In vitro antibacterial effect of yogurt on Escherichia coli

Effect of acidified milk feeding on the intake, average daily gain and fecal microbiological diversity of Holstein dairy calves

OBJECTIVE

To evaluate the effect of feeding acidified milk on the growth and fecal microbial diversity of dairy calves.

METHODS

Twenty healthy 3-day-old female Holstein calves with similar body weights were selected and randomly divided into two groups. One group was fed pasteurized milk (PM, Control), while the other was fed acidified milk (AM) ad libitum until weaned (day 60). The experiment lasted until day 180.

RESULTS

There was no difference in the nutritional components between PM and AM. The numbers of Escherichia coli and total bacteria in AM were lower than in PM. At 31 to 40 and 41 to 50 days of age, the milk intake of calves fed AM was higher than that of calves fed PM (p<0.05), and the solid feed intake of calves fed AM was higher than that of calves fed PM at 61 to 90 days (p<0.05). The average daily gain of calves fed AM was also higher than that of calves fed PM at 31 to 60, 61 to 180, and 7 to 180 days (p<0.05). The calves fed AM tended to have a lower diarrhea rate than those fed PM (p = 0.059). Bacteroides had the highest abundance in the feces of calves fed AM on day 50, while Ruminococcaceae_UCG_005 had the highest abundance in the feces of calves fed AM on day 90 and calves fed PM on days 50 and 90. At the taxonomic level, the linear discriminant analysis scores of 27 microorganisms in the feces of calves fed AM and PM on days 50 and 90 were higher than 4.0.

CONCLUSION

Feeding AM increased calf average daily gain and affected fecal bacterial diversity.

Modeling the effect of temperature on survival rate of Listeria monocytogenes in yogurt

The aim of the study was to (i) evaluate the behavior of Listeria monocytogenes in a commercially produced yogurt, (ii) determine the survival/inactivation rates of L. monocytogenes during cold storage of yogurt and (iii) to generate primary and secondary mathematical models to predict the behavior of these bacteria during storage at different temperatures. The samples of yogurt were inoculated with the mixture of three L. monocytogenes strains and stored at 3, 6, 9, 12 and 15°C for 16 days. The number of listeriae was determined after 0, 1, 2, 3, 5, 7, 9, 12, 14 and 16 days of storage. From each sample a series of decimal dilutions were prepared and plated onto ALOA agar (agar for Listeria according to Ottaviani and Agosti). It was found that applied temperature and storage time significantly influenced the survival rate of listeriae (p<0.01). The number of L. monocytogenes in all the samples decreased linearly with storage time. The slowest decrease in the number of the bacteria was found in the samples stored at 6°C (D-10 value = 243.9 h), whereas the highest reduction in the number of the bacteria was observed in the samples stored at 15°C (D-10 value = 87.0 h). The number of L. monocytogenes was correlated with the pH value of the samples (p<0.01). The natural logarithm of the mean survival/inactivation rates of L. monocytogenes calculated from the primary model was fitted to two secondary models, namely linear and polynomial. Mathematical equations obtained from both secondary models can be applied as a tool for the prediction of the survival/inactivation rate of L. monocytogenes in yogurt stored under temperature range from 3 to 15°C, however, the polynomial model gave a better fit to the experimental data.

Modeling the effect of temperature on survival rate of Salmonella Enteritidis in yogurt

The aim of the study was to determine the inactivation rates of Salmonella Enteritidis in commercially produced yogurt and to generate primary and secondary mathematical models to predict the behaviour of these bacteria during storage at different temperatures. The samples were inoculated with the mixture of three S. Enteritidis strains and stored at 5oC, 10oC, 15oC, 20oC and 25oC for 24 h. The number of salmonellae was determined every two hours. It was found that the number of bacteria decreased linearly with storage time in all samples. Storage temperature and pH of yogurt significantly influenced survival rate of S. Enteritidis (p < 0.05). In samples kept at 5oC the number of salmonellae decreased at the lowest rate, whereas at 25°C the reduction in number of bacteria was the most dynamic. The natural logarithm of mean inactivation rates of Salmonella calculated from primary model was fitted to two secondary models: linear and polynomial. Equations obtained from both secondary models can be applied as a tool for prediction of inactivation rate of Salmonella in yogurt stored under temperature range from 5 to 25°C; however, polynomial model gave the better fit to the experimental data.

