Screening method for detecting staphylococci with reduced susceptibility to teicoplanin

Epidemiological and molecular characterization of community and hospital acquired Staphylococcus aureus strains prevailing in Shenyang, Northeastern China

In order to obtain adequate information for the treatment of methicillin resistant Staphylococcus aureus (MRSA) infections, it is crucial to identify trends in epidemiological and antimicrobial resistance patterns of local S. aureus strains. Community and hospital acquired S. aureus isolates (n = 202) were characterized using staphylococcal cassette chromosome mec (SCCmec) typing, pulse field gel electrophoresis (PFGE) analysis, spa typing and minimal inhibitory concentration (MIC) determination. The prevalence of the Panton-Valentine leukocidine (pvl) and several antibiotic resistance genes among the isolates were also detected by PCR. All of the S. aureus isolates were susceptible to vancomycin, daptomycin and linezolid. Three hospital isolates were resistant to teicoplanin while 14 showed intermediate resistance to teicoplanin. The resistance patterns of community-acquired MRSA (CA-MRSA) isolates to other antimicrobials were similar to those of hospital-acquired MRSA (HA-MRSA) isolates except for clindamycin and gentamicin. There was excellent correlation between phenotypes and genotypes in the determination of S. aureus resistance to erythromycin, gentamicin, and tetracycline. The SCCmec type II and SCCmec type IV were the predominant types detected in hospital and community isolates, respectively. The most frequently encountered spa types were t002 and t030 both in HA- and CA-MRSA isolates. Pulsotype A was the most predominant pulsotype identified among the isolates tested, followed by pulsotype B. Seventy-two hospital isolates (19 HA-MRSA and 53 HA-MSSA) and 10 CA-MRSA were positive for the pvl gene. This study shows that the combination of susceptibility testing and various molecular methods has provided useful information on the antibiotic resistance and molecular diversity of S. aureus in a specific region of China. The high proportion of pvl positive MSSA and MRSA isolates observed in this study indicates that adequate measures are needed to curtail the spread of those MRSA and MSSA clones prevailing both in hospital and the community.

Investigation of reduced susceptibility to glycopeptides among methicillin-resistant Staphylococcus aureus isolates from patients in Ireland and evaluation of agar screening methods for detection of heterogeneously glycopeptide-intermediate S. aureus

Methicillin-resistant Staphylococcus aureus (MRSA) isolates (n = 3,189) from 2,990 patients were investigated by agar screening and by the Etest macromethod for reduced susceptibility to glycopeptide. No vancomycin-resistant S. aureus or glycopeptide-intermediate S. aureus (GISA) isolates were detected, but 178 isolates were confirmed as hetero-GISA (hGISA) by vancomycin population analysis profile (vPAP)-area under the curve (AUC) ratio determination and/or teicoplanin PAP (tPAP) methods. Of 139 isolates detected using the recommended Etest macromethod cutoff values of > or =8 mg/liter for both vancomycin and teicoplanin or > or =12 mg/liter for teicoplanin alone, 73 were confirmed as hGISA by vPAP-AUC, 95 were confirmed as hGISA by tPAP, and 108 were confirmed as hGISA by both methods. An Etest macromethod cutoff value of 8 mg/liter for teicoplanin alone detected a further 70 hGISA (17 were confirmed by vPAP-AUC and 70 were confirmed by tPAP). Agar screening utilizing brain heart infusion (BHI) agar containing 6 mg of vancomycin/liter (BHIV6) and Mueller-Hinton (MH) agar containing 8 mg of teicoplanin/liter (MHT8) failed to detect hGISA. MH agar containing 5 mg of teicoplanin/liter (MHT5) and BHI containing 5 mg of teicoplanin/liter (BHIT5) were evaluated using 10-microl volumes of three inoculum concentrations (with densities equivalent to 0.5 and 2.0 McFarland turbidity standards and stationary-phase BHI broth subcultures [MHT5(0.5), MHT5(2.0), MHT5(S), BHIT5(0.5), BHIT5(2.0), and BHIT5(S)]). The sensitivity of all methods except MHT5(0.5) and MHT5(2.0) was 100%. The specificity ranged from 4 to 82%. BHIT5(0.5) yielded the best performance, with a specificity of 84% for detecting isolates with teicoplanin Etest macromethod values of > or =8 mg/liter. Screening on BHIT5(0.5) is useful where screen-positive isolates are investigated with the Etest macromethod and confirmed by vPAP-AUC and tPAP. The prevalence of hGISA among patients with blood culture isolates recovered in Irish hospitals between 1999 and 2003 was 2.6%, whereas the prevalence among patients with isolates from all specimen sites collected during a 2-week survey in 1999 was 12%. The prevalence in one hospital decreased from 5.3% in 2003 to 1.5% in 2004.

