Houseflies as Vectors of ESBL-Producing Enterobacterales: Insights from Hospital Settings in a Low- to Middle-Income Country

The spread of extended-spectrum beta-lactamase-producing Enterobacterales (ESBL-E) in communities has been facilitated by direct contact with humans or animal carriers and insects such as houseflies. Houseflies may have an increased risk of human exposure to antimicrobial-resistant pathogens, including ESBL-E. In this study, we determined the presence of ESBL-E in houseflies and ready-to-eat food samples from selected food vending sites in five health care facilities in Greater Accra, Ghana. Sixty (60) food vending sites were included in this study. Flies (10) were pooled, and food (5 g) was macerated and homogenized aseptically in brain-heart infusion agar. Suspensions were cultured on MacConkey agar supplemented with 4 µg/mL cefotaxime for ∼18 h. Phenotypic and molecular characterization of ESBL-E was performed using a combination disk diffusion method, multiplex polymerase chain reaction, and direct nucleotide sequencing. Of the 60 food vending sites, 62% (37) of the food vendors had flies within their premises that carried ESBL-E, and 15% (9) of the food samples collected from the vendors were contaminated with ESBL-E. The most predominant ESBL-producing Enterobacterales from housefly samples was Proteus vulgaris (54%) and that of food samples were P. vulgaris (22.5%) and Escherichia coli (22.5%). All Enterobacterales from flies and food samples harbored an ESBL gene with bla_CTX-M, mostly bla_CTX-M-15, being the predominant gene and gene type, respectively. Houseflies may be potential contributors to the spread of ESBL-producing Enterobacterales in Ghana.