Effect of yoghurt or yoghurt serum on microbial quality of cig kofte

Cig kofte, raw meatball is a traditionally produced meat product in Turkey and some other Middle East countries. It is prepared from mixtures of finely minced raw beef, bulgur, onions, various spices and tap water. Cig kofte is an uncooked product and popularly consumed with lettuce and lemon juice. In this study, yoghurt or yoghurt serum (YS) were added to the mixtures of cig kofte instead of tap water to reduce microbial risks of the raw meatball. Additionally, the effects of yoghurt and YS on some physicochemical characteristics of cig kofte were investigated. Cig kofte is generally consumed within a few hours after the preparation because of its raw nature. Also, it is generally sold under unhygienic conditions in restaurants and restaurant-like places. For this purpose, reducing of the microbial load of cig kofte is important. In the results, Escherichia coli and Listeria monocytogenes were not detected in any samples. While lactic acid bacteria count increased by addition of yoghurt and YS, the number of other microorganisms except for total aerobic mesophilic bacteria (TAMB) were decreased. The aw values and% moisture contents of the samples were varied between 0.88-0.94 and 46.25-49.72, respectively. The pH values of the samples were slightly changed during the storage of 24 h while no changes detected in the control samples during the storage. In conclusion, it can be suggested that using the yoghurt or YS instead of tap water in the preparation of cig kofte might ensure the microbial safety, increase the nutritional value and its flavour or aroma.

A randomized clinical trial of the effect of yoghurt on the human salivary microflora

Yoghurt is active against some human pathogens, so this experiment tested whether it is also active against the salivary microflora. A clinical trial was designed, with volunteers aged between 23 and 37 years. Initially, for 8 weeks, they consumed neither yoghurt nor casein-free soybean ice cream (phase 1). They were then split randomly into test (yoghurt) and control (ice cream) groups and required to consume 125 g of these foods twice daily for 8 weeks (phase 2) and then to avoid them for the following 2 weeks (phase 3). Many potential sources of microbial fluctuation were standardized. Salivary samples were then collected at regular intervals of 2 weeks. For each group and phase, the mean logarithms of the salivary counts for total viable flora, oral streptococci, mutans streptococci, lactobacilli and Candida were calculated. The prevalence of Streptococcus thermophilus and Lactobacillus bulgaricus was also assessed. Twenty test and 22 control participants completed the study. At phase 2, the mean for mutans streptococci was lower in the test than in the control group (3.6 vs. 4.0 log colony-forming units/ml; P=0.02). Moreover, the mean had decreased in all test participants with high phase 1 means for lactobacilli as compared to only 36.4% of those with low phase 1 means (P=0.01). L. bulgaricus was transiently detected in three test participants during phase 2. These results suggest that yoghurt does have some activity against the salivary microflora, but this does not seem to be due to the installation of yoghurt microorganisms in the mouth.

Effect of lactic acid bacteria on diarrheal diseases

Microbial balance is an important factor in the maintenance of intestinal homeostasis, and yogurt or fermented milk supplementation has been proposed to control diarrheal diseases. A number of studies using animal models and clinical studies in humans have confirmed the beneficial effect of such fermented products in case of lactose intolerance, viral diarrhea or antibiotics-associated diarrhea. The mechanisms by which lactic acid bacteria exert their effects are multiple. Bacterial lactase improves the absorption of lactose, but fermented products slow down the intestinal transit facilitating the action of residual intestinal lactase. The transient passage of lactic acid bacteria in the digestive tract may represent a microbial barrier against the development of pathogenic bacteria, probably due to the release of compounds contributing to the maintenance of colonization resistance to pathogens. The beneficial effects are mainly described in the presence of live bacteria, but inactivated bacteria may also present preventive or curative capacities in diarrheal diseases. Moreover, lactic acid bacteria has been described as reinforcing the non-specific immune defence but also specific immunity, particularly the secretory immune system mediated by secretory IgA or IgM in response to particulate infectious antigens and perhaps to soluble food antigens. Other possible mechanisms include the trophic effect on the intestinal layer, and a down-regulatory activity in cow's milk allergy as well as anti-inflammatory effects have also been suggested.

