Efficiency of various bacterial suspensions derived from cecal floras of conventional chickens in reducing the population level of Salmonella typhimurium in gnotobiotic mice and chicken intestines

The antagonistic effect exerted towards Salmonella typhimurium by the flora issued from conventional chickens was studied in gnotobiotic animals. In germfree chickens and mice inoculated with S. typhimurium, the highest bacterial counts were observed in ceca, and were not significantly different in either host. The protection afforded by the inoculation of cecal flora issued from a conventional chicken was more effective when this flora was inoculated first into germfree chickens than when it was given only after inoculation with S. typhimurium. Administration of a cecal flora from a 15-day-old chick to gnotobiotic mice and chicken resulted in the inhibition of a further intestinal colonization by S. typhimurium in both hosts. Sixteen strains were isolated among the predominant populations of the fecal flora from chicken flora recipient mice. Association of 14 strains of strictly anaerobic bacteria with 2 strains of Escherichia coli and Streptococcus faecium only decreased the number of S. typhimurium in the ileum of gnotobiotic mice, but not in their cecum. Anaerobe cultures were obtained from 10(-6) and 10(-8) dilutions prepared from the fecal flora of gnotobiotic recipient mice. Antagonistic bacteria were present only in cultures from the 10(-6) dilution. Cecal concentrations of volatile fatty acids were shown not to be the sole factor implicated in the antagonistic effect against S. typhimurium.     

A common virulence region on plasmids from eleven serotypes of Salmonella

Cured derivatives of Salmonella dublin and S. typhimurium showed reduced virulence following oral infection of mice (10(4)-10(5)-fold for S. dublin, 10(2)-fold for S. typhimurium). Large plasmids from S. dublin and S. typhimurium independently restored virulence to the cured S. dublin but truncated S. dublin plasmids with deletions in a previously identified virulence region did not. This common virulence region identified in plasmids from S. dublin and S. typhimurium was shown to be carried on plasmids from 11 other serotypes of Salmonella but was absent from 10 plasmid-containing serotypes. TnA and Tn10 were transduced from the virulence region of two TnA-insertion mutants of S. dublin and one Tn10-insertion mutant of S. typhimurium that showed diminished virulence to recipient wild-type strains of S. dublin, S. enteritidis and S. typhimurium. Each transductant showed a decrease in mouse virulence within the range 10(3)-10(5). It is therefore proposed that similar virulence determinants are expressed in different serotypes. It was also shown that integration that occurred during curing was Tn10 dependent.     

Detection of porin antigen in serum for early diagnosis of mouse infections with Salmonella typhimurium

Abstract The monoclonal antibodies to porin, an outer membrane protein isolated from Salmonella typhimurium and sandwich enzyme linked immunosorbent assay (ELISA) has made possible the detection of porin from sera of S. typhimurium -infected mice. The specificity of the monoclonal antibodies was ascertained based on their cross-reactivity with porins isolated from S. typhi, Shigella flexneri and Escherichia coli and lipopolysaccharide (LPS) of S. typhimurium and E. coli . Serum samples were found to be positive for porin as early as 3 days after intravenous and 5 days after oral infection. In addition, a positive correlation was observed between the bacterial load and the concentration of porin detected in the sera. On the other hand, analysis of sera for anti-porin antibody showed diametrically opposite time kinetics with antigenaemia. These results indicate that porin accumulates in the serum of infected mice much earlier than the appearance of antibodies to porin. Thus detection of porin holds promise for early diagnosis of typhoid.     

