Methicillin-resistant Staphylococcus aureus (MRSA) detection: comparison of two molecular methods (IDI-MRSA PCR assay and GenoType MRSA Direct PCR assay) with three selective MRSA agars (MRSA ID, MRSASelect, and CHROMagar MRSA) for use with infection-control swabs

Methicillin-resistant Staphylococcus aureus (MRSA) is an increasing problem. Rapid detection of MRSA-colonized patients has the potential to limit spread of the organism. We evaluated the sensitivities and specificities of MRSA detection by two molecular methods (IDI-MRSA PCR assay and GenoType MRSA Direct PCR assay) and three selective MRSA agars (MRSA ID, MRSASelect, and CHROMagar MRSA), using 205 (101 nasal, 52 groin, and 52 axillary samples) samples from consecutive known MRSA-infected and/or -colonized patients. All detection methods had higher MRSA detection rates for nasal swabs than for axillary and groin swabs. Detection of MRSA by IDI-MRSA was the most sensitive method, independent of the site (94% for nasal samples, 80% for nonnasal samples, and 90% overall). The sensitivities of the GenoType MRSA Direct assay and the MRSA ID, MRSASelect, and CHROMagar MRSA agars with nasal swabs were 70%, 72%, 68%, and 75%, respectively. All detection methods had high specificities (95 to 99%), independent of the swab site. Extended incubation for a further 24 h with selective MRSA agars increased the detection of MRSA, with a corresponding decline in specificity secondary to a significant increase in false-positive results. There was a noticeable difference in test performance of the GenoType MRSA Direct assay in detection of MRSA (28/38 samples [74%]) compared with detection of nonmultiresistant MRSA (17/31 samples [55%]) (susceptible to two or more non-beta-lactam antibiotics). This was not observed with selective MRSA agar plates or IDI-MRSA. Although it is more expensive, in addition to rapid turnaround times of 2 to 4 h, IDI-MRSA offers greater detection of MRSA colonization, independent of the swab site, than do conventional selective agars and GenoType MRSA Direct.     

Rapid confirmation of suspected methicillin-resistant Staphylococcus aureus colonies on chromogenic agars by a new commercial PCR assay, the GenomEra MRSA/SA Diagnose

A new automated closed tube PCR assay, the GenomEra(?) MRSA/SA Diagnose (Abacus Diagnostica Oy, Finland) was evaluated for rapid confirmation of methicillin-resistant Staphylococcus aureus (MRSA) from cultured screening specimens. The ability of the assay to detect genotypically different MRSA strains was studied with a collection of 304 MRSA isolates covering 68 spa types. The specificity was investigated with a collection of 146 non-MRSA staphylococcus isolates. The usefulness of the assay for clinical purposes was assessed by a sequential combination of MRSA screening culture and confirmation of the colonies with the GenomEra MRSA/SA Diagnose assay. A total of 145 suspected MRSA colonies on chromogenic plates were analyzed this way. All MRSA isolates from the culture collection and from the clinical screening specimens were confirmed as MRSA with the GenomEra MRSA/SA Diagnose assay and none of the non-MRSA staphylococci caused false-positive results, which indicates both sensitivity and specificity of 100%. The combination of GenomEra MRSA/SA Diagnose with preceding culture on selective MRSA agar permitted MRSA confirmation within 24 h. This practice offers a reliable and quick detection of MRSA that is also suitable in areas where several strain types cause epidemics.     

Previous healthcare exposure is the main antecedent for methicillin-resistant Staphylococcus aureus carriage on hospital admission in Belgium

This study aimed to estimate the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) carriage upon hospital admission and to study the molecular epidemiology of MRSA in order to assess the proportion of Panton-Valentine leukocidin (PVL)-positive community-associated (CA) and livestock-associated (LA) MRSA strains. Epidemiological data on MRSA carriage upon hospital admission (2006-2009) were collected in a compulsory, continuous, national MRSA surveillance in Belgian acute-care hospitals. Additionally, 328 MRSA strains in 2005 and 314 strains in 2008 were collected in a separate, multicenter microbiological survey. Spa-typing, SCCmec-typing and MLST were performed; toxin genes were detected by PCR. The overall prevalence of MRSA carriage upon hospital admission was 8.9 cases/1,000 admissions between 2006 and 2009. Of MRSA carriers, 37.5% had a known MRSA history, 39.4% had stayed in a care facility, 12.2% reported no contact with healthcare. Over 90% of MRSA belonged to five healthcare-associated clones. Of these, MRSA spa-CC038-ST45-IV was in decline, mainly in favor of spa-CC008-ST8-IV. MRSA spa-CC002-ST5-IV, spa-CC002-ST5-II and spa-CC032-ST22-IV remained relatively stable. The proportion of PVL-positive CA-MRSA and LA-MRSA ST398 was below 2% of all MRSA. The extra-hospital MRSA reservoir in Belgium mainly consists of persons with previous healthcare exposure. PVL-positive CA-MRSA and LA-MRSA strains remained infrequent among hospitalized patients.     

