A treatment plant receiving waste water from multiple bulk drug manufacturers is a reservoir for highly multi-drug resistant integron-bearing bacteria

PLoS One. 2013 Oct 29;8(10):e77310. doi: 10.1371/journal.pone.0077310. eCollection 2013.

Abstract

The arenas and detailed mechanisms for transfer of antibiotic resistance genes between environmental bacteria and pathogens are largely unclear. Selection pressures from antibiotics in situations where environmental bacteria and human pathogens meet are expected to increase the risks for such gene transfer events. We hypothesize that waste-water treatment plants (WWTPs) serving antibiotic manufacturing industries may provide such spawning grounds, given the high bacterial densities present there together with exceptionally strong and persistent selection pressures from the antibiotic-contaminated waste. Previous analyses of effluent from an Indian industrial WWTP that processes waste from bulk drug production revealed the presence of a range of drugs, including broad spectrum antibiotics at extremely high concentrations (mg/L range). In this study, we have characterized the antibiotic resistance profiles of 93 bacterial strains sampled at different stages of the treatment process from the WWTP against 39 antibiotics belonging to 12 different classes. A large majority (86%) of the strains were resistant to 20 or more antibiotics. Although there were no classically-recognized human pathogens among the 93 isolated strains, opportunistic pathogens such as Ochrobactrum intermedium, Providencia rettgeri, vancomycin resistant Enterococci (VRE), Aerococcus sp. and Citrobacter freundii were found to be highly resistant. One of the O. intermedium strains (ER1) was resistant to 36 antibiotics, while P. rettgeri (OSR3) was resistant to 35 antibiotics. Class 1 and 2 integrons were detected in 74/93 (80%) strains each, and 88/93 (95%) strains harbored at least one type of integron. The qPCR analysis of community DNA also showed an unprecedented high prevalence of integrons, suggesting that the bacteria living under such high selective pressure have an appreciable potential for genetic exchange of resistance genes via mobile gene cassettes. The present study provides insight into the mechanisms behind and the extent of multi-drug resistance among bacteria living under an extreme antibiotic selection pressure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / classification
  • Anti-Bacterial Agents / pharmacology
  • Bacteria / classification
  • Bacteria / drug effects
  • Bacteria / genetics*
  • Conjugation, Genetic
  • Drug Resistance, Multiple, Bacterial / drug effects
  • Drug Resistance, Multiple, Bacterial / genetics*
  • Gene Transfer, Horizontal
  • Genome, Bacterial*
  • Humans
  • Integrons / genetics*
  • Microbial Sensitivity Tests
  • RNA, Ribosomal, 16S / classification
  • RNA, Ribosomal, 16S / genetics
  • RNA, Ribosomal, 16S / isolation & purification
  • Wastewater / microbiology*
  • Water Microbiology*

Substances

  • Anti-Bacterial Agents
  • RNA, Ribosomal, 16S
  • Waste Water

Grants and funding

The work was funded by the Swedish International Development Agency (SIDA) project nr. 348-2008-6146; this funding enabled the exchange of NPM between India and Sweden. The work was also funded by the Swedish Research Council (VR), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) and The Swedish Foundation for Strategic Environmental Research (MISTRA). Nachiket Marathe held a fellowship from Council of Scientific and Industrial Research (CSIR), New Delhi, during the completion of this work. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.