Differences in initial rate of intracellular killing of Salmonella typhimurium by granulocytes of Salmonella-susceptible C57BL/10 mice and Salmonella-resistant CBA mice

The contribution of granulocytes to differences in the innate susceptibility of mouse strains to infection by Salmonella typhimurium was assessed on the basis of the size and composition of the inflammatory exudate after i.p. injection of bacteria and the intracellular killing of the bacteria by exudate peritoneal cells and blood granulocytes of resistant CBA and susceptible C57BL/10 mice. The increase in the numbers of both peritoneal granulocytes and macrophages 24 hr after i.p. injection of various numbers of live S. typhimurium was two to four times higher in C57BL/10 mice (p less than 0.05) than in CBA mice. However, despite the larger number of phagocytes in the inflammatory exudate, the numbers of viable S. typhimurium in the peritoneal cavity 24 hr after injection was higher (p less than 0.01) in C57BL/10 mice than in CBA mice. Because the proportion of noningested bacteria was similar in the two mouse strains (less than 30%), these findings indicate a difference in the rate of intracellular killing of the bacteria by exudate peritoneal cells (greater than 75% granulocytes) of the two mouse strains. Subsequent determination of the initial rate of intracellular killing (Kk) of S. typhimurium revealed that after phagocytosis of the bacteria in vivo, exudate peritoneal granulocytes (harvested 24 hr after i.p. injection of 10(3) live S. typhimurium) of CBA mice killed S. typhimurium twice as efficiently (Kk = 0.014 min-1; p less than 0.01) as exudate granulocytes of C57BL/10 mice (Kk = 0.008 min-1) did. Similarly, the initial rate of intracellular killing of the ingested S. typhimurium by blood granulocytes of CBA mice (Kk = 0.017 min-1) was two times higher (p less than 0.01) than that of C57BL/10 mice (Kk = 0.007 min-1). These findings may be specific for S. typhimurium, because L. monocytogenes were killed with equal efficiency by exudate granulocytes and blood granulocytes of these mouse strains (p greater than 0.20). The results of the present study are relevant with respect to the innate resistance of mice to S. typhimurium, particularly during the initial phase of infection when the inflammatory exudate contains predominantly granulocytes.     

Salmonella-typhimurium-specific difference in rate of intracellular killing by resident peritoneal macrophages from salmonella-resistant CBA and salmonella-susceptible C57BL/10 mice

The aim of the present study was to determine whether the difference between the rate of intracellular killing of Salmonella typhimurium by macrophages of salmonella-resistant CBA and salmonella-susceptible C57BL/10 mice also holds for other salmonellae and other bacteria species. After in vivo phagocytosis, the initial rate of in vitro intracellular killing of S. typhimurium phagetype 505, S. typhimurium phagetype 510, and S. typhimurium M206 by macrophages of CBA mice amounted always to approximately 1.7 times the value found for macrophages of C57BL/10 mice (p less than 0.001), indicating that the difference in killing efficiency between CBA and C57BL/10 macrophages holds for various strains of S. typhimurium. However, some other salmonella species, i.e., S. dublin and S. heidelberg, as well as E. coli 054 and 02K1+, Listeria monocytogenes EGD and L347, and Staphylococcus aureus were killed equally efficiently by macrophages of both mouse strains. These findings indicate that the difference between the rates of intracellular killing by macrophages of salmonella-resistant CBA and salmonella-susceptible C57BL/10 does not hold for several other bacteria species and thus might be specific for S. typhimurium. Subsequent experiments showed that the in vivo proliferation of S. typhimurium 510 in the first 2 days after i.v. injection was 2.0-fold to 3.0-fold higher in the spleens and livers of C57BL/10 mice than in those of CBA mice, whereas the in vivo proliferation of S. dublin and S. heidelberg was between 1.0-fold to 1.4-fold higher in the C57BL/10 mice. These findings suggest that the differences between the rate of in vitro intracellular killing of salmonella by CBA and C57BL/10 macrophages are reflected in differences in the rate of in vivo proliferation of these microorganisms in CBA and C57BL/10 mice. To gain insight into the involvement of the oxidative metabolism of CBA and C57BL/10 macrophages in the difference in the rate of intracellular killing of S. typhimurium, the O2 consumption and H2O2 release by resident peritoneal macrophages was determined. The amplitudes of the respiratory burst and the release of H2O2 was identical in macrophages of the two mouse strains after triggering by either preopsonized heat-killed S. typhimurium or phorbol myristic acetate. These findings indicate that the mouse species-associated difference in the intracellular killing of S. typhimurium is not caused by a difference in the oxidative metabolism of CBA and C57BL/10 macrophages.     

