Evaluating the antagonistic effect of Lactobacillus acidophilus against Shiga toxigenic and non-toxigenic Escherichia coli strains in bioyogurt.

This study was conducted to determine the effect of acidophilus yoghurt (yoghurt fortified with Lactobacillus acidophilus) in comparison to traditional plain yoghurt (St. thermophilus and L. bulgaricus starter cultures) on the survival of three pathogenic Escherichia coli strains; Shiga toxigenic O157 (STx O157), non-toxigenic O157 (Non-STx O157) and Shiga toxigenic non-O157 (STx O145). After six days of refrigerated storage of laboratory-manufactured yoghurt inoculated with the three strains of E. coli separately, all were eliminated in acidophilus yoghurt, while their survival extended in the traditional yoghurt along the storage period (17 d). Reduction percentages of the tested strains in acidophilus yoghurt were 99.93, 99.93 and 99.86%, with log reduction of 3.176, 3.176, and 2.865 cfu/g for Stx O157, Non-Stx O157, and Stx O145 E. coli, respectively, in comparison to 91.67, 93.33 and 93.33%, with log reduction of 1.079, 1.176 and 1.176 cfu/g in traditional yoghurt. Statistical analysis showed a significant effect of acidophilus yoghurt in reducing the count of Stx E. coli O157 (P = 0.001), Non-Stx E. coli O157 (P < 0.01) and Stx E. coli O145 (P < 0.01) compared to the traditional yoghurt. These findings emphasize the potential use of acidophilus yoghurt as a biocontrol alternative method for eliminating pathogenic E. coli, as well as other similar applications in the dairy industry.

Genotypic analysis of nontuberculous mycobacteria isolated from raw milk and human cases in Wisconsin.

Nontuberculous mycobacteria (NTM) compose a group of mycobacteria that do not belong to the Mycobacterium tuberculosis complex group. They are frequently isolated from environmental samples such as water, soil, and, to a lesser extent, food samples. Isolates of NTM represent a major health threat to humans worldwide, especially those who have asthma or are immunocompromised. Human disease is acquired from environmental exposures and through consumption of NTM-contaminated food. The most common clinical manifestation of NTM disease in human is lung disease, but lymphatic, skin and soft tissue, and disseminated disease are also important. The main objective of the current study was to profile the farm-level contamination of cow milk with NTM by examining milk filters and bulk tank milk samples. Five different NTM species were isolated in one dairy herd in Wisconsin, with confirmed 16S rRNA genotypes including Mycobacterium fortuitum, Mycobacterium avium ssp. hominissuis, Mycobacterium abscessus, Mycobacterium simiae, and Mycobacterium avium ssp. paratuberculosis (Mycobacterium paratuberculosis). In tank milk samples, M. fortuitum was the predominant species in 48% of the samples, whereas M. chelonae/abscessus and M. fortuitum were the only 2 species obtained from 77 and 23% of the examined filters, respectively. Surprisingly, M. avium ssp. hominissuis, M. paratuberculosis, and M. simiae were isolated from 16.7, 10.4, and 4% of the examined milk samples, respectively, but not from milk filters. Interestingly, NTM isolates from human clinical cases in Wisconsin clustered very closely with those from milk samples. These findings suggest that the problem of NTM contamination is underestimated in dairy herds and could contribute to human infections with NTM. Overall, the study validates the use of bulk tank samples rather than milk filters to assess contamination of milk with NTM. Nontuberculous mycobacteria represent one type of pathogens that extensively contaminate raw milk at the farm level. The significance of our research is in evaluating the existence of NTM at the farm level and identifying a simple approach to examine the potential milk contamination with NTM members using tank milk or milk filters from dairy operations. In addition, we attempted to examine the potential link between NTM isolates found in the farm to those circulating in humans in Wisconsin.

The inhibitory effect of nisin on Mycobacterium avium ssp. paratuberculosis and its effect on mycobacterial cell wall.

Infection with Mycobacterium avium ssp. paratuberculosis (M. paratuberculosis) is a widespread problem in the United States and worldwide, and it constitutes a significant health problem for dairy animals with a potential effect on human health. Mycobacterium paratuberculosis is easily transmitted through consumption of contaminated milk; therefore, finding safe methods to reduce the mycobacterial load in milk and other dairy products is important to the dairy industry. The main objective of the current study was to investigate the effect of natural products, such as bacteriocins designated as "generally regarded as safe" (GRAS), on the survival of M. paratuberculosis in milk. Commercially synthesized bacteriocin (nisin) was used to examine its effect on the survival of laboratory and field isolates of M. paratuberculosis and in contaminated milk. Surprisingly, nisin had a higher minimum inhibitory concentration (MIC) against the laboratory strain (M. paratuberculosis K10), at 500 U/mL, than against field isolates (e.g., M. paratuberculosis 4B and JTC 1281), at 15 U/mL. In milk, growth of M. paratuberculosis was inhibited after treatment with levels of nisin that are permissible in human food at 4°C and 37°C. Using both fluorescent and scanning electron microscopy, we were able to identify defects in the bacterial cell walls of treated cultures. Our analysis indicated that nisin reduced membrane integrity by forming pores in the mycobacterial cell wall, thereby decreasing survival of M. paratuberculosis. Thus, nisin treatment of milk could be implemented as a control measure to reduce M. paratuberculosis secreted in milk from infected herds. Nisin could also be used to reduce M. paratuberculosis in colostrum given to calves from infected animals, improving biosecurity control in dairy herds affected by Johne's disease.