Anti-listerial activity of lactic acid bacteria isolated from artisanal cheeses produced in the State of Minas Gerais, Brazil
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Introduction: Brazilian artisanal cheeses, among them Minas cheeses, are highly appreciated by consumers. Nonetheless, some cheeses have
been regularly found to harbour high-risk pathogens, such as Listeria monocytogenes, mainly arising from their elaboration with raw milk and informal
production. However, cheese matrices are complex systems whose microbial competing factors (i.e., indigenous lactic acid bacteria (LAB)) and intrinsic
properties (acidity, temperature, and water activity) can act as effective hurdles against L. monocytogenes proliferation.
Purpose: The aim of this study was to evaluate the capacity of LAB strains isolated from Minas artisanal cheeses as anti-listerial agents.
Methods: A total of 891 LAB strains were isolated from 244 Minas artisanal cheese samples (466 using MRS agar (MRSLAB) and 425 using M17 agar
(M17LAB)), which were tested qualitatively for anti-listerial activity by the deferred antagonism assay at 30oC (24 h). Two L. monocytogenes strains,
serotypes 1/2b and 4b, isolated from cheese and crude milk, respectively, were used. LAB strains with positive anti-listerial activity at 30oC were further
tested at 7oC (10 days).
Results: MRSLAB strains presented significantly better anti-listerial activity at 30oC (73.0% and 70.8% for serotypes 1/2b and 4b, respectively) compared
to M17LAB strains (21.2% and 23.1%, respectively), and there was no significant difference between listeria serotypes (P<0.05). Selected MRSLAB
and M17LAB strains were able to keep anti-listerial activity at 7oC, with no significant differences between MRSLAB (96.8% and 97.2% for listeria 1/2b
and 4b, respectively) and M17LAB (95.2% and 96.8%, respectively) or between Listeria serotypes (P<0.05).
Significance: These results suggested that LAB isolated from Minas cheeses using MRS agar present a better inhibitory effect against L. monocytogenes
at different temperatures. These strains can be used as starter cultures in order to inhibit pathogen survival.