The trend of environmental and clinical methicillin-resistant Staphylococcus aureus in a hospital in Taiwan: Impact of USA300

BackgroundThe environment may facilitate transmission of health care-associated methicillin-resistant Staphylococcus aureus (MRSA) and the pathogen is frequently shed by patients. However, the molecular characteristics and genetic relatedness between clinical and environmental MRSA isolates remain largely unclear in the clinical setting.MethodsA total of 100 hospitalized patients with MRSA infection and 25 hospitalized patients without MRSA infection were enrolled in a medical center, Taiwan in 2019. Environmental and clinical MRSA isolates were characterized by antibiotic susceptibility testing and molecular methods.ResultsIn the study, we detected 17 MRSA isolates in the environment that surrounded 15 MRSA-infected patients and one environmental MRSA isolate from one patient without MRSA infection. The molecular analysis revealed a high genetic diversity within either environmental or clinical MRSA isolates, while the USA300 clone (pulsotype AI, SCCmec IV, ST8, PVL-positive) accounts for 39% (7/18) of environmental and 33% (7/21) of clinical MRSA isolates. Moreover, 13 of the 15 MRSA-infected patients had identical paired clinical-environmental MRSA isolates, which exhibited indistinguishable genetic relatedness and highly similar antibiotic susceptibility phenotype, suggesting a possible transmission cycle of MRSA in the hospital.ConclusionsThe environmental MRSA was closely linked to MRSA isolated from patients, suggesting that the environment may act as a reservoir of MRSA. Besides, the USA300 MRSA has become a major clone in the hospital setting. An effective and rigorous approach to environmental cleaning and decontamination is suggested to eradicate MRSA in the hospital.     

Performance evaluation of a modified chromogenic medium, ChromID MRSA New, for the detection of methicillin-resistant Staphylococcus aureus from clinical specimens

A novel chromogenic medium for the detection of methicillin-resistant Staphylococcus aureus (MRSA), ChromID MRSA New, was evaluated and compared with the original ChromID MRSA agar, using 355 consecutive screening specimens from nose (120), throat (121) and perineum (114). The specimens were collected with an E-swab and inoculated within 24 hours onto both ChromID MRSA New and on ChromID MRSA. ChromID MRSA New was more sensitive than ChromID MRSA in detecting MRSA after 24 hours of incubation (94.3% versus 81.4%; p < 0.05). With the ChromID MRSA New, processing time is reduced from 48 h to 24 h and confirmation of the resistance to methicillin is redundant.     

Development and evaluation of a chromogenic agar medium for methicillin-resistant Staphylococcus aureus

We describe here the development and evaluation of MRSA ID, a new chromogenic agar medium for the specific isolation and identification of methicillin-resistant Staphylococcus aureus (MRSA). We used S. aureus ID (bioMérieux, La Balme Les Grottes, France) and supplemented it with various antimicrobials, including cefoxitin, ciprofloxacin, oxacillin, and methicillin. Cefoxitin proved to be superior to the other antimicrobials for the selection of MRSA from other strains of S. aureus. MRSA ID (consisting of S. aureus ID supplemented with 4 mg of cefoxitin/liter) was evaluated by the use of 747 swabs from various clinical sites. All specimens were also cultured on CHROMagar MRSA and oxacillin resistance screening agar base (ORSAB) and in selective mannitol broth (SMB). A total of 85 MRSA strains were isolated by a combination of all methods. After 22 to 24 h of incubation, 80% of the MRSA strains were isolated as green colonies on MRSA ID, compared with 59 and 62% of the strains that were isolated as colored colonies on CHROMagar MRSA and ORSAB, respectively. After 48 h of incubation, 89, 72, and 78% of the MRSA strains were isolated on MRSA ID, CHROMagar MRSA, and ORSAB, respectively. Sixty-five percent of the strains were isolated by growth in SMB. The specificities of MRSA ID, CHROMagar MRSA, ORSAB, and SMB were 99.5, 99.3, 97.9, and 92.8%, respectively, after 22 to 24 h of incubation. We conclude that MRSA ID is a sensitive and specific medium for the isolation and identification of MRSA.     

