Assessment of the comparability of CLSI, EUCAST and Stokes antimicrobial susceptibility profiles for Escherichia coli uropathogenic isolates.

BACKGROUND: As many clinical laboratories convert between Stokes, Clinical and Laboratory Standards Institute (CLSI) and European Committee for Antimicrobial Susceptibility Testing (EUCAST) methods, the problem of comparing differently derived sets of antimicrobial susceptibility testing (AST) data with each other arises, owing to a scarcity of knowledge of inter-method comparability. The purpose of the current study was to determine the comparability of CLSI, EUCAST and Stokes AST methods for determining susceptibility of uropathogenic Escherichia coli to ampicillin, amoxicillin-clavulanate, trimethoprim, cephradine/cephalexin, ciprofloxacin and nitrofurantoin. METHODS: A total of 100 E. coli isolates were obtained from boric acid urine samples from patients attending GP surgeries. For EUCAST and CLSI, the Kirby-Bauer disc diffusion method was used and results interpreted using the respective breakpoint guidelines. For the Stokes method, direct susceptibility testing was performed on the urine samples. RESULTS: The lowest levels of agreement were for amoxicillin-clavulanate (60%) and ciprofloxacin (89%) between the three AST methods, when using 2017 interpretive guidelines for CLSI and EUCAST. A comparison of EUCAST and CLSI without Stokes showed 82% agreement for amoxicillin-clavulanate and 94% agreement for ciprofloxacin. Discrepancies were compounded by varying breakpoint susceptibility guidelines issued during the period 2011-2017, and through the inclusion of a definition of intermediate susceptibility in some cases. CONCLUSIONS: Our data indicate that the discrepancies generated through using different AST methods and different interpretive guidelines may result in confusion and inaccuracy when prescribing treatment for urinary tract infection.

Application and assessment of cloacin typing of Enterobacter cloacae.

Three methods, O-serotyping, phage typing and susceptibility to bacteriocins, were used to type 357 clinical isolates of Enterobacter cloacae cultured from 219 patients. One hundred and sixty isolates were typed by serology and phage typing. When these two methods were used, primary classification of isolates was based on serology (65.7% typable) and phage typing for further subdivision (94.1% typable). When all the isolates were typed by cloacin susceptibility, 81.5% of them were typable. Maximum discrimination between cultures was achieved when the three methods were used together; no single method was sufficiently discriminatory. There was a close parallel between serotyping and bacteriocin lysis pattern. The latter was easy to perform and the results were achieved within 48 h. By applying this typing system two episodes of cross-infection were identified in a haematology/oncology unit and intensive care unit.