Rapid detection of methicillin-resistant Staphylococcus aureus directly from sterile or nonsterile clinical samples by a new molecular assay

A rapid procedure was developed for detection and identification of methicillin-resistant Staphylococcus aureus (MRSA) directly from sterile sites or mixed flora samples (e.g., nose or inguinal swabs). After a rapid conditioning of samples, the method consists of two main steps: (i) immunomagnetic enrichment in S. aureus and (ii) amplification-detection profile on DNA extracts using multiplex quantitative PCR (5'-exonuclease qPCR, TaqMan). The triplex qPCR assay measures simultaneously the following targets: (i) mecA gene, conferring methicillin resistance, common to both S. aureus and Staphylococcus epidermidis; (ii) femA gene from S. aureus; and (iii) femA gene from S. epidermidis. This quantitative approach allows discrimination of the origin of the measured mecA signal. qPCR data were calibrated using two reference strains (MRSA and methicillin-resistant S. epidermidis) processed in parallel to clinical samples. This 96-well format assay allowed analysis of 30 swab samples per run and detection of the presence of MRSA with exquisite sensitivity compared to optimal culture-based techniques. The complete protocol may provide results in less than 6 h (while standard procedure needs 2 to 3 days), thus allowing prompt and cost-effective implementation of contact precautions.

Low-level resistance to glycopeptides amongst staphylococcus species: surveillance in a university hospital and evaluation of a vancomycin screening agar

The prevalence of low-level resistance to glycopeptides (teicoplanin MIC > or = 8 microg/mL and vancomycin MIC > or = 4 microg/mL) among staphylococci was investigated over a 15 month period. A total of 2,279 isolates (1,519 S. aureus, 760 coagulase-negative staphylococcus (CNS)) were screened using inoculum of 10(6) CFU/mL and Mueller-Hinton agars supplemented with 8 microg/mL of teicoplanin. Of these, 218 isolates (136 S. aureus and 82 CNS) grew on the screening agar. For these isolates, teicoplanin and vancomycin MICs were determined by agar dilution method and a vancomycin agar screening method was evaluated. The prevalence of low-level resistance to teicoplanin and vancomycin was 7.8% and 0.1% for S. aureus and 8.8% and 0.8% for CNS, respectively. The brain heart infusion agar containing 4 microg/mL of vancomycin failed to detect two out of eight staphylococcal isolates with vancomycin MICs of 4 microg/mL. Furthermore, the method appeared to lack reproducibility. Considering the increasing incidence of vancomycin treatment failure in staphylococcal infection, a more reliable screening method is required.

Absence of mutation in the region (nt. 710-1010) of pbp4 gene in clinical isolates of Staphylococcus aureus with low-level teicoplanin resistance

Resistance to teicoplanin in clinical isolates of Staphylococcus aureus has increased in frequency. Detection is difficult due to heterogeneous phenotypes of these strains. Two mutations in pbp4 have recently been identified in glycopeptide resistant laboratory strains. We investigated to determine if these mutations could be used to screen clinical isolates for teicoplanin resistance. Of 41 clinical isolates screened, none contained the mutations in pbp4 indicating these mutations cannot be used as a molecular diagnostic tool for glycopeptide resistance.