Raw milk and traditional fermented foods such as artisanal cheese represent a natural source of lactic acid bacteria (LAB). They can produce antimicrobial compounds, such as bacteriocins and lactic acid, which may be exploited in dairy biopreservation. This study aimed to conduct a systematic review and meta-analysis to synthesize the inhibition diameter (ID) of LAB against L. monocytogenes, S. aureus, and Salmonella spp. Literature electronic searches were performed on PubMed, Scopus, and Web of Science, to identify articles that reported data on in-vitro antimicrobial activity by LAB isolated from dairy foods. A total of 1665 papers were retrieved, and 20 primary studies were selected according to the selection criteria, of which 397 observations were extracted. Random-effects meta-regression models were employed to describe the effects of LAB genus, pathogen concentration, susceptibility method, incubation time, inoculation volume, agar type and pH on the IDs for L. monocytogens, S. aureus, and Salmonella spp. L. monocytogens was the most susceptible pathogen (p < 0.05) to the LAB effects, followed by S. aureus and Salmonella spp. As a whole, LAB from the Lacticaseibacillus genus were the most effective (p < 0.05) in inhibiting L. monocytogens (21.49 ± 2.654 mm), followed by S. aureus (21.06 ± 2.056 mm). Salmonella spp. presented higher (p < 0.05) susceptibility to Lactobacillus genus (19.93 ± 2.456 mm). From the results, a general trend could be observed for the well-diffusion method to produce higher (p < 0.05) ID estimates than the spot and disk methods (30.73 ± 2.530 mm vs. 21.98 ± 1.309 mm vs. 13.39 ± 1.403 mm for L. monocytogenes; 22.37 ± 1.073 mm vs. 14.91 ± 2.312 mm vs. 20.30 ± 2.319 mm for Salmonella spp.), respectively. Among the tested moderators, the pathogen’s inoculum concentration, the in vitro susceptibility assay itself, incubation time and inoculation volume on agar are determinant parameters to be looked at when designing a robust and reproducible experimental plan. The in vitro results reinforced that LAB can be useful in controlling the development of pathogenic bacteria frequently found in the dairy industry.

Previous research showed that three strains of lactic acid bacteria (LAB)—Leuconostoc mesenteroides, Lacticaseibacillus paracasei and Loigolactobacillus coryniformis—exhibited in vitro anti-listerial activity. The objectives of the present study was: (1) to determine whether the initial pH of heat-treated reconstituted milk affects the growth of Listeria monocytogenes, in monoculture and coculture with each of the LAB strains; and (2) to compare the capacity of the LAB strains to inhibit L. monocytogenes in the milk model. Monoculture and coculture challenge tests were conducted in milk adjusted to three initial pH levels of 5.5, 6.0, and 6.5. A pH-driven model and a Jameson-effect model were fitted to the growth curves. The former provided more precise estimates than the latter. In monoculture, L. mesenteroides exhibited the fastest development at all initial pH levels whereas, in coculture, this strain more effectively controlled L. monocytogenes by reducing its growth rates. As the initial milk pH increased, the maximum concentration of L. monocytogenes in monoculture and in coculture also increased, although the LAB strains were all able to reduce the pathogen’s maximum concentration. These findings demonstrated that adjusting milk to a more acidic pH before fermentation provides an additional barrier against the development of L. monocytogenes.

This systematic review and meta-analysis compile the in vitro antimicrobial efficacy of lactic acid bacteria (LAB) supernatants against three common pathogenic bacteria found in dairy products: Salmonella spp., L. monocytogenes, and Staphylococcus aureus. After screening and analysis of full papers, identified by searches in PubMed, Scopus, and Web of Science databases, thirty-nine studies were regarded as relevant, and a total of 510 observations were recorded. The effects of moderators on inhibition diameters were assessed by adjusting three pathogen-specific meta-regression models. Results showed that, in general terms, strains from the Enterococcus genus displayed the highest inhibition values against L. monocytogenes (15.90 ± 2.138 mm), whereas Lacticaseibacillus strains were more effective against S. aureus (11.89 ± 0.573 mm). The well diffusion test outperformed the spot and disk diffusion tests, and more acidic LAB supernatants resulted in higher measurements of inhibition diameters (p < 0.001). Meta-regression models incorporating LAB genus, pathogen concentration, and incubation time explained 33.8%, 52.3%, and 19.8% of the total variance in inhibition diameters for L. monocytogenes, Salmonella spp., and S. aureus, respectively. None of the three models showed evidence of publication bias. This meta-regression study demonstrated that LAB strains present in dairy products possess a variable capacity to inhibit any of the three foodborne pathogens. Overall, L. monocytogenes was found to exhibit greater susceptibility than Salmonella spp. and S. aureus; thus, the antilisterial capacity of the selected LAB strains could be exploited in developing biocontrol strategies for cheese-making.

