Control of milk pH reduces biofilm formation of Bacillus licheniformis and Lactobacillus paracasei on stainless steel

Microbial biofilms present in dairy farms may contaminate milk during milk harvest and transfer diseases from the environment to cows. In order to reduce biofilm formation with respect to the role of pH, a study involving the control of milk pH during long-term biofilm formation of Bacillus licheniformis NBRC 12195 and Lactobacillus paracasei subsp. paracasei NBRC 15889 on stainless steel coupons in different dilutions of skim milk (0.1%, 1.0% and 5.0%) was conducted. During long incubation at 30 °C, pH decreased due to bacterial development in unadjusted samples. In pH-adjusted samples, pH was kept at around 7.0 by the addition of sterile sodium hydroxide. Biofilms formed on stainless steel coupons were daily stained by 0.1% Crystal Violet solution and assessed by the evaluation of optical density. The bacterial count of the suspensions showed that the control of pH enhanced the growth of bacteria in free-floating form. In contrast, optical densities of biofilms formed in the pH-adjusted samples were significantly lower than in the pH-unadjusted samples in all of three skim milk dilutions. Comparison of maximum OD values of adhered cells at different nutrient levels also implicated that for both tested strains, thicker biofilms were formed in milk dilutions at higher nutrient levels. These results suggested that, control of milk pH and milk residue level could significantly reduce biofilm formation of the tested bacteria.     

Occurrence and distribution of species of Enterobacteriaceae in selected Ethiopian traditional dairy products: A contribution to epidemiology

A total of 316 samples of traditional milk and milk products (66 milk, 52 Ergo – naturally fermented milk, 66 butter, 66 buttermilk and 66 Ayib, Ethiopian cottage cheese); 20 samples of cleaning water and 20 samples of udder swabs were collected in the central highlands of Ethiopia to assess the occurrence and distribution of enteric bacteria. A total of 534 isolates distributed among 10 genera and 20 species were identified. Klebsiella, Escherichia and Enterobacter were the dominant genera in their order of abundance with Escherichia coli, the most prevalent species. Erwinia, Klyuvera and Providentia were the least abundant genera. Most of the genera/species identified were isolated predominantly from milk samples followed by butter and buttermilk during the dry season and from milk, buttermilk and butter during the wet season in order of their abundance. The overall mean aerobic mesophilic, coliform and enterobacterial counts of dairy products were 8.3, 4.5 and 5.2 log cfu mL⁻¹ or g⁻¹, respectively. Ergo samples had 0.7 more log cfu of aerobic mesophilic count than butter samples. Coliform and enterobacterial counts were generally lower in samples of fermented milk products than milk with the largest difference being 1.2 log cfu mL⁻¹ for coliform and 1 log cfu mL⁻¹ for enterobacteria between milk and Ergo samples. The highest and lowest coliform counts were 5.2 and 3.9 log cfu mL⁻¹ or g⁻¹ in samples collected from cooperative centers and smallholder producers, respectively. The knowledge of the enteric bacterial properties of traditional dairy products is essential for the improvement of quality and preservation of the products thereby provide a wholesome product to the consumer with minimum health risk.     

Inactivation of thermoduric aerobic sporeformers in milk by ultrasonication

Thermoduric sporeformers can survive milk pasteurization and cause spoilages of dairy products. In the present study, ultrasonication was evaluated as a non-thermal processing technique to inactivate the thermally resistant vegetative cells of spore forming Bacillus spp. During the challenge studies, vegetative cells of Bacillus coagulans (ATCC^® 12245), Anoxybacillus flavithermus (DSM 2641), Bacillus sporothermodurans (DSM 10599), Bacillus licheniformis (ATCC^®6634), and Geobacillus stearothermophilus (ATCC^® 15952) were studied for their survivability to batch pasteurization (63 °C/30 min) in skim and whole milk samples. Experiments were conducted to study the effect of ultrasonication alone or in combination with pasteurization on inactivation of vegetative cells of some thermoduric Bacillus spp. Effect of ultrasonication on milk pH, color, and alkaline phosphatase activity was also investigated. Vegetative cells of B. coagulans and A. flavithermus survived pasteurization treatment in both skim and whole milk samples. Ultrasonication at 80% amplitude for 10 min however, inactivated the vegetative cells of B. coagulans and A. flavithermus in skim milk by 4.53, and 4.26 logs, respectively. A combined treatment of pasteurization (63 °C/30 min) followed by ultrasonication completely eliminated approximately log 6 cfu/mL of these cells in skim milk. As visualized under the scanning electron microscope, ultrasonication physically disintegrated vegetative cells of sporeformers. Ultrasonication treatment caused significant reduction (P < 0.05) in brightness and greenness of milk; whereas, blueness (b*) of milk was increased. However, pH and alkaline phosphatase activity (P > 0.05) of treated skim milk were not affected.     

