Ninth CRL-Salmonella interlaboratory comparison study (2004) on typing of Salmonella spp

Abstract

The ninth interlaboratory comparison study on the typing of Salmonella was organised by the Community Reference Laboratory for Salmonella (CRL-Salmonella, Bilthoven, the Netherlands) in collaboration with the Health Protection Agency (HPA, London, United Kingdom) and the Central Institute for Animal Disease Control (CIDC, Lelystad, the Netherlands) in spring 2004. Twenty-five National Reference Laboratories for Salmonella (NRLs-Salmonella) including Norway and Candidate Country Romania and eighteen Enter-Net Laboratories (ENLs) participated in the study. In total, 20 strains of the species Salmonella enterica subspecies enterica were selected for serotyping. Ten strains of Salmonella Enteritidis (SE) and 10 strains of Salmonella Typhimurium (STM) were selected for phage typing. Ten strains of Salmonella spp. were selected for antimicrobial susceptibility testing. In general, no problems were encountered with the typing of the O-antigens. Some laboratories had problems with typing of the H-antigens. Many problems occurred with the distinction between S. Banana and S. California. Ninety-eight percent of all participating laboratories were able to correctly type the O-antigens. The H-antigens were typed correctly by 90 % of the NRLs and by 96 % of the ENLs. Ninety percent of the NRLs and 95 % of the ENLs indicated correct serovar names for the 20 serotyping strains. The phage typing of some of the Salmonella Enteritidis strains caused problems for the NRLs as well as for the ENLs. Most laboratories performed the antimicrobial susceptibility testingtowards a panel of fourteen antibiotics. Some problems occurred with the interpretation of the results obtained with antibiotics amoxicillin-clavanulate and trimethoprim/sulphamethoxazole. This study demonstrated that less deviating results were produced by Minimal Inhibition Concentration determinations than by disc diffusion.