Extended-spectrum β-lactamase and AmpC β-lactamase Production among Gram-negative Bacilli Isolates Obtained from Urinary Tract Infections and Wound Infections

Abstract

Extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases continue to be a major problem in healthcare settings. Due
to the scarcity of information regarding the antibiotic susceptibility patterns particularly from urinary tract infection (UTI)
and wound infections, the current study was carried out to assist the clinicians to prescribe appropriate antibiotics against
Gram-negative clinical isolates. In the current study, urine (n = 620) and pus (n = 228) samples were collected from different
sites (at various clinical departments) and subjected to direct microscopic examination, culture and antibiotic susceptibility
testing (AST). In the AST testings, the isolates that exhibited reduced zone of inhibition to one or more of the antibiotics
such as cefotaxime (≤27 mm), ceftriaxone (≤25 mm), ceftazidime (≤22 mm), cefpodoxime (≤17 mm) and aztreonam (≤27 mm)
were considered as potential ESBL producers and the ESBL production was confirmed using phenotypic screening test
(double-disk synergy test) and phenotypic confirmatory test (combined-disk test). However, isolates showing resistance or
decreased sensitivity to cefoxitin, cefotaxime, ceftriaxone, ceftazidime, cefpodoxime or aztreonam and sensitive to cefepime
were considered as a screen positive AmpC producer and subjected to AmpC disk tests. The current study concluded that
72.41% and 21.76% of ESBL and AmpC producers were detected, respectively in our hospital. It was also observed that the
double-disk synergy and combined-disk tests were equally effective for ESBL detection. Further, AmpC disk test is simple,
easy to perform and interpret, requiring less expertise for the rapid detection of AmpC isolates.