Effect of the R plasmids of Salmonella typhimurium strains of various origins on salmonella virulence

Antibiotic-multiresistant S. typhimurium strains, phagovars 20 and 25, of different origin (isolated in hospital infections transferred through everyday contacts and by alimentary route, as well as from samples taken from open water basins and sewage) have been found to carry both transmissible and nontransmissible R plasmids. The frequency of the transfer of R plasmids to Escherichia coli K-12 C 600 rif varies within 0.6 X 10(-5) and 0.7 X 10(-3) per donor cell. The direct transfer of plasmids to S. typhimurium has been mostly realized only in the presence of the mobilizing plasmid, the transfer frequency being 1.0 X 10(-7) to 2.2 X 10(-4) per donor cell. S. typhimurium transconjugates show decreased virulence in both enteral and intraperitoneal infection of mice.     

Transmissive drug resistance and virulence of "epidemic" strains of S. typhimurium]

A total of 59 "epidemic" strains of S. typhimurium and 52 cultures isolated from the cases with sporadic diseases were studied with respect to the nature of their resistance to 10 antibiotics and virulence for albino mice under conditions of subcutaneous and oral inoculation. The virulence of the cultures isolated from the cases with sporadic diseases was higher in the strains sensitive to antibiotics. The "epidemic" strains were characterized by the lowest virulence for the mice and resistance to 8-10 antibiotics simultaneously with the transmissive nature of resistance to 1-5 drugs. The transmissive nature of resistance to antibiotics and its spectrum may serve an additional epidemiological marker of the strains.     

Large outbreak of food poisoning caused by Salmonella typhimurium definitive type 49 in mayonnaise.

An investigation was conducted to determine the vehicle of infection of an outbreak of food poisoning in a large metropolitan building early in 1988. A questionnaire was distributed to 700 people who had eaten in the building during the week of the outbreak, and attack rates for specific food were calculated. Food and stool samples, environmental samples, and eggs and environmental swabs from the egg suppliers were examined microbiologically. Altogether 474 questionnaires were returned, 120 people reporting gastrointestinal illness. The illness was significantly associated with foods containing mayonnaise. Salmonella typhimurium definitive type 49 was isolated from 76 of the 84 stool samples containing salmonella and from five of the eight samples taken from the chicken house of the main egg supplier. Mayonnaise was probably the vehicle of infection, which was caused by S typhimurium definitive type 49.     

Ribosomal ribonucleic acid isolated from Salmonella typhimurium: absence of the intact 23S species.

Ribonucleic acid (RNA) isolated by four distinct methods and from a variety of Salmonella typhimurium strains lacked intact 23S ribosomal RNA (rRNA). On sucrose gradients which minimize aggregation, the vast majority of S. typhimurium rRNA sedimented as a 16S peak with a 14S shoulder. RNA from this region of the gradient was resolved into three discrete bands by electrophoresis in formamide. Two very minor S. typhimurium RNA peaks were resolved at 21S and 10S on sucrose gradients, and each peak formed discrete bands in electrophoresis. It is concluded that if S. typhimurium does possess an intact 23S rRNA species, this species is extremely "labile." The absence of isolatable S. typhimurium 23S rRNA possibly reflected in vivo processing of the rRNA before isolation. Under certain conditions, S. typhimurium rRNA formed discrete aggregates which sedimented similarly to intact Escherichia coli 23S rRNA.     

Experimental study of vaccines against Salmonella typhimurium infection.

