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PubMed2025

The Salmonella pathogenicity island 1-encoded small RNA InvR mediates post-transcriptional feedback control of the activator HilA in Salmonella.

UNLABELLED: Salmonella Pathogenicity Island 1 (SPI1) encodes a Type-3 secretion system (T3SS) essential for Salmonella invasion of intestinal epithelial cells. Many environmental and regulatory signals control SPI1 gene expression, but in most cases, the molecular mechanisms remain unclear. Many regulatory signals control SPI1 at a post-transcriptional level, and we have identified a number of small RNAs (sRNAs) that control the SPI1 regulatory circuit. The transcriptional regulator HilA activates the expression of the genes encoding the SPI1 T3SS structural and primary effector proteins. Transcription of hilA is controlled by the AraC-like proteins HilD, HilC, and RtsA. The hilA mRNA 5' untranslated region (UTR) is ~350 nucleotides in length and binds the RNA chaperone Hfq, suggesting it is a likely target for sRNA-mediated regulation. We used rGRIL-seq (reverse global sRNA target identification by ligation and sequencing) to identify sRNAs that bind to the hilA 5' UTR. The rGRIL-seq data, along with genetic analyses, demonstrate the SPI1-encoded sRNA invasion gene-associated RNA (InvR) base pairs at a site overlapping the hilA ribosome binding site. HilD and HilC activate both invR and hilA. InvR, in turn, negatively regulates the translation of the hilA mRNA. Thus, the SPI1-encoded sRNA InvR acts as a negative feedback regulator of SPI1 expression. Our results suggest that InvR acts to fine-tune SPI1 expression and prevents overactivation of hilA expression, highlighting the complexity of sRNA regulatory inputs controlling SPI1 and Salmonella virulence. IMPORTANCE: Salmonella Typhimurium infections pose a significant public health concern, leading to illnesses that range from mild gastroenteritis to severe systemic infection. Infection requires a complex apparatus that the bacterium uses to invade the intestinal epithelium. Understanding how Salmonella regulates this system is essential for addressing these infections effectively. Here, we show that the small RNA (sRNA) InvR imposes a negative feedback regulation on the expression of the invasion system. This work underscores the role of sRNAs in Salmonella's complex regulatory network, offering new insights into how these molecules contribute to bacterial adaptation and pathogenesis.

Genomic Islands↗

PubMed2003

Comparison of Salmonella chromogenic medium with DCLS agar for isolation of Salmonella species from stool specimens.

Salmonella chromogenic medium (SCM; Oxoid, Basingstoke, United Kingdom), a new selective chromogenic medium, was compared to DCLS agar (Oxoid) for the detection and presumptive identification of Salmonella species from stool samples. This medium contains two chromogenic substrates, Magenta-cap (5-bromo-6-chloro-3-indolylcaprylate), which is hydrolyzed by Salmonella species to give magenta colonies, and X-Gal (5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside), which is incorporated to visualize beta-D-galactosidase-producing organisms as blue colonies. Thus, non-Salmonella organisms appear blue or are not stained by any of the chromogens of the medium. A total of 500 stool samples were investigated by plating them directly and after selenite enrichment on DCLS agar and SCM. A total of 44 Salmonella-positive stool samples were detected. The sensitivities for direct plating and after enrichment were 22.7 and 81.8%, respectively, for DCLS agar, and for SCM these values were 34.1 and 100%, respectively. The specificities for direct plating and after enrichment were 82.5 and 72.8%, respectively, for DCLS agar and 98.5 and 95.8%, respectively, for SCM. According to these results, the sensitivities of SCM and DCLS agar were comparable on primary plating. However, the sensitivity of SCM was significantly higher after enrichment. In addition, the specificity of SCM was also significantly higher than that of DCLS agar both before and after enrichment. On the basis of these results, SCM can be recommended for the isolation of Salmonella species from stool samples in preference to DCLS agar.

Agar↗

PubMed1991

Use of a Salmonella typhimurium-derived virulence probe in the detection of Salmonella sp. and in the characterization of S. cholerae-suis virulence plasmids.

