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…     

Correlation between methicillin-resistance and resistance to fluoroquinolones in Staphylococcus aureus and Staphylococcus epidermidis

Fluoroquinolones resistance in Staphylococci is associated to point mutations in grlA (80,84 and 116) grlB, gyrA (84,88) and gyrB genes. Almost all MRSA strains are ciprofloxacin and levofloxacin resistant while, in a lesser degree, MRCoN staphylococci show to be resistant to levofloxacin. This observation made possible to predict a different correlation between methicillin-resistance and the resistance to FQs in this two different species. In this study, we compare genomic analysis of S. aureus and S. epidermidis with the resistance to FQs. Our results show that strains of MRSA are distributed in 4 different PFGE-types while 12 MRSE strains are distributed in 9. MRSA resistant to FQs showed a unique PFGE pattern; on the contrary of FQs susceptible MRSA and MSSA. Furthermore mecA and gyrA genes are located in the same SmaI fragment in MRSA and in different in MRSE. MSSE and MRSE show more ClaI/mecA polymorphisms than MRSA. All this data confirm the clonal origin of MRSA and show that FQs resistance is linked to the presence of mec locus and both clonally spread. On the contrary in MRSE FQs-resistance is independent from MR and arise with the normal frequence of antibiotic induction.     

In vitro activity of the pristinamycin against the isolated staphylococci in the french hospitals in 1999-2000

One thousand six hundred and fifty clinically significant, consecutive and non redundant strains of staphylococci, including 863 Staphylococcus aureus and 787 coagulase negative staphylococci (CNS), were isolated between October 1999 and March 2000 in 35 French hospital laboratories. Susceptibilities were determined in each center by a standard diffusion method according to the recommendations of CA-SFM. Strains with vancomycin zone size diameter <17 mm were sent to the central laboratory for MIC determination of vancomycin by agar dilution, as recommended by the CA-CSFM. Frequencies of resistance to oxacillin were 38.6% for S. aureus (MRSA), 54% for the CNS, all species and 62% for S. epidermidis, respectively. The antibiotics tested showed a good activity against strains of S. aureus susceptible to oxacillin, more than 95% of strains being susceptible except for erythromycin (82.6%). Against MRSA, vancomycin and prisitinamycin had the highest rates of susceptible strains, greater than 93% for the later antibiotic. More than 92% of strains of CNS susceptible or resistant to oxacillin were sensitive to pristinamycin. Pristinamycin displayed a good activity whether the strains were constitutively or inducibly resistant to MLS(B). It comes out from this in vitro study that the rate of resistance of staphylococci to pristinamycin remains weak and stable in France. Pristinamycin is a good alternative for oral treatment of staphylococcal infections.     

Nationwide Survey Shows that Methicillin-Resistant Staphylococcus aureus Strains Heterogeneously and Intermediately Resistant to Vancomycin Are Not Disseminated throughout Japanese Hospitals

A total of 6,625 methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates obtained from 278 hospitals throughout Japan were obtained between November and December 1997 and were examined for their sensitivities to vancomycin using Mueller Hinton (MH), brain heart infusion (BHI), agar plates, or the broth microdilution method. A concentrated inoculum of an MRSA strain or the use of highly enriched medium, such as BHI medium, allows an individual cell to grow on agar plates containing a vancomycin concentration greater than the MIC for the parent strain. However, cells of the colonies which grew on BHI agar plates containing the higher vancomycin concentrations did not acquire a level of vancomycin resistance greater than that of the parent strain and were not subpopulations of heterogeneously vancomycin-resistant MRSA. There was no significance in the fact that these colonies grew on the higher concentration of vancomycin: none showed stable resistance to vancomycin at a concentration above the MIC for the parent strain, and no cell from these colonies showed a relationship between the MIC and the ability of these colonies to grow on higher concentrations of vancomycin. The vancomycin MIC was not above 2 microg/ml for any of the cells originating from these colonies. No Mu3-type heterogeneously resistant MRSA strains, which constitutively produce subpopulations from MRSA clinical isolates with intermediate vancomycin resistance at a high frequency, were detected. There was a unipolar distribution of the MICs ranging from 0.25 to 2 microg of vancomycin/ml among the 6,625 MRSA clinical isolates, indicating that there was no Mu50-type intermediately vancomycin-resistant MRSA (MIC, 8 microg/ml by National Committee for Clinical Laboratory Standards criteria) among the clinical isolates, and there was no evidence of dissemination of Mu3-type MRSA heteroresistant to vancomycin.     

