Antibiotics are frequently used on commercial hog farms not only to fight disease, but also to help pigs gain weight faster. New research from North Carolina State University and Kansas State University shows that the common pests that live on these farms acquire antibiotic-resistant bacteria and have the potential to spread these bacteria throughout the farm and to residential settings.
Cockroaches and house flies on swine farms in North Carolina and Kansas contained many of the same drug-resistant bacteria present in hog feces, suggesting that these common pests acquired the bacteria from contact with swine manure. These drug-resistant bacteria are rarely found in cockroaches and flies collected in urban areas.
The bacteria, different members of a family of common digestive bacteria called enterococci, found in the digestive tracts of farm flies and roach feces contained certain genes that provide resistance to antibiotics, says Dr. Coby Schal, Blanton J. Whitmire Distinguished Professor of Entomology at NC State and a co-author of a paper describing the research, which was published online this week in the journal BMC Microbiology. Some of these bacteria are resistant not only to single common infection-killing antibiotics like tetracycline and streptomycin, but also to combinations of antibiotics, making them multi-drug resistant.
“The big concern is not that humans will acquire drug-resistant bacteria from their properly cooked bacon or sausage, but rather that the bacteria will be transferred to humans from the common pests that live with pigs and then move in with us,” Schal says. “It’s also possible that these farm flies and farm roaches carry other microbes of great importance to human health.”
Antibiotic-resistant bacteria – “superbugs” in the popular parlance – are an increasing problem in the United States, causing increased health-care costs, prolonged hospitalization for infections and higher human mortality rates.
“Pest-management strategies are important – the fly at your picnic or roach scuttling across the living room floor can be more than just a nuisance,” Schal adds.
The research was funded by the U.S. Department of Agriculture and NC State’s Blanton J. Whitmire Endowment.
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Note to editors: An abstract of the paper follows.
“Insects in confined swine operations carry a large antibiotic resistant and potentially virulent enterococcal community”
Authors: Ludek Zurek, Anuradha Ghosh and Aqeel Ahmad, Kansas State University; Coby Schal, North Carolina State University
Published: Online Jan. 26, 2011, in BMC Microbiology
Abstract: Extensive use of antibiotics as growth promoters in the livestock industry constitutes strong selection pressure for evolution and selection of antibiotic resistant bacterial strains. Unfortunately, the microbial ecology and spread of these bacteria in the agricultural, urban, and suburban environments are poorly understood. Insects such as house flies (Musca domestica) and German cockroaches (Blattella germanica) can move freely between animal waste and food and may play a significant role in the dissemination of antibiotic resistant bacteria within and between animal production farms and from farms to residential settings. Enterococci from the digestive tract of house flies (n = 162), and feces of German cockroaches (n = 83) and pigs (n = 119), collected from two commercial swine farms were isolated, quantified, identified, and screened for antibiotic resistance and virulence. The majority of samples (93.7%) were positive for enterococci with concentrations 4.2 ± 0.7 x 104 CFU/house fly, 5.5 ± 1.1 x 106 CFU/g of cockroach feces, and 3.2 ± 0.8 x 105 CFU/g of pig feces. Among all the identified isolates (n=639) Enterococcus faecalis was the most common (55.5%), followed by E. hirae (24.9%), E. faecium (12.8%), and E. casseliflavus (6.7%). E. faecalis was most prevalent in house flies and cockroaches, and E. hirae was most common in pig feces. Our data showed that multi-drug (mainly tetracycline and erythromycin) resistant enterococci were common from all three sources and frequently carried antibiotic resistance genes including tet(M) and erm(B) and Tn916/1545 transposon family. E. faecalis frequently harbored virulence factors gelE, esp, and asa1. PFGE analysis of selected E. faecalis and E. faecium isolates demonstrated that cockroaches and house flies shared some of the same enterococcal clones that were detected in the swine manure indicating that insects acquired enterococci from swine manure. This study shows that house flies and German cockroaches in the confined swine production environment likely serve as vectors and/or reservoirs of antibiotic resistant and potentially virulent enterococci and consequently may play an important role in animal and public health.