Serological and protective activities of vaccines from S. typhimurium and S. minnesota were studied. It has been demonstrated that active protection against infection in experimental salmonellosis in mice can only be obtained by immunization of the animals using vaccines from complete antigenic complexes isolated from S-strains. It has been found that expressed anti-infection immunity (unlike anti-endotoxic immunity) is induced to the same extent by either high-molecular components (2,000,000 daltons and more), showing great serological activity, or components with relatively low molecular weight (15,000--20,000 daltons) and minimum serological activity. Vaccines from Ra- and Re-strains of S. minnesota do not induce resistance to S. typhimurium infection in mice in either active protection tests or passive protection tests.     

The role of metabolic activation of promutagens in the genome destabilization under pheromonal stress in the house mouse (Mus musculus)

The hypothesis on a relationship between the high frequency of mitotic disturbances in bone marrow cells and the change in the activity of the S9 liver fraction containing promutagen-activating enzymes under olfactory stress in the house mouse Mus musculus has been tested. For this purpose, the effect of the pheromone 2,5-dimethylpyrazine on the frequency of mitotic disturbances in mouse bone marrow cells has been measured by the anaphase-telophase assay. The Ames test using Salmonella typhimurium has been employed to compare the capacities of the S9 liver fractions from stressed and intact mice for activating the promutagen 2-aminofluorene. It has been demonstrated that the increased frequency of mitotic disturbances in bone marrow cells induced by the pheromonal stressor in male house mice is accompanied by an increased promutagen-activating capacity of the S9 liver fraction. The model system used in the study allowed the genetic consequences of the exposure to the olfactory stressor to be estimated and the possible mechanisms of genome destabilization to be assumed.     

Activation of mouse peritoneal macrophages during infection with Salmonella typhimurium does not result in enhanced intracellular killing

Our study was performed to investigate whether macrophages become activated during an infection with Salmonella typhimurium and, if so, whether these activated macrophages kill S. typhimurium faster than resident macrophages. Mice received i.v. injections with a sublethal number of S. typhimurium; on about day 12 of the infection the numbers of bacteria in the liver and the spleen were maximal. During the infection, activation of peritoneal macrophages could be demonstrated on the basis of three criteria, i.e., the ability to inhibit the proliferation of Toxoplasma gondii, an enhanced production of H2O2 and an increased expression of Ia Ag. The rate of in vitro intracellular killing of S. typhimurium by these activated macrophages was not increased compared to that for resident macrophages. To determine the growth of S. typhimurium in activated mice a nalidixic acid-resistant mutant strain, called S. typhimurium 510R, was used. The net growth rates of the mutant S. typhimurium 510R in the spleen of S. typhimurium 510-activated and normal mice were similar. However, in the liver of S. typhimurium 510-activated mice the number of S. typhimurium 510R did not change during 3 to 48 h after injection. The role of specific antibodies during the initial phase of the infection was negligible, because only low levels of antibodies were detected during the first 15 days of infection and the growth rates of S. typhimurium 510 in the spleen and liver of mice with high titers of antibodies were not significantly different from the rates in normal mice. The results of this study demonstrate that although macrophages become activated during an infection with S. typhimurium, these cells do not display an enhanced bactericidal activity in vitro and in vivo no significant effect on the growth rate of S. typhimurium in the spleen and a bacteriostatic effect in the liver is found. Hence macrophage activation is probably not very important in the host defense against S. typhimurium.     

The characteristics of the O-specific humoral immune response of mice vaccinated with Salmonella choleraesuis antigens]

