Abstract:
The spread and emergence of antimicrobial-resistant bacteria has emerged as a
public health major problem worldwide. The usage of antimicrobials for prevention
and treatment in humans and animals possibly contributes to an increasing occurrence
of resistant bacteria. An epidemiology of resistant genes in fecal-indicator bacteria
including Escherichia coli and enterococci originating from humans, pets, vegetables,
water and chickens was studied using dot blot hybridization. Resistant genes of tetM,
tetA, catI, cmlA, sulI and qnrA in E. coli isolates and tetM, tetL, ermB, aadA and vatD
in enterococci were determined. Two multiplex-polymerase chain reaction (PCR) for
simultaneous detection of five resistant genes for E. coli and of three resistant genes
for Enterococcus spp. were developed. Moreover, a duplex PCR for species
identification of E. faecium and E. faecalis was successfully developed in this study.
Among E. coli isolates, tetA was frequently observed followed by cmlA, sulI, tetM and
catI, respectively. High prevalence of resistant genes including tetA (71.3%), catI
(10.4%) and sulI (34.8%) was observed in isolates from chickens, while the highest
frequency of tetM (31.4%) and cmlA (33.3%) was seen in isolates from rivers. Among
enterococci isolates, tetM was highly observed followed by tetL and ermB,
respectively. Isolates from chickens carried a large amount of resistant genes, tetM,
tetL and ermB, for more than 80% and up to 75% contained three genes together.
Various plasmid profiles were observed in E. coli especially from isolates of chickens.
Mutational analysis on quinolone resistance determining region (QRDR) of gyrA
showed 10 single-strand conformation polymorphism (SSCP) patterns with 9 patterns
found in vegetables and water and 7 patterns in pets. Amino acid changes in position
83 and/or 87 were revealed in 4 patterns with alteration of Ser-83-Leu and Asp-87-
Asn. The pattern with the double mutation was detected only in human and pet isolates
and they were not found in ciprofloxacin susceptible isolates. The molecular
characterization by identification of resistant genes indicated high degree of resistant
gene distribution among E. coli and enterococci.