BACKGROUND: Staphylococcus epidermidis is a leading cause of nosocomial infections, and resistance to methicillin is common in clinical isolates. The distribution of oxacillin MIC for S. epidermidis is not clearly bimodal and it is suspected that the sensitivities for detection of oxacillin resistance by standard susceptibility assays with National Committee for Clinical Laboratory Standards (NCCLS) MIC interpretive criteria (< OR =2 g/mL, > OR =4 g/mL) in S. epidermidis strains are lower than that in Staphylococcus aureus strains. To evaluate the relationship between MIC results and true methicillin resistance, we examined the oxacillin MICs and methicillin MICs by agar dilution and detection of mecA gene by PCR for 41 S. epidermidis strains. METHODS: A total of 41 S. epidermidis strains were examined antimicrobial susceptibility test by VITEK system with GPS-AA card, oxacillin MICs and methicillin MICs by agar dilution and detection of mecA gene by PCR. RESULTS: In antimicrobial susceptibility test by VITEK system with GPS-AA card, 24 strains (58.5%) showed oxacillin resistance. 13 strains (31.7%) required MICs of > OR =4 g/mL in oxacillin MIC test and 19 strains (46.3%) required MICs of > OR =16 g/mL in methicillin MIC test. But 27 strains (65.9%) were mecA positive. One of 15 strains that required oxacillin MICs of < OR =0.5 g/mL, all 3 strains that required oxacillin MICs of 1 g/mL and all 10 strains that required oxacillin MICs of 2 g/mL were mecA positive. CONCLUSIONS: It is suspected that NCCLS MIC interpretive criteria underestimate methicillin resistance among S. epidermidis strains and the PCR method is a reliable reference method.
Agar ; Cross Infection ; Methicillin Resistance* ; Methicillin* ; Oxacillin ; Polymerase Chain Reaction ; Staphylococcus aureus ; Staphylococcus epidermidis* ; Staphylococcus*

BACKGROUND: It is now recognized that screening for methicillin-resistant Staphylococcus aureus (MRSA) in hospital is an effective infection control measure, and selective media-based methods have been commonly used. MRSASelect (MRSAS; Bio-Rad, Hercules, CA, USA) is MRSA selective agar incorporating chromogenic enzymatic substrates, and have been found to be more sensitive and specific than other selective media. The aim of present study was to evaluate MRSAS for discrimination of MRSA from other staphylococci by comparison with mannitol-salt agar with oxacillin (MSO) which is widely used as a MRSA selective medium. METHODS: Ninety-eight staphylococcal strains which were isolated from blood culture specimen, representing 16 MRSA, 6 methicillin-susceptible S. aureus, 59 methicillin-resistant coagulase- negative staphylococci (MRCNS), and 17 methicillin-susceptible coagulase-negative staphylococci were tested. The isolated colonies from pure culture were directly inoculated onto MSO and MRSAS respectively. On MRSAS any growth appearing pink after 24 hours incubation, and on MSO any growth appearing yellow after 48 hours incubation was interpreted as positive for the presence of MRSA. RESULTS: Sensitivities of MRSAS and MSO for MRSA detection were equal (93.8%). Specificities for MRSA discrimination from other staphylococci were 98.8% and 89.0%, and especially from MRCNS were 100% and 84.7%, for MRSAS and MSO, respectively. CONCLUSIONS: The MRSAS showed equal sensitivity compared with MSO for the detection of MRSA. MRSAS showed higher specificity than MSO in discrimination MRSA from MRCNS. It was suggested that the implementation of MRSAS in MRSA screening could decrease the work needed for MRCNS identification.
Agar ; Discrimination (Psychology) ; Infection Control ; Mass Screening ; Methicillin Resistance ; Methicillin-Resistant Staphylococcus aureus ; Oxacillin ; Sensitivity and Specificity

All of the methicillin-resistant Staphylococcus aureus (MRSA) strains exhibit resistance to oxacillin by producing PBP2a encoded by mecA, whereas methicllin-susceptible Staphylococcus aureus (MSSA) strains do not. To investigate phenotypic differences other than oxacillin resistance level in responses to oxacillin between MSSA and MRSA, we compared alterations of viability and ultrastructure of MSSA by oxacillin treatment with those of MRSA. When MSSA and MRSA strains were exposed to oxacillin of their respective MICs, and then were assayed for viability and observed by transmission electron microscope, increase in thickness of cell wall was more prominent in MRSA strains than in MSSA strains, while decrease in number of surviving cells was more evident and change in morphology of growing cross wall was greater in MSSA strains than in MRSA strains. It is assumed that these different responses to oxacillin between MSSA and MRSA strains may be due to activation of some PBP2a unbound to oxacillin. In conclusion, MSSA and MRSA showed different functional and morphological responses to oxacillin, although they were treated with oxacillin of concentrations that respectively inhibit their proliferation.
Adenosine ; Cell Wall ; Electrons ; Methicillin-Resistant Staphylococcus aureus ; Oxacillin ; Staphylococcus aureus

