Antibacterial activity of lactic acid bacteria against spoilage and pathogenic bacteria isolated from the same meat small-scale facility

The background microbiota and sanitization agent drive the fate of Listeria monocytogenes in multispecies biofilms formed on a plasma-polymerized coating applied on stainless steel

The present study evaluates the anti-biofilm activity of a coating applied with an atmospheric-pressure plasma jet system on AISI 316 stainless steel (SS) against multispecies biofilms containing Listeria monocytogenes (using background microbiota from three different meat industries) using culture-dependent and culture-independent approaches. Also, the disinfection effectiveness and biofilm evolution after sanitization with two food industry biocides were assessed. The anti-biofilm activity of the coating against L. monocytogenes, observed on mono-species biofilms (p < 0.05), was lost on the multispecies biofilms developed for 7 days at 12 °C (p > 0.05), with L. monocytogenes counts ranging from 5.5 ± 0.7 to 6.1 ± 0.5 CFU/cm² on the uncoated SS and from 4.4 ± 0.2 to 6.4 ± 0.5 CFU/cm² on the coated SS. The taxonomic composition of the formed biofilms was highly dependent on the industry but not affected by the artificial inoculation with L. monocytogenes and the nature of the surface (coated vs uncoated SS). When L. monocytogenes was artificially inoculated, its growth was partially controlled in the biofilms developed, with the magnitude of this effect being lower (p < 0.05 on coated SS) for the industry with the lowest taxonomy richness and diversity (3.8 ± 0.2 CFU/cm²), as compared the other two sampled industries (2.4 ± 0.4 and 1.6 ± 0.2 CFU/cm²). The 15-min disinfection treatments with either sodium hypochlorite or peracetic acid at 0.5 % resulted in total viable and L. monocytogenes counts below the limit of detection in most cases, immediately after treatment. The subsequent incubation of the sanitized plates for another 7 days at 12 °C in fresh BHI media led to the development of biofilms with lower bacterial richness and alpha diversity, and higher beta diversity. Even though sodium hypochlorite was in general slightly less effective than peracetic acid immediately after application, it caused a stronger growth control (p < 0.05) of the naturally present L. monocytogenes on the multispecies biofilms developed. This finding highlights the importance of understanding the interspecific competitive relationships between the members of the background microbiota and L. monocytogenes for the long-term control of this pathogen in food processing facilities.

Isolation and Characterization of Competitive Exclusion Microorganisms from Animal Wastes-Based Composts against Listeria monocytogenes

AIM

To isolate the slow-growing or viable but non-culturable competitive exclusion (CE) microorganisms from composts and then verify the anti-Listeria monocytogenes activities of those CE isolates in compost.

METHODS AND RESULTS

CE strains were isolated from composts using double- or triple-layer agar methods, purified, and then characterized. Both compost extracts and solid compost samples were spiked with a cocktail of 3 L. monocytogenes strains which were co-inoculated with or without CE strain cocktail and incubated at both 22°C and 35°C for 168 h. Results indicated that the addition of resuscitation promoting factor (Rpf) promoted the growth of slow-growing species from composts. About 50% of the isolated CE strains (n=40) were identified as Bacillus spp., 17 strains can inhibit more than ten tested L. monocytogenes strains, and 9 strains were motile and competitive biofilm formers. In compost extracts, the growth potentials of L. monocytogenes were reduced up to 2.2 logs when co-culturing with CE strains. In compost samples, the addition of CE strains reduced L. monocytogenes population by ca. 1.3 log CFU/g at 22°C after 24 to 168 h incubation.

CONCLUSION

Our modified double/triple-layer agar procedure with Rpf as growth supplement coupled with spot-on-lawn testing can be a quick and efficient method for isolating CE candidates from composts. The efficacy of CE strains against L. monocytogenes in compost extracts and compost samples was affected by compost type, nutrient level, and incubation temperature.

SIGNIFICANCE AND IMPACT OF THE STUDY

Compost is a rich source of CE microorganisms and compost-adapted CE microorganisms have the potential as a biological agent to control L. monocytogenes in agricultural environments.

