Potential Spread of Antimicrobial Resistant Gram-negative Bacteria by Houseflies (Musca domestica) in Urban Areas, Dar es Salaam, Tanzania

Abstract

Background: Owing to their abundance and proximity to human surroundings, houseflies (Musca domestica) are a major annoyance and serve as carriers of infectious disease-causing microorganisms to both humans and animals. They can spread many infections through ingestion of contaminated food, drinks, water, and other items as they dwell and feed on waste and decomposing matter. Our study aimed to determine the rate of antibiotic-resistant bacteria colonizing houseflies against commonly used antibiotics.

Materials and methods: Houseflies were collected from the randomly selected fast-food and beverage vending sites using sterilized trapping nets and deposited in capped containers and aseptically transported to the Pharmaceutical Laboratory within 2 hours of collection for analysis. Then each housefly was transferred into a universal bottle containing sterile normal saline and thoroughly shaken for a few seconds. An aliquot of the solution was sub-cultured on MacConkey agar and incubated at 28°C for 24 hours. The resultant discrete colonies were isolated and identified using the conventional methods, then subjected to antibiotic sensitivity tests against 6 selected antibiotics. The multiple antibiotic resistance index (MARI) was determined to ascertain the antibiotic resistance level.

Results: The study indicates that houseflies carried a significant number of antibiotic‐resistant bacteria that pose threats to public health. Escherichia coli, P. aeruginosa, P. vulgaris and K. oxytoca are four Gram-negative bacterial species that colonized the collected houseflies. Over half (54%) of the bacteria were resistant to the antibiotics. The majority (93%) of the bacteria exhibited MARI above 0.2, suggesting that they were previously exposed to antibiotics.

Conclusion: The antibiotic resistance among the isolated bacteria was notably high. Most of the bacteria exhibited a MARI higher than 0.2, indicating prior exposure to the antibiotics. Isolation of the enteric bacteria points to unsanitary surroundings or inadequate hygiene among vendors.