Evaluation of phenotypic and genotypic methods for coagulase typing of MRSA isolates from diverse sources

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in both human and veterinary medicine due to its resistance to multiple antibiotics and its zoonotic potential. This study aimed to compare the phenotypic detection of coagulase using the tube coagulase test (TCT) with plasma from humans and seven animal species, against genotypic detection through coa gene PCR among MRSA isolates from various sources. A total of 203 samples were collected from human pus, animal pus, mastitis milk, and unprocessed meat in Bikaner, Rajasthan, out of which 78 isolates were confirmed as MRSA based on 23S rRNA and mecA gene amplification. TCT results showed that 75 (96.15%) isolates were coagulase-positive at 5 hours, and one additional isolate turned positive at 24 hours. Human plasma showed the strongest and earliest coagulation, followed by plasma from camel, buffalo, horse, sheep, goat, cattle, and chicken. Coagulation strength was often higher when the plasma origin matched the host species of the isolate. All 78 isolates tested positive for the coa gene by PCR, showing greater sensitivity than TCT. Amplicon sizes varied from 350 bp to 850 bp, with five distinct profiles: 700 bp (38.46%), 600 bp (33.33%), 850 bp (20.51%), 350 bp (3.85%), and dual bands (600 and 850 bp) in 3.85% of isolates, with the dual bands observed only in animal-origin isolates. Among human-derived isolates, 700 bp and 850 bp genotypes were equally dominant, while 700 bp was most frequent in meat samples. The findings highlighted the limitations of TCT, particularly with animal isolates, and emphasized the value of coa gene PCR for accurate detection and genotypic characterization of MRSA.