No abstract

Glycopeptide-intermediate Staphylococcus aureus (GISA) and, in particular, heterogeneous GISA (hGISA) are difficult to detect by standard MIC methods, and thus, an accurate detection method for clinical practice and surveillances is needed. Two prototype Etest strips designed for hGISA/GISA resistance detection (GRD) were evaluated using a worldwide collection of hGISA/GISA strains covering the five major clonal lineages. A total of 150 strains comprising 15 GISA and 60 hGISA strains (defined by population analysis profiles-area under the curve [PAP-AUC]), 70 glycopeptide-susceptible S. aureus (GSSA) strains, and 5 S. aureus ATCC reference strains were tested. For standardized Etest vancomycin (VA) MIC testing, the modified Etest macromethod with VA and teicoplanin (TP) strips tested with a heavier inoculum using brain heart infusion agar (BHI) and two glycopeptide screening agar plates (6 g/ml VA/BHI and 5 g/ml Mueller-Hinton agar [MHA]) were tested in parallel with the two new Etest GRD strips: a VA 32 (0.5-g/ml)-TP 32 (0.5-g/ml) double-sided gradient (E-VA/TP) with one prototype overlaid with a nutrient (E-VA/TP؉S) to enhance the growth of hGISA. The Etest GRD strips were tested with a standard 0.5-McFarland standard inoculum using MHA and MHA plus 5% blood (MHB) and were read at 18 to 24 and 48 h. The interpretive MIC cutoffs used for the new Etest GRD strips at 24 and 48 h were as follows: for GISA, TP or VA, >8, and a standard VA MIC of >6; for hGISA, TP or VA, >8, and a standard VA MIC of <4. The results on MHB at 48 h showed that E-VA/TP؉S had high specificity (94%) and sensitivity (95%) in comparison to PAP-AUC and was able to detect all GISA (n ‫؍‬ 15) and 98% of hGISA (n ‫؍‬ 60) strains. In contrast, the glycopeptide screening plates performed poorly for hGISA. The new Etest GRD strip (E-VA/TP؉S), utilizing standard media and inocula, is a simple and acceptable tool for detection of hGISA/GISA for clinical and epidemiologic purposes.

Thirty-five Bacteroides fragilis clinical isolates with varying susceptibility to meropenem were analysed with a prototype of a double-ended Etest strip containing meropenem +/- EDTA, designed for the detection of the CfiA metallo-beta-lactamase. Phenotypic results obtained with this new Etest strip were related to the genotype and compared to the results of the Etest containing imipenem +/- EDTA. Whereas the Etest with imipenem +/- EDTA only allowed detection of isolates with high-level resistance (both MICs of imipenem and meropenem >32 mg/L), reflecting the possible underestimation of CfiA prevalence in B. fragilis, the Etest with meropenem +/- EDTA proved to be more accurate, particularly for isolates with low-level carbapenem resistance, suggesting its potential for broader detection of CfiA production.

Detection of methicillin resistance in S. aureus using the cefoxitin disc method with a semi-confluent inoculum on Iso-Sensitest agar is influenced by incubation temperature, and the temperature should not exceed 35 degrees C for the reliable detection of MRSA.

We investigated the performance of blood and chocolate agar as alternatives to Middlebrook 7H11 agar for testing the susceptibility of Mycobacterium tuberculosis to first-and second-line drugs by the Etest method. A total of 39 strains of M. tuberculosis including 22 multidrug-resistant M. tuberculosis strains and 17 susceptible strains were tested. In conclusion, our results showed that chocolate agar gave insufficient growth, needing up to 21 days of incubation, while results on blood agar were comparable to those on Middlebrook 7H11 agar and can be further explored as an alternative for Etest-based susceptibility testing of M. tuberculosis.Early clinical diagnosis of tuberculosis, identification of multidrug-resistant (MDR) Mycobacterium tuberculosis strains, and appropriate treatment are the most effective strategies to control the spread of MDR tuberculosis (18). Therefore, rapid and efficient methods are needed to accurately diagnose and control this disease efficiently. The CLSI reference method for susceptibility testing of M. tuberculosis is the agar proportion method (22) performed with Middlebrook 7H10 to -11 agar. On the other hand, there are semiautomated and automated systems (BACTEC 460 TB and BACTEC MGIT [mycobacterium growth indicator tube] 960; Becton Dickinson Diagnostic Systems, Sparks, MD) for susceptibility testing of M. tuberculosis, but they are available only in developed countries. Blood agar is a basic medium widely and routinely used in clinical microbiology laboratories worldwide. In addition, blood agar is suitable for isolation and culture of mycobacteria, including the causative agents of tuberculosis (11).Etest (AB Biodisk, Solna, Sweden) is used for quantitative antibiotic susceptibility testing of numerous microorganisms, including various species of mycobacteria, including M. tuberculosis (1,2,(12)(13)(14)(15)(17)(18)(19)(20). The current recommended Etest procedure for M. tuberculosis is based on Middlebrook 7H11 agar supplemented with oleic acid, albumin, dextrose, and catalase (OADC) (1). In recent years, it has been reported that M. tuberculosis isolates could be grown on blood agar in 1 to 2 weeks (4,10,11,16). In addition, the results of our previous reports have shown that blood agar can be used as an alternative medium for testing M. tuberculosis with isoniazid (IZ), rifampin (RI), streptomycin (SM), and ethambutol (EB) (6-8, 31).In this study, the performance of blood and chocolate agar was compared to that of Middlebrook 7H11 agar with the aim to evaluate them as possible alternatives for susceptibility testing of M. tuberculosis clinical isolates against IZ, RI, SM, EB, ofloxacin (OF), ciprofloxacin (CI), levofloxacin (LE), linezolid (LZ), and ethionamide (ET) by Etest.A total of 39 strains of M. tuberculosis and H37Rv (control strain susceptible to all antituberculous drugs) were tested. While 22 MDR M. tuberculosis strains were isolated from sputum of chronic pulmonary tuberculosis patients in Istanbul, Turkey, 17 susceptible strains were isolated from sputum of p...