Prevalence of SCCmec Type IV in Nosocomial Bloodstream Isolates of Methicillin-Resistant Staphylococcus aureus
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微生物临床杂志 2005年第7期
Departments of Infectious Diseases and Hospital Infection Control, LIM 54, Hospital das Clínicas, University of So Paulo, So Paulo, Brazil
LIM 03, Hospital das Clínicas, University of So Paulo, So Paulo, Brazil
Department of Clinical Analyses, Faculdade de Ciências Farmacêuticas, University of So Paulo, So Paulo, Brazil
ABSTRACT
Over a period of 7 months, 151 consecutive methicillin-resistant Staphylococcus aureus blood isolates were evaluated. None was community acquired. Twenty (13%) were susceptible to four or more antimicrobials, and 95% of these isolates were identified as SCCmec type IV. Molecular typing demonstrated four patterns, with one predominant pattern. Although usually community acquired, SCCmec type IV in our setting is clearly nosocomial.
TEXT
Staphylococcus aureus has long been recognized as an important and versatile human pathogen (11). In Brazil, the frequency of isolation of S. aureus is high, mainly as an important cause of nosocomial infection (21). S. aureus is responsible for 20% of nosocomial primary bloodstream infections at the Hospital das Clínicas, and 40 to 70% of the isolates are methicillin resistant (E. Giro, personal communication). Methicillin resistance in staphylococci is caused by the expression of PBP2a encoded by the mecA gene (15) that is located on a genetic element called the staphylococcal cassette chromosome (SCC). SCCmec is a group of mobile DNA elements of 21 to 67 kb that is integrated into the chromosome of methicillin-resistant S. aureus (MRSA) (8, 10). To confer motility, SCCmec carries two specific genes, designated cassette chromosome recombinase A and B (ccrA and ccrB), that encode recombinases of the invertase/resolvase family (9). In the presence of CcrA and CcrB, SCCmec integrates into the chromosome and is also precisely excised from the chromosome. Hospital-acquired MRSA isolates are typically resistant to multiple antibiotics. Recently, the appearance of community-acquired MRSA strains has been described (6). In contrast to hospital-acquired MRSA, these strains are commonly susceptible to the majority of other non--lactam antibiotics, present multiple patterns by pulsed-field gel electrophoresis (PFGE), and have a type IV SCCmec (13). During the last year we observed in our hospital an increasing proportion of MRSA strains that are susceptible to non--lactam antimicrobials. These strains, designated as nonmultiresistant oxacillin-resistant S. aureus (NORSA), were also reported as nosocomial agents in Australia and the United States (5, 18). The aim of this study was to evaluate the presence of SCCmec type IV and the predominant clones among NORSA bloodstream isolates from our hospital.
One isolate per patient was identified using an automated system (VITEK; BioMerieux, Durham, NC). Clinical data on the patients were obtained from their records. The infection was then classified as follows: nosocomial, according to definitions of the Centers for Disease Control and Prevention (4); community acquired if culture isolates were positive within 48 h of admission; or healthcare associated if the patient had been admitted to a hospital or to a nursing home or another healthcare-assistance unit within the previous 12 months (3).
MICs were determined by the broth microdilution method according to the Clinical and Laboratory Standards Institutes (formerly the National Committee for Clinical Laboratory Standards) (16). Strains susceptible to four or more antibiotics were considered NORSA and further studied.
The presence of the mecA gene was confirmed by amplifying a 214-bp fragment using an NCL-SA-PS kit (Novo Castra, United Kingdom). Molecular typing was done by digesting whole-cell DNA with SmaI macrorestriction enzyme and determining the fragment-size patterns obtained on PFGE using a CHEF DR-II apparatus (Bio-Rad Laboratories) (2). Patterns were analyzed as recommended by Tenover et al. (25). Types were identified using letters, and subtypes were numbered. SCCmec typing was done using a multiplex PCR method as described by Oliveira et al. (20). MRSA strains NCTC 10442, N315, 85/2082, and JSCS 1968 were included as controls for SCCmec types I, II, III, and IV, respectively. The ccr gene complex was determined using PCR as described previously (10).
