Exploration of virulence and resistance profiles of newly emerging MDR B. cereus in wild birds, as the first report in Egypt.

Abstract

Bacillus cereus (B. cereus) is a widespread bacterium that poses a significant threat to public health. Wild birds play an important role as reservoirs of bacteria, contributing to the dissemination of environmental and zoonotic pathogens to humans. However, data on the occurrence and characteristics of B. cereus in wild birds are limited. This study aimed to determine the prevalence, molecular typing, antibiogram profile, phenotypic virulence traits, pathogenicity, and distribution of key virulence genes (hbl, nhe, cytK, and pc-plc) and antibiotic resistance genes (bla1, tetA, and ermA) associated with natural B. cereus infections in wild birds. A total of 78 wild birds (39 Passer montanus and 39 Bubulcus ibis) were collected from Ismailia Province, Egypt, and subjected to bacteriological examinations. B. cereus was isolated from 10.3% (8/78) of the birds, including 37.5% (3/8) of positive isolates from P. montanus and 62.5% (5/8) from B. ibis. Phylogenetic and sequence analyses of the groEL gene revealed that the two examined B. cereus isolates showed high genetic similarity to B. cereus strains from diverse sources. All isolates exhibited β-hemolysis and lecithinase activities. All isolates were phenotypically resistant to ampicillin, amoxicillin, and doxycycline and remained susceptible to ciprofloxacin, with high resistance rates to amoxicillin-clavulanic acid (87.5%), streptomycin (75%), and erythromycin (62.5%). The multiple antibiotic resistance (MAR) indices ranged from 0.6 to 0.8, indicating exposure to high-risk contamination sources. PCR analysis revealed that the examined isolates harbored hbl (100%), pc-plc (100%), nhe (50%), and cytK (37.5%) virulence genes and carried bla1, tetA, and ermA resistance genes in 100%, 100%, and 75% of isolates, respectively. To the authors' knowledge, this study is the first to report MDR B. cereus in wild birds in Egypt and suggests that these birds may serve as environmental carriers and potential reservoirs of toxigenic and antimicrobial-resistant B. cereus strains.