Carriage of Livestock-Associated MRSA on North Carolina Swine Farms and Occurrence and Persistence in the Surrounding Environment

EPA Grant Number: FP917289
Title: Carriage of Livestock-Associated MRSA on North Carolina Swine Farms and Occurrence and Persistence in the Surrounding Environment
Investigators: Nadimpalli, Maya L
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Lee, Sonja
Project Period: August 1, 2011 through July 31, 2014
Project Amount: $126,000
RFA: STAR Graduate Fellowships (2011) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Human Health: Public Health Sciences


It has been hypothesized that the emergence of livestock-associated MRSA in swine workers in the United States may be related to the subtherapeutic use of antibiotics in industrial animal production. To characterize the impact of this practice on MRSA carriage, this study will compare MRSA prevalence among industrial hog farm workers to MRSA prevalence among organic antibiotic-free swine farmers in North Carolina. Furthermore, this study intends to investigate the potential for livestock-associated MRSA to be transmitted through the environment. The study will genotype and confirm the presence of MRSA in surface waters proximate to concentrated animal feeding operations (CAFOs) in Duplin County, North Carolina, and will assess the environmental persistence of MRSA spread through swine waste.


MRSA prevalence will be assessed in 50 consenting antibiotic-free swine farm workers, 50 industrial hog farm workers, and up to two members of each worker’s household via a short questionnaire and nasal swabs. Although the questionnaire will establish occupational, environmental and healthcare exposures to MRSA, swabbing will determine actual carriage of MRSA. Whole-genome sequence typing at TGen, Inc. will confirm whether colonies from MRSA-positive swabs belong to a livestock-associated strain. To investigate the presence of MRSA in surface waters near CAFOs, the study will use molecular methods to confirm more than 600 “presumptive MRSA” isolates already collected during a field campaign in Duplin County from 2010 through 2011. S. aureus isolates positive for the methicillin-resistance gene also will be submitted for whole genome sequence typing at TGen Inc., allowing for genetic comparisons among MRSA strains isolated from the environment and from humans. Lastly, the persistence of MRSA spread through swine waste will be assessed using bench-scale microcosm studies. Microcosms will replicate the natural conditions of Duplin County surface waters, and other waters or sediments of interest.

Expected Results:

Studies in Europe have found a significantly lower prevalence of livestock-associated MRSA in organic, antibiotic-free swine farmers compared to industrial hog farmers. European studies have also documented the transmission of livestockassociated MRSA from farmers to members of their households. Although no comparable studies have been published yet in the United States, this study expects to find similar results. The study also expects to confirm the presence of MRSA in the environment surrounding swine farm manure spray fields, as the “presumptive MRSA” isolates collected from Duplin County surface waters exhibited the anticipated phenotype on MRSA-specific agar plates. Research on MRSA persistence in the environment, both in situ and in the laboratory, is limited. However, a Swedish study examining MRSA persistence in treated wastewater suggests that this pathogen may indeed be able to survive for a significant period of time, even under stress. This study expects to reach similar conclusions using benchscale microcosm studies.

Potential to Further Environmental / Human Health Protection

MRSA is carried by up to 53 million people worldwide and is responsible for more fatalities in the United States than HIV/AIDS. Certain practices distinctive to CAFOs may be directly related to the increasing prevalence of livestock-associated MRSA, and may be responsible for its introduction into the environment. Research focused specifically on the links between MRSA carriage and industrial animal production will be critical in advancing the discussion as to whether some of these practices should be readdressed through legislation. In addition, research that is able to confirm the presence of livestock-associated MRSA in the waters surrounding CAFOs will provide important evidence of both surface water pollution and a potential human health impact.

Supplemental Keywords:

MRSA, swine production, CAFO, antibiotic resistance, North Carolina

Progress and Final Reports:

  • 2012
  • 2013
  • Final