Staphylococcus aureus strains isolated from bloodstream infections changed significantly in 2006

We studied 358 Staphylococcus aureus strains isolated from bloodstream infections (BSI) observed during an epidemiological study covering 2,007,681 days of hospitalization in 32 healthcare institutions (HCIs) between 2004 and 2006. The strains were tested for antibiotic susceptibility and characterized genetically. The incidence of S. aureus BSI declined regularly through 2004 and 2005 and then significantly increased in 2006 (+80%). This was largely due to an increase in BSI involving methicillin-sensitive S. aureus (MSSA) strains and nonmultiresistant methicillin-resistant S. aureus (NORSA) strains. Ninety-six percent of the NORSA strains were resistant only to methicillin and fluoroquinolones. Most of the MSSA strains belonged to a small number of pulsed-field gel electrophoresis (PFGE) divisions and were associated with epidemic phenomena in HCIs. The NORSA strains also clustered into a limited number of PFGE divisions but could not be related to any local outbreak in HCIs. In 2006, there was a significant increase in the incidence of BSI associated with tst gene-positive MSSA strains (+275%) and the first three BSI associated with tst gene-positive MRSA were observed. PFGE data revealed a limited heterogeneity among the tst gene-positive strains without any outbreak in the HCIs. Our study underlines the need for infection control teams to focus efforts on preventing both MRSA and MSSA BSI. As recently demonstrated in vitro, fluoroquinolones may enhance horizontal transfer of virulence and antibiotic resistance genes. These antibiotics are widely used in France, so our findings raise the issue of whether their use has contributed to the acquisition of mecA and tst genes by S. aureus strains.     

Impact of methicillin resistance in S. aureus

The prevalence of methicillin resistance among Staphylococcus aureus strains and the incidence of clinical infections due to methicillin-resistant S. aureus (MRSA) are disturbingly high in France. Evaluations of the negative impact of methicillin-resistance in S. aureus are needed to establish priorities for infection control programs. Whether methicillin resistance independently affects the frequency of S. aureus infections remains unclear. It follows that the impact of methicillin resistance in terms of morbidity, mortality, economic costs, and ecology should be assessed using both infection-free patients and patients infected with susceptible strains as controls. There is abundant direct and indirect evidence that morbidity related to MRSA is at least as high as that related to methicillin-susceptible S. aureus (MSSA). Whether MRSA strains are more virulent than MSSA strains is controversial. Serious MRSA infections are associated with significant mortality and account for a very large part of the overall infection-related mortality rate. Opinion remains divided as to whether multiple-drug resistant S. aureus strains are associated with higher mortality rates than other S. aureus strains. The economic cost of MRSA infections is huge and considerably higher than that of MSSA infections. The heavy glycopeptide use related to the high prevalence of MRSA infections has generated problems in the management of patients with enterococcal infections and may in the near future result in a pandemic of glycopeptide-resistant MRSA infections. The development of programs designed to control the clonal dissemination of MRSA strains is a top priority from both a medical and an economic viewpoint.     

Staphylococcus aureus as source of catheter‐related bloodstream infection evaluated by PFGE and rep‐PCR typing in a Brazilian hospital

Staphylococci are a common cause of catheter‐related bloodstream infection (CR‐BSI), and epidemiological typing is an important tool for effective infection control. This study evaluated by PFGE and rep‐PCR whether Staphylococcus aureus strains isolated from skin and catheter tips were related to specimens isolated from blood. A prospective observational study, carried out in a clinical surgical ward at a Brazilian hospital between September 2000 and November 2002, investigated non‐tunneled central venous catheters from 179 patients. S. aureus isolates were mainly obtained from blood (41.4%), while coagulase‐negative staphylococci strains were more often isolated from the skin at the catheter insertion site (49.7%) and from the catheter tip (57.5%). Among the 21 strains isolated from 9 patients at 2 or 3 sites simultaneously, 9 were methicillin‐resistant S. aureus (MRSA) and 12 were methicillin‐susceptible S. aureus (MSSA). Seven patients harbored the same S. aureus strain isolated from the skin, blood and/or catheter tip cultures. MRSA isolates belonged to one PFGE pattern (type A‐ subtypes A₁, A₂ and A₃), and to two rep‐PCR patterns (a and b). MSSA isolates were distinguished in five PFGE (B to F) and in three rep‐PCR (c, d and e) patterns. Both PFGE and rep‐PCR methods indicated that the skin at the catheter insertion site was the origin of CR‐BSI caused by S. aureus.     

