptibility test results. Bacterial isolation and identification Staphylococcus isolates were acquired by routine aerobic culture methods as previously described. 8,9 Coagulase-positive Staphylococcus species were identified via conventional biochemical tests, which were adapted from standard diagnostic tables. 17 In our experience and that of others, 18 primary testing by such means has correlated well with molecular-based identification of canine skin isolates. Tests included tube coagulase, Voges Proskauer (VP, Barritt method), and fermentation tests for maltose, lactose and trehalose. Staphylococcal isolates that were haemolytic on blood agar, tube coagulase negative, VP positive, maltose, trehalose and lactose fermentation negative, were confirmed as Staphylococcus schleiferi ssp. schleiferi with a commercial biochemical identification system (Crystal Gram Positive ID Kit; BBL, BD Diagnostic Systems, Sparks, MD, USA). Isolates not confirmed as S. schleiferi ssp. schleiferi were not further speciated and are therefore reported as coagulase-negative Staphylococcus spp. Antimicrobial susceptibility tests were performed by the reference disc diffusion method in accordance with the Clinical and Laboratory Standards Institute (CLSI) guidelines. 19,20 PCR analysis to identify the meca gene was performed on all cases of MRSP as previously described. 9,21 Statistical analysis All of the statistical analyses were carried out using a commercial software package (SAS, version 9.2 for Windows; SAS Institute Inc., Cary, NC, USA). Continuous variables (age, weight, antimicrobial dose and number of visits) were summarized using the mean ± 1 SD or the median and range depending on the distribution of data. Comparisons of categorical data were done with a chi-squared or Fisher s exact test depending on whether there was an expected cell size of less than five in the table. Doses of chloramphenicol associated with adverse effects were compared with doses not associated with adverse effects using a unpaired t-test procedure. Fit of the data to a normal distribution was evaluated with the test statistic of Shapiro Wilk. A P-value of <0.05 was considered significant in all tests. Results Signalment Of the 216 cases included in the study, 123 (56.9%) were identified as MSSP and 93 (43.1%) as MRSP. The mean ages for dogs with MSSP and MRSP pyoderma were 6.8 years (range years) and 6.8 years (range years), respectively. Of the total number of MSSP cases, 48 (39.0%) were spayed females, six (4.9%) intact females, 48 (39.0%) neutered males and 21 (17.1%) intact males. Of the total number of MRSP cases, 38 (40.9%) were spayed females, four (4.3%) intact females, 37 (39.8%) neutered males and 14 (15.0%) intact males. The most prevalent dog breeds included 16 (7.4%) Labrador retrievers, 15 (7.0%) golden retrievers, 13 (6.0%) cocker spaniels, 13 (6.0%) German shepherds, five (2.3%) miniature schnauzers and four (1.9%) boxers. Mixed breed dogs accounted for 21.8% of the total number of cases. Antimicrobial therapy and adverse effects Cases diagnosed with MSSP pyoderma were treated with cefalexin, cefpodoxime (Simplicef; Pfizer Animal Health, New York, NY, USA), clindamycin, amoxicillin clavulanic acid (Clavamox; Pfizer Animal Health), doxycycline, ormetoprim sulfamethoxazole (Primor; Pfizer Animal Health) or topical therapy alone (Table 1). Topical therapy consisted of chlorhexidine shampoo, solution and spray, chlorhexidine and ketoconazole shampoo, wipes and flush, miconazole and chlorhexidine shampoo, mupirocin ointment, and benzoyl peroxide shampoo (various commercial brands). Cases diagnosed with MRSP pyoderma were treated with chloramphenicol, doxycycline, clindamycin, minocycline, amikacin, amoxicillin clavulanic acid, marbofloxacin (Zeniquin; Pfizer Animal Health), enrofloxacin (Baytril; Bayer Animal Health LLC, Shawnee Mission, KS, USA), trimethoprim sulfamethoxazole or topical therapy alone (Table 2). Of the 216 total cases, there were 38 (17.6%) cases with reported adverse effects associated with antimicrobial therapy. Seven adverse effects were reported in cases of MSSP pyoderma and 31 in cases of MRSP pyoderma. Gastrointestinal adverse effects accounted for 29 of 38 of reported adverse effects. Other adverse effects reported included lethargy, shaking, increased liver enzymes, including alkaline phosphatase [ U L (normal range U L)], alanine transaminase [ U L (normal range U L)] and aspartate aminotransferase [62 86 U L (normal range 9 51 U L)], anaemia [haematocrit 34.4% (normal %)], thrombocytopenia [ ll (normal range to ll)], hearing loss, erythema, pruritus, panting, pemphigus-like drug reaction and aggression (Tables 1 and 2). 362 ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e65.

