Analysis of borderline-resistant strains of methicillin-resistant Staphylococcus aureus using polymerase chain reaction.

Identification of methicillin-resistant Staphylococcus aureus by drug-susceptibility tests alone poses a serious problem, because a considerable number of clinical S. aureus isolates are borderline resistant to methicillin. To circumvent this problem, we have developed a quick and sensitive method of PCR amplification for the detection of mecA gene, which, coding for PBP2', is the specific genetic element of methicillin-resistant Staphylococcus aureus. This method made it possible to identify MRSA strains in a short time using as few as 30 cells as a starting material for template DNA. Using this method, we found that the strains of borderline methicillin-resistance could be accurately identified. We also found one S. aureus clinical strain, T3, which lacked mecA gene in spite of its resistance to methicillin.     

Antimicrobial Susceptibility Profiles and Strain Type Diversity of Campylobacter jejuni Isolates from Turkeys in Eastern North Carolina

Campylobacter jejuni is one of the most common bacterial causes of human gastroenteritis, and recent findings suggest that turkeys are an important reservoir for this organism. In this study, 80 C. jejuni isolates from eastern North Carolina were characterized for resistance to nine antimicrobials, and strain types were determined by fla typing, pulsed-field gel electrophoresis (PFGE) with SmaI and KpnI, and (for 41 isolates) multilocus sequence typing (MLST). PFGE analysis suggested that many of the isolates (37/40 [ca. 93%]) in a major genomic cluster had DNA that was partially methylated at SmaI sites. Furthermore, 12/40 (30%) of the isolates in this cluster were completely resistant to digestion by KpnI, suggesting methylation at KpnI sites. MLST of 41 isolates identified 10 sequence types (STs), of which 4 were new. Three STs (ST-1839, ST-2132 and the new ST-2934) were predominant and were detected among isolates from different farms. The majority of the isolates (74%) were resistant to three or more antimicrobials, and resistance to ciprofloxacin was common (64%), whereas resistance to the other drug of choice for treatment of human campylobacteriosis, erythromycin, was never encountered. Most (33/34) of the kanamycin-resistant isolates were also resistant to tetracycline; however, only ca. 50% of the tetracycline-resistant isolates were also kanamycin resistant. Isolates with certain antimicrobial resistance profiles had identical or closely related strain types. Overall, the findings suggest dissemination of certain clonal groups of C. jejuni isolates in the turkey production industry of this region.     

Intestinal colonization of newborns treated in intensive care units by multiple drug resistant microorganisms

The aim of the study was to examine the digestive tract colonisation of the newborns by multiple drug resistant bacteria during hospitalization. On the day of admission, after 5 days of hospitalization and at the day of discharge swabs from the anus of the 31 newborns hospitalized in OITiPN were taken and cultured on nutrient and selective media for staphylococci, enterococci, gram negative bacilli and fungi. Susceptibility to antibiotics of bacteria was determined, with giving attention to such resistance mechanisms as: methicillin resistant staphylococci (MRS), high level aminoglycoside resistant (HLAR) and vancomycin resistant enterococci (VRE) and the production of extended spectrum beta-lactamases (type ESBL) by gram negative bacilli. On the day of admission in 7 newborns methicillin resistant staphylococci (MRSCN) were grown in 24 no multiple drug resistant bacteria were found. Among those in 23 already after 5 days of hospitalization, colonization by multiple drug resistant strains was determined: coagulase-negative methicillin resistant staphylococci (MRSCN) were found in 16 children, strains of enterococci (HLAR) in 3 newborns and gram negative ESBL (+) bacilli also in 3 cases. On the day of discharge from hospital (after 13-141 days) in 23 out of 24 newborns enteric tract colonization by multiple drug resistant strains was assessed. In the enteric tract of 3 newborns hospitalized up to 2 weeks coagulase-negative methicillin resistant staphylococci (MRSCN) and/or HLAR enterococci were found; gram negative bacilli that produce ESBL appeared in newborns hospitalized for longer than 14 days. They were isolated in 12 out of 21 newborns. Forming of the enteric tract bacterial flora of the long hospitalized newborns depends on the time of hospitalization as well as on the used therapy.     

