Aminoglycosides resistance of methicillin-resistant Staphylococcus aureus]

In the last decade, there has been a dramatic increase in the isolation frequency of methicillin-resistant Staphylococcus aureus (MRSA) in Japan. Especially, a high incidence of multiple resistant MRSA strains has been reported. These strains are resistant not only to beta-lactams but to aminoglycosides and macrolides. About 90% of MRSA strains were resistant to gentamicin (GM) and/or tobramycin (TOB), producing an aminoglycoside modifying enzyme, mainly, APH (2")/AAC (6) and/or AAD (4',4"). Based on these modifying enzymes produced, MRSA strains were classified into three groups; group 1 produced APH (2")/AAC (6), belonging to phage group I and coagulase IV, group 2 produced AAD (4',4"), belonging to phage group III and coagulase II, and group 3 produced APH (2")/AAC (6) and AAD (4',4"), belonging to phage group III and coagulase II. The epidemiological results suggest that MRSA strains changed from group 1 to group 2, and then to group 3. Recently, arbekacin (ABK), a new anti-MRSA aminoglycoside, has been introduced into clinical practice. ABK shows a potent activity to GM-resistant strains, due to poorly modification by APH (2")/AAC (6'). However, there were few ABK- and GM-resistant strains in clinical isolates. These strains produced a higher amount of the enzyme than ABK-susceptible and GM-resistant strains. This observation suggests that ABK-resistant strains might be derived from GM-resistant strains by mutation of the gene coding APH (2")/AAC (6').     

Comparison of phage typing, plasmid mapping, and antibiotic resistance patterns as epidemiologic markers in a nosocomial outbreak of methicillin-resistant Staphylococcus aureus infections

Isolates of methicillin-resistant Staphylococcus aureus obtained during a nosocomial outbreak were analyzed by phage typing, plasmid mapping, and antibiotic susceptibility patterns for epidemiologic markers. Antibiotic susceptibility patterns were of limited use epidemiologically because of multiple resistance and similarity of the strains. Phage typing demonstrated that the outbreak consisted of multiple introductions of MRSA organisms into the hospital from the community and from other hospitals, and of circulation of one predominant phage type, 6/47/54/81. Plasmid mapping further subdivided the organisms of this phage type into two different groups, one of which carried two particular plasmids. Organisms carrying these plasmids were significantly more resistant to methicillin and cephalosporins and were isolated from patients who had received prior antibiotic treatment.     

Cefoxitin resistance as a surrogate marker for the detection of methicillin-resistant Staphylococcus aureus

OBJECTIVES: To evaluate the usefulness of cefoxitin when used as a surrogate marker for the detection of methicillin resistance. PATIENTS AND METHODS: Eight hundred and seventy-one strains of Staphylococcus aureus, collected from eight tertiary referral centres serving diverse socio-economic populations, were included in the study using NCCLS disc diffusion and the agar dilution methods. RESULTS: Using cefoxitin and NCCLS criteria for disc diffusion, the sensitivity and specificity for recognizing methicillin resistance were both 100%. Similar results were obtained when the strains were tested by the agar dilution method. The cefoxitin MICs for methicillin-susceptible strains were < or = 4 mg/L. CONCLUSIONS: Testing with cefoxitin as a surrogate marker for the detection of methicillin resistance was very accurate with both disc diffusion and agar dilution methods. Such testing clearly distinguished methicillin-resistant strains of S. aureus from methicillin-susceptible strains.     

