Multi–drug resistance and β–lactamase production among clinical isolates of staphylococci

Abstract

Thirty–eight isolates of staphylococci isolated from diseased eyes of human were distinguished as methicillin resistant S. aureus (MRSA) 11, methicillin sensitive S. aureus (MSSA) 19, and coagulase negative staphylococci (CNS) 8 isolates. Antibiotic resistance against β–lactam antibiotics was exhibited by 81.81–100% of the isolates belonging to MRSA, followed by MSSA (0–89.47%) and CNS (25–87.50%). Similarly, resistance to other antibiotics like streptomycin, tetracycline, doxycycline and nalidixic acid was also higher among MRSA isolates than MSSA and/or CNS isolates. Overall resistance was higher to penicillin–G (78.95%) followed by ampicillin (73.68%), cefixime and nalidixic acid (68.42% each), cloxacillin (60.52%), streptomycin (57.89%), methicillin (39.40%) and least to tetracycline and doxycycline (21.05% each). Resistance to β–lactam drugs was common and cross–resistance was observed in several strains. Multiple antibiotic resistance in staphylococci was exhibited by 73.68% of the isolates. All the MRSA strains showed resistance to multiple antibiotics. Minimum inhibitory concentrations (MIC) of β–lactam antibiotics ranged from 6.25μg/ml to 2000μg/ml. High level of MIC value (≥800μg/ml) was detected against penicillin, ampicillin and cloxacillin in the 15, 7 and 21 isolates respectively. The β–lactamases of few isolates showed substrate specificity, hydrolyzing one or more β–lactam antibiotics. No significant difference was noticed in the production of β–lactamase among the three groups of staphylococci (MRSA, MSSA and CNS). No co–relation was established between the resistance level against antibiotics and β– lactamases production in the staphylococci isolates from diseased eyes. Staphylococci associated with the human eye infection showed resistance to β–lactams and other antibiotics and β–lactamase production is a common traits.

Keywords: MRSA, β–lactamase, antibiotics, antibiotic resistance, β–lactamase, coagulase negative staphylococci

Journal of Tropical Microbiology and Biotechnology Vol. 2(1) 2006: 18-23