Abstract:
Increasing resistance to antibiotics among the Enterococcus spp., to a point where
some clinical isolates are resistant to all standard therapies reduces the choices of
antibiotics available to treat infections caused by them. These organisms can cause
serious invasive infections including endocarditis, bacteraemia, intra-abdominal and
urinary tract infections. Enterococcus faecalis causes 80-90 percent of human
enterococcal infections while Enterococcus faecium accounts for majority of the
remainder. The aim of this study was to determine prevalence, antimicrobial resistance
patterns and resistance genes in Enterococcus faecium and Enterococcus faecalis
isolates from patients attending the Aga Khan University Hospital (AKUH) Nairobi,
Kenya. All consecutive clinically significant enterococcal isolates from patients,
collected between March 2008 and February 2009 were used. Species level
Identification was done using API 20 STREP kits. Antibiotic susceptibility testing was
done using Disk diffusion and Minimum Inhibitory Concentration (MIC).
Interpretation of the susceptibility results was done using the Clinical and Laboratory
Standards Institute (CLSI) guidelines. Resistance gene analysis using Polymerase
Chain Reaction (PCR) was done for tetracycline (tet M (696bp)), floroquinolones (gyr
a (241bp) and chloramphenicol (catpip501 gene (540bp)) resistant isolates.
Enterococcus faecalis was found in a greater proportion, where 128/150 (85%)
isolates, followed by Enterococcus faecium 7/150 (5%), while 15/150 (10%) were not
Enterococcus spp. and no further tests were done on them. Both species were highly
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resistant to aminoglycosides and tetracyclines while they were most susceptible to
glycopeptides. The gyrA gene was present in 75.9% of the Enterococcus faecalis
isolates and in 100% of the Enterococcus faecium isolates. The tet M gene was present
in 61.8% and 60% of the Enterococcus faecalis isolates and Enterococcus faecium
isolates respectively. The cat pIP501 gene was present in 63% of the Enterococcus
faecalis isolates and 100% of Enterococcus faecium isolates. There being no
resistance to penicillin and vancomycin drugs, the PCR process to identify the genes
coding for penicillin resistance (Pbp5) and vancomycin (vanA and vanB) resistance
was omitted. With the high levels of Enterococcus spp. resistance to aminoglycosides
and tetracyclines and emerging resistance to fluoroquinolones, routine susceptibility
testing will be required before treatment is instituted using commonly available drugs
in the hospital. The isolates that did not code for tet M resistance-gene in tetracycline
resistant isolates should be tested for the other classes of tetracycline- resistance genes.
More studies should be done to determine the resistant genes in the other category of
antibiotics.