The effect of cooling and warming rates on the survival of a variety of bacteria

Concentrations of fecal bacteria and nutrients in soil surrounding round-bale feeding sites1,2

An experiment was conducted over 7 mo (January to July 2003) to evaluate fecal bacteria and nutrient concentrations in soil surrounding round-bale feeders at 10 winter feeding sites. Soil samples 15 cm in depth were taken monthly from each site at distances of 3, 12, 21, and 30 m from the feeder. Soil samples were taken before livestock access to the sites (January), during the feeding period (February, March, and April), and after cattle removal from the sites (May, June, and July). Results indicated that fecal bacteria concentrations increased over the feeding period and were greatest at close proximity to round-bale feeders. Fecal Escherichia coli concentrations were greater in April (P < 0.03) at 3 and 12 m than in all other months, except March. At 21 and 30 m from the feeders, fecal E. coli concentrations were greater in April (P < 0.01) than in other months. At 3 m from the feeder, fecal Streptococci concentrations were greater in March and April (P < 0.01) than in other months. Although fecal E. coli concentrations in July had returned to levels similar to those in the prefeeding period, fecal Streptococci remained at higher concentrations (P < 0.05) than at the prefeeding period. The concentration of soil P at 3 m was greater in April (P < 0.02) than in January, February, and May. After cattle access to the sites, soil DM content was consistently less for samples taken at 3 m from the feeder compared with the other distances, with quadratic decreases (P < 0.02) noted in March, April, and July, and linear decreases (P < 0.01) in May and June, as distance from the feeder decreased.

Development of methods for the detection and quantification of 7alpha-dehydroxylating clostridia, Desulfovibrio vulgaris, Methanobrevibacter smithii, and Lactobacillus plantarum in human feces

BACKGROUND

Mounting evidence suggests a relationship between bacterial metabolism of certain dietary and endogenous factors and the development of colorectal cancer. Deoxycholic acid (DCA) is a well studied co-carcinogen and bio-transformation product of 7alpha-dehydroxylating Clostridia. H2S is a cytotoxic metabolite produced primarily by sulfate-reducing bacteria (SRB). The production of methane indicates low levels of active SRB. Lactic acid bacteria (LAB) have received attention recently due to their putative anti-tumor properties.

METHOD

Human stool was spiked with pure cultures of bacteria and diluted in several enriched media. Each dilution titer was analyzed for the presence of the organism by PCR and biochemical assays. Duplicate stool aliquots were stored under various conditions for a 1 month period at -20 degrees C to test viability and detection.

RESULTS

Growth and enumeration of each spiked organism was confirmed by PCR and biochemical assays. The combination of bead beating and chemical lysis steps produced the greatest DNA yields. PCR assays detected as low as 75 fg target DNA. The ability to detect Methanobrevibacter smithii, and Desulfovibrio vulgaris by either PCR or biochemical assay declined significantly after storage at -20 degrees C for 1 month.

CONCLUSIONS

Accurate detection and quantification of each bacterium using the described methods resulted when stool was processed immediately after collection. Storage of some members of the gut flora results in decrease in or loss of viability.

Adsorption of endogenous polyphenols relieves the inhibition by fruit juices and fresh produce of immuno-PCR detection of Escherichia coli O157:H7

The immuno-polymerase chain reaction (PCR) approaches facilitate rapid (8 h) detection of Escherichia coli O157:H7 in contaminated dairy products and ground beef samples with detection sensitivities approaching 1 colony forming unit (cfu) g-1 ml-1. However, no PCR products were obtained when the method was applied to identify E. coli O157:H7 in tainted apple juice. Enzyme-linked immuno-assay (ELISA) results suggested non-specific binding of endogenous polyphenols (ubiquitous in plant products) to antibodies present on the surface of the immunobeads, making the latter unavailable for capturing the target bacteria Treatment of the test sample, prior to IMS, with a synthetic fining agent, polyvinylpyrrolidone, restored the full function and sensitivity of the immuno-PCR. The study demonstrates the suitability of the improved method as a generic strategy for rapid screening of fruit juices and plant produce for E. coli O157:H7.

Bioluminescence as a real-time monitor of injury and recovery in Salmonella typhimurium

Bioluminescence provides a novel tool with which to probe in real time the recovery of microorganisms such as Salmonella typhimurium from sub-lethal injury, a condition of immense importance in the enumeration of microorganisms in food and environmental samples such as from estuarine waters. We describe the application of in vivo bioluminescence to monitor the recovery of S. typhimurium from freeze injury and, in addition, we explore the effect of multiple stress conditions on microbial recovery where we compare bioluminescence with viable count measurement.

Inactivation and injury of Yersinia enterocolitica by radiation and freezing

Cell inactivation and cell injury by irradiation and freezing of the potentially enteropathogenic, food-borne gram-negative rod Yersinia enterocolitica strain WA was investigated. The radiation dose necessary to kill 90% of the initial population, i.e., one D-value, was 10.0, 14,3, and 24.0 krad when irradiation was carried out at 2 to 0, -18, and -75 degrees C, respectively. On the other hand, cell injury, i.e., inability to form colonies in agar containing 2.5% NaCl, was 32, 42 and 54% when cells were irradiated to one D-value at 2 to 0, -18, and -75 degrees C, respectively. Freezing alone (without irradiation) at -18 and -75 degrees C for 1 h resulted in 7 and 42% cell inactivation and 55 and 83% cell injury, respectively. These data show that given the same extent of cell inactivation, freezing caused substantially greater cell injury than radiation. For purposes of radiation sterilization, doses of 100 and 150 krad would be sufficient to inactivate 10 log cycles of Y. enterocolitica strain WA if irradiated at 2 to 0 and -18 degrees C, respectively. Presence of 2.5% NaCl may result in a further 50% reduction of the dose required to achieve sterility.

Factors affecting inactivation of Moraxella-Acinetobacter cells in an irradiation process

The effect of various stages of the irradiation processing of beef on the injury and inactivation of radiation-resistant Moraxella-Acinetobactor cells was studied. Moraxella-Acinetobacter cells were more resistant to heat inactivation and injury when heated in meat with salts (0.75% NaCl and 0.375% sodium tripolyphosphate) then in meat without salts. These salts had no effect on radiation resistance. Both radiation- and heat-injured cells were unable to form colonies at 30 degrees C in plate count agar containing 0.8% NaCl. Neither unstressed nor heat-stressed cells were able to multiply in minced beef incubated at 30 degrees C for 12 h. Only after the beef was diluted 1:10 with peptone water were the heat-injured cells able to repair and eventually multiply. Heated cells were more sensitive to radiation inactivation and injury than unheated cells. After repair, the cells regained their resistance to both NaCl and irradiation. Freezing and storage at -40 degrees C for 14 days had only a slight effect on either unstressed or heat-stressed cells.