PREVALENCE, CHARACTERIZATION, AND EMERGENCE OF EXTENDED-SPECTRUM Β-LACTAMASE PRODUCING- AND CARBAPENEM-RESISTANT GRAM-NEGATIVE BACTERIA ISOLATED FROM HOUSEFLIES (Musca domestica) IN TUNISIA

Houseflies (Musca domestica) live in close contact with humans. They are carriers of human pathogenic bacteria in the digestive tract and on their body. This study aimed to assess the prevalence of antibiotic-resistant Gram-negative bacteria in flies.Sixty-one isolates were collected from 100 houseflies at three different locations: a laying hen farm, a market, and three houses, comprising 23 Escherichia coli, 31 Klebsiella pneumoniae and 7 Pseudomonas aeruginosa. Antimicrobial sensitivity was determined by the disk diffusion method, and the ESBL-producing isolates were screened by the double-disc synergy test. β-lactamase genes, associated resistance genes, and integrons were studied by PCR.The ESBL-producing isolates comprised14.8% (9/61) of the isolates, seven K. pneumoniae isolates, and two E. coli isolates. The highest rate of ESBL-producing strains was observed in houses (7/22; 31.8%), followed by the market (2/43; 4.7%). Multi-drug-resistant bacteria were detected in 19/61 (31.2%) insects. Third-generation cephalosporin-resistant isolates (n= 30) were used to identify the resistance genes. The following resistance genes were identified in the isolates; blaCTX-M-G-1 (76.7%, 23/30), blaSHV-1 (43.3%, 13/30), blaTEM-1 (36.7%, 11/30), blaIMP (16.7%, 5/30), blaOXA-48 (10%, 3/30) and blaNDM (3.3%, 1/30). The quinolone resistance genes qnrs, aac(6′)-Ib-cr, qnrB and qnrA were found in 11, 11, 7 and 5 isolates, respectively. Integron 1 (intI1) was detected in 15 (50%) isolates, qacEΔ1+sul1 was identified in ten intI1-positive isolates. Class 2 integron was detected in three isolates. Houseflies collected from houses and markets may be implicated in the spread of multi-drug resistant bacteria which constitute a considerable threat to human public health. The ESBLs in flies reflect the contamination status of the environment and can be used as indicators of contamination.