Abstract
BackgroundAntibiotic resistance genes [ARGs] in aquatic systems have drawn increasing attention they could be transferred horizontally to pathogenic bacteria. Water treatment plants (WTPs) are intended to provide quality and widely available water to the local populace they serve. However, WTPs in developing countries may not be dependable for clean water and they could serve as points of dissemination for antibiotic resistant bacteria. Only a few studies have investigated the occurrence of ARGs among these bacteria including tetracycline resistance genes in water distribution systems in Nigeria.MethodologyMulti-drug resistant (MDR) bacteria, including resistance to tetracycline, were isolated from treated and untreated water distribution systems in southwest Nigeria. MDR bacteria were resistant to >3 classes of antibiotics based on break-point assays. Isolates were characterized using partial 16S rDNA sequencing and PCR assays for six tetracycline-resistance genes. Plasmid conjugation was evaluated using E. coli strain DH5α as the recipient strain.ResultsOut of the 105 bacteria, 85 (81 %) and 20 (19 %) were Gram- negative or Gram- positive, respectively. Twenty-nine isolates carried at least one of the targeted tetracycline resistance genes including strains of Aeromonas, Alcaligenes, Bacillus, Klebsiella, Leucobacter, Morganella, Proteus and a sequence matching a previously uncultured bacteria. Tet(A) was the most prevalent (16/29) followed by tet(E) (4/29) and tet30 (2/29). Tet(O) was not detected in any of the isolates. Tet(A) was mostly found with Alcaligenes strains (9/10) and a combination of more than one resistance gene was observed only amongst Alcaligenes strains [tet(A) + tet30 (2/10), tet(A) + tet(E) (3/10), tet(E) + tet(M) (1/10), tet(E) + tet30 (1/10)]. Tet(A) was transferred by conjugation for five Alcaligenes and two E. coli isolates.ConclusionsThis study found a high prevalence of plasmid-encoded tet(A) among Alcaligenes isolates, raising the possibility that this strain could shuttle resistance plasmids to pathogenic bacteria.
Highlights
Tetracycline antibiotics have been used to treat infectious diseases for more than half a century [1]; they have been used nearly as long to promote growth in food animal production systems [2,3,4]
This study found a high prevalence of plasmid-encoded tet(A) among Alcaligenes isolates, raising the possibility that this strain could shuttle resistance plasmids to pathogenic bacteria
Once resistance genes are introduced into the environment, they are exposed to selective pressure, such as antibiotics produced by indigenous antibiotic producers in soil
Summary
Tetracycline antibiotics have been used to treat infectious diseases for more than half a century [1]; they have been used nearly as long to promote growth in food animal production systems [2,3,4]. Growth-promoting properties of tetracyclines were first described in 1949 for chickens fed chlortetracycline supplemented feed [5]. They were widely applied in animal husbandry thanks to improving the growth rate to feed intake ratio [6,7,8]. Resistance to tetracycline is usually conferred through acquisition of resistance genes associated with mobile genetic elements [9]. These genes could be disseminated by interspecies transfer mediated by plasmids, transposons, and bacteriophage [10, 11].
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