A standard set of testing methods reliably enumerates spores across commercial milk powders.

Contamination of dairy powders with sporeforming bacteria is a concern for dairy processors who wish to penetrate markets with stringent spore count specifications (e.g., infant powders). Despite instituted specifications, no standard methodology is used for spore testing across the dairy industry. Instead, a variety of spore enumeration methods are in use, varying primarily by heat-shock treatments, plating method, recovery medium, and incubation temperature. Importantly, testing the same product using different methodologies leads to differences in spore count outcomes, which is a major issue for those required to meet specifications. As such, we set out to identify method(s) to recommend for standardized milk powder spore testing. To this end, 10 commercial milk powders were evaluated using methods varying by (1) heat treatment (e.g., 80°C/12 min), (2) plating method (e.g., spread plating), (3) medium type (e.g., plate count milk agar), and (4) incubation time and temperature combinations (e.g., 32°C for 48 h). The resulting data set included a total of 48 methods. With this data set, we used a stepwise process to identify optimal method(s) that would explain a high proportion of variance in spore count outcomes and would be practical to implement across the dairy industry. Ultimately, spore pasteurized mesophilic spore count (80°C/12 min, incubated at 32°C for 48 h), highly heat resistant thermophilic spore count (100°C/30 min, incubated at 55°C for 48 h), and specially thermoresistant spore enumeration (106°C/30 min, incubated at 55°C for 48 h) spread plating on plate count milk agar were identified as the optimal method set for reliable enumeration of spores in milk powders. Subsequently, we assessed different powder sampling strategies as a way to reduce variation in powder spore testing outcomes using our recommended method set. Results indicated that 33-g composite sampling may reduce variation in spore testing outcomes for highly heat resistant thermophilic spore count over 11-g and 33-g discrete sampling, whereas there was no significant difference across sampling strategies for specially thermoresistant spore enumeration or spore pasteurized mesophilic spore count. Finally, an interlaboratory study using our recommended method set and a modified method set (using tryptic soy agar with 1% starch) among both university and industry laboratories showed increased variation in spore count outcomes within milk powders, which not only was due to natural variation in powders but also was hypothesized to be due to technical errors, highlighting the need for specialized training for technicians who perform spore testing on milk powders. Overall, this study addresses challenges to milk powder spore testing and recommends a method set for standardized spore testing for implementation across the dairy industry.

Nevertheless, She Resisted - Role of the Environment on Listeria monocytogenes Sensitivity to Nisin Treatment in a Laboratory Cheese Model.

The growth of Listeria monocytogenes on refrigerated, ready-to-eat food products is a major health and economic concern. The natural antimicrobial nisin targets the bacterial cell wall and can be used to inhibit L. monocytogenes growth on cheese. Cell wall composition and structure, and therefore the efficacy of cell wall acting control strategies, can be severely affected by environmental and stress conditions. The goal of this study was to determine the effect of a range of pH and temperatures on the efficacy of nisin against several strains of L. monocytogenes in a lab-scale, cheese model. Cheese was made with or without the addition of nisin at different pH and then inoculated with L. monocytogenes; L. monocytogenes numbers were quantified after 1, 7, and 14 days of incubation at 6, 14, or 22°C. While our data show that nisin treatment is able to reduce L. monocytogenes numbers, at least initially, growth of this pathogen can occur even in the presence of nisin, especially when cheese is stored at higher temperatures. Several environmental factors were found to affect nisin efficacy against L. monocytogenes. For example, nisin is more effective when cheese is stored at lower temperatures. Nisin is also more effective when cheese is made at higher pH (6 and 6.5), compared to cheese made at pH 5.5, and this effect is at least partially due to the activity of cell envelope modification genes dltA and mprF. Serotype was also found to affect nisin efficacy against L. monocytogenes; serotype 4b strains showed lower susceptibility to nisin treatment compared to serotype 1/2 strains. Overall, our results highlight the importance of considering environmental conditions specific to a food matrix when developing and applying nisin-based intervention strategies against L. monocytogenes.