Previous research showed that a strain of Leuconostoc mesenteroides, isolated from goat’s raw milk cheese, was effective in slowing down the growth and reducing the maximum concentration of L. monocytogenes when evaluated in a milk model; furthermore, the extent of inhibition was dependent on the milk’s initial pH. The objectives of this study were as follows: (1) to determine whether the growth of L. monocytogenes in goat’s pasteurized milk cheese during maturation could be approximated from growth data obtained in the milk model medium, either in monoculture or in coculture with L. mesenteroides, and if so, (2) to model a milk-to-cheese conversion factor (Cf) for L. monocytogenes growth rate. Challenge tests were conducted by inoculating L. monocytogenes in monoculture and in coculture with L. mesenteroides in goat’s pasteurized milk adjusted at initial pH levels of 5.5, 6.0, and 6.5. The process of cheesemaking continued, and cheeses were ripened at 12 °C for 12 days. Each experimental growth curve was adjusted to a pH-driven dynamic model where the microbial maximum growth rate is a function of pH. As observed in the milk model medium, in coculture with L. mesenteroides, the optimum growth rate (μ_opt) of L. monocytogenes in maturing cheese was affected by the initial pH of milk: the lowest rate of 0.863 ± 0.042 day⁻¹ was obtained at the initial pH 5.5, in comparison to 1.239 ± 0.208 and 1.038 ± 0.308 day⁻¹ at pH 6.0 and 6.5, respectively. Regardless of the milk’s initial pH, L. mesenteroides did not reduce the maximum load of L. monocytogenes in maturing cheeses, as it did in the milk medium. On the contrary, at the milk’s initial pH of 5.5, 6.0, and 6.5, L. mesenteroides was able to decrease, on average, 2.2-fold, 1.5-fold, and 1.9-fold the μ_opt of L. monocytogenes in both milk medium and cheese, without significant differences between matrices. Following such validation in goat’s cheese, the square root of milk-to-cheese Cf for L. monocytogenes was estimated as 0.751 (SE = 0.0108), and the type of culture (monoculture and coculture) was not found to affect Cf (p = 0.320). In conclusion, this work validated the pre-acidification of milk as an efficient strategy that, when combined with the use of a protective culture, can synergically enhance the control of L. monocytogenes in cheese.

Previous research showed that strains of three lactic acid bacteria (LAB) isolated from goat’s raw milk cheeses – Leuconostoc mesenteroides, Lacticaseibacillus paracasei and Loigolactobacillus coryniformis – exhibited promising antilisterial activity and acidification properties. The objectives of the present study was twofold: (1) to determine whether the initial pH of heat-treated reconstituted milk (HTRM, as a fermenting milk model medium to produce cheese) affects the growth kinetics of Listeria monocytogenes, in monoculture and coculture with each of the LAB strains; and (2) to quantify and compare the capacity of the LAB strains to inhibit L. monocytogenes in the same milk model. Challenge tests were conducted in HTRM adjusted to three initial pH levels of 5.5, 6.0, and 6.5, inoculating L. monocytogenes in monoculture, and each of the LAB strains in monoculture and in coculture with the pathogen. Milk samples were incubated at 12ºC during 8 days to track population changes during fermentation. A pH-driven dynamic growth model was fitted to all monoculture and coculture growth curves; and, in addition, a Jameson-effect model to all coculture growth curves. Although both models described well the growth kinetics; the pH-driven dynamic model mostly rendered better goodness-of-fit statistics and hence higher precision for the kinetic parameters. In monoculture, L. mesenteroides consistently exhibited the highest growth rates and maximum concentrations in milk at all initial pH levels. Similarly, in coculture, this strain more effectively controlled L. monocytogenes by reducing its growth rates (day^-1) from 3.201 ± 0.045, 3.416 ± 0.177, and 3.432 ± 0.073 at initial pHs 5.5, 6.0 and 6.5, to 1.469 ± 0.205, 2.293 ± 0.284, and 1.552 ± 0.132, respectively. Furthermore, as the initial milk pH increased, the maximum concentration of L. monocytogenes in monoculture and in coculture also increased, although the three LAB strains were able to reduce the maximum concentration of L. monocytogenes at all pH values (p < 0.01). These findings indicate that, among the three tested LAB strains, L. mesenteroides is the most efficient in slowing down the growth and decreasing the maximum load of L. monocytogenes in fermenting milk, although for all LAB strains, it was demonstrated that the initial pH of milk has an effect on the extent of inhibition of L. monocytogenes. Thus, adjusting milk to a more acidic pH before fermentation has a synergistic effect with the addition of lactic acid bacteria on the control of L. monocytogenes.

This systematic review and meta-analysis compile the in vitro antimicrobial efficacy of lactic acid bacteria (LAB) supernatant against three common dairy product pathogenic bacteria. After screening and analysis of full papers, identified by searches in PubMed, Scopus, and Web of Science databases, thirty-nine studies were regarded as relevant, and a total of 510 were extracted thereof. The effects of moderators, namely, pathogen’s concentration, susceptibility test method, agar type, incubation time and temperature, LAB supernatant pH and aliquot volume, on inhibition diameters were assessed by adjusting three pathogen-specific meta-regression models. Results showed that, in general terms, strains from the Enterococcus genus (15.90 ± 2.138 mm) displayed the highest inhibition values against L. monocytogenes, whereas Lacticaseibacillus strains were more effective against Staphylococcus aureus (11.89 ± 0.573 mm). Whereas the well diffusion test outperformed spot and disk diffusion tests; the pH of LAB supernatant resulted in high measurements of inhibition diameters (p