Staphylococcus aureus colonization of anterior nares of school going children

To determine the colonization rates of S. aureus in anterior nares of school going children, evaluate the antimicrobial resistance of such isolates against various antibiotics.

Nasal swabs taken for S. aureus in 392 healthy school going children aged between 5 and 15 yr belonging to three schools surrounding Kamineni Institute of Medical Sciences, Narketpally, Andhra Pradesh, India. Swabs were inoculated in to Mannitol Salt Agar (MSA) and incubation at 37 degrees C for 24hr, Staphylococcus aureus isolates were identified by standard microbiological methods such as Gram's stain, catalase and coagulase. MICs were determined by Agar dilution technique against Vancomycin, Ciprofloxacin, Sparfloxacin, Sparfloxacin beta Cyclodextrin. Antimicrobial resistance patterns of all the isolates against Oxacillin (1 microg) Penicillin (10 units), Ampicillin (10 microg), Co-trimoxazole (23.75 microg), Erythromycin (15 microg), Tetracycline (30 microg) and Gentamicin (10 microg) were tested using Kirby-Baeur disk diffusion method in accordance with CLSI standards.

Of the 392 samples screened 63(16%) showed the growth of Staphylococcus aureus. 12(19%) isolates were found to be MRSA. Antimicrobial susceptibility testing using Agar dilution method against Vancomycin, ciprofloxacin, Sparfloxacin, and Sparfloxacin beta Cyclodextrin revealed MICs in the range of 0.52 microg/ml, 0.51 microg/ml, 0.5 microg/ml and <0.0312-0.250 microg/ml respectively. Disk diffusion method showed that all the isolates were resistant to Penicillin and Ampicillin. A resistance of 14.3%, 25% and 22.2% was observed against Co-trimoxazole, Erythromycin and Tetracycline respectively. Gentamiicin was the only antibiotic against which most of the isolates were sensitive.

Our results suggests that healthy school going children under 16 yr of age are potential carriers of S. aureus and in particular MRSA and multi-drug resistant strains.