3 Treatment of MRSP pyoderma in dogs Table 1. Antibiotics used to treat 123 cases of meticillin-susceptible Staphylococcus pseudintermedius (MSSP) and their adverse effects Antimicrobial Number of cases* Mean weight (kg) Dose range (mg kg) Dosage interval (h) Number of adverse effects Adverse effects Cefalexin Vomiting, diarrhoea; erythema Cefpodoxime Diarrhoea, inappetance, lethargy; pemphigus-like drug reaction Clindamycin Vomiting, diarrhoea Amoxicillin clavulanic acid Erythema, pruritus Doxycycline Lethargy Ormetoprim sulfamethoxazole Topical treatment alone 9 0 *One case received multiple antimicrobials for a single episode of pyoderma. Includes chlorhexidine shampoo, solution and spray, chlorhexidine and ketoconazole shampoo, wipes and flush, miconazole and chlorhexidine shampoo, mupirocin ointment, and benzoyl peroxide shampoo. Six cases with focal pyoderma received a topical preparation as part of a study. Table 2. Antibiotics used to treat 93 cases of meticillin-resistant Staphylococcus pseudintermedius (MRSP) and their adverse effects Antimicrobial Number of cases* Mean weight (kg) Dose range (mg kg) Dosage interval (h) Number of adverse effects Adverse effects (n) Chloramphenicol Gastrointestinal signs (24), lethargy (7), shaking (4), increased liver enzymes (3), anaemia (1), panting (1) aggression (1) Doxycycline Diarrhoea Clindamycin Minocycline Amikacin Hearing loss Amoxicillin clavulanic acid Marbofloxacin Enrofloxacin Trimethoprim sulfamethoxazole Thrombocytopenia Topical treatment alone 28 0 *Several cases received multiple antimicrobials for a single episode of pyoderma; therefore, the total number of treatments exceeds the total number of MRSP cases. Gastrointestinal signs include vomiting, diarrhoea, weight loss, nausea, anorexia and decreased appetite. Includes chlorhexidine shampoo, solution and spray, chlorhexidine and ketoconazole shampoo, wipes and flush, miconazole and chlorhexidine shampoo, mupirocin ointment, and benzoyl peroxide shampoo. Eleven dogs in which initial treatment was topical; 17 dogs in which topical treatment alone was used after systemic treatment failures and or adverse effects of medication. Chloramphenicol was associated with the highest number of adverse effects, reported in 27 of 51 dogs receiving chloramphenicol. The mean dose of chloramphenicol with adverse effects was 50.7 mg kg (range mg kg), while the mean dose for cases without adverse effects was 47.9 mg kg (range mg kg), which was not statistically different (P = 0.145). Adverse effects were also reported in three of 18 dogs receiving doxycycline, two of 55 dogs receiving cefalexin, two of 43 dogs receiving cefpodoxime, and one dog each receiving amikacin, amoxicillin clavulanic acid, clindamycin and trimethroprim sulfamethoxazole. Adverse effects led to discontinuation of therapy in 23 of 38 dogs (three MSSP and 20 MRSP) with reported adverse reactions. Discontinuation of therapy occurred in 16 dogs receiving chloramphenicol, two dogs each receiving cefalexin and doxycycline, and one dog each receiving amikacin, amoxicillin clavulanic acid and trimethroprim sulfamethoxazole. Of the cases in which the antimicrobial was discontinued, 17 were switched to topical therapy alone, five had different antimicrobials dispensed, and one case did not have any alternative therapy dispensed owing to the owner s discontinuation of the systemic therapy. Outcome Follow-up information was available for 164 of 216 (75.9%) total cases (88 cases of MSSP pyoderma and 76 cases of MRSP pyoderma). When assessed at the first visit, 43 of 88 (48.9%) dogs with MSSP pyoderma had resolution of their clinical signs and 29 of 76 (38.2%) dogs with MRSP pyoderma had resolution of their clinical signs. These numbers were not statistically different (P = 0.17). When assessing final outcome of dogs with MSSP, 64 of 88 (72.7%) had resolution of their clinical signs, 21 of 88 (23.9%) had improvement of their clinical signs and three of 88 (3.4%) showed no evidence of improvement. The median number of visits for MSSP cases at final outcome was one, with a range of one to four visits. When assessing final outcome of dogs with MRSP pyoderma, 47 of 76 (61.8%) had resolution of their clinical signs, 22 of 76 (29.0%) had improvement of their clinical signs and seven of 76 (9.2%) showed no evidence of improvement. The median number of visits for MRSP cases at final outcome was also one, with a range of one to eight visits. Topical antimicrobial therapy alone was used in nine cases of MSSP pyoderma and 28 cases of MRSP ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e