The work deals with the results of the comparative enzyme immunoassay (EIA) of serum samples taken from (CBA X C57BL/6) F1 mice immunized with O-specific polysaccharides, O-antigens (O-Ag) obtained by Boivin's method and antigenic preparations isolated with hydroxylamine (HA) from S. choleraesuis and S. typhimurium. O-Ag and lipopolysaccharide (LPS) of the corresponding bacterial species were used as antigens for the sensitization of polystyrene plates. The primary and secondary humoral immune response was studied by means of EIA. As revealed in this investigation, the immunization of mice with HA-isolated antigenic preparations and O-Ag, obtained from S. typhimurium, in a single injection (in doses of 1-100 micrograms) led to the development of weak specific immune response to O-Ag. Response to LPS was absent. After the second immunization of the animals pronounced immune response to O-Ag and LPS was observed. It developed as a response of both IgM and IgG type. The immunization of mice, made in a single injection, with HA-isolated antigenic preparations and O-Ag, obtained from S. choleraesuis, did not lead to the development of O-specific immune response. After the immunization of mice with these antigens in two injections sharply pronounced nonspecific activity of IgM and IgG serum antibodies with respect to O-Ag and LPS of homologous and heterologous bacterial species was noted in EIA. Neither S. typhimurium O-polysaccharide, nor S. choleraesuis O-polysaccharide did not induce O-specific immune response even after the second immunization.     

Monoclonal antibodies to Salmonella lipopolysaccharide: anti-O-polysaccharide antibodies protect C3H mice against challenge with virulent Salmonella typhimurium

The present investigation reports the production of monoclonal antibodies to antigenic determinants of the O-polysaccharide of Salmonella typhimurium lipopolysaccharide (LPS), and assesses the effectiveness of these antibodies in protecting C3H mice against the lethal effects of Salmonella infection. Hybridomas were generated by fusing spleen cells from (BALB/c X A/J)F1 (CAF1) mice hyperimmunized by i.v. injection with acetone-killed S. typhimurium SR-11 with X63-Ag8.653 murine myeloma cells. Hybridomas producing antibodies reactive with S. typhimurium SR-11 whole cells were subcloned, and seven of the resulting clones as well as one previously described clone were selected for use in the studies reported here. Monoclonal antibodies from these eight clones were of the IgG1 (1), IgG3 (6), or IgM (1) isotype and were specific for the O-polysaccharide region of Salmonella LPS, reacting with LPS from smooth S. typhimurium SR-11 and LT-2, but not with LPS from rough S. minnesota R60 (Ra), R345 (Rb), or R595 (Re). The effectiveness of each monoclonal antibody in protecting C3H/HeN and C3H/HeJ mice against the lethal effects of Salmonella infection was evaluated by comparing the median length of survival of groups of mice given antibody by i.p. injection before i.p. challenge with virulent S. typhimurium SR-11 to that of animals that received no antibody. Three out of eight monoclonal anti-O-polysaccharide antibodies, ST-1 (IgM), 10-5-47 (IgG3), and 10-5-6 (IgG3), provided significant (p less than 0.01) protection to C3H/HeN mice challenged with approximately 10(4) LD100 of Salmonella. Only antibodies ST-1 and 10-5-6, however, extended the median length of survival of C3H/HeJ mice beyond that of infected controls. Mouse antiserum prepared against S. typhimurium SR-11 was equally protective in C3H/HeJ mice. In an attempt to understand the contribution of antibody specificity to the relative differences in the protective capacities of the monoclonal antibodies, their reactivities with several Salmonella reference strains of different classical serotypes were examined. Although some differences in reactivity against the different strains were apparent, this approach was not adequate for defining the fine specificity of these monoclonal antibodies. The results of this study provide evidence that monoclonal antibodies with specificity to the O-polysaccharide region of Salmonella LPS can protect C3H mice against challenge with the homologous bacterial strain.     

