TITLE:
Clinical Isolates of Staphylococcus aureus Show Variation in β-Lactamase Production and Are More Susceptible to Antibiotics Conjugated with β-Lactamase Inhibitors
AUTHORS:
Uzal Umar, Umar Ahmed Faruk, Damoroem M. Tanko, Mohammed B. Yerima
KEYWORDS:
β-Lactamase, Peptidoglycan, Transpeptidation, Haemolysis, Resistance, Antibiotics
JOURNAL NAME:
Open Journal of Medical Microbiology,
Vol.6 No.4,
December
13,
2016
ABSTRACT: β-Lactam antibiotics are a
cornerstone in the treatment of bacterial infections on account of its high
therapeutic index and selective toxicity—they act by inhibiting the
biosynthesis of peptidoglycan, a key
component in bacterial cell wall. Ninety (90) clinical specimens obtained from
the microbiology unit Specialist Hospital Bauchi were screened for S. aureus, positive isolates were
examined for β-Lactamase expression by using two Penicillin G
concentrations (5000 IU/ml and 25,000 IU/ml) in acidometric agar technique with phenol red as indicator, and the susceptibility pattern
of the isolates to β-Lactam
antibiotics was also determined. S. aureus prevalence of 31% (28/90)
was obtained, of
which 96% (27/28) of strains were β-Lactamase
positive in the standard test, while 63% (17/27) were able to hydrolyze
penicillin G concentration of 25,000 IU/ml
(5X the concentration in the standard test), and a strain was found to be β-Lactamase negative. The resistance to five β-Lactams, ampicillin, cephalexin,
amoxicillin, cloxacillin and flucloxaillin, were 100%, 96%, 89%, 74% and 56% respectively.
When ampicillin and amoxicillin were conjugated to β-Lactamase
inhibitors sulbactam and clavulanic acid respectively the resistance to
ampicillin decreased to 21% and to amoxicillin to 15%. The antibiotic susceptibility profile revealed β-Lactamase elaboration to be the major
mechanism of resistance to the β-Lactams. β-Lactam utilization as therapeutic
option would thus require the search for sensitive irreversible β-Lactamase
inhibitors for the β-Lactamase enzymes or
agents to block the release of β-Lactamase
by strains.