Genome Analysis of Multi- and Extensively-Drug-Resistant Tuberculosis from KwaZulu-Natal,South Africa

The KZN strain family of Mycobacterium tuberculosis is a highly virulent strain endemic to the KwaZulu-Natal region of South Africa, which has recently experienced an outbreak of extensively-drug resistant tuberculosis. To investigate the causes and evolution of drug-resistance, we determined the DNA sequences of several clinical isolates - one drug-susceptible, one multi-drug resistant, and nine extensively drug-resistant - using whole-genome sequencing. Analysis of polymorphisms among the strains is consistent with the drug-susceptibility profiles, in that well-known mutations are observed that are correlated with resistance to isoniazid, rifampicin, kanamycin, ofloxacin, ethambutol, and pyrazinamide. However, the mutations responsible for rifampicin resistance in rpoB and pyrazinamide in pncA are in different nucleotide positions in the multi-drug-resistant and extensively drug-resistant strains, clearly showing that they acquired these mutations independently, and that the XDR strain could not have evolved directly from the MDR strain (though it could have arisen from another similar MDR strain). Sequencing of eight additional XDR strains from other areas of KwaZulu-Natal shows that they have identical drug resistant mutations to the first one sequenced, including the same polymorphisms at sites associated with drug resistance, supporting the theory that this represents a case of clonal expansion.     

Virulence and resistance determinants of German Staphylococcus aureus ST398 isolates from nonhuman sources

A series of 100 Staphylococcus aureus isolates ascribed to sequence type 398 (ST398) and recovered from different sources (healthy carrier and diseased pigs, dust from pig farms, milk, and meat) in Germany were investigated for their virulence and antimicrobial resistance genetic background. Antimicrobial resistance was determined by the disk diffusion method. Virulence and resistance determinants (37 and 31 genes, respectively) were tested by PCR. Only two virulence profiles, including the accessory gene regulator agrI and three or four hemolysin-encoding genes, were detected. In contrast, 33 resistance profiles were distinguished (only 11 were shown by more than one isolate). Fifty-nine isolates were multiresistant (four or more antimicrobial classes), and 98 were methicillin resistant (mecA positive). All of the ST398 isolates showed resistance to tetracycline [encoded by tet(M) alone or together with tet(K) and/or tet(L)]. In addition, 98% were resistant to other antimicrobials, including macrolide-lincosamine-streptogramin B (70%, encoded by ermA, ermB, and ermC, alone or in combination), trimethoprim (65%, mostly due to dfrK and dfrG), kanamycin and gentamicin [29% and 14%, respectively, mainly related to aac(6')-Ie-aph(2″)-Ia and/or ant(4')-Ia but also to aph(3')-IIIa], chloramphenicol (9%, fexA or cfr), quinupristin-dalfopristin (9%), ciprofloxacin (8%), and trimethoprim-sulfamethoxazole (4%). The heterogeneity of the resistance profiles underlines the ability of the ST398 clone to acquire multiple antimicrobial resistance genes. However, the virulence gene content of the tested isolates was low. Continuous surveillance is needed to clarify whether its pathogenicity potential for animals and humans will increase over time.     

凝固酶阴性葡萄球菌耐药基因和粘附基因检测及耐药性分析

目的了解凝固酶阴性葡萄球菌（CoNS）耐药基因和粘附基因的分布及其耐药性情况。方法收集45株凝固酶阴性葡萄球菌临床分离株,采用PCR检测其耐药基因mecA和粘附基因c弘知如B,并分析其耐药性。结果（1）凝固酶阴性葡萄球菌中mecA、cva、fn6pB的阳性率依次为86．7％（39／45）、11．1％（5／45）、71．1％（32／45）。（2）凝固酶阴性葡萄球菌中耐甲氧西林凝固酶阴性葡萄球菌（MRCoNS）的检出率为88．9％,对β-内酰胺类抗生素的耐药率都在80％以上,对利福平、左氧氟沙星、林可霉素的耐药率较低,未发现对万古霉素、利奈唑胺耐药菌株。结论CoNS中MRCoNS检出率很高,对常用抗生素耐药率高,且有一定的粘附能力,临床上应该根据药敏试验结果慎重及合理的使用抗生素。     

