STREPTOCOCCI IN CONTEMPORARY INFECTIONS: IS S. DYSGALACTIAE DIFFERENT? Sample ES-02 (2018) was a simulated wound aspirate from a 57-year-old diabetic patient with a high fever (sepsis). Participants were requested to identify any potential pathogen and to perform antimicrobial susceptibility testing using the methods routinely applied by the laboratory. 1-6 The sample contained a Streptococcus dysgalactiae strain having a multidrug-resistant (MDR) pattern for a typically very susceptible β-hemolytic streptococcus species. This challenge specimen was distributed as an educational sample (ES-02, 2018) and grading of results was not performed. Identification responses (874 overall) of S. dysgalactiae (335; 38.3%), Streptococcus group G (339; 38.8%), β-hemolytic streptococcus (81; 9.3%), and Gram-positive organism or Streptococcus spp. (20; 2.3%) were the most common identifications considered acceptable (89.7% overall). Among unacceptable laboratory identifications, the most frequent errors were S. pyogenes (Group A Streptococcus) and S. agalactiae (Group B Streptococcus). These erroneous results accounted for 6.3% of responses. Table 1 lists the identification performance from five methods/commercial systems. The rank order of accuracy was (no. responses; % acceptable): MALDI-TOF (12; 100.0%) > Vitek 2 (372; 92.7%) > manual (87; 89.7%) > MicroScan (390; 87.7%) > BD Phoenix (11: 81.8%). S. pyogenes identification errors were most common in laboratories using the MicroScan product (30 sites with errors). Table 1. Performance accuracy of five methods/systems used to identify the S. dysgalactiae in sample ES-02 (2018). % of response by method/system (no.):ª Identification BD Phoenix Manual MALDI-TOF MicroScan Vitek 2 (11) (87) (12) (390) (372) S. dysgalactiae 72.7 6.9 91.7 31.5 51.1 Streptococcus Gr. G 9.1 59.7 8.3 43.3 31.7 β-hemolytic Streptococcus -- 19.5 -- 11.3 6.7 (% acceptable) (81.8) (89.7) (100.0) (87.7) (92.7) S. pyogenes (Gr. A) -- 2.3 -- 7.7 1.3 S. agalactiae (Gr. B) 18.2 2.3 -- 0.1 3.0 a. A total of 874 responses. American Proficiency Institute - 2018 2 nd Test Event 1
Organism Identification, Features and Taxonomy S. dysgalactiae is a pyogenic species that was first discovered as an animal pathogen. It is becoming more prevalent in the human host with a wide-spread disease spectrum similar to that of S. pyogenes. S. dysgalactiae isolated from humans are predominantly β-hemolytic streptococci that form >0.5 mm colonies after 24 hours of incubation (35-37 C) on blood agar media. Streptococci are also facultative anaerobes where growth may be enhanced in 5% CO2 or anaerobic environments. 7 Common types of infection by S. dysgalactiae range from pharyngitis and superficial skin infections to more invasive infections such as osteomyelitis, intra-abdominal and epidural abscesses, endocarditis, necrotizing fasciitis, and streptococcal toxic shock-like syndromes. 8 S. dysgalactiae is a heterogenous species that was first categorized into two subspecies in 1996. These subspecies, S. dysgalactiae subsp. equisimilis (SDSE) and S. dysgalactiae subsp. dysgalactiae (SDSD), were differentiated solely on their isolation source, i.e., human vs. animal, respectively. In 1998, further distinction was made classifying all human-isolated large colony-forming beta-hemolytic with Lancefield Group C or G antigen strains as SDSE, and alpha or non-hemolytic group C streptococci as SDSD. There are exceptions in the literature against the current classification with SDSE strains being detected containing Lancefield A antigens and SDSE strains that are non-hemolytic. Additionally, there are documented cases of SDSD causing human infections and SDSE causing animal infections. Due to these taxonomic inconsistencies, genetic characterization could have a role in more accurate division of the subspecies. 7,9 Commercial identification products (Vitek 2, MicroScan, etc.) generally perform well for commonly isolated streptococci, but lack accuracy identifying within the viridans group. 7,8,10 MALDI-TOF methodology also has limitations, which still makes identifying S. dysgalactiae to the species level challenging. Discriminating between S. dysgalactiae, S. pyogenes, and other beta-hemolytic streptococcus like S. canis (animal pathogen) can be difficult with MALDI-TOF methods. 11,12 A positive bacitracin American Proficiency Institute - 2018 2 nd Test Event 2