During the study 151 MRSA isolates were obtained. None was community acquired. There were 20 (13%) NORSA isolates: 18 were nosocomial and 2 were healthcare associated. The median age of study subjects was 28 years (range, 3 days to 70 years). These NORSA isolates were selected for further characterization. The oxacillin MICs for the NORSA isolates varied from 4 to >128 mg/liter. All isolates were susceptible to vancomycin (MIC 1 mg/liter), trimethoprim/sulfamethoxazole (MIC 2/38 mg/liter), and ciprofloxacin (MIC 1 mg/liter). Susceptibility was 70% for gentamicin and tetracycline and 20% for erythromycin.
All isolates were positive for the gene mecA. PFGE demonstrated four major profiles with a predominant one present in 13 (65%) isolates. Fifteen (75%) isolates presented SCCmec type IV, four were type IV variant, and one was type IIIA. All isolates presenting SCCmec type IV or IV variant presented a type 2 ccr complex gene.
SCCmec type IV occurred in patients from different hospital areas. The four SCCmec type IV variant isolates were from patients who were in the same hospital unit or had been in the unit, and all of them presented a similar PFGE profile that differed from the predominant one (Fig. 1).
A number of studies have reported the emergence of community-acquired MRSA (6, 12, 14, 17, 24), but in many of these studies the definition of community acquired was not given or varied greatly (22). These community-acquired isolates, although resistant to beta-lactams, are susceptible to other classes of drugs and belong to clones that are different from the nosocomial isolates (1).
Our NORSA isolates presented SCCmec type IV, which is similar to the isolates described in the community (7, 19), and demonstrated four PFGE patterns with one predominant clone. This predominant clone of NORSA was present in different units and is distinct from the Brazilian endemic clone of MRSA. These isolates could represent a new lineage of MRSA emerging in the hospital.
All isolates were susceptible to sulfamethoxazole-trimethoprim, suggesting that this profile could be used as a phenotypic marker. This strategy should be viewed with caution, as the acquisition of other resistance genes by these strains is possible due to the presence of the insertion sequence IS431 in the SCCmec type IV (7). Also, one of the isolates that was susceptible to sulfamethoxazole-trimethoprim presented a type IIIA SCCmec, which is characteristic of the multiresistant Brazilian endemic clone (19).
It is possible that these NORSA clones originated in the community and were introduced by patients who were hospitalized. However, during the study period there were no truly community-acquired cases, suggesting that this is a rare occurrence. In that case, once introduced into the hospital, the SCCmec type IV strains may present a competitive advantage over the predominant endemic multiresistant MRSA clone. It has been suggested that their multiplication and transmission rates could be superior to those of MRSA strains with other SCCmec types (18). Growth regulatory factors (23) or virulence factors (1) may explain their success. Less probably, SCCmec type IV S. aureus is originally nosocomial and has spread to the community.
In conclusion, although typically described as a predominantly community-acquired pathogen, SCCmec type IV S. aureus in our setting is clearly nosocomial.
ACKNOWLEDGMENTS
We thank K. Hiramatsu and Teruyo Ito for providing isolates NCTC 10442, N315, 85/2082, and JSCS 1968.
This study was supported by grants from Fundao de Amparo a Pesquisa do Estado de So Paulo (FAPESP 03/02568-2, 03/01818-5 and 03/01817-9).
REFERENCES
Baba, T., F. Takeuchi, M. Kuroda, H. Yuzawa, K. Aoki, A. Oguchi, Y. Nagai, N. Iwama, K. Asano, T. Naimi, H. Kuroda, L. Cui, K. Yamamoto, and K. Hiramatsu. 2002. Genome and virulence determinants of high virulence community-acquired MRSA. Lancet 359:1819-1827.
Bannerman, T. L., G. A. Hancock, F. C. Tenover, and J. M. Miller. 1995. Pulsed-field gel electrophoresis as a replacement for bacteriophage typing of Staphylococcus aureus. J. Clin. Microbiol. 33:551-555.
