Rapid detection of epidemic strains of methicillin-resistant Staphylococcus aureus

Multidrug-resistant bacteria in geriatric clinics, nursing homes, and ambulant care--prevalence and risk factors

Colonization/infection with multidrug-resistant bacteria (MDRB) such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and extended-spectrum beta-lactamase (ESBL) producing Enterobacteriaceae, is an increasing problem not only in hospitals but also in long-term care facilities. The aim of this study was to determine the prevalence as well as the risk factors of colonization/infection with MRSA, VRE, and ESBL producing Enterobacteriaceae in geriatric clinics, nursing homes, and ambulant care in Frankfurt am Main, Germany. 288 patients from 2 geriatric clinics (n=46), 8 nursing homes (n=178), and 2 ambulant care facilities (n=64) as well as 64 staff members were screened for MDRB in the time period from October 2006 to May 2007. 58 patients (20.1%) and 4 staff members (6.2%) were colonized with MDRB. Among patients, 27 (9.4%) were colonized with MRSA, 11 (3.8%) were screened positive for VRE, and 25 (8.7%) were found to be colonized with ESBL producing Enterobacteriaceae. Prevalence of MDRB in geriatric clinics, nursing homes, and ambulant care facilities were 32.6%, 18.5%, and 15.6%, respectively. Significant risk factors for MDRB were immobility (OR: 2.7, 95% CI: 1.5-4.9; p=0.002), urinary catheter (OR: 3.1, 95% CI: 1.7-5.9; p<0.001), former hospitalization (OR: 2.1, 95% CI: 1.1-4.0; p=0.033), and wounds/decubiti (OR: 2.3, 95% CI: 1.5-4.9; p=0.03). Finally, the high level of MDRB in geriatric clinics, nursing homes, and ambulant care points to the importance of these institutions as a reservoir for dissemination.

Evaluation of methicillin resistance by cefoxitin disk diffusion and PBP2a latex agglutination test in mecA-positive Staphylococcus aureus, and comparison of mecA with femA, femB, femX positivities

Methicillin resistance in staphylococci is primarily due to the presence of a mecA gene which encodes the novel penicillin binding protein2a. Some chromosomal factors such as femA and femB also participate in the expression of methicillin resistance. This study was designed to detect methicillin resistance by cefoxitin disk diffusion and penicillin binding protein2a latex agglutination methods, and to compare mecA, femA, femB and femX gene positivities. A total of 60 MRSA isolates were included in the evaluation. PCR analysis showed that all isolates were positive for mecA and femA genes. Seven of these isolates tested negative by the latex agglutination test. Fifteen isolates were positive for femB and 28 isolates for femX gene. This study implicated that for the determination of methicillin resistance, latex agglutination test is the least reliable method when compared to PCR and cefoxitin disk diffusion test. femA gene shows more correlation than femB and femX with methicillin resistance.

Prevalence and clinical significance of Staphylococcus aureus small-colony variants in cystic fibrosis lung disease

Small-colony variants (SCVs) of Staphylococcus aureus can be isolated from the chronically infected airways of patients suffering from cystic fibrosis (CF). These slow-growing morphological variants have been associated with persistent and antibiotic-resistant infections, such as osteomyelitis and device-related infections, but no information is available to date regarding the clinical significance of this special phenotype in CF lung disease. We therefore investigated the prevalence of S. aureus SCVs in CF lung disease in a 12-month prospective study and correlated the microbiological culture results with the patients' clinical data. A total of 252 patients were screened for the presence of SCVs. The prevalence rate was determined to be 17% (95% confidence interval, 10 to 25%) among S. aureus carriers. S. aureus isolates with the SCV phenotype showed significantly higher antibiotic resistance rates than those with the normal phenotype. Patients positive for SCVs were significantly older (P = 0.0099), more commonly cocolonized with Pseudomonas aeruginosa (P = 0.0454), and showed signs of more advanced disease, such as lower forced expiratory volume in 1 s (P = 0.0148) than patients harboring S. aureus with a solely normal phenotype. The logistic regression model determined lower weight (P = 0.016), advanced age (P = 0.000), and prior use of trimethoprim-sulfamethoxazole (P = 0.002) as independent risk factors for S. aureus SCV positivity. The clinical status of CF patients is known to be affected by multiple parameters. Nonetheless, the independent risk factors determined here point to the impact of S. aureus SCVs on chronic and persistent infections in advanced CF lung disease.

