Frequent major errors in antimicrobial susceptibility testing of bacterial strains distributed under the Deutsches Krebsforschungszentrum Quality Assurance Program

Abstract

The Quality Assurance Program (QAP) of the Deutsches Krebsforschungszentrum (DKFZ) was a proficiency testing system developed to service the laboratory animal discipline. The QAP comprised the distribution of bacterial strains from various species of animals for identification to species level and antibiotic susceptibility testing (AST). Identification capabilities were below acceptable standards. This study evaluated AST results using the DKFZ compilations of test results for all bacterial strains showing the number of participants reporting the strain as resistant (R), sensitive (S) or intermediate susceptible (I) to each antibiotic substance used. Due to lack of information about methods used, it was assumed that what the majority of the participants reported (R or S) was the correct test result and that an opposite result was a major error (ME). MEs occurred in 1375 of 14,258 (9.7%) of test results and ME% ranged from 0% to 23.2% per bacterial group–agent group combination. Considerable variation in MEs was found within groups of bacteria and within groups of agents. In addition to poor performance in proper species classification, the quality of AST in laboratory animal diagnostic laboratories seems far below standards considered acceptable in human diagnostic microbiology.

Testing the efficacy of Mueller Hinton agar over Nutrient agar for optimal antibiotic sensitivity testing response by selected clinical bacterial pathogens

“…Common sources of error encountered in clinical Microbiology laboratory which may compromise the reliability and accuracy of AST results include improper disc storage, inoculum not properly adjusted (being too light or too heavy), incubation temperature deviating from 35-37 o C, use of an increased CO2 atmosphere, reading plates before or after 16-18hrs incubation, transcribing errors, reader error when measuring zone diameters, deterioration of the McFarland turbidity standard and contamination or mutation in the control strains [20].…”