Phenotypic Identification and Antibiotic Susceptibility Pattern of AmpC beta-Lactamase Producing Escherichia coli and Klebsiella pneumoniae Isolated from Urinary Tract Infections from a Tertiary Care Hospital of Rawalpindi, Pakistan

Emergence of antimicrobial resistance amongst uropathogenic Escherichia coli and Klebsiella pneumoniae has become a major public health concern of the 21st century [1]. According to World Health Organization (WHO) report 2014, alarming rates of resistance have been reported in all WHO regions due to resistant pathogens like E. coli, K. pneumoniae and Staphylococcus saprophyticus causing urinary tract infections (UTI), bloodstream infections, wound infections and pneumonia [2]. Hence, emergence of antimicrobial resistance due to AmpC beta-lactamase producing uropathogenic E. coli and K. pneumoniae are of accelerating, augmenting and increasing clinical concern accounting for 80% of community and hospital acquired UTI [3]. The appropriate selection of antibiotic for the treatment of UTI is inadequate and restricted by the increasing rates of antibiotic resistance due to AmpC beta-lactamase producing uropathogenic bacteria [4]. Hence, AmpC beta-lactamases are cephalosporinases, which are associated with in vitro resistance to all beta-lactam antibiotics except for carbapenems and cefepime [5]. These beta-lactamases are chromosomally encoded as well as plasmid encoded [6]. Uropathogenic E. coli and K. pneumoniae, producing plasmid-mediated AmpC beta-lactamases contribute towards nosocomial outbreaks of infection [7]. Detection and discernment of AmpC beta-lactamases is a challenge and trial for the clinical diagnostic laboratories [8]. Hence, absence and unavailability of an authentic method for identifying these resistant pathogens cause their rapid dissemination [9]. Currently there are no Clinical and Laboratory Standards Institute (CLSI) recommended guidelines for identification of AmpC beta-lactamase harboring pathogens [10]. Therefore, there is a great need to implement simple and authentic methods in routine laboratory investigations to accurately detect these resistant pathogens especially in developing countries. Researchers have used various test methods for AmpC beta-lactamase detection, like the three dimensional extract test (3-DET) method [11], inhibitor based method [12], cefoxitin agar method [13] and Disc Approximation Test (DAT) methods [14]. The prevalence of AmpC beta-lactamase producing bacteria increases the burden of implementing infectious disease management globally [15]. Introduction: This study is aimed to compare phenotypic test methods and determine antibiotic susceptibility pattern of AmpC beta-lactamase producing uropathogenic Escherichia coli and Klebsiella pneumoniae in clinical isolates. Method: E. coli and K. pneumoniae were identified by standard microbiological procedures. Screening of AmpC beta-lactamase production was done by using cefoxitin disc (30 μg) showing inhibition zone diameter of <18 mm. Then, screen-positive isolates were subjected to Disc Approximation Test (DAT) and three dimensional extract test (3-DET) methods. Antibiotic susceptibility testing was performed by Kirby Bauer Disc diffusion technique. Results: A total of 120 Gram Negative Rods (GNRs) were included in the study. Amongst them cefoxitin resistant isolates were 68.33% (n=82/120). In these 82 isolates, E. coli were n=57 (69.51%) and K. pneumoniae were n=25 (30.48%). DAT identified 52.43% of AmpC beta-lactamase producing isolates, sensitivity of DAT was found to be 88% with specificity of 92%, Positive Predictive Value of 92.68%, Negative Predictive Value of 87.80%, and Diagnostic Accuracy of 90.24%. Antibiotic susceptibility testing by Kirby Bauer Disc diffusion technique showed that carbapenems (meropenem) and tigecycline were of higher therapeutic effects against these resistant pathogens. Conclusion: Introducing simple tests like DAT in the laboratories can control the spread of AmpC beta-lactamase harboring organisms. Carbapenems (meropenem) and tigecycline are of suitable therapeutic effect against these resistant pathogens. J Med Microbiol Infec Dis, 2014, 2 (4): 143-146