The accuracy of extended-spectrum beta-lactamase detection in Escherichia coli and Klebsiella pneumoniae in South African laboratories using the Vitek 2 Gram-negative susceptibility card AST-N255

Background: Phenotypic detection of extended-spectrum beta-lactamases (ESBLs) is based on the inhibition of ESBL enzymes by ß-lactamase inhibitors and on the comparison of cephalosporin activity with or without a ß-lactamase inhibitor. Many South African diagnostic laboratories rely on the Vitek 2 for automated susceptibility testing and for ESBL detection. However, the Gram-negative susceptibility card currently used locally (AST-N255) has been modified and its accuracy for ESBL detection is not known.Methods: We randomly selected 50 isolates of Klebsiella pneumoniae and Escherichia coli from a collection of clinical bloodstream isolates from Groote Schuur Hospital from 2015 to 2016, including ESBL-producing and non-ESBL-producing strains. We used standardised phenotypic (disc diffusion and broth microdilution) and genotypic (conventional polymerase chain reaction (PCR) for blaCTX-M, blaSHV and blaTEM) methods for detection of ESBLs. We compared ESBL detection by Vitek 2 to a composite reference standard comprising ESBL detection either by both phenotypic methods or by one phenotypic method together with genotypic detection.Results: The sensitivity of Vitek 2 system for detection of ESBLs was 33/36 or 92% (78% ­ 97%) for E. coli, and 40/40 or 100% (91% ­ 100%) for K.pneumoniae, whilst specificity was 10/10 or 100% (72% ­ 100%) and 9/10 or 90% (60% ­ 98%), respectively. This is comparable with previous studies.Conclusion: Using a composite reference standard of the phenotypic and genotypic methods employed in this study, no Vitek-categorised ESBL E. coli or K. pneumoniae was found to be a non-ESBL with the exception of possible misinterpretation with K. pneumoniae SHV-hyper-producing isolates

Antimicrobial Susceptibility Patterns of Escherichia Coli Strains Isolated From Urine Samples in South Africa from 2007-2011

Escherichia coli is the most common cause of urinary tract infections. Knowledge of its local antimicrobial susceptibility patterns can be used to inform choice of empiric antimicrobial therapy. In this article; we review data on antimicrobial susceptibility patterns of E. coli isolated from unselected urine specimens; in both the private and public sectors of South Africa from 2007-2011. Between 65 000-84 000 E. coli urinary isolates were reported annually from 19 laboratories located across South Africa. Susceptibility to fluoroquinolone and beta-lactam antibiotics decreased significantly and steadily in both private and public sectors over the five-year period; although laboratory-based surveillance data may underestimate susceptibility rates due to selection bias and lack of differentiation between community- and hospital-acquired infections. Our data suggest that fluoroquinolones; co-amoxiclav and first- and second-generation cephalosporins can still be used for empiric treatment in many local settings; but clinicians should be alert to the risk of treatment failure. With the withdrawal of nitrofurantoin from the local market; other oral antibiotic options are limited; and fosfomcyin may become increasingly important. Given their sustained high susceptibility rates; aminoglycosides should be considered to treat pyelonephritis more often. Judicious use of laboratory testing is advised and further research and surveillance is warranted