Not to be unscientific, but: Ick.
A team from the Bloomberg School of Public Health at Johns Hopkins (who have done a number of studies on the spread of antibiotic-resistant organisms from farms to the outside world) decided to test the links in a chain of hypothesis that goes like this:
- Antibiotics are used in large amounts in poultry production.
- Antibiotic-resistant organisms are produced within the birds.
- Antibiotic-resistant organisms leave the batteries via poultry litter ("excreta, feathers, spilled feed, bedding material, soil and dead birds").
- Poultry litter is stored in open sheds until it can be used as a soil amendment.
- Flies have unrestricted access to poultry litter.
And the findings were: Oh, lots and lots. Litter piles at all three farms contained resistant organisms — E. faecium, E. faecalis and our particular interest, Staphylococcus (multiple species, including three strains of S. aureus) — throughout the 120-day study period. All 8 fly traps did as well. All of the litter contained enterococci and staph strains that were resistant to 3 or more antibiotic classes. Seven of the 8 fly traps yielded multi-drug resistant enterococci, and 3 yielded multi-drug resistant staph. The resistance factors identified were for drugs that the FDA classifies as "critically or highly important" to human medicine: "penicillin, tetracyclines, macrolides, lincosamides, aminoglycosides and streptogramins." Oh, and the fly species captured in the traps had an average range of 2 miles.
Of note, among the isolates discovered was one staphylococcus with high-level resistance to vancomycin.
The authors say:
This study strongly suggests that flies in intensive poultry production areas, such as the Delmarva Peninsula, can disperse antibiotic resistant bacteria in their digestive tracts and on their exterior surfaces. Dispersion of resistant bacteria from poultry farms by flies could contribute to human exposures, although at present it is difficult to quantify the contribution of flies. Flies may also transfer bacteria from fields amended with poultry waste.
The cite is: Graham JP et al., Antibiotic resistant enterococci and staphylococci isolated from flies collected near confined poultry feeding operations, Sci Total Environ (2009), doi:10.1016/j.scitotenv.2008.11.056. The ahead-of-print abstract is here.