Bukharie, H. A., M. S. Abdelhadi, I. A. Saeed, A. M. Rubaish, and E. B. Larbi. 2001. Emergence of methicillin-resistant Staphylococcus aureus as a community pathogen. Diagn. Microbiol. Infect. Dis. 40:1-4.
Garner, J. S., W. R. Jarvis, T. G. Emori, T. C. Horan, and J. M. Hughes. 1988. CDC definitions for nosocomial infections, 1988. Am. J. Infect. Control 16:128-140.
Healy, M. C., K. G. Hulten, D. L. Palazzi, J. R. Campbell, and C. J. Baker. 2004. Emergence of new strains of methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit. Clin. Infect. Dis. 39:1460-1466.
Herold, B. C., L. C. Immergluck, M. C. Maranan, D. S. Lauderdale, R. E. Gaskin, S. Boyle-Vavra, C. D. Leitch, and R. S. Daum. 1998. Community-acquired methicillin-resistant Staphylococcus aureus in children with no identified predisposing risk. JAMA 279:593-598.
Hiramatsu, K., L. Cui, M. Kuroda, and T. Ito. 2001. The emergence and evolution of methicillin-resistant Staphylococcus aureus. Trends Microbiol. 9:486-493.
Ito, T., Y. Katayama, K. Asada, N. Mori, K. Tsutsumimoto, C. Tiensasitorn, and K. Hiramatsu. 2001. Structural comparison of three types of staphylococcal cassette chromosome mec integrated in the chromossome in methicillin-resistant Staphylococcus aureus. Antimicrob. Agents Chemother. 45:1323-1336.
Ito, T., Y. Katayama, and K. Hiramatsu. 1999. Cloning and nucleotide sequence determination of the entire mec DNA of pre-methicillin-resistant Staphylococcus aureus N315. Antimicrob. Agents Chemother. 43:1449-1458.
Katayama, Y., T. Ito, and K. Hiramatsu. 2000. A new class of genetic element, staphylococcus cassette chromosome mec, encodes methicillin-resistance in Staphylococcus aureus. Antimicrob. Agents Chemother. 44:1549-1555.
Kluitmans, J., A. Van Belkum, and H. Verbrugh. 1997. Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms and associated risks. Clin. Microbiol. 10:505-520.
Lindenmayer, J. M., S. Shoenfeld, R. O'Grady, and J. K. Carney. 1998. Methicillin-resistant Staphylococcus aureus in a high school wrestling team and the surrounding community. Arch. Intern. Med. 158:895-899.
Ma, X. X., T. Ito, C. Tiensasitorn, M. Jamklang, P. Chongtrakool, S. Boyle-Vavra, R. S. Daum, and K. Hiramatsu. 2002. Novel type of staphylococcal cassette chromosome mec identified in community-acquired methicillin-resistant Staphylococcus aureus strains. Antimicrob. Agents Chemother. 46:1147-1152.
Maguire, G. P., A. D. Arthur, P. J. Boustead, B. Dwyer, and B. J. Currie. 1996. Emerging epidemic of community-acquired methicillin-resistant Staphylococcus aureus infection in the Northern Territory. Med. J. Aust. 164:721-723.
Matsuhashi, M., M. D. Song, F. Ishino, M. Wachi, M. Doi, M. Inoue, K. Ubukata, N. Yamashita, and M. Konno. 1986. Molecular cloning of the gene of a penicillin-binding protein supposed to cause high resistance to beta-lactam antibiotics in Staphylococcus aureus. J. Bacteriol. 167:975-980.
National Committee For Clinical Laboratory Standards. 2002. Performance standard for antimicrobial susceptibility testing. Document M100-S12. National Committee for Clinical Laboratory Standards, Wayne, Pa.
Nimmo, G. R., J. Schooneveldt, G. O'Kane, B. McCall, and A. Vickery. 2000. Community acquisition of gentamicin-sensitive methicillin-resistant Staphylococcus aureus in Southeast Queensland, Australia. J. Clin. Microbiol. 38:3926-3931.