susceptibility or PYR (pyrrolidonyl aminopeptidase) test can discriminate S. pyogenes from S. dysgalactiae, which is negative for both phenotypic tests. 7 Antimicrobial Susceptibility Testing (Ungraded) Participants were instructed to perform antimicrobial susceptibility testing (AST) on this less commonly isolated β-hemolytic streptococcus spp. (S. dysgalactiae) having elevated MIC values to antimicrobials in several drug classes. The strain was selected to challenge proper identification of an evolving pathogen group with changing taxonomy and emerging resistances. The reference laboratory AST was conducted in triplicate by CLSI/ISO broth microdilution method 1 and susceptibility categorical interpretations were assigned based on CLSI document M100Ed28E (2018). 3 The reference laboratory reported MIC results for 38 agents (Table 2), and results for 17 drugs were received from participants in sufficient numbers (>10 responses) to allow comment on AST practices and to determine accuracy (Table 3). Consensus grading criteria ( 80% categorical agreement among reporting laboratories by method [disk diffusion and MIC]) are presented in Table 3. Among the analyzed results, dominantly acceptable test accuracy was observed, although grading was not applied to participant results. The DD method categorizations from approximately 37 laboratories for 17 antimicrobials (250 results) are summarized in Table 3. Only 13 drugs could be tabulated, as three drugs (moxifloxacin, tigecycline, and TMP-SMX) do not have DD zone diameter breakpoint criteria in the CLSI document 3 and daptomycin does not have a reliable DD method (no values reported). The performance accuracy among the 13 antimicrobials ranged from 53.8% (tetracycline) to 100.0% (eight drugs). The tetracycline accuracy was compromised by the organism harboring a resistance gene and producing a dominant reference "Intermediate" level of potency (MIC, 4 µg/ml). Two susceptibility categories were assigned to tetracycline allowing consensus and comparison to MIC methods. Excluding moxifloxacin, tigecycline, TMP-SMX, and tetracycline, the DD accuracy was 98.3% overall. American Proficiency Institute - 2018 2 nd Test Event 3
Table 2. List of expected susceptibility testing MIC and categorical interpretation results from reference methods for the S. dysgalactiae strain found in ES-02 (2018). Antimicrobial agents listed by CLSI susceptibility category (MIC in µg/ml) a Susceptible Resistant or Non- Susceptible No Criteria b Amoxicillin-Clavulanate ( 0.03/0.015) Azithromycin (>4) Ceftazidime-Avibactam ( 0.25/4) Ampicillin ( 0.25) Clarithromycin (>16) Ceftazidime (0.25) Ampicillin-Sulbactam ( 0.5/0.25) Clindamycin (>2) Ceftobiprole (0.015) c Cefepime (0.03) Erythromycin (>16) Ceftolozane-Tazobactam (0.25/4) Ceftaroline ( 0.008) Levofloxacin (>4) Ciprofloxacin (>4) Ceftriaxone ( 0.06) Tetracycline (4) Delafloxacin (0.12) Chloramphenicol (4) Doripenem ( 0.06) Dalbavancin (0.015) Lefamulin (0.03) c Daptomycin ( 0.06) Meropenem-Vaborbactam (0.03/4) Imipenem ( 0.12) Moxifloxacin (2) Linezolid (1) Omadacycline (0.5) c Meropenem (0.03) Piperacillin-Tazobactam (0.06/4) Oritavancin (0.12) Tigecycline (0.25) Penicillin (0.03) TMP/SMX ( 0.12) d Quinupristin-Dalfopristin (0.5) Tedizolid (0.25) Telavancin (0.015) Vancomycin (0.25) a. Susceptibility categories determined by CLSI M100-S28 (2018), where available. b. FDA-approved and investigational agents without published CLSI table breakpoint criteria or available surrogate drug to predict susceptibility category (see text). c. Examples of investigational drugs demonstrating in vitro potency against this Gram-positive pathogen. d. TMP/SMX = trimethoprim-sulfamethoxazole. American Proficiency Institute - 2018 2 nd Test Event 4
