Multiple Genetic Mutations Associated with Polymyxin Resistance in Acinetobacter baumannii.

We studied polymyxin B resistance in 10 pairs of clinical Acinetobacter baumannii isolates, two of which had developed polymyxin B resistance in vivo. All polymyxin B-resistant isolates had lower growth rates than and substitution mutations in the lpx or pmrB gene compared to their parent isolates. There were significant differences in terms of antibiotic susceptibility and genetic determinants of resistance in A.

Six cases of daptomycin-non-susceptible Staphylococcus aureus bacteraemia in Singapore.

We report what we believe to be the first six cases of daptomycin-non-susceptible Staphylococcus aureus infections from Singapore. These strains were rapidly isolated after bacteraemic patients were switched to daptomycin following initial prolonged unsuccessful therapy with vancomycin, despite confirmation of daptomycin susceptibility just prior to initiating daptomycin therapy. The majority of post-vancomycin therapy strains exhibited marked thickening of their cell walls on electron microscopic examination.