Assessment of House Fly Dispersal between Rural and Urban Habitats in Kansas, USA

House flies, Musca domestica L. (Diptera: Muscidae), are of medical and veterinary importance due to their capacity to act as mechanical vectors of microorganisms originating in animal manure and other decaying organic substrates. House flies that disperse from rural to urban areas may also transport antibiotic resistant bacterial strains. To assess the potential of house flies to disperse from rural to urban areas and distribute antibiotic-resistant bacteria, we undertook a two part study: (i) we quantified the dispersal rate of house flies from farms (rural areas) into a city (urban area) using multilocus DNA fingerprinting and (ii) we profiled the antibiotic resistance patterns of enterococci harbored by house flies collected in rural and urban environments. The population genetic analysis indicated that there was considerable dispersal between rural and urban habitats. Although there was a significant difference in allele frequency between the urban and rural samples, genetic divergence was low (mean F-ST = 0.07) and migration rate relatively high (N-m = 3 individuals per generation). Almost 95% of the genetic diversity occurred within populations, suggesting a nearly panmictic population. Profiling of antibiotic resistance of enterococci isolated from house fly guts showed that house flies collected in all five urban sites carried substantial numbers of antibiotic-resistant enterococci, supporting the results of the population genetic analyses. The results of this study imply that house flies, because of their dispersal behavior and capacity to transport antibiotic-resistant bacteria, pose a serious threat to public health. We suggest that area wide management of house fly populations is therefore likely to be the most effective strategy for minimizing public health risks.