Because of their movement between waste and food materials, cockroaches can acquire, carry, and transfer pathogens. Our recent studies suggest that cockroaches (and house flies) are potentially important agents in the transmission of antibiotic resistant microbes in livestock production systems. Livestock production uses antibiotics therapeutically, but many bacterial agents are also used as prophylactic feed additives and to promote growth, and therefore are common in animal manure and in farm effluents. Because exposure to antimicrobial agents is the most important evolutionary force in the development of antibiotic tolerance, animal production facilities might be significant incubators of resistant bacteria that may affect the human population.
We are screening the gastrointestinal microbial community of German cockroaches from various facilities, including farms and homes, for antibiotic sensitivity to two clinically important bacterial species, Escherichia coli and Enterococcus faecalis. Most recently, we hypothesized that extensive use of antibiotics as growth promoters in the livestock industry may constitute strong selection pressure for evolution and selection of antibiotic resistant bacterial strains, and that insects such as house flies and German cockroaches, which can move freely between animal waste and food, may play a significant role in the dissemination of antibiotic resistant bacteria within and between animal production farms and from farms to residential settings. We isolated, quantified, identified, and screened for antibiotic resistance and virulence of Enterococci from the digestive tract of house flies, and feces of German cockroaches and pigs. The majority of samples were positive for enterococci. Among all the identified isolates Enterococcus faecalis was the most common, followed by E. hirae, E. faecium, and E. casseliflavus. Our data also 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 (see Link at http://www.biomedcentral.com/1471-2180/11/23).