Antifungal Activity of Lactobacillus plantarum ZZUA493 and Its Application to Extend the Shelf Life of Chinese Steamed Buns

Lactic acid bacteria (LAB) can produce many kinds of antifungal substances, which have been widely proven to have antifungal activity. In this study, 359 strains of LAB were screened for antifungal activity against Aspergillus niger (A. niger) using the 96-well microtiter plate method, and three showed strong activity. Of these, ZZUA493 showed a broad-spectrum antifungal ability against A. niger, Aspergillus oryzae, Trichoderma longibrachiatum, Aspergillus flavus and Fusarium graminearum. ZZUA493 was identified as Lactobacillus plantarum. Protease treatment, the removal of hydrogen peroxide with catalase and heat treatment had no effect on the antifungal activity of the cell-free supernatant (CFS) of ZZUA493; organic acids produced by ZZUA493 appeared to have an important role in fungal growth inhibition. The contents of lactic acid, acetic acid and phenyllactic acid in the CFS tended to be stable at 48 h, and amounted to 28.5, 15.5 and 0.075 mg/mL, respectively. In addition, adding ZZUA493, as an ingredient during their preparation, prolonged the shelf life of Chinese steamed buns. Overall, ZZUA493 appears to have good potential as a fungal inhibitor for food preservation.

Effect of Oral Administration with Lactobacillus plantarum CAM6 Strain on Sows during Gestation-Lactation and the Derived Impact on Their Progeny Performance

Background

To evaluate the biological response of the sows and their offspring with oral administration of Lactobacillus plantarum CAM6 in breeding sows, a total of 20 Pietrain breeding sows with three farrowings and their descendants were used, randomly divided into two groups of 10 sows each. Treatments included a basal diet (T0) and basal diet +10 mL biological agent containing 10⁹ CFU/mL L. plantarum CAM6 (T1). No antibiotics were used throughout the entire experimental process of this study.

Results

The L. Plantarum CAM6 supplementation in sows' feeding did not affect (P > 0.05) the reproductive performance of the sows; however, the number of deaths for their offspring before weaning (P ≤ 0.05) decreased. In addition, the oral administration of Lactobacillus plantarum CAM6 in sows increased (P ≤ 0.05) the content of lactose, nonfat solids, mineral salts, and the density of sows' milk, with a decrease in milk fat. Moreover, the probiotic feed orally to the sows improved the body weight (P ≤ 0.05) and reduced the diarrhea incidence of their offspring (P ≤ 0.05). Also, the probiotic administration of sows changed (P ≤ 0.05) the serum concentration of Na⁺, pCO₂, and D-β-hydroxybutyrate and increased (P ≤ 0.05) the leukocytes, lymphocytes, and platelets in their piglets.

Conclusion

Oral administration of Lactobacillus plantarum CAM6 in breeding sows improved body weight, physiological status, and the health of their offspring. And preparing the neonatal piglets physiologically is of great importance to the pig farming industry which could decrease the operational cost and medication (especially antibiotics) consumption of the pig producers.

Behavior of Foodborne Pathogens Listeria monocytogenes and Staphylococcus aureus in Mixed-Species Biofilms Exposed to Biocides

In nature and man-made environments, microorganisms reside in mixed-species biofilms, in which the growth and metabolism of an organism are different from these behaviors in single-species biofilms. Pathogenic microorganisms may be protected against adverse treatments in mixed-species biofilms, leading to health risk for humans. Here, we developed two mixed five-species biofilms that included one or the other of the foodborne pathogens Listeria monocytogenes and Staphylococcus aureus The five species, including the pathogen, were isolated from a single food-processing environmental sample, thus mimicking the environmental community. In mature mixed five-species biofilms on stainless steel, the two pathogens remained at a constant level of ∼105 CFU/cm2 The mixed five-species biofilms as well as the pathogens in monospecies biofilms were exposed to biocides to determine any pathogen-protective effect of the mixed biofilm. Both pathogens and their associate microbial communities were reduced by peracetic acid treatments. S. aureus decreased by 4.6 log cycles in monospecies biofilms, but the pathogen was protected in the five-species biofilm and decreased by only 1.1 log cycles. Sessile cells of L. monocytogenes were affected to the same extent when in a monobiofilm or as a member of the mixed-species biofilm, decreasing by 3 log cycles when exposed to 0.0375% peracetic acid. When the pathogen was exchanged in each associated microbial community, S. aureus was eradicated, while there was no significant effect of the biocide on L. monocytogenes or the mixed community. This indicates that particular members or associations in the community offered the protective effect. Further studies are needed to clarify the mechanisms of biocide protection and to identify the species playing the protective role in microbial communities of biofilms.IMPORTANCE This study demonstrates that foodborne pathogens can be established in mixed-species biofilms and that this can protect them from biocide action. The protection is not due to specific characteristics of the pathogen, here S. aureus and L. monocytogenes, but likely caused by specific members or associations in the mixed-species biofilm. Biocide treatment and resistance are a challenge for many industries, and biocide efficacy should be tested on microorganisms growing in biofilms, preferably mixed systems, mimicking the application environment.