Increasing incidence and widespread dissemination of methicillin-resistant Staphylococcus aureus (MRSA) in hospitals in central Europe, with special reference to German hospitals

Objective: to present data on prevalence and interregional spread of methicillin-resistant Staphylococcus aureus (MRSA) in Germany.
Methods: A nationwide collection of MRSA isolates from nosocomial infections in 143 hospitals was established from isolates ( n =4368) sent to a microbiological reference center during 1993–95. As chosen by distinguishable resistance phenotypes at each time of occurrence during the study period, 1830 isolates were subjected to molecular typing by means of Sma l macrorestriction patterns, PCR for RNA gene spacer patterns, and PCR for patterns of DNA stretches flanked by the ERIC-2 sequence and flanked by Tn 976 and ribosomal binding site. In addition, data from a multicenter study on the incidence of antibiotic resistance have been analyzed (32 centers, 637 S. aureus isolates).
Results: In 1995 the prevalence of MRSA among S. aureus isolates was 8.7% overall in central Europe (including Germany), in comparison to 1.7% in 1990. From 1993 until now, a continuous interregional dissemination of six epidemic strains, which were identified by molecular typing, was recorded. Besides these epidemic strains, 15 MRSA strains were identified which could not be allocated to the epidemic MRSA or to the known clonal groups of the species S. aureus. MRSA from three cases of sporadic nosocomial infections exhibited characteristics of the clonal group of S. aureus with the capacity for toxic shock syndrome formation. The pattern of one MRSA corresponded to those of the S. aureus group exhibiting phage pattern 94,96.
Conclusions: The prevalence of MRSA has increased in central Europe (and Germany) during the last 5 years, to 8.7%. The main source of infection with MRSA is obviously interregional dissemination of epidemic strains. At the same time, the mecA gene has been acquired by strains previously sensitive to methicillin.     

Molecular epidemiologic analysis of Staphylococcus aureus isolated from clinical specimens.

Nosocomial infections caused by Staphylococcus aureus are clinically serious and control of such infections requires strain typing to identify the source of contamination. Recently, pulsed-field gel electrophoresis (PFGE) and random amplified polymorphic DNA (RAPD) assay have been introduced and have provided a high level of strain discrimination of S. aureus isolated from clinical specimens. This study was performed to classify 82 strains of S. aureus isolated from 4 hospitals in the Kwangju-Chonnam area by PFGE and RAPD assay. Methicillin-resistant S. aureus (MRSA) was identified by disk diffusion method using the oxacillin disk and polymerase chain reaction of mecA gene was done in 69 strains. Eight-three strains including S. aureus ATCC 25923 were classified into 10 groups by RAPD assay, and into 8 groups by PFGE. Classified groups were not related to area or hospital. Classification was not characteristic between MRSA and methicillin-susceptible strains. Nosocomial infections due to outbreak were suggested because some strains disclosed identical band patterns by PFGE. These results indicate that medical personnels and instruments are routes of nosocomial infections caused by MRSA. PFGE and RAPD assay are powerful tools for the epidemiological study of S. aureus, but PFGE is more effective than RAPD assay. RAPD assay needs optimal combination of primers.     

An outbreak of methicillin-resistant Staphylococcus aureus infection in patients of a pediatric intensive care unit and high carriage rate among health care workers.