Evaluation of a new chromogenic medium, MRSA select, for detection of methicillin-resistant Staphylococcus aureus

We compared MRSA Select to mannitol-salt agar with 8 microg/ml cefoxitin for the detection of methicillin-resistant Staphylococcus aureus (MRSA) from 6,199 clinical samples submitted for MRSA screening. The sensitivities and specificities of MRSA Select and mannitol-salt agar with cefoxitin were 98% and 92% versus 90% and 78%, respectively (P<0.0001). Most (96%) MRSA were detected after overnight incubation using MRSA Select.     

Community acquired methicillin resistant Staphylococcsus aureus: a new threat for hospital outbreaks?

Methicillin resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen. Recently, there have been reports of increasing prevalence of MRSA in the community. We here report an outbreak of post operative wound sepsis by MRSA in the surgical ward of LN hospital. A surveillance study for MRSA was undertaken in the corresponding surgical ward, operation theater and OPD and the source of this outbreak was traced to an outdoor patient with community acquired MRSA infection. A total of 320 clinical and environmental samples were screened for MRSA. Seventy (21.8%) S. aureus were obtained, of which 12.8% were resistant to methicillin. 14% of the MRSA infections were from the community. Nasal carriage rates of MRSA in the screened hospital staff and admitted patients were 5.8% and 4.3% respectively. None of the environmental sites sampled yielded MRSA. A study of antibiogram revealed that all the MRSA were uniformly resistant to penicillin, erythromycin, gentamicin, tobramycin and tetracycline and sensitive to vancomycin. All isolates belonged to the same biotype and were nontypable by the standard set of phages.     

Evaluation of the Xpert MRSA assay for rapid detection of methicillin-resistant Staphylococcus aureus from nares swabs of geriatric hospitalized patients and failure to detect a specific SCCmec type IV variant

Rapid and reliable detection of methicillin-resistant Staphylococcus aureus (MRSA) carriers is crucial for control of MRSA nosocomial transmission. We aimed to evaluate the performance of the GeneXpert real-time PCR system using the Xpert MRSA assay on a collection of 40 representative Belgian MRSA strains and for MRSA screening of geriatric inpatients. Double nasal swabs were used: the first swab for the Xpert MRSA assay and the second for culture onto chromogenic selective medium and enrichment broth. All but 1 of the 40 collection strains were recognized as MRSA by the Xpert MRSA assay. Nares swabs were prospectively collected from 246 inpatients including 25 nasal MRSA carriers. Compared with enriched cultures, the sensitivity, the specificity, and the positive and negative predictive values of the Xpert MRSA assay were 69.2%, 97.7%, 78.3%, and 96.3% respectively. The 7 evaluable false-negative results according to the assay were due to its possible lack of sensitivity (n = 3) and to the occurrence of a Belgian MRSA clone carrying a particular staphylococcal chromosomal cassette mec (SCCmec) type IV variant (n = 4) not targeted by the current Xpert MRSA assay. Because of the evolution of SCCmec in MRSA, new primers should be designed and further studies are warranted to ensure continuous monitoring of this assay.     

Prevalence of methicillin-resistant Staphylococcus aureus in infected and uninfected diabetic foot ulcers

This study investigated the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in infected and uninfected diabetic foot ulcers of 84 patients with the two types of diabetes. S. aureus was the most common pathogen among the Gram-positive bacteria isolated from ulcers, and almost 50% of S. aureus isolates were MRSA. The prevalence of MRSA was significantly higher in patients with infected foot ulcers. MRSA infection or colonisation was not associated with factors (previous hospitalisation, use of antibiotics, etc.) known to predispose to MRSA colonisation or infection. The high prevalence of MRSA in patients with foot ulcers may reflect the increased prevalence of MRSA in the community.     

Gastrointestinal colonization by methicillin-resistant Staphylococcus aureus in immunosuppressed mice.

ICR mice were inoculated intranasally with methicillin-resistant Staphylococcus aureus (MRSA) N133, and the inoculated MRSA was quantitatively recovered from the ceca and feces. The viable counts of the MRSA recovered from ceca correlated well with those from feces. Some mice eliminated MRSA from the cecum by 14 days after inoculation. Intraperitoneal administration of cyclophosphamide at a dose of 200 mg/kg 3 days before inoculation inhibited the elimination of the MRSA from both ceca and feces. All mice treated with cyclophosphamide excreted more than 10(4) CFU of the MRSA per g of feces for at least 70 days, indicating persistent colonization of the MRSA in the gastrointestinal tract. Some beta-lactam antibiotics decreased the colonization level, but others did not. The colonization level was suggested to depend on the antibacterial activity of the antibiotic against the MRSA and the degree of disturbance of intestinal flora by the antibiotic.     