A genetic probe encoding a virulence gene from Salmonella typhimurium was useful in the detection of Salmonella from feces during an outbreak of salmonellosis at a local dairy. A 3.2-kb BamHI restriction endonuclease fragment of the S. typhimurium virulence plasmid, pStSR100, has been useful as a DNA probe for both detection of Salmonella sp. and characterization of virulence plasmids from numerous field isolates. This virA probe hybridizes to a highly conserved gene carried on the large virulence plasmids of invasive Salmonella isolates. Colony blots prepared from feces directly plated onto MaConkey's agar failed to detect low numbers of Salmonella sp. However, hybridization of the VirA probe to vacuum blots or colony blots prepared from feces in tetrathionate enrichment broth incubated for 16 hours at 37 C was effective for detecting Salmonella sp. and resulted in an 85.9% correlation with culture results. The probe also demonstrated the highly conserved nature (96%) of the virulence gene among S. cholerae-suis isolate plasmids detected using Southern blot analysis.

Animals↗

PubMed2004

Salmonella enterica serovars from pigs on farms and after slaughter and validity of using bacteriologic data to define herd Salmonella status.

The primary objective of this study was to evaluate the validity of using data obtained from slaughtered pigs for farm-level epidemiologic studies of Salmonella. The study involved groups of pigs from five farms. Salmonella isolates were obtained from on-farm samples, and a total of 370 on-farm and an additional 486 isolates from samples collected after commercial slaughter were subsequently tested. Preharvest samples included feces of individual animals from defined groups of nursery and finishing pigs on commercial farms and swabs from trucks. Postslaughter samples were cecal contents and mesenteric lymph node samples. The concordance between Salmonella serovars isolated from on-farm samples and those serovars isolated after slaughter varied widely among farms. Results of paired lymph node and cecal cultures were strongly associated (odds ratio, 7.0), but the agreement between on-farm and postslaughter results at the pig level was poor (kappa = 0.34). The results support recent findings that risk of exposure to Salmonella during transport and lairage remains a concern under contemporary industry conditions. The findings further imply that slaughter plant studies based on phenotyping of Salmonella alone (such as serovars) may not reliably indicate the Salmonella status of commercial swine farms.

Abattoirs↗

PubMed1999

[Salmonella serovars determined in the National Salmonella Center between 1995 and 1997].

A total of 897 human and non-human (from animal, food, feed and other sources) isolates of Salmonella were serotyped in the National Salmonella Centre during the period 1995-1997. They had been referred to the Centre by several field laboratories all over the country. Serological and biochemical identification was performed according to the standard methods. Forty seven Salmonella serovars were isolated from human sources. The most common Salmonella serovars were S. Thompson, S. Mbandaka and S. Enteritidis. The other were S. Hadar, S. Infantis, S. Albany, S. Typhimurium and S. Virchow. The serovars isolated from the food products were almost the same as from human sources. A total of 37 Salmonella serovars were found in isolates from animal sources. The dominating serovars were S. Enteritidis, S. Mbandaka, S. Bredeney, S. Infantis, S. Anatum, S. Typhimurium, S. Hadar, S. Saintpaul, S. Agona, S. Virchow, S. Heidelberg and S. Thompson. The fact that a number of the same serovars were found on lists of the most commonly isolated serovars from human and animal sources underlines the importance of the relationship. The lack of information of Salmonella contaminated food products and animal infections was noticed More detail examination of isolates from animal sources is advised to help the fight against human salmonellosis.

Foodborne Diseases↗

PubMed2004

[Salmonella enterica serotypes and Salmonella infections: a multicenter study covering ten provinces in Turkey].