4 Bryan et al. Table 3. Distribution of underlying diseases associated with cases* of MSSP and MRSP Meticillin status Allergies Hypothyroidism Cushing s disease Neoplasia Pemphigus foliaceus Other No concurrent disease identified MSSP (n = 123) MRSP (n = 93) *Some dogs had multiple diseases. Includes flea allergy, food allergy and atopy. Includes mast cell tumour, T- and B-cell lymphoma, epitheliotropic lymphoma, Sertoli cell tumour, thyroid carcinoma, histiocytic sarcoma, soft tissue sarcoma, pheochromocytoma, osteosarcoma, oral melanoma and haemangiosarcoma. Includes vasculitis, Ehlers Danlos syndrome, Addison s disease, immune-mediated polyarthropathy, megaoesophagus, hepatopathy, inflammatory bowel disease, diabetes mellitus, juvenile cellulitis, lymphangiectasia, demodicosis, mural folliculitis and lymphoplasmacytic rhinitis. pyoderma. Six MSSP cases were involved in a topical study for focal pyoderma and were not included in further assessment of topical therapy alone. 22 Of the remaining three cases, two resolved at assessment of final outcome, while one was lost to follow up. Of the 28 cases of MRSP, 11 cases were started on topical antimicrobial therapy alone, while 17 cases had topical therapy instituted as the sole treatment following adverse effects from systemic antibiotics and or treatment failure. At final outcome, 15 cases of MRSP resolved, four cases improved, five cases showed no evidence of improvement and four were lost to follow up. Regardless of meticillin susceptibility, 17 of 26 cases with follow up cleared on topical therapy alone, four cases improved and five showed no evidence of improvement when assessed at final outcome. Underlying diseases and immunosuppressive immunomodulatory therapies Diseases diagnosed concurrently with skin infections in this study included hypothyroidism, hyperadrenocorticism, allergic dermatitis, neoplasia, pemphigus foliaceus and diseases grouped into the other category, including vasculitis, Ehlers Danlos syndrome, Addison s disease, immune-mediated polyarthropathy, megaoesophagus, hepatopathy, inflammatory bowel disease, diabetes mellitus, juvenile cellulitis, lymphangiectasia, demodicosis, mural folliculitis and lymphoplasmacytic rhinitis. The distributions of these diseases for dogs with MSSP and MRSP pyoderma are shown in Table 3. There was a statistically significant association between allergic dermatitis and MSSP pyoderma (P = ). The association of the other disease category with the diagnosis of MRSP pyoderma approached significance (P = 0.07). While the association of pemphigus foliaceus with the diagnosis of MRSP pyoderma approached significance (P = 0.08), the numbers in this group were small (n = 3); therefore, this finding is not discussed further. Immunosuppressive immunomodulatory medications that dogs were receiving at the time of S. pseudintermedius isolation included corticosteroids, ciclosporin and chemotherapeutics. Chemotherapeutics used concurrently in pyoderma cases included carboplatin, adriamycin, azathioprine, vincristine and N-(2-chloroethyl)- N -cyclohexyl-n-nitrosourea (CCNU). The distributions of these medications for dogs with MSSP and MRSP pyoderma are shown in Table 4. There were no statistically significant associations of these medications with the diagnosis of MSSP or MRSP pyoderma. Table 4. Distribution of immunosuppressive immunomodulatory medication use associated with cases of MSSP and MRSP Methicillin status Corticosteroids Ciclosporin Chemotherapeutics* MSSP (n = 123) MRSP (n = 93) *Includes carboplatin, adriamycin, azathioprine, vincristine and N-(2-chloroethyl)-N -cyclohexyl-n-nitrosourea (CCNU). Two chemotherapeutic agents were used in one case. Fifteen cases on anti-inflammatory doses. Nine cases on anti-inflammatory doses. Lack of resolution at the first recheck examination was significantly associated with neoplasia, regardless of meticillin susceptibility (P = 0.04), with only one of 10 dogs with cancer having resolution of pyoderma. In addition, there was a significant association between corticosteroid use and lack of resolution at the first recheck examination regardless of meticillin susceptibility (P = 0.009), with only six of 28 dogs receiving corticosteroids having resolution of pyoderma. When this finding was further examined, there was a significant association between corticosteroid use in cases of MRSP pyoderma that did not resolve at the first recheck examination (P = 0.04), with only two of 14 cases having resolution of pyoderma. There was no significant association between the other diseases and medications with lack of resolution at the first recheck examination regardless of meticillin status. At the final outcome assessment, only 10 cases of pyoderma failed to resolve or improve (Table 5). This included three cases of MSSP and seven cases of MRSP. Discussion The prevalence of meticillin- and multidrug-resistant Staphylococcus spp. in dogs has been increasing in recent years. 