Characteristics of Clinically Significant Invasive Staphylococcus aureus Infections in a Tertiary Care Centre

The purpose of this study was to evaluate the antibiotic susceptibility of clinically significant Staphylococcus aureus and its association with biofilm production. The antibiotic resistance pattern and biofilm production by S. aureus isolated from invasive sites such as deep tissue and bone, deep seated pus, blood and other sterile body fluids were studied. The prevalence of multidrug resistant strains and the associated risk factors and co-morbidities were noted. Samples were subjected to antibiotic susceptibility testing using modified Kirby-Bauer disc diffusion method and biofilm production was detected by using microtiter plate assay. Of the total 80 clinically significant invasive S. aureusstrains, resistance to penicillin was observed in 70(88.6%) isolates and 38 (47.5%) isolates were resistant to cephalothin. Resistance to erythromycin was observed in 42(52.5%) isolates and 14(17.5%) isolates were resistant to clindamycin. Resistance to ciprofloxacin was 79.5%(n=63). Resistance to rifampicin was observed in 1 isolate (2.1%) and 1 isolate (1.3%) was resistant to teicoplanin. All the isolates were sensitive to vancomycin, tigecycline and linezolid. Out of the 80 S. aureus strains, 21 (26.3%) strains were biofilm producers and 59(73.75%) strains were non-biofilm producers. Among the biofilm producers, resistance to penicillin (57.14%), cephalothin (57.1%) and ciprofloxacin (57.14%) was higher compared to non-biofilm producers. (penicillin 45.7%, cephalothin 35.6% and ciprofloxacin 38.9%,). The rate of MRSA isolated from invasive infections was high (41.25%). We conclude that MRSA and biofilm-producing strains exhibit higher resistance to antibiotics and hence beta-lactams may not be a good empirical antibiotic of choice, especially in biofilm producers. Clindamycin may be an effective alternative substitute to vancomycin forin MSSA and MRSA treatment. Since the patients improved after appropriate antibiotic treatment, we support the role of an early start of appropriate and adequate antibiotic therapy for better patient outcome. We conclude that S. aureus strains exhibited a high resistance to penicillin, β-lactam, macrolide and fluoroquinolones. The rate of MRSA was found to be 41.25%. MRSA and biofilm producing strains exhibit higher resistance to antibiotics. The high prevalence of MDRSA was high (53.75%), which could potentially pose beas a threat to public health, antibiotic use and patient outcome.