汕头大学医学院附属第一医院耐甲氧西林金黄色葡萄球菌(MRSA)耐药谱分析

目的:了解汕头大学医学院附属第一医院分离的92株耐甲氧西林金黄色葡萄球菌(MRSA)的耐药情况。方法:琼脂稀释法测定17种抗菌药物对MRSA的最低抑菌浓度(MIC)。结果:92株MRSA对实验中所有β-内酰胺类抗生素的耐药率均在80%以上。绝大部分菌株对庆大霉素、红霉素、氟喹诺酮类也不敏感。超过半数的MRSA菌株对利福平保持敏感,对氯霉素、多西环素及米诺环素也普遍敏感,未发现耐万古霉素的MRSA菌株。结论:我院附属第一医院的MRSA呈多重耐药,但对氯霉素,半合成四环素及万古霉素仍然敏感。     

Antimicrobial resistance of <Emphasis Type="Italic">Staphylococcus</Emphasis> from otorrhea in chronic suppurative otitis media and comparison with results of all isolated <Emphasis Type="Italic">Staphylococci</Emphasis>

Staphylococcus is one of the most important pathogenic bacteria in chronic suppurative otitis media (CSOM). The prevalence of pathogenic bacteria in patients with CSOM has not been compared with the prevalence rates in patients from other fields of medicine. We investigated the pathogenic bacteria in CSOM throughout Korea and annual isolation rates of methicillin-resistant Staphylococcus aureus (MRSA) over 6 years. Routine culture results and susceptibility data of CSOM isolated from 2000 to 2005 were collected from six general hospitals in Korea, along with the results of all clinically isolated Staphylococci from one tertiary care teaching hospital. Of the 1,162 bacteria identified in 1,360 CSOM patients, 628 (54.0%) were Staphylococci in CSOM. Of the latter, 288 (45.9%) were MRSA, which accounted for 24.8% of identified bacteria. Of the 5,988 clinically isolated Staphylococci from one tertiary care hospital, 3,712 (61.9%) were MRSA. All MRSA isolated from CSOM patients were sensitive to vancomycin and teicoplanin, and 88.2% were sensitive to sulfamethoxazole/trimethoprim. In contrast, these strains showed little or no sensitivity to oxacillin, clindamycin, penicillin, and erythromycin. Annual MRSA isolation rates showed no tendencies to increase or decrease. MRSA was the most frequently identified Staphylococcus in patients with otorrhea. The isolation rate of MRSA has not changed over 6 years. Continuous and periodic surveillance of MRSA is necessary to reduce the spread of antibiotic-resistant pathogens and to guide appropriate antibacterial therapy.     

异质性万古霉素耐药葡萄球菌分离及生物学特性观察

目的　了解本地区临床标本中异质性万古霉素耐药葡萄球菌 (h VRS)分离率 ,并对其生物学特性进行观察。方法　采用琼脂筛选和菌谱分析法对 5 6株甲氧西林耐药的葡萄球菌进行检测 ,同时对分离细菌的生长特性和超微结构进行观察 ,并与同源性敏感菌株及金黄色葡萄球菌标准菌株相比较。结果　本地区h VRS检出率为 14 .3% ,其中血浆凝固酶阴性葡萄球菌的分离率 (2 3.1% )明显高于金黄色葡萄球菌 (6 .7% ) ;耐药亚群与同源性敏感菌株和标准菌株比较 ,生长速度减慢 ,在固体培养基上菌落大小不等 ,在液体培养基中呈沉淀生长 ,电镜观察可见细胞壁增厚。结论　h VRS在本地区的临床标本中有一定的分离率 ,应引起重视 ;该菌的很多生物学特性与同源性敏感菌株有所不同 ,其中细胞壁增厚是比较明显的改变 ,并与该菌的耐药性有关。     

