Antibiotic-resistant bacterial infections result in higher patient mortality rates, prolonged hospitalizations, and increased health care costs. Extensive use of antibiotics as growth promoters in the animal industry represents great pressure for evolution and selection of antibiotic-resistant bacteria on farms. Despite growing evidence showing that antibiotic use and bacterial resistance in food animals correlate with resistance in human pathogens, the proof for direct transmission of antibiotic resistance is difficult to provide. In this review, we make a case that insects commonly associated with food animals likely represent a direct and important link between animal farms and urban communities for antibiotic resistance traits. Houseflies and cockroaches have been shown to carry multidrug-resistant clonal lineages of bacteria identical to those found in animal manure. Furthermore, several studies have demonstrated proliferation of bacteria and horizontal transfer of resistance genes in the insect digestive tract as well as transmission of resistant bacteria by insects to new substrates. We propose that insect management should be an integral part of pre- and postharvest food safety strategies to minimize spread of zoonotic pathogens and antibiotic resistance traits from animal farms. Furthermore, the insect link between the agricultural and urban environment presents an additional argument for adopting prudent use of antibiotics in the food animal industry.

Aggregation of the German cockroach, Blattella germanica, is regulated by fecal aggregation agents (pheromones), including volatile carboxylic acids (VCAs). We demonstrate that the gut microbial community contributes to production of these semiochemicals. Chemical analysis of the fecal extract of B. germanica revealed 40 VCAs. Feces from axenic cockroaches (no microorganisms in the alimentary tract) lacked 12 major fecal VCAs, and 24 of the remaining compounds were represented at extremely low amounts. Olfactory and aggregation bioassays demonstrated that nymphs strongly preferred the extract of control feces over the fecal extract of axenic cockroaches. Additionally, nymphs preferred a synthetic blend of 6 fecal VCAs over a solvent control or a previously identified VCA blend. To test whether gut bacteria contribute to the production of fecal aggregation agents, fecal aerobic bacteria were cultured, isolated, and identified. Inoculation of axenic cockroaches with individual bacterial taxa significantly rescued the aggregation response to the fecal extract, and inoculation with a mix of six bacterial isolates was more effective than with single isolates. The results indicate that the commensal gut microbiota contributes to production of VCAs that act as fecal aggregation agents and that cockroaches discriminate among the complex odors that emanate from a diverse microbial community. Our results highlight the pivotal role of gut bacteria in mediating insect–insect communication. Moreover, because the gut microbial community reflects the local environment, local plasticity in fecal aggregation pheromones enables colony-specific odors and fidelity to persistent aggregation sites. Significance There is great interest in elucidating the diverse roles of microbes in biology, in general and, specifically, in mediating animal communication. We demonstrate that the gut bacterial community plays a pivotal role in production of aggregation pheromones in the German cockroach. The feces of normal and gut bacteria-inoculated cockroaches emits highly attractive volatile carboxylic acids (VCAs) that elicit aggregation whereas bacteria-free feces contains few VCAs and is relatively unattractive. VCAs may reflect the gut microbiota and, in turn, the cockroach9s local environment, explaining why divergent chemical structures have been proposed as aggregation pheromones. This new insight emphasizes the importance of gut microbes in insect–insect communication and highlights the plasticity of the chemistry and function of fecal aggregation pheromones.

The bacterial diversity in the intestinal tract of Musca domestica L. was examined in larvae collected from turkey bedding and corn silage. Aerobic c

In this project, enterococci from the digestive tracts of 260 houseflies ( Musca domestica L.) collected from five restaurants were characterized. Houseflies frequently (97% of the flies were positive) carried enterococci (mean, 3.1 × 10 ³ CFU/fly). Using multiplex PCR, 205 of 355 randomly selected enterococcal isolates were identified and characterized. The majority of these isolates were Enterococcus faecalis (88.2%); in addition, 6.8% were E. faecium , and 4.9% were E. casseliflavus. E. faecalis isolates were phenotypically resistant to tetracycline (66.3%), erythromycin (23.8%), streptomycin (11.6%), ciprofloxacin (9.9%), and kanamycin (8.3%). Tetracycline resistance in E. faecalis was encoded by tet (M) (65.8%), tet (O) (1.7%), and tet (W) (0.8%). The majority (78.3%) of the erythromycin-resistant E. faecalis isolates carried erm (B). The conjugative transposon Tn 916 and members of the Tn 916/ Tn 1545 family were detected in 30.2% and 34.6% of the identified isolates, respectively. E. faecalis carried virulence genes, including a gelatinase gene ( gelE ; 70.7%), an aggregation substance gene ( asa1 ; 33.2%), an enterococcus surface protein gene ( esp ; 8.8%), and a cytolysin gene ( cylA ; 8.8%). Phenotypic assays showed that 91.4% of the isolates with the gelE gene were gelatinolytic and that 46.7% of the isolates with the asa1 gene aggregated. All isolates with the cylA gene were hemolytic on human blood. This study showed that houseflies in food-handling and -serving facilities carry antibiotic-resistant and potentially virulent enterococci that have the capacity for horizontal transfer of antibiotic resistance genes to other bacteria.

The ecology of Escherichia coli O157:H7 is not well understood. The aims of this study were to determine the prevalence of and characterize E. coli O157:H7 associated with houseflies (HF). Musca domestica L. HF ( n = 3,440) were collected from two sites on a cattle farm over a 4-month period and processed individually for E. coli O157:H7 isolation and quantification. The prevalence of E. coli O157:H7 was 2.9 and 1.4% in HF collected from feed bunks and a cattle feed storage shed, respectively. E. coli O157:H7 counts ranged from 3.0 × 10 ¹ to 1.5 × 10 ⁵ CFU among the positive HF. PCR analysis of the E. coli O157:H7 isolates revealed that 90.4, 99.2, 99.2, and 100% of them ( n = 125) possessed the stx1 , stx2 , eaeA , and fliC genes, respectively. Large populations of HF on cattle farms may play a role in the dissemination of E. coli O157:H7 among animals and to the surrounding environment.