Molecular characterization of antibiotic resistance in clinical Salmonella typhi isolated in Ghana

Fifty-eight clinical Salmonella typhi strains isolated from patients suspected of suffering from typhoid fever were obtained at the Korle-Bu Teaching Hospital and the Noguchi Memorial Institute for Medical Research, both located in Ghana, Africa. Each isolate was examined for susceptibility to ampicillin, chloramphenicol, streptomycin, tetracycline, and trimethoprim/sulfamethoxazole by the disk diffusion assay. Five of the isolates were resistant to all five antibiotics while 10 isolates were resistant to ampicillin, chloramphenicol, and trimethoprim/sulfamethoxazole, which are considered 'first line' antibiotics in the treatment of typhoid fever. Thirty-four isolates were resistant to at least one of the antibiotics tested and 62% of these isolates possessed conjugable plasmids belonging to incompatibility group IncHI. Ninety percent of the conjugable plasmids conferred a multiple drug-resistant phenotype on the strains harboring them. Additionally, 14 strains contained plasmids that were transformable and six of them encoded multiple drug resistance. Our findings indicate that multiple drug resistance to the 'first line' antibiotics in S. typhi may be more prevalent in Africa than previously thought.     

Environmental Vibrio spp., isolated in Mozambique, contain a polymorphic group of integrative conjugative elements and class 1 integrons

Circulation of mobile genetic elements linked to drug resistance spread was studied in Vibrio strains isolated from surface urban water (river and sea) and shellfish samples in 2002-2003 in Maputo, Mozambique. Class 1 integrons and integrating conjugative elements (ICE) were investigated by PCR and mating experiments in strains of major health interest: 10 Vibrio cholerae, six Vibrio parahaemolyticus, two Vibrio alginolyticus and one Vibrio fluvialis. Resistance to at least two antibiotics (predominantly beta-lactams) was detected in all the strains, with additional resistances to sulfamethoxazole, spectinomycin, streptomycin and/or trimethoprim. Class 1 integrons contributed partially to the expression of drug resistance and were found in five isolates: four V. cholerae (blaP1 cassette, one strain also contained the dfrA15 cassette) and one V. alginolyticus (aadA2 cassette). ICEs, apparently devoid of resistance genes, were found in eight V. cholerae, three V. parahaemolyticus and one V. fluvialis isolates. A wide variability was observed by molecular characterization of ICEs. Five ICEs were included in the SXT/R391 family and seven ICEs were not classified. Our results indicate that the SXT/R391 family and related ICEs comprise a large class of polymorphic genetic elements widely circulating in environmental Vibrio strains in Africa, beside those evidently linked to drug resistance in clinical isolates.     

Mutation in the C-Di-AMP Cyclase dacA Affects Fitness and Resistance of Methicillin Resistant Staphylococcus aureus

Faster growing and more virulent strains of methicillin resistant Staphylococcus aureus (MRSA) are increasingly displacing highly resistant MRSA. Elevated fitness in these MRSA is often accompanied by decreased and heterogeneous levels of methicillin resistance; however, the mechanisms for this phenomenon are not yet fully understood. Whole genome sequencing was used to investigate the genetic basis of this apparent correlation, in an isogenic MRSA strain pair that differed in methicillin resistance levels and fitness, with respect to growth rate. Sequencing revealed only one single nucleotide polymorphism (SNP) in the diadenylate cyclase gene dacA in the faster growing but less resistant strain. Diadenylate cyclases were recently discovered to synthesize the new second messenger cyclic diadenosine monophosphate (c-di-AMP). Introduction of this mutation into the highly resistant but slower growing strain reduced resistance and increased its growth rate, suggesting a direct connection between the dacA mutation and the phenotypic differences of these strains. Quantification of cellular c-di-AMP revealed that the dacA mutation decreased c-di-AMP levels resulting in reduced autolysis, increased salt tolerance and a reduction in the basal expression of the cell wall stress stimulon. These results indicate that c-di-AMP affects cell envelope-related signalling in S. aureus. The influence of c-di-AMP on growth rate and methicillin resistance in MRSA indicate that altering c-di-AMP levels could be a mechanism by which MRSA strains can increase their fitness levels by reducing their methicillin resistance levels.     

