SUSCEPTIBILITY TESTING OF KLEBSIELLA SPP - AN INTERNATIONAL COLLABORATIVE STUDY IN QUALITY ASSESSMENT

In order to compare the prevalence of antibiotic resistance in differe nt geographical areas, it is necessary to ensure agreement between lab oratories on the assignment of strains to 'susceptible' and 'resistant ' categories. An international quality assessment was performed to inv estigate the performance of susceptibility testing of Klebsiella spp. Ninety-five strains of klebsiellae were selected from clinical isolate s at the London Hospital Medical College (LHMC). These included strain s with a diversity of susceptibility profiles to amoxycillin/clavulana te, piperacillin, ceftazidime, cefuroxime, ciprofloxacin, gentamicin a nd trimethoprim. The strains were sent to 13 participating laboratorie s in Europe and the USA and laboratories were asked to test the suscep tibility of these strains to these antibiotics by their usual methods. They were also asked to provide details of the method used to test su sceptibility. Several different standard recommended testing methods w ere 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 an d ciprofloxacin, as well as the assignment of susceptibility and resis tance to piperacillin and amoxycillin/clavulanate. Some discrepancies could be attributed to the use of different breakpoints, leading to di ffering assignment of susceptibility. Methodological variations includ ing disc content, inoculum and failure to measure and interpret zone s izes consistently also led to anomalies. This quality assessment progr amme has helped to identify problems in susceptibility testing which s hould be investigated further.