In order to find the distinctive features of Salmonellae and Salmonella infections in Turkey, 620 Salmonellae strains, isolated from various clinical samples (481 stool, 108 blood, 12 urine, 3 bone marrow, 3 cerebrospinal fluid, 9 pus, and one from each of the bile, pleural fluid, wound, catheter samples) in 13 clinical microbiology laboratories of 10 provinces in Turkey (Ankara, Antalya, Bursa, Edirne, Eskişehir, Istanbul, Izmir, Kayseri, Konya and Trabzon) between July 1, 2000 and June 30, 2002, were serotyped. Among the patients 43% were female, 57% were male, 63.2% were from outpatient clinics and 36.8% were hospitalized patients. Seventy eight percent of the patients had gastroenteritis, 10.7% had septicemia/local infection, 9.8% had typhoid/paratyphoid fever and 1.5% were carriers. Incidence of gastroenteritis was higher in 0-5 years age group (p<0.001). Of the 620 Salmonella enterica isolates, 47.7% were S. Enteritidis, 34.7% S. Typhimurium, 6% S. Paratyphi B, 2.9% S. Typhi, 0.2% S. paratyphi A, 6.1% serogroup C1, and 2.4% serogroup C2. S. Enteritidis was the most common serotype in all provinces except for Kayseri, where S. Typhimurium was found to be the most common serotype (68.2%). Overall, the most frequently isolated serotype was S. Enteritidis, also being the most common serotype in stool and blood cultures. During the surveillance period two outbreaks have occurred, the first one by S. Enteritidis strains in Edirne, and the second one by S. Typhimurium strains in Kayseri. As a result, Salmonella infections are still a common health problem in Turkey, and active surveillance of Salmonella infections has vital importance.

Adolescent↗

PubMedDate not supplied

Frequency of Salmonella enteritidis and other salmonellae in the ceca of spent hens at time of slaughter.

A study was conducted to determine the frequency of Salmonella enteritidis (SE) and other Salmonella serovars in the cecal contents of spent laying hens at a hen-processing plant in the southeastern United States over a 4 1/2-month period, from October 1990 through February 1991. A total of 1920 pooled cecal samples (three ceca per sample) from 38 flocks representing 23 producers were obtained and tested for the presence of SE and other Salmonella serovars. A total of 359 samples (18.7%) from 37 of the 38 flocks (97.4%) showed characteristic reactions for salmonellae on triple sugar iron agar (TSIA) slants. Twenty-nine of the 359 Salmonella-positive samples (8.1%) were Group D-positive, all of which were found to be SE on further serotyping. The SE-positive samples were from seven of the 38 flocks (18.4%); four flocks originated from the USDA/APHIS-designated Northern Region of the United States, and three were from the Southeastern Region. Serotyping of the 330 TSIA-positive Group-D negative Salmonella revealed 37 different serovars. S. heidelberg, the predominant serovar, was identified in 49.1% of these isolates.

Abattoirs↗

PubMed1989

Prevalence of Salmonella and multiple antimicrobial-resistant Salmonella in California dairies.

A cross-sectional survey was conducted on 75 randomly selected dairies in one California county. Salmonella was isolated from 12 (16%) dairies; S newport was isolated from 6 (8%). Chloramphenicol-resistant S newport and S dublin were isolated from 8 (10.7%) dairies. Dairies with Salmonella had higher average calf mortality rates (P = 0.064; odds ratio [OR], 3.8). Dairies with S newport had a greater than expected occurrence of illnesses in adult cows compared with dairies with no S newport (P = 0.048; OR, 6.7) or with no Salmonella serotypes isolated (P = 0.047; OR, 6.9). Dairies with chloramphenicol-resistant Salmonella were more likely to have used chloramphenicol during the preceding 18-month period compared with dairies with chloramphenicol-susceptible Salmonella or no Salmonella (P = 0.023; OR, 9.5).

Animals↗

PubMed1981

[Epidemiological studies on Salmonella in a particular area ('Walcheren Project'). V. Studies on the possibility of fattening pigs free from Salmonella (author's transl)].

Four trials were made to study the possibility of fattening pigs free from Salmonella under field conditions. One pig-sty on a Salmonella-contaminated farm was used in these studies. Previous studies had shown that Salmonella-free fattening pigs could be produced under experimental conditions. A number of hygienic measures were adopted on the farm, such as the purchase of Salmonella-free piglets, the use of correctly pelleted feed, thorough cleaning and disinfecting of the pig-sty, and the prevention of all infections originating from the environment. Notwithstanding all these measures, completely Salmonella-free pigs could not be obtained. In three out of four experiments, even a mass infection with Salmonella even became apparent among the pigs. During the experiments a number of possible routes of infection were detected. The presence of these possible routes of infection was due to the fact that the measures referred to were not carried out accurately. This suggests that it will be very difficult to satisfy the requirements of strict hygiene under field conditions. Further experimental studies will have to show whether this is usually the case. During the third and fourth trial, studies were not confined to the farm, but also extended to the period of slaughter. From these investigations it became apparent that transport to as well as the period of waiting in the slaughter-house also provide several opportunities for contamination of the pigs, in spite of extensive cleaning and disinfection of both cattle-truck and lairages.