Comparison of methods for the detection of methicillin resistance in Staphylococcus aureus isolates from food products

AIMS: To compare several methods for detection of methicillin resistance in Staphylococcus aureus isolates from food. METHODS AND RESULTS: Two hundred S. aureus isolates from food of animal origin were screened for methicillin resistance by a PCR assay specific for the mecA gene, an oxacillin agar screen test and a cefoxitin disk diffusion test. Six out of 200 strains (3%) were found to be methicillin-resistant Staphylococcus aureus (MRSA) by PCR. The oxacillin agar screen test detected only one of the MRSA isolates (sensitivity of 16.7%) and mischaracterized three additional strains as MRSA (specificity of 98.45%). None of the MRSA strains was detected by the cefoxitin test (sensitivity of 0%), while 15 methicillin-susceptible S. aureus (MSSA) strains were misclassified as resistant (specificity of 92.3%). Fifteen MSSA strains displayed a beta-lactamase hyperproducer-like phenotype. The six MRSA (mecA-positive) strains resembled the characteristics of heteroresistant strains. CONCLUSIONS: As MRSA of animal origin may display atypical phenotypes, PCR appears to be more reliable for detection of methicillin resistance in animal strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The study stresses the need for implementing the methods of screening S. aureus from food of animal origin for methicillin resistance.     

Resistance to gentamicin and related aminoglycosides in Staphylococcus aureus isolated in Brazil

Isolates of Staphylococcus aureus obtained from a Brazilian university hospital were characterized in relation to resistance to gentamicin and related aminoglycosides. Thirty-six isolates were susceptible to methicillin (MSSA) and 14 were resistant (MRSA). All isolates were sensitive to nucleic acid-binding compounds. All MRSA isolates and one MSSA isolate were demonstrated to be resistant to gentamicin and were coincidentally resistant to amikacin, kanamycin, neomycin and tobramycin. Among the gentamicin sensitive MSSA isolates, five isolates were found to be resistant only to kanamycin/neomycin. The resistance to gentamicin (and related aminoglycosides: kanamycin and tobramycin) must be due to AAC(6')-APH(2") activity. As these isolates also showed resistance to neomycin, they must carry an additional genetic element, probably the one responsible for APH(3')III activity, which accounts for the high level of resistance to kanamycin and to amikacin. The resistance to kanamycin/neomycin in the gentamicin sensitive isolates could not be attributed to the AAD(4')(4") activity because of the tobramycin sensitivity, and so could be ascribed to the APH(3')III activity. Curing and transfer experiments, as well as electrophoresis procedures, indicate that gentamicin resistance in Staph. aureus strains here studied has, characteristically, chromosomal localization.     

Extrachromosomal Control of Methicillin Resistance and Toxin Production in Staphylococcus aureus

All of 41 naturally occurring coagulase-positive methicillin-resistant strains of Staphylococcus aureus isolated in various laboratories were resistant to several antibiotics and were lipase-negative. Most strains produced hemolysins, and 38 strains produced enterotoxin B. Acriflavine treatment of four strains resulted in elimination of resistance to methicillin and mercury; in one strain, resistance to cadmium was also lost. Production of enterotoxin B and beta-hemolysin was eliminated in all four strains and penicillinase production was eliminated in one strain. In transduction experiments, methicillin resistance and enterotoxin B production were transferred together at a frequency of 0.2 x 10(-8) to 1.1 x 10(-8) by use of ultraviolet-induced phage lysates from naturally lysogenic methicillin-resistant strains. Cotransductions of resistance to mercury and cadmium, as well as production of penicillinase and beta-hemolysin, were obtained to some extent. The extrachromosomal character of these determinants and their possible genetic association are discussed.     

