An epidemiological study of methicillin-resistant Staphylococcus aureus (MRSA) isolated from medical staff, inpatients, and hospital environment in one ward at our hospital.

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causative microorganisms for nosocomial infections. Recently, the incidence of isolation of MRSA has been increasing every year in Japan and is, notably, much more frequently found in inpatients than in outpatients. Therefore, we have done epidemiological studies of MRSA isolated from medical staff, inpatients, and the hospital environment in one ward of our hospital. Thereafter, we examined the antibiotic susceptibility (ABPC, DMPPC, CET, CMZ, IPM, GM, MINO, OFLX, EM, CLDM, VCM), phage typing, and coagulase typing of these MRSA. MRSA were isolated more frequently from anterior nares of inpatients than from doctors and nurses. MRSA were isolated more frequently from the environment near carriers of MRSA. Coagulase type II and phage type N.T. (not typable) were the dominant types of MRSA in our hospital (69% and 61%). MRSA strains were resistant to most antibiotics with a few exceptions (VCM, IPM, CMZ, CET). The high isolation frequency of MRSA in our hospital seems to suggest that inpatients who are carrying MRSA spread MRSA throughout the hospital environment and that the anterior nares of inpatients are the major MRSA harbor.     

Comparison of DNA fingerprinting by PFGE and PCR-RFLP of the coagulase gene to distinguish MRSA isolates

Staphylococcus aureus isolates were collected from epidemiologically unrelated clinical sources in Japan between 1991 and 1993. A total of 40 isolates, five each of eight coagulase types, were analysed by polymerase chain reaction (PCR) of the coagulase gene, PCR-restriction fragment length polymorphism (RFLP) after AluI digestion, and pulsedfield gel electrophoresis (PFGE) of chromosomal DNA after SmaI digestion. The efficiency of discrimination among the isolates increased in the order of PCR < PCR-RFLP < PFGE, yielding five, 13 and 31 different types, respectively. To assess the clinical use of these methods, 42 additional methicillin-resistant S. aureus (MRSA) isolates collected from 27 inpatients in a hospital were analysed. PFGE and PCR-RFLP were able to discriminate 11 and four types, respectively. PFGE analysis detected cross-infection between four postoperative patients in an intensive-care unit, and in six neonates in intensive care. We conclude that of the three methods tested, PFGE analysis currently allows the most effective discrimination of MRSA strains.     

Mueller–Hinton agar is superior to PDM blood agar for detection of methicillin-resistant Staphylococcus aureus

The aim of this study was to compare the expression of oxacillin resistance in methicillin-resistant Staphylococcus aureus (MRSA) on Paper Disc Method agar supplemented with 5% defibrinated blood (PDM blood agar) and Mueller–Hinton agar supplemented with 2% NaCl (MH NaCl agar) using different susceptibility tests. Fifty mecA- containing isolates of S. aureus, exhibiting 46 different pulsed-field gel electrophoresis patterns, were comparatively tested using the E test, the single disk diffusion test, and the multipoint inoculation technique, under various culture conditions. The E test incubated at 35 °C for 24 h (breakpoint of resistance ≥2.0 mg/L) detected 94% of the isolates on MH NaCl agar, compared with 28% for PDM blood agar ( P  < 0.05). The disk diffusion test (breakpoint ≤ 10 mm in diameter) under these incubation conditions detected resistance in 100% of the isolates on MH NaCl agar and in 80% of the isolates on PDM blood agar ( P  < 0.05). The multipoint technique (breakpoint ≥1 mg/L), applied at 35 °C for 24 h, detected 100% on MH NaCl agar and 46% on PDM blood agar ( P  < 0.05). Irrespective of the method of susceptibility testing evaluated, MH NaCl agar was superior to PDM blood agar for the detection of oxacillin resistance in mecA -containing S. aureus .     

Characterisation of non-multiresistant methicillin-resistant Staphylococcus aureus (including EMRSA-15) in Kuwait Hospitals

This study characterised non-multiresistant methicillin-resistant Staphylococcus aureus (nmMRSA) isolates from Kuwait hospitals to ascertain whether they were community-acquired MRSA (CA-MRSA). Forty-two nmMRSA isolates obtained between July 2001 and October 2003 were analysed by staphylococcal cassette chromosome mec (SCCmec) typing, bacteriophage typing, production of Panton-Valentine leukocidin (PVL), urease and staphylococcal enterotoxins A, B, C and D, TSST-1, and by pulsed-field gel electrophoresis (PFGE). Forty-one isolates were SCCmec type IV, and one isolate was SCCmec type III. The isolates belonged to six PFGE patterns, with two types, A and D, distributed in six and four hospitals, respectively. Most (n = 26; 61.9%) isolates produced urease. These isolates were mainly from wound and skin infections, showed low-level methicillin resistance (MIC 8-48 mg/L), and nine carried genes for PVL. These characteristics, together with their carriage of the type-IV SCCmec, identified the isolates as CA-MRSA. Ten of the 16 urease-negative isolates produced staphylococal enterotoxin C; 12 reacted weakly with phage 75, and were resistant to clindamycin and/or erythromycin, which are characteristics of EMRSA-15. Thus, this study identified the co-existence of two types of nmMRSA, i.e., CA-MRSA and EMRSA-15, in Kuwait hospitals.     

