Houseflies: not simple mechanical vectors of enterohemorrhagic Escherichia coli O157:H7.

Abstract

Abstract. An epidemic of enterohemorrhagic colitis caused by Escherichia coli O157:H7 (EHEC-O157) occurred in a nursery school in a rural area of Japan in September 1996. The EHEC-O157 were isolated both from patients and houseflies collected at the school. The flies were suspected to be mechanical vectors of the pathogen. Feeding experiments of EHEC-O157 to houseflies showed that the ingested bacteria were harbored in the intestine of flies and continued to be excreted at least for 3 days after feeding. Scanning electron microscopy showed that a large number of EHEC-O157 adhered to the surface of the housefly mouthparts and actively proliferated in the minute spaces of the labellum. Food masses containing EHEC-O157 in the fly intestine were completely surrounded by a peritrophic membrane during digestion and discharged rapidly. The persistence of bacteria in the intestine and feces is mainly a result of proliferation in the mouthparts and accumulation in the crop. Our results strongly suggest that houseflies are not simple mechanical vectors of EHEC. The epidemiologic potential of houseflies to disseminate EHEC-O157 may be greater than initially suspected.The housefly (Musca domestica vicina) and flies in general are considered to be mechanical vectors of many kinds of pathogens such as bacteria, 1,2 protozoa, 3 viruses, 4 and helminth eggs. 5,6 In recent outbreaks of enterohemorrhagic colitis in nursery schools in Japan, the epidemiologic survey isolated enterohemorrhagic Escherichia coli O157:H7 (EHEC-O157) from both houseflies collected in the school and from patients. The DNA patterns and the type of verotoxin were identical in EHEC-O157 isolated from both flies and patients. 7,8 This result strongly indicated that houseflies in nursery schools disseminated EHEC-O157 to foods, drinks, plates, and utensils, although direct evidence of the transmission has not been clarified. The infective dose for EHEC-O157 is considered to be very low, similar to that of Shigella flexneri or S. dysenteriae. 9,10 There are many qualitative reports of microbial flora in flies, but there are no reports of the number of bacteria that are harbored in the intestine or crop or how long the potential for dissemination of bacteria persists. We investigated the vector potential of houseflies for EHEC-O157 by feeding the flies with bacteria and monitoring them for several days after feeding. We also used scanning electron microscopy to determine whether EHEC-O157 adhered to the surface of housefly mouthparts and transmission electron microscopy to determine whether bacteria proliferated and persisted in the alimentary canal of flies. MATERIALS AND METHODS Experimental feeding of EHEC-O157 to houseflies.Houseflies maintained in our insectary were used. Two strains of EHEC-O157 (verotoxin 1-or verotoxin 1Ϫ and 2Ϫproducing strains) were grown in trypticase soy broth (Becton Dickinson, Cockeysville, MD). The concentration of bacteria was approximately 10 9 colony-forming units (CFU)/ml. Adult (6-8-day old), female flies were allowed to fe...

Study of pathogenic bacteria detected in fly samples using universal primer-multiplex PCR

“…All detected bacteria from M. domestica in the current study are pathogenic. These findings agree with the previous reports of Alam & Zurek (2004), in which E. coli O157:H7 was detected in both farm and urban environments and Greenburg (1965), Kobayashi et al, (1999) and Moriya et al, (1999). In conclusion, we developed an easy and rapid Universal Primer-Multiplex PCR showing high specificity capable of detecting three bacteria.…”

“…Previous studies have shown that filth flies can disseminate viable pathogens such as Helicobacter pylori (Grubel et al, 1997), Salmonella (Greenburg 1965), and E. coli O157 (Kobayashi et al, 1999) has not yet been investigated in this study whether or not these organisms were carried externally or internally. All detected bacteria from M. domestica in the current study are pathogenic.…”

Enterococcus faecalis OG1RF:pMV158 Survives and Proliferates in the House Fly Digestive Tract

“…Several recent studies have highlighted the efÞciency at which house ßies can acquire and disperse antibiotic resistant enterococci (Graham et al 2009, Chakrabarti et al 2010, Ahmad et al 2011. Further, the ability of various microbes to proliferate and possibly spread antibiotic resistance genes horizontally in the house ßy digestive tract underscores the potential of house ßies to amplify bacterial pathogens (Kobayashi et al 1999(Kobayashi et al , 2002Sasaki et al 2000;Petridis et al 2006;Akhtar et al 2009;McGaughey and Nayduch 2009). This current study adds to our understanding of the fate of E. faecalis in the house ßy digestive tract.…”

“…Furthermore, it is probable that the bacteria that multiplied in the crop were not only periodically transferred to the midgut but were also regurgitated and led to E. faecalis recovered in the labelum after the Þrst 24 h. Additionally, while the relative bacterial counts in the midgut and hindgut were lower at 96 h, the foregut retained a mean CFU count of 7.2 Ϯ 7.0 ϫ 10 5 , suggesting that the bacterium continued to proliferate in the crop/foregut. Kobayashi et al (1999) found the pseudotracheae of the labelum to be important for proliferation of E. coli O157: H7. Concentrations of E. faecalis in the labelum in our study were variable but did reveal a trend of higher counts during the latter part of the assay indicating that E. faecalis either multiplied on the surface of the labelum or propagated in the foregut/crop and were regurgitated during feeding.…”

“…House ßies ingest microbes with their food and microbes reside transiently in the ßy digestive tract but can also proliferate and be disseminated and deposited to various sites through ßy feeding and defecation (Sasaki et al, 2000, Kobayashi et al 2002. Kobayashi et al (1999) proposed the term "bioenhanced transmission" to describe this phenomenon, which is more than simple mechanical transmission and reßects the microbial growth in the house ßy digestive tract.…”