Listeria monocytogenes and Salmonella spp. in raw milk produced in Brazil: occurrence and interference of indigenous microbiota in their isolation and development

Probiotic Lactic Acid Bacteria from Goat’s Milk Potential Producer of Bacteriocin: Evidence from Liquid Chromatography-Mass Spectrometry

The diverse microbial populations in milk produce a range of antimicrobial compounds that confer preservative action. Goat milk characterized by high nutritional value, medicinal properties and hypoallergenic in nature, constitutes the most prevalent non-bovine milk consumed globally. Lactic acid bacteria (LAB), renowned for their probiotic properties, are important constituents of goat milk microflora. In this study, bacterial strains with probiotic potential were isolated and characterized from milk samples of indigenous Indian goat breeds. On MRS medium, Gram-positive rods were observed after anaerobic culture. Based on 16s rRNA technique LAB from goat milk were identified to belong to Enterococcus durans and Lactobacuillus plantarum. Antimicrobial activities were observed against known pathogens (Staphylococcus aureus, Klebsiella pneumoniae, Escherichia. coli and Salmonella typhimurium) and minimum inhibitory concentration was found to be low (6.5 mg/ml) for most of the isolates. High resistance to both acidic condition (pH 2.0) and 0.3% bile salts was observed along with marginal increase in cell counts in some isolates. Adherence to Caco-2 cell lines was observed in all the four identified LABs and was higher in case of Enterococcus durans compared to Lactobacillus plantarum. LC-MS analysis revealed the presence of lacticin as one of the key component of cell free extracts (CFE) of selected isolate. Goat milk as a source of possible LAB probiotics opens up a whole new avenue of probiotics from non-bovine milk sources. LAB strains isolated in this study are potential probiotic candidates that can be employed as antimicrobial agents in food and pharmaceutical industries.

Listeria monocytogenes in Milk: Occurrence and Recent Advances in Methods for Inactivation

Milk is one of the most important food items consumed by humans worldwide. In addition to its nutritional importance, milk is an excellent culture medium for microorganisms, which may include pathogens such as Listeria monocytogenes (L. monocytogenes). Traditional processing of milk for direct consumption is based on thermal treatments that efficiently eliminate pathogens, including pasteurization or sterilization. However, the occurrence of L. monocytogenes in milk as a consequence of failures in the pasteurization process or postpasteurization contamination is still a matter of concern. In recent years, consumer demand for minimally processed milk has increased due to the perception of better sensory and nutritional qualities of the products. This review deals with the occurrence of L. monocytogenes in milk in the last 10 years, including regulatory aspects, and recent advances in technologies for the inactivation of this pathogen in milk. The results from studies on nonthermal technologies, such as high hydrostatic pressure, pulsed electric fields, ultrasounds, and ultraviolet irradiation, are discussed, considering their potential application in milk processing plants.

QUALIDADE FÍSICO-QUÍMICA E MICROBIOLÓGICA DE LEITE DE CABRA PRODUZIDO NO DISTRITO FEDERAL

Resumo O objetivo desse trabalho foi avaliar a qualidade físico-química e microbiológica do leite de cabra produzido no Distrito Federal, Brasil. As amostras foram coletadas diretamente dos tetos e em pool de cada três animais (n=40) e de leite de conjunto (n=10). Nas análises físico-químicas, os resultados médios foram: gordura (animais: 3,01% ± 0,679, conjunto: 4,45% ± 1,223); sólidos não gordurosos (animais: 9,24% ± 0,651, conjunto: 9,2% ± 0,615); densidade (animais: 1,033g/mL ± 0,002, conjunto: 1,032g/mL± 0,002); proteínas (animais: 3,5% ±0,551, conjunto: 3,67% ±0,778); lactose (animais: 5,0% ± 0,035, conjunto: 4,94% ± 0,015); acidez Dornic (animais: 18,47ºD ±0,552, conjunto: 18,5ºD ± 0,5); pH (animais e conjunto: 6,9 ±0,098); crioscopia (animais: -0,560ºH ±0,010, conjunto: -0,558ºH ± 0,005). Nenhuma amostra apresentou resíduos de antibióticos. As contagens médias microbiológicas foram: aeróbios mesófilos 1,2x103 UFC/mL (animais) e 7,6x103 UFC/mL (conjunto); coliformes totais 1,0 UFC/mL (animais) e 1,2x104 UFC/mL (conjunto); Escherichia coli 2,0 UFC/mL (conjunto); psicrotróficos 1,0x104 UFC/mL (conjunto); bactérias ácido-láticas 4,7x102 UFC/mL (animais) e 7,8x103 UFC/mL (conjunto); bolores e leveduras 1,0 UFC/mL (animais) e 4,9x103 UFC/mL (conjunto) e Staphylococcus aureus 2,1x102 UFC/mL (animais) e 2,8x102 UFC/mL (conjunto). Listeria monocytogenes e Salmonella spp. não foram detectadas nas amostras analisadas. Os resultados obtidos permitem concluir que o leite de cabra produzido no Distrito Federal apresenta qualidade satisfatória e esses dados podem contribuir para o estímulo da produção na região.

