Abstract
<p>The decreased vancomycin susceptibility and subsequent emergence of vancomycin resistant <em>Staphylococcus aureus </em>(VRSA) strains already multi-resistant to antibiotics is a major public health problem. In 2009, the Clinical and Laboratory Standards Institute (CLSI) altered its guidelines for vancomycin susceptibility testing in <em>S. aureus</em> and recent data suggests the possibility that VRSA may emerge more frequently than previously expected. Against this background, we conducted a study to ascertain the susceptibility status of clinical <em>S. aureus</em> isolates to vancomycin in our environment using vancomycin agar screen, disk diffusion and broth dilution methods. Of the total 49 <em>S. aureus </em>invasive strains isolated, 25 (51.0%) had vancomycin MIC of ≤2µg/ml by the CLSI standard broth dilution method and are classed as vancomycin susceptible; 18 (36.7%) had MIC of 4-8µg/ml (vancomycin intermediate resistant) and 6 (12.2%) had MIC of &gt;256µg/ml (high level vancomycin resistant). Vancomycin agar screen with Mueller-Hinton agar containing 3µg/ml vancomycin (MHA-V3) correctly identified 20 of 25 (80%) vancomycin susceptible isolates; detected all 6 vancomycin resistant isolates and 16 of 18 (88.9%) vancomycin intermediate strains. Similarly, Mueller-Hinton agar containing 6µg/ml vancomycin (MHA-V6) correctly identified 23 of 25 (92%) vancomycin susceptible isolates and all 6 vancomycin resistant isolates but detected 14 (77.8%) of 18 vancomycin intermediate strains. Vancomycin disk diffusion test correctly identified all the 25 vancomycin susceptible <em>S. aureus</em> isolates giving 100% specificity but detected only 1 of 18 (5.6%) vancomycin intermediate and none (0%) of vancomycin resistant isolates. This result shows the occurrence of VISA and high level VRSA isolates in our environment, which contrary to current belief, may indicate widespread dissemination of VRSA. MHA-V3 agar is a useful alternative screening medium for vancomycin non-susceptibility detection in clinical <em>S. aureus</em> isolates but vancomycin disk diffusion is not useful in this regard.</p>
Highlights
Scientist, and Mr Girish Kulkarni, Senior Research Fellow of Molecular Biology Unit, National Centre for Cell Sciences, Pune for the phylogenetic analysis of the isolate
Streptomyces coelicolor, isolated from the litn toral soil of Lonar Lake situated in Buldhana o district of Maharashtra, India, a lake characterised by high alkalinity, carbonates, bicare bonates, and algal blooms
The agar degrading property was ia detected by the appearance of depressions around each colony after 48 h of growth
Summary
Soil samples collected from the littoral zone of Lonar Lake were subjected to enrichment of nitrogen fixing bacteria on Ashby’s Nitrogen free Mannitol broth with pH-10.5 and NaCl-2% amended as per the chemical characteristics of Lonar Lake soil. Loopfuls of enriched medium from each tube were streak inoculated on Ashby’s Nitrogen free Mannitol solid medium contain-. Confirmation was done by growing the isolate on a simple medium of composition Agar-20.0 g/L, NaCl-20.0g/L and incubated at 40°C for 48 h. The main constituent, is a neutral polysaccharide that forms a linear chain structure consisting of repeating units of agarobiose, which is an alternating polymer of D-galactose and 3,6anhydro-L-galactose linked by alternating β(1,4) and α-(1,3) bonds.. The main constituent, is a neutral polysaccharide that forms a linear chain structure consisting of repeating units of agarobiose, which is an alternating polymer of D-galactose and 3,6anhydro-L-galactose linked by alternating β(1,4) and α-(1,3) bonds.1 It is widely employed as a gelling agent for microbiological culture The main constituent, is a neutral polysaccharide that forms a linear chain structure consisting of repeating units of agarobiose, which is an alternating polymer of D-galactose and 3,6anhydro-L-galactose linked by alternating β(1,4) and α-(1,3) bonds. It is widely employed as a gelling agent for microbiological culture
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