BACKGROUND AND PURPOSE: Methicillin-resistant Staphylococcus aureus (MRSA) has been the leading cause of nosocomial infections in many hospitals. To investigate the impact of carriage by health care workers (HCWs) on patient transmission, surveillance culture was performed following an outbreak of MRSA in a pediatric intensive care unit (PICU). METHODS: Isolates from 61 HCWs and 10 environmental sites were collected. Pulsed-field gel electrophoresis (PFGE) and antibiogram analysis were performed to determine the clonal relationship between isolates and potential routes of transmission. RESULTS: The overall carriage rate of HCWs was 67.2% (41/61) for S. aureus and 26.2% (16/61) for MRSA. One MRSA was isolated from the 10 environmental sites sampled. Two major MRSA clusters were identified based on the PFGE patterns. Isolates with indistinguishable PFGE patterns (pulsotype A) were found in all patient isolates from the outbreak, from several HCWs plus the environmental isolate; all were resistant to ciprofloxacin, clindamycin, erythromycin, gentamicin, tetracycline, and trimethoprim-sulfamethoxazole. Interestingly, the isolate from a patient who had prolonged hospitalization in PICU had PFGE patterns (pulsotype B) distinct from the strains involved in the outbreak. This strain was susceptible to ciprofloxacin and trimethoprim-sulfamethoxazole, and was also found in several HCWs. Thus, there appeared to be 2 main MRSA clones circulating in the PICU of our hospital. CONCLUSIONS: Person-to-person and environment-to-person (or vice versa) transmissions are documented in this study. Strict hand washing before and after patient contact must be enforced and closely monitored, as it is the principal preventive measure in containing the spread of MRSA. To prevent the emergence of vancomycin-resistant MRSA and the further transmission of multidrug-resistant organisms, implementation of periodic and routine active surveillance cultures as part of infection control measures may also be evaluated.     

Clinical isolates of Staphylococcus aureus from the Arkhangelsk region,Russia: antimicrobial susceptibility,molecular epidemiology,and distribution of Panton‐Valentine leucocidin genes

A total of 91 consecutive clinical isolates of Staphylococcus aureus were collected at the Regional Hospital of Arkhangelsk, Russia, from May to December 2004, and examined for antimicrobial susceptibility, methicillin resistance and presence of Panton‐Valentine leucocidin (PVL) genes. Epidemiological typing was performed by pulsed‐field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Methicillin‐resistant S. aureus (MRSA) isolates were examined by staphylococcal cassette chromosome mec (SCCmec) typing. High‐to‐moderate rates of resistance to penicillin (β‐lactamase production; 93%), tetracycline (40%), erythromycin and clindamycin (32%) were observed. Forty out of ninety‐one (44%) isolates were positive for PVL genes. Thirty‐six (40%) PVL‐positive methicillin‐susceptible S. aureus (MSSA) strains were shown by PFGE and MLST typing (ST121, ST681, ST837) to be part of a nosocomial outbreak caused by clonal complex (CC) 121. PFGE, MLST and SCCmec typing revealed three MRSA clones. Sequence type (ST) 239‐III (n=11), ST1097‐III (n=1) and ST8‐IV (n=3) belong to CC8 of epidemic multiresistant MRSA, whereas ST426‐MRSA‐IV/CC395 (n=1) has not been reported previously. All MRSA strains were PVL negative. The overall results underline the necessity of microbiological sampling, antimicrobial susceptibility testing, and epidemiological typing as a rational basis for antimicrobial treatment of S. aureus infections, and infection control measures to limit the spread of multiresistant MRSA and epidemic MSSA clones.     

