Antimicrobial susceptibility pattern and plasmid-mediated antibacterial resistance in Staphylococcus aureus and coagulase-negative staphylococci

Abstract

Background: Staphylococcal infections constitute problems to health care institutions. Its resistance to antibiotic has been associated with resistant plasmids (R-plasmid) that have the ability to mediate the production of drug inactivated  enzymes such as â-lactamase.
Method: Forty five Staphylococcus aureus (S. aureus) and 15 Coagulase-negative Staphylococci (CoNS) were isolated from clinical samples and isolates subjected to antibiotic susceptibility testing, plasmid curing and plasmid DNA isolation.
Result: The highest percentages isolates were recovered from urine samples and the least from high vagina swab and wound swab for S. aureus and CoNS respectively. The antibiogram showed that majority of S. aureus (95.6%) was resistant to cefuroxime and ceftazidime, while CoNS (93.3%) were more resistance to cefuroxime and gentamycin. (p=0.17). 24.4% S. aureus and 20% CoNS were resistant to more than 5 antibiotics with multiple antibiotic resistances (MAR) index of 0.33 to 0.89 for S. aureus and 0.56 to 0.78 for CoNS. Most of the S. aureus and CoNS were cured of their resistant markers showing that their R-markers may have been borne on plasmid. However, resistance to ciprofloxacin and ceftriaxone for CoNS may have been borne on chromosome as all the resistant markers were not cured. The percentage of S. aureus and CoNS cured of their R-plasmid were similar (p=0.25). Plasmids ranging from 2.03kbp to 23.13kbp were harboured by both S. aureus and CoNS.
Conclusion: There is widespread antimicrobial resistance patterns and diverse plasmid profile of S. aureus and CoNS in this study. This data will be a useful baseline for further epidemiological investigations.

Keywords: Plasmid, Staphylococcus, susceptibility, antimicrobials, resistance, curing