Role of nuc gene in Staphylococcus aureus to phagocytic activity in different cattle infections

Staphylococcus aureus is a typical pathogenic agent that causes several morbidities and mortalities which variable largely following the severity of bacteria and activity of host immunity.

Isolation of S. aureus from different cattle infections, molecular detection of nuc gene in positive S. aureus isolates, and identification of the effectiveness of the phagocytic activity.

Totally, 100 cattle with various infections (25 wounds, 25 abscesses, 25 nasal discharges, and 25 ear swaps) were selected and subjected to collection of swabs under controlled conditions. All collected samples were cultured on mannitol salt agar (MSA) and assessed by biochemical tests. Targeting the nuc gene, all study MSA positive isolates were examined molecularly by conventional polymerase chain reaction (PCR), and then subjected to antibiotic susceptibility test. Jugular venous blood was collected from all infected animals in addition to 20 healthy cattle that were selected as a control group to estimate the phagocytic activity of S. aureus isolates.

The findings of MSA culture revealed a total of 80 positive samples of S. aureus as 23, 21, 20, and 16 positive isolates for nasal discharge, abscess, wound, and ear swab, respectively; based on its morphology, cultural trait, and biochemical test. Subsequently, PCR assaying of MSA-positive isolates demonstrated an overall 59 positive samples as 14, 16, 12, and 17 positive isolates for nasal discharge, abscess, wound, and ear swabs, respectively. Antibiotic susceptibility testing of S. aureus-positive PCR isolates reported a significantly high sensitivity to chloramphenicol and vancomycin, and a high resistance to penicillin. Finally, there was a considerable decline in phagocytic activity in particular 2 weeks post-infection as a result of bacterial invasion.

This study shows a high prevalence of S. aureus in cattle infections, and the protocol includes a regular screening of cattle infection and suitable therapy based on antibacterial susceptibility test is of great importance in the long-term control of the pathogen. However, additional molecular studies targeting other genes of S. aureus and the role of immune markers in different infections should be aimed.