Detection of new methicillin-resistant Staphylococcus aureus clones containing the toxic shock syndrome toxin 1 gene responsible for hospital- and community-acquired infections in France

Methicillin-resistant Staphylococcus aureus (MRSA) clones harboring the toxic shock syndrome toxin 1 (tst) gene have been detected in France and in Switzerland since 2002. During a passive survey conducted between 2002 and 2003, we collected 103 tst-positive S. aureus isolates from 42 towns in France, of which 27 were resistant to methicillin. The tst-positive MRSA belonged to two clones: a major clone comprising 25 isolates of sequence type (ST) 5 and agr group 2 and a minor clone comprising two isolates of ST30 and agr3. The tst-positive MRSA clones were associated with both hospital-acquired (12 cases) and community-acquired (8 cases) infections. The MRSA clones were mainly isolated from children (overall median age, 3 years). They caused a variety of clinical syndromes, including toxic shock syndrome and suppurative infections. Both clones were found to harbor a type IV staphylococcal chromosomal cassette mec (SCCmec) and to have similar antibiotic resistance profiles (usually resistant to oxacillin, kanamycin, and tobramycin and with intermediate resistance to fusidic acid). The origin of these clones is unclear. The tst-positive agr2 MRSA clone has the same sequence type (ST5) of two pandemic nosocomial MRSA clones, namely, the Pediatric clone and the New York/Japan clone. These findings suggest that all these clones are phylogenetically related. The pulsotype of the tst-positive MRSA clones differed from that of methicillin-sensitive S. aureus (MSSA) clones by a single band involving the SCCmec element. These findings suggest that the tst-positive MRSA clones may have emerged from their respective MSSA counterparts.     

Nosocomial infection caused by methicillin-resistant Staphylococcus aureus in Palestine

This report presents the prevalence of Palestinian isolates of methicillin-resistant Staphylococcus aureus (MRSA) in nosocomial infections and their antibiotic resistant pattern. A total of 321 clinical isolates of S. aureus were identified from different patients. The prevalence of methicillin resistance among S. aureus isolates was 8.7% (28 isolates). Resistance rates of MRSA to other antibiotics were as follows: 82.1% resistant to erythromycin, 67.9% to clindamycin, 64.3% to gentamicin, and 32.1% to ciprofloxacin. No co-trimoxazole- and vancomycin-resistant isolates were identified in this study. The proportion of methicillin resistance was highest among S. aureus isolates associated with upper respiratory specimens (42.8%); the proportion of methicillin resistance was 39.3% among skin ulcer isolates, 10.7% among urinary tract infection isolates, and lowest among isolates associated with blood and prostate discharge (3.6% each).     

mecA gene is widely disseminated in Staphylococcus aureus population

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causes of hospital infections worldwide. High-level resistance to methicillin is caused by the mecA gene, which encodes an alternative penicillin-binding protein, PBP 2a. To determine the clonal relationships between methicillin-susceptible S. aureus (MSSA) and MRSA, we typed 1,069 S. aureus isolates (493 MSSA isolates and 576 MRSA isolates), collected mainly in North American and European hospitals between the 1960s and the year 2000, using pulsed-field gel electrophoresis and ribotyping. Of 10 widespread S. aureus lineages recognized, 8 had corresponding mecA-positive strains. Multiresistant MRSA strains are found in hospitals worldwide, while unrelated and more susceptible strains represent less than 1% of the MRSA population. This supports the hypothesis that horizontal transfer plays an important role in the dissemination of the mecA gene in the S. aureus population.     

Molecular epidemiology of community-associated antimicrobial-resistant Staphylococcus aureus in Seoul, Korea (2003): pervasiveness of multidrug-resistant SCCmec type II methicillin-resistant S. aureus

There is an extremely high incidence of antimicrobial resistance of the clinical isolates of Staphylococcus aureus in Korea. This study carried out a molecular investigation to determine the prevalence of the community-associated antimicrobial-resistant S. aureus and methicillin-resistant S. aureus (MRSA). The percentage resistance from the nasal swabs of healthy volunteers in 2003 in Seoul is as follows: penicillin (91%), erythromycin (EM, 14%), gentamicin (GM, 9.3%), tetracycline (TE, 8.2%), cephalothin (4%), oxacillin (OX, MRSA; 3.8%), clindamycin (CC, 2.6%), ciprofloxacin (CIP, 0.8%), and sulfamethoxazole/trimethoprim (0.6%). The community-associated MRSA (C-MRSA) strains were examined by pulsed-field gel electrophoresis (PFGE) analysis of the SmaI macro-fragments, multilocus sequence typing (MLST), and staphylococcal cassette chromosome mec (SCCmec) typing using the PCR analysis. The Korean C-MRSA isolates were clustered into three distinct groups. One PFGE group containing the C-MRSA strains showed resistance to CC, EM, and GM, a high level (32-96 microg/ml) of resistance to methicillin, sequence type 5 (ST5), and SCCmec type II, which is the most common hospital associated-MRSA (H-MRSA) isolated in Korea. These results highlight the heterogeneous genetic background of the C-MRSA as well as the pervasiveness of the H-MRSA isolates in this community.     