耐甲氧西林金黄色葡萄球菌耐药性及分子流行病学研究

目的了解耐甲氧西林金黄色葡萄球菌(MRSA)的耐药特点和分子流行病学情况。方法对临床分离的金黄色葡萄球菌应用VITEK-32微生物分析仪及配套GPS118药敏卡测定其对12种抗菌药物的敏感性,头孢西丁纸片扩散法筛选MR-SA。对已筛选的12株MRSA,应用随机扩增多态DNA(RAPD)技术进行基因型别分析。结果 12株MRSA对氨苄西林、苯唑西林、青霉素G和红霉素全部耐药;对氯洁霉素、庆大霉素、左氧氟沙星均出现8株耐药;对万古霉素、利奈唑烷、喹努普汀/达福普汀全部敏感。RAPD将检测菌株分为3个型别(A～C)其中RAPD A型和B型是本院的主要流行菌株。结论 MRSA表现为多重耐药菌,本地区存在两种不同型别的MRSA流行克隆。     

An assessment of nosocomial infections of methicillin-resistant Staphylococcus aureus based on coagulase typing and phage typing]

An epidemiologic investigation was carried out in Ogaki Municipal Hospital to clarify the status of nosocomial MRSA Infection between 1989 and 1991. In 1989, coagulase type IV, enterotoxin A-producing, and phage group I strains, which were highly resistant to multiple antibiotics and isolated in the internal wards, accounted for 43.4% of all MRSA strains clinically isolated in the entire hospital. In 1990, coagulase type II strains that were sensitive to GM but resistant to FMOX and IPM increased. There were significant differences in the frequency of detection of various strains among wards, suggesting an inter-ward variation in MRSA strains. Changes in environmental strains reflected those in clinical strains. The findings suggest the necessity of measures not only for long-hospitalized MRSA carriers themselves but also for the environment of patients, medical staff, and those taking care of patients.     

医院感染耐甲氧西林金黄色葡萄球菌基因分型研究

目的分析医院不同科室来源的耐甲氧西林金黄色葡萄球菌(MRSA)菌株基因分型同源性,为控制MRSA医院感染流行提供科学依据。方法使用细菌基因组重复序列聚合酶链反应(REP-PCR)以及高级微生物基因分型系统(DiversiLab)细菌同源性分析技术对23株医院感染的MRSA进行基因分型。结果 23株MRSA分为4个基因型,A型、D型主要分布于急诊观察室,B型、C型主要分布于中医外科。结论中医外科存在以B型、C型基因型为流行株的MRSA医院感染爆发;REP-PCR技术和DiversiLab自动化细菌同源性分型技术可成为医院感染病原研究的有效手段。     

Development of new antibiotic resistance in methicillin-resistant but not methicillin-susceptible Staphylococcus aureus.

The frequency of infections caused by multidrug-resistant Staphylococcus aureus continues to increase while the numbers of alternative therapeutic agents remain limited. To investigate the changing patterns of in-vitro susceptibility of S. aureus to 16 antibiotics, 190 clinical isolates from two different years were studied. The MICs of methicillin-susceptible (MSSA) and methicillin-resistant (MRSA) strains isolated in 1987 were compared with those of similar numbers of strains isolated in 1989. For MRSA > or = 90% of isolates from both years were resistant to clindamycin, gentamicin and erythromycin. These strains remained highly susceptible to vancomycin (100%), minocycline (90%) and rifampicin (100%). The greatest increase in resistance was observed for ofloxacin (2% in 1987 vs 62% in 1989); cross-resistance to all of the quinolones tested was demonstrated. MSSA strains remained susceptible to vancomycin (100%), minocycline (98%), rifampicin (100%), clindamycin (90%), gentamicin (90%) and ciprofloxacin (98%). It is concluded that methicillin susceptibility is a useful marker for selecting potential agents for the treatment of infections caused by S. aureus. A combination of minocycline and rifampicin may be a useful alternative to vancomycin for treating MRSA infections.     