Okuma, K., K. Iwakawa, J. D. Turnidge, W. B. Grubb, J. M. Bell, F. G. O'Brien, G. W. Coombs, J. W. Pearman, F. C. Tenover, M. Kapi, C. Tiensasitorn, T. Ito, and K. Hiramatsu. 2002. Dissemination of new methicillin-resistant Staphylococcus aureus clones in the community. J. Clin. Microbiol. 40:4289-4294.
Oliveira, D. C., A. Tomasz, and H. de Lancastre. 2002. Secrets of success of a human pathogen: molecular evolution of pandemic clones of methicillin-resistant Staphylococcus aureus. Lancet Infect. Dis. 2:180-189.
Oliveira, D. C., and H. de Lancastre. 2002. Multiplex PCR strategy for rapid identification of structural types and variants of the mec element in methicillin-resistant Staphylococcus aureus. Antimicrob. Agents Chemother. 46:2155-2161.
Oliveira, G. A., J. B. Faria, C. E. Levy, and E. M. Mamizuka. 2001. Characterization of the Brazilian endemic clone of methicillin-resistant Staphylococcus aureus (MRSA) from hospitals throughout Brazil. Braz. J. Infect. Dis. 5:163-170.
Salgado, C. D., B. M. Farr, and D. P. Calfee. 2003. Community-acquired methicillin-resistant Staphylococcus aureus: a meta-analysis of prevalence and risk factors. Clin. Infect. Dis. 36:131-139.
Shopsin, B., B. Mathema, P. Alcabes, B. Said-Salim, G. Lina, A. Matsuka, J. Martinez, and B. N. Kreiswirth. 2003. Prevalence of agr specificity groups among Staphylococcus aureus strains colonizing children and their guardians. J. Clin. Microbiol. 41:456-459.
Stacey, A. R., K. E. Endersby, P. C. Chan, and R. R. Marples. 1998. An outbreak of methicillin-resistant Staphylococcus aureus infection in a rugby football team. Br. J. Sports Med. 32:153-154.
Tenover, F., R. Arbeit, R. Goering, P. A. Mickelsen, B. E. Murray, D. H. Persing, and B. Swaminathan. 1995. Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. J. Clin. Microbiol. 33:2233-2239.(Priscila de A. Trindade, )
LIM 03, Hospital das Clínicas, University of So Paulo, So Paulo, Brazil
Department of Clinical Analyses, Faculdade de Ciências Farmacêuticas, University of So Paulo, So Paulo, Brazil
ABSTRACT
Over a period of 7 months, 151 consecutive methicillin-resistant Staphylococcus aureus blood isolates were evaluated. None was community acquired. Twenty (13%) were susceptible to four or more antimicrobials, and 95% of these isolates were identified as SCCmec type IV. Molecular typing demonstrated four patterns, with one predominant pattern. Although usually community acquired, SCCmec type IV in our setting is clearly nosocomial.
TEXT
Staphylococcus aureus has long been recognized as an important and versatile human pathogen (11). In Brazil, the frequency of isolation of S. aureus is high, mainly as an important cause of nosocomial infection (21). S. aureus is responsible for 20% of nosocomial primary bloodstream infections at the Hospital das Clínicas, and 40 to 70% of the isolates are methicillin resistant (E. Giro, personal communication). Methicillin resistance in staphylococci is caused by the expression of PBP2a encoded by the mecA gene (15) that is located on a genetic element called the staphylococcal cassette chromosome (SCC). SCCmec is a group of mobile DNA elements of 21 to 67 kb that is integrated into the chromosome of methicillin-resistant S. aureus (MRSA) (8, 10). To confer motility, SCCmec carries two specific genes, designated cassette chromosome recombinase A and B (ccrA and ccrB), that encode recombinases of the invertase/resolvase family (9). In the presence of CcrA and CcrB, SCCmec integrates into the chromosome and is also precisely excised from the chromosome. Hospital-acquired MRSA isolates are typically resistant to multiple antibiotics. Recently, the appearance of community-acquired MRSA strains has been described (6). In contrast to hospital-acquired MRSA, these strains are commonly susceptible to the majority of other non--lactam antibiotics, present multiple patterns by pulsed-field gel electrophoresis (PFGE), and have a type IV SCCmec (13). During the last year we observed in our hospital an increasing proportion of MRSA strains that are susceptible to non--lactam antimicrobials. These strains, designated as nonmultiresistant oxacillin-resistant S. aureus (NORSA), were also reported as nosocomial agents in Australia and the United States (5, 18). The aim of this study was to evaluate the presence of SCCmec type IV and the predominant clones among NORSA bloodstream isolates from our hospital.