Abattoirs↗

PubMed1982

Epidemiological studies on Salmonella in a certain area ("Walcheren Project") V. Studies into the possibility of fattening pigs free from Salmonella.

Studies performed some years ago showed that Salmonella-free pigs for slaughter could be produced under experimental conditions if a number of hygienic measures were taken, such as the purchase of Salmonella-free piglets, the use of properly pelletized feed, thorough cleaning and disinfecting of the pigsty and the prevention of all contamination from the surroundings. In this paper four trials are described which examined whether pigs could also be fattened free from Salmonella under practical conditions on the farm. For this purpose one pigsty on a Salmonella-contaminated farm was used, in which the aforementioned hygienic measures were taken. Despite all these precautions it proved impossible to obtain Salmonella-free pigs. In fact, in three of the four experiments a massive Salmonella infection became manifest among the pigs. The experiments revealed a number of ways in which contamination might have occurred. The existence of these routes of infection was caused by the fact that the measures described above were not carried out accurately, an indication that it will be very difficult to meet the hygiene requirements under farming conditions. Further experiments will have to ascertain whether this is generally the case. In the third and fourth trials, the investigations were not confined to the farm, but were also extended to the period of slaughtering. These made it clear that transportation as well as the waiting time in the slaughterhouse also provided many opportunities for contamination of the pigs, in spite of extensive cleaning and disinfecting of both the cattle-truck and the lairages.

Abattoirs↗

PubMed1982

Effects of Salmonella infection on hemopoietic stem cells in mice immunized with Salmonella vaccines.

Effects of Salmonella enteritidis infection on hemopoietic stem cells were examined in mice immunized with killed bacteria and in those immunized with viable bacteria. The results are summarized as follows: i) Mice immunized with the killed salmonellae showed hemopoietic responses similar to those of normal, nonimmunized mice, i. e., increase in CFUs and CFUc in the spleen and decrease in these cells in the bone marrow. ii) Mice immunized with viable salmonellae were protected from such decreases in bone marrow stem cells, but showed a decrease in spleen CFUc, with a concomitant decrease in the peripheral granulocytes. iii) Hemopoietic responses to viable salmonellae of mice immunized with viable bacteria differed from the responses to killed salmonellae of normal, non-immunized mice. These results suggest that both LPS and cell-mediated immune responses affect hemopoietic stem cells in mice infected with salmonellae.

Animals↗

PubMed1993

Fate of Salmonella enteritidis and Salmonella typhimurium during the fermentation of ergo, a traditional Ethiopian sour milk.

The growth potential of Salmonella enteritidis and Salmonella typhimurium in milk in smoked and non-smoked containers and their inhibition by lactic acid bacteria was determined. In the absence of lactic acid bacteria, both Salmonella strains could grow to the level of 10(8) cfu/ml within 12 h. Smoking of containers significantly retarded Salmonella growth only until 12 h. Growth of lactic acid bacteria in souring milk retarded growth of Salmonella strains and complete inhibition was observed between 48 and 60 h at pH and titratable acidity values of 3.7 and 0.70%, respectively. The synergistic effect of lower pH, acids and smoking was important in the complete inhibition of the test organisms. Although ergo was preferably consumed after 24 h of fermentation, the Salmonella strains were not completely inhibited at this time. Thus, traditional making of ergo by the natural fermentation of raw milk could be hazardous to health. The use of a three-day old ergo as a starter for boiled milk is recommended to ensure the wholesomeness of ergo.

Animals↗

PubMed1996

Protection against oral challenge three months after i.v. immunization of BALB/c mice with live Aro Salmonella typhimurium and Salmonella enteritidis vaccines is serotype (species)-dependent and only partially determined by the main LPS O antigen.