Environmental conditions and serotype affect Listeria monocytogenes susceptibility to phage treatment in a laboratory cheese model.

Listeria monocytogenes can survive and grow in a variety of environments, including refrigeration, making it difficult to control and highlighting the importance of optimizing control strategies against this pathogen. Listeria phages are attractive biocontrol agents because phages bind to specific wall teichoic acids (WTA) on the bacterial cell wall, inhibiting pathogens without disrupting the normal microbiota or structure of the food. Common stresses found on dairy products can affect cell wall composition and structure and subsequently affect the efficiency of control strategies that target the cell wall. The goal of this study was to determine the effect of a range of pH and temperatures on the effectiveness of a commercial phage cocktail treatment against several strains of L. monocytogenes in a cheese matrix. We developed a laboratory-scale cheese model that was made at different pH, treated with phage, and then inoculated with L. monocytogenes. Cheeses were incubated at 6, 14, or 22°C for 14 d, and bacterial counts were determined on d 1, 7, and 14. Our data show that phage treatment has a limited ability to reduce L. monocytogenes counts at each temperature tested; however, it was more effective on specific strains of L. monocytogenes when cheese was stored at higher temperatures. More specifically, the average counts of L. monocytogenes on phage-treated cheese stored at 22°C were significantly lower than those on phage-treated cheese stored at 6 or 14°C. Similarly, phage treatment was significantly more effective at inhibiting L. monocytogenes on cheese made at higher pH (6 and 6.5) compared with counts on cheese made at pH 5.5, where L. monocytogenes did not grow. Furthermore, serotype was found to affect the susceptibility of L. monocytogenes to phage treatment; serotype 1/2 strains showed significantly higher susceptibility to phage treatment than serotype 4b strains. Overall, our results suggest the importance of considering the efficacy of phage under conditions (i.e., temperature and pH) specific to a given food matrix when applying interventions against this important foodborne pathogen.

Transjugular intrahepatic portosystemic shunts.

Management of bleeding esophageal varices due to portal hypertension has traditionally relied on endoscopic sclerotherapy and operative intervention with placement of a portosystemic shunt. Although percutaneous decompression of portal hypertension was investigated 25 years ago, it was not clinically feasible until recently. With the advent of intravascular stents, the technique of creating a transjugular intrahepatic portosystemic shunt (TIPS) can now be effectively applied to treat the complications of portal hypertension, including variceal hemorrhage and refractory ascites. Since its introduction in 1989, TIPS has enjoyed widespread clinical application. The initial results with this procedure are encouraging and suggest that it is an effective means of reducing the frequency of variceal hemorrhage in patients with portal hypertension. The long-term patency rate and frequency of complications, however, have not been clearly defined. Similarly, the role of TIPS in the treatment of refractory ascites, Budd-Chiari syndrome, and hepatorenal syndrome remains unclear because sufficient data do not yet exist to support its general use in these settings.

Bronchiolitis obliterans in heart-lung transplantation patients: radiologic findings in 11 patients.

Patients who survive the postoperative period after combined heart-lung transplantation are at risk for developing progressive airway damage consisting of central bronchiectasis and bronchiolitis obliterans. The cause of these abnormalities is uncertain, but they are thought to represent a form of chronic rejection. The chest radiographs and medical records of 11 transplantation patients with proved bronchiolitis obliterans were reviewed retrospectively. A pathologic diagnosis was made by open-lung biopsy (five patients), transbronchial biopsy (three patients), and autopsy (two patients). Clinical criteria alone were used for diagnosis in one patient. In all patients, the chest radiographs showed parenchymal abnormalities consisting of linear-nodular, nodular, confluent nodular, or diffuse alveolar opacities. Radiographic evidence of central bronchiectasis was present in nine of the 11 patients. This feature was not present on chest radiographs of five randomly selected asymptomatic transplant patients. We conclude that the parenchymal lung changes in bronchiolitis obliterans in transplant patients are nonspecific and are radiographically indistinguishable from other infectious and noninfectious complications. The presence of central bronchiectasis (nine of the 11 patients) may be a distinctive radiographic finding in this group of patients.