Survival of Enterobacter cloacae and Pseudomonas paucimobilis in yoghurts manufactured from cow's milk and soymilk during storage at different temperatures

The survival of two microbial contaminants, Enterobacter cloacae and Pseudomonas paucimobilis, in yoghurts manufactured from cow's milk and soymilk was investigated during storage for 45 days at 4 and 12 degrees C. Sensory panel tests performed before microbiological investigation, showed that the flavor of soy-yoghurts made with cocoa powder or malt added did not have the beany taste of soy beans. Both contaminants were significantly resistant to low pH values during storage for 32 days at 4 degrees C. The survival at 4 degrees C was remarkable in both plain and flavored yoghurts and a population close to 10(2) C.F.U./ml was observed after 38 days of storage. Experiments performed with soymilk yoghurts showed an enhanced survival of P. paucimobilis at 4 degrees C compared to the storage in cow's milk yoghurts; microbial values were close to 7-8 x 10(6) C.F.U./ml after 16 days. Soymilk exhibited a protective effect on L. delbrueckii subsp. bulgaricus and S. thermophilus at 12 degrees C and, compared to the survival in cow's milk yoghurts, a larger number of viable cells of both probiotic microorganisms (10(6) and 10(8) C.F.U./ml, respectively) were observed after 36 days of storage.

Fermented Products with Probiotic Qualities

For several centuries, fermented products derived from plant or animal materials have been an acceptable and essential part of the diet in most parts of the world. Health benefits have also often been associated with them. Probiotics can be defined as fermented food containing specific live microorganisms or a live microbial food or feed supplement, which beneficially effects the human or the host animal by improving its intestinal microbial balance. Nearly all probiotics currently on the market contain Lactobacilli, Streptococci, Enterococci or Bifidobacteria. In contrast to Japan, where freeze-dried microorganisms are consumed by a substantial part of the human population, in Europe, probiotic action towards humans are only claimed for certain fermented dairy products (e.g. yoghurts). Those species that have been extensively studied so far, with several experimental trials on man, are the two yoghurt bacteria Streptocaccus thermophilus and Lactobacillus bulgaricus, L. casei and Bifidobacteria. L. acidophilus has also received important scientific interest, however, only a few human studies have been carried out. From the technological point of view a good probiotic should be stable and viable for long periods under storage, should be able to survive the low pH levels of the stomach, be able to colonise the epithelium of the gastro-intestinal tract of the host, should not be pathogenic and, last but not least, must be capable of exerting a growth promoting effect or a resistance to infectious diseases. The beneficial effects of probiotics are mainly contributed to a direct antagonistic effect against specific groups of microorganisms (Enteropathogenes), by an effect on the metabolism in the gut or by a stimulation of systemic or mucosal immunity. We will present major proven health benefits of milks fermented with those bacterial species and discuss, where possible, the impact of the specific selection and utilisation of particular strains.

Effect of yogurt on clindamycin-induced Clostridium difficile colitis in hamsters

Yogurt exhibits in vitro bactericidal activity against a variety of pathogenic microorganisms, including Clostridium difficile. In the present studies, we tested whether yogurt ingestion could prevent or ameliorate antibiotic associated colitis in the clindamycin-treated hamster model. Male golden Syrian hamsters were given 5 mg/kg clindamycin subcutaneously 24 hr before and 6 hr following inoculation with 0.5 ml of less than 10, 10(3), 10(5), or 10(6) CFU/ml of C. difficile. Hamsters in the control group ingested chow and water ad libitum, whereas the experimental group ingested chow and a 1:1 (v/v) mixture of yogurt and water ad libitum, beginning 24 hr before the first injection of clindamycin and continuing throughout the course of the study. Animals were monitored for colonization with C. difficile, pathological evidence of colitis, and death. Mortality was 100% in yogurt-treated animals, and all animals showed histological changes of severe colitis. Fecal and intestinal segment cultures were positive for C. difficile in all animals. Thus, in the hamster model, we found no evidence to support the possible efficacy of yogurt in the prevention of C. difficile colitis.