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.     

A Protocol to Infect Caenorhabditis elegans with Salmonella typhimurium

In the last decade, C. elegans has emerged as an invertebrate organism to study interactions between hosts and pathogens, including the host defense against gram-negative bacterium Salmonella typhimurium. Salmonella establishes persistent infection in the intestine of C. elegans and results in early death of infected animals. A number of immunity mechanisms have been identified in C. elegans to defend against Salmonella infections. Autophagy, an evolutionarily conserved lysosomal degradation pathway, has been shown to limit the Salmonella replication in C. elegans and in mammals. Here, a protocol is described to infect C. elegans with Salmonella typhimurium, in which the worms are exposed to Salmonella for a limited time, similar to Salmonella infection in humans. Salmonella infection significantly shortens the lifespan of C. elegans. Using the essential autophagy gene bec-1 as an example, we combined this infection method with C. elegans RNAi feeding approach and showed this protocol can be used to examine the function of C. elegans host genes in defense against Salmonella infection. Since C. elegans whole genome RNAi libraries are available, this protocol makes it possible to comprehensively screen for C. elegans genes that protect against Salmonella and other intestinal pathogens using genome-wide RNAi libraries.     

Isolation and characterization of proline peptidase mutants of Salmonella typhimurium

The proline requirement of Salmonella typhimurium strain proB25 can be satisfied by either of the peptides Leu-Pro or Gly-Pro-Ala. A mutant derivative of strain proB25 isolated by penicillin selection in medium containing Leu-Pro as proline source fails to use either Leu-Pro or Gly-Pro-Ala as a source of proline. This strain is a double mutant that lacks two aminoacyl-proline-specific peptidases. One of these enzymes (peptidase Q) catalyzes the rapid hydrolysis of Leu-Pro but does not hydrolyze Gly-Pro-Ala or poly-l-proline. Mutations at a site (pepQ) near metE lead to loss of this activity. The other peptidase (peptidase P) catalyzes the hydrolysis of Gly-Pro-Ala and poly-l-proline but is only weakly active with Leu-Pro as substrate. This enzyme is similar to aminopeptidase P previously described in Escherichia coli (16). Mutations at a locus (pepP) near serA lead to loss of this enzyme.     

Comparison of Methods for the Isolation of Salmonella from Bone Meal

The efficiency of some methods for the isolation of Salmonella from bone meal was studied. Grinding of the granulated, industrial product was found to increase Salmonella recovery. An improvement in the efficiency of the pre-enrichment method was obtained by adding deoxycholate (1%) to mannitol broth. Selective enrichment in selenite cystine medium gave better results than in Kauffmann-Müller medium, when small inocula were used. Experimental data showed that, in the presence of large numbers of coliforms and very small numbers of Salmonella, the Kauffman-Müller medium offers better results, but, in the presence of smaller numbers of coliforms, selenite cystine is preferable. As solid selective medium, Brilliant Green Agar gave, in our laboratory, better results than S S medium.     

Isolation and characterization of lon mutants in Salmonella typhimurium.

In this paper we report the isolation and characterization of lon mutants in Salmonella typhimurium. The mutants were isolated by using positive selection by chlorpromazine resistance. The physiological and biochemical properties of the lon mutants in S. typhimurium are very similar to those of Escherichia coli lon mutants. Mutants altered at this locus contain little or no activity of the ATP-dependent protease La and show a number of pleiotropic phenotypes, including increased production of capsular polysaccharides, increased sensitivity to UV light and other DNA-damaging agents, and a decreased ability to degrade abnormal proteins.     

Reference collection of strains of the Salmonella typhimurium complex from natural populations

A collection of 72 reference strains of the Salmonella typhimurium complex of clones recovered from a variety of hosts and environmental sources in diverse geographic locations has been established for use in studies of variation in natural populations. Included are strains of the serovars S. typhimurium, S. saintpaul, S. heidelberg, S. paratyphi B (including variety java) and S. muenchen. The strains, which have been characterized by enzyme electrophoresis for allelic variation in 24 chromosomal structural genes and represent 48 distinctive multilocus genotypes (electrophoretic types or ETs), exemplify the full range of genotypic variation in the S. typhimurium complex. Evolutionary genetic relationships among the ETs are indicated in a phylogenetic tree generated by the neighbour-joining method from a matrix of Nei's standard genetic distance.     

