Phenotype of mice and macrophages deficient in both phagocyte oxidase and inducible nitric oxide synthase.
The two genetically established antimicrobial mechanisms of macrophages are production of reactive oxygen intermediates by phagocyte oxidase (phox) and reactive nitrogen intermediates by inducible nitric oxide synthase (NOS2). Mice doubly deficient in both enzymes (gp91(phox-/-)/NOS2(-/-)) formed massive abscesses containing commensal organisms, mostly enteric bacteria, even when reared under specific pathogen-free conditions with antibiotics. Neither parental strain showed such infections. Thus, phox and NOS2 appear to compensate for each other's deficiency in providing resistance to indigenous bacteria, and no other pathway does so fully. Macrophages from gp91(phox-/-)/NOS2(-/-) mice could not kill virulent Listeria. Their killing of S. typhimurium, E. coli, and attenuated Listeria was markedly diminished but demonstrable, establishing the existence of a mechanism of macrophage antibacterial activity independent of phox and NOS2. (+info)
Effect of transforming growth factor beta on experimental Salmonella typhimurium infection in mice.
We have investigated the effect of the in vivo administration of recombinant transforming growth factor beta (rTGF-beta) on the pathogenic mechanisms involved in Salmonella typhimurium experimental infection in mice. The protective response elicited by macrophages was induced by rTGF-beta1 by 2 days after experimental infection, as demonstrated by an increased NO production, while the humoral protective effect began with cytokine mRNA expression 2 days after the challenge and continued after 5 days with cytokine release and lymphocyte activation. We demonstrated that all mice who received rTGF-beta1 survived 7 days after infection. The number of bacteria recovered in the spleens and in the livers of rTGF-beta1-treated mice 2 and 5 days after infection was significantly smaller than that found in the same organs after phosphate-buffered saline (PBS) inoculation. Furthermore, 2 and 5 days after infection, splenic macrophages from rTGF-beta1-treated mice showed a greater NO production than did those from PBS-treated mice. The effect of rTGF-beta1 on S. typhimurium infection in mice was correlated with the expression of cell costimulatory CD28 molecules. Five days after S. typhimurium infection, the percentage of CD28(+)-expressing T cells in splenic lymphocytes from rTGF-beta1-treated mice increased with respect to that from control mice. Gamma interferon (IFN-gamma) mRNA was present in a greater amount in spleen cells from rTGF-beta1-treated mice after 2 days, although the intensity of the band decreased 5 days after the challenge. A similar pattern was obtained with the mRNAs for interleukin-1alpha (IL-1alpha), IL-6, TGF-beta, and inducible nitric oxide synthase, which showed greater expression in cells obtained from rTGF-beta1-treated and S. typhimurium-infected mice 2 days after challenge. The treatment with rTGF-beta1 induced an increase in IL-1alpha and IFN-gamma release in the supernatant of splenocyte cultures 5 days after the experimental infection with S. typhimurium. Moreover, we demonstrated that 5 days after infection, the IFN-gamma titer was significantly greater in the sera of rTGF-beta-treated mice than in those of PBS-treated mice. Also, hsp60 showed greater expression 2 days after the challenge in splenocytes from rTGF-beta1-treated mice. The role played by proinflammatory and immunoregulatory cytokines and by CD28 is discussed. (+info)
A case of canine salmonellosis due to Salmonella infantis.
A 7-year-old male dog kept outdoors manifested severe watery diarrhea with generalized weakness. Salmonella Infantis was isolated from a fecal sample and the dog recovered soon after medication with ampicillin, to which the isolate was highly sensitive. The present case was diagnosed as S. Infantis infection. Due to the importance of Salmonella in public health, soil samples were collected from the garden where the dog was kept and were examined for Salmonella, Some of them were positive for S. Infantis, however, no Salmonella was isolated from any soil samples collected after thorough disinfection of the surrounded environment. (+info)
Dietary calcium phosphate stimulates intestinal lactobacilli and decreases the severity of a salmonella infection in rats.
We have shown recently that dietary calcium phosphate (CaPi) has a trophic effect on the intestinal microflora and strongly protects against salmonella infection. It was speculated that precipitation by CaPi of intestinal surfactants, such as bile acids and fatty acids, reduced the cytotoxicity of intestinal contents and favored growth of the microflora. Because lactobacilli may have antagonistic activity against pathogens, the main purpose of the present study was to examine whether this CaPi-induced protection coincides with a reinforcement of the endogenous lactobacilli. In vitro, Salmonella enteritidis appeared to be insensitive to bile acids and fatty acids, whereas Lactobacillus acidophilus was killed by physiologically relevant concentrations of these surfactants. Additionally, after adaptation to a purified diet differing only in CaPi concentration (20 and 180 mmol CaHPO4. 2H2O/kg), rats (n = 8) were orally infected with S. enteritidis. Besides reducing the cytotoxicity and the concentration of bile acids and fatty acids of ileal contents and fecal water, CaPi notably changed the composition of ileal bile acids in a less cell-damaging direction. Significantly greater numbers of ileal and fecal lactobacilli were detected in noninfected, CaPi-supplemented rats. As judged by the lower urinary NOx excretion, which is a biomarker of intestinal bacterial translocation, dietary CaPi reduced the invasion of salmonella. Additionally, the colonization resistance was improved considering the reduction of excreted fecal salmonella. In accordance, fewer viable salmonella were detected in ileal contents and on the ileal mucosa in the CaPi group. In conclusion, reducing the intestinal surfactant concentration by dietary CaPi strengthens the endogenous lactobacilli and increases the resistance to salmonella. (+info)
Clonal expansion of antigen-specific CD4 T cells following infection with Salmonella typhimurium is similar in susceptible (Itys) and resistant (Ityr) BALB/c mice.