BACKGROUND: The detection of methicillin resistance is complicated because of its heterogeneous phenotypic expression, and the oxacillin-salt agar screen (OSA) test has been recommended by the National Committee for Clinical Laboratory Standards (NCCLS). The OSA test is recognized as a sensitive and specific test, but the sensitivity and specificity of this test vary among different investigators. In this study, we evaluated the OSA test for detection of methicillin-resistant S. aureus (MRSA) by comparing it to the disk diffusion test and to the MRSA-Screen test (Denka Seiken Co., Ltd., Tokyo, Japan). METHODS: A total of 1,130 S. aureus clinical isolates collected between September 1999 and September 2000 were used. The disk diffusion and OSA tests were carried out on all the isolates according to the NCCLS guidelines. In performing the OSA test, all isolates were inoculated on a growth control plate containing 4% NaCl (without oxacillin). For isolates with discrepant results through the disk diffusion and the OSA tests, the MRSA-Screen test that detects PBP 2a with a monoclonal antibody was performed. RESULTS: Of 1,130 S. aureus isolates, 1,120 isolates (99.1%) yielded concordant results with the disk diffusion and the OSA tests. Ten isolates (0.88%) yielded discrepant results between two methods: three isolates were oxacillin susceptible with the disk diffusion test but grew on the OSA plate. Of these three isolates, two isolates were MRSA-Screen negative. One isolate was oxacillin resistant with the disk diffusion test but did not grow on the OSA plate and was MRSA-Screen positive. Six isolates (0.53%) did not grow either on the OSA plate or the growth control plate. CONCLUSIONS: Only one isolate (0.09%) that was not detectable using the disk diffusion test was correctly classified as MRSA by the OSA test. Also, for accurate detection of MRSA by the OSA test, 4% NaCl-containing growth control plate should be included.
Agar* ; Diffusion ; Humans ; Methicillin Resistance* ; Methicillin-Resistant Staphylococcus aureus* ; Oxacillin ; Research Personnel ; Sensitivity and Specificity

BACKGROUND: Coagulase negative staphylococcus (CNS) spp. is a major pathogenic organism of nosocomial and community-acquired urianry tract infections, and causes infrctions in the immunocompromised host, and in particular, bloodstream infetions in patent with indwelling devices. High prevalance of methicillin resistance has been noticed in CNS which also have been recongnized as an important multidrug resistant pathogen. The optimal phenotypic method for detecting methicillin resistance still remains controversial, and new guidelines for detecting methicillin resistance of CNS was proposed by NCCLS in January 1999. We evaluated the relationship between mecA gene by PCR method and antimicrobial susceptibility tests according to the new NCCLS guidelines. METHODS: A total of 82 CNS isolates were examined for MICs and penicillin MICs by disk diffusion and agar dilution method according to NCCLS guidelines, and detections, and detection of mecA gene by PCR. RESULT: In disk diffusion method, 66 strains (80.5%) and 63 strains (76.8%) showed resistance to penicillin and oxacillin, respectively, and in agar dilution method, 71 strains(86.6%) and 53 strains (64.6%), respectively. In PCR method, mecA genes were detected in 49 strains(59.8%). Comparing with mecA gene detection by PCR method, the sensitivity of disk diffusion and agar dilution method was 95.8% and 89.8%, repectively. However, the sensitivity of disk diffusion and agar dilution method was 65.3% and 75.5%, respectively using previous NCCLS criteria. CONCLUSION: The new criteria of NCCLS detects the methicillin resistance induced by mecA gene more sensitively than previous one.
Agar ; Coagulase* ; Diffusion ; Immunocompromised Host ; Methicillin Resistance ; Oxacillin ; Penicillins ; Polymerase Chain Reaction ; Staphylococcus*