Prevalence of methicillin resistant Staphylococcus aureus in a tertiary referral hospital in eastern Uttar Pradesh

We report the prevalence of methicillin resistant Staphylococcus aureus (MRSA) infections and their antibiotic susceptibility pattern in our hospital located in eastern Uttar Pradesh. Out of total 549 strains of Staphylococcus aureus isolated from different clinical specimens 301 (54.85%) were found to be methicillin resistant. More than 80% of MRSA were found to be resistant to penicillin, cotrimoxazole, ciprofloxacin, gentamicin, erythromycin, tetracycline, 60.5% to amikacin and 47.5% to netilmicin. However, no strains were resistant to vancomycin. Many MRSA strains (32.0%) were multi-drug resistant. To reduce the prevalence of MRSA, the regular surveillance of hospital associated infection, monitoring of antibiotic sensitivity pattern and formulation of definite antibiotic policy may be helpful.     

Molecular characterization and antibiotic susceptibility of Staphylococcus aureus from a multidisciplinary hospital in Romania

From 2004 to 2005, 60%-72% of invasive Staphylococcus aureus isolates from Romanian hospitals were resistant to methicillin (methicillin-resistant S. aureus [MRSA]), the highest frequency for any European nation. Few reports, however, have addressed the molecular characteristics of S. aureus in Romania. In this study, we utilized spa typing, multilocus sequence typing, staphylococcal cassette chromosome mec (SCCmec) typing, dru typing, pulsed-field gel electrophoresis, and detection of virulence factors to characterize 146 S. aureus strains isolated from 2004 to 2005 at the Clinic County Hospital in Bra?ov. Antibiotic susceptibility patterns for all MRSA isolates and patient demographic data were also obtained. Fifty-six strains (38.4%) were determined to be MRSA by susceptibility testing and SCCmec typing. All MRSA strains were resistant to beta-lactams and tetracycline, but susceptible to nitrofurans, vancomycin, and clindamycin, with inducible clindamycin resistance in 23/28 clindamycin-sensitive/erythromycin-resistant isolates. Molecular typing identified 15 clonal backgrounds (CC 1, 5, 8, 8/239, 9, 15, 20, 22, 25, 30, 45, 80, 97, 101, and 121), only 4 of which were associated with MRSA (CC 1, 8/239, 30, and 80). Spa types 35 (t127, CC 1) and 351 (t030, CC 8/239) accounted for 27.4% and 21.9% of all S. aureus strains, respectively, and 19.6% and 57.1% of all MRSA strains. Both hospital-associated (SCCmec type III) and community-associated (SCCmec type IV) elements were identified within MRSA strains, whereas Panton-Valentine leukocidin was detected in 10 MRSA and 12 methicillin-sensitive S. aureus strains. These results demonstrate the presence of various endemic S. aureus clones within the Clinic County Hospital in Bra?ov, suggestive of ongoing nosocomial and community transmission.     