12,21 In the present study, 43.1% of canine S. pseudintermedius pyoderma cases were associated with MRSP isolation. This high prevalence may reflect the fact that this study was performed at a referral institution, to which more challenging pyoderma cases may be referred or where there may be a selection bias for cases with chronic antibiotic use or lack of response to empirical therapy, because not all cases of pyoderma are routinely cultured. Isolation of MRSP from cultures submitted to the UTVMC had increased dramatically between 2000 and 2005, with a frequency of 15.6%. 8 This value increased to almost 30% in Reports of the prevalence of canine MRSP-associated infections vary worldwide and range from 7.4 to 68.1%, depending on the country. 2, ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e65.

5 Treatment of MRSP pyoderma in dogs Table 5. Demographics of the cases that had not improved or resolved when assessed at final outcome Case no. MSSP versus MRSP Deep versus superficial pyoderma Antibiotic dispensed Dose (mg kg) Dosage interval (h) Concurrent diseases Immunomodulatory medications 1 MSSP Deep Cefpodoxime Hypothyroidism (controlled on None supplementation) 2 MSSP Superficial Amoxicillin clavulanic acid None None 3 MSSP Both Cefalexin Inflammatory bowel disease None (controlled on metoclopramide) 4 MRSP Superficial Chloramphenicol Mural folliculitis Anti-inflammatory corticosteroids 5 MRSP Superficial Doxycycline Oral melanoma None 6 MRSP Superficial Doxycycline Allergies None 7 MRSP Deep Doxycycline 8 12 None None 8 MRSP Superficial Doxycycline None None 9 MRSP Superficial Chloramphenicol Vasculitis Immunosuppressive corticosteroids, ciclosporin Doxycycline MRSP Superficial Chloramphenicol 55 8 Allergies None In the present study, the majority of adverse effects resulting from systemic antimicrobials were associated with MRSP infections. This can probably be attributed to the frequent use of chloramphenicol to treat cases of MRSP infection, which resulted in 27 of 38 (71.1%) total reported adverse effects. Most adverse effects reported in the present study were gastrointestinal in origin and included vomiting, diarrhoea, decreased appetite, weight loss and anorexia. In the literature, chloramphenicol has been associated not only with gastrointestinal adverse effects, but also with bone marrow suppression and hepatotoxicity. 27,28 In the present study, complete blood counts and chemistry panels were seldom performed on dogs with adverse effects; however, increased liver enzymes were documented in three dogs and anaemia in one dog, supporting the occurrence but not the frequency of these adverse effects. Optic neuritis and peripheral neuropathy have been described in people 29,30 and anecdotally in animals. The owners of four patients on chloramphenicol did describe shaking as an adverse reaction. Owing to the retrospective nature of this study, it is impossible to know whether the shaking was a presentation of peripheral neuropathy or whether it resolved following discontinuation of chloramphenicol. Chloramphenicol was discontinued more often than other antibiotics that resulted in adverse effects and was withdrawn due to adverse effects in 16 of 51 of dogs receiving chloramphenicol. A future prospective study to identify the frequency of systemic adverse reactions secondary to chloramphenicol use in cases of canine MRSP pyoderma may provide a more accurate estimate of the true prevalence. Along with the increased use of chloramphenicol in dogs in recent years, amikacin and rifampin use have also increased secondary to the emergence of meticillin- and multidrug-resistant staphylococcal spp. Reported adverse effects of amikacin include nephrotoxicity, ototoxicity, hypersensitivity reactions, peripheral neuropathy and gastrointestinal signs. 27 In addition, rifampin use in both people and nonhuman animals has been reported to cause orange discolouration of bodily fluids, idiosyncratic hepatotoxicity which can result in death, thrombocytopenia, haemolytic anaemia, and gastrointestinal adverse effects. 