ORIGINAL ARTICLE 10.1111/j.1469-0691.2007.01718.x Clonal spread of SCCmec type IV methicillin-resistant Staphylococcus aureus between community and hospital Y. H. Huang 1, S. P. Tseng 1,J.M.Hu 1, J. C. Tsai 2,3, P. R. Hsueh 4 and L. J. Teng 1,4 1 Department of Clinical Laboratory Sciences and Medical Biotechnology, 2 Center for Optoelectronic Biomedicine, National Taiwan University College of Medicine, 3 Division of Neurosurgery, Department of Surgery, and 4 Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan ABSTRACT The staphylococcal chromosome cassette (SCC)mec types of 382 hospital-acquired methicillin-resistant Staphylococcus aureus (HA-MRSA) isolates in Taiwan were analysed over a 7-year period (1999 2005). There was an abrupt increase in SCCmec type IV in HA-MRSA during 2005. The molecular epidemiology of a subset (n = 69) of HA-MRSA isolates with SCCmec types III, IV or V was characterised and compared with that of community-acquired MRSA (CA-MRSA) (n = 26, collected during 2005). Pulsed-field gel electrophoresis revealed three major pulsotypes (A, B and C) and 15 minor clones. Pulsotypes B and C, which contained isolates carrying SCCmec types IV and V, respectively, included both CA-MRSA and HA-MRSA isolates. Among 24 toxin genes analysed, five genes had significant differential distribution between CA-MRSA and SCCmec type III HA-MRSA. Furthermore, among SCCmec type IV isolates, the seb gene was detected more commonly in HA-MRSA. Analysis of representative members of the three major pulsotypes by multilocus sequence typing revealed two sequence types (STs), namely ST239 (SCCmecIII) and ST59 (SCCmecIV or SCCmecV). This suggests that ST59:SCCmecIV, which is usually community-acquired, has become an important nosocomial pathogen in the hospital studied. Keywords Community-acquired, epidemiology, multilocus sequence typing, MRSA, pulsed-field gel electrophoresis, SCCmec type Original Submission: 2 July 2006; Revised Submission: 10 December 2006; Accepted: 29 January 2007 Clin Microbiol Infect 2007; 13: 717 724 INTRODUCTION The increasing occurrence worldwide of antibiotic-resistant bacteria, especially in hospitalised patients, is a considerable concern. Established risk-factors for hospital-acquired infection include recent hospitalisation, surgery, residence in a long-term care facility, dialysis, and indwelling percutaneous medical devices and catheters [1,2]. Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of hospital-acquired infection. As in other countries, the prevalence of MRSA has Corresponding author and reprint requests: L.-J. Teng, Department of Clinical Laboratory Sciences and Medical Biotechnology, National Taiwan University College of Medicine, 1 Chang-Te Street, Taipei 100, Taiwan E-mail: ljteng@ha.mc.ntu.edu.tw increased in Taiwan during the past 10 years [3], and MRSA infections in healthy individuals without established risk-factors have now been documented in the community in Taiwan and many other countries [4 8]. There are substantial differences between community-acquired MRSA (CA-MRSA) and hospital-acquired MRSA (HA-MRSA) in terms of staphylococcal chromosome cassette (SCC) mec types, distribution of toxin genes and antimicrobial susceptibility [9 14]. CA-MRSA strains often carry a smaller methicillin resistance cassette (i.e., SCCmecIV or SCCmecV) and Panton Valentine leukocidin (PVL) genes, and are commonly more susceptible to non-b-lactam antibiotics [15]. In contrast, HA-MRSA strains often carry SCCmecI, SCCmecII or SCCmecIII, and are usually multidrug-resistant. However, the Journal Compilation Ó 2007 European Society of Clinical Microbiology and Infectious Diseases