Molecular identification of bacteriocins produced by Lactococcus lactis dairy strains and their technological and genotypic characterization

In this study, the bacteriocins produced by ten Lactococcus lactis subsp. lactis strains, previously isolated from raw milk and traditional Sardinian cheeses, were identified by targeting and sequencing the bacteriocin encoding genes. The inhibitory activity against different food borne and spoilage bacteria, and the technological and genotypic characteristics of the bacteriocinogenic L. lactis strains were also analysed. The presence of the nisin structural gene was confirmed for all L. lactis strains. Three strains were shown to harbour the Lactococcins B structural gene. The sequences of PCR products for the nisin gene from the ten bacteriocinogenic strains were compared with that of L. lactis strain ATCC 11454 (nisin A producer strain). Differences were observed in strain 6LS5 indicating its ability to produce the nisin Z variant. Five strains presented a wider inhibitory spectrum resulting in activity towards Pseudomonas aeruginosa and all the Bacillus, Listeria, Staphylococcus and Clostridium strains tested. High β-galactosidase and moderate aminopeptidase activities, that promote the desirable flavours in cheese, were detected in the majority of the strains. Rep-PCR with primer (GTG)₅ revealed high diversity among the strains and allowed discrimination at both interspecific and intraspecific level. The autochthonous bacteriocinogenic isolates from Sardinian dairy products described in this work may potentially find application as starter, co-starter or protective adjunct cultures in the manufacturing of cheeses.     

Listeria spp. in the raw milk and dairy products in Antakya,Turkey

In this study, the presence of Listeria spp. was investigated in a total of 157 raw milk and dairy product samples sold in Antakya (Antioch). The prevalence of Listeria spp. in raw milk and Turkish white cheese samples was found to be 2.12% and 8.23%, respectively. Listeria monocytogenes was not isolated from raw milk and found in only two cheese samples (2.35%). No Listeria spp. were isolated in any of the butter and yoghurt samples.     

Characteristics of Batzos cheese made from raw,pasteurized and/or pasteurized standardized goat milk and a native culture

Experimental cheeses were made from raw (R), raw with starter (RS), pasteurized with starter (PS) and standardized, pasteurized with starter (PSS) goat milk to study the influence of the starter and pasteurization on the quality of Batzos cheese. Lactococcus lactis subsp lactis strains from raw milk cheese used as starter proliferated significantly (P < 0.05) only in PSS cheese. Heat treatment lowered (P < 0.05) the levels of most microbial groups. However, TC and LAB counts were higher (P < 0.05) in PSS cheese and this was accompanied by lower (P < 0.05) pH; thus, a higher rate of decrease of undesirable microorganisms in PSS cheese was recorded. Degradation of αs-casein was in R > RS and in PS > PSS, while a small reduction of β-casein during ripening and storage was recorded. The proportions of aminoacids and lipolysis products increased throughout ripening and storage.     

Microbiological,biochemical and sensory characteristics of artisanal and industrial Manchego cheeses

Manchego cheese production may be artisanal or industrial, according to whether the cheeses are manufactured with raw or pasteurised ewe’s milk. This work was designed in order to study the predominant microflora in artisanal and industrial Appellation of Origin Manchego cheeses and its influence on the biochemical characteristics and the gustative profile of the cheeses at 60 days of ripening (just the moment that the cheeses can be marketed). Only two biotypes of the same species of Lactococcus lactis subsp. lactis were found in the industrial cheeses, while in the artisanal cheeses the microflora was much more heterogeneous. At 60 days of ripening, the artisanal cheeses accounted for higher values of pH, salt content, total nitrogen and nitrogen fractions than the industrial cheeses. Besides, the artisanal cheeses obtained higher scores for most of the gustative attributes evaluated than the industrial cheeses. This could be due to the more complex enzymatic system of the artisanal cheeses compared to the industrial ones, that could perform stronger biochemical changes in the cheeses made with raw milk.     