27,31 33 Although rifampin use was not reported in cases included in the present study, amikacin was associated with ototoxicity in one of the two cases that received it. Owing to the increased incidence of meticillin- and multidrug-resistant staphylococcal spp., use of these potentially harmful systemic antibiotics is likely to become increasingly common. In the present study, topical antimicrobial therapy alone was used both initially and after adverse effects of treatment and treatment failures, especially in cases of MRSP pyoderma. Topical antimicrobial shampoo therapy has previously been shown to resolve 50% of cases with superficial pyoderma when used three times per week. 34 In the present study, the infections of 17 of 26 (65.4%) cases treated with topical antimicrobial therapy alone cleared. As the majority of cases treated with topical antimicrobial therapy alone were cases of MRSP, this higher rate of cure could be attributed to the more aggressive treatment regimen used, such as shampoo treatment every other day with twice daily chlorhexidine spray and excellent owner compliance when systemic options were unsatisfactory. Topical antimicrobial ingredients proven effective in cases of pyoderma include chlorhexidine, benzoyl peroxide, ethyl lactate, mupirocin, nisin and fusidic acid. 22,34 38 A recent study compared in vitro efficacy of shampoos containing antimicrobial ingredients, including chlorhexidine, benzoyl peroxide, ethyl lactate, chloroxylenol and acetic acid boric acid, with chlorhexidine-containing shampoos determined to be the most efficacious topical antibacterial therapy for cases of MSSP and MRSP pyoderma. 39 A secondary objective of the present study was to identify factors, such as underlying diseases or immunosuppressive immunomodulatory medications, which may be associated with the development of MRSP pyoderma. Allergic diseases have been associated with increased colonization of coagulase-positive staphylococci and the development of secondary pyoderma. 40,41 In the present study, when evaluating whether allergic disease was associated with meticillin susceptibility, there was a significant association between MSSP and allergic disease. Dogs with MRSP were only one-third as likely as ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e

6 Bryan et al. dogs with MSSP to have an allergic disease. The implications of this finding remain to be determined. The category of other diseases, which included vasculitis, Ehlers Danlos syndrome, Addison s disease, immune-mediated polyarthropathy, megaoesophagus, hepatopathy, inflammatory bowel disease, diabetes mellitus, juvenile cellulitis, lymphangiectasia, demodicosis, mural folliculitis and lymphoplasmacytic rhinitis, did have an association with the development of MRSP infection that approached statistical significance. While this group of diseases is quite varied, treatment of these conditions or the conditions themselves could have resulted in alterations in the immune system, leading to the development of a more resistant infection. 4 However, hyperadrenocorticism, hypothyroidism, neoplasia and immunosuppressive immunomodulatory medications, including corticosteroids, ciclosporin and chemotherapeutics, were not significantly associated with MSSP or MRSP pyoderma. Further investigation into possible associations between diseases and MRSP pyoderma was beyond the scope of this study in light of the small number of cases in this category. The association of underlying diseases and medications and lack of resolution of pyoderma regardless of meticillin status at the first recheck examination was also evaluated in the present study. Neoplasia was significantly associated with lack of resolution at the first visit. These patients are likely to have altered immune systems and, therefore, may not respond to antimicrobial therapy as effectively as patients with healthy immune systems. 4 There was also a statistically significant association between corticosteroid use and lack of resolution at the first recheck examination, regardless of meticillin susceptibility. When this was evaluated further, cases with MRSP pyoderma and concurrent corticosteroid use were significantly associated with lack of resolution at the first recheck examination. For those cases in which the corticosteroid dose was known, the majority were receiving anti-inflammatory doses. Corticosteroid use may promote infection secondary to systemic immunosuppression, and frequent treating of infections may predispose to selection of resistant organisms. 