718 Clinical Microbiology and Infection, Volume 13 Number 7, July 2007 epidemiology of MRSA is changing, and the emergence of healthcare-associated CA-MRSA infections has been reported recently [16 18]. In order to better understand the changing epidemiology of MRSA in the National Taiwan University Hospital and the surrounding community, HA-MRSA isolates from 1999 to 2005 and CA-MRSA isolates from 2005 were investigated by molecular typing methods and analysed for the presence of virulence genes. MATERIALS AND METHODS Bacterial isolates and case definitions In total, 382 HA-MRSA and 26 CA-MRSA non-duplicate clinical isolates were tested for the presence of different SCCmec types. The 382 HA-MRSA isolates were selected randomly from a collection of 2013 blood isolates at the Bacteriology Laboratory of National Taiwan University Hospital, a 2000-bed teaching hospital in northern Taiwan, between 1999 and 2005. Only one isolate patient was included in the study. The 26 CA-MRSA clinical isolates were recovered from various specimens (skin and soft-tissue, sputum, blood, urine, abscess, etc.) during 2005. None of these isolates was obtained from a screening or surveillance culture for MRSA. The diagnosis of infection was based on clinical and laboratory findings. A CA-MRSA case was defined as a patient with an MRSA infection identified within 48 h of admission without any of the following established risk-factors: (i) a history of hospitalisation, surgery, dialysis or residence in a long-term care facility within 1 year of the MRSA culture; (ii) a permanent indwelling catheter or percutaneous medical device present at the time of culture; and (iii) a known positive culture for MRSA before the study period [14]. An HA-MRSA case was defined as a patient with an MRSA infection identified >72 h after admission with at least one of the above established risk-factors. Bacterial identification and antimicrobial susceptibility testing Identification as S. aureus was based on colony morphology, Gram s stain and a positive catalase reaction and slide agglutination test result (biomérieux, Marcy l Etoile, France), and or results obtained with the Phoenix system (Becton Dickinson, Sparks, MD, USA). Antimicrobial susceptibilities were determined using the disk-diffusion method, performed according to CLSI guidelines [19], for oxacillin, clindamycin, erythromycin, gentamicin, minocycline, trimethoprim sulphamethoxazole, vancomycin, ciprofloxacin and rifampicin. Resistance to oxacillin was confirmed by detecting the presence of the meca gene by PCR [20]. SCCmec typing, agr grouping and detection of virulence genes by PCR Characterisation of SCCmec elements [21,22] and agr groups, and detection of 24 specific staphylococcal virulence genes (sea, seb, sec, sed, see, seg, seh, sei, sej, sen, seo, sem, tst, eta, etb, pvl, lukde, lukm, hla, hlb, hld, hlg, hlg-2 and edin), were performed by PCR as described by Jarraud et al. [23]. Pulsed-field gel electrophoresis, multilocus sequence typing and spa gene typing A subset (n = 69) of HA-MRSA isolates carrying SCCmec types III, IV or V, and 26 CA-MRSA isolates (including all SCCmec types), were typed by pulsed-field gel electrophoresis (PFGE) [24]. The 69 HA-MRSA isolates included 30 with SCCmecIII (four isolates year in 1999 2003, and five isolates year in 2004 and 2005), 29 with SCCmecIV (one to five isolates year in 1999 2004, and 11 in 2005), and ten with SCCmecV (one to three isolates year). DNA fragments were separated using a CHEF- DR III electrophoresis system (Bio-Rad