Table 3. Participant AST performance for 17 selected agents tested by disk agar diffusion (DD) or quantitative MIC methods when applied to the S. dysgalactiae ES-02 (2018). Only agents with 10 responses for either test method were tabulated. Satisfactory DD MIC Antimicrobial susceptibility category No. % a No. % a Ampicillin Susceptible 15 100.0 288 99.3 Azithromycin Resistant 4 100.0 84 98.8 Cefepime Susceptible 3 100.0 151 99.3 Cefotaxime Susceptible 8 100.0 234 100.0 Ceftriaxone Susceptible 28 100.0 297 99.3 Chloramphenicol Susceptible 6 66.7 80 92.5 Clindamycin Resistant 32 96.9 334 98.8 Daptomycin Susceptible 0 -- 11 100.0 Erythromycin Resistant 36 97.2 330 98.2 Levofloxacin Resistant 25 96.0 280 97.5 Linezolid Susceptible 4 100.0 105 100.0 Moxifloxacin b -- 0 -- 33 -- Penicillin Susceptible 35 100.0 321 99.7 Tetracycline c Susceptible-Intermediate 13 53.8 171 93.6 Tigecycline b -- 1 -- 33 -- TMP-SMX b -- 3 -- 36 -- Vancomycin Susceptible 37 100.0 342 99.7 a. Percentage of categorical responses considered correct by consensus among participant results and/or reference laboratory values; see Table 2. b. Antimicrobial having no interpretive criteria published in the CLSI M100Ed28E (2018) document. Categorical report interpretations would be considered inappropriate. c. Consensus categorization was achieved using two categories. A total of 3,130 MIC test-based categorical results are found in Table 3. Excellent accuracy for these methods was also observed with correct results recorded for 92.5% (chloramphenicol) to 100.0% (four drugs) of responses. The overall rate of accurate categorization by MIC tests was 98.6%. In addition to the 17 drugs listed in Table 3, category results for 23 other antimicrobials (73 total responses) were received, ranging from one to eight results per agent tested. Of these 23 antimicrobials, 11 did not have interpretive criteria in the CLSI tables: 3 amikacin, aztreonam, cefixime, cefoxitin, ceftazidime, ciprofloxacin, gentamicin, oxacillin, piperacillin-tazobactam, rifampin, and tobramycin (28 results). This testing and category reporting practice is discouraged, and results could misguide infection American Proficiency Institute - 2018 2 nd Test Event 5
therapies. Six other agents were reported in small numbers with susceptibility inferred by a surrogate marker drug in the same class (amoxicillin-clavulanic acid, ampicillin-sulbactam, cefazolin, doxycycline, imipenem, and meropenem). These 28 results represent an acceptable practice. Finally, two drugs (clarithromycin, quinupristin-dalfopristin) had published interpretive criteria, but were reported in small numbers (eight and three responses, respectively); all results were correct. Two additional participants tested trimethoprim susceptibility but did so without interpretive criteria 3 for an antimicrobial indicated primarily for urinary tract infections, not for a serious SSSI and sepsis as noted for this challenge. Overall across the DD and MIC method results, excellent identification and AST performance was observed. Emerging Resistances and Molecular Epidemiology Among β-hemolytic Streptococci The prevalence of the macrolide lincosamide streptogramin B (MLSB) phenotype among β-hemolytic streptococci (BHS) remains relatively low. In a recent study that evaluated the prevalence of this phenotype among European isolates, a total of 9.8 and 8.1% of BHS displayed macrolide (M; resistance to macrolide only) and constitutive MLSB (cmlsb) phenotypes, respectively. 