The role of the main LPS O antigen in the specificity of protection as mediated by systemic mechanisms following immunization with live attenuated Aro Salmonella vaccines was studied in mice. Innately Salmonella-susceptible (Itys) BALB/c mice were immunized intravenously with a single dose of either Salmonella typhimurium SL3261 aroA (LPS O4,5,12) or Salmonella enteritidis Se795aroA (LPS O1,9,12), and challenged orally 2-3 months later with either S. typhimurium C5 or S. enteritidis Thirsk. Nearly isogenic transductants of the two challenge strains expressing either their own LPS or that of the other serotype (S. typhimurium C5 O4 or O9, and S. enteritidis Thirsk O9 or O4) were also used. Both vaccines conferred similar high protection against the virulent strain of the homologous serotype expressing its own LPS. There was no protection against the heterologous serotype expressing its own LPS. However, when vaccinated mice were challenged with either the same serotype as the vaccine but expressing the heterologous LPS, or with the heterologous serotype expressing the LPS of the vaccine, protection was always lower than protection against the fully homologous serotype. Anti-smooth LPS antibodies showed higher titres against the homologous LPS, but with significant crossreactivity with the heterologous LPS. Antibodies to O-rough S. typhimurium and S. enteritidis LPS were present following immunization with either of the two vaccine strains. The LPS alone cannot fully account for the specificity of protection in this model; other (protein) antigens may be responsible. It remains to be seen whether there is a T-cell mediated component to the specificity of protection conferred by live Salmonella vaccines.

Animals↗

PubMed1998

Salmonella virulence plasmid. Modular acquisition of the spv virulence region by an F-plasmid in Salmonella enterica subspecies I and insertion into the chromosome of subspecies II, IIIa, IV and VII isolates.

The spv operon is common to all Salmonella virulence plasmids. DNA hybridization analysis indicates that the spv region is limited in distribution to serovars of Salmonella enterica subspecies I, II, IIIa, IV, and VII and is absent from Salmonella bongori isolates. Among strains of subspecies II, IIIa, and VII, all isolates examined contained sequences that hybridized with the spv region. However, among isolates of subspecies I, DNA sequences capable of hybridizing with the spv region were found in some isolates of certain serovars. Furthermore, in isolates of subspecies I, the virulence plasmid was found in the same set of isolates as an F-related plasmid, as determined by the presence of the spv region of the virulence plasmid and the finO, traD, and repA sequences of the F-plasmid. The concordance of the virulence plasmid and all three F-plasmid sequences in subspecies I serovar Choleraesuis, Paratyphi, and Typhimurium is most easily explained if the spv region is carried in an F-related plasmid in these isolates. In contrast, among S. enterica subspecies II, IIIa, IV, and VII, the isolates that contain spv sequences did not hybridize with an F-related plasmid or any other identifiable plasmid. With the use of pulse-field gel electrophoresis, the spv region in subspecies II, IIIa, and VII was found to be encoded on the chromosome. Analysis of the phylogenetic distribution of spv among Salmonella isolates and comparative nucleotide sequence analysis of spvA and spvC suggests that the spv region was acquired very recently, after speciation of the salmonellae.

Base Sequence↗

PubMedDate not supplied

Effects of prior coinfection with different Salmonella serovars on the progression of a Salmonella enterica serovar enteritidis infection in hens undergoing induced molt.

Four trials were conducted to evaluate whether prior infection with Salmonella enterica serovar typhimurium (S. typhimurium) or Salmonella enterica serovar muenchen (S. muenchen) would modify the severity or the transmission of Salmonella enterica serovar enteritidis (S. enteritidis) challenge in hens undergoing molt via feed withdrawal. Hens were separated into two groups where one group received a prior S. typhimurium or S. muenchen infection, whereas the other group remained untreated until S. enteritidis challenge. In trials 1 and 2, one group of hens was infected with S. typhimurium 5 days prior to feed withdrawal. Both groups of hens were then challenged with S. enteritidis on day 4 post feed withdrawal. In trials 3 and 4, one group of hens received S. typhimurium or S. muenchen, respectively, 1 day after feed was withdrawn. Transmission of S. enteritidis was evaluated by challenging the center hen in rows of 11 hens per row with S. enteritidis at 4 days post feed withdrawal and following the progression of the S. enteritidis down the row of hens over time. In trials 1 and 2, where hens received S. typhimurium 5 days prior to feed withdrawal, shedding of the S. enteritidis challenge was significantly reduced in hens on day 10 postchallenge in trial 1 and on days 3 and 10 postchallenge in trial 2 compared with the hens subjected only to the molt procedure. Significantly fewer S. enteritidis were recovered in livers and spleens at day 9 postchallenge in trial 2 from hens receiving the prior S. typhimurium infection. In trial 3, where hens received S. typhimurium 1 day after feed withdrawal, S. enteritidis transmission was significantly reduced in these hens on days 3, 10, and 24 postchallenge. In trial 4, similar in methodology to trial 3 except that, rather than S. typhimurium, hens received S. muenchen, a Salmonella organism totally lacking any antigen cross-reactive with S. enteritidis, S. enteritidis transmission was significantly reduced on days 3, 10, 17, and 24 postchallenge, suggesting that factors other than specific immunity were involved in the observed resistance to S. enteritidis infection. These results indicate that prior infection of a flock with a non-S. enteritidis paratyphoid Salmonella can reduce S. enteritidis problems that may occur during a molt.