Laboratories, Hercules, CA, USA) at 6.0 V cm for 24 h, with pulse times ramped from 5 to 60 s. Analysis of PFGE patterns was performed using GelCompar software (Applied Maths, Austin, TX, USA). The genetic similarity of isolates was determined by the unweighted pair-group method with arithmetic averages, and a dendrogram was generated. Isolates were considered to be closely related and to belong to the same pulsotype when their similarity was >80%. Some of the above isolates were also analysed by multilocus sequence typing (MLST) [25] or spa gene typing [26]. Bacterial growth rate An overnight culture of MRSA, grown at 37 C in LB broth (BBL; Becton Dickinson, Cockeysville, MD, USA), was diluted 1:200 with fresh LB broth and incubated at 37 C with constant agitation (230 rpm) for 6 h. Aliquots were removed, serially diluted, and plated on Mueller Hinton agar (BBL; Becton Dickinson) every 30 min. The plates were incubated at 37 C for 18 h and the number of colonies was then counted. The doubling time during the log phase was calculated using a standard method (http://textbookofbacteriology.net/ growth.html). Biofilm assays Biofilm production was evaluated by the Congo red agar (CRA) method, with minor modifications, and the microtitre plate method [27,28]. CRA contained 0.8 g of Congo red (Sigma-Aldrich, St Louis, MO, USA) and various amounts (36, 18, 1 and 0.5 g) of saccharose (Merck, Darmstadt, Germany) in 1 L of brain heart infusion agar. Isolates were inoculated on the plate, incubated at 37 C for 24 h, and kept at room temperature overnight. Black colonies were indicative of biofilm-producing isolates, while red colonies indicated an absence of biofilm production. RESULTS Distribution of SCCmec types among MRSA isolates The distribution of SCCmec types among the selected 382 HA-MRSA isolates, which represented 19% of the total MRSA isolates recovered in the hospital between 1999 and 2005, together with
Huang et al. Clonal spread of SCCmec type IV MRSA 719 Table 1. Distribution of SCCmec types among 382 hospital-acquired methicillin-resistant Staphylococcus aureus (MRSA) isolates between 1999 and 2005, and 26 community-acquired MRSA isolates during 2005 MRSA Isolation year the 26 CA-MRSA isolates from 2005, is shown in Table 1. No SCCmecI isolate was found. SCCmecIII was the predominant type among HA-MRSA isolates, while most CA-MRSA isolates carried either SCCmecIV (42%) or SCCmecV (42%). The prevalence of SCCmecIV in HA-MRSA isolates was low during 1999 2004, ranging from 3-20%, but increased to 43% in 2005. Thus, HA-MRSA shifted from having a predominance of SCCmecIII in early 2004, to a similar frequency of isolation of SCCmecIII and SCCmecIV in 2005. Virulence gene analysis SCCmec types, n (%) II III IV V Total Hospital-acquired 1999 5 (9) 35 (65) 11 (20) 3 (6) 54 2000 2 (3) 42 (72) 9 (16) 5 (9) 58 2001 5 (9) 46 (79) 6 (10) 1 (2) 58 2002 8 (13) 49 (82) 2 (3) 1 (2) 60 2003 7 (13) 42 (75) 2 (4) 5 (9) 56 2004 4 (7) 42 (75) 8 (14) 2 (4) 56 2005 2 (5) 19 (48) 17 (43) 2 (5) 40 Community-acquired 2005 1 (4) 3 (12) 11 (42) 11 (42) 26 The agr group and the presence of virulence genes were compared for the 26 CA-MRSA and 69 HA-MRSA isolates with SCCmecIII, SCCmecIV or SCCmecV (Table 2). Most isolates were agr group 1. Among the 24 toxin genes analysed, five genes had significantly different distributions between CA-MRSA and SCCmecIII HA-MRSA. The seb gene (which encodes staphylococcal enterotoxin B) and the luks lukf (PVL) genes were detected in 62% and 50% of CA-MRSA isolates, respectively, but in none of the SCCmecIII HA-MRSA isolates. The hlg gene, which