The dominant methicillin‐resistant Staphylococcus aureus clone from hospitals in Cape Town has an unusual genotype: ST612

There is currently limited information available on the molecular epidemiology of methicillin‐resistant Staphylococcus aureus (MRSA) in South Africa. A molecular characterization of 100 MRSA from five hospitals in Cape Town was carried out in this study. The strains were separated into six clusters by pulsed‐field gel electrophoresis, indicating transmission of MRSA between local hospitals. None of the strains carried the Panton‐Valentine Leukocidin gene. SCCmec typing, multilocus sequence typing and spa typing were used to further characterize the MRSA. Three clones corresponded to frequently described pandemic clones: ST239‐MRSA‐III, ST36‐MRSA‐II and ST5‐MRSA‐I. ST239‐MRSA‐III and ST36‐MRSA‐II were minor clones and collectively accounted for 16% of the isolates. ST5‐MRSA‐I was the second‐most prevalent clone and accounted for 37% of the isolates. The dominant local clone was the infrequently described ST612‐MRSA‐IV (44% of isolates), which has only been described in South Africa and Australia.     

ICU中MRSA耐药基因检测及其PFGE分型

目的对耐甲氧西林金黄色葡萄球菌（MRSA）菌株进行分子分型,探讨ICU中MRSA医院感染的特点和流行规律。方法采用表型筛选和PCR扩增mecA基因方法鉴定MRSA菌株。脉冲场凝胶电泳方法（PFGE）进行分子分型。结果12株金黄色葡萄球菌表型筛选为MRSA,MRSA产生A型、B型、C型和D型4种耐药表型,优势耐药模式是A型（75．0％）,MRSA对苯唑西林、阿莫西林／克拉维酸和氨苄西林／舒巴坦等10种抗生素产生100％耐药性,11株MRSA携带mecA基因,携带率为91．7％,PFGE指纹图谱分两型,分别为R1型和R2型,11株MRSA为R1型（91．7％）,R1型各株间相似度为100％。结论ICU可存在MRSA爆发流行,MRSA产生多重耐药性（MDR）,MRSA携带mecA基因可表现为MDR,PFGE分型是理想的分子流行病学溯源手段。     

Comparative evaluation of two fully-automated real-time PCR methods for MRSA admission screening in a tertiary-care hospital

We evaluated two fully-automated real-time PCR systems, the novel QIAGEN artus MRSA/SA QS-RGQ and the widely used BD MAX MRSA assay, for their diagnostic performance in MRSA admission screening in a tertiary-care university hospital. Two hundred sixteen clinical swabs were analyzed for MRSA DNA using the BD MAX MRSA assay. In parallel, the same specimens were tested with the QIAGEN artus MRSA/SA QS-RGQ. Automated steps included lysis of bacteria, DNA extraction, real-time PCR and interpretation of results. MRSA culture was additionally performed as a reference method for MRSA detection. Sensitivity values were similar for both assays (80 %), while the QIAGEN artus MRSA/SA QS-RGQ reached a slightly higher specificity (95.8 % versus 90.0 %). Positive (PPVs) and negative predictive values (NPVs) were 17.4 % and 99.4 % for the BD MAX MRSA assay and 33.3 % and 99.5 % for the QIAGEN artus MRSA/SA QS-RGQ, respectively. Total turn-around time (TAT) for 24 samples was 3.5 hours for both assays. In conclusion, both assays represent reliable diagnostic tools due to their high negative predictive values, especially for the rapid identification of MRSA negative patients in a low prevalence MRSA area.     

