Evidences of Gentamicin Resistance Amplification in Klebsiella pneumoniae Isolated from Faeces of Hospitalized Newborns

The intestinal microbiota, a barrier to the establishment of pathogenic bacteria, is also an impor-tant reservoir of opportunistic pathogens. It plays a key role in the process of resistance-genes dissemi-nation, commonly carried by specialized genetic elements, like plasmids, phages, and conjugative transposons. We obtained from strains of enterobacteria, isolated from faeces of newborns in a university hospital nursery, indication of phenothypical gentamicin resistance amplification (frequencies of 10-3 to 10-5, compatible with transposition frequencies). Southern blotting assays showed strong hybridization signals for both plasmidial and chromossomal regions in DNA extracted from variants selected at high gentamicin concentrations, using as a probe a labeled cloned insert containing aminoglycoside modi-fying enzyme (AME) gene sequence originated from a plasmid of a Klebsiella pneumoniae strain previ-ously isolated in the same hospital. Further, we found indications of inactivation to other resistance genes in variants selected under similar conditions, as well as, indications of co-amplification of other AME markers (amikacin). Since the intestinal environment is a scenario of selective processes due to the therapeutic and prophylactic use of antimicrobial agents, the processes of amplification of low level antimicrobia