Molecular genotyping of methicillin-resistant Staphylococcus aureus strains in a teaching hospital in Turkey

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes of nosocomial infections in our hospital. Therefore, we aimed to characterize MRSA isolates phenotypically from patients with nosocomial infections at Cumhuriyet University Hospital between December, 1999, and June, 2001, in Sivas by analysis of antibiotic patterns and genotypically using pulsed-field gel electrophoresis (PFGE) and repetitive element sequence-based polymerase chain reaction (rep-PCR). Forty-three nosocomial isolates were collected from various wards. All isolates were resistant to penicillin, tetracycline, oxacillin, and gentamicin. By rep-PCR and by separation of SmaI fragments of genomic DNA using PFGE, one major type (eight subtypes with PFGE) was identified among the strains. This clone was found to be different than some clones such as Iberian, Brazilian, and a major clone that was found in another Turkish University Hospital in Ankara. According to our results, there is a major MRSA clone with a potential to spread in our hospital. Infection control measures should be directed toward restricting the further spread of this clone. Therefore, in accordance with these findings, a surveillance culturing program should be established.

Rapid PCR-based identification of methicillin-resistant Staphylococcus aureus from screening swabs

A PCR identification of methicillin-resistant Staphylococcus aureus (MRSA), obviating the need for subculture on agar media, was investigated. The combination of MRSA detection by mecA femB PCR with prior enrichment in selective broth was tested for 439 swabs. PCR identified 36 MRSA-positive samples, in concordance with conventional methods.

Rapid molecular typing of methicillin-resistant Staphylococcus aureus by PCR-RFLP

OBJECTIVE

To establish a new, rapid, and reliable genotypic fingerprinting technique for methicillin-resistant Staphylococcus aureus (MRSA) typing in routine epidemiological surveillance.

DESIGN

The method is based on polymerase chain reaction (PCR) restriction fragment-length polymorphism (RFLP) following HaeII digestion of simultaneously amplified parts of the protein A gene, the coagulase gene, and the hypervariable region adjacent to mecA. A total of 46 MRSA initial isolates were analyzed, including 14 isolates from five countries; the six German epidemic strains; 16 isolates from the Frankfurt metropolitan area, which were known to be heterogeneous by pulsed-field gel electrophoresis (PFGE); and 10 isolates obtained during three epidemics, all of which displayed an identical genotype.

RESULTS

Restriction analysis by PCR-RFLP permitted discrimination of 10 of 14 international isolates, all six German epidemic strains, and 15 of 16 national isolates. It also confirmed the homogeneous character of the 10 outbreak isolates.

CONCLUSIONS

This new and rapid PCR-RFLP typing method is an attractive tool in routine epidemiological surveillance. Its impressive characteristics are ease of performance and interpretation, while at the same time guaranteeing good discriminatory power, reproducibility, and typeability.

A Shared noncapsular antigen is responsible for false-positive reactions by Staphylococcus epidermidis in commercial agglutination tests for Staphylococcus aureus

Many of the commercial slide agglutination tests for Staphylococcus aureus incorporate antibodies against cell surface antigens associated with methicillin resistance, including capsular polysaccharides and an uncharacterized antigen, serotype 18. These tests are more sensitive than the first-generation agglutination procedures that detected only bound coagulase and protein A, but they suffer from false-positive reactions with some coagulase-negative staphylococci. The aim of this study was to elucidate the mechanism for false-positive agglutination by S. epidermidis in these tests. A group of methicillin-resistant S. aureus (MRSA) isolates, including a serotype 18 strain, that were not detectable in the first-generation tests were found to be of capsular polysaccharide type 8. All of these isolates were deficient in bound coagulase and/or protein A, and they possessed a heat-stable, proteinaceous antigen that was absent from a prototype capsule type 8 strain. Enzyme-linked immunosorbent assay and agarose gel immunodiffusion experiments demonstrated that this proteinaceous antigen was also present on both methicillin-sensitive and methicillin-resistant S. epidermidis clinical isolates. S. epidermidis strains that gave false-positive agglutination test results had a considerably higher level of this antigen than strains that gave the correct negative result. These findings reveal the importance of the careful selection of MRSA strains for raising anti-capsular type 8 antibodies for use in agglutination tests. Strains devoid of the antigen shared with S. epidermidis should be used to eliminate potential cross-reactions with this coagulase-negative coccus.