Antibiotic resistance of lactobacilli isolated from two Italian hard cheeses

One hundred forty-one lactobacilli strains isolated from natural whey starter cultures and ripened Grana Padano and Parmigiano Reggiano cheeses were tested for their susceptibility to 13 antibiotics, in particular, penicillin G, ampicillin, amoxicillin, oxacillin, cephalotin, cefuroxime, vancomycin, gentamicin, tetracycline, erythromycin, clindamycin, co-trimoxazole, and nitrofurantoin. The strains belonged to the species Lactobacillus helveticus, L. delbrueckii subsp. lactis, L. rhamnosus, and L. casei. The strains of the first two species were isolated from whey starter cultures, and the strains of the last two species were from the ripened cheeses. Significant differences among the strains in their antibiotic resistance were found in relation to the type of cheese and, especially, the strains from Parmigiano Reggiano were more resistant to gentamicin and penicillin G. The strains isolated in the ripened cheese were generally more resistant than those isolated from natural whey starter cultures; in particular, significant differences regarding oxacillin, vancomycin, cephalotin, and co-trimoxazole were observed. Finally, no significant difference in relation to the type of cheese was found among the thermophilic lactobacilli isolated from whey cultures, while the facultatively heterofermentative lactobacilli isolated from Parmigiano Reggiano showed higher resistance toward gentamicin and penicillin G than did the same species isolated from Grana Padano.