上海地区五所医院耐甲氧西林金黄色葡萄球菌耐药性及分子流行病学调查

目的 了解上海地区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 从上海5所医院收集140株MRSA,采用琼脂稀释法和肉汤稀释法检测其耐药性;利用PCR方法检测MRSA的PVL基因和SCCmec型别;采用脉冲场凝胶电泳(PFGE)技术对MRSA做同源性分析并且将主要流行型别的39株MRSA进行spa分型.结果 140株MRSA对庆大霉素、磺胺甲嚼唑和克林霉素的耐药率分别为98.6%(138/140)、98.6%(138/140)和97.9%(137/140);对红霉素、环丙沙星和四环素的耐药率均在80%以上,对利福平的耐药率为10.7%(15/140);未发现对达托霉素、替考拉宁和万古霉素耐药的菌株.菌株MRSA PvL均为阴性,以SCCmecⅢ为主,达45.7%(64/140);其他型别依次为SCCmecⅢ a 25.0%(35/140)、SCCmecⅢb 14.3%(20/140)、SCCmecⅢ10.7%(15/140).SCCmecⅣ最少,占4.3%(6/140).PFGE图谱有16种类型(A～P型),以C型[30.7%(43/140)]、B型[13.6%(191140)]和Ⅰ型[10.7%(15/140)]为主;对主要流行克隆的39株MRSA进行spa分型,共得到t002[33.33%(13/39)]、t030[12.82%(5/39)]、t037[51.28%(20/39)]、t459[2.57%(1/39)]4种类型.结论 上海地区5所医院MRSA共有16种流行克隆株和4种spa型,其中PVL阴性、SCCmecⅢ对红霉素、环丙沙星、克林霉素、四环素、庆大霉素、磺胺甲唑耐药的MRSA克隆可能是上海地区HA-MRSA主要流行克隆株,是医院感染控制的重点,因此临床医生在治疗HA-MRSA感染患者时,要谨慎使用抗菌药物.     

Adaptation of methicillin-resistant Staphylococcus aureus during antibiotic therapy

Colonization of a patient by methicillin-resistant Staphylococcus aureus (MRSA) of a single phage-type for over four years is described. During this period we observed the appearance and disappearance of resistance to erythromycin, clindamycin, gentamicin, kanamycin, tobramycin, neomycin and mupirocin. We also saw stepwise increases in methicillin resistance and reversible changes in physical appearance and the colonizer pathogen role. Correlation of clinical observations, details of antibiotic therapy and laboratory studies demonstrated that adaptation of MRSA during antibiotic therapy favoured MRSA establishment and predominance.     

耐甲氧西林金黄色葡萄球菌医院感染研究进展

抗生素的大量应用,以及新的广谱抗生素的不断问世,致使细菌耐药性日趋严重,已经成为世界关注的公共卫生问题。医院感染的重要病原菌-耐甲氧西林金黄色葡萄球菌(MRSA)临床感染十分常见,因其表现为多重耐药,易引起感染的暴发流行,是临床治疗非常棘手的一大难题和研究热点。MRSA医院感染严重,社区获得性MRSA感染也有增加的趋势而备受关注。且国外已经出现耐万古霉素的金黄色葡萄球菌(VRSA),被称为超级细菌(Superbug)或沉默的杀手(Sillent killer)。本文论述了MRSA医院感染的研究进展及其防治。     

An attempt to control nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infection]

A strain of Methicillin-Resistant Staphylococcus aureus (MRSA) was first isolated in our hospital in March 1986. Since then, MRSA has become a difficult pathogen and a cause of sepsis, bacterial endocarditis, and pneumonia in 1988. Rigorous hospital-wide control measures have been planned. The major control measures, based on the various investigations reported, consist of the following three points; improvement of environmental control, reinforcement of handwashing practices during care and control usage of antibiotics. The frequency of isolation of MRSA among the S. aureus isolates was 43.3% in 1988 and this was further reduced to 31.7% in 1990. The total number of MRSA isolates from decubitus, bile, and blood samples have also declined. This decline resulted in a reduction of cases of severe MRSA infection. As yet, MRSA strain are still isolated on incubation. There may be a limit to complete control by measures in a single hospital. It is desired that regional measures and national consensus on nosocomial infection be established.     