Quantitative risk assessment of Mycobacterium avium subsp. paratuberculosis survival in pasteurized milk in three dairy plants in Italy

The objective of this study was to carry out a quantitative risk assessment (QRA) of Mycobacterium avium subsp. paratuberculosis (MAP) survival in pasteurized milk produced by industrial dairy plants. Data were collected in three dairy plants (A, B and C) located in three different Italian regions and processing 38.75 (plant A), 89.29 (plant B) and 190.56 million litres (Plant C) of milk yearly. Plants A and plant C produce pasteurized milk, soft and hard industrial cheeses and yogurt; plant B produces only pasteurized milk. In-line milk filter (ILMF) samples and/or bulk milk samples were collected from all 569 herds delivering milk to the three dairy plants. Samples were analysed by quantitative real-time PCR (qPCR). The QRA considered the presence of MAP in ILMF and in bulk milk of all the dairy herds delivering milk to the three investigated dairy plants, estimating MAP concentration in raw milk on the basis of these data, the dilution effect due to mixing milk in collecting trucks and in plant silos, and the effect of pasteurization in reducing the MAP load. The expected fraction of litres of pasteurized milk with 0 MAP would be 99.02%, 99.45% and 99.12%, in plants A, B and C respectively, and an overall percentage 0.55% to 0.98% of pasteurized milk having a MAP contamination >0 colony forming units (CFU)/l and 0.04%–0.11% of pasteurized litres with a MAP contamination > 100 CFU/l was predicted. A daily variation was observed in the proportion of MAP-contaminated litres of milk. The study demonstrated that milk in the dairy plants investigated may be a source of MAP exposure for humans. The between-herd and within-herd MAP apparent prevalence in the investigated areas are likely comparable to those in other areas in Italy, Europe and North America, and the results are applicable to other geographical areas.     

Quality of raw milk intended for direct consumption in Estonia

The main aim of the present study was to estimate the occurrence of zoonotic bacteria in raw milk intended for sale directly to consumers in Estonia. In-line milk filters, bulk milk samples and milk samples from selling points were collected from a total of 14 dairy farms and respective retail selling points. The somatic cell counts, total bacterial counts and the presence of Salmonella spp and Listeria monocytogenes were studied from bulk milk samples. Campylobacter spp., Salmonella spp., L. monoscytogenes and Shiga-toxin producing Escherichia coli (STEC) were studied in farms in-line milk filters. The total bacterial counts exceeded 100,000 cfu/ml in three (21.4%) bulk milk samples and in 10 samples (71.4%) collected at the retail level. STEC genes were detected in 64.3% of the in-line milk filter samples. More than one STEC serogroup-specific gene was detected in four dairy farms. L. monocytogenes was found in 36% of the in-line milk filters. Neither Salmonella spp. nor Campylobacter spp. were found in any samples.     

Effects of blackberry juice on growth inhibition of foodborne pathogens and growth promotion of Lactobacillus

Berries such as blueberry, blackberry and raspberry possess several biological activities including antimicrobial and nutritional effects. In this study, the antimicrobial activities of blackberry (Rubus fruticosus) juice against foodborne pathogens including Listeria monocytogenes, Salmonella Typhimurium and Escherichia coli O157:H7 were investigated. Inhibition of growth of these foodborne pathogens was measured in broth (Luria–Bertani broth for E. coli O157:H7 and S. Typhimurium, and brain heart infusion broth for L. monocytogenes), skim milk and whole milk supplemented with 10% blackberry juice at different time points (0, 24, 48 and 72 h). The effects of blackberry juice on the growth of Lactobacillus casei, Lactobacillus plantarum and Lactobacillus rhamnosus were also investigated in Man–Rogosa–Sharpe (MRS) broth and skim and whole milk supplemented with blackberry juice. The growth of L. monocytogenes, S. Typhimurium and E. coli O157:H7 were significantly inhibited by blackberry juice by 1–3 logs in both milk and broth. We also observed that the growths of Lactobacillus strains were significantly stimulated (1–4 logs CFU/mL) by blackberry juice in both milk and MRS broth. These data clearly demonstrate that diluted blackberry juice can be used as a preservative in food processing and a preventive in foodborne infections as a natural antimicrobial.     