Isolation, Molecular Characterization and Probiotic Potential of Lactic Acid Bacteria in Saudi Raw and Fermented Milk

Probiotic bacteria can confer health benefits to the human gastrointestinal tract. Lactic acid bacteria (LAB) are candidate probiotic bacteria that are widely distributed in nature and can be used in the food industry. The objective of this study is to isolate and characterize LAB present in raw and fermented milk in Saudi Arabia. Ninety-three suspected LAB were isolated from thirteen different types of raw and fermented milk from indigenous animals in Saudi Arabia. The identification of forty-six selected LAB strains and their genetic relatedness was performed based on 16S rDNA gene sequence comparisons. None of the strains exhibited resistance to clinically relevant antibiotics or had any undesirable hemolytic activity, but they differed in their other probiotic characteristics, that is, tolerance to acidic pH, resistance to bile, and antibacterial activity. In conclusion, the isolates Lactobacillus casei MSJ1, Lactobacillus casei Dwan5, Lactobacillus plantarum EyLan2, and Enterococcus faecium Gail-BawZir8 are most likely the best with probiotic potentials. We speculate that studying the synergistic effects of bacterial combinations might result in a more effective probiotic potential. We suspect that raw and fermented milk products from animals in Saudi Arabia, especially Laban made from camel milk, are rich in LAB and have promising probiotic potential.

Antagonistic lactic acid bacteria isolated from goat milk and identification of a novel nisin variant Lactococcus lactis

Background

The raw goat milk microbiota is considered a good source of novel bacteriocinogenic lactic acid bacteria (LAB) strains that can be exploited as an alternative for use as biopreservatives in foods. The constant demand for such alternative tools justifies studies that investigate the antimicrobial potential of such strains.

Results

The obtained data identified a predominance of Lactococcus and Enterococcus strains in raw goat milk microbiota with antimicrobial activity against Listeria monocytogenes ATCC 7644. Enzymatic assays confirmed the bacteriocinogenic nature of the antimicrobial substances produced by the isolated strains, and PCR reactions detected a variety of bacteriocin-related genes in their genomes. Rep-PCR identified broad genetic variability among the Enterococcus isolates, and close relations between the Lactococcus strains. The sequencing of PCR products from nis-positive Lactococcus allowed the identification of a predicted nisin variant not previously described and possessing a wide inhibitory spectrum.

Conclusions

Raw goat milk was confirmed as a good source of novel bacteriocinogenic LAB strains, having identified Lactococcus isolates possessing variations in their genomes that suggest the production of a nisin variant not yet described and with potential for use as biopreservatives in food due to its broad spectrum of action.