Treatment and outcomes of infections by methicillin-resistant Staphylococcus aureus at an ambulatory clinic

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) skin and soft tissue infections (SSTI) have become increasingly common. This study's objectives were to describe the clinical spectrum of MRSA in a community health center and to determine whether the use of specific antimicrobials correlated with increased probability of clinical resolution of SSTI. A retrospective chart review of 399 sequential cases of culture-confirmed S. aureus SSTI, including 227 cases of MRSA SSTI, among outpatients at Fenway Community Health (Boston, MA) from 1998 to 2005 was done. The proportion of S. aureus SSTI due to MRSA increased significantly from 1998 to 2005 (P<0.0001). Resistance to clindamycin was common (48.2% of isolates). At the beginning of the study period, most patients with MRSA SSTI empirically treated with antibiotics received a beta-lactam, whereas by 2005, 76% received trimethoprim-sulfamethoxazole (TMP-SMX) (P<0.0001). Initially, few MRSA isolates were sensitive to the empirical antibiotic, but 77% were susceptible by 2005 (P<0.0001). A significantly higher percentage of patients with MRSA isolates had clinical resolution on the empirical antibiotic by 2005 (P=0.037). Use of an empirical antibiotic to which the clinical isolate was sensitive was associated with increased odds of clinical resolution on empirical therapy (odds ratio=5.91), controlling for incision and drainage and HIV status. MRSA now accounts for the majority of SSTI due to S. aureus at Fenway, and improved rates of clinical resolution on empirical antibiotic therapy have paralleled increasing use of empirical TMP-SMX for these infections. TMP-SMX appears to be an appropriate empirical antibiotic for suspected MRSA SSTI, especially where clindamycin resistance is common.     

Multisensitive community-acquired methicillin-resistant Staphylococcus aureus infections in Malaysia

The 1st 9 clinical isolates of multisensitive community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) from Malaysia carry SCCmec type IV and predominantly cause skin and soft-tissue infections. Seven were classified as nosocomially acquired. There was considerable clonal diversity, with both pandemic and novel multilocus sequence types detected. CA-MRSA rates appear to be increasing in our hospital, warranting close surveillance.     

Effective single and combined chemotherapeutic regimens as regards to antibiotic resistance patterns of methicillin-resistant Staphylococcus aureus (MRSA) in Japan]

The incidence of gentamicin-resistant MRSA (GMr-MRSA) has been gradually increasing since early 1980's in Japan. The GMr-MRSA mainly belongs to Group-I phage type and to Group-IV coagulase type. It is rather difficult to induce methicillin-resistance in the GMr-MRSA in the presence of beta-lactam antibiotics. Since late 1980's tobramycin-resistant MRSA (TOBr-MRSA) has been increasing rapidly in place of GMr-MRSA. The TOBr-MRSA mostly belongs to Group III phage type and Group II coagulase type. It rapidly acquires resistance to methicillin and becomes highly resistant to many other related antibiotics as evidenced by statistics in 1980's in Japan. A combination chemotherapy with imipenem/cilastatin and 1st or 2nd generation cephem, or minocycline plus cephem is considered to be effective for MRSA infections. However, a combination chemotherapy with arbekacin (ABK), or vancomycin (VCM) plus beta-lactam antibiotic is recommended especially for the treatment of respiratory tract infections.     

Genomic DNA fingerprinting by pulsed-field gel electrophoresis for study of nosocomial infection caused by methicillin-resistant Staphylococcus aureus]

In this study, we have compared genomic DNA fingerprintings among isolates of methicillin-resistant Staphylococcus aureus (MRSA) by using pulsed-field gel electrophoresis (PFGE). Chromosomal fragments digested with Sma I were most suitable for the PFGE separation, giving 15-20 fragments of sizes ranging from about 30-1,500 kb. Thirty-one distinctive fragment patterns were identified in 111 isolates of MRSA. On the basis of the genomic typing by PFGE, we performed an epidemiological investigation of an outbreak of nosocomial MRSA infection among 18 inpatients in Nagoya University Hospital. Ten types of chromosomal digestion were identified in 21 isolates of MRSA. The clarity and polymorphism of the chromosomal digestion patterns enabled us to discriminate between isolates. Classification of the genomic DNA fingerprinting patterns by PFGE is therefore proposed as a useful method for investigating the source, transmission, and spread of nosocomial MRSA infections.     

