Antibiotic resistance and microbial composition along the manufacturing process of Mozzarella di Bufala Campana.
The use of antibiotics as growth promoters in livestock, banned in all EU member states in January 2006, has led to selection of antibiotic resistant strains within environmental bacteria, including gram-positive, non pathogenic bacteria that colonize the GI tract of humans and animals. In Italy and in other Mediterranean countries, fermented foods employing environmental bacteria pre-existing in the raw substrates, rather than industrial starters of defined genotype, represent a significant proportion of cheese and meat products carrying the official PDO designation (Protected Designation of Origin). Our study focused on the microbiological and molecular analysis of lactobacilli and of other lactic acid bacteria (LABs) isolated from the Italian PDO product water buffalo Mozzarella cheese, with the aim of identifying genes responsible for tetracycline, erythromycin and kanamycin resistance. We isolated over 500 LAB colonies from retail products, as well as from raw milk and natural whey starters employed in their production. Microbiological analysis showed that about 50% of these isolates were represented by lactobacilli, which were further characterized in terms of species and strain composition, as well as by determining phenotypic and genotypic antibiotic resistance. To overcome the limits of culture-dependent approaches that select only cultivable species, we have also extracted total DNA from the whole microbiome present in the cheese and investigated the presence of specific antibiotic resistance genes with molecular approaches. Genetic determinants of antibiotic resistance were identified almost exclusively in bacteria isolated from the raw, unprocessed substrates, while the final, marketed products did not contain phenotypically resistant lactobacilli, i.e. displaying MIC values above the microbiological breakpoint. Overall, our results suggest that the traditional procedures necessary for manufacturing of this typical cheese, such as high temperature treatments, lead to a final product with low bacterial counts, lower biodiversity and lack of significant presence of antibiotic resistant lactobacilli.
Devirgiliis
Chiara
C
INRAN-National Research Institute on Food & Nutrition, Via Ardeatina 546, 00178 Roma, Italy.
Caravelli
Antonella
A
Coppola
Doriana
D
Barile
Simona
S
Perozzi
Giuditta
G
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000009:adverse effects; D015373:Bacterial Typing Techniques / Q000379:methods; D044822:Biodiversity; D002020:Buffaloes; D002611:Cheese / Q000382:microbiology*; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D016172:DNA Fingerprinting / Q000379:methods; D004269:DNA, Bacterial / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005838:Genotype; D006801:Humans; D007778:Lactobacillus / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D008892:Milk / Q000382:microbiology*; D010641:Phenotype; D013045:Species Specificity
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial