The intestinal microbiota, a barrier to the establishment
of pathogenic bacteria, is also an important reservoir of
opportunistic pathogens. It plays a key role in the process of
resistance-genes dissemination, 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
modifying enzyme (AME) gene sequence originated from a plasmid of a
Klebsiella pneumoniae strain previously 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
antimicrobial resistance (not usually detected or sought by common
methods used for antibiotic resistance surveillance) might
compromise the effectiveness of antibiotic chemotherapy.
