ABSTRACT
Infections with Mycoplasma gallisepticum (MG) in poultry are associated with a wide range of disease conditions, including those affecting the respiratory and reproductive systems. The purpose of this study was to endorse the more sensitive diagnostic scheme for MG infection and identify the best molecular marker for MG phylogenetic analysis using six housekeeping genes: mgc2, mraW, atpG, ugpA, DUF31196, and lgT. For these purposes, 55 poultry flocks of different species were screened using either qRT-PCR or PCR techniques analogous to conventional culturing from non-cultured and cultured swabs on PPLO broth. The rate of MG positivity was the highest when using qRT-PCR from cultured broth (89.0%) and the lowest when using conventional culturing (34.5%). Compared to qRT-PCR from broth, statistical analysis using the Roc curve in MedCalc statistical software showed that the PCR schemes (qRT-PCR from swabs and PCR from swabs and broth) performed better than conventional culturing in terms of sensitivity, accuracy, and area under the curve (AUC), suggesting that they may be more reliable schemes. Further support was added by Cohen's kappa test, showing moderate agreement between the molecular approaches. Among the six screened genes, mgc2 and mraW had the highest detection rates (69% and 65.4%, respectively). The comparative phylogenetic analysis revealed that mgc2 or atpG gene sequences distinguished MG isolates into different clades with high discriminatory power.
ABSTRACT
Bovine respiratory disease (BRD) is a complex syndrome associated with high mortality in young calves and causes severe economic losses in the cattle industry worldwide. The current study investigated the prevalence and molecular characterization of common bacterial pathogens associated with respiratory symptoms in young calves from Sadat City, one of the largest industrial cities in Menoufiya Governorate, Egypt. In between December 2020 and March 2021, 200 mixed-breed young calves of 6-12 months were examined clinically. Of them, sixty (30%) calves showed signs of respiratory manifestations, such as coughing, serous to mucopurulent nasal discharges, fever, and abnormal lung sound. Deep nasal (Nasopharyngeal) swabs were collected from the affected calves for bacteriological investigation. Phenotypic characterization and identification revealed Mycoplasma bovis, Mycoplasma bovigenitalium, Pasteurella multocida, and Staphylococcus aureus in 8.33%, 5%, 5%, and 5% of the tested samples, respectively. The PCR technique using species-specific primer sets successfully amplified the target bacterial DNA in all culture-positive samples, confirming the identity of the isolated bacterial species. Partial gene sequencing of 16S rRNA gene of M. bovigenitalium, P. multocida, and S. aureus, and mb-mp 81 gene of M. bovis revealed high nucleotide similarity and genetic relationship with respective bacterial species reported from Egypt and around the world, suggesting transmission of these bacterial species between animal host species and localities. Our study highlights the four important bacterial strains associated with respiratory disorders in calves and suggests the possible spread of these bacterial pathogens across animal species and different geographic locations. Further studies using WGS and a large number of isolates are required to investigate the realistic lineage of Egyptian isolates and globally.