Aflatoxin M1 contamination in dairy products marketed in Iran during winter and summer

In the present study, 298 dairy product samples consisting of pasteurized milk (91 samples), yoghurt (68 samples), white cheese (72 samples), butter (31 samples) and ice cream (36 samples) collected from popular markets in four large Iranian cities were examined for aflatoxin M₁ (AFM₁) by thin layer chromatography (TLC) technique. The toxin was detected in 66 (72.5%) pasteurized milk samples (mean: 0.052 μg/l; range: 0.013–0.250 μg/l), 45 (66.1%) yoghurt samples (mean: 0.032 μg/kg; range: 0.015–0.119 μg/kg), 59 (81.9%) white cheese samples (mean: 0.297 μg/kg; range: 0.030–1.200 μg/kg), 8 (25.8%) butter samples (mean: 0.005 μg/kg; range: 0.013–0.026 μg/kg) and 25 (69.4%) ice cream samples (mean: 0.041 μg/kg; range: 0.015–0.132 μg/kg). The concentration of AFM₁ in 36.2%, 20.6%, 30.5%, 9.6% and 27.7% of pasteurized milk, yoghurt, white cheese, butter and ice cream samples, respectively, were higher than Iranian national standard limits. Levels of AFM₁ in samples of pasteurized milk, yoghurt, butter and ice cream collected in winter were significantly higher (P < 0.05) than those collected in summer. In the case of white cheese, level of AFM₁ was higher in winter than in summer, but the difference was not statistically significant (P > 0.05). The results indicated that the contamination of the dairy products in such a level could be a serious public health problem at the moment.     

Evaluation of the factors affecting the activity of sakacin C2 against E. coli in milk

Sakacin C2 is a novel, broad spectrum bacteriocin secreted by Lactobacillus sake C2 isolated from Chinese traditional fermented cabbage. Effects of milk fat, emulsifiers, preservatives and homogenization on the activity of sakacin C2 against Escherichia coli ATCC 25922 in milk were evaluated by determined the changes of viable cell counts of E. coli ATCC 25922 after inoculation (10⁵ CFU/ml) then storage at 4 °C. Milk fat in pasteurized and homogenized milk products (low fat milk and whole milk) decreased the activity of sakacin C2 against E. coli ATCC 25922. Addition of 5 μl/ml of Tween 80 decreased the effect of sakacin C2 against E. coli ATCC 25922, but 5 mg/ml of lecithin increased the effect against E. coli ATCC 25922 in pasteurized and homogenized whole milk. Nisin and ε-Polylysine significantly increased the effect of sakacin C2 against E. coli ATCC 25922 in pasteurized and homogenized whole milk. Homogenization interfered with the activity of sakacin C2 against E. coli ATCC 25922 in pasteurized skim milk and whole milk. This study might lay the groundwork for the application of sakacin C2 as bio-preservative in milk and dairy products.     

Antilisterial activity and stability of nanovesicle-encapsulated antimicrobial peptide P34 in milk

Bacillus sp. P34, a strain isolated from aquatic environments of Brazilian Amazon basin, produces a bacteriocin-like substance (BLS) which was encapsulated in nanovesicles prepared from partially purified soy lecithin. The efficiency of free and encapsulated BLS P34 to control the development of L. monocytogenes and maintenance of antimicrobial activity was assessed over time in milk. The antimicrobial activity of free and encapsulated BLS P34 decreased approximately 50% after 4 days of storage (<4 °C) in skim and whole milk. After this period there was not significant loss of activity up to 21 days. The viable counts of Listeria monocytogenes in skim and whole milk containing 3200 AU/ml of free or encapsulated BLS P34 were always lower than those observed in controls without bacteriocin at both 30 °C and 7 °C. At 1600 AU/ml concentration, free and encapsulated BLS P34 were inhibitory to L. monocytogenes in skim milk, when compared with the control at 7 days. Nanovesicle-encapsulated and free BLS P34 shows potential use as biopreservative for application in milk-derived products.     