In vitro activities of eight antibiotics against methicillin-resistant S. aureus and S. epidermidis strains isolated in Korea

Staphylococcus aureus and Staphylococcus epidermidis strains isolated at eight large medical centers in Korea were examined for methicillin resistance and resistance to eight other antibiotics; cefazolin, cefamandole, cefuroxime, cefoxitin, cefotaxime, moxalactam, penicillin G and vancomycin. Methicillin resistance was found in 296 of 1225 strains (24.2%) of S. aureus and 126 of 348 strains (36.2%) of S. epidermidis. Methicillinresistant strains were isolated from all sources with the frequency of isolation ranging from 11% to 60%. From pleural effusion, throat swab and blood, methicillin-resistant strains of S. aureus were more frequently isolated with statistical significance (Chi-squared test, 95% confidence). Almost all of Methicillin-resistant S. aureus (MRSA) and S. epidermidis (MRSE) strains were multiply resistant to one or more tested eight antibiotics. However only 7(2.4%) of 296 MRSA strains and 2(1.6%) of 126 MRSE strains were resistant to vancomycin. Vancomycin was the most effective antibiotic against staphylococcal isolates as well as MRSA and MRSE.     

Methicillin resistance among isolates of Staphylococcus aureus: antibiotic sensitivity pattern & phage typing

Out of 3988 clinical specimens from hospital admitted patients 230 strains of Staphylococcus aureus were isolated, 45 strains (19.56%) were Methicillin resistance Staphylococcus aureus (MRSA). All MRSA strains were beta lactamase producers. Multidrug resistance was observed among MRSA strains more commonly than in methicillin sensitive strains of Staphylococcus aureus (MSSA). Maximum strains were resistant to penicillin (100%), co-trimoxa zole (97%) & chloramphenicol (93.33%). As least resistant to gentamicin & ciprofloxacin shown by MRSA, these drugs can be used in few situations after susceptibility test. All strains of MRSA were sensitive to vancomicin (100%). Majority of strains (34 out of 45) showed MIC values of 4 ug/ml. Twenty eight out of 44 strains were non typable using routine phages. Study revealed that MRSA with associated multidrug resistance is common in this region. There is need to develop local set of MRSA phages for improvement of typability.     

Relationship of MIC and bactericidal activity to efficacy of vancomycin for treatment of methicillin-resistant Staphylococcus aureus bacteremia

We attempted to find a relationship between the microbiological properties of bloodstream isolates of methicillin-resistant Staphylococcus aureus (MRSA) and the efficacy of vancomycin in the treatment of bacteremia. Vancomycin susceptibility testing was performed, and bactericidal activity was determined for 30 isolates from 30 different patients with MRSA bacteremia for whom clinical and microbiological outcome data were available. The majority of these patients had been previously enrolled in multicenter prospective studies of MRSA bacteremia refractory to conventional vancomycin therapy. Logistic regression found a statistically significant relationship between treatment success with vancomycin and decreases in both vancomycin MICs (< or =0.5 microg/ml versus 1.0 to 2.0 microg/ml; P = 0.02) and degree of killing (reduction in log(10) CFU/milliliter) by vancomycin over 72 h of incubation in vitro (P = 0.03). For MRSA isolates with vancomycin MICs < or = 0.5 microg/ml, vancomycin was 55.6% successful in the treatment of bacteremia whereas vancomycin was only 9.5% effective in cases in which vancomycin MICs for MRSA were 1 to 2 microg/ml. Patients with MRSA that was more effectively killed at 72 h by vancomycin in vitro had a higher clinical success rate with vancomycin therapy in the treatment of bacteremia (log(10) < 4.71 [n = 9], 0%; log(10) 4.71 to 6.26 [n = 13], 23.1%; log(10) > 6.27 [n = 8], 50%). We conclude that a significant risk for vancomycin treatment failure in MRSA bacteremia begins to emerge with increasing vancomycin MICs well within the susceptible range. Elucidating the mechanisms involved in intermediate-level glycopeptide resistance in S. aureus should begin by examining bacteria that begin to show changes in vancomycin susceptibility before the development of obvious resistance. Prognostic information for vancomycin treatment outcome in MRSA bacteremia may also be obtained by testing the in vitro bactericidal potency of vancomycin.     