One isolate per patient was identified using an automated system (VITEK; BioMerieux, Durham, NC). Clinical data on the patients were obtained from their records. The infection was then classified as follows: nosocomial, according to definitions of the Centers for Disease Control and Prevention (4); community acquired if culture isolates were positive within 48 h of admission; or healthcare associated if the patient had been admitted to a hospital or to a nursing home or another healthcare-assistance unit within the previous 12 months (3).
MICs were determined by the broth microdilution method according to the Clinical and Laboratory Standards Institutes (formerly the National Committee for Clinical Laboratory Standards) (16). Strains susceptible to four or more antibiotics were considered NORSA and further studied.
The presence of the mecA gene was confirmed by amplifying a 214-bp fragment using an NCL-SA-PS kit (Novo Castra, United Kingdom). Molecular typing was done by digesting whole-cell DNA with SmaI macrorestriction enzyme and determining the fragment-size patterns obtained on PFGE using a CHEF DR-II apparatus (Bio-Rad Laboratories) (2). Patterns were analyzed as recommended by Tenover et al. (25). Types were identified using letters, and subtypes were numbered. SCCmec typing was done using a multiplex PCR method as described by Oliveira et al. (20). MRSA strains NCTC 10442, N315, 85/2082, and JSCS 1968 were included as controls for SCCmec types I, II, III, and IV, respectively. The ccr gene complex was determined using PCR as described previously (10).
During the study 151 MRSA isolates were obtained. None was community acquired. There were 20 (13%) NORSA isolates: 18 were nosocomial and 2 were healthcare associated. The median age of study subjects was 28 years (range, 3 days to 70 years). These NORSA isolates were selected for further characterization. The oxacillin MICs for the NORSA isolates varied from 4 to >128 mg/liter. All isolates were susceptible to vancomycin (MIC 1 mg/liter), trimethoprim/sulfamethoxazole (MIC 2/38 mg/liter), and ciprofloxacin (MIC 1 mg/liter). Susceptibility was 70% for gentamicin and tetracycline and 20% for erythromycin.
All isolates were positive for the gene mecA. PFGE demonstrated four major profiles with a predominant one present in 13 (65%) isolates. Fifteen (75%) isolates presented SCCmec type IV, four were type IV variant, and one was type IIIA. All isolates presenting SCCmec type IV or IV variant presented a type 2 ccr complex gene.
SCCmec type IV occurred in patients from different hospital areas. The four SCCmec type IV variant isolates were from patients who were in the same hospital unit or had been in the unit, and all of them presented a similar PFGE profile that differed from the predominant one (Fig. 1).
A number of studies have reported the emergence of community-acquired MRSA (6, 12, 14, 17, 24), but in many of these studies the definition of community acquired was not given or varied greatly (22). These community-acquired isolates, although resistant to beta-lactams, are susceptible to other classes of drugs and belong to clones that are different from the nosocomial isolates (1).
Our NORSA isolates presented SCCmec type IV, which is similar to the isolates described in the community (7, 19), and demonstrated four PFGE patterns with one predominant clone. This predominant clone of NORSA was present in different units and is distinct from the Brazilian endemic clone of MRSA. These isolates could represent a new lineage of MRSA emerging in the hospital.
All isolates were susceptible to sulfamethoxazole-trimethoprim, suggesting that this profile could be used as a phenotypic marker. This strategy should be viewed with caution, as the acquisition of other resistance genes by these strains is possible due to the presence of the insertion sequence IS431 in the SCCmec type IV (7). Also, one of the isolates that was susceptible to sulfamethoxazole-trimethoprim presented a type IIIA SCCmec, which is characteristic of the multiresistant Brazilian endemic clone (19).
