Enumeration and identification of pediococci in powder-based products using selective media and rapid PFGE

Positive biofilms to control surface-associated microbial communities in a broiler chicken production system - a field study

In the One Health concept, the use of beneficial bacteria to form positive biofilms that prevent the settlement of undesirable bacteria is a promising solution to limit the use of antimicrobials on farms. However, there is a lack of field studies reporting the onset of these beneficial bacteria after application and the effects on autochthonous surface microbiota. In the study reported here, the inner surfaces of commercial broiler chicken houses were treated or not with a bacterial consortium composed of Bacillus spp. and Pediococcus spp. strains, able to form covering biofilms in different laboratory models. Preinstalled coupons were sampled over time to capture microbial biofilm dynamics on-farm surfaces. The results showed that the bacterial consortium can establish on the farm surfaces, modulate microbial communities, and limit the implantation of Enterobacteriaceae and Enterococcaceae, two families containing potential pathogens.

Applicability of potentially probiotic Lactobacillus casei in low-fat Italian type salami with added fructooligosaccharides: in vitro screening and technological evaluation

The aim was to evaluate the use of Lactobacillus casei strains in the fermentation process of low-fat Italian type salami with fructooligosaccharides (FOS). A screening using probiotic strains was performed at pH 5.5, 5.0 and 4.5 and incubation temperatures of 15 and 25 °C. Lactobacillus casei SJRP66 and Lactobacillus casei SJRP169 were selected and added to the low-fat fermented sausage - C (control), FOS (25% reduced fat with 2% FOS), FOS_66 (25% reduced fat with 2% FOS and L.casei SJRP 66) and FOS_169 (25% reduced fat with 2% FOS and L.casei SJRP 169). The evaluation included pH, moisture, lactic acid bacteria count, probiotic count, weight loss, instrumental color, TBARS and texture parameters. FOS_66 and FOS_169 presented a good probiotic count (8 log CFU/g) and similar technological behavior to the control. The addition of the probiotic showed no effect on lipid oxidation and * value. These strains of probiotic showed promising properties for applications in low-fat Italian type salami with healthier appeal.

Cultivation media for lactic acid bacteria used in dairy products

This review aims to familiarize the reader with research efforts on the cultivation media of lactic acid bacteria (LAB). We have also included a brief discussion on standard ingredients used in LAB media and chemically defined media as related to bacterial growth requirements. Recent research has focused on modifying standard media for the enumeration, differentiation, isolation, and identification of starter cultures and probiotics. Even though large numbers of these media have been developed to serve dairy microbial control, they have failed to provide consistent results. The research consequently points to the need to develop a reliable lactobacilli growth medium for the dairy industry.

Assessment of microbial communities on freshly killed wild boar meat by MALDI-TOF MS and 16S rRNA amplicon sequencing

Wild boars (Sus scrofa) are the most widely distributed large mammals and recent increase in consumption of wild boar meat urges the need of microbiological quality criteria. The aim of the study was to characterize the initial bacterial contamination on freshly-killed wild boar meat using a culture-dependent approach with ISO-methods combined with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry identification and 16S rRNA amplicon sequencing. Moreover, the presence of foodborne pathogens was examined using Real-Time-PCR and confirmed by classical isolation. Analysing 22 unrelated wild boar meat samples showed a higher bacterial contamination level compared to pork, with Salmonella present in almost one third of the samples. A great variability of the microbial contamination between the samples was recorded, as well as complementary results between culturing and 16S rRNA amplicon sequencing as frequently isolated genera were not always detected, and vice versa. Furthermore, the foodborne pathogen Salmonella was never detected with 16S rRNA amplicon sequencing, demonstrating the necessity for a cautious approach in the implementation of new analysis techniques in food safety. The present work determines that attention should be paid to the trade of non-inspected meat directly to retail or consumers.