Molecular Epidemiology of Oxacillin-resistant Staphylococcus aureus and in vitro Activity of Glycopeptides against Staphylococcus species

Oxacillin resistant Staphylococcus aureus and coagulase negative Staphylococcus species (MRSA and MRSCoN)have become major pathogens in nosocomial infections.The first MRSA isolate in the world was identified in En gland in 1961 [1]. Since that tim…     

Strategies for molecular characterisation of methicillin- and gentamicin-resistant Staphylococcus aureus in a Canadian nosocomial outbreak

Sixteen methicillin-resistant Staphylococcus aureus (MRSA) isolates, from a single nosocomial outbreak, were tested for molecular and phenotypic relationships. Two of the 16 outbreak strains were gentamicin resistant (Gmr) and the plasmids that they carried were characterised by reverse field electrophoresis, restriction endonuclease analysis and gene hybridisation. The gentamicin-resistant (Gmr) strains harboured two plasmids, a Gmr plasmid of 36.5 kb and a cryptic plasmid of 25.4 kb, whereas the other 14 isolates contained only the cryptic plasmid. Gentamicin resistance was encoded by a 2.5-kb HindIII fragment of the 32.8-kb plasmid and is similar to the 2.5-kb HindIII fragment also described for S. aureus Gmr plasmids from Australia and the USA. The Gmr plasmid was non-conjugal and was cured by ethidium bromide at a frequency of 4%. Two MRSA strains isolated subsequently from the same hospital were also Gmr and had identical plasmid and restriction endonuclease profiles to the two Gmr strains studied initially. Two other S. aureus isolates from the original carrier detected in this study and from his son were methicillin and gentamicin susceptible and had novel profiles. Since large plasmids show anomalous migration in agarose gels, more definitive analyses than simple plasmid identification should be considered when studying nosocomial outbreaks.     

Usefulness of double locus sequence typing (DLST) for regional and international epidemiological surveillance of methicilin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of nosocomial infections worldwide. To differentiate reliably among S. aureus isolates, we recently developed double locus sequence typing (DLST) based on the analysis of partial sequences of clfB and spa genes. In the present study, we evaluated the usefulness of DLST for epidemiological investigations of MRSA by routinely typing 1242 strains isolated in Western Switzerland. Additionally, particular local and international collections were typed by pulsed field gel electrophoresis (PFGE) and DLST to check the compatibility of DLST with the results obtained by PFGE, and for international comparisons. Using DLST, we identified the major MRSA clones of Western Switzerland, and demonstrated the close relationship between local and international clones. The congruence of 88% between the major PFGE and DLST clones indicated that our results obtained by DLST were compatible with earlier results obtained by PFGE. DLST could thus easily be incorporated in a routine surveillance procedure. In addition, the unambiguous definition of DLST types makes this method more suitable than PFGE for long-term epidemiological surveillance. Finally, the comparison of the results obtained by DLST, multilocus sequence typing, PFGE, Staphylococcal cassette chromosome mec typing and the detection of Panton-Valentine leukocidin genes indicated that no typing scheme should be used on its own. It is only the combination of data from different methods that gives the best chance of describing precisely the epidemiology and phylogeny of MRSA.     

An international multicenter study of antimicrobial resistance and typing of hospital Staphylococcus aureus isolates from 21 laboratories in 19 countries or states

During 1996, 4065 consecutive Staphylococcus aureus strains from different patients were collected in 21 worldwide hospital laboratories. The strains, their resistance pattern, and hospital demographic data were forwarded to Statens Serum Institut where the strains were typed and data analyzed. Resistance patterns varied by region and resistance to other antibiotics than methicillin were mainly related to the occurrence of methicillin resistance, except for mupirocin, rifampicin, and fusidic acid. Methicillin-resistant S. aureus (MRSA) occurred with low levels in hospitals in Northern Europe (<1%), increasing levels in middle-European countries, United States, New Zealand, and Australia (6-22%), and very high levels in Southern European countries as well as in parts of the United States, Asia, and South Africa (28-63%). MRSA found in large hospitals were more resistant to other antibiotics than MRSA found in smaller hospitals serviced by the same laboratory. No difference in resistance levels was seen for methicillin-susceptible S. aureus (MSSA) isolated in large or small hospitals. Intensive Care Units had the highest level of MRSA. Strains from the lower respiratory tract showed the highest resistance levels and blood isolates the lowest. A dominating MRSA clone was found in hospitals with an MRSA frequency of more than 10%. Pulsed-field gel electrophoresis (PFGE) typing recognized several of these clones as international epidemic MRSA (E-MRSA). All MSSA isolates were phage typed (typeability 85.4%) and divided in seven major phage patterns. Isolates of all patterns were found in all hospitals except one, indicating that the MSSA seldom represented the spread of clones within the hospital. The comparison should evaluate the prevalence of community-acquired MRSA and identify internationally E-MRSA. The present study gives a snapshot of the MRSA situation, but it is important to build up a continuous national and international surveillance, because MRSA is a global socioeconomic problem. Global infection control procedures, including rational antibiotic use, should be agreed on. The accompanying paper will address the issue of antibiotic consumption and MRSA.     