Antimicrobial Activity of some <i>Lactobacillus</i> Species against Intestinal Pathogenic Bacteria

Probiotics have antibacterial effects against pathogenic bacteria in the gut while maintaining the balance of intestinal flora such as Lactobacillus. This study aimed to evaluate the antimicrobial activity of four Lactobacillus species against intestinal pathogenic. Four different species of Lactobacillus (Lactobacillus bulgaricus (PTCC 1332), Lactobacillus casei (PTCC 1608), Lactobacillus plantarum (PTCC 1058) and Lactobacillus Fermentum (PTCC 1638)) were experimented to investigate the inhibitory activity against 4 bacterial enteric pathogens (Escherichia coli, Staphylococcus aureus, Shigella dysenteriae and Salmonella paratyphi A) which were separately inoculated in MRS medium (de Man, Rogosa and Sharpe medium) for 48 hours at 37 °C and pH 7. Our results showed that enteropathogens growth was stopped in the presence of all Lactobacillus and inhibition zone was between 12 and 32 millimeter. It can be concluded that these four Lactobacillus strains had potential antimicrobial compounds against human enteric pathogens and should be further studied for their human health benefits.

Antimicrobial Activity of some <i>Lactobacillus</i> Species against Intestinal Pathogenic Bacteria

Probiotics have antibacterial effects against pathogenic bacteria in the gut while maintaining the balance of intestinal flora such as Lactobacillus. This study aimed to evaluate the antimicrobial activity of four Lactobacillus species against intestinal pathogenic. Four different species of Lactobacillus (Lactobacillus bulgaricus (PTCC 1332), Lactobacillus casei (PTCC 1608), Lactobacillus plantarum (PTCC 1058) and Lactobacillus Fermentum (PTCC 1638)) were experimented to investigate the inhibitory activity against 4 bacterial enteric pathogens (Escherichia coli, Staphylococcus aureus, Shigella dysenteriae and Salmonella paratyphi A) which were separately inoculated in MRS medium (de Man, Rogosa and Sharpe medium) for 48 hours at 37 °C and pH 7. Our results showed that enteropathogens growth was stopped in the presence of all Lactobacillus and inhibition zone was between 12 and 32 millimeter. It can be concluded that these four Lactobacillus strains had potential antimicrobial compounds against human enteric pathogens and should be further studied for their human health benefits.

Characterization and Antibacterial Potential of Lactic Acid Bacterium Pediococcus pentosaceus 4I1 Isolated from Freshwater Fish Zacco koreanus