42,43 As there is overlap between the anti-inflammatory and immunosuppressive effects of corticosteroids, it is possible that dogs receiving anti-inflammatory doses of corticosteroids could still have immune system impairment, affecting the ability of the animal to clear infection. 44 Use of corticosteroids can also inhibit cytokine production and inflammatory responses, which are essential for fighting infections. 45 Furthermore, chronic corticosteroid use can result in an impaired skin barrier via skin, hair follicle and sebaceous gland atrophy, 43,44 which in turn may result in longer treatment duration. Nonetheless, this is an important finding because glucocorticoid use is commonplace in the management of many canine skin diseases. The majority of cases included in this study resolved regardless of meticillin susceptibility. These results imply that MRSP is not more virulent than MSSP, because resistant and susceptible strains responded to treatment in a similar manner. Although some cases of MRSP pyoderma took longer to treat, this may be less dependent on the causative bacterial strain than on the chronicity of infections, discontinuation of therapy secondary to adverse effects, owner noncompliance, and concurrent diseases and or medications. Investigating this further was beyond the scope of this study. As presented in Table 5, doxycycline failed to cure five dogs with pyoderma caused by MRSP. The doses of doxycycline for all five cases were within the therapeutic range, so it is unlikely that the dose was the major cause for treatment failure. The MRSP isolates from three of these dogs were resistant to tetracycline and either intermediate or susceptible to doxycycline. The MRSP isolates from the other two dogs were susceptible to tetracycline. Resistance to tetracyclines in S. pseudintermedius is commonly mediated by the tet(k) and tet(m) genes, with tet(k) conferring resistance to tetracycline but not doxycycline or minocycline, while tet(m) confers resistance to all three. With S. aureus, pre-incubation of the bacteria with tetracycline or doxycycline can induce resistance to doxycycline but not minocycline in tet(k)- positive organisms. 46,47 To date, the North American MRSP isolates all contain tet(m), 12 making doxycycline or any tetracycline a poor choice to treat MRSP in this region. Therefore, the most likely explanation for treatment failure in these five dogs was that their causative MRSP strain was resistant to doxycycline despite apparent susceptibility or intermediate susceptibility in vitro. It is likely that these cases would have had a better outcome if they were dispensed an alternative antibiotic. Two other cases that failed to resolve at final outcome assessment were receiving immunomodulatory medications which, as discussed earlier, may have contributed to the infection failing to respond to treatment. This study is limited by its retrospective nature. Many cases were not available for rechecks and were excluded from outcome analysis. There were only a limited number of patients available for specific associations (i.e. pemphigus foliaceus), limiting the ability to detect statistical significance among these factors. Some cases may have had underlying diseases or medications that were not present in the record or not identified during the study period. Lastly, whether or not the patient had received the prescribed antibiotics correctly could not be assessed. A future prospective study in which these variables are controlled may provide more accurate insight into prevalence of MSSP versus MRSP pyoderma and any associated conditions or medications. In conclusion, cases of MRSP pyoderma are commonly treated with antimicrobials, such as chloramphenicol, which can cause substantial adverse effects and result in discontinuation of therapy. Topical therapy alone was shown to be effective in clearing cases of pyoderma. Neoplasia and corticosteroid administration were significantly associated with lack of resolution of all S. pseudintermedius-mediated pyodermas at the first recheck examination. There was a significant association between MRSP pyoderma and corticosteroid use in cases that did not resolve at the first recheck examination. Inappropriate choice of antibiotic, as demonstrated by the five cases that received doxycycline and did not resolve, may have led to treatment failure. All of these factors need to be taken in account when treating cases of canine MRSP. 366 ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e65.

