Lactic acid bacteria (LAB), and in particular, Lactococcus lactis species, are the main components of the mesophilic starter cultures for cheesemaking, being responsible for the sensory attributes of cheeses. This research topic seeks to provide LAB strains to standardize cheesemaking while keeping the identity of artisanal cheeses. For this purpose, the screening and selection of wild LAB with specific technological activities have been approached. Regarding this, a wide collection of LAB isolated from raw milk cheeses is available. Likewise, an autochthonous mixed starter for Afuega’l Pitu cheese was designed and its production in biorreactors optimized. Nowadays, the response mechanisms to stress conditions, which are inherent to the technological processes, are being examined in order to select robust strains and, consequently, with enhanced technological aptitudes.
Lactococcus lactis cells under the scanning electron microscope
|Biotechnology of bacteriocins|
Bacteriocins are antimicrobial peptides synthesized by bacteria, Bacteriocins produced by LAB are biotechnologically relevant because they contribute to improve the hygienic quality of feremented foods due to their ability to inhibit the growth of undesirable microorganisms. The DairySafe team has approached the design of protective-starter cultures which are able to lead milk fermentation while reducing the levels of undesirable microbiota and the risk of foodborne diseases.
In addition, bacteriocins provide novel molecular structures with potent antimicrobial activity, along with unique modes of action different to those of traditional antibiotics. In this context, we are studying the mode of action of lactococcin 972 (Lcn972), a bacteriocin that exclusively targets other lactococci and inhibits cell wall biosynthesis when cells are dividing. Our main goal is to determine the molecular basis of its mode of action to pave the way towards species-specific antimicrobials for clinical and/or food applications.
Detection of the antimicrobial activity of bacteriocins by the agar diffusion test
In this research topic, we study bacteriophages and phage lytic enzymes as novel biocontrol agents to inhibit the growth of pathogens throughout the food chain. Bacteriophages are viruses that exclusively infect bacteria and often lead to cell lysis. The bacteriophage’s DNA also encodes enzymes able to degrade the peptidoglycan and other bacterial structures, resulting in bacterial death. Of note, the phage specificity allows the selective removal of undesirable bacteria without affecting the endogenous microbiota of particular environments. Our team has pioneered the use of bacteriophages and their lytic enzymes (endolysins and peptidoglycan hydrolases) to inhibit S. aureus in milk and cheese, along with their combined use with bacteriocins (hurdle technology).
This biocontrol strategy is currently implemented to disrupt biofilms (bacterial structures highly resistant to antimicrobials and disinfectants). Besides phages and endolysins, exopolysaccharide depolymerases synthesized by some phages seem to play an important role in removing biofilms.
The Staphylococcus aureus bacteriophage vB_SauM_phiIPLA-RODI under the transmission electron microscope