Antimicrobial susceptibility patterns of Staphylococcus aureus in Poland obtained by the National Quality Assurance Programme

As part of the Polish external quality assurance scheme, clinical laboratories were asked to send five consecutive isolates of Staphylococcus aureus and the corresponding susceptibility results to the national Centre of Quality Control in Microbiology. Of 1376 isolates submitted as S. aureus from 276 medical centres, 13 (< 1%) had been misidentified by local laboratories. Of 181 (13.5%) methicillin-resistant S. aureus (MRSA) isolates, most were identified correctly (c. 98% of laboratories). Although all MRSA isolates were fully susceptible to vancomycin, teicoplanin and linezolid, they were usually multiresistant; almost 23% were resistant to seven antimicrobial agents. Most (> 90%) MSSA isolates were susceptible to the tested antibiotics, except penicillin (21% susceptible) and tetracycline (62.4% susceptible). In addition to evaluating the proficiency of testing by local laboratories, the study yielded valuable information regarding the susceptibility patterns of S. aureus isolates in Poland.     

Subtyping of MRSA isolates belonging to a widely disseminated clonal group by polymorphism of the dru sequences in mec-associated DNA

During the past 7 years the "Berlin epidemic MRSA" has spread throughout whole Germany. SmaI macrorestriction patterns of this clonal group are rather stable as are the length polymorphisms at the 3' end of the coagulase gene and the x-region of spa. However, the dru region (direct repeat units) of mec-associated DNA exhibits a length polymorphism due to deletion of one or more direct repeat units. Five different subclones could be discriminated by dru region length polymorphism. Location of deletions and of a few point mutations allow a delineation of these subclones.     

A new multiplex PCR for easy screening of methicillin-resistant Staphylococcus aureus SCCmec types I–V

A multiplex PCR with four primer-pairs was designed to identify the five main known SCCmec types. A clear and easily discriminated band pattern was obtained for all five types. The SCCmec type was identified for 98% of 312 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). SCCmec type IV was by far the most common SCCmec type among both hospital- and community-acquired MRSA isolates in Denmark.     

Evolution, antimicrobial susceptibility and assignment to international clones of methicillin-resistant Staphylococcus aureus isolated over a 9-year period in two Spanish hospitals

Antimicrobial resistance profiles, restriction fragment length polymorphism of the coagulase gene and repetitive element sequence-based PCR were used to classify 210 methicillin-resistant Staphylococcus aureus isolates recovered between 1997 and 2005 in two hospitals in Vigo, north-west Spain. Representative isolates belonging to the epidemic clones were analysed by spa typing and multilocus sequence typing, and the staphylococcal chromosomal cassette (SCC)mec type was determined for all isolates. The New York/Japan clone (t002-ST5-II) was detected in Spain for the first time. However, the New York/Japan and the Brazilian (t037-ST239-IIIA) clones were replaced by EMRSA-16 (t018-ST36-II), which at present is the predominant clone.     

Comparative in vitro activity of l-ofloxacin and FK037 to other agents against 10,040 fresh clinical isolates

Fresh clinical isolates collected from November 1, 1992 through November 1, 1993, were tested by agar dilution against 26 different antimicrobial agents including FK037 and l-ofloxacin. Among the 10 040 organisms tested were Staphylococcus aureus (n = 1222), methicillin-resistant Staphylococcus aureus (MRSA, n = 455), Staphylococcus epidermidis (n = 533), Staphylococcus hominis (n = 90), Staphylococcus hemolyticus (n = 89), Streptococcus pneumoniae (n = 144), Escherichia coli (n = 2326), Klebsiella pneumoniae (n = 745), Enterobacter cloacae (n = 258), Proteus mirabilis (n = 445), Pseudomonas aeruginosa (n = 998), and Stenotrophomonas (Xanthomonas) maltophilia (n = 102). Both l-ofloxacin and FK037 inhibited 98% of S. aureus strains at 4 mug/ml. FK037 was at least 4 times more effective than the third generation cephalosporins against MRSA, inhibiting 79% of the strains at 16 mug/ml. While the potency of these agents looks promising, their clinical utility will depend in part upon the maximal dosage that can be safely administered.