The results show that CD4 T cells specific for a recombinant antigen expressed in Salmonella typhimurium proliferate normally in mice that express the susceptible form of the Ity gene at early times after infection but do not retain the capacity to produce gamma interferon later in the infection. (+info)
Ferrioxamine-mediated Iron(III) utilization by Salmonella enterica.
Utilization of ferrioxamines as sole sources of iron distinguishes Salmonella enterica serotypes Typhimurium and Enteritidis from a number of related species, including Escherichia coli. Ferrioxamine supplements have therefore been used in preenrichment and selection media to increase the bacterial growth rate while selectivity is maintained. We characterized the determinants involved in utilization of ferrioxamines B, E, and G by S. enterica serotype Typhimurium by performing siderophore cross-feeding bioassays. Transport of all three ferric siderophores across the outer membrane was dependent on the FoxA receptor encoded by the Fur-repressible foxA gene. However, only the transport of ferrioxamine G was dependent on the energy-transducing protein TonB, since growth stimulation of a tonB strain by ferrioxamines B and E was observed, albeit at lower efficiencies than in the parental strain. Transport across the inner membrane was dependent on the periplasmic binding protein-dependent ABC transporter complex comprising FhuBCD, as has been reported for other hydroxamate siderophores of enteric bacteria. The distribution of the foxA gene in the genus Salmonella, as indicated by DNA hybridization studies and correlated with the ability to utilize ferrioxamine E, was restricted to subspecies I, II, and IIIb, and this gene was absent from subspecies IIIa, IV, VI, and VII (formerly subspecies IV) and Salmonella bongori (formerly subspecies V). S. enterica serotype Typhimurium mutants with either a transposon insertion or a defined nonpolar frameshift (+2) mutation in the foxA gene were not able to utilize any of the three ferrioxamines tested. A strain carrying the nonpolar foxA mutation exhibited a significantly reduced ability to colonize rabbit ileal loops compared to the foxA+ parent. In addition, a foxA mutant was markedly attenuated in mice inoculated by either the intragastric or intravenous route. Mice inoculated with the foxA mutant were protected against subsequent challenge by the foxA+ parent strain. (+info)
Multidrug-resistant human and animal Salmonella typhimurium isolates in France belong predominantly to a DT104 clone with the chromosome- and integron-encoded beta-lactamase PSE-1.
Epidemiologic relationships were investigated in 187 ampicillin-resistant Salmonella typhimurium strains (86 human, 101 animal) from >2000 strains isolated in 1994. Of 23 resistance patterns, the most frequent (ampicillin [Am], chloramphenicol [Cm], tetracycline [Tc], streptomycin and spectinomycin [Sm], and sulfonamides [Su]) was found in 69.5% of human and 64.8% of animal isolates. Four beta-lactamase genes were identified, blaTEM (24%), blaPSE-1 (78%), and blaSHV and oxa-2 (each <3%). blaPSE-1 and the integrase gene, intI1, but not blaTEM, blaSHV or oxa-2, were chromosomeborne and found almost exclusively in the AmCmTcSmSu strains. In these, polymerase chain reaction mapping revealed two distinct integrons carrying blaPSE-1 or aadA2. Lysotypes, plasmid profiles, and restriction fragment length polymorphisms (IS200) were determined for 50 representative isolates and for 3 DT104 strains from the United Kingdom (UK). The phage type of the PSE-1-producing AmCmTcSmSu strains was 12 atypic, indistinguishable from that of the DT104 strains. The combined data indicate that the same multiresistant clone has spread through human and animal ecosystems in the UK and France. (+info)
The medium-/long-chain fatty acyl-CoA dehydrogenase (fadF) gene of Salmonella typhimurium is a phase 1 starvation-stress response (SSR) locus.
Salmonella enterica serovar Typhimurium (S. typhimurium) is an enteric pathogen that causes significant morbidity in humans and other mammals. During their life cycle, salmonellae must survive frequent exposures to a variety of environmental stresses, e.g. carbon-source (C) starvation. The starvation-stress response (SSR) of S. typhimurium encompasses the genetic and physiological realignments that occur when an essential nutrient becomes limiting for bacterial growth. The function of the SSR is to produce a cell capable of surviving long-term starvation. This paper reports that three C-starvation-inducible lac fusions from an S. typhimurium C-starvation-inducible lac fusion library are all within a gene identified as fadF, which encodes an acyl-CoA dehydrogenase (ACDH) specific for medium-/long-chain fatty acids. This identification is supported by several findings: (a) significant homology at the amino acid sequence level with the ACDH enzymes from other bacteria and eukaryotes, (b) undetectable beta-oxidation levels in fadF insertion mutants, (c) inability of fad insertion mutants to grow on oleate or decanoate as a sole C-source, and (d) inducibility of fadF::lac fusions by the long-chain fatty acid oleate. In addition, the results indicate that the C-starvation-induction of fadF is under negative control by the FadR global regulator and positive control by the cAMP:cAMP receptor protein complex and ppGpp. It is also shown that the fadF locus is important for C-starvation-survival in S. typhimurium. Furthermore, the results demonstrate that fadF is induced within cultured Madin-Darby canine kidney (MDCK) epithelial cells, suggesting that signals for its induction (C-starvation and/or long-chain fatty acids) may be present in the intracellular environment encountered by S. typhimurium. However, fadF insertion mutations did not have an overt effect on mouse virulence. (+info)