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Abstract
The purpose of this study was to investigate the prevalence, antibiotic resistance and certain virulence genes of the most predominant bacterial pathogens causing BRD. A total of 225 calves; 55 apparently healthy and 170 diseased; were sampled. Bacteriological examination, antimicrobial susceptibility testing and PCR based detection of some virulence genes were performed. In addition, the serotyping of E. coli was performed using the slide agglutination test. The most predominant bacterial pathogens retrieved from apparently healthy calves were E. coli (16.4%) and S. aureus (10.9%), and in pneumonic calves were E. coli (23.5%), P. vulgaris (12.4%) and S. aureus (11.8%). The most prevalent virulence gene in E. coli was the fimH gene (100%), followed by eaeA gene (24.5%) and hly gene (20.4%). All the examined S. aureus strains harbored spa and coa genes; likewise, all P. multocida strains harbored toxA gene. The majority of the isolated strains displayed remarkable sensitivity to norfloxacin and enrofloxacin; furthermore, the retrieved E. coli strains exhibited multidrug-resistance to gentamicin, erythromycin, streptomycin and trimethoprim-sulphamethoxazole, in addition, the isolated S. aureus and P. aeruginosa strains showed multidrug-resistance to amoxicillin, ampicillin and tetracycline. E. coli serogroups including O18, O143, O1, and O6 were retrieved from pneumonic calves as the first report in Egypt. In conclusion, the synergism between the conventional and genotypic analysis is an effective gadget for the characterization of bacterial pathogens causing BRD. Continuous surveillance of antimicrobial susceptibility is essential to select the drug of choice due to the development of multidrug-resistant strains.
Highlights
Bovine respiratory disease (BRD) is one of the major risks to the health of calves and younger cattle, causing significant economic losses (Zeineldin et al 2017)
Prevalence of bacterial pathogens in apparently healthy and diseased calves Bacterial pathogens were isolated from 57% of the examined calves with or without BRD (Table 2)
The most prevalent bacterial pathogen isolated from calves with BRD was E. coli (23.5%), followed by P. vulgaris (12.4%) and S. aureus (11.8%)
Summary
Bovine respiratory disease (BRD) is one of the major risks to the health of calves and younger cattle, causing significant economic losses (Zeineldin et al 2017). The emergence of multidrug-resistant pathogens associated with BRD has been recorded that threatens the livestock industry (Klima et al 2014). The continuous surveillance of antimicrobial susceptibility should be applied as well as the proper use of antibiotics in order to reduce the spread of multidrug-resistant strains between livestock and to humans (Holman et al 2015; Klima et al 2014). The current work aimed to determine the prevalence of bacterial pathogens in apparently healthy and pneumonic calves and to monitor the antibiotic susceptibility of the isolated strains, and to perform PCRbased detection of certain virulence genes
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