Analysis of Antibiotics Susceptibility of Old and Fresh ATCC Strain of <i>Staphylococcus aureus</i> by Standard Agar Diffusion Technique

Abstract

A comparative study of an old and fresh ATCC strain of Staphylococcus aureus was carried out to determine the mechanism of antibiotic resistance of the old one, which had been preserved in lyophilized condition. Five different antibiotics having five different modes of action were used. They included amoxicillin, azithromycin, neomycin, ciprofloxacin and polymixin B. Agar diffusion technique was followed to determine the antibiotic sensitivity. It was observed that the old strain showed the highest resistance against amoxicillin, whereas no remarkable changes in the sensitivity pattern were observed against polymixin B and neomycin. In case of azithromycin and ciprofloxacin, the old strain showed resistance up to some extent. From these results it was clearly evident that in the controlled preserved conditions, cell wall-mediated resistance was predominating, while the cell membrane- and 30S ribosome-mediated resistance were the least likely ones. The nucleic acid synthesis inhibitors and the 50S ribosomal protein synthesis inhibitor lied in between these two extremes showing variations up to some extent in the sensitivity pattern between the old and fresh ATCC strain of S. aureus.

Keywords: Staphylococcus aureus, Antibiotic resistance mechanism

DOI: http://dx.doi.org/10.3329/bjm.v24i2.1259

Bangladesh J Microbiol, Volume 24, Number 2, December 2007, pp 137-142