Prevalence and risk factor analysis for methicillin-resistant Staphylococcus aureus nasal colonization in children attending child care centers

Children attending child care centers (CCCs) are at increased risk for infections, including those caused by methicillin-resistant Staphylococcus aureus (MRSA). Nasal colonization often precedes infection, and MRSA colonization has been associated with increased infection risk. Community-associated MRSA (CA-MRSA) has caused increased MRSA infections in the general population, including children. Little is known about the frequency of MRSA nasal colonization in young children, particularly in those attending CCCs where disease transmission is common. We sampled the nares of 1,163 children in 200 classrooms from 24 CCCs in North Carolina and Virginia to assess S. aureus colonization. MRSA strains were molecularly analyzed for staphylococcal cassette chromosome mec (SCCmec) type, Panton-Valentine leukocidin status, and multilocus sequence type. A case-control study was performed to identify risk factors for MRSA colonization. We found that 18.1% children were colonized with S. aureus and 1.3% with MRSA. Molecular analysis of the MRSA strains identified 47% as CA-MRSA and 53% as health care-associated MRSA (HA-MRSA). Although two centers had multiple children colonized with MRSA, genotyping indicated that no transmission had occurred within classrooms. The case-control study did not detect statistically significant risk factors for MRSA colonization. However, MRSA-colonized children were more likely to be nonwhite and to have increased exposure to antibiotics and skin infections in the home. Both CA-MRSA and HA-MRSA strains were found colonizing the nares of children attending CCCs. The low frequency of colonization observed highlights the need for a large multicenter study to determine risk factors for MRSA colonization and subsequent infection in this highly susceptible population.     

Frequency and possible infection control implications of gastrointestinal colonization with methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of health care-associated infections. Multiple factors, including transmission from unrecognized reservoirs of MRSA, are responsible for failure to control the spread of MRSA. We conducted prospective surveillance to determine the frequency of gastrointestinal colonization with MRSA among patients and its possible impact on nosocomial transmission of MRSA. Stool specimens submitted for Clostridium difficile toxin A/B assays were routinely inoculated on colistin-naladixic acid agar plates, and S. aureus was identified by using standard methods. Methicillin resistance was confirmed by growth on oxacillin-salt screening agar. For patients whose stool yielded MRSA, information regarding any previous cultures positive for MRSA or other organisms that would require contact precautions was obtained from the laboratory's computer system. During a 1-year period, 151 (9.8%) of 1,543 patients who had one or more stool specimens screened had MRSA in their stool. Ninety-three (62%) of the 151 patients had no previous history of MRSA colonization or infection. Of these 93, 75 were inpatients. Sixty (80%) of the 75 inpatients with no previous history of MRSA were not under "contact precautions." The 60 patients would have spent an estimated total of 267 days without being placed under contact precautions if their positive stool cultures had not resulted in their being isolated. Placing patients under contact precautions based on their positive stool cultures prevented an estimated 35 episodes of MRSA transmission. We conclude that gastrointestinal colonization with MRSA may serve as an unrecognized reservoir from which transmission of MRSA may occur in health care facilities.     

Phenotypic and molecular typing of nosocomial methicillin-resistant Staphylococcus aureus strains susceptible to gentamicin isolated in france from 1995 to 1997

Methicillin-resistant strains susceptible to gentamicin (Gm(s) MRSA) have emerged since 1993 in several French hospitals. To study whether particular clones have spread in various French cities and whether some clones are related to gentamicin-resistant (Gm(r)) MRSA strains, various methods (antibiotyping, phage typing, determination of SmaI macrorestriction patterns before and after hybridization with IS256 transposase and aacA-aphD probes) were used to compare 62 Gm(s) MRSA strains isolated from 1995 to 1997 in nine cities and 15 Gm(r) MRSA strains. Eighteen major SmaI genotypes were identified, of which 11 included only Gm(s) MRSA strains and 5 included only Gm(r) MRSA strains. Each of the Gm(r) MRSA strains contained 6 to 13 SmaI fragments hybridizing with the insertion sequence IS256, of which a single band also hybridized with the aacA-aphD gene. No such hybridizing sequences were detected in 60 of the 62 Gm(s) MRSA strains. Thus, the divergence between Gm(r) and Gm(s) MRSA strains is revealed, not only by their distributions in distinct SmaI genotypes but also by the differences in hybridization patterns. Two of the 62 Gm(s) MRSA strains had the uncommon feature of carrying several SmaI bands hybridizing with IS256, suggesting that they are possibly related to the Gm(r) MRSA strains grouped in the same SmaI genotype. Five of the 11 SmaI genotypes including only Gm(s) MRSA strains contained strains from diverse cities, isolated during different years and with different antibiograms, suggesting that some clones have spread beyond their cities of origin and persisted.     

