Evidences of gentamicin resistance amplification in Klebsiella pneumoniae isolated from faeces of hospitalized newborns

The intestinal microbiota, a barrier to the establishment of pathogenic bac teria, is also an important reservoir of opportunistic pathogens. It plays a key role in the process of resistance-genes dissemination, commonly carri ed by specialized genetic elements, like plasmids, phages, and conjugative transposons. We obtained from strains of enterobacteria, isolated from faeces of newborn s bl a university hospital nursery indication of phenothypical gentamicin r esistance amplification (frequencies of 10(-3) to 10(-5) compatible with tr ansposition frequencies). Southern blotting assays showed strong hybridizat ion signals for both plasmidial and chromossomal regions in DNA extracted f rom variants selected at high gentamicin concentrations, using as a probe a labeled cloned insert containing aminoglycoside modifying enzyme (AME) gen e sequence originated from a plasmid of a Klebsiella pneumoniae strain prev iously isolated in the same hospital. Further we found indications of inact ivation to other resistance genes in variants selected under similar condit ions, as well as, indications of co-amplification of other AME markers (ami kacin). Since the intestinal environment is a scenario of selective processes due t o the therapeutic and prophylactic use of antimicrobial agents, the process es of amplification of low level antimicrobial resistance (not usually dete cted or sought by common methods used for antibiotic resistance surveillanc e) might compromise the effectiveness of antibiotic chemotherapy.