Emergence of homogeneously methicillin-resistant Staphylococcus aureus.

Forty-seven clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), collected between 1986 and 1990 from 29 institutions, were analyzed for susceptibility to various antibiotics. Twenty-six strains were homogeneously methicillin resistant (i.e., greater than or equal to 10% of the cells in these strains were able to grow on Mueller-Hinton agar containing 50 micrograms of methicillin per ml). The MICs of gentamicin, clindamycin, trimethoprimsulfamethoxazole, methicillin, and imipenem for homogeneous MRSA strains were higher than those for heterogeneously resistant strains. Both types of strains were, for the most part, susceptible to vancomycin and trimethoprim-sulfamethoxazole. Ciprofloxacin-resistant MRSA strains were not isolated prior to 1988 but made up 40% of the post-1987 strains. The level of methicillin resistance correlated well with the imipenem MIC, suggesting that susceptibility to imipenem may serve as a marker to identify and monitor the prevalence of homogeneous MRSA strains.     

First report of methicillin-resistant Staphylococcus aureus with reduced susceptibility to vancomycin in Thailand

To investigate whether there are methicillin-resistant Staphylococcus aureus (MRSA) strains with reduced susceptibility to vancomycin in Thailand, a total of 155 MRSA strains isolated from patients hospitalized between 1988 and 1999 in university hospitals in Thailand were tested for glycopeptide susceptibility. All the strains were classified as susceptible to vancomycin and teicoplanin when judged by NCCLS criteria for glycopeptide susceptibility using the agar dilution MIC determination. Vancomycin MICs at which 50 and 90% of the isolates tested were inhibited (MIC50 and MIC(90), respectively) were 0.5 and 1 microg/ml, respectively, with a range of 0.25 to 2 microg/ml. For teicoplanin, MIC50 and MIC90 were 2 microg/ml, with a range of 0.5 to 4 microg/ml. However, one-point population analysis identified three MRSA strains, MR135, MR187, and MR209, which contained subpopulations of cells that could grow in 4 microg of vancomycin per ml. The proportions of the subpopulations were 2 x 10(-4), 1.5 x 10(-6), and 4 x 10(-7), respectively. The subsequent performance of a complete population analysis and testing for the emergence of mutants with reduced susceptibility to vancomycin (MIC > or = 8 microg/ml) confirmed that these strains were heterogeneously resistant to vancomycin. Two of these strains caused infection that was refractory to vancomycin therapy. Pulsed-field gel electrophoresis showed that the two strains had identical SmaI macrorestriction patterns and that they were one of the common types of MRSA isolated in the hospital. This is the first report of heterogeneous resistance to vancomycin in Thailand and an early warning for the possible emergence of vancomycin resistance in S. aureus in Southeast Asia.     

耐甲氧西林金黄色葡萄球菌的临床分布及耐药性分析

目的 熟悉耐甲氧西林金黄色葡萄球菌（MRSA）的临床分布及其耐药性,为临床提供参考。方法 采用VITEK2 COMPACT全自动微生物分析系统进行鉴定,筛选出MRSA菌株。结果 2017年1~12月我院分离出459株金黄色葡萄球菌,其中MRSA 98株,检出率为21.4%。儿科、创伤修复烧伤整形外科、神经外科检出MRSA较多。98株MRSA中,耐药率较高的抗菌药物有青霉素G、红霉素、克林霉素和四环素,万古霉素、利奈唑胺和呋喃妥因敏感率均为100.00%。结论 我院MRSA的检出率和耐药率形式仍然严     