This study was undertaken to characterize a lactic acid bacterium 4I1, isolated from the freshwater fish, Zacco koreanus. Morphological, biochemical, and molecular characterization of 4I1 revealed it to be Pediococcus pentosaceus 4I1. The cell free supernatant (CFS) of P. pentosaceus 4I1 exhibited significant (p < 0.05) antibacterial effects (inhibition zone diameters: 16.5-20.4 mm) against tested foodborne pathogenic bacteria with MIC and MBC values of 250-500 and 500-1,000 μg/mL, respectively. Further, antibacterial action of CFS of P. pentosaceus 4I1 against two selected bacteria Staphylococcus aureus KCTC-1621 and Escherichia coli O157:H7 was determined in subsequent assays. The CFS of P. pentosaceus 4I1 revealed its antibacterial action against S. aureus KCTC-1621 and E. coli O157:H7 on membrane integrity as confirmed by a reduction in cell viability, increased potassium ion release (900 and 800 mmol/L), reduced absorption at 260-nm (3.99 and 3.77 OD), and increased relative electrical conductivity (9.9 and 9.7%), respectively. Gas chromatography-mass spectrometry (GC-MS) analysis of the CFS of P. pentosaceus 4I1 resulted in the identification of seven major compounds, which included amino acids, fatty acids and organic acids. Scanning electron microscopic-based morphological analysis further confirmed the antibacterial effect of CFS of P. pentosaceus 4I1 against S. aureus KCTC-1621 and E. coli O157:H7. In addition, the CFS of P. Pentosaceus 4I1 displayed potent inhibitory effects on biofilms formation by S. aureus KCTC-1621 and E. coli O157:H7. The study indicates the CFS of P. pentosaceus 4I1 offers an alternative means of controlling foodborne pathogens.

Effect of Lactic Acid Bacteria on Beef Steak Microbial Flora Stored Under Modified Atmosphere and on Listeria Monocytogenes in Broth Cultures

Beef steaks were inoculated with one or other of two protective strains of lactic acid bacteria, the bacteriocinogenic Lactobacillus sakei CTC 372 or the uncharacterised Lactobacillus CTC 711. They were stored under modified atmospheres (20–40% CO2). Inoculation of meat with both strains inhibited the growth of the spoilage bacteria. Neither CO2 in the pack atmosphere, inoculation with protective strains, nor a combination of both, affected formation of metmyoglobin or the development of off-odours. The formation of metmyoglobin in meat pigments and the sensory odour scores were compatible to those of fresh meat which had not undergone either oxidative deterioration or microbial spoilage. Listeria monocytogenes were inhibited in broth by meat surface microbiota containing either of the protective strains. With an initial population of 5.6 log cfu/mL, after 7 days incubation at 3°C, Listeria monocytogenes were recovered at log mean population of 2.8 log cfu/mL when neither protective strain was present. At 8°C, the population of Listeria monocytogenes recovered were reduced by about 2.5 or 1.5 log cfu/mL in the presence of Lactobacillus sakei CTC 372 or Lactobacillus CTC 711, respectively. At 25°C, the population of Listeria monocytogenes recovered from broth containing either protective strain were about 5 log cfu/mL less than the population recovered from broth containing Listeria monocytogenes only.

Removing Lead from Iranian Industrial Wastewater

Metals and chemicals have been increased in industrial processes which they contain a high level of toxic heavy metals and cause a lot of disadvantages for the environment and human health .Biosorption of Pb (П) ions has been studied from aqueous solutions in a batch system by using a bacterial strain isolated from petrochemical wastewaters. Strain 8-I was selected to study the impact of different factors on removal rate. According to morphological, physiological and biochemical characterizations of the strain and in comparison with other studies the strain was tentatively identified as Bacillus sp strain8-I. The maximum Lead biosorption capacity of 8-I isolate was determined to be 41.58 % at pH 4.0 with 80 mg/l concentration in 48 hours equilibrium time. The comparison between the biosorption capacity of live (45.50 mg/g), heat inactivated (30.23 mg/g) and NaN3 pretreated biomass (26.86 mg/g) were indicated that the ability of live biomass for both of active and passive uptake of lead.

Contribution of Lactococcus lactis reducing properties to the downregulation of a major virulence regulator in Staphylococcus aureus, the agr system

Staphylococcus aureus is a major cause of food poisoning outbreaks associated with dairy products, because of the ingestion of preformed enterotoxins. The biocontrol of S. aureus using lactic acid bacteria (LAB) offers a promising opportunity to fight this pathogen while respecting the product ecosystem. We had previously established the ability of Lactococcus lactis, a lactic acid bacterium widely used in the dairy industry, to downregulate a major staphylococcal virulence regulator, the accessory gene regulator (agr) system, and, as a consequence, agr-controlled enterotoxins. In the present paper, we have shown that the oxygen-independent reducing properties of L. lactis contribute to agr downregulation. Neutralizing lactococcal reduction by adding potassium ferricyanide or maintaining the oxygen pressure constant at 50% released agr downregulation in the presence of L. lactis. This downregulation still occurred in an S. aureus srrA mutant, indicating that the staphylococcal respiratory response regulator SrrAB was not the only component in the signaling pathway. Therefore, this study clearly demonstrates the ability of L. lactis reducing properties to interfere with the expression of S. aureus virulence, thus highlighting this general property of LAB as a lever to control the virulence expression of this major pathogen in a food context and beyond.