A bacterial study of the conjunctival sac of 115 patients with an anophthalmic eye has compared the kinds of normal flora in the conjunctival sac of normal and anophthalmic eyes and investigated the susceptibility of the isolated bacteria to various antibiotics. Detection rate of bacteria were 35.7% and 69.6% in normal and anophthalmic eyes, respectively. In normal eyes S. epidermidis(40.4%) were isolated more frequently than S. aureus(21.3%), but the detection rate for each bacteria in anophthalmic eyes showed no significant differences. The incidence rate in kinds of bacterial flora in both conjunctival sacs of a person who has one anophthalmic eye was 37.5%, lower than that of a person with normal eyes(71.4% to 96.5%). Bacteria isolated from normal and anophthalmic conjunctiva were similarly sensitive to amikacin, cefazolin, erythromycin, oxacillin. and tobramycin and were resistant to ampicillin and penicllin.
Amikacin ; Ampicillin ; Anophthalmos ; Anti-Bacterial Agents ; Bacteria ; Cefazolin ; Conjunctiva ; Erythromycin ; Eye ; Humans ; Incidence ; Oxacillin ; Tobramycin

PURPOSE: Pneumoccocus is one of the most important causes of invasive infection through the childhood period and the prevelance of antibiotics resistance of pneumococcus is increasing worldwide. A 7-valent conjugate vaccine has been developed. It is important to know the prevalence of each serotype of pneumococci in the countries where the vaccine is used to estimate the coverage rate by the vaccine. METHODS: One hundred and twenty seven strains of clinical isolates and 72 strains from healthy carriers recovered from Korean children during the period from 1997 to 2002 were subjected to determination of serotype by Quellung reaction and penicillin susceptibility with oxacillin disc diffusion test. RESULTS: Forty-three per cent of clinical isolates were obtained from children under two years of age. Thirty strains(24%) were isolated from normally sterile body fluids. The frequent serotypes were 19F, 19A, 23F, 6A, 6B and 9V. Fifty-six per cent of the clinical isolates were represented in the current 7-valent protein conjugate pneumococccal vaccine, and 84% when the cross-reactive serotypes were included. Frequent serotypes of strains isolated from one to five year-old healthy children were 19F, 14, 11A, 23F, 18C, and 19A. Seventy-one per cent of the carrier strains were included in the 7-valent vaccine. Ninety-three per cent of the clinical isolates and 86% of carrier strains were not susceptible to penicilline. CONCLUSION: Fifty-six to 84% of pneumococci recovered from Korean children are covered by the current 7-valent protein conjugate pneumococcal vaccine and the prevalence of penicillin resistance was very high.
Anti-Bacterial Agents ; Body Fluids ; Child* ; Diffusion ; Humans ; Oxacillin ; Penicillin Resistance ; Penicillins* ; Prevalence ; Streptococcus pneumoniae* ; Streptococcus*

BACKGROUND: Staphylococci are major nosocomial pathogens and reveal an increase in resistant strains such as methicillin-resistant Staphylococcus aureus. For treatment of infection and prevention of dissemination, rapid and reliable identification methods are required but the conventional bacterial identification and susceptibility tests require at least 24 hours. In this study, we evaluated the polymerase chain reaction (PCR) of the antibiotic resistant genes by comparing with the disk diffusion susceptibility test for the detection of resistance to penicillin, oxacillin and gentamicin. METHODS: A hundred-thirty-five staphylococci including 95 S. aureus and 40 S. epidermidis were from clinical specimens from June to December 2000. Antimicrobial susceptibility tests were done using the NCCLS disk diffusion method. PCRs were performed with primer sets specific for mecA, blaZ and aac(6')-aph(2"). The species-specific PCR was also used to identify S. aureus and S. epidermidis. RESULTS: All four penicillin-susceptible staphylococci were negative for blaZ and 108 of 131 penicillin resistant-staphylococci were positive for blaZ. The concordance rate for PCR of the blaZ gene and penicillin disk diffusion test was 83.0%. 110 of 115 oxacillin-resistant staphylococci were positive for mecA and all five mecA negative oxacillin-resistant strains were positive for blaZ and have the phenotype beta-Lactamase hyperproducer. One of the oxacillin-susceptible S. aureus was positive for mecA. The concordance rate of PCR for the mecA gene and oxacillin disk diffusion test and those of the aac(6')-aph(2") gene and gentamicin disk diffusion test was 95.6% and 97.8%, respectively. CONCLUSTIONS: The disk diffusion tests misdiagnosed 25% of the mecA negative staphylococci as methicillin-resistant staphylococci (MRS) and lost one of the mecA positive strain. We considered that the detection of the mecA and blaZ gene using the PCR was more useful than the disk diffusion test for detection of methicillin-resistant staphylococci.
beta-Lactamases ; Diffusion ; Gentamicins ; Methicillin Resistance ; Methicillin-Resistant Staphylococcus aureus ; Oxacillin ; Penicillins ; Phenotype ; Polymerase Chain Reaction*

