Antimicrobial susceptibility and proposed microbiological cut-off Values of lactobacilli by phenotypic determination

Summary

This article summarizes published and unpublished data of antibiotic resistances in strains (n = 675) of fourteen Lactobacillus species. Minimum inhibitory concentrations (MICs) were determined against antibiotics representing different classes, namely ampicillin (penicillins), tetracycline (tetracyclines), gentamicin and streptomycin (aminoglycosides), and erythromycin and clindamycin (macrolide-lincosamide-and streptogramin B group, MLSB).The Lactobacillus species under study included the L. delbrueckii group (n = 218), L. plantarum (n = 121), L. sakei (n = 83), L. rhamnosus (n = 75), L. paracasei (n = 66, including one L. casei), L. reuteri (n = 56) and L. fermentum (n = 56). The strains were of human, animal and food origin. The MICs were determined with microdilution and/or Etest methods using LSM (Lactic acid bacteria susceptibility test medium) agar and broth. In general, the results obtained with the microdilution method were one or two dilution steps higher than with the E-test. Accordingly, tentative microbiological cut-off values are given separately according to the method and species used. A vast majority of the strains were phenotypically susceptible to ampicillin and erythromycin, whereas many species showed a wide range of MICs for tetracycline. A broad range in distribution of MICs was also observed with aminoglycosides and clindamycin, especially in L. plantarum.