Isolation and molecular characterization of staphylococcus aureus isolated from clinical cases in broilers

Abstract

Background: Staphylococcus aureus (S. aureus) causes a difficult problem in the poultry industry because it causes diseases that are difficult to treat due to the resistance of these bacteria to antibiotics and their possession of a battery of virulence and resistance genes in addition to their ability to produce thick biofilms. Method: A cross-sectional study conducted to collect a total of 53 samples from different clinical cases in broilers during the period from August 2019 to February 2020 in Al-Najaf and Karbala cities, The clinical isolates were determined by using the conventional standard biochemical tests. All the specimens cultured on blood agar medium supplemented with 5% blood for primary isolation and selected by using selective media mannitol salt agar (MSA) for confirmation the mannitol fermentation, then subjected to gram’s staining, catalase, oxidase, and further slide coagulase test, then all S. aureus isolates tested by antibiotic susceptibility test, and screened for the presence of mecA and mecC genes using PCR for the detection of MRSA isolates, then subjected to the detection of virulence genes (pvl and eta), antibiotic resistance gene (cfr), identification of integron class 1, biofilm formation assay, the multi-druge resistance profiles (MDR) and multible antibiotics resistance (MAR) indexes were calculated. Results: the isolation rate of S. aureus from the broilers' clinical samples was 37.7%. The antibiotic susceptibility test revealed that 85% of S. aureus isolates were resistant to one or more of the antibiotic tested. All 53 isolates were assessed for the presence of mecA and mecC genes by using PCR. The mecA gene-specific PCR product was seen in 7 (35%) isolates and considered as MRSA. Among all S. aureus isolates, two isolates were positive for the eta gene, and 15 (75%) isolates harboring integron class 1, while the biofilm formation test revealed that 7 (35%) was positive biofilm producers and three of them were strong producers, consequentlly, 13 (65%) of the isolates were resisted to three or more antibiotics and considered as MDR strains. While pvl, cfr, and mecC gene were not detected among S. aureus isolates. Conclusion: the current study revealed that S. aureus possess a real threat in the poultry industry reflecting a public health problem due to the large acquisition of antibiotic resistance genes by these bacteria, the results indicated a high percentage of isolates having MDR characteristic, and two of them were resistant to all antibiotics tested. In addition to the presence of two MRSA isolates carrying the eta gene, this indicating that they are of human origin.