Susceptibility testing of Klebsiella spp.--an international collaborative study in quality assessment

Abstract

In order to compare the prevalence of antibiotic resistance in different geographical areas, it is necessary to ensure agreement between laboratories on the assignment of strains to 'susceptible' and 'resistant' categories. An international quality assessment was performed to investigate the performance of susceptibility testing of Klebsiella spp. Ninety-five strains of klebsiellae were selected from clinical isolates at the London Hospital Medical College (LHMC). These included strains with a diversity of susceptibility profiles to amoxycillin/clavulanate, piperacillin, ceftazidime, cefuroxime, ciprofloxacin, gentamicin and trimethoprim. The strains were sent to 13 participating laboratories in Europe and the USA and laboratories were asked to test the susceptibility of these strains to these antibiotics by their usual methods. They were also asked to provide details of the method used to test susceptibility. Several different standard recommended testing methods were used. Reporting of susceptibilities was generally accurate, but a number of anomalies were noted. Discrepancies of reporting between the LHMC and the participating laboratories was more marked for resistant strains, particularly in the detection of resistance to cefuroxime and ciprofloxacin, as well as the assignment of susceptibility and resistance to piperacillin and amoxycillin/clavulanate. Some discrepancies could be attributed to the use of different breakpoints, leading to differing assignment of susceptibility. Methodological variations including disc content, inoculum and failure to measure and interpret zone sizes consistently also led to anomalies. This quality assessment programme has helped to identify problems in susceptibility testing which should be investigated further.

Setting interpretive breakpoints for antimicrobial susceptibility testing using disk diffusion

“…Manninen et al [20] in Finland analysed E. coli and Staphylococcus aureus resistance data before and after a change of the standard and concluded that the interlaboratory variation called for laboratory-specific interpretive breakpoints. The problem of interlaboratory variation has not been adequately dealt with by any reference authority and calls for further analysis and action [19,21,22]. Laboratories that measure and save their quantitative measurements, be they MIC values or inhibition zone diameters, are better equipped to compare data over time, to compare with other laboratories and to prove the validity of results in general and resistance surveillance trends in particular.…”

Effects of chlorine, peracetic acid and low-pressure ultra violet light on antibiotic resistant E. coli isolates with regards to their survival and changes in their antibiotic resistance profiles

“…Other disadvantages of this method include the tedious preparation of the antibiotic solutions for each test, the high chance of errors in preparing the antibiotic solutions, and large number of reagents required (Jenks et al, 1998). The advantage is that this method does provide a quantitative result in the MIC, but it is harder to observe subtle changes in antibiotic resistance profiles using this method.…”