Salmonella growth rate

Large quantities of feed are produced daily, transported, and stored, and even a minor contamination with pathogens, for example, Salmonella, has the potential to affect many herds (Sauli et al., 2005). To enhance the nutritional value of feed, large-scale producers treat their feed with organic acids or heat, or both. Dietary inclusion of organic acids has been found to positively affect the growth rate and efficiency of feed utilization (Giesting and Easter, 1991 Mroz et al., 2000), whereas heat treatment... 

FIGURE 8.12 Relative growth rate (arbitrary scale) of some microorganisms as a function of water activity (aw). (a) A xerophilic mold, Xeromyces bisporus. (b) A common mold, Aspergillus flavus. (c) A yeast, Saccharomyces cerevisiae. (d) A bacterium, Salmonella sp. 

Koroyasu, S., Yamazato, M., Hirano, T. and Aizawa, S.I. (1998). Kinetic analysis of the growth rate of the flagellar hook in Salmonella typhimurium by the population balance method. Biophys. J. 74, 436- 43. 

It is crucial that the incubator remains at 37 °C throughout the subculture. Incubators that are opened and closed frequently may not maintain steady temperature and will result in changes in the growth rate of the Salmonella. 

It is not entirely clear why a mutation in pur A creates a selection for a secondary mutation in purR. The answer may be related to the marked difference between Class I and Class II mutants in their growth response to exogenous adenine. The growth of wild-type Salmonella is inhibited by adenine in the medium (125). The inhibition can be prevented by thiamine or its pjrrimidine moiety probably because elevated levels of adenine repress the de novo pathway, thus reducing the concentration of aminoimidazole ribotide which is a thiamine precursor (126). This notion was consistent with the observation that Class I strains are markedly sensitive to adenine inhibition of growth rate under conditions where Class II strains are completely resistant. 

Campylobacter is notoriously fastidious and has very specific growth conditions. The bacterium can survive for short periods outside the host environment but not to the same extent as Salmonella and E. coli (Alter and Scherer, 2006 Garenaux et al., 2008 Mihaljevic et al., 2007). However, despite such fragility, C. jejuni, and to a lesser extent Campylobacter coli, has been the main cause of gastroenteritis for several years 0anssen et al., 2008). This is likely due to the low infectious dose (<500 cells) required to cause symptoms in susceptible hosts and the high carriage rate in livestock (Ozcakir, 2007). 

Figure 1 illustrates the growth of the organism and recovery from the peritoneal cavity as a function of time. The Salmonella are able to multiply at nearly the normal rate in the animal, and with up to 5 hr of incubation no obvious effects of the organism on the animal have been observed. 

The blended mixture of formic and propionic acid was able to stop the growth of salmonella within the recommended dosage rate (3-5 kg/t) at a level of 10 to 10 CFU/ml in the inoculated medium. This demonstrates that the acid blend is effective in the suppression of further growth of Salmonella enteritidis in-vitro. It corresponds well with data obtained from Adams (2001), who used a mixture of propionic and formic acid to successfully reduce the initial Salmonella enteritidis contamination in wheat by 59% at 3 kg/t. 

This review discusses the means by which the bacterium Salmonella typhimurium controls its rate of histidine biosynthesis. Through the use of such control, the bacterium is able to rapidly and efficiently adjust its metabolism to the environmental conditions. For example, the presence or absence of histidine in the growth medium determines whether or not the bacterium synthesizes its own supply of this amino acid. Because a considerable expenditure of energy and material is involved in histidine biosynthesis (see Section II,F), the bacterium preferentially utilizes exogenous histidine when it is available. When this occurs, biosynthesis of the amino acid is stopped, so that metabolic resources may be conserved. 

In cases where assays were not performed at the normal growth temperature of Salmonella (3TC), adjustment of the reaction rates was made by assuming that the reaction rates double every 10°. Values obtained from bacteria derepressed for the histidine biosynthetic enzymes have been corrected for the level of derepression relative to LT-2 growing on minimal salts-glucose. No corrections have been made for substrate concentrations or pH. All assays were conducted at a pH between 7.5 and 8.6. 

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