Phenotypic and genotypic characterization of Staphylococcus aureus of animal origin
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Date
2023-01-24
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CSK HPKV, Palampur
Abstract
Staphylococcus aureus is an opportunistic pathogen of humans and animals causing both acute and chronic
infections. Several virulence-related factors have been described in S. aureus with multiple roles in attachment,
multiplication, invasion, and evasion of host immune responses. The disease outcome therefore, does not merely
depend on the host’s immune status but also on S. aureus phenotypic and genotypic virulence-associated factors.
Several strains of S. aureus are being recovered from livestock suffering from various diseases; however, their
true virulence potential and antibiotic resistance status never become known. This poses a huge challenge to
veterinarians, owners and, the livestock industry because of losses associated with such isolates, their transmission
and subsequent animal and human infections. Under this study, a total of 50 isolates of livestock origin were
genotypically and phenotypically characterized. All isolates were nuc and catalase positive. Most of the isolates
exhibited coagulase, biofilms, and hemolysins production. The mecA was detected in 38% of isolates; lukpv in
76%, tsst in 2%, sdrD in 80%, sdrE in 58%, clfA in 78%, cna in 34%, CC398 in 56% isolates. No isolate was
positive for sea, scn, sak, vanA and icaA. The S. aureus were tested for their susceptibility to cloxacillin,
amoxicillin, cephalexin, neomycin, tobramycin, doxycycline, erythromycin, vancomycin, enrofloxacin and
levofloxacin. Only 12% isolates were susceptible to all the tested antibiotics; whereas 78% were resistant to one
or more antibiotics. The isolates revealed 100% susceptibility to levofloxacin and enrofloxacin followed by
vancomycin (98%), cephalexin (96%), erythromycin (94%), doxycycline (94%), neomycin (94%), tobramycin
(84%), cloxacillin (70%), amoxicillin (46%). Amoxicillin was the least effective drug. About 16% isolates also
exhibited MDR involving amoxicillin, erythromycin, doxycycline, tobramycin and cephalexin. A MAR index >
0.2 was recorded in 26% of isolates. Out of 50 isolates, 30% belonged to the highly virulent class, 54 % to the
medium and 16% to low virulent class, respectively. This study confirmed that these isolates were livestock
adapted and majority of them belonged to a single lineage comprising of CC398 cluster. In vivo pathogenic
potential of isolates will allow S. aureus better classification enabling epidemiological tools in the hands of
researchers and clinicians for better outcomes.