It is possible that these NORSA clones originated in the community and were introduced by patients who were hospitalized. However, during the study period there were no truly community-acquired cases, suggesting that this is a rare occurrence. In that case, once introduced into the hospital, the SCCmec type IV strains may present a competitive advantage over the predominant endemic multiresistant MRSA clone. It has been suggested that their multiplication and transmission rates could be superior to those of MRSA strains with other SCCmec types (18). Growth regulatory factors (23) or virulence factors (1) may explain their success. Less probably, SCCmec type IV S. aureus is originally nosocomial and has spread to the community.
In conclusion, although typically described as a predominantly community-acquired pathogen, SCCmec type IV S. aureus in our setting is clearly nosocomial.
ACKNOWLEDGMENTS
We thank K. Hiramatsu and Teruyo Ito for providing isolates NCTC 10442, N315, 85/2082, and JSCS 1968.
This study was supported by grants from Fundao de Amparo a Pesquisa do Estado de So Paulo (FAPESP 03/02568-2, 03/01818-5 and 03/01817-9).
REFERENCES
Baba, T., F. Takeuchi, M. Kuroda, H. Yuzawa, K. Aoki, A. Oguchi, Y. Nagai, N. Iwama, K. Asano, T. Naimi, H. Kuroda, L. Cui, K. Yamamoto, and K. Hiramatsu. 2002. Genome and virulence determinants of high virulence community-acquired MRSA. Lancet 359:1819-1827.
Bannerman, T. L., G. A. Hancock, F. C. Tenover, and J. M. Miller. 1995. Pulsed-field gel electrophoresis as a replacement for bacteriophage typing of Staphylococcus aureus. J. Clin. Microbiol. 33:551-555.
Bukharie, H. A., M. S. Abdelhadi, I. A. Saeed, A. M. Rubaish, and E. B. Larbi. 2001. Emergence of methicillin-resistant Staphylococcus aureus as a community pathogen. Diagn. Microbiol. Infect. Dis. 40:1-4.
Garner, J. S., W. R. Jarvis, T. G. Emori, T. C. Horan, and J. M. Hughes. 1988. CDC definitions for nosocomial infections, 1988. Am. J. Infect. Control 16:128-140.
Healy, M. C., K. G. Hulten, D. L. Palazzi, J. R. Campbell, and C. J. Baker. 2004. Emergence of new strains of methicillin-resistant Staphylococcus aureus in a neonatal intensive care unit. Clin. Infect. Dis. 39:1460-1466.
Herold, B. C., L. C. Immergluck, M. C. Maranan, D. S. Lauderdale, R. E. Gaskin, S. Boyle-Vavra, C. D. Leitch, and R. S. Daum. 1998. Community-acquired methicillin-resistant Staphylococcus aureus in children with no identified predisposing risk. JAMA 279:593-598.
Hiramatsu, K., L. Cui, M. Kuroda, and T. Ito. 2001. The emergence and evolution of methicillin-resistant Staphylococcus aureus. Trends Microbiol. 9:486-493.
Ito, T., Y. Katayama, K. Asada, N. Mori, K. Tsutsumimoto, C. Tiensasitorn, and K. Hiramatsu. 2001. Structural comparison of three types of staphylococcal cassette chromosome mec integrated in the chromossome in methicillin-resistant Staphylococcus aureus. Antimicrob. Agents Chemother. 45:1323-1336.
Ito, T., Y. Katayama, and K. Hiramatsu. 1999. Cloning and nucleotide sequence determination of the entire mec DNA of pre-methicillin-resistant Staphylococcus aureus N315. Antimicrob. Agents Chemother. 43:1449-1458.
Katayama, Y., T. Ito, and K. Hiramatsu. 2000. A new class of genetic element, staphylococcus cassette chromosome mec, encodes methicillin-resistance in Staphylococcus aureus. Antimicrob. Agents Chemother. 44:1549-1555.
Kluitmans, J., A. Van Belkum, and H. Verbrugh. 1997. Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms and associated risks. Clin. Microbiol. 10:505-520.