Molecular genotyping of methicillin-resistant Staphylococcus aureus strains in a teaching hospital in Turkey

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes of nosocomial infections in our hospital. Therefore, we aimed to characterize MRSA isolates phenotypically from patients with nosocomial infections at Cumhuriyet University Hospital between December, 1999, and June, 2001, in Sivas by analysis of antibiotic patterns and genotypically using pulsed-field gel electrophoresis (PFGE) and repetitive element sequence-based polymerase chain reaction (rep-PCR). Forty-three nosocomial isolates were collected from various wards. All isolates were resistant to penicillin, tetracycline, oxacillin, and gentamicin. By rep-PCR and by separation of SmaI fragments of genomic DNA using PFGE, one major type (eight subtypes with PFGE) was identified among the strains. This clone was found to be different than some clones such as Iberian, Brazilian, and a major clone that was found in another Turkish University Hospital in Ankara. According to our results, there is a major MRSA clone with a potential to spread in our hospital. Infection control measures should be directed toward restricting the further spread of this clone. Therefore, in accordance with these findings, a surveillance culturing program should be established.     

ICU中MRSA耐药基因检测及其PFGE分型

目的对耐甲氧西林金黄色葡萄球菌（MRSA）菌株进行分子分型,探讨ICU中MRSA医院感染的特点和流行规律。方法采用表型筛选和PCR扩增mecA基因方法鉴定MRSA菌株。脉冲场凝胶电泳方法（PFGE）进行分子分型。结果12株金黄色葡萄球菌表型筛选为MRSA,MRSA产生A型、B型、C型和D型4种耐药表型,优势耐药模式是A型（75．0％）,MRSA对苯唑西林、阿莫西林／克拉维酸和氨苄西林／舒巴坦等10种抗生素产生100％耐药性,11株MRSA携带mecA基因,携带率为91．7％,PFGE指纹图谱分两型,分别为R1型和R2型,11株MRSA为R1型（91．7％）,R1型各株间相似度为100％。结论ICU可存在MRSA爆发流行,MRSA产生多重耐药性（MDR）,MRSA携带mecA基因可表现为MDR,PFGE分型是理想的分子流行病学溯源手段。     

Molecular genetics of methicillin-resistant Staphylococcus aureus

A large and growing proportion of Staphylococcus aureus clinical isolates are methicillin resistant, and are resistant to practically all beta-lactam antibiotics. Methicillin-resistant S. aureus (MRSA) strains harbor mecA, which is carried by a unique mobile genetic element, staphylococcal cassette chromosome mec (SCCmec) integrated into the S. aureus chromosome. The mecA gene encodes a methicillin-insensitive transpeptidase, the production of which confers resistance to otherwise inhibitory concentrations of beta-lactam antibiotics. Several distinct clones have been identified among MRSA that apparently have been generated by integration of distinct types of SCCmec. While MRSA are primarily nosocomial pathogens, recent observations indicate that other MRSA clones are colonizing a significant proportion of healthy individuals in the community as well. Community-acquired MRSA (C-MRSA), may become a new threat to humans, and international cooperation of researchers and clinicians will be of cardinal importance in addressing this problem.