BACKGROUND: Daptomycin is a novel cyclic lipopeptide antibiotic that exhibits in vitro bactericidal activity against gram-positive pathogens including methicillin-resistant staphylococci and vancomycin-resistant enterococci. The aim of this study is to determine the in vitro activities of daptomycin against recent clinical isolates of methicillin-resistant staphylococci and vancomycin-resistant enterococci in Korea. MATERIALS AND METHODS: A total of 117 clinical strains of methicillin-resistant staphylococci and vancomycin-resistant enterococci were isolated at a tertiary-care hospital in Korea in 2004. Susceptibility to daptomycin was tested by the CLSI broth microdilution method using Mueller-Hinton broth (MHB) which was adjusted to contain a final concentration of 50 microgram/mL of ionized calcium (Ca2+). Susceptibilities to ampicillin, oxacillin, levofloxacin, vancomycin, and linezolid were tested by the CLSI agar dilution method. RESULTS: All isolates of methicillin-resistant S. aureus and coagulase-negative staphylococci were inhibited by 1 microgram/mL of daptomycin, and MIC90s were 1 microgram/mL, which were similar to those of vancomycin and linezolid. MIC90s of daptomycin for vancomycin-resistant E. faecalis and E. faecium were 0.5 microgram/mL and 2 microgram/mL, respectively, and all isolates were susceptible to daptomycin. MIC90s of linezolid and levofloxacin for vancomycin-resistant enterococci were 1-2 microgram/mL and 64 microgram/mL, respectively. Resistance rates of vancomycin-resistant E. faecalis and E. faecium to levofloxacin were 100% and 96%, respectively. Daptomycin MICs in MHB supplemented to 20-25 microgram/ml of Ca2+ were 2-8 fold higher than those in MHB supplemented to 50 microgram/mL of Ca2+. CONCLUSION: Daptomycin is very active in vitro against methicillin-resistant staphylococci and vancomycin-resistant enterococci isolated in Korea, and it is important to test in vitro activity of daptomycin using MHB containing 50 microgram/mL of Ca2+.
Agar ; Ampicillin ; Calcium ; Daptomycin* ; Korea* ; Levofloxacin ; Linezolid ; Methicillin Resistance* ; Methicillin-Resistant Staphylococcus aureus ; Oxacillin ; Vancomycin

BACKGROUND: Daptomycin is a novel cyclic lipopeptide antibiotic that exhibits in vitro bactericidal activity against gram-positive pathogens including methicillin-resistant staphylococci and vancomycin-resistant enterococci. The aim of this study is to determine the in vitro activities of daptomycin against recent clinical isolates of methicillin-resistant staphylococci and vancomycin-resistant enterococci in Korea. MATERIALS AND METHODS: A total of 117 clinical strains of methicillin-resistant staphylococci and vancomycin-resistant enterococci were isolated at a tertiary-care hospital in Korea in 2004. Susceptibility to daptomycin was tested by the CLSI broth microdilution method using Mueller-Hinton broth (MHB) which was adjusted to contain a final concentration of 50 microgram/mL of ionized calcium (Ca2+). Susceptibilities to ampicillin, oxacillin, levofloxacin, vancomycin, and linezolid were tested by the CLSI agar dilution method. RESULTS: All isolates of methicillin-resistant S. aureus and coagulase-negative staphylococci were inhibited by 1 microgram/mL of daptomycin, and MIC90s were 1 microgram/mL, which were similar to those of vancomycin and linezolid. MIC90s of daptomycin for vancomycin-resistant E. faecalis and E. faecium were 0.5 microgram/mL and 2 microgram/mL, respectively, and all isolates were susceptible to daptomycin. MIC90s of linezolid and levofloxacin for vancomycin-resistant enterococci were 1-2 microgram/mL and 64 microgram/mL, respectively. Resistance rates of vancomycin-resistant E. faecalis and E. faecium to levofloxacin were 100% and 96%, respectively. Daptomycin MICs in MHB supplemented to 20-25 microgram/ml of Ca2+ were 2-8 fold higher than those in MHB supplemented to 50 microgram/mL of Ca2+. CONCLUSION: Daptomycin is very active in vitro against methicillin-resistant staphylococci and vancomycin-resistant enterococci isolated in Korea, and it is important to test in vitro activity of daptomycin using MHB containing 50 microgram/mL of Ca2+.
Agar ; Ampicillin ; Calcium ; Daptomycin* ; Korea* ; Levofloxacin ; Linezolid ; Methicillin Resistance* ; Methicillin-Resistant Staphylococcus aureus ; Oxacillin ; Vancomycin