Antibiotics resistance of Stenotrophomonas maltophilia strains isolated from various clinical specimens.

Background: A limited number of antibiotics are recommended for the therapy of Stenotrophomonas maltophilia infections due to therapy difficulties caused by its numerous mechanisms of resistance. Objectives: In this study conducted over a period of approximately 5 years we aimed to determine resistance rates of S. maltphilia based on drug classification recommended by Clinical and Laboratory Standards Institute. Methods: A total of 118 S. maltphilia strains isolated from various clinical specimens between January 2006 and June 2012 were included in the study. BD Phoenixautomated microbiology system (Becton Dickinson, USA) was utilized for species level identification and antibiotic susceptibility testing. Results: Sixty seven of S. maltphilia strains were isolated from tracheal aspirate isolates, 17 from blood, 10 from sputum, 10 from wound and 14 from other clinical specimens. Levofloxacin was found to be the most effective antibiotic against S. maltphilia strains with resistance rate of 7.6%. The resistance rates to other antibiotics were as follows: chloramphenicol 18.2%, trimethoprim-sulfamethoxazole 20.3% and ceftazidime 72%. Conclusion: The study revealed that S. maltphilia is resistant to many antibiotics. The treatment of infections caused by S. maltphilia should be preferred primarily as levofloxacin, chloramphenicol, and TMP-SXT, respectively.

The prevalence of genotypes that determine resistance to macrolides, lincosamides, and streptogramins B compared with spiramycin susceptibility among erythromycin-resistant Staphylococcus epidermidis

Coagulase-negative staphylococci, particularly Staphylococcus epidermidis , can be regarded as potential reservoirs of resistance genes for pathogenic strains, e.g., Staphylococcus aureus . The aim of this study was to assess the prevalence of different resistance phenotypes to macrolide, lincosamide, and streptogramins B (MLSB) antibiotics among erythromycin-resistant S. epidermidis, together with the evaluation of genes promoting the following different types of MLSB resistance: ermA, ermB, ermC, msrA, mphC, and linA/A’. Susceptibility to spiramycin was also examined. Among 75 erythromycin-resistant S. epidermidis isolates, the most frequent phenotypes were macrolides and streptogramins B (MSB) and constitutive MLSB (cMLSB). Moreover, all strains with the cMLSB phenotype and the majority of inducible MLSB (iMLSB) isolates were resistant to spiramycin, whereas strains with the MSB phenotype were sensitive to this antibiotic. The D-shape zone of inhibition around the clindamycin disc near the spiramycin disc was found for some spiramycin-resistant strains with the iMLSB phenotype, suggesting an induction of resistance to clindamycin by this 16-membered macrolide. The most frequently isolated gene was ermC, irrespective of the MLSB resistance phenotype, whereas the most often noted gene combination was ermC, mphC, linA/A’. The results obtained showed that the genes responsible for different mechanisms of MLSB resistance in S. epidermidis generally coexist, often without the phenotypic expression of each of them.