Technological characterisation, antibiotic susceptibility and antimicrobial activity of wild-type Leuconostoc strains isolated from north Italian traditional cheeses

Genotypic and technological properties, antibiotic susceptibility and antimicrobial activity of 35 Leuconostoc strains, isolated from different Italian raw milk cheeses, were investigated. RAPD-PCR was used to study genetic variability and to distinguish closely related strains. The results showed a high degree of heterogeneity among isolates. All the strains had weak acidifying activity and showed low proteolytic and lipolytic activities. Reduction activity, was generally low. All the Leuconostoc were susceptible to ampicillin, mupirocin, erythromycin, quinupristin/dalfopristin and tetracycline. Many strains were classified as resistant to oxacillin, ciprofloxacin and nitrofurantonin, while all isolates were found resistant to vancomycin. PCR-based detection did not identify any of the common genetic determinants for vancomycin (vanA, vanB, vanC1, vanC2, vanC3, vanD, vanE, vanG) or erythromycin (ermB and ermC). Tetracycline resistance genes were detected in 25 tetracycline susceptible strains, the most frequent one being tetM. One strain, belonging to Ln. pseudomesenteroides species, was positive for the presence of the int gene of the Tn916/Tn1545 trasposon family. This is the first time the conjugative transposon Tn916 has been detected inside the Leuconostoc species. All strains showed antimicrobial ctivity against Enterococcus faecalis and Ent. faecium. The presence of genes encoding amino-acid decarboxylases (hdc and tdc) was not detected. Some strains are interesting in view of their use in cheese production as starter and non starter cultures.