encodes b-haemolysin components A, B and C, was detected more often in CA-MRSA than in SCCmecIII HA-MRSA. In contrast, the lukde gene and the sea gene (which encodes staphylococcal enterotoxin A) were commonly seen in SCCmecIII HA-MRSA (100% and 77%, respectively), but were detected rarely in CA-MRSA (15% and 12%, respectively). Furthermore, the seb gene was detected more commonly in SCCmecIV HA-MRSA than in SCCmecIV CA-MRSA. There was no difference between SCCmecV CA-MRSA and SCCmecV HA-MRSA with respect to the occurrence of the 24 virulence genes. Characteristics of patients CA-MRSA patients were younger than HA-MRSA patients with SCCmecIII and SCCmecIV (median age 37 years vs. 59 and 58 years, respectively), and most CA-MRSA patients were aged <10 years. In contrast, HA-MRSA infections with SCCmecIII, SCCmecIV or SCCmecV were seen mostly in the elderly. Hospital-acquired infection with MRSA carrying SCCmecIV or SCCmecV was more common among male patients (n = 29; 74%), while infection with CA-MRSA was more common among females (n = 18; 69%). The most common underlying disease associated with SCCmecIII HA-MRSA was pulmonary disease, followed by cardiovascular disease. Compared with the SCCmecIII group, patients with SCC meciv HA-MRSA were associated with a higher frequency of cardiovascular disease, and a lower frequency of pulmonary or liver disease. Cardiovascular disease was more common in the SCCmecIV HA-MRSA group (n = 17; 58%) than in the SCCmecV HA-MRSA group (n =1; 10%). PFGE, MLST, spa gene typing and antimicrobial susceptibility PFGE analysis grouped the 95 MRSA isolates into three major clusters (pulsotypes), A, B and C, which accounted for 77% of all isolates, and 15 minor clones (Fig. S1; see Supplementary material). Among the 30 SCCmecIII HA-MRSA isolates, 25 (83%) belonged to pulsotype A. The five remaining isolates belonged to either pulsotype D or pulsotype E. Eight (73%) of 11 SCCmecIV CA-MRSA isolates were grouped into pulsotype B, and 23 (79%) of 29 SCCmecIV HA-MRSA isolates were also closely related to pulsotype B. Ten (91%) of 11 SCCmecV CA-MRSA isolates and four (40%) of ten HA-MRSA isolates carrying SCCmecV were clustered together in pulsotype C. These results suggest that pulsotype B and C isolates carrying SCCmec types IV and V, respectively, had spread between the community and the hospital. Antimicrobial susceptibilities were compared for SCCmecIII and SCCmecIV V isolates. All were susceptible to vancomycin, but most SCCmecIII
720 Clinical Microbiology and Infection, Volume 13 Number 7, July 2007 Table 2. Comparison of virulence genes and patient characteristics for community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and hospital-acquired MRSA (HA-MRSA) CA-MRSA SCCmec type HA-MRSA SCCmec type Virulence gene or patient characteristics II III (n =4) IV (n = 11) V (n = 11) Total (n = 26) III (n = 30) IV (n = 29) V (n = 10) Total (n = 69) agr group 1 4 9 11 24 (92%) 27 27 10 64 (93%) 2 0 1 0 1 (4%) 3 1 0 4 (6%) 3 0 1 0 1 (4%) 0 1 0 1 (1%) Staphylococcal enterotoxin genes sea 3 0 0 3 (12%) 23 3 0 26 (38%) seb 0 6 10 16 (62%) 0 27 9 36 (52%) sec 0 1 0 1 (4%) 0 1 0 1 (1%) sed 0 0 0 0 0 0 0 0 see 0 0 0 0 3 0 0 3 (4%) seg 0 2 1 3 (12%) 0 1 0 1 (1%) seh 0 1 0 1 (4%) 0 1 0 1 (1% sei 0 2 1 3 (12%) 0 1 0 1 (1%) sej 0 0 0 0 0 0 0 0 sem 1 1 0 2 (8%) 0 2 0 2 (2%) sen 0 3 1 4 (15%) 1 1 0 2 (2%) seo 1 2 1 4 (15%) 0 1 0 1 (1%) tst 0 0 0 0 0 1 0 1 (1%) Exfoliative toxin genes eta 1 0 0 1 (4%) 1 0 0 1 (1%) etb 1 0 0 1 (4%) 0 0 0 0 Leukocidin genes luk PV SF 0 2 11 13 (50%) 0 2 9 11 (16%) luked 3 1 0 4 (15%) 30 1 1 32 (46%) lukm 0 0 0 0 0 0 