Genetic control of the innate resistance of mice to Salmonella typhimurium: expression of the Ity gene in peritoneal and splenic macrophages isolated in vitro

The mouse Chromosome 1 locus Ity regulates the extent to which Salmonella typhimurium replicates within the reticuloendothelial cell system (RES) during the first days of infection. If animals are homozygous for the Itys susceptibility allele, the Gram-negative bacterium undergoes rapid net multiplication, and mice die of a typhoid fever-like disease by day 10 of infection. Animals that are homozygous or heterozygous for the resistance allele, Ityr, control net bacterial replication and survive the first phase of salmonellosis. Indirect studies have implicated the resident macrophage as the effector cell for regulation of early in vivo salmonellae growth. To verify this supposition and to evaluate the phenotypic expression of Ity, we developed an in vitro assay to compare kinetics of S. typhimurium growth within Ityr and Itys macrophages. Resident peritoneal and splenic macrophages were used from inbred Ityr and Itys mice and from Ity congeneic mice. With these mice and through the use of radiolabeled S. typhimurium and an avirulent temperature-sensitive mutant of the bacterium, we found that: phagocytosis of S. typhimurium by Ityr and by Itys macrophages was the same; S. typhimurium grew to a greater extent in Itys peritoneal and splenic macrophages than in Ityr cells; Ityr macrophages killed intracellular salmonellae more efficiently than did Itys macrophages. Thus, we have demonstrated directly that Ity is expressed by the macrophage and have shown for the first time with Ity congeneic mice that the basis for differential net growth of virulent S. typhimurium in Ityr and Itys macrophages is a variation in the degree of bacterial kill.     

Cutting edge: role of B lymphocytes in protective immunity against Salmonella typhimurium infection

Infection of mice with Salmonella typhimurium gives rise to a disease similar to human typhoid fever caused by S. typhi. Since S. typhimurium is a facultative intracellular bacterium, the requirement of B cells in the immune response against S. typhimurium is a longstanding matter of debate. By infecting mice on a susceptible background and deficient in B cells (Igmu-/- mice) with different strains of S. typhimurium, we could for the first time formally clarify the role of B cells in the response against S. typhimurium. Compared with Igmu+/+ mice, LD50 values in Igmu-/- mice were reduced during primary, and particularly secondary, oral infection with virulent S. typhimurium. After systemic infection, Igmu-/- mice cleared attenuated aroA- S. typhimurium, but vaccine-induced protection against systemic infection with virulent S. typhimurium involved both B cell-dependent and -independent effector mechanisms. Thus, B cell-mediated immunity plays a distinct role in control of S. typhimurium in susceptible mice.     

Inability of recombinant interferon-gamma to activate the antibacterial activity of mouse peritoneal macrophages against Listeria monocytogenes and Salmonella typhimurium

The effect of recombinant murine interferon-gamma (rIFN-gamma) as single stimulus for the activation of antibacterial activity of macrophages was investigated on the basis of the rate of intracellular killing of Listeria monocytogenes and Salmonella typhimurium by normal and rIFN gamma-activated peritoneal macrophages of CBA and C57BL/10 mice, which differ in natural resistance to infection by these bacteria. Eighteen hours after i.p. injection of 10 to 1 X 10(4) U rIFN-gamma, resident and exudate peritoneal macrophages which had phagocytosed L. monocytogenes or S. typhimurium in vivo, killed both species in vitro just as efficiently as did resident macrophages of normal mice. Similar results were obtained after 18 hr of in vitro incubation of resident or exudate peritoneal macrophages with 0.1 to 1 X 10(4) U/ml rIFN-gamma. Consistent with the in vitro findings, two i.v. injections of 5 X 10(4) U rIFN-gamma did not affect the rate of in vivo proliferation of L. monocytogenes or S. typhimurium in the spleens of mice during the first 2 days after i.v. injection of the bacteria. Compared with the effect on the controls, two i.p. injections of 5 X 10(2) to 5 X 10(4) U rIFN-gamma did not decrease the numbers of viable S. typhimurium in either the peritoneal cell suspension or the spleen 24 hr after i.p. injection of the bacteria. Checking the state of activation of rIFN-gamma-activated macrophages on the basis of two commonly used criteria for macrophage activation showed that rIFN-gamma-activated macrophages inhibited the intracellular replication of Toxoplasma gondii and displayed enhanced O2 consumption and H2O2 release after stimulation with phorbol myristate acetate compared with macrophages from normal CBA and C57BL/10 mice. The present findings show that as single activating stimulus, rIFN-gamma is not capable of activating the antibacterial effector functions of peritoneal macrophages against facultative intracellular pathogens such as L. monocytogenes and S. typhimurium.     