Animal Husbandry↗

PubMed1991

Resistance to fecal shedding of salmonellae in pigs and chickens vaccinated with an aromatic-dependent mutant of Salmonella typhimurium.

The purpose of this study was to evaluate the effectiveness of an aromatic-dependent mutant of Salmonella typhimurium as a parenteral vaccine for prevention of fecal shedding of Salmonella spp. Pigs and chickens were vaccinated IM, with 1 x 10(9) and 1 x 10(8) organisms, respectively, followed by a second identical vaccination 2 weeks later. Salmonella organisms were not detected by analysis of fecal or cloacal swab specimens from any animal after vaccination. Deleterious side effects were not noticed after vaccination. Pigs were challenge-inoculated PO with 1 x 10(12) virulent S typhimurium 1 week after the second vaccination. Chickens were challenge-inoculated PO with 3 x 10(8) organisms of either S enteritidis or the virulent parent strain of S typhimurium 3 weeks after the second vaccination. Vaccinated pigs shed Salmonella spp significantly less frequently than did nonvaccinated pigs. Vaccinated chickens challenge-inoculated with either S enteritidis or S typhimurium also shed Salmonella less frequently than the corresponding nonvaccinated control birds; however, the difference was not significant.

Animals↗

PubMed1985

Immunological relationships between Salmonella flagella and their potential application for salmonellae detection by immunoassay.

Native flagella of ten Salmonella serotypes were shown to possess serotype-specific antigenic determinants as well as a multiple of common antigenic determinants, which varied in concentration. Each common antigenic determinant was shared by certain, but not all, serotypes. This has been demonstrated from agglutination and radioimmunometric assay (RIMA) results, using ten antisera raised in rabbits against purified polymeric flagellins from ten Salmonella serotypes as immunogens. The minimum detectable populations of salmonellae, as determined by RIMA varied considerably, due to variation in concentrations (and possibly types) of common antigenic determinants. However, the results demonstrated the feasibility of utilizing RIMA for the qualitative detection of salmonellae, using a mixture of only the ten antisera and 125I-labelled protein A as a general tracer. In this way, 77 different salmonellae were detected in less than 8 h after culturing in selective broth. The RIMA developed was specific for salmonellae and showed no cross-reactions with high populations of other members within the family Enterobacteriaceae.

Agglutination↗

PubMedDate not supplied

Smooth lipopolysaccharide of Salmonella adelaide has an atypical Salmonella Ra core.

Two wild isolates as well as two laboratory strains of Salmonella adelaide obtained from different geographical areas failed to react with a monoclonal antibody directed against the terminal alpha-1,2-linked N-acetylglucosamine residue of the outer core of Salmonella lipopolysaccharide (LPS). This finding was confirmed by the lack of reactivities of Salmonella Ra LPS with S. adelaide antiserum or of S. adelaide R oligosaccharide with Salmonella Ra serum. Furthermore, S. adelaide proved to be resistant to lysis by phage FO1, which binds to a receptor also believed to involve the terminal alpha-1,2-linked N-acetylglucosamine of the Salmonella R oligosaccharide. These results suggest that the outer core structure of S. adelaide LPS may be different from that of S. typhimurium and other Salmonella strains.

Antibodies, Monoclonal↗