INSIGHTS ALONG THE PATH TO SUSTAINABILITY| November 30, 2005

Genetic Characterization of Antibiotic-resistant Bacterial Pathogens Detected in Air, Water and Cess Pit Samples Collected at a Concentrated Animal Feeding Operation

KELLOGG J. SCHWAB, PhD, Assistant Professor, Department of Environmental Health Sciences, JHSPH (Presenter)
AMY SAPKOTA, PhD, Postdoctoral Fellow, Department of Environmental Health Sciences, JHSPH

SUMMARY

Recent studies suggest that waste contaminating the water and air surrounding animal production facilities could be important sources of human exposure to antibiotic-resistant bacteria.  However, the potential for these waterborne and airborne bacteria to serve as environmental reservoirs of antibiotic resistance genes has not been extensively investigated.  In this study, multidrug-resistant bacteria previously recovered from the indoor air of a concentrated swine feeding operation were tested for 14 macrolide, lincosamide, and streptogramin (MLS) resistance genes and 7 tetracycline (tet) resistance genes.  Enterococcus spp. (n=16) and Streptococcus spp. (n=16) were analyzed using DNA-DNA hybridization, PCR, and oligoprobing of PCR products.  All isolates carried multiple MLS resistance genes, while 50% of the Enterococcus spp. and 44% of the Streptococcus spp. also carried multiple tet resistance genes.  All Enterococcus spp. carried the erm(A) and erm(B) genes, 69% carried the erm(F) gene and 44% carried the mef(A) gene.  Seventy-five percent of the Enterococcus spp. carried the tet(M) gene, 69% carried the tet(L) gene, and 19% carried the tet(K) gene.  All Streptococcus spp. carried the erm(B) gene, 94% carried the erm(F) gene, 75% carried the erm(A) gene, and 38% carried the mef(A) gene.  Fifty percent of the Streptococcus spp. carried the tet(M) gene, 81% carried the tet(L) gene, and 13% carried the tet(K) gene. The high prevalence of multiple antibiotic resistance genes observed in this study suggests that airborne gram-positive bacteria from swine operations may serve as a significant environmental reservoir of antibiotic resistance genes.  In addition, bacterial isolates recovered from cess pits, surface and groundwater surrounding a concentrated swine feeding operation are being further characterized for antibiotic resistance genes.  Results from this study indicate that large animal production facilities can significantly contribute to the development of multidrug-resistant bacteria that are transported away from production facilities.  These bacteria have a strong potential to adversely impact the surrounding environment and human health.

PRESENTER BIOGRAPHY

Kellogg Schwab is an Assistant Professor of Environmental Health Sciences at The Johns Hopkins University Bloomberg School of Public Health.  Dr. Schwab’s main area of research deals with the fate and transport of human and zoonotic pathogenic microorganisms (viral, bacterial and protozoa) in the environment.  This work includes extensive laboratory-based research designed to develop and evaluate molecular methods of detection leading to the application of these methods in field-based investigations.  Data gathered during these studies are then integrated into exposure assessments for risk analysis.