Avian Pathogenic <i>Escherichia coli</i> Isolated in Poultry Farms in Bangladesh that Use Antibiotics Extensively

Colibacillosis caused by avian pathogenic <i>Escherichia coli</i> (APEC) is causing economic losses to the global poultry industry. Increased prevalence of antibiotic resistance in APEC is the leading cause for increased indiscriminate use of various antimicrobial compounds in farms. The study aimed to investigate the presence of phenotypic and genotypic markers for antibiotic resistance, metals, and biocides in APEC from Bangladeshi poultry and details about the antimicrobials used in poultry farms. In total, 55 APEC were isolated from hearts or liver samples of 86 sick or dead chickens using culture on agar plate and biochemical testing. APEC isolates were tested for antibiotic susceptibility to 14 antimicrobial agents according to the European Committee on Antimicrobial Susceptibility Testing. A series of PCRs was performed to screen the presence of genes for quinolones, colistin, aminoglycosides, ESBL, metals, and biocides. Detailed information regarding antibiotic use was collected from farmers during clinical investigations. Resistance was found to 10 antibiotics and prevalence was as follows: ampicillin (86%), ciprofloxacin (86%), trimethoprim-sulphamethoxazole (73%), chloramphenicol (33%), mecillinam (13%), gentamicin (11%), cefoxitin (11%), cefotaxime (9%), tigecycline (2%), and nitrofurantoin (2%). The most common multiresistance phenotype was CIP-AMP-SXT, and 35% of isolates were multidrug resistant. Genotypic analysis confirmed the presence of quinolone resistance genes [<i>qnrS1</i> and <i>aac-(6')-lb-cr</i>], silver-resistant genes (<i>silE</i>), and mercury-resistant genes (<i>merA</i>) but not others. In total, 88% farmers were using different antimicrobial compounds, and, of them, 56% were using antimicrobials without prescriptions from veterinarians. Ciprofloxacin was most extensively used followed by oxytetracycline. Critically important antibiotics like ciprofloxacin, colistin, and gentamicin are extensively used in the farms. This study confirmed the presence of antibiotics, metals, and biocide-resistant APEC in poultry farms in Bangladesh. Increased resistance to quinolones is a serious ongoing problem. The indiscriminate use of antibiotics in poultry farms is alarming and should be stopped.