7 Treatment of MRSP pyoderma in dogs Acknowledgements The authors would like to thank Luke Watson for assistance with data entry. References 1. Bannoehr J, Zakour NL, Waller AS et al. Population genetic structure of the Staphylococcus intermedius group: insights into agr diversification and the emergence of methicillin-resistant strains. J Bacteriol 2007; 189: Sasaki T, Kikuchi K, Tanaka Y et al. Methicillin-resistant Staphylococcus pseudintermedius in a veterinary teaching hospital. J Clin Microbiol 2007; 45: Biberstein EL, Jang SS, Hirsh DC. Species distribution of coagulase-positive staphylococci in animals. J Clin Microbiol 1984; 19: Scott DW, Miller WH, Griffin CE. Bacterial skin diseases. In: Muller and Kirk s Small Animal Dermatology. 6th edition. Philadelphia, PA: WB Saunders Co., 2001: Fitzgerald JR. The Staphylococcus intermedius group of bacterial pathogens: species re-classification, pathogenesis and the emergence of methicillin resistance. Vet Dermatol 2009; 20: Lloyd DH. 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8 Bryan et al. 41. Fazakerley J, Nuttall T, Sales D et al. Staphylococcal colonization of mucosal and lesional skin sites in atopic and healthy dogs. Vet Dermatol 2009; 20: Pressler B. Immunosuppressive drugs: beyond glucocorticoids. Vet Med 2010; 105: Scott DW, Miller WH, Griffin CE. Dermatologic therapy. In: Muller and Kirk s Small Animal Dermatology. 6th edition. Philadelphia, PA: WB Saunders Co., 2001: Ettinger SJ, Feldman EC. Glucocorticoid therapy. In: Textbook of Veterinary Internal Medicine. 6th ed. Amsterdam: Elsevier Saunders, 2005: Rhen T, Cidlowski JA. Antiinflammatory action of glucocorticoids new mechanisms for old drugs. N Engl J Med 2005; 353: Schwartz BS, Graber CJ, Diep BA et al. Doxycycline, not minocycline, induces its own resistance in multidrug-resistant, community-associated methicillin-resistant Staphylococcus aureus clone USA 300. Clin Infect Dis 2009; 48: Trzcinski K, Cooper BS, Hryniewicz W et al. Expression of resistance to tetracyclines in strains of methicillin-resistant Staphylococcus aureus. J Antimicrob Chemother 2000; 45: Résumé Contexte La prévalence des Staphylococcus pseudintermedius (MRSP) résistants à la méticilline ou multirésistants dans les pyodermites canines est en augmentation ces dernières années; leur traitement est ainsi devenu un défi. Hypothèse Objectif Comparer les résultats des traitements (durée du traitement et de la guérison clinique), leurs effets secondaires, les maladies et traitements concomitants des chiens atteints de pyodermites à MRSP et à MSSP (Staphylococcus pseudintermedius sensible à la méticilline). Animaux Les dossiers médicaux ont été revus rétrospectivement et 123 cas de MSSP et 93 cas de MRSP ont été inclus entre janvier 2008 et avril Résultats Dans les infections liées à MSSP, la céphalexine et la cefpodroxime ont été les antimicrobiens les plus fréquemment prescrits, représentant respectivement 43.2% et 34.4% des cas. Dans les infections liées à MRSP, le chloramphénicol et la doxycycline étaient les plus fréquemment prescrits, correspondant respectivement à 52.6% et 14.4% des cas. Des effets secondaires ont été rapportés dans sept cas de MSSP et 31 cas de MRSP. Les effets secondaires les plus fréquemment observés étaient gastro-intestinaux, nécessitant un arrêt de l antibiothérapie dans 3 cas de MSSP et 20 cas de MRSP. Le chloramphénicol était associé avec la plus grande incidence d effets secondaires (27 patients sur 51). Parmi les 164 cas avec suivi, infections à MSSP et infections à MRSP ont atteint une guérison clinique complète au premier suivi clinique. Trois cas de MSSP et sept cas de MRSP n ont montré aucune amélioration au cours des visites de suivi à 3 ou 4 semaines d intervalle. Conclusions et importance clinique Les résultats de cette étude montrent que la majorité des pyodermites s est résolue indépendant de la susceptibilité à la méticilline. Bien que certains cas de pyodermites à MRSP prennent plus de temps à traiter, ceci semble être lié à leur chronicité et non à l organisme. En outre, les effets secondaires étaient fréquemment associésàl administration de chloramphénicol. Resumen Introducción Durante los últimos años se ha producido un incremento del número de aislamientos de Staphylococcus pseudintermedius resistente a meticilina y a múltiples fármacos (MRSP) en pioderma