Triclosan and antibiotic resistance in Staphylococcus aureus

Triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) is an antimicrobial agent used in hygiene products, plastics and kitchenware, and for treating methicillin-resistant Staphylococcus aureus (MRSA) outbreaks. S. aureus strains with low-level resistance to triclosan have emerged. It has been claimed that strains with decreased susceptibility to biocides may also be less susceptible to antibiotics. We tested the susceptibility of S. aureus clinical isolates to triclosan and several antibiotics. Triclosan MICs ranged between 0.025 and 1 mg/L. Some, but not all, strains were resistant to several antibiotics and showed low-level triclosan resistance. S. aureus mutants with enhanced resistance to triclosan (< or =1 mg/L) were isolated. In several cases this resistance was stably inherited in the absence of triclosan. These mutants were not more resistant than the parent strain to several antibiotics. Changes in triclosan MICs associated with the acquisition of a plasmid encoding mupirocin resistance were not observed, suggesting that the triclosan/mupirocin co-resistance seen in a previous study was not the result of a single resistance gene or separate genes on the same plasmid. The continuous exposure of a triclosan-sensitive S. aureus strain to sub-MIC concentrations of triclosan for 1 month did not result in decreased susceptibility to triclosan or to several antibiotics tested. Triclosan-induced potassium leakage and bactericidal effects on a triclosan-sensitive strain, a resistant strain and a strain selected for increased resistance were compared with those of non-growing organisms, exponentially growing organisms and organisms in the stationary phase. No significant differences between the strains were observed under these conditions despite their different MICs. Biocides have multiple target sites and so MICs often do not correlate with bactericidal activities. The ability of S. aureus to develop resistance to triclosan and the current view that triclosan may have a specific target in Escherichia coli, namely enoyl reductase, underline the need for more research on the mechanisms of action and resistance.     

耐甲氧西林金黄色葡萄球菌不同来源株耐药性及流行特征分析

目的 探索耐甲氧西林金黄色葡萄球菌（MRSA）在动物食品、动物临床及人医临床中的分布和流行情况,对其耐药情况进行研究分析,为控制MRSA的感染和临床用药提供理论支持。方法 对采集安徽省不同地区动物食品、动物临床及人医临床的标本进行分离培养。采用法国生物梅里埃公司的Vitek全自动微生物分析系统,对分离菌株进行细菌鉴定和药敏试验;应用聚合酶链反应（PCR）方法检测mecA基因;应用脉冲场凝胶电泳（PFGE）对MRSA进行脉冲电泳,BioNumerics软件进行聚类分析。结果 从安徽省淮北、合肥和马鞍山地区共采集动物性食品450份、动物临床标本90份、人医临床标本150份。共分离MRSA 82株,其中动物性食品MRSA（Food-MRSA）14株、动物临床MRSA（La-MRSA）23株、人医临床MRSA（Hu-MRSA）45株,分离培养率为3.1%、30.0%和25.6%;不同来源的MRSA菌株对万古霉素、达福普丁和利奈唑胺100%敏感;对青霉素和苯唑西林100%耐药;对头孢唑啉、红霉素、克林霉素、四环素、庆大霉素、左氧氟沙星、利福平、甲氧嘧啶和氨苄西林有不同程度的耐药,但不同来源MRSA间无差异。82株不同来源的MASA经PFGE分型可分为49个型别,同源性较低。结论 动物临床标本和人医临床标本的MRSA的分离培养率显著高于动物食品的分离率,不同来源的MRSA在药物敏感性方面差异无统计学意义。PFGE 和聚类分析显示,安徽省不同地区不同来源的MRSA其亲缘关系较远,显示其菌株来源的多克隆特征。