Dynamics of bacterial communities during the ripening process of different Croatian cheese types derived from raw ewe's milk cheeses

Microbial communities play an important role in cheese ripening and determine the flavor and taste of different cheese types to a large extent. However, under adverse conditions human pathogens may colonize cheese samples during ripening and may thus cause severe outbreaks of diarrhoea and other diseases. Therefore in the present study we investigated the bacterial community structure of three raw ewe's milk cheese types, which are produced without the application of starter cultures during ripening from two production sites based on fingerprinting in combination with next generation sequencing of 16S rRNA gene amplicons. Overall a surprisingly high diversity was found in the analyzed samples and overall up to 213 OTU97 could be assigned. 20 of the major OTUs were present in all samples and include mostly lactic acid bacteria (LAB), mainly Lactococcus, and Enterococcus species. Abundance and diversity of these genera differed to a large extent between the 3 investigated cheese types and in response to the ripening process. Also a large number of non LAB genera could be identified based on phylogenetic alignments including mainly Enterobacteriaceae and Staphylococcacae. Some species belonging to these two families could be clearly assigned to species which are known as potential human pathogens like Staphylococcus saprophyticus or Salmonella spp. However, during cheese ripening their abundance was reduced. The bacterial genera, namely Lactobacillus, Streptococcus, Leuconostoc, Bifidobacterium, Brevibacterium, Corynebacterium, Clostridium, Staphylococcus, Thermoanerobacterium, E. coli, Hafnia, Pseudomonas, Janthinobacterium, Petrotoga, Kosmotoga, Megasphaera, Macrococcus, Mannheimia, Aerococcus, Vagococcus, Weissella and Pediococcus were identified at a relative low level and only in selected samples. Overall the microbial composition of the used milk and the management of the production units determined the bacterial community composition for all cheese types to a large extend, also at the late time points of cheese ripening.

Microbiological quality of milk in Tanzania: from Maasai stable to African consumer table

In Tanzania, pastoralists such as the Maasai and small urban farmers are responsible for the country's milk production, and 95% of the national milk supply is sold without regulation. This study was conducted using hygiene checklists and milk sampling to investigate milk quality and safety at various steps throughout the milk production chain. In regions of Dar es Salaam and Lake Victoria, 196 milk samples were collected: 109 samples of raw milk, 41 samples of packed or open served heat-treated products, and 46 samples of fermented products. Samples were taken from (i) the production level (pastoralists and urban farmers), (ii) the collection level (middlemen and depots), (iii) processors (dairies), and (iv) retailers (kiosks). Samples were analyzed for hygiene criteria (total bacteria, total coliforms, Escherichia coli, and coagulase-positive staphylococci) and foodborne pathogens such as Salmonella, enterohemorrhagic E. coli O157:H7, and Listeria monocytogenes. Adequate heating of milk for drinking was determined via heat labile alkaline phosphatase and lactoperoxidase analysis. Total bacterial counts indicated that only 67% (73 of 109) of raw milk samples and 46% (19 of 41) of heat-treated samples met national Tanzanian standards. Bulk milk samples taken from the traditional milking vessels of Maasai pastoralists had the lowest total bacterial counts: ≥ 1 × 10(2) CFU/ml. Foodborne pathogens such as E. coli O157:H7 and Salmonella were isolated from 10.1% (11 of 109) of raw milk samples but were not detected in heat-treated or fermented products, and 83% of heat-treated milk samples were lactoperoxidase negative, indicating overpasteurization. Coliforms were detected in 41% (17 of 41) of processed milk samples, thus indicating a high rate of recontamination. A progressive decrease in microbial quality along the milk production chain was attributed to departures from traditional methods, inadequate milk containers, long transport distances, lack of cooling, and lack of a basic understanding of hygiene.

Hazard identification and exposure assessment for bacterial risk assessment of informally marketed milk in Abidjan, Côte d'Ivoire

BACKGROUND

Animal-source foods are important causes of food-borne illness, and milk and dairy products can contain pathogenic microorganisms.

OBJECTIVE

We conducted a stochastic assessment of the risk of ingesting milk contaminated with specific microbial pathogens (Escherichia coli, Staphylococcus aureus, and Enterococcus spp.) in Abidjan, Côte d'Ivoire.

METHODS

We carried out structured interviews and focus group discussions with farmers (n = 15), vendors (n = 17), and consumers (n = 188) to characterize dairy production systems and milk consumption behavior. Microbiological sampling was conducted at different points between milking and sale. A risk model was developed, and the risk of consuming contaminated raw milk was estimated by Monte Carlo simulation.