Evaluation of electrolyzed water as cleaning and disinfection agent on stainless steel as a model surface in the dairy industry

In the dairy industry, cleaning and disinfection of surfaces are important issues and development of innovative strategies may improve food safety. This study was aimed to optimize the combined effect of alkaline electrolyzed water (AEW) and neutral electrolyzed water (NEW) as alternative cleaning and disinfection procedure on stainless steel plates (SSP) with and without electropolishing. NEW at 10 ppm total available chlorine (TAC), achieved a ˃5 log CFU/mL reduction of milk spoilage bacterial suspension, grown in trypticase soy broth (8.7 log CFU/mL of each bacterial strain: Pseudomonas aeruginosa, Enterococcus faecalis and Micrococcus luteus) contacted for 30 s. An optimal design of experiments was used to assess the combined effect of cleaning with AEW, followed by disinfection with NEW (40 ppm TAC, contact time 3 min). Tested factors were contact time (10, 20 and 30 min), concentration of AEW (100, 200 and 300 mg NaOH/L), temperature (30, 40 and 50 °C), and surface type (304-2B SSP with or without electropolishing), using sixteen treatments with two replicates. The response variable was bacterial cells removal (log CFU/cm²). All main effects, two factors interactions and a quadratic term significantly influenced cells removal, and were modeled using a second order polynomial. Best cleaning procedures were significantly affected by surface roughness; electropolished SSP required 10 min, 100 mg/L AEW at 30 °C, whereas SSP without modification required 30 min, 300 mg/L AEW at 30 °C. From confirmatory tests cells removed were 3.90 ± 0.25 log CFU/cm² for electropolished SSP, and 3.20 ± 0.20 log CFU/cm² for SSP without modification. NEW is non-corrosive, and can be advantageously used for environmentally friendly cleaning and disinfection processes.     

Transfer of chloramphenicol from milk to commercial dairy products – Experimental proof

The purpose of the study was to investigate the chloramphenicol (CAP) residue in dairy products after experimental CAP transferring from milk to butter, sour cream, white cheese and whey. In order to determine the CAP residue in dairy products, the new approach for the extraction process was developed. The original, simple and fast analytical method is based on QuEChERS and LC-MS/MS. The homogenized sample was extracted and partitioned after the adding of sodium chloride with acetonitrile. The experiment was conducted to check if CAP is transferred from milk to dairy products, and also to check the extraction of CAP from the different dairy matrices. Average recovery ranged from 97.8 to 102.8% and within-laboratory reproducibility was lower than 8.7%. The suggested method is sensitive, the calculated limit of decision (CCα) was from 0.06 to 0.10 μg kg⁻¹ and detection capability (CCβ) from 0.08 to 0.15 μg kg⁻¹. The results of the experiment (butter 4.86 μg kg⁻¹, sour cream 3.5 μg kg⁻¹, white cheese 2.36 μg kg⁻¹ and whey 0.14 μg kg⁻¹) and validation demonstrated that this method is suitable for determination and confirmation of CAP in a variety of dairy product matrices.     

Microbial safety and quality attributes of milk following treatment with atmospheric pressure encapsulated dielectric barrier discharge plasma

This study evaluated the microbial and physicochemical characteristics of milk that was treated with encapsulated dielectric barrier discharge (DBD) plasma. Encapsulated DBD plasma was generated in a plastic container (250 W, 15 kHz, ambient air) and DBD plasma treatment was applied to milk samples for periods of 5 and 10 min. The total aerobic bacterial count in the untreated control sample was 0.98 log CFU/mL. Following plasma treatment, no viable cells were detected in the milk samples. When milk samples were inoculated with Escherichia coli, Listeria monocytogenes, and Salmonella Typhimurium, plasma treatment for 10 min resulted in a reduction in bacterial counts by approximately 2.40 log CFU/mL. The pH of the sample milk was found to decrease after the 10-min plasma treatment. Hunter color L* and b* values of milk increased, and the a* value decreased as a result of the plasma treatment. The production of 2-thiobarbituric acid reactive substances increased slightly, but not significantly, following plasma treatment. The results of this study indicate that encapsulated DBD plasma treatment for less than 10 min improved the microbial quality of milk with slight changes in physicochemical quality of milk.     

