Novel homologs of the multiple resistance regulator marA in antibiotic-contaminated environments

Sara Castiglioni, Francesco Pomati, Kristin Miller, Brendan P. Burns, Ettore Zuccato, Davide Calamari, Brett A. Neilan

Research output: Contribution to journalArticle


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.

Original languageEnglish
Pages (from-to)4271-4280
Number of pages10
JournalWater Research
Issue number16
Publication statusPublished - Oct 2008



  • Antibiotic contamination
  • Antibiotic resistance
  • Aquatic environment
  • Bacillus
  • E. coli
  • marA

ASJC Scopus subject areas

  • Ecological Modelling
  • Pollution
  • Waste Management and Disposal
  • Water Science and Technology

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