13 In addition, 6.4% of BHS isolates demonstrated a MDR phenotype, which was characterized by resistance to at least three classes of drugs. In this same study, occurrences of M, cmlsb, and MDR phenotypes in S. dysgalactiae were 14.0, 5.6, and 1.0%, respectively, while resistance to fluoroquinolones accounted for 2.8%. 13 In a multicenter surveillance study in the United States, resistance for penicillins in S. dysgalactiae was not detected, whereas resistance to macrolides, lincosamides, fluoroquinolones, and tetracyclines was observed in 29, 4, 1, and 58% of isolates, respectively. 14 Overall, BHS isolates remain susceptible to penicillins and other β-lactam (e.g., ceftaroline, ceftriaxone, meropenem), fluoroquinolone, and glycopeptide agents; however, some differences in susceptibility rates are observed among the main BHS species recovered from human clinical samples. The rate for the cmlsb resistance phenotype among S. agalactiae (29.3%) tends to be higher than those observed for S. dysgalactiae (11.4%) and S. pyogenes (8.5%). 15 Macrolide non-susceptibility rates also follow a American Proficiency Institute - 2018 2 nd Test Event 6
similar profile (S. agalactiae, 47.6%; S. dysgalactiae, 31.1%; and S. pyogenes, 14.8%), as do tetracycline rates (S. agalactiae, 82.6%; S. dysgalactiae, 38.2%; and S. pyogenes, 19.8%). 15 In contrast, the newer lipoglycopeptide agent oritavancin shows slightly higher (2-fold) susceptible range MIC results when tested against S. dysgalactiae (MIC50/90, 0.06/0.25 µg/ml) when compared to S. pyogenes and S. agalactiae (MIC50/90, 0.03/0.12 µg/ml for both). 13 The S. dysgalactiae isolate found in ES-02 (2018) demonstrated a cmlsb phenotype with elevated MIC results for erythromycin (>16 µg/ml) and clindamycin (>2 µg/ml). However, the additional resistance phenotypes noted for fluoroquinolones (levofloxacin and ciprofloxacin MIC, >4 µg/ml) and tetracycline (MIC, 4 µg/ml; intermediate and resistant by CLSI and EUCAST, respectively) would necessitate this strain being characterized as an MDR isolate. 3,4 This challenge strain had its genome sequenced for screening of known resistance determinants to various classes of antimicrobial agents and the presence of mutations in the quinolone resistance-determining region (QRDR). Sequencing analysis showed that the cmlsb and tetracycline resistance phenotypes were caused by the presence of erm(a) and tet(m), respectively. Although a series of tetracycline genes have been observed in streptococci, 16 tet(m) appears to be more commonly detected in S. dysgalactiae. 17-20 In addition, the substitutions of Ser81Phe in GyrA and Ser79Phe in ParC were found in the QRDR region, explaining the elevated MIC values for the fluoroquinolones. Moreover, this S. dysgalactiae isolate exhibited a delafloxacin MIC value of 0.12 µg/ml, which would be defined as non-susceptible if the FDA-approved breakpoints for S. pyogenes and S. agalactiae (i.e., 0.06 µg/ml) were applied to this species. 21 This recently available fluoroquinolone is routinely and significantly more potent than levofloxacin, moxifloxacin or ciprofloxacin, and active against many strains having QRDR mutations. 9 American Proficiency Institute - 2018 2 nd Test Event 7
Treatment of S. dysgalactiae Infections Individuals with diabetes can have any infection that affects the general patient population. However, people with diabetes are at increased risk for a variety of specific infectious complications. 22,23 Infections associated with either increased frequency or severity among individuals with diabetes include mucormycosis; cystitis; complicated urinary tract infections, including pyelonephritis; intrarenal abscesses; perinephric abscesses; pneumonia; lower-extremity soft tissue infection, including polymicrobial gangrene; emphysematous cholecystitis; and malignant otitis externa. Soft tissue infections of the lower extremities and gangrene are among the most dreaded complications associated with diabetes, potentially leading to ulceration and subsequent amputation. Skin and skin structure infections (SSSIs) are common, often of mild to moderate severity and readily treatable. 