0 0 Haemolysin genes hla 4 11 11 26 (100%) 30 29 10 69 (100%) hlb 4 10 11 25 (96%) 29 22 10 61 (88%) hld 4 11 11 26 (100%) 30 29 10 69 (100%) hlg 3 10 9 22 (85%) 11 29 10 49 (71%) hlg-2 3 9 10 22 (85%) 30 28 10 68 (98%) Other edin 0 0 0 0 0 0 0 0 Patient characteristics Diabetes mellitus 0 3 1 4 (15%) 8 9 0 17 (25%) Cardiovascular disease 1 1 1 3 (12%) 15 17 1 33 (48%) Pulmonary disease 1 0 1 2 (8%) 17 8 2 27 (39%) History of malignancy 1 1 0 2 (8%) 10 8 3 21 (30%) History of liver disease 0 0 0 0 6 2 0 8 (12%) Previous antimicrobial chemotherapy 0 0 0 0 22 21 27 5 9 48 66 (73%) Previous invasive procedure 0 0 0 0 20 18 27 3 9 41 66 (62%) HA-MRSA isolates were resistant to multiple drugs, e.g., ciprofloxacin (97%), clindamycin (90%), erythromycin (100%), gentamicin (100%), minocycline (77%) and trimethoprim sulphamethoxazole (97%). The SCCmecIV V isolates, regardless of origin, were susceptible to numerous antimicrobial agents, including ciprofloxacin (92% susceptible), minocycline (95% susceptible) and trimethoprim sulphamethoxazole (95% susceptible). Susceptibilities to clindamycin, erythromycin and gentamicin for SCCmecIV V HA-MRSA isolates were 13%, 8% and 59%, respectively. Two sequence types (STs), ST239 and ST59, were identified by MLST of randomly selected isolates from the three major pulsotypes A, B and C. Overall, the results were in agreement with those obtained following PFGE. Thus, all five isolates from pulsotype A with SCCmecIII belonged to ST239. Isolates from pulsotypes B and C with SCCmecIV or SCCmecV, whether isolated from community or hospital, belonged to ST59. Isolates representing the three major clones were also examined by spa gene typing. ST239 isolates shared the spa repeat codes WGKAOMQ, while ST59 isolates shared ZDMDMOB. Growth rate and biofilm activity The reason for the abrupt increase in the number of SCCmecIV MRSA infections during 2005 in this hospital is unclear. As a shorter doubling time and or increased biofilm formation may play a role in enhancing the ecological fitness of SCCmecIV isolates (leading to an increased incidence of infection), the growth rate was measured by calculating the doubling time during exponential
Huang et al. Clonal spread of SCCmec type IV MRSA 721 Table 3. Growth rate and biofilm assay for methicillin-resistant Staphylococcus aureus (MRSA) isolates Isolate SCCmec type Doubling time time (mean ± SD, min) a Biofilm assay Colony phenotype on Congo red agar 3.6% sucrose 0.05% sucrose Microtitre plate (absorbance at 490 nm) a HA8270 II 30.9 ± 4.97 Black Red 0.308 ± 0.044 HA5584 II 32.7 ± 1.28 Black Red 0.180 ± 0.028 HA2370 III 32.7 ± 3.40 Black Red 0.196 ± 0.033 HA6436 III 34.2 ± 1.68 Black Black 0.441 ± 0.085 HA9471 III ND Black Red ND HA163 III ND Black Red ND HA819 III ND Black Red ND HA6688 III ND Black Red ND CA748 IV 31.3 ± 0.12 Black Red 0.185 ± 0.008 CA1576 IV 34.5 ± 1.50 Black Red 0.174 ± 0.057 CA5704 IV ND Black Red ND CA4939 IV ND Black Red ND CA4136 IV ND Black Black ND HA586 IV 33.2 ± 0.81 Black Red 0.202 ± 0.043 (dry and rough) HA312 IV 29.6 ± 1.40 Black Red 0.171 ± 0.020 HA1436 IV 33.1 ± 1.89 Black Black 0.427 ± 0.098 HA3850 IV 27.2 ± 1.87 Black Black 0.418 ± 0.032 HA8993 IV ND Black Black ND CA7796 V 28.6 ± 4.32 Black Red 0.167 ± 0.068 CA7584 V 30.5 ± 2.25 Black Black 0.113 ± 0.015 HA2841 V 33.3 ± 3.85 Black Black 0.183 ± 0.039 HA3165 V 33.8 ± 2.69 Black Red 0.095 ± 0.049 a Average of data from three experiments. HA, hospital-acquired; CA-community-acquired; ND, not done. growth for selected isolates with different SCCmec types. Some, but not all, isolates with SCCmecIV grew