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Grubel and colleagues set out to show whether houseflies might harbor Helicobacter pylori after ingesting the bacterium and, in turn, contaminate the human environment. Caged houseflies were allowed to feed on freshly grown H. pylori cultured on agar in Petri dishes. The plates were then removed and replaced by sterile Petri dishes containing a droplet of sterile brucella broth. Small numbers of houseflies were removed at regular intervals for microbiological and histological analysis, and the Petri dishes were replaced with fresh sterile plates with fresh drops of brucella broth. Control flies were handled in the same way, except that they were not exposed to the bacterium. H. pylori was recovered from the flies’ bodies for up to 12 hours after the initial feeding period, and from the alimentary tract and excreta for at least 30 hours. Thereafter, cultures yielded a variety of enteric gram-negative bacilli, including Pseudomonas aeruginosa and Staphylococcus aureus. Despite disinfection of the pupae and aseptic handling making further detection of H. pylori impossible, Helicobacter-like organisms were seen in the gut lumen and attached to intestinal epithelial cells.
The housefly is a notorious scavenger with the most abominable eating habits imaginable, consuming anything and everything from sweat to sugar to feces and, being prolific pukers and poopers, they will vomit it up and excrete it in no time. So, it is not really any great surprise that, when presented with the rich pickings off a Petri dish full of H. pylori, they will gorge themselves, as is their wont.
Moreover, they will transmit any viable bacteria to each other via body contact, vomit, and excreta and, perhaps, to us, as is known to occur with fecal pathogens Salmonella spp., Shigella spp., and Vibrio cholera.
However tempting it is, before we can lay the blame on these undoubtedly repugnant creatures for giving us H. pylori, we need to know whether houseflies can harbor viable H. pylori for any great length of time. We know they can for at least 30 hours, and perhaps longer. We also need to know just how long these bacteria can survive on the sorts of materials and surfaces houseflies frequent. An educated guess would be that H. pylori would not survive desiccation very long, nor would the bacterium be happy at the concentrations of oxygen and carbon dioxide present in the atmosphere given its microaerophilic nature. The bacterium has been found in drinking water but is apparently dead due to a combination of too much oxygen and too little acid.
Neither is the mode of transmission of H. pylori known, but it is presumably ingested continually throughout life. Houseflies thrive wherever sanitary conditions are poor and where there is overcrowding, giving these ubiquitous insects every opportunity of devouring all manner of excrement and communicating their findings to all and sundry. Also, we now know that it is at least possible to get H. pylori from houseflies. Perhaps, in time, we might see the familiar motto "Flies spread diseases" being augmented by the new line "And might give you ulcers." (Dr. Donnelly is Clinical Microbiologist, University Hospital, Nijmegen, The Netherlands.)