The heat resistance of Listeria monocytogenes

Heat resistance data for Listeria monocytogenes are reviewed. The organism is appreciably more resistant than common Salmonella serotypes but less resistant than Salmonella senftenberg 775W. Reports that the organism can survive heating at 80°C have not been substantiated and are incompatible with carefully determined D and z values in milk and a range of foods. Cooking food to an internal temperature of 70°C for 2 min is adequate to ensure destruction of L. monocytogenes. Normal pasteurization procedures will inactivate L. monocytogenes in milk but the margin of safety is greater for vat pasteurization than for high temperature short time treatment.     

A method for freezing synchronous mitotic and G1 cells

A modification of the protocol developed by Kawamoto, J C & Barrett, J N, Brain res (1986), in press for freezing primary neuron cultures in a solution containing low sodium and high lactate and potassium concentrations was used to freeze synchronous mitotic and G1 CHO cells. After thawing, the cells behaved as if they had never been frozen with respect to cell growth, cell division, plating efficiency, and hyperthermic sensitivity.     

A reexamination of Gilligan’s analysis of the female moral system

Gilligan’s (1982) refinement of Kohlberg’s theory on moral development operates on two theses: (1) females, more so than males, reach moral decisions based on the personalities of the relevant individuals; and (2) female behaviors stemming from moral decisions are based upon “care” and “responsibility for others.” This article accepts the first thesis but argues that the second is incorrect. That is, self-interest—i.e., aiding “blood” kin and/or carefully monitoring reciprocity—rather than “altruism” is argued to be the operant dynamic in forging distaff morality and resultant behavior. Six empirical examples are presented as contraindicative of Gilligan’s second thesis. Finally, it is suggested that selection for the psychological traits of independence and the mastery of subtle social chess yielded ancestral females who had more descendants—us—than did females with alternative profiles. Nancy S. Coney is a professor at Western Illinois University and is interested in both clinical and nonclinical aspects of women’s psychology. Wade C. Mackey is interested in biocultural anthropology and has authored two books on fathering:Fathering Behaviors (Plenum, 1995) andThe American Father (Plenum, 1996).     

Effect of stress treatments on the detection of Listeria monocytogenes and enterotoxigenic Escherichia coli by the polymerase chain reaction

The relationship between viability assessed by plate counts and detectability by gene probe-polymerase chain reaction (PCR) techniques was examined with cells of Escherichia coli and Listeria monocytogenes previously exposed to a range of stress treatments. In all cases the organisms were detectable by PCR after plate counts had declined to zero. Treatment with acid or hydrogen peroxide caused loss of PCR soon after viability was lost, but strong PCR signals were obtained from starved or desiccated cells long after cells became non-viable. Exposure to temperatures up to 100°C had little effect on detection by PCR and even autoclaving cells at 121°C for 15 min failed to abolish PCR detection completely. There is thus no simple relationship between viability and detectability by PCR. Detection of pathogens by PCR in environmental monitoring requires additional evidence of viability before risk can be properly assessed.     

Peroxide sensitivity of cold-shocked Salmonella typhimurium and Escherichia coli and its relationship to minimal medium recovery

Cold-shocked Salmonella typhimurium displayed minimal medium recovery (MMR), viable counts on M9 minimal agar being much higher than those on tryptone soya yeast extract agar (TSYA). The addition of catalase to TSYA restored counts to the level found on M9 agar. Peroxide concentrations between 12 and 30 μmol/1 were measured in TSYB but none was detected in M9 medium. Cold-shocked cells were sensitive to reagent hydrogen peroxide at a concentration similar to that found in TSYB. The minimal medium recovery phenomenon of cold-shocked cells is thus a manifestation of peroxide sensitivity. Changing the composition of growth media affected both cellular catalase activity and the magnitude of the MMR effect but the two properties were not directly related. Factors additional to cellular catalase activity must therefore affect susceptibility to peroxide following cold shock. Muta tional loss of catalase, exonuclease III or recA -dependent DNA repair functions all increased the sensitivity of cold-shocked Escherichia coli to the inhibitory effects of peroxide present in rich medium. The peroxide resistant fraction of a cold-shocked population of Salm. typhimurium (i.e. those cells able to grow on TSYA) was more resistant to gamma radiation than the population as a whole. Cold shock thus sensitizes cells to more than one form of oxidative stress. Prior exposure of growing cells to 30 μ mol/1 hydrogen peroxide abolished their sensitivity to rich medium following cold shock implying that Salm. typhimurium contains an inducible system protecting against oxidative stress.     

Minimizing therapeutically induced anemia

A model for erythroid production based on a continuous maturationproliferation scheme is developed. The model includes a simple control mechanism operating at the proliferating cell level, and analytic solutions for the time dependent response of the model are derived. Using this model, the response of the erythron to a massive depletion of the proliferating cell compartment (due for example to cytostatic drugs or radiation) is calculated. It is demonstrated that a therapeutic measure designed to decrease the erythroid precursor maturation velocity may considerably ameliorate the deleterious effects of proliferating cell destruction. One way to decrease the erythroid cell maturation rate would be by having the patient breathe in an oxygen enriched atmosphere.Deceased