Analysis of plasmid profile of antibiotic-resistant Enterobacteriaceae circulating in hospitals

Certain pheno- and genotype properties of S. typhimurium and some other representatives of Enterobacteriaceae resistant to antimicrobial drugs were studied. The strains were isolated from children with salmonellosis within 4 months when an infection hospital was subjected to microbiological observation. It was shown that by their antibiotic resistance, phagovars and molecular weights of the plasmid DNas, the strains S. typhimurium were similar to those isolated during hospital infections. The conjugative plasmids responsible for antibiotic resistance in some strains did not differ in their molecular weights and antibiotic resistance markers. The strains S. typhimurium similar in their pheno- and genotype properties were isolated only from 2 patients which allowed one to consider it possible that the patients were infected by the strains of common genesis. Analysis of nonpathogenic representatives of Enterobacteriaceae isolated from the patients along with the S. typhimurium strains confirmed the fact that the patients were infected with the same pathogenic strain.     

Mutation of flgM attenuates virulence of Salmonella typhimurium, and mutation of fliA represses the attenuated phenotype.

Salmonella typhimurium ST39 exhibits reduced virulence in mice and decreased survival in mouse macrophages compared with the parent strain SL3201. Strain ST39 is nonmotile, carries an indeterminate deletion in and near the flgB operon, and is defective in the mviS (mouse virulence Salmonella) locus. In flagellum-defective strains, the flgM gene product of S. typhimurium negatively regulates flagellar genes by inhibiting the activity of FliA, the flagellin-specific sigma factor. In this study, flgM of wild-type S. typhimurium LT2 was found to complement the mviS defect in ST39 for virulence in mice and for enhanced survival in macrophages. Transduction of flgM::Tn10dCm into the parent strain SL3201 resulted in attenuation of mouse virulence and decreased survival in macrophages. However, a flgM-fliA double mutant was fully virulent in mice and survived in macrophages at wild-type levels. Thus, the absolute level of FliA activity appears to affect the virulence of S. typhimurium SL3201 in mice. DNA hybridization studies showed that flgM-related sequences were present in species other than Salmonella typhimurium and that sequences related to that of fliA were common among members of the family Enterobacteriaceae. Our results demonstrate that flgM and fliA, two genes previously shown to regulate flagellar operons, are also involved in the regulation of expression of virulence of S. typhimurium and that this system may not be unique to the genus Salmonella.     

Nifedipine administration impairs natural resistance of mice to Salmonella typhimurium

Administration of Ca²⁺ channel blockers in cardiac disorders and the central role of Ca ²⁺ in modulating neutrophil functions, prompted us to investigate whether administration of nifedipine to mice would alter their natural resistance to infectious agents like Salmonella typhimurium. Neutrophil chemiluminescence (CL) in response to S. typhimurium was significantly (p < 0.01) decreased in mice fed with nifedipine (0.015 mg/kg body weight) over a period of six months. Intracellular killing of S. typhimurium by isolated neutrophils also decreased significantly (p < 0.01) and exponentially with nifedipine administration, representing a 42% fall at six months. In addition the drug administration lowered the survival rate of animals following challenge by a lethal dose of S. typhimurium (LD₅₀ = 1 × 10⁴ bacteria/animal). Our data suggest that long term administration of nifedipine lowers the natural resistance of mice to S. typhimurium owing to impaired neutrophil functions.Accepted for presentation at XIII Congress of International Society for Heart Research, Ann Arbor, Michigan (USA). Accepted for publication in Molec. Cellular Biochem. (1989). Nifedipine impairs neutrophil respiratory burst by a mechanism other than calcium channel blockade.