Characterization of the dominant bacterial communities of traditional fermentation starters for Hong Qu glutinous rice wine by means of MALDI-TOF mass spectrometry fingerprinting, 16S rRNA gene sequencing and species-specific PCRs

The main goal of this work was to investigate the bacterial flora present in the traditional fermentation starters using matrix-assisted laser desorption/ionisation time of flight (MALDI-TOF) mass spectrometry fingerprinting combined with 16S rRNA gene sequencing and species-specific PCRs. A total of 1314 bacterial strains were obtained from ten kinds of representative wine fermentation starters (5 Hong Qu and 5 Yao Qu) and classified by MALDI-TOF mass spectrometry. Sixteen different bacterial species belonging to six different genera (Bacillus, Staphylococcus, Leuconostoc, Pediococcus, Lactobacillus and Lactococcus) were identified with high accuracy by comparing them with generated spectra of MALDI Biotyper database. Comparison of 16S rRNA gene phylogeny and MALDI-TOF mass spectrometry analysis showed that MALDI-TOF mass spectrometry fingerprinting was a good complementary approach to 16S rRNA sequencing and even a more powerful tool in the accurate differentiation and classification of Bacillus species, especially for differentiating between Bacillus subtilis, Bacillus amyloliquefaciens and Bacillus methylotrophicus. MALDI-TOF mass spectrometry was also found to provide valuable information at species levels for the genus of Lactobacillus. The identification revealed that most strains isolated from traditional fermentation starters were B. amyloliquefaciens (31.81%), followed by Bacillus megaterium (16.89%), Lc. lactis subsp. lactis (8.60%) and B. subtilis (8.14%). In the culture-dependent quantitative analysis, 69.01% of the detected isolates were Bacillus species, and 30.44% of the detected isolates belonged to the class of lactic acid bacteria (LAB), including Leu. mesenteroides, Pediococcus pentosaceus, Lactobacillus plantarum, Lactobacillus paracasei, Lactobacillus brevis, Pediococcus acidilactici, Lactobacillus coryniformis and Lc. lactis subsp. lactis. This study provides detailed evaluation of bacterial communities in the traditional fermentation starters for Hong Qu glutinous rice wine using a fast and cost-effective technique—MALDI-TOF mass spectrometry fingerprinting. Information provided by this study is fundamental and useful to develop effective strategies for the selection of beneficial bacterial strains and improve of quality of Hong Qu glutinous rice wine.     

Metabolites produced during the growth of probiotics in cocoa supplementation and the limited role of cocoa in host-enteric bacterial pathogen interactions

Cocoa contains various compounds that can significantly affect the growth of a broad range of bacteria, and have multiple human health-promoting properties. In this study, the effects of cocoa powder on the growth of Lactobacillus, common milk resident bacteria, and three major foodborne enteric bacterial pathogens; enterohemorrhagic Escherichia coli O157:H7 (EHEC), Salmonella enterica serovar Typhimurium, and Listeria monocytogenes, were investigated in vitro. Significant (p < 0.05) growth stimulation on beneficial bacteria including Lactobacillus and other resident bacteria in milk was observed in the presence of 3% cocoa powder. In contrast, growth of three foodborne enteric pathogens was significantly (p < 0.05) inhibited within 9 h, but no stimulation was found with longer incubation. In addition, cocoa powder significantly (p < 0.05) inhibited adhesion to and invasion of INT407 cells by these bacterial pathogens in a dose dependent manner. These results suggest that addition of cocoa into dairy products could improve the beneficial effect of probiotics by stimulating their growth, without raising the risk of cross-contamination with enteric pathogens.     

Incidence and genetic variability of Listeria species from three milk processing plants

The presence of Listeria in three milk processing environments as a potential source of milk contamination was assessed. Swab samples (n = 210) taken from milk processing plants were examined. Sample sites included the milk processing equipment, besides areas handling raw and pasteurized milk. The USDA Listeria-selective enrichment procedure was used to process the samples. Forty one (19.52%) Listeria isolates were recovered. The isolates were further subjected to biochemical and genotypic characterization. Out of 41 isolates, 16 (7.62%) were confirmed as Listeria monocytogenes, 2 (0.95%) as L. ivanovii, 19 (9.05%) as L. innocua. 1 (0.48%) as L. seeligeri and 3 (1.43%) as L. grayi. All the L. monocytogenes isolates were positive for the hlyA gene. PCR based serotyping revealed all L. monocytogenes to be of 1/2a, 1/2c, 3a and 3c serovar group. AscI and ApaI restriction analysis yielded four PFGE clusters for 16 L. monocytogenes isolates obtained from raw milk collector, milk silos, buttermilk mixer, cheese and other milk product processor. No predominant PFGE cluster was observed among these L. monocytogenes isolates. The main sources of L. monocytogenes were found to be raw milk collector and milk silos. In the present study L. monocytogenes was isolated from milk and milk products processing plants which could cross-contaminate the processed products and may possess a potential threat to public health.