BACKGROUND: Escherichia coli is part of the natural flora of the gastrointestinal system in birds, such as ostrich, and causes intestinal infections. Antibacterial drugs, such as beta-lactam drugs, are widely used to reduce the damage caused by E. coli infections in birds; however, the production of extended-spectrum beta-lactamases (ESBLs) by some strains has rendered these infections difficult to treat. OBJECTIVES: The present study was conducted to perform a phenotypic and genotypic investigation of broad-spectrum beta-lactamases in fecal E. coli isolates from healthy ostrich chicks and those exhibiting digestive symptoms in the northeast of Iran. METHODS: This descriptive cross-sectional study was performed on 121 fecal Escherichia coli isolates from ostrich chicks in 2022. For this purpose, 121 cloacal swabs were collected from 53 apparently healthy chicks and 68 chicks with gastrointestinal disorders located in the farms of South Khorasan and Razavi provinces. The swabs were cultured on selective media and confirmed as E. coli using biochemical tests. The antibiotic susceptibility of the isolates was determined using the Kirby-Bauer disk diffusion method. All isolates were screened for the presence of ESBLs using the combination disk method. PCR assays were performed to detect the presence of ESBL genes belonging to the SHV, TEM, CTX-M, and OXA families. Gene distribution data were analyzed using SPSS software version 21 and the Chi-square test. RESULTS: In the antibiotic susceptibility test, the isolates showed the highest resistance and sensitivity to lincomycin (100%) and ceftiofur (88.42%), respectively. Out of the total of 121 E. coli isolates, 42 (34.7%) isolates (21 out of 53 healthy isolates and 21 out of 68 sick isolates) were positive for at least one of the genes. The blaTEM gene, present in 37 (30.5%) isolates, had the highest frequency, which included 17 healthy isolates and 20 sick isolates, while the blaCTX-M gene was observed in only five (4.1%) isolates, including 3 healthy isolates and two sick isolates. In the phenotypic examination, a total of 13 isolates (10.74%) were identified as producing ESBL isolates; however, no ESBL genes were detected in five isolates. Two isolates had the TEM β-lactamase gene, 5 five isolates had all four β-lactamase genes (SHV, TEM, CTX-M, and OXA) simultaneously, and one isolate had three β-lactamase genes (SHV, TEM, and OXA). No statistical correlation was observed between the distribution of genes in healthy and diseased ostrich chicks. CONCLUSIONS: In the phenotypic and genotypic studies, 13 and 42 isolates were identified as positive for the presence of ESBLs, respectively. No ESBL gene was isolated from the five phenotypic-positive isolates. Out of 42 genotypic positive isolates, 34 isolates had no phenotypic manifestation. The blaTEM gene had the highest frequency in fecal E. coli isolates from ostrich chicks.

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