Genetic Diversity of OXA-like Genes in Multidrug-Resistant Acinetobacter baumannii Strains from ICUs.

BACKGROUND: This study aimed to investigate the genetic diversity of OXA-51-like, OXA-23-like, OXA-24, and OXA-58-like genes and the role of ß-lactamases in carbapenem resistance among multidrug resistant Acinetobacter baumannii strains recovered from patients in intensive care units (ICUs). METHODS: Non-duplicate clinical isolates of A. baumannii from ICUs that were identified as imipenem and meropenem resistant were collected. Antimicrobial susceptibilities were determined by PhoenixTM system (Becton Dickinson, USA). Minimum inhibitory concentrations (MICs) for imipenem and meropenem were determined by using gradient strip method (E-test) and interpreted according to CLSI. Presence of carbapenemase activity was determined by the modified Hodge test (MHT) and detection of metallo-ß-lactamase (MBL) was performed by the double-disk synergy test (DDST) and MBL E-test. Detection of the four groups of OXA carbapenemase genes (OXA-23, OXA-24, OXA-51, and OXA-58) was carried out using a multiplex PCR assay. Sequencing of the products in both directions was performed by ABI 3130XL genetic analyzer (Life Technologies Corporation, CA, USA). The resulting DNA sequence was analyzed by the BLAST program, available at the NCBI website. RESULTS: Sixty-one non-duplicate, multidrug resistant clinical A. baumannii isolates were studied. MHTs were positive for all 61 A. baumannii strains, but none of them showed MBL activity. As determined through multiplex PCR, all of the 61 isolates had blaOXA-51 genes including blaOXA-64, blaOXA-66, and blaOXA-91, 50 isolates had blaOXA-23, and 11 isolates had blaOXA-58 genes. Alleles encoding OXA-24-like enzymes were not detected in any isolates. CONCLUSIONS: This study indicated that the major cause of carbapenem resistance in our region was OXA-type car-bapenemase encoded by blaOXA-51, blaOXA-23, and blaOXA-58 genes and as we know, this is the first report from Turkey identifying blaOXA-51-like sequences.

Molecular characterization of acutely and gradually heavy metal acclimated aquatic bacteria by FTIR spectraoscopy.

In the environment, bacteria can be exposed to the concentration gradient of toxic heavy metals (gradual) or sudden high concentration of them (acute). In both situations, bacteria get acclimated to toxic heavy metal concentrations. Acclimation causes metabolic and molecular changes in bacteria. In this study, we aimed to understand whether there are differences between molecular profiles of the bacteria (Brevundimonas, Gordonia and Microbacterium) which are under acute or gradual exposure to cadmium or lead by using ATR-FTIR spectroscopy. Our results revealed the differences between the acclimation groups in membrane dynamics including changes in the structure and composition of the membrane lipids and proteins. Furthermore, protein concentrations decreased in acclimated bacterial groups. Also, a remarkable increase in exopolymer production occurred in acclimated groups. Interestingly, bacteria under acute cadmium exposure produced the significantly higher amount of exopolymer than they did under gradual exposure. On the contrary, under lead exposure gradually acclimate strains produced significantly higher amounts of exopolymer than those of acutely acclimated ones. This information can be used in bioremediation studies to obtain bacterial strains producing a higher amount of exopolymer.

Aspects of silver tolerance in bacteria: infrared spectral changes and epigenetic clues.

In this study, the molecular profile changes leading to the adaptation of bacteria to survive and grow at inhibitory silver concentration were explored. The profile obtained through infrared (IR)-based measurements indicated extensive changes in all biomolecular components, which were supported by chemometric techniques. The changes in biomolecular profile were prominent, including nucleic acids. The changes in nucleic acid region (1350-950 cm-1 ) were encountered as a clue for conformational change in DNA. Further analysis of DNA by IR spectroscopy revealed changes in the backbone and sugar conformations. Moreover, Enzyme-Linked Immunosorbent Assay-based measurements of DNA methylation levels were performed to see if epigenetic mechanisms are in operation during bacterial adaptation to this environmental challenge. The results indicated a notable demethylation in Escherichia coli and methylation in Staphylococcus aureus likely to be associated with their elaborate adaptation process to sustain survival and growth.

High level multiple antibiotic resistance among fish surface associated bacterial populations in non-aquaculture freshwater environment.

Freshwater fish, Alburnus alburnus (bleak), were captured from Lake Mogan, situated in Ankara, during spring. The surface mucus of the fish was collected and associated bacteria were cultured and isolated. By sequencing PCR-amplified 16S RNA encoding genes, the isolates were identified as members of 12 different genera: Acinetobacter, Aeromonas, Bacillus, Brevundimonas, Gordonia, Kocuria, Microbacterium, Mycobacterium, Pseudomonas, Rhodococcus, and Staphylococcus, in addition to one strain that was unidentified. The mucus-dwelling bacterial isolates were tested for resistance against ampicillin, kanamycin, streptomycin and chloramphenicol. About 95% of the isolates were found to be resistant to ampicillin, 93% to chloramphenicol, and 88% to kanamycin and streptomycin. A Microbacterium oxydans and the unidentified environmental isolate were resistant to all four antibiotics tested at very high levels (>1600 µg/ml ampicillin and streptomycin; >1120 µg/ml kanamycin; >960 µg/ml chloramphenicol). Only a Kocuria sp. was sensitive to all four antibiotics at the lowest concentrations tested (3.10 µg/ml ampicillin and streptomycin; 2.15 µg/ml kanamycin; 1.85 µg/ml chloramphenicol). The rest of the isolates showed different resistance levels. Plasmid isolations were carried out to determine if the multiple antibiotic resistance could be attributed to the presence of plasmids. However, no plasmid was detected in any of the isolates. The resistance appeared to be mediated by chromosome-associated functions. This study indicated that multiple antibiotic resistance at moderate to high levels is common among the current phenotypes of the fish mucus-dwelling bacterial populations in this temperate, shallow lake which has not been subjected to any aquaculturing so far but under anthropogenic effect being in a recreational area.