24,25 Mild infections such as cutaneous abscesses may respond to incision and drainage alone. 24 In the case of more severe disease, rapid progression, associated comorbidities, or immunosuppression, antimicrobial therapy would be indicated. 24,25 The less severe forms of the disease (referred to as uncomplicated SSSI [usssi]) include simple abscesses, impetigo, furuncles, and cellulitis. The more severe and complicated form, csssi, includes major abscesses, infected burns, infected bite wounds, and diabetic foot infections. 24,25 Certain infection types may require surgical intervention and are likely to be polymicrobial, potentially involving Gram-negative bacilli and anaerobes. 24,25 SSSI may be responsible for up to 10% of hospital admissions and the significant use of intravenous antimicrobials. Most skin infections are caused by Gram-positive bacteria such as S. aureus and β-hemolytic streptococci (BHS). Gram-negative pathogens such as Enterobacteriaceae and Pseudomonas aeruginosa are less common. Although Lancefield group A streptococci (GAS; S. pyogenes) and group B (S. agalactiae) streptococci are considered the major pathogenic BHS, other non-group A or B BHS (NABS) that are frequently inhabitants of the oropharynx, skin, and gastrointestinal and genitourinary tracts are also capable of causing significant disease. 8,14,26 These include groups C, G, F, and L, of which the most common are American Proficiency Institute - 2018 2 nd Test Event 8
groups G and C. 8,14,26 Several studies have reported an increasing incidence of disease due to β-hemolytic group G streptococci, which have surpassed GAS as a leading cause of invasive streptococcal infection in some medical centers. 8,14,17,27 Human streptococci that belong to SDSE have long been known under the name of β-hemolytic groups C and G streptococci. 8,14 SDSE primarily presents as skin and soft-tissue infections, including pyoderma, cellulitis, wound infections, abscesses, erysipelas, and necrotizing fasciitis. An increase in cases of bacteremia and of severe infection due to group G BHS in humans has been recently documented. 17,27 The literature suggests a distinct association between group G streptococcal bacteremia or other invasive infection and underlying conditions, such as diabetes, alcoholism, or cardiovascular or neoplastic diseases. 8,14,17,27 Treatment of SSSI ranges from empirical administration of oral antimicrobial agents (cephalexin, clindamycin, dicloxacillin, or penicillin VK [trimethoprim-sulfamethoxazole in penicillin-allergic individuals]) to incision and drainage/surgical debridement coupled with intravenous agents. These latter therapies include administration of vancomycin plus either a carbapenem or piperacillin-tazobactam (with or without clindamycin) or one of several newer agents with favorable pharmacokinetics and/or expanded spectrum of activity, including coverage of CA-MRSA (ceftaroline, dalbavancin, daptomycin, linezolid, oritavancin, tedizolid, or telavancin). 24 SDSE isolates remain almost uniformly susceptible to penicillin and other β-lactam agents, and penicillin is still considered the drug of choice. 8,14,28,29 However, resistances to macrolides, lincosamides, and tetracyclines are more common among isolates of SDSE, 8,14 precluding their use for empiric coverage of SSSI where SDSE may be suspected. Although SDSE are generally susceptible to the fluoroquinolones, resistance has been described among clinical isolates of SDSE and other streptococci. 28 The strain of SDSE in this present challenge (ES-02, 2018), exhibits an MDR phenotype with resistance to clindamycin, macrolides, tetracyclines and fluoroquinolones. Under current protocols in many clinical laboratories, additional characterization of NABS, including antimicrobial susceptibility testing, could be American Proficiency Institute - 2018 2 nd Test Event 9