白色念珠菌体外诱导氟康唑耐药性的实验研究（简报）

随着广谱抗生素的普遍应用以及免疫缺陷人群的增加,机会性致病菌念珠菌感染日益增多。深部念珠菌感染已经成为重症患者死亡的重要原因,白色念珠菌(C．albicans)是其中的主要致病菌。低毒广谱的唑类抗真菌药氟康唑是既能治疗严重真菌感染又不会产生明显副作用的少数抗真菌药之一,它的广泛使用取得良好治疗效果,但也导致菌株耐药率增加而使临床治疗失败。近10年来,在治疗     

Molecular epidemiology of clinical and carrier strains of methicillin resistant Staphylococcus aureus (MRSA) in the hospital settings of north India

Background

The study was conducted between 2000 and 2003 on 750 human subjects, yielding 850 strains of staphylococci from clinical specimens (575), nasal cultures of hospitalized patients (100) and eye & nasal sources of hospital workers (50 & 125 respectively) in order to determine their epidemiology, acquisition and dissemination of resistance genes.

Methods

Organisms from clinical samples were isolated, cultured and identified as per the standard routine procedures. Susceptibility was measured by the agar diffusion method, as recommended by the Nat ional Committee for Clinical Laboratory Standards (NCCLS). The modified method of Birnboin and Takahashi was used for isolation of plasmids from staphylococci. Pulsed-field gel electrophoresis (PFGE) typing of clinical and carrier Methicillin resistant Staphylococcus aureus (MRSA) strains isolated during our study was performed as described previously.

Results

It was shown that 35.1% of Staphylococcus aureus and 22.5% of coagulase-negative staphylococcal isolates were resistant to methicillin. Highest percentage of MRSA (35.5%) was found in pus specimens (n = 151). The multiple drug resistance of all MRSA (n = 180) and Methicillin resistant Coagulase-negative Staphylococcus aureus (MRCNS) (n = 76) isolates was detected. In case of both methicillin-resistant as well as methicillin-sensitive Saphylococcal isolates zero resistance was found to vancomycin where as highest resistance was found to penicillin G followed by ampicillin. It was shown that the major reservoir of methicillin resistant staphylococci in hospitals are colonized/infected inpatients and colonized hospital workers, with carriers at risk for developing endogenous infection or transmitting infection to health care workers and patients. The results were confirmed by molecular typing using PFGE by SmaI-digestion. It was shown that the resistant markers G and T got transferred from clinical S. aureus (JS-105) to carrier S. aureus (JN-49) and the ciprofloxacin (Cf) and erythromycin (E) resistance seemed to be chromosomal mediated. In one of the experiments, plasmid pJMR1O from Staphylococcus aureus coding for ampicillin (A), gentamicin (G) and amikacin (Ak) resistance was transformed into Escherichia coli. The minimal inhibitory concentrations (MICs) for A and G were lower in E. coli than in S. aureus. However, the MIC for Ak was higher in E. coli transformants than in S. aureus.

Conclusion

There is a progressive increase in MRSA prevalence and multi-drug resistance in staphylococci. Vancomycin is still the drug of choice for MRSA infections. The major reservoir of methicillin resistant staphylococci in hospitals is colonized/infected inpatients and colonized hospital workers. Resistance transfer from staphylococci to E. coli as well as from clinical to carrier staphylococci due to antibiotic stress seemed to be an alarming threat to antimicrobial chemotherapy.     

Frequency of antibiotic and heavy metal resistance, pigmentation, and plasmids in bacteria of the marine air-water interface.

