The Effect of pH Adjustment on the Microbiology of Chicken Scald-tank Water with Particular Reference to the Death Rate of Salmonellas

In laboratory experiments adjustment of the pH of chicken scald-tank water to 9.0 ± 0.2 lowered the D 52°C value of a strain of Salmonella typhimurium from 34.5 to 1.25 min. Factory trials where the scald water was maintained at pH 9.0 ± 0.2 for the after-lunch period showed that both the total bacterial population and the number of coli-aerogenes organisms were substantially reduced. Addition of sodium hydroxide also increased the rate of accumulation of total dry matter in the water. Sodium carbonate was as effective as NaOH in increasing the death rate of Salm. typhimurium and would appear to be a suitable alternative.     

TEMPORAL ASPECTS OF HEDONIC RESPONSES1

Continuous measurement of degree of liking for chocolate milk varying in milkfat (0–36%) showed significant fluctuations over the 80 s test period. For 17 judges, samples with intermediate fat levels received maximum liking 20–30 s after placement in the mouth then declined to neutral (neither like nor dislike). The nonfat sample gave a flat, neutral response across time while the 36% fat sample was initially neutral, reached maximum dislike at approximately 20 s then gradually returned to neutral. For 5 judges, increasing degree of liking was expressed for increasing fat levels. For both groups, maximum and minimum time-intensity (T-I) measurements correlated significantly with results from conventional hedonic scaling on a 20-cm line. Degree of liking was unaffected by swallowing or expectorating samples by either T-I or scaling. Thus, similar to perceived intensity, hedonic responses are not static, but show systematic changes during tasting, i.e., from the time the sample is placed into the mouth, through expectoration (or swallowing) until a steady (usually neutral) state is reached.     

The effect of Heterodera avenae, on the root system of susceptible and resistant oat seedlings

The effects of invasion by the cereal cyst nematode, Heterodera avenae, on the root growth of susceptible and resistant oat seedlings were similar. Nematode invasion directly inhibited root extension and lateral root production, which was dependent upon the developmental status of the invaded root tissue and the nematode density cm-¹ root. Both responses are caused by mechanical damage due to nematode invasion leading to decreased top growth in the host. Reduced root development, decreased efficiency of water and nutrient uptake in invaded plants being indirect effects of nematode invasion.     

A Cell Culture System for Study of the Development of Toxoplasma gondii Bradyzoites

ABSTRACT. Toxoplasma gondii is a ubiquitous apicomplexan parasite and a major opportunistic pathogen under AIDS-induced conditions, where it causes encephalitis when the bradyzoite (cyst) stage is reactivated. A bradyzoite-specific Mab, 74.1.8, reacting with a 28 kDa antigen, was used to study bradyzoite development in vitro by immuno-electron microscopy and immunofluorescence in human fibroblasts infected with ME49 strain T. gondii . Bradyzoites were detected in tissue culture within 3 days of infection. Free floating cyst-like structures were also identified. Western blotting demonstrated the expression of bradyzoite antigens in these free-floating cysts as well as in the monolayer. Bradyzoite development was increased by using media adjusted to pH 6.8 or 8.2. The addition of γ-interferon at day 3 of culture while decreasing the total number of cysts formed prevented tachyzoite overgrowth and enabled study of in vitro bradyzoites for up to 25 days. The addition of IL-6 increased the number of cysts released into the medium and increased the number of cysts formed at pH 7.2. Confirmation of bradyzoite development in vitro was provided by electron microscopy. It is possible that the induction of an acute phase response in the host cell may be important for bradyzoite differentiation. This system should allow further studies on the effect of various agents on the development of bradyzoites.     

Modulation of Complement Resistance and Virulence of Naegleria fowleri Amoebae by Alterations in Growth Media

ABSTRACT. Highly-pathogenic, mouse-passaged Naegleria fowleri amoebae are complement resistant. The present study evaluates the effect of complement on N. fowleri and the virulence of the amoebae after animal passage and growth in two different axenic media. Pathogenic N. fowleri maintained in "enriched" Cline medium are virulent for mice and resistant to complement lysis. A rapid decline in resistance to complement and virulence for mice is observed when highly-pathogenic N. fowleri are grown in Nelson medium lacking hemin. N. fowleri maintained in Nelson medium can be rendered complement-resistant by shifting the amoebae to growth in Cline medium for 2 h prior to the addition of complement. Cycloheximide treatment of N. fowleri maintained in Nelson medium blocks the transition to a complement-resistant phenotype following a shift in growth medium. Proteins were radiolabeled with [³⁵S] during a shift from Nelson to Cline medium to identify specific polypeptides which may be associated with the functional activities related to virulence and resistance to complement.     

Physiology of Rana pipiens Reproductive Behavior: A Proposed Mechanism for Inhibition of the Release Call

SYNOPSIS. Non-gravid femaleRana pipiens clasped by sexuallyactive males emit a release call and thereby signal their unreceptivestatus to the clasping male. The receptive condition of gravidfemales is indicated by absence, or inhibition, of the call.This paper provides evidence that arginine-8 vasotocin (AVT)can inhibit the release call by causing water uptake when afemale is in an aquatic environment, and suggests that watermight exert this effect by means of a mechanical distensionof the body wall or internal pressure. This paper also includesevidence that the ovaries are not necessary for AVT's inhibitionof the call. The literature dealing with the physiological basisof female frog reproductive behavior and the physiological basisof the release call are reviewed.