uncommon. However, it is clear that these contemporary β-hemolytic strains can express an MDR phenotype and cause significant infections that can lead to substantial morbidity and mortality. This suggests that accurate speciation and susceptibility testing may be warranted if NABS are isolated from a sterile site or from compromised patients. 8,14,26 In the worldwide SENTRY Antimicrobial Surveillance Program, all SDSE isolates have remained susceptible to vancomycin, quinupristin-dalfopristin, linezolid, and several newer agents (ceftaroline, dalbavancin, daptomycin, oritavancin, tedizolid, and telavancin). 28,29 In contrast, tetracyclines no longer represent an option for the empirical treatment of SDSE isolates; resistance rates of 60% and higher have been reported. 8,14 Given the incidence of invasive NABS infection, the distinct clinical presentations, and potential for increasing resistance to macrolides and tetracycline, an accurate speciation of this heterogeneous group of bacteria is becoming important for optimal clinical management and to improve understanding of NABS epidemiology. References 1. CLSI. M07Ed11E. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically; approved standard: eleventh edition. Wayne, PA: Clinical and Laboratory Standards Institute, 2018. 2. CLSI. M02Ed13E. Performance standards for antimicrobal disk susceptibility tests; Thirteenth Edition. Wayne, PA: Clinical and Laboratory Standards Institute, 2018. 3. CLSI. M100Ed28E. Performance standards for antimicrobial susceptibility testing: 28th informational supplement. Wayne, PA: Clinical and Laboratory Standards Institute, 2018. 4. EUCAST (2018). Breakpoint tables for interpretation of MIC's and zone diameters. Version 8.0, January 2018. Available at http://www.eucast.org/fileadmin/src/media/pdfs/eucast_files/breakpoint_tables/v_8.0_breakpoint _Tables.pdf. January 2018. 5. USCAST (2017). Breakpoint tables for interpretations of MICs and Zone Diameters, Version 3.0, January 2017. Available at http://www.uscast.org/breakpoints.html. March 2017. 6. Tygacil. Tygacil Package Insert. Philadelphia, PA: Pfizer, Inc. 2016. Available at http://labeling.pfizer.com/showlabeling.aspx?id=491. Date Accessed February 23, 2017. American Proficiency Institute - 2018 2 nd Test Event 10
7. Jorgensen JH, Pfaller MA, Carroll KC, et al. Manual of Clinical Microbiology. 11th ed. Washington, D.C.: ASM Press, 2015. 8. Brandt CM, Spellerberg B. Human infections due to Streptococcus dysgalactiae subspecies equisimilis. Clin Infect Dis. 2009; 49:766-772. 9. Ciszewski M, Zegarski K, Szewczyk EM. Streptococcus dysgalactiae subsp. equisimilis isolated from infections in dogs and humans: Are current subspecies identification criteria accurate? Curr Microbiol. 2016; 73:684-688. 10. Wallet F, Loiez C, Renaux E, Lemaitre N, Courcol RJ. Performances of VITEK 2 colorimetric cards for identification of Gram-positive and Gram-negative bacteria. J Clin Microbiol. 2005; 43:4402-4406. 11. Jensen CS, Dam-Nielsen C, Arpi M. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry identification of large colony beta-hemolytic streptococci containing Lancefield groups A, C, and G. Infectious Diseases. 2015; 47:575-579. 12. Schulthess B, Brodner K, Bloemberg GV, Zbinden R, Bottger EC, Hombach M. Identification of Gram-positive cocci by use of matrix-assisted laser desorption ionization-time of flight mass spectrometry: Comparison of different preparation methods and implementation of a practical algorithm for routine diagnostics. J Clin Microbiol. 2013; 51:1834-1840. 