甲氧西林耐药的金黄色葡萄球菌耐药性及分子流行病学调查

目的了解甲氧西林耐药的金黄色葡萄球菌(MRSA)的耐药性及分子流行病学特点。方法采用纸片扩散法及琼脂稀释法检测2002年从北京协和医院住院患者分离的165株MRSA的耐药性；采用脉冲场凝胶电泳(PFGE)技术对其中重症监护病房(ICU)和呼吸重症监护病房(RCU)分离的65株MRSA作同源性分析。结果165株MRSA对万古霉素和替考拉宁的敏感率为100％，对庆大霉素的耐药率为100％；对左氧氟沙星、四环素、红霉素耐药率分别为98．2％、96．3％、93．9％。对甲氧苄啶，磺胺甲噁唑和氯霉素敏感率分别为95．8％及98．8％；ICU和RCU病房分离MRSA的PFGE图谱有5种类型(A—E型)，以A型为主(56株)，A型又包括A1亚型(55株)和A2亚型(1株)。结论医院获得性MRSA是多重耐药菌，在ICU和RCU病房发生了基因型为A1亚型的MRSA菌株暴发流行。     

In vitro Analysis of the Minimal Inhibitory Concentration Values of Different Generations of Anti-Methicillin-Resistant Staphylococcus aureus Antibiotics

Methicillin-resistant Staphylococcus aureus (MRSA) resistance to antimicrobials may result in the increased risk of treatment failure. The objective of the study was to analyse in vitro MRSA susceptibility to vancomycin, linezolid, daptomycin, tigecycline, ceftaroline, dalbavancin, clindamycin, ciprofloxacin and trimethoprim/sulfamethoxazole. All MRSA strains isolated from hospitalised patients were analysed according to the current microbiological recommendations. Finally, a total of 124 MRSA strains were analysed; all were susceptible to tested antibiotics. Dalbavancin had the lowest minimum inhibitory concentration (MIC), and vancomycin the highest MIC value. There were 28/124 strains of MRSA susceptible for clindamycin, 36/124 for ciprofloxacin and 121/124 for trimethoprim/sulfamethoxazole. Dalbavancin was the most effective antimicrobial in our study.     

Evolution of a vancomycin-intermediate Staphylococcus aureus strain in vivo: multiple changes in the antibiotic resistance phenotypes of a single lineage of methicillin-resistant S. aureus under the impact of antibiotics administered for chemotherapy

A number of methicillin-resistant Staphylococcus aureus (MRSA) isolates were recovered over a period of several weeks from blood samples and from the heart valve of a patient who underwent extensive vancomycin chemotherapy for persistent S. aureus bacteremia. Consecutive isolates showed gradually decreasing growth rates during in vitro cultivation and increasing vancomycin MICs, from an MIC of 1 micro g/ml for the initial isolate to an MIC of 8 micro g/ml for the final MRSA isolates, which also became tolerant to vancomycin. Major changes were observed in the oxacillin resistance phenotype of several of the isolates-apparently related to in vivo exposure to imipenem, which was also used during a period of chemotherapy. Both the gradually increasing vancomycin MICs and the changes in oxacillin resistance could be reproduced by appropriate exposure of the initial MRSA isolate to antibiotics in vitro. All isolates had the same pulsed-field gel electrophoresis pattern, spaA type, and multilocus sequence type (MLST), which was identified as a single-locus variant of ST5, the MLST characteristic of previously characterized MRSA isolates with reduced susceptibility to vancomycin in the United States and Japan.     

The VISA/GISA problem: therapeutic implications

The emergence of vancomycin intermediate resistant Staphylococcus aureus (VISA) isolates in Japan, USA, France, Hong Kong and Korea among methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates, is of great concern. Vancomycin has been the drug of choice for the treatment of multiresistant MRSA infections in the last three decades, but the management of invasive MRSA infections will become a serious problem if VISA strains become widespread. VISA isolates reported to date have a vancomycin MIC of 8 mg/L, and were isolated from patients with underlying diseases whose long-term vancomycin treatment apparently failed. Since many VISA isolates also have been resistant to teicoplanin, the term glycopeptide-intermediate S. aureus (GISA) is more appropriate. The frequency of GISA isolates appears to be extremely low; to date, only 10 GISA infections have been reported worldwide. However, heterogeneous resistance to glycopeptides (h-GISA) have been reported in Japan, Europe and Thailand. These h-GISA strains showed vancomycin MICs ranging from 1 to 4 mg/L, but had subpopulations that could grow on agar plates containing 4–8 mg/L, which may represent the first step in the development of GISA strains. Although GISA isolates have shown resistance to many antimicrobials, all GISA isolates remain susceptible to co-trimoxazole and some of them to other common antimicrobials. Currently, there are no recommended therapy guidelines for GISA infections, although in recent studies, several new drugs have shown promising activity against GISA strains. In addition, synergy between glycopeptides and β-lactams against GISA strains was observed in some in vivo and in vitro studies. Specific MRSA/GISA control programs, rational antibiotic policies, including the reduction of glycopeptide use, and rapid laboratory detection of GISA and h-GISA strains are the key measures in preventing the spread of these strains.     