Biopreservation potential of antimicrobial protein producing Pediococcus spp. towards selected food samples in comparison with chemical preservatives

The present study elucidates biopreservation potential of an antimicrobial protein; bacteriocin, producing Pediococcus spp. isolated from dairy sample and enhancement of their shelf life in comparison with two chemical preservatives. The antimicrobial protein producing Pediococcus spp. was isolated from selected diary samples and characterised by standard microbiology and molecular biology protocols. The cell free supernatant of Pediococcus spp. was applied on the selected food samples and monitored on daily basis. Antimicrobial potential of the partially purified protein from this bacterium was tested against clinical isolates by well diffusion assay. The preservation efficiency of bacteriocin producing isolate at various concentrations was tested against selected food samples and compared with two chemical preservatives such as sodium sulphite and sodium benzoate. The bacteriocin was partially purified and the microbiological qualities of the biopreservative treated food samples were assessed. The present study suggested that 100 μg/l of bacteriocin extract demonstrated antimicrobial potential against E. coli and Shigella spp. The treatment with the Pediococcus spp. showed enhanced preservation at 15 mL/kg of selected samples for a period of 15 days in comparison with sodium sulphite and sodium benzoate. The microbiological quality of food samples treated with biopreservative showed lesser total bacterial count (CFU/g) in comparison with the food samples applied with chemicals (p ≤ 0.05). Thus, the present study suggests that bacteriocin producing Pediococcus probably provides enhanced shelf life to the selected food samples and can be used as biopreservatives.

Advancement in LH-PCR methodology for multiple microbial species detections in fermented foods

The length-heterogeneity PCR is a low throughput molecular biology methods explored to monitor bacteria populations in different environments. It could be more used in food microbiology analysis, not only for fingerprinting analysis, but it has been hampered until now by a limiting factor which relates to the high percentage of secondary peaks. With the aim to overcome this problem, different experiments were performed focusing on changing PCR parameters in order to obtain more specific amplicon patterns and also to reduce the complexity of community patterns. With this purpose, different annealing temperatures were tested on complex fermented food matrices taken from both animal and vegetable origin and also on the bacteria isolated from the same food source. In particular, the optimal annealing temperature identified for the fermented food samples is 59 °C and the optimal for bacterial strains varied between 63 °C and 65 °C. The approach allowed the modification of the LH-PCR protocol increasing the amplification efficiency and therefore the bacteria species discrimination. These temperatures also allowed the implementation of the previous LH-PCR published database. The modification in the level of accuracy of the LH-PCR technique could also allow an improvement in the relative species quantification by the peak area evaluation.

Survival and Metabolic Activity of Pediocin Producer Pediococcus acidilactici UL5: Its Impact on Intestinal Microbiota and Listeria monocytogenes in a Model of the Human Terminal Ileum

Pediococcus acidilactici UL5 is a promising probiotic candidate due to its high survival rate under gastric and duodenal conditions and to its ability to produce the antilisterial bacteriocin pediocin PA-1. Its survival, metabolic activity, and impact on Listeria monocytogenes in a continuous stirred tank reactor containing immobilized human intestinal microbiota were studied over a period of 32 days of feeding a nutrient medium simulating ileal chyme. The impact of P. acidilactici UL5 on different bacterial groups of intestinal origin as well as its survival and its impact on L. monocytogenes were quantified using quantitative polymerase chain reaction coupling with propidium monoazide (PMA-qPCR), which was shown to detect and quantify viable bacteria only. P. acidilactici UL5 and its non-pediocin-producing mutant had no effect on the microbiota, but the producing strain induced an increase in the production of acetic and propionic acids. P. acidilactici survived but appeared to be a poor competitor with intestinal microbiota, dropping by 1.3 and 2.8 log₁₀ after 8 h of fermentation to 10⁴ colony-forming units (cfu) mL^-1. A 1.64 log but non-significant reduction of Listeria was observed when P. acidilactici UL5 was added at 10⁸ cfu mL^-1. P. acidilactici UL5 isolated from the reactor after 3 days was still able to produce the active bacteriocin. These data demonstrate that P. acidilactici UL5 is capable of surviving transit through the ileum without losing its ability to produce pediocin PA-1 but seems to not be enough competitive with the great diversity of organisms found in the ileum.

Pediococcus acidilactici UL5 and Lactococcus lactis ATCC 11454 are able to survive and express their bacteriocin genes under simulated gastrointestinal conditions

AIMS

The aim of this work is to study the expression of stress genes and those involved in pediocin and nisin production in Pediococcus acidilactici UL5 and Lactococcus lactis ATCC11454 under simulated gastrointestinal (GI) physiological conditions.