Characterization of PVL‐positive MRSA from Norway

Norway is a country in which the Methicillin‐resistant Staphylococcus aureus (MRSA) prevalence has been low for the last decades. There are virtually no epidemic, hospital‐acquired MRSA because of an emphasis on strict infection control rules and restrictive use of antibiotics. However, community‐acquired and/or Panton‐Valentine leucocidin (PVL)‐positive MRSA need to be monitored as these strains are transmitted outside of healthcare facilities and cannot be contained by healthcare‐centred strategies. All 179 non‐repetitive isolates of PVL‐positive MRSA that were received during 2011 at the regional infection control laboratory at Akershus University Hospital were preserved and spa typed. Seventy isolates were further characterized by DNA microarray hybridization. The most common PVL‐MRSA lineages were ST8‐MRSA‐IV and CC30‐MRSA‐IV. Further common clones were CC80‐MRSA‐IV and CC5‐MRSA‐IV. Other clones were found sporadically. These included ST772‐MRSA‐V and ST834‐MRSA‐IV, the latter in patients with epidemiological connections to the Philippines. Small‐scale family outbreaks affecting at least 49 individuals were noted, with numbers of known cases per outbreak ranging from two to seven. At least 24 cases were related to foreign travel to Eritrea, India, Iraq, Macedonia, Pakistan, the Philippines, Poland, Singapore, Turkey, the USA and Vietnam. These data show that community‐acquired/PVL‐positive MRSA are not yet a major public health problem in Southern Norway. Our study corroborates the current practice of mandatory screening of patients and staff with travel histories, admissions or employment in healthcare institutions outside the Scandinavian countries or with known MRSA contacts.     

苏州地区耐甲氧西林金黄色葡萄球菌的临床分布特点及耐药性分析

目的 探讨苏州高新区人民医院耐甲氧西林金黄色葡萄球菌(MRSA)的临床分布特点及其耐药性,为临床治疗葡萄球菌属感染提供正确选药依据.方法 对2015年1月至2017年8月苏州高新区人民医院临床各科送检的各类标本中分离鉴定出的MRSA,采用MIC法进行药敏试验,并探讨其临床分布与耐药特点.结果 分离出的170株金黄色葡萄球菌中,MRSA有40株,占23.5%,以呼吸科病房为最多(20株),占50.0%、其次是重症监护病房(ICU)、儿科、神经内科;多重耐药的MRSA对所有β-内酰胺类高度耐药,对大环内酯类耐药率为67.5%;对克林霉素类耐药性较高,其中红霉素诱导的克林霉素耐药率为47.5%,提示该药在苏州地区已不能够用于MRSA 感染的治疗.对氨基糖苷类、氟喹诺酮类耐药率较低(耐药率<30%),磺胺甲噁唑、甲氧苄啶及利福平具有良好的活性,尚未发现耐糖肽类和利萘唑胺的菌株.结论苏州地区近3年来MRSA菌株检出率较低;对常用抗菌素呈多重耐药,尤其是对大环内酯-克林霉素抗菌药物耐药率高.因此应加强对MRSA耐药率的监测,合理选抗菌药物,从而减少MRSA 的产生和传播.     

Antimicrobial agent of susceptibilities and antiseptic resistance gene distribution among methicillin-resistant Staphylococcus aureus isolates from patients with impetigo and staphylococcal scalded skin syndrome

The susceptibilities to antimicrobial agents of and distributions of antiseptic resistance genes in methicillin-resistant Staphylococcus aureus (MRSA) strains isolated between 1999 and 2004 in Japan were examined. The data of MRSA strains that are causative agents of impetigo and staphylococcal scalded skin syndrome (SSSS) were compared with those of MRSA strains isolated from patients with other diseases. The susceptibilities to antiseptic agents in MRSA isolates from patients with impetigo and SSSS were higher than those in MRSA isolates from patients with other diseases. The distribution of the qacA/B genes in MRSA strains isolated from patients with impetigo and SSSS (1.3%, 1/76) was remarkably lower than that in MRSA strains isolated from patients with other diseases (45.9%, 95/207). Epidemiologic typings of staphylococcal cassette chromosome mec (SCCmec) and pulsed-field gel electrophoresis (PFGE) showed that MRSA strains isolated from patients with impetigo and SSSS had type IV SCCmec (75/76), except for one strain, and 64.5% (49/76) of the strains had different PFGE types. In addition, the patterns of restriction digestion of all tested qacA/B plasmid in MRSA isolates having different PFGE types were identical. The results showed that a specific MRSA clone carrying qacA/B was not prevalent, but qacA/B was spread among health care-associated MRSA strains. Therefore, it was concluded that the lower distribution rate of qacA/B resulted in higher susceptibilities to cationic antiseptic agents in MRSA isolated from patients with impetigo and SSSS.