Role of House Flies in the Ecology of Enterococcus faecalis from Wastewater Treatment Facilities

Abstract

Enterococci are important nosocomial pathogens with Enterococcus faecalis most commonly responsible for human infections. In this study, we used several measures to test the hypothesis that house flies, Musca domestica (L.), acquire and disseminate antibiotic resistant and potentially virulent E.faecalis from wastewater treatment facilities (WWTF) to the surrounding urban environment. House flies and sludge from four WWTF (1-4) as well as house flies from three urban sites close to WWTF-1 were collected and cultured for enterococci. Enterococci were identified, quantified, screened for antibiotic resistance and virulence traits, and assessed for clonality. Of the eleven antibiotics tested, E. faecalis was most commonly resistant to tetracycline, doxycycline, streptomycin, gentamicin and erythromycin and these traits were intra-species horizontally transferrable by in vitro conjugation. Profiles of E. faecalis (prevalence, antibiotic resistance, and virulence traits) from each of WWTF sludge and associated house flies were similar, indicating that flies successfully acquired these bacteria from this substrate. The greatest number of E. faecalis with antibiotic resistance and virulence factors (i.e., gelatinase, cytolysin, enterococcus surface protein, and aggregation substance) originated from WWTF-1 that processed meat waste from a nearby commercial meat processing plant, suggesting an agricultural rather than human clinical source of these isolates. E. faecalis from house flies collected from three sites 0.7 -1.5 km away from WWTF-1 were also similar in their antibiotic resistance profiles; however, antibiotic resistance was significantly less frequent. Clonal diversity assessment using pulsed-field gel electrophoresis revealed the same clones of E. faecalis from sludge and house flies from WWTF-1 but not from the three urban sites close to WWTF-1. This study demonstrates that house flies acquire antibiotic resistant enterococci from WWTF and potentially disseminate them to the surrounding environment.

Housefly (Musca domestica) as Carrier of Enterotoxigenic Staphylococcus aureus in Broiler Farms in Iran: Is it Important for Public Health?

“…These findings agree with the results of Barreiro et al (22) in Portugal, which showed presence of Enterobacteriaceae, Escherichia coli, ETSA, and Listeria monocytogenes collected from kitchens, and kitchens situated in the closest proximity to the animal husbandry. Our results are in accordance with other reports which highlight the importance of houseflies in carrying various pathogenic bacteria, suggesting that these insects may serve as an important avenue of disseminating disease-causing agents like ETSA to the environment (9,23,24). ETSA were isolated from 14 % of M. domestica that sampled from the nine sites of broiler farms.…”

Significance and Survival of Enterococci During the House Fly Development

“…It is possible that the gut microbiome of adult house ßies changes over time depending on their food sources and E. hirae in adult house ßies is digested and replaced by other enterococcal species, primarily by E. faecalis. This is corroborated indirectly by the fact that although E. faecalis supported the larval development of house ßies to the least extent, it was the most commonly detected enterococcal species in the digestive tract of adult house ßies collected from various environments (Macovei and Zurek 2006, Graham et al 2009, Ahmad et al 2011, Doud et al 2014. In addition, our recent study (Doud and Zurek 2012) reported the colonization and proliferation of E. faecalis in the crop and midgut of adult house ßies, demonstrating that this insect is a bioenhanced vector for E. faecalis.…”

“…Enterococcus hirae is also the most common enterococcal species detected in manure of pigs (Ahmad et al 2011), pastured cattle and bison (Anderson et al 2008), and feedlot cattle (L. Z., unpublished). In contrast, E. hirae was not detected in wild house ßy adults, including those from fast foodrestaurants (Macovei and Zurek 2006) and poultry farms (Graham et al 2009), and it was found only in very low prevalence in house ßies from swine farms (Ahmad et al 2011), feedlot and pastured cattle (L. Z., unpublished), and waste water treatment plants (Doud et al 2014). It is possible that the gut microbiome of adult house ßies changes over time depending on their food sources and E. hirae in adult house ßies is digested and replaced by other enterococcal species, primarily by E. faecalis.…”

Insects Represent a Link between Food Animal Farms and the Urban Environment for Antibiotic Resistance Traits

“…Interestingly, the highest prevalence of multidrug-resistant enterococci was detected from a WWTF (sludge and associated houseflies) that processed the waste from a nearby sausage factory, pointing again to animal agriculture as a source of these bacteria (61). Genotypic analysis (PFGE) revealed the same clones of E. faecalis present in the waste and the housefly digestive tract.…”