Evaluation of bacterial growth inhibition by mercaptopropionic acid in metallo-β-lactamase detection on multidrug-resistant Acinetobacter baumannii

INTRODUCTION: Metallo-β-lactamase (MBL) has been reported all over the world. METHODS: The inhibitory effect of mercaptopropionic acid (MPA) on bacterial growth was evaluated by comparison between disk diffusion and broth dilution methodology with determination of the minimum inhibitory concentration (MIC) for multidrug-resistant Acinetobacter baumanni strains. RESULTS: MPA significantly inhibited growth of the strains. CONCLUSIONS: The use of MPA can affect the results in phenotypic methods of MBL detection

The genetic content of chromosomal inversions across a wide latitudinal gradient

There is increasing evidence regarding the role of chromosomal inversions in relevant biological processes such as local adaptation and speciation. A classic example of the adaptive role of chromosomal polymorphisms is given by the clines of inversion frequencies in Drosophila subobscura, repeatable across continents. Nevertheless, not much is known about the molecular variation associated with these polymorphisms. We characterized the genetic content of ca. 600 individuals from nine European populations following a latitudinal gradient by analysing 19 microsatellite loci from two autosomes (J and U) and the sex chromosome (A), taking into account their chromosomal inversions. Our results clearly demonstrate the molecular genetic uniformity within a given chromosomal inversion across a large latitudinal gradient, particularly from Groningen (Netherlands) in the north to Málaga (Spain) in the south, experiencing highly diverse environmental conditions. This low genetic differentiation within the same gene arrangement across the nine European populations is consistent with the local adaptation hypothesis for th evolutionof chromosomal polymorphisms. We also show the effective role of chromosomal inversions in maintaining different genetic pools within these inverted genomic regions even in the presence of high gene flow. Inversions represent thus an important barrier to gene flux and can help maintain specific allelic combinations with positive effects on fitness. Consistent patterns of microsatellite allele-inversion linkage disequilibrium particularly in loci within inversions were also observed. Finally, we identified areas within inversions presenting clinal variation that might be under selection

Detection of <it>P. aeruginosa </it> harboring <it>bla </it>_CTX-M-2, <it>bla </it>_GES-1 and <it>bla </it>_GES-5,<it>bla </it>_IMP-1 and <it>bla </it>_SPM-1 causing infections in Brazilian tertiary-care hospital

<p>Abstract</p> <p>Background</p> <p>Nosocomial infections caused by <it>Pseudomonas aeruginosa</it> presenting resistance to beta-lactam drugs are one of the most challenging targets for antimicrobial therapy, leading to substantial increase in mortality rates in hospitals worldwide. In this context, <it>P. aeruginosa</it> harboring acquired mechanisms of resistance, such as production of metallo-beta-lactamase (MBLs) and extended-spectrum beta-lactamases (ESBLs) have the highest clinical impact. Hence, this study was designed to investigate the presence of genes codifying for MBLs and ESBLs among carbapenem resistant <it>P. aeruginosa</it> isolated in a Brazilian 720-bed teaching tertiary care hospital.</p> <p>Methods</p> <p>Fifty-six carbapenem-resistant <it>P. aeruginosa</it> strains were evaluated for the presence of MBL and ESBL genes. Strains presenting MBL and/or ESBL genes were submitted to pulsed-field gel electrophoresis for genetic similarity evaluation.</p> <p>Results</p> <p>Despite the carbapenem resistance, genes for MBLs (<it>bla</it>_SPM-1 or <it>bla</it>_IMP-1) were detected in only 26.7% of isolates. Genes encoding ESBLs were detected in 23.2% of isolates. The <it>bla</it>_CTX-M-2 was the most prevalent ESBL gene (19.6%), followed by <it>bla</it>_GES-1 and <it>bla</it>_GES-5 detected in one isolate each. In all isolates presenting MBL phenotype by double-disc synergy test (DDST), the <it>bla</it>_SPM-1 or <it>bla</it>_IMP-1 genes were detected. In addition, <it>bla</it>_IMP-1 was also detected in three isolates which did not display any MBL phenotype. These isolates also presented the <it>bla</it>_CTX-M-2 gene. The co-existence of <it>bla</it>_CTX-M-2 with <it>bla</it>_IMP-1 is presently reported for the first time, as like as co-existence of <it>bla</it>_GES-1 with <it>bla</it>_IMP-1.</p> <p>Conclusions</p> <p>In this study MBLs production was not the major mechanism of resistance to carbapenems, suggesting the occurrence of multidrug efflux pumps, reduction in porin channels and production of other beta-lactamases. The detection of <it>bla</it>_CTX-M-2,<it>bla</it>_GES-1 and <it>bla</it>_GES-5 reflects the recent emergence of ESBLs among antimicrobial resistant <it>P. aeruginosa</it> and the extraordinary ability presented by this pathogen to acquire multiple resistance mechanisms. These findings raise the concern about the future of antimicrobial therapy and the capability of clinical laboratories to detect resistant strains, since simultaneous production of MBLs and ESBLs is known to promote further complexity in phenotypic detection. Occurrence of intra-hospital clonal dissemination enhances the necessity of better observance of infection control practices.</p