Prevalence and antimicrobial susceptibility pattern of methicillin resistant Staphylococcus aureus: a multicentre study

Purpose: Methicillin resistant Staphylococcus aureus (MRSA) is an important nosocomial pathogen. We report the prevalence and antibiotic susceptibility pattern of MRSA in major southern districts of Tamilnadu. Methods: A total of 7172 clinical specimens and 1725 carrier screening samples were collected from different centers and subjected to MRSA screening using conventional microbiological methods. Subsequently the antibiotic sensitivity test was performed for the confirmed MRSA isolates. Results: Out of 906 strains of S. aureus isolated from clinical and carrier samples, 250 (31.1%) and 39 (37.9%) were found to be methicillin resistant respectively. Almost all clinical MRSA strains (99.6%) were resistant to penicillin, 93.6% to ampicillin, and 63.2% towards gentamicin, co-trimoxazole, cephalexin, erythromycin, and cephotaxime. All MRSA strains (100%) of carrier screening samples had resistance to penicillin and about 71.8% and 35.9% were resistant to ampicillin and co-trimoxazole respectively. Multidrug resistance was observed among 63.6% of clinical and 23% of carrier MRSA isolates. However, all strains of clinical and carrier subjects were sensitive to vancomycin. Conclusion: The determination of prevalence and antibiotic sensitivity pattern of MRSA will help the treating clinicians for first line treatment in referral hospitals.     

Presence of Staphylococcus aureus with Reduced Susceptibility to Vancomycin in Germany

 A total of 457 Staphylococcus aureus strains from the culture collection of the National Reference Center for Staphylococci in Bonn, Germany, were screened for susceptibility to vancomycin because some Staphylococcus aureus strains are able to form subpopulations that show intermediate resistance to vancomycin. Two methicillin-resistant Staphylococcus aureus strains (isolated in 1993) exhibited intermediate resistance. One of these, Staphylococcus aureus 137-93, which displayed the genomic DNA fragment pattern of the northern German epidemic strain, appeared homogeneously resistant. Neither of these strains had been identified by routine susceptibility testing. The resistance of the German isolates was lower than that of the Japanese isolate Mu50. To determine whether a similar mechanism confers vancomycin resistance in Staphylococcus aureus Mu50 and 137-93, the intracellular cell wall precursor concentration was measured and was not found to be comparably increased in Staphylococcus aureus 137-93. In conclusion, strains showing intermediate resistance have been present in Germany for some time (at least since 1993), but the subpopulations with decreased sensitivity were overlooked during antibiotic susceptibility testing.     

耐甲氧西林金黄葡萄球菌高变区基因分型及其与耐药性的关系

目的 调查本地区耐甲氧西林金黄葡萄球菌(MRSA)的高变区(HVR)基因分型,分析HVR基因型与MRSA耐药谱的关系,并初步探讨其在分子流行病学分析中的作用.方法 收集80株MRSA,采用PCR方法扩增MRSA的HVR,并根据扩增片段大小进行基因分型.同时统计各MRSA菌株对多种抗菌药物的药敏结果,并分析基因型与耐药性的关系.结果 根据PCR产物片段大小,80株MRSA被分为A、B、C、D、E 5种基因型,其中以D和E型多见,分别占61.25%和21.25%,A(3.75%)、B(5.00%)、C(8.75%)型少见.各基因型MRSA除对万古霉素敏感外,对头孢唑啉、庆大霉素、红霉素、阿奇霉素、克林霉素、环丙沙星、复方新诺明、阿米卡星的耐药率为61.5%～100%.结论 MRSA的HVR基因分型是一种快速、简单、可靠的分型方法,适用于MRSA感染的流行病学调查,有利于抗菌药物的选用.