Staphylococcus aureus virulence and metabolism are dramatically affected by Lactococcus lactis in cheese matrix

In complex environments such as cheeses, the lack of relevant information on the physiology and virulence expression of pathogenic bacteria and the impact of endogenous microbiota has hindered progress in risk assessment and control. Here, we investigated the behaviour of Staphylococcus aureus, a major foodborne pathogen, in a cheese matrix, either alone or in the presence of Lactococcus lactis, as a dominant species of cheese ecosystems. The dynamics of S. aureus was explored in situ by coupling a microbiological and, for the first time, a transcriptomic approach. Lactococcus lactis affected the carbohydrate and nitrogen metabolisms and the stress response of S. aureus by acidifying, proteolysing and decreasing the redox potential of the cheese matrix. Enterotoxin expression was positively or negatively modulated by both L. lactis and the cheese matrix itself, depending on the enterotoxin type. Among the main enterotoxins involved in staphylococcal food poisoning, sea expression was slightly favoured in the presence of L. lactis, whereas a strong repression of sec4 was observed in cheese matrix, even in the absence of L. lactis, and correlated with a reduced saeRS expression. Remarkably, the agr system was downregulated by the presence of L. lactis, in part because of the decrease in pH. This study highlights the intimate link between environment, metabolism and virulence, as illustrated by the influence of the cheese matrix context, including the presence of L. lactis, on two major virulence regulators, the agr system and saeRS.

Staphylococcus aureus virulence expression is impaired by Lactococcus lactis in mixed cultures

Staphylococcus aureus is responsible for numerous food poisonings due to the production of enterotoxins by strains contaminating foodstuffs, especially dairy products. Several parameters, including interaction with antagonistic flora such as Lactococcus lactis, a lactic acid bacterium widely used in the dairy industry, can modulate S. aureus proliferation and virulence expression. We developed a dedicated S. aureus microarray to investigate the effect of L. lactis on staphylococcal gene expression in mixed cultures. This microarray was used to establish the transcriptomic profile of S. aureus in mixed cultures with L. lactis in a chemically defined medium held at a constant pH (6.6). Under these conditions, L. lactis hardly affected S. aureus growth. The expression of most genes involved in the cellular machinery, carbohydrate and nitrogen metabolism, and stress responses was only slightly modulated: a short time lag in mixed compared to pure cultures was observed. Interestingly, the induction of several virulence factors and regulators, including the agr locus, sarA, and some enterotoxins, was strongly affected. This work clearly underlines the complexity of L. lactis antagonistic potential for S. aureus and yields promising leads for investigations into nonantibiotic biocontrol of this major pathogen.

Investigation of the physicochemical and sensory homogeneity of traditional French dry sausages

The aim of this study was to investigate the homogeneity of the traditional dry sausages manufactured in small scale facilities from the Massif Central region in France by taking into account the diversity of the production in this area. The homogeneity was estimated by analysis of the physicochemical parameters of 6 types of traditional dry sausages chosen as representatives of the production diversity. The homogeneity was evaluated (i) within the product, (ii) in the production batch and (iii) over 2 different seasons for each type of dry sausage. When heterogeneity was detected, sensory analysis was performed in order to check if the physicochemical differences found were perceived by a sensory panel. The physicochemical results showed that there was no significant heterogeneity within the product nor there was in the production batch. Over the 2 seasons studied, 3 out of the 6 dry sausages were heterogeneous in composition and this feature was perceived by the sensory panel. The possible causes of this heterogeneity (amounts of ingredients added, type and composition of the raw materials used, length of drying) are discussed.