METHODS AND RESULTS

The two strains were fed to a dynamic GI model (TIM-1). Samples were taken from different compartments and analysed for strain survival as well as for the expression of pediocin PA-1 operon, nisin A production gene and stress genes using RT-qPCR. Ileal-delivered efflux showed a survival rate of 17 and 0·0007% for Ped. acidilactici and La. lactis, respectively. Pediocin operon genes from stressed cells were generally expressed at least at the same level as for unstressed cells. However, pedA is up-regulated in the effluent at 120 and 180 min. Nisin A genes were always up-regulated with particularly in the stomach after 70 min compared with control.

CONCLUSIONS

Bacteriocin production of Ped. acidilactici UL5 and Lc. lactis ATCC 11454 are not affected by upper GI simulated conditions and thus could be considered as relevant probiotic candidates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates the capacity of lactic acid bacteria to survive and express their bacteriocins genes under simulated GI conditions.

Study of the physicochemical and biological stability of pediocin PA-1 in the upper gastrointestinal tract conditions using a dynamic in vitro model

AIMS

To evaluate the survival of Pediococcus acidilactici UL5 and its ability to produce pediocin PA-1 during transit in an artificial gastrointestinal tract (GIT). To investigate the physicochemical and biological stability of purified pediocin PA-1 under GIT conditions.

METHODS AND RESULTS

Skim milk culture of Ped. acidilactici UL5 was fed to a dynamic gastrointestinal (GI) model known as TIM-1, comprising four compartments connected by computer-controlled peristaltic valves and simulating the human stomach, duodenum, jejunum and ileum. This strain tolerated a pH of 2·7 in the gastric compartment, while lower pH reduced its viability. Bile salts in the duodenal compartment brought a further 4-log reduction after 180 min of digestion, while high viable counts (up to 5 × 10(7) CFU ml(-1) fermented milk) of Ped. acidilactici were found in both the jejunal and ileal compartments. Pediococcus acidilactici recovered from all four compartments was able to produce pediocin at the same level as unstressed cells. The activity of the purified pediocin in the gastric compartment was slightly reduced after 90 min of gastric digestion, while no detectable activity was found in the duodenal, jejunal and ileal compartments during 5 h of digestion. HPLC analysis showed partial degradation of the pediocin peptide in the duodenal compartment and massive breakdown in the jejunal and ileal compartments.

CONCLUSIONS

Pediococcus acidilactici UL5 showed high resistance to GIT conditions, and its ability to produce pediocin was not affected, suggesting its potential as a probiotic candidate. The physicochemical and biological stability of pediocin was significantly poor under GIT conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

Pediococcus acidilactici UL5 appears to be a potential probiotic candidate because its capacity to produce pediocin PA-1 is not affected by the GI conditions as well as the strain shows an acceptable survival rate. Meanwhile, purified pediocin PA-1 losses activity during GIT transit; microcapsules could be used to deliver it to the target site.

In vivo study on the effectiveness of pediocin PA-1 and Pediococcus acidilactici UL5 at inhibiting Listeria monocytogenes

The anti-listerial effect of pediocin PA-1 and its producing strain, Pediococcus acidilactici UL5, was investigated in vivo using an ICR mouse model. The effect of intra-gastric administration of a single dose of P. acidilactici UL5 (4 x 10(10) CFU/animal) on the propagation of Listeria monocytogenes LSD348 in intestine, liver and spleen was negligible. P. acidilactici UL5 did not appear competitive with the mouse intestinal flora and was not detectable in fecal samples collected two days after administration. However, double-agar-layer activity assay showed the ability of P. acidilactici UL5 colonies recovered from fecal samples one day after administration to produce pediocin PA-1 and inhibit L. monocytogenes. Moreover, repeated doses (250 microg/day for three consecutive days) of purified pediocin PA-1 provided up to 2-log reductions in fecal listerial counts compared to the infected control group and slowed pathogen translocation into the liver and spleen, leading to the disappearance of L. monocytogenes infection in these two organs within six days. Neither P. acidilactici UL5 nor ingested purified pediocin PA-1 had any negative effect on feed intake or body weight development. Pediocin PA-1 did not affect the composition of the mouse intestinal flora, suggesting a potential advantage over other inhibitory agents as a prophylactic measure against L. monocytogenes.