title: Novel homologs of the multiple resistance regulator marA in antibiotic-contaminated environments.
abstract: Antibiotics are commonly detected in the environment as contaminants. Exposure to antibiotics may induce antimicrobial-resistance, as well as the horizontal transfer of resistance genes in bacterial populations. We selected the resistance gene marA, mediating resistance to multiple antibiotics, and explored its distribution in sediment and water samples from surface and sewage treatment waters. Ciprofloxacin and ofloxacin (fluoroquinolones), sulphamethoxazole (sulphonamide), erythromycin, clarythromycin, and spiramycin (macrolides), lincomycin (lincosamide), and oxytetracycline (tetracycline) were measured in the same samples to determine antibiotic contamination. Bacterial populations from environmental samples were challenged with antibiotics to identify resistant isolates. The gene marA was found in almost all environmental samples and was confirmed by PCR amplification in antibiotic-resistant colonies. 16S rDNA sequencing revealed that the majority of resistant isolates belonged to the Gram-positive genus Bacillus, not previously known to possess the regulator marA. We assayed the incidence of marA in environmental bacterial populations of Escherichia coli and Bacillus by quantitative real-time PCR in correlation with the levels of antibiotics. Phylogenetic analysis indicated the possible lateral acquisition of marA by Bacillus from Gram-negative Enterobacteriaceae revealing a novel marA homolog in Bacillus. Quantitative PCR assays indicate that the frequency of this gene in antropised environments seems to be related to bacterial exposure to water-borne antibiotics.
authors.affiliation: Department of Environmental Health Sciences, Mario Negri Institute for Pharmacological Research, Via La Masa 19, 20156 Milano, Italy. castiglioni@marionegri.it
authors.forename: Sara
authors.initials: S
authors.lastname: Castiglioni
authors.forename: Francesco
authors.initials: F
authors.lastname: Pomati
authors.forename: Kristin
authors.initials: K
authors.lastname: Miller
authors.forename: Brendan P
authors.initials: BP
authors.lastname: Burns
authors.forename: Ettore
authors.initials: E
authors.lastname: Zuccato
authors.forename: Davide
authors.initials: D
authors.lastname: Calamari
authors.forename: Brett A
authors.initials: BA
authors.lastname: Neilan
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism*; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D014644:Genetic Variation; D010802:Phylogeny; D045483:Rivers; D014867:Water / Q000737:chemistry; D014871:Water Microbiology; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D014874:Water Pollutants, Chemical; D014867:Water