13. Mendes RE, Castanheira M, Farrell DJ, Flamm RK, Sader HS, Jones RN. Prevalence of macrolidelincosamide resistance and multidrug resistance phenotypes in streptococcal isolates causing infections in European hospitals: Evaluation of the in vitro activity of oritavancin and comparator agents. J Glob Antimicrob Resist. 2017; 8:28-32. 14. Broyles LN, Van Beneden C, Beall B, et al. Population-based study of invasive disease due to betahemolytic streptococci of groups other than A and B. Clin Infect Dis. 2009; 48:706-712. 15. Pfaller MA, Sader HS, Rhomberg PR, Flamm RK. In vitro activity of delafloxacin against contemporary bacterial pathogens from the United States and Europe, 2014. Antimicrob Agents Chemother. 2017; 61:e02609. 16. Chopra I, Roberts M. Tetracycline antibiotics: Mode of action, applications, molecular biology, and epidemiology of bacterial resistance. Microbiol Mol Biol Rev. 2001; 65:232-260. 17. Loubinoux J, Plainvert C, Collobert G, et al. Adult invasive and noninvasive infections due to Streptococcus dysgalactiae subsp. equisimilis in France from 2006 to 2010. J Clin Microbiol. 2013; 51:2724-2727. 18. Traverso F, Blanco A, Villalon P, et al. Molecular characterization of invasive Streptococcus dysgalactiae subsp. equisimilis. Multicenter study: Argentina 2011-2012. Rev Argent Microbiol. 2016; 48:279-289. 19. Lu B, Fang Y, Huang L, et al. Molecular characterization and antibiotic resistance of clinical Streptococcus dysgalactiae subsp. equisimilis in Beijing, China. Infection, genetics and evolution : American Proficiency Institute - 2018 2 nd Test Event 11
journal of molecular epidemiology and evolutionary genetics in infectious diseases. 2016; 40:119-125. 20. Gherardi G, Imperi M, Palmieri C, et al. Genetic diversity and virulence properties of Streptococcus dysgalactiae subsp. equisimilis from different sources. J Med Microbiol. 2014; 63:90-98. 21. Baxdela TM (2017). BAXDELA package insert. Available at https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/208610s000,208611s000lbl.pdf. September 2017. 22. Casqueiro J, Casqueiro J, Alves C. Infections in patients with diabetes mellitus: A review of pathogenesis. Indian J Endocrinol Metab. 2012; 16 Suppl 1:S27-36. 23. Schaberg DS, Norwood JM. Case Study: Infections in diabetes mellitus. Diabetes Spectrum. 2002; 15:37-40. 24. Chahine EB, Sucher AJ. Skin and soft tissue infections. In: Murphy JE, Lee MW, eds. PSAP Infectious Diseases. American College of Clinical Pharmacy, 2015; 5-26. 25. Stevens DL, Bisno AL, Chambers HF, et al. Practice guidelines for the diagnosis and management of skin and soft tissue infections: 2014 update by the Infectious Diseases Society of America. Clin Infect Dis. 2014; 59:e10-52. 26. Jeng A, Beheshti M, Li J, Nathan R. The role of beta-hemolytic streptococci in causing diffuse, nonculturable cellulitis: a prospective investigation. Medicine (Baltimore). 2010; 89:217-226. 27. Kittang BR, Langeland N, Skrede S, Mylvaganam H. Two unusual cases of severe soft tissue infection caused by Streptococcus dysgalactiae subsp. equisimilis. J Clin Microbiol. 2010; 48:1484-1487. 28. Biedenbach DJ, Toleman MA, Walsh TR, Jones RN. Characterization of fluoroquinolone-resistant beta-hemolytic Streptococcus spp. isolated in North America and Europe including the first report of fluoroquinolone-resistant Streptococcus dysgalactiae subspecies equisimilis: report from the SENTRY Antimicrobial Surveillance Program (1997-2004). Diagn Microbiol Infect Dis. 2006; 55:119-127. 29. Sader HS, Flamm RK, Mendes RE, Farrell DJ, Jones RN. Antimicrobial activities of ceftaroline and comparator agents against bacterial organisms causing bacteremia in patients with skin and skin structure infections in U.S. Medical Centers, 2008 to 2014. Antimicrob Agents Chemother. 2016; 60:2558-2563. American Proficiency Institute - 2018 2 nd Test Event 12