Lindenmayer, J. M., S. Shoenfeld, R. O'Grady, and J. K. Carney. 1998. Methicillin-resistant Staphylococcus aureus in a high school wrestling team and the surrounding community. Arch. Intern. Med. 158:895-899.
Ma, X. X., T. Ito, C. Tiensasitorn, M. Jamklang, P. Chongtrakool, S. Boyle-Vavra, R. S. Daum, and K. Hiramatsu. 2002. Novel type of staphylococcal cassette chromosome mec identified in community-acquired methicillin-resistant Staphylococcus aureus strains. Antimicrob. Agents Chemother. 46:1147-1152.
Maguire, G. P., A. D. Arthur, P. J. Boustead, B. Dwyer, and B. J. Currie. 1996. Emerging epidemic of community-acquired methicillin-resistant Staphylococcus aureus infection in the Northern Territory. Med. J. Aust. 164:721-723.
Matsuhashi, M., M. D. Song, F. Ishino, M. Wachi, M. Doi, M. Inoue, K. Ubukata, N. Yamashita, and M. Konno. 1986. Molecular cloning of the gene of a penicillin-binding protein supposed to cause high resistance to beta-lactam antibiotics in Staphylococcus aureus. J. Bacteriol. 167:975-980.
National Committee For Clinical Laboratory Standards. 2002. Performance standard for antimicrobial susceptibility testing. Document M100-S12. National Committee for Clinical Laboratory Standards, Wayne, Pa.
Nimmo, G. R., J. Schooneveldt, G. O'Kane, B. McCall, and A. Vickery. 2000. Community acquisition of gentamicin-sensitive methicillin-resistant Staphylococcus aureus in Southeast Queensland, Australia. J. Clin. Microbiol. 38:3926-3931.
Okuma, K., K. Iwakawa, J. D. Turnidge, W. B. Grubb, J. M. Bell, F. G. O'Brien, G. W. Coombs, J. W. Pearman, F. C. Tenover, M. Kapi, C. Tiensasitorn, T. Ito, and K. Hiramatsu. 2002. Dissemination of new methicillin-resistant Staphylococcus aureus clones in the community. J. Clin. Microbiol. 40:4289-4294.
Oliveira, D. C., A. Tomasz, and H. de Lancastre. 2002. Secrets of success of a human pathogen: molecular evolution of pandemic clones of methicillin-resistant Staphylococcus aureus. Lancet Infect. Dis. 2:180-189.
Oliveira, D. C., and H. de Lancastre. 2002. Multiplex PCR strategy for rapid identification of structural types and variants of the mec element in methicillin-resistant Staphylococcus aureus. Antimicrob. Agents Chemother. 46:2155-2161.
Oliveira, G. A., J. B. Faria, C. E. Levy, and E. M. Mamizuka. 2001. Characterization of the Brazilian endemic clone of methicillin-resistant Staphylococcus aureus (MRSA) from hospitals throughout Brazil. Braz. J. Infect. Dis. 5:163-170.
Salgado, C. D., B. M. Farr, and D. P. Calfee. 2003. Community-acquired methicillin-resistant Staphylococcus aureus: a meta-analysis of prevalence and risk factors. Clin. Infect. Dis. 36:131-139.
Shopsin, B., B. Mathema, P. Alcabes, B. Said-Salim, G. Lina, A. Matsuka, J. Martinez, and B. N. Kreiswirth. 2003. Prevalence of agr specificity groups among Staphylococcus aureus strains colonizing children and their guardians. J. Clin. Microbiol. 41:456-459.
Stacey, A. R., K. E. Endersby, P. C. Chan, and R. R. Marples. 1998. An outbreak of methicillin-resistant Staphylococcus aureus infection in a rugby football team. Br. J. Sports Med. 32:153-154.
Tenover, F., R. Arbeit, R. Goering, P. A. Mickelsen, B. E. Murray, D. H. Persing, and B. Swaminathan. 1995. Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. J. Clin. Microbiol. 33:2233-2239.(Priscila de A. Trindade, )