A field investigation of marine coastal waters revealed that the frequency of pigmented bacteria and the occurrence of bacterial antibiotic resistance were higher at the air-water interface than in the bulk water. The differences in the frequency of pigmented colonies at the surface and in the bulk-water samples could not be explained by the degree of cell surface hydrophobicity or by bacterial adhesion to air-water interfaces. Pigmented strains exhibited a higher degree of multiple drug resistance than did nonpigmented strains. However, the frequency of multiple drug resistance in nonpigmented strains was also substantial. An average of 91% of all strains were resistant to more than one antibiotic, and 21% of the bacteria isolated were resistant to five of the eight antibiotics tested. High numbers of plasmid-carrying strains were found among selected surface isolates, but the presence of detectable plasmids could not be correlated with either pigmentation or multiple drug resistance. Furthermore, selected surface isolates were significantly more resistant to mercury than were bulk-water bacteria. The higher frequency of pigmented, antibiotic-resistant, and mercury resistant strains at the air-water interface than in the bulk water are discussed in terms of various forms of selective pressure and genetic exchange at the surface.     

Frequency of antibiotic and heavy metal resistance, pigmentation, and plasmids in bacteria of the marine air-water interface

A field investigation of marine coastal waters revealed that the frequency of pigmented bacteria and the occurrence of bacterial antibiotic resistance were higher at the air-water interface than in the bulk water. The differences in the frequency of pigmented colonies at the surface and in the bulk-water samples could not be explained by the degree of cell surface hydrophobicity or by bacterial adhesion to air-water interfaces. Pigmented strains exhibited a higher degree of multiple drug resistance than did nonpigmented strains. However, the frequency of multiple drug resistance in nonpigmented strains was also substantial. An average of 91% of all strains were resistant to more than one antibiotic, and 21% of the bacteria isolated were resistant to five of the eight antibiotics tested. High numbers of plasmid-carrying strains were found among selected surface isolates, but the presence of detectable plasmids could not be correlated with either pigmentation or multiple drug resistance. Furthermore, selected surface isolates were significantly more resistant to mercury than were bulk-water bacteria. The higher frequency of pigmented, antibiotic-resistant, and mercury resistant strains at the air-water interface than in the bulk water are discussed in terms of various forms of selective pressure and genetic exchange at the surface.     

Genetic diversity of human isolates of Salmonella enterica serovar Enteritidis in Malaysia

AIMS: The study was undertaken to determine clonal relationship and genetic diversity of the human strains of Salmonella enterica serovar Enteritidis isolated from 1995 to 2002 from different parts of Malaysia. METHODS AND RESULTS: Antimicrobial susceptibility test, plasmid profiling and pulsed-field gel electrophoresis were applied to analyse 65 human isolates of S. Enteritidis obtained over an eight year period from different parts of Malaysia. Four nonhuman isolates were included for comparison. A total of 14 distinct XbaI-pulsed-field profiles (PFPs) were observed, although a single PFP X1 was predominant and this particular clone was found to be endemic in Malaysia. The incidence of drug resistant S. Enteritidis remained relatively low with only 37% of the strains analysed being resistant to one or more antimicrobial agents. All except one resistant strain carried at least one plasmid ranging in size from 3.7 to 62 MDa giving nine plasmid profiles. The three isolates from raw milk and one from well-water had similar PFPs to that of the human isolates. CONCLUSIONS: Salmonella Enteritidis strains were more diverse than was previously thought. Fourteen subtypes were noted although one predominant clone persisted in Malaysia. The combination of pulsed-field gel electrophoresis, plasmid profiling and antibiograms provided additional discrimination to the highly clonal strains of S. Enteritidis. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report to assess the genotypes of the predominant clinical S. Enteritidis in different parts of the country. As S. Enteritidis is highly endemic in Malaysia, the data generated would be useful for tracing the source during outbreaks of gastroenteritis in the study area.     

