Pathogens associated with houseflies from different areas within a New York State dairy

Abstract

Houseflies (Musca domestica) are nonbiting muscoids of importance because they can be mechanical vectors of many kinds of pathogens such as bacteria, protozoa, viruses, and helminth eggs. This study aimed to evaluate the bacterial communities associated with houseflies captured in 3 different areas on a dairy farm located in New York State. Variations in the bacterial community were also evaluated based on the flies' sex and external or internal location where the bacteria were isolated. A total of 101 flies were collected: 27 flies from the sick pen, 42 from calf hutches, and 32 from the milking parlor. A total of 485 organisms were isolated, 233 (48.0%) from 53 female flies and 252 (52.0%) from 48 male flies. Most (74%) bacteria were found in the internal parts of the flies, with only 26% isolated from the external surfaces. The number of isolates detected per fly ranged between 1 and 11. A total of 392 bacteria were identified at the species level. We isolated 26 species reported to be bovine contagious or environmental mastitis pathogens. Within the group of organisms considered contagious, we isolated Staphylococcus aureus and Mycoplasma arginini. This was the first time that a Mycoplasma species was isolated from houseflies. We identified 5 organisms considered foodborne pathogens that affect human health: Salmonella spp., Escherichia coli, Staph. aureus, Bacillus cereus, and Bacillus subtilis. Four of the organisms isolated in this study were also linked with milk spoilage, including Pseudomonas aeruginosa, Bacillus cereus, Bacillus licheniformis, and Paenibacillus lactis. This study confirmed that houseflies carry a high bacterial diversity, including organisms associated with animal infections, organisms that could be a concern for public health, or organisms that could negatively affect milk quality.

Summary: Houseflies in dairy farms can be a concern since they could play a crucial role in increased bacterial counts in milk and the potential occurrence of transmitted diseases that affect public and animal health. This study evaluated the bacterial communities associated with houseflies captured on a dairy farm in New York State. A total of 101 flies were collected at 3 farm sites: hospital pen, calf hutches, and milking parlor. Each housefly was tested by bacteriological analysis for microbial identification, and a total of 304 bacterial isolates were obtained. Twelve percent of the identified organisms are well known to affect dairy farms. We identified 26 bacterial species with implications for animal health since these are mastitis-causing pathogens; 5 bacteria are considered foodborne pathogens and, for this reason, represent a concern for human health, and last, but not least, we identified 5 milk spoilage bacteria species that affect the quality of dairy products.

Figure 1

Bacterial isolate counts found in 101 houseflies obtained from 3 sites of 1 dairy farm. (A) Taxonomic classification of the isolates. Bacteria are classified as gram positive, gram negative, and fungus. (B) Bacteria count distribution between farm locations where flies were collected. (C) Bacteria count distribution between female and male flies. (D) Bacteria count distribution based on the flies' body site.