Preparation of qualitative reference strains for antibiotic susceptibility determination of foodborne pathogens

Abstract

ObjectiveBased on the fact that the quality control bacteria used for bacterial drug sensitivity determination are commonly sensitive to antibiotics, while most foodborne pathogens isolated in China are relatively tolerant to these antibiotics, the concentration range of antibiotics used for antimicrobial sensitivity test is very wide, which resulting in antibiotic wastes and inaccurate test result.MethodsIn this study, five standard samples with clear minimum inhibitory concentration (MIC) were successfully developed for sensitivity test of common antibiotics(streptomycin, gentamicin, chloramphenicol, cefoxitin and ampicillin). Agar dilution and microbroth dilution method were respectively used to determine the susceptibility of isolates to the antibiotics, the reference strains were developed via vacuum freeze-drying.ResultsThe reference strains with clear MICs assignment of streptomycin, gentamicin, chloramphenicol, cefoxitin and ampicillin were developed respectively. The antibiotic susceptibility of the reference strains was genetically stable, and the uniform and storage stability of them were good. When stored at 37 ℃ for 13 d, 4 ℃ for 90 d and -80 ℃ for 360 d, respectively, the viable bacteria number basically remained above 105 CFU/vial. All confirmed antibiotic resistance phenotypes could be detected, and the MICs value of the certain antibiotics did not show apparent fluctuation or drift.ConclusionThe development of reference strains that in line with the characteristics of drug resistance of foodborne pathogens in China with clear MICs assignment to certain antibiotics would help to enrich the types of reference strains in China, and further strengthen the monitoring of drug-resistant bacteria to ensure food safety and public health.

Keywords

• reference strain
• antibiotic susceptibility
• uniformity
• storage stability