Microbiology of Nigerian Palm Wine with Particular Reference to Bacteria

The bacteria isolated from samples of wine produced by the fermentation of the saps of Elaeis and Raphia palms were identified as Micrococcus, Leuconostoc, Streptococcus, Lactobacillus, Acetobacter, Serratia, Aerobacter (Klebsiella), Bacillus, Zymomonas and Brevibacterium . The organisms occurring most frequently belonged to the first 5 genera. The change from c. pH 7 to c. pH 4.5 during fermentation appeared to be due to lactic acid bacteria and/or certain Gram negative bacteria, e.g. Serratia and Aerobacter (Klebsiella) spp. From about the 3rd day onwards, Acetobacter spp. were recovered.     

Isolation and characterization of FliK-independent flagellation mutants from Salmonella typhimurium.

A flagellum of Salmonella typhimurium and Escherichia coli consists of three structural parts, a basal body, a hook, and a filament. Because the fliK mutants produce elongated hooks, called polyhooks, lacking filament portions, the fliK gene product has been believed to be involved in both the determination of hook length and the initiation of the filament assembly. In the present study, we isolated two mutants from S. typhimurium which can form flagella even in the absence of the fliK gene product. Flagellar structures were fractionated from these suppressor mutants and inspected by electron microscopy. The suppressor mutants produced polyhook-filament complexes in the fliK mutant background, while they formed flagellar structures apparently indistinguishable from those of the wild-type strain in the fliK+ background. Genetic and sequence analyses of the suppressor mutations revealed that they are located near the 3'-end of the flhB gene, which has been believed to be involved in the early process of the basal body assembly. On the basis of these results, we discuss the mechanism of suppression of the fliK defects by the flhB mutations and propose a hypothesis on the export switching machinery of the flagellar proteins.     

Seroepidemiological Survey of Lymphocytic Choriomeningitis Virus in Wild House Mice in China with Particular Reference to Their Subspecies

Serum samples from 337 wild house mice (Mus musculus) from 35 sites in China, collected in 1992 and 1993, were examined for antibodies against lymphocytic choriomeningitis virus (LCMV). Ten samples from eight sites were found to contain such antibodies. Six of the eight positive sites were located in the territory of M. m. gansuensis. One of the other two sites was located in the territory of M. m. castaneus in southern China and the other site was in a habitat of M. m. castaneus which had invaded into the western end of the territory of M. m. homourus. It seems likely that LCMV is distributed in the territories of M. m. gansuensis and M. m. castaneus in China. This is the first report of detection of these antibodies in wild house mice in China and specifically in the territories of M. m. gansuensis and M. m. castaneus.     

Susceptibility of Salmonella typhimurium and Salmonella typhi to oxygen metabolites

Abstract The susceptibility of Salmonella typhimurium LT2 and of S. typhi 1079 to oxygen metabolites were compared. S. typhimurium LT2 and S. typhi 1079 were killed to an equal extent (about 40%) by the xanthine-xanthine oxidase (200 mU/ml) system. Among the various scavengers of oxygen metabolites, catalase alone inhibited the killing of S. typhimurium LT2 and S. typhi 1079 by the xanthine-xanthine oxidase system, indicating that hydrogen peroxide contributed to the killing of Salmonellae . The respiratory burst of murine macrophages was efficiently triggered by the ingestion of S. typhimurium LT2, S. typhimurium SL1102, and S. typhi 1079 and all to the same extent. However, in the range of the concentration of hydrogen peroxide produced by murine macrophages, neither S. typhimurium LT2 nor S. typhi 1079 were killed. Only S. typhimurium SL1102, a rough mutant of S. typhimurium LT2, was markedly susceptible under these conditions. The findings suggest that both S. typhimurium LT2 and S. typhi 1079 are resistant to oxygen-dependent killing mechanisms.     

Susceptibility of Salmonella typhimurium and Salmonella typhi to oxygen metabolites

The susceptibility of Salmonella typhimurium LT2 and S. typhi 1079 to oxygen metabolites were compared. S. typhimurium LT2 and S. typhi 1079 were killed to an equal extent (about 40%) by the xanthine-xanthine oxidase (200 mU/ml) system. Among the various scavengers of oxygen metabolites, catalase alone inhibited the killing of S. typhimurium LT2 and S. typhi 1079 by the xanthine-xanthine oxidase system, indicating that hydrogen peroxide contributed to the killing of Salmonellae. The respiratory burst of murine macrophages was efficiently triggered by the ingestion of S. typhimurium LT2, S. typhimurium SL1102, and S. typhi 1079 and all to the same extent. However, in the range of the concentration of hydrogen peroxide produced by murine macrophages, neither S. typhimurium LT2 nor S. typhi 1079 were killed. Only S. typhimurium SL1102, a rough mutant of S. typhimurium LT2, was markedly susceptible under these conditions. The findings suggest that both S. typhimurium LT2 and S. typhi 1079 are resistant to oxygen-dependent killing mechanisms.