slightly faster than MRSA isolates carrying other SCCmec types (Table 3). Isolates carrying different SCCmec types were also tested for their biofilm (or slime-producing) ability by the modified CRA method and microtitre plate method. All isolates examined formed black colonies on CRA containing saccharose at concentrations of 36, 18 or 1 g L, and several isolates were still able to form black colonies at a very low saccharose concentration of 0.5 g L. A wide range of biofilm-forming ability was detected among isolates by the microtitre method (Table 3). DISCUSSION It has been reported previously that SCCmecIII is the main type of HA-MRSA, while SCCmecIV and SCCmecV are the main types of CA-MRSA in Taiwan and other Asian countries [29 31]. In the present study, the distribution of SCCmec types remained unchanged between 1999 and 2004, but there was an increase in SCCmecIV during 2005, to a level similar to that of SCCmecIII in HA-MRSA. Wisplinghoff et al. [33] reported a decreasing prevalence of SCCmecIII in Germany between 1984 and 1998, while de A Trindade et al. [17] reported a high (95%) prevalence of SCCmecIV among nosocomial bloodstream isolates of MRSA collected during a 7-month period in Brazil. An increased incidence of MRSA clones carrying SCCmecIV has been reported during recent years in Norway [34]. A recent study from Taiwan also demonstrated a high (40%) prevalence of SCCmecIV among HA-MRSA isolates [35]. These studies implied that there is an increasing incidence of SCCmecIV and a decreasing incidence of SCCmecIII. High morbidity and mortality caused by CA-MRSA infections have raised concerns worldwide in recent years [36]. Several previous studies have compared cases of CA-MRSA and HA- MRSA infection in terms of clinical characteristics, antibiotic susceptibility and genetic background [10,37]. In agreement with these reports, the results of the present study showed that cases of CA-MRSA infection occurred most frequently among children, females and patients with diabetes, while HA-MRSA infection occurred significantly more often among the elderly and patients with underlying cardiovascular or bronchopulmonary disease. The present study revealed that three genes (seb, pvl and hlg) were present more frequently in CA-MRSA than in SCCmecIII HA-MRSA isolates. However, within SCCmecIV isolates, the seb gene was detected at a higher frequency in HA-MRSA
722 Clinical Microbiology and Infection, Volume 13 Number 7, July 2007 than in CA-MRSA isolates. The significance of this difference is unclear. The seb gene has been found frequently among S. aureus isolates from children with staphylococcal toxic shock syndrome [38]. The PVL genes are associated frequently with community-acquired staphylococcal skin infections and necrotising pneumonia [39,40]. In the present study, half of the CA-MRSA isolates carried the PVL genes, and among 13 patients with PVL-positive CA-MRSA infection, 62% had skin infections or necrotising pneumonia. However, PVL genes were also detected in most (9 10) SCCmecV HA-MRSA isolates. Among 11 patients with PVL-positive HA-MRSA infections, five were associated with skin infections or necrotising pneumonia. This indicates that PVL may also play a role in HA-MRSA infections. However, the study compared a selection of non-consecutive HA-MRSA infections with consecutive CA-MRSA infections, which may lead to a potential bias in terms of differences in virulence factors or patient variables, which is a limitation of this study. Previous studies have shown that CA-MRSA strains, which are generally only resistant to b-lactam antibiotics, are