Abstract

Expression of drug-hydrolyzing enzymes such as extended-spectrum beta-lactamases (ESBL) is
an important mechanism of bacterial resistance. This study was conducted to estimate the
prevalence of ESBL production in urinary isolates of E. coli and K. pneumoniae in samples
submitted for bacteriological examination at A.B.U.T.H., Shika, Zaria; assess the in vitro
susceptibility of these strains to the other antimicrobial agents that could be used for the
empirical treatment of infections due to ESBL-producing organisms; determine the frequency of
co-existence of ESBL production and resistance to other drugs such as the fluoroquinolones and
the aminoglycosides; and identify the molecular types of the ESBLs expressed by the isolates.
From January to June 2014, consecutive urine samples submitted for culture and antimicrobial
susceptibility testing at A.B.U.T.H. were inoculated on CLED agar and incubated. The isolates
were identified using the computer-aided Oxoid Microbact system. The first 100 isolates
comprising E. coli and K. pneumoniae were screened for ESBL production by testing for
susceptibility against ceftriaxone and cefotaxime and also tested for susceptibility to ampicillin,
gentamycin, tetracycline, ciprofloxacin, and sulphamethoxazole-trimethoprim. ESBL production
was confirmed with combination E-test strips and the isolated were tested for susceptibility to
imipenem, amikacin, tigecycline, nitrofurantoin, and fosfomycin. The ESBL-producing isolates
were then subjected to polymerase chain reaction and agarose gel electrophoresis for molecular
typing.
Out of the 100 isolates screened for ESBL production 43 (43%) were positive and 38 of these
were confirmed to be ESBL producers. These ESBL producers harboured genes in the CTX-M,
TEM, and SHV families. The prevalence of ESBL production among the E. coli and K.
pneumoniae isolates were 40.7% (95% CI= 30.0-52.2) and 26.3% (95% CI= 9.2-51.2)
respectively. Resistance to commonly used antibiotics was found to be highly prevalent among
the E. coli isolates – 88.9%, 88.9%, 92.4%, and 73.1% to ampicillin, sulphamethoxazole
trimethoprim, tetracycline, and ciprofloxacin respectively. The prevalence of resistance was
almost as high among the K. pneumoniae isolates – 57.9%, 50%, and 50% to
sulphamethoxazole-trimethoprim, tetracycline, and ciprofloxacin respectively. For the ESBL
producing isolates, there was 100% susceptibility to amikacin and imipenem in both E. coli and
K. pneumoniae isolates. But susceptibility to fosfomycin, tigecycline, and nitrofurantoin was
lower in K. pneumoniae compared to E. coli. Forty-eight percent, 60.9%, 45.1%, and 44.6% of
the ESBL-producing isolates were also resistant (or of intermediate susceptibility) to
ciprofloxacin, gentamicin, tetracycline, and sulphamethoxazole-trimethoprim respectively.
Extended-spectrum beta-lactamase expression in Escherichia coli and Klebsiella pneumonia
isolated from urine was found to be highly prevalent. CTX-M, SHV, and TEM enzymes were
found. The isolates were also found to be highly resistant to the commonly used antimicrobial
agents. The ESBL-producing isolates were uniformly susceptible to the alternative
antimicrobials amikacin and imipenem but demonstrated a lower frequency of susceptibility to
fosfomycin, tigecycline, and nitrofurantoin. ESBL production was found to coexist with a high
frequency with resistance to gentamicin, ciprofloxacin, tetracycline, and sulphamethoxazole
trimethoprim.