Clonal population of Mycobacterium tuberculosis strains reside within multiple lung cavities

Background

Unsuccessful treatment outcomes among patients with multi-/extensively- drug resistant tuberculosis (TB) have hampered efforts involved in eradicating this disease. In order to better understand the etiology of this disease, we aimed to determine whether single or multiple strains of Mycobacterium tuberculosis (MTB) are localized within lung cavities of patients suffering from chronic progressive TB.

Methodology/Findings

Multiple cavity isolates from lung of 5 patients who had undergone pulmonary resection surgery were analyzed on the basis of their drug susceptibility profile, and genotyped by spoligotyping and 24-loci MIRU-VNTR. The patients past history including treatment was studied. Three of the 5 patients had extensive drug resistant TB. Heteroresistance was also reported within different cavity isolates of the lung. Both genotyping methods reported the presence of clonal population of MTB strain within different cavities of the each patient, even those reporting heteroresistance. Four of the 5 patients were infected with a population of the Beijing genotype. Post-surgery they were prescribed a drug regimen consisting of cycloserine, a fluoroquinolone and an injectable drug. A 6 month post-surgery follow-up reported only 2 patients with positive clinical outcome, showing sputum conversion.

Conclusion

Identical spoligotype patterns and MIRU-VNTR profiles between multiple cavities of each patient, characterize the presence of clonal population of MTB strains (and absence of multiple MTB infection).     

长沙地区临床分离金黄色葡萄球菌的耐药监测

目的了解长沙地区临床分离金黄色葡萄球菌（以下简称金葡菌）对常用抗菌药物的耐药现状,探讨金黄色葡萄球菌对甲氧西林的耐药水平。方法收集长沙地区11家医院2009年11月至2010年11月临床分离的非重复金葡菌279株,应用Vitek-2全自动微生物分析系统进行鉴定,K-B法检测金葡菌对24种药物的敏感性,产色头孢菌素试验检测β-内酰胺酶以及D试验检测诱导型克林霉素耐药。应用头孢西丁和苯唑西林纸片扩散法筛查耐甲氧西林的金葡菌（MRSA）,琼脂稀释法检测头孢西丁和苯唑西林的最低抑菌浓度（MIC）。结果在被检测的24种药物中,敏感率〉50%的药物为9种,未发现对万古霉素、替考拉宁和利奈唑胺耐药菌株;耐药率〉50%的抗菌药物有11种,其中以青霉素和氨苄西林的耐药率最高（均为97.1%）。MRSA的分离率达54.5%,且对常用的16种抗菌药物的耐药率均显著高于甲氧西林敏感金黄色葡萄球菌（MSSA）。279株金葡菌中,β-内酰胺酶阳性250株（89.6%）;红霉素耐药而克林霉素敏感或中介的30株中,D试验阳性22株（73.3%）。苯唑西林（OXA）和头孢西丁（FOX）MIC范围分别为0.125～〉256μg/mL和2～〉256μg/mL,苯唑西林的MIC50和MIC90分别为128μg/mL和256μg/mL,头孢西丁的MIC50和MIC90分别为64μg/mL和256μg/mL。结论长沙地区临床分离金葡菌对常用抗菌药物呈多重耐药;MRSA不仅分离率高,而且对甲氧西林呈高水平耐药。     

Molecular typing of Staphylococcus aureus isolates from an intensive care unit

Seventeen S. aureus clinical isolates, collected from an Intensive Care Unit (ICU) during a seven-month period were analyzed to investigate their antimicrobial susceptibility and clonal diversity. Eleven isolates (65%) were found to be resistant to methicillin (MRSA). Pulsed-field gel electrophoresis (PFGE) profiles of genomic DNAs, and analysis of the polymorphisms of the variable regions of the protein A (spa) and coagulase (coa) genes revealed a lower clonal heterogeneity among MRSA than among methicillin-susceptible isolates (MSSA). Two of the MRSA clones were repeatedly isolated in different patients, within a variable period of time, suggesting the presence in the ward of a resident, endemic and multi-drug resistant MRSA population. Our results also emphasize the lower discriminatory power of spa and coa typing compared with PFGE typing.