Antibiotic survey ofLactococcus lactisstrains to six antibiotics by Etest, and establishment of new susceptibility-resistance cut-off values

Abstract

In order to establish cut-off values for Lactococcus lactis to six antibiotics to distinguish susceptible and intrinsically resistant strains from those having acquired resistances, the minimum inhibitory concentration (MIC) of tetracycline, erythromycin, clindamycin, streptomycin, chloramphenicol and vancomycin was determined in 93 different Lc. lactis strains using the Etest. These bacterial strains were originally isolated from dairy and animal sources in widely separated geographical locations. Cut-offs were defined on the basis of the distribution of the MICs frequency of the studied antibiotics, which in the absence of acquired determinants should approach to a normal statistical distribution. In general, the new cut-off values proposed in this study are higher than previously defined (European Commission, 2005. The EFSA Journal 223, 1-12). Based on these new values, all the strains tested were susceptible to erythromycin, chloramphenicol and vancomycin, and 79 susceptible to all six antibiotics. However, 11 strains (around 12%) were considered resistant to tetracycline (six of which had been identified after screening of a large collection of lactococci strains for tetracycline resistance) and five (5.4%) resistant to streptomycin. Of these, two fish isolates proved to be resistance to both tetracycline and streptomycin. From the tetracycline resistant strains, tet(M) and mosaic tet(L/S) genes were amplified by PCR, demonstrating they harboured acquired antibiotic resistance determinants.

Safety assessment, genetic relatedness and bacteriocin activity of potential probiotic Lactococcus lactis strains from rainbow trout (Oncorhynchus mykiss, Walbaum) and rearing environment

“…Our results revealed a high incidence (40 %) of L. lactis strains showing acquired (multi)resistance to tetracycline, streptomycin, kanamycin clindamycin, vancomycin and gentamicin. The resistance to tetracycline has been previously found in L. lactis from bovine milk and derived products, and it has been associated with the common use of this antibiotic for the treatment of bovine infections [20,41]. The phenotypic resistance to clindamycin was previously described in three strains of L. lactis isolated from raw milk [40].…”

Intra- and Interspecies Conjugal Transfer of Tn 916 -Like Elements from Lactococcus lactis In Vitro and In Vivo

“…The MIC for streptomycin for the L. lactis Bu2-60 recipient strain and its transconjugants was 1,024 g/ml. Both recipient types, lactococcal and enterococcal, were susceptible to tetracycline, and the MIC was Ͻ1 g/ml (18). In vivo conjugation experiments in germfree rats.…”

“…Nevertheless, many investigators have recently speculated that commensal bacteria, including lactic acid bacteria (LAB), may act as reservoirs of antibiotic resistance determinants (40). Genes conferring acquired resistance to tetracycline, erythromycin, and vancomycin have been detected and characterized for Lactococcus, Enterococcus, and Lactobacillus species isolated from fermented meat and milk products (13,18,23,49,50,56). Introduction of such bacteria into humans through ingestion of commercial food products may have negative consequences by dissemination of antibiotic resistance genes via the food chain to the resident microbiota of the human gastrointestinal tract and, in the worst case, to pathogenic bacteria (4,17,55).…”

Influence of Selected Per Orally Administered ATB on Microflora of GIT in Experimental Animals

“…This method is particularly useful in the study of the efect of probiotics, which are often required to identify probiotic bacteria of the commensal microlora [17]. Recently it was reported that the simultaneous use of ATB and supportive probiotic therapy, which can help to restore intestinal microbiota, can also expand the antibiotic resistance of bacterial intestinal bacteria [18,19].…”