typically more susceptible to antibiotics than HA-MRSA strains [10 17]. In the present study, the CA-MRSA isolates were resistant not only to b-lactam antibiotics, but also to erythromycin, clindamycin and gentamicin. In agreement with other reports from Taiwan, SCCmecIII HA-MRSA isolates were resistant to multiple drugs, including erythromycin, clindamycin, gentamicin, trimethoprim sulphamethoxazole, minocycline and ciprofloxacin [8,30]. Moreover, the susceptibility patterns of SCCmecIV or SCCmecV HA-MRSA isolates were similar to those of the CA-MRSA isolates, which were usually susceptible to minocycline, ciprofloxacin and trimethoprim sulphamethoxazole, 59% susceptible to gentamicin, and mostly resistant to erythromycin and clindamycin. SCCmecIV CA-MRSA is usually considered to be genetically heterogeneous. Unexpectedly, SCCmecIV-containing CA-MRSA and HA-MRSA isolates in the present study were shown to be clonally related by PFGE, and shared the same ST59 genetic background. In addition, the susceptibility patterns of SCCmecIV or SCCmecV HA-MRSA isolates were the same as those of CA-MRSA isolates. Although CA-MRSA isolates usually have distinct molecular features compared with HA-MRSA isolates [17,18], the genotype of the SCCmecIV or SCCmecV CA-MRSA isolates was similar to that of HA-MRSA isolates with SCCmecIV or SCCmecV (clones B and C), respectively. Thus, in addition to the existing clone A (ST239, SCCmecIII) in the hospital, clones B (ST59, SCCmecIV) and C (ST59, SCCmecV), which were relatively more susceptible, had spread in both the community and the hospital. Although the origin of these clones could not be traced to the hospital or community (because CA-MRSA isolates were not collected before 2005), the clone that was SCCmecIV or SCCmecV, ST59, PVL-positive, and that was usually considered to be community-acquired, appeared to have become nosocomial. The ST239 type (clonal complex (CC) 239, regarded as a lineage within CC8) resembles the Hungarian clone; this is a common MLST type among HA-MRSA isolates in Taiwan [31] and other Asian countries [32], and was reported to be the earliest predominant ST between 1984 and 1988 in Germany [33]. ST59 (CC59) is the predominant CA-MRSA clone with SCCmecIV or SCCmecV in Taiwan [8], but has been described infrequently in other countries [34]. The possible reasons for the dramatic increase in the prevalence of SCCmecIV HA-MRSA during 2005 in this hospital remain unclear. It has been suggested previously that CA-MRSA may have enhanced ecological fitness because of a shorter doubling time than HA-MRSA [41]. Different growth rates were revealed for SCCmecIV MRSA isolates, and some multiplied faster than SCC meciii HA-MRSA isolates. Moreover, patients with SCCmecIV HA-MRSA infections were found to have a higher incidence of underlying cardiovascular disease and prosthetic devices. This suggests that biofilm-producing ability, together with a rapid growth rate, may enhance the fitness of SCCmecIV MRSA. Although CA-MRSA is responsible for community-acquired infections, the appearance of CA-MRSA isolates causing nosocomial infections is a more recent phenomenon. The present data suggest an increasing incidence of SCCmecIV MRSA, which may become one of the dominant types in hospitals in the future. In addition, clones B and C appear to have spread between the community and the hospital. Continued surveillance of the ST59:SCCmecIV and ST59:SCCmecV clones, as well as analysis of their virulence factors, will therefore be important for monitoring this spread.
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