RESULTS

The investigation into local raw milk consumption patterns showed that the proportion of raw milk consumption was 51.6% in people who consume milk. The probability of ingestion of marketed raw milk that failed to meet standards for this group of bacteria was 29.9% and about 652 consumers per day were estimated to ingest contaminated milk. Microbiological tests from the farm showed that 7.2% of samples taken from milkers' hands, 4.4% of water samples (water used to rinse milk containers or milking utensils (calabash, plastic bottle, filters, buckets), 4.4% of environmental samples (air pollution), 13.2% of samples from milking utensils, and 4.9% of samples from cows' udders were contaminated with one or more of these pathogens. About 624.6 L of marketed raw milk would need to be discarded per day if discarding milk was chosen as the option of risk reduction. The destruction of this milk would result in a potential loss of Euro623.9 per day for all producers.

CONCLUSIONS

The risk of human illness from consumption of raw milk could be mitigated by raising awareness about heat treatment of milk and good hygiene practices in the dairy chain.

Lantibiotics biosynthesis genes and bacteriocinogenic activity of Lactobacillus spp. isolated from raw milk and cheese

Lactobacillus species are usually used as starters for the production of fermented products, and some strains are capable of producing antimicrobial substances, such as bacteriocins. Because these characteristics are highly desirable, research are continually being performed for novel Lactobacillus strains with bacteriocinogenic potential for use by food industries. The aim of this study was to characterise the bacteriocinogenic potential and activity of Lactobacillus isolates. From a lactic acid bacteria culture collection obtained from raw milk and cheese, 27 isolates were identified by 16S rDNA as Lactobacillus spp. and selected for the detection of lantibiotics biosynthesis genes, bacteriocin production, antimicrobial spectra, and ideal incubation conditions for bacteriocin production. Based on the obtained results, 21 isolates presented at least one of the three lantibiotics biosynthesis genes (lanB, lanC or lamM), and 23 isolates also produced antimicrobial substances with sensitivity to at least one proteinase, indicating their bacteriocinogenic activity. In general, the isolates had broad inhibitory activity, mainly against Listeria spp. and Staphylococcus spp. strains, and the best antimicrobial performance of the isolates occurred when they were cultivated at 25 °C for 24 or 48 h or at 35 °C for 12 h. The present study identified the bacteriocinogenic potential of Lactobacillus isolates obtained from raw milk and cheese, suggesting their potential use as biopreservatives in foods.

How human brucellosis incidence in urban Kampala can be reduced most efficiently? A stochastic risk assessment of informally-marketed milk

BACKGROUND

In Kampala, Uganda, studies have shown a significant incidence of human brucellosis. A stochastic risk assessment involving two field surveys (cattle farms and milk shops) and a medical record survey was conducted to assess the risk of human brucellosis infection through consumption of informally marketed raw milk potentially infected with Brucella abortus in Kampala and to identify the best control options.

METHODOLOGY/PRINCIPAL FINDINGS

In the cattle farm survey, sera of 425 cows in 177 herds in the Kampala economic zone were sampled and tested for brucellosis using a competitive enzyme-linked immunosorbent assay (CELISA). Farmers were interviewed for dairy information. In the milk shop surveys, 135 milk sellers in the urban areas were interviewed and 117 milk samples were collected and tested using an indirect enzyme-linked immunosorbent assay (IELISA). A medical record survey was conducted in Mulago National Referral Hospital for serological test results. A risk model was developed synthesizing data from these three surveys. Possible control options were prepared based on the model and the reduction of risk was simulated for each scenario. Overall, 12.6% (6.8-18.9: 90%CI) of informally marketed milk in urban Kampala was contaminated with B.abortus at purchase and the annual incidence rate was estimated to be 5.8 (90% CI: 5.3-6.2) per 10,000 people. The best control option would be the construction of a milk boiling centre either in Mbarara, the largest source of milk, or in peri-urban Kampala and to ensure that milk traders always sell milk to the boiling centre; 90% success in enforcing these two options would reduce risk by 47.4% (21.6-70.1: 90%CI) and 82.0% (71.0-89.0: 90%CI), respectively.

CONCLUSION/SIGNIFICANCE

This study quantifies the risk of human brucellosis infection through informally marketed milk and estimates the incidence rate in Kampala for the first time; risk-based mitigation strategies are outlined to assist in developing policy.