canina y por lo tanto el tratamiento de estos casos puede convertirse en algo problemático. Hipótesis objetivo Comparar resultados del tratamiento (resolución y duración clínica del tratamiento), efectos secundarios de la medicación, y enfermedades concurrentes y medicaciones en perros con S. pseudintermedius susceptible a meticilina (MSSP) y casos de pioderma producida por MRSP. Animales Se revisaron de forma retrospectiva los historiales clínicos, encontrándose 123 y 93 casos clínicos de MSSP y MRSP, respectivamente entre enero de 2008 y abril del 2010, que fueron incluidos en el estudio. Resultados En infecciones por MSSP, la cefalexina y la cefpodoxima fueron los antimicrobianos más comúnmente utilizados, con un total de 43,2% y 34,4% de casos, respectivamente. En infecciones por MRSP, el cloranfenicol y la doxiciclina fueron los antimicrobianos más frecuentemente utilizados, con un total de 52,6% y 14,4% de casos, respectivamente. Efectos adversos se observaron en siete infecciones por MSSP y 31 casos de infecciones por MRSP. Los efectos adversos más comúnmente descritos fueron gastrointestinales causando la interrupción del tratamiento en tres casos de infección por MSSP y en 20 casos de infección por MRSP. El cloranfenicol causó el mayor número de reacciones adversas (27 51 de los pacientes). De 164 casos con seguimiento clínico, infecciones por MSSP y infecciones por MRSP habían alcanzaron resolución clínica completa en la primera visita de revisión. Tres casos de infección por MSSP y siete casos de infección por MRSP no pudieron mejorar o resolver en las visitas siguientes realizadas cada tres a cuatro semanas. Conclusiones e importancia clínica Los resultados de este estudio demostraron que mayoría de las piodermas se resuelven con el tratamiento sin importar la susceptibilidad a meticilina. Aunque algunos casos de pioderma causada por MRSP necesitaron un tratamiento más prolongado, esto fue posiblemente debido a la cronicidad y no al organismo. Además, los efectos secundarios fueron asociados con frecuencia a la administración de cloranfenicol. Zusammenfassung Hintergrund Das Vorkommen von Methicillin und multi-resistenten Staphylococcus pseudintermedius (MRSP) bei der caninen Pyodermie hat in den letzten Jahren zugenommen; daher ist die Behandlung dieser Fälle zur Herausforderung geworden. 368 ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e65.

9 Treatment of MRSP pyoderma in dogs Hypothese Ziel Die Behandlungsergebnisse (klinische Abheilung und Dauer der Behandlung), Nebenwirkungen der Medikamente und begleitende Erkrankungen und Medikationen bei Hunden mit Methicillinempfänglichen Staphylococcus pseudintermedius (MSSP) und MRSP Pyodermie zu vergleichen. Tiere Die Krankengeschichten wurden retrospektiv durchgesehen und davon wurden für den Zeitraum zwischen Jänner 2008 und April klinische Fälle mit MSSP und 93 Fälle mit MRSP in der Studie inkludiert. Ergebnisse Bei MSSP Infektionen waren Cefalexin und Cefpodoxim bei 43,2% beziehungsweise bei 34,4% der Fälle die am häufigsten verschriebenen Antibiotika. Bei MRSP Infektionen wurden Chloramphenicol und Doxycyclin bei 52,6% beziehungsweise bei 14,4% der Fälle am häufigsten verschrieben. Nebenwirkungen wurden bei sieben MSSP und bei 31 MRSP Fällen beschrieben. Die am häufigsten beschriebenen Nebenwirkungen waren gastrointestinaler Natur, was bei drei MSSP und bei 20 MRSP Fällen zum Abbruch der Antibiotika Therapie führte. Bei Chloramphenicol traten die häufigsten Nebenwirkungen auf (27 von 51 Patienten). Von den 164 Fällen, bei denen ein Follow-up möglich war, bestand bei der ersten Kontrolluntersuchung bei 43 von 88 MSSP Infektionen und bei 29 der 76 MRSP Infektionen eine komplette klinische Abheilung. Drei MSSP und sieben MRSP Fälle zeigten bei nachfolgenden Untersuchungen (in Intervallen von 3-4 Wochen) keine Verbesserung bzw Abheilung. Zusammenfassung und klinische Bedeutung Die Ergebnisse dieser Studie zeigten, dass die Mehrheit der Pyodermien unabhängig von der Empfindlichkeit auf Methicillin abheilte. Die Tatsache, dass einige Fälle mit MRSP Pyodermie eine längere Behandlung benötigten, liegt vermutlich an der Chronizität der Erkrankung und nicht am auslösenden Organismus. Zusätzlich traten Nebenwirkungen am häufigsten bei der Verabreichung von Chloramphenicol auf.. ª 2012 ESVD and ACVD, Veterinary Dermatology, 23, 361 e65. e65