The lpf fimbrial operon mediates adhesion of Salmonella typhimurium to murine Peyer's patches.

We investigated the role of the Salmonella typhimurium fimbrial operon formed by the genes lpfABCDE in infection of mice. A mutant in lpfC, the gene encoding the fimbrial outer membrane usher, had an approximately 5-fold increased 50% lethal dose when administered orally to mice. When mice were infected with a mixture of the lpfC mutant and isogenic wild-type S. typhimurium, the lpfC mutant was recovered in lower numbers from Peyer's patches, mesenteric lymph nodes, liver, and spleen. In an organ culture model using murine intestinal loops, lpfC mutants were shown to be associated in lower numbers than wild-type bacteria with Peyer's patches but not with villous intestine. The defect of the lpfC mutant in adhesion to Peyer's patches could be complemented by introducing lpfABCDE on a cosmid. Similarly, heterologous expression of the Salmonella lpf operon in Escherichia coli resulted in an increased adhesion to histological thin sections of Peyer's patch lymph follicles. Electron microscopic analysis of histological sections taken from Peyer's patches after intragastric infection of mice showed that, in contrast to the S. typhimurium wild type, the isogenic lpfC mutant did not destroy M cells of the follicle-associated epithelium. These data show that the Salmonella lpf operon is involved in adhesion to murine Peyer's patches.

Relationship between evolutionary rate and cellular location among the Inv/Spa invasion proteins of Salmonella enterica.

For 21 strains of Salmonella enterica, nucleotide sequences were obtained for three invasion genes, spaO, spaP, and spaQ, of the chromosomal inv/spa complex, the products of which form a protein export system required for entry of the bacteria into nonphagocytic host cells. These genes are present in all eight subspecies of the salmonellae, and homologues occur in a variety of other bacteria, including the enteric pathogens Shigella and Yersinia, in which they are plasmid borne. Evolutionary diversification of the invasion genes among the subspecies of S. enterica has been generally similar in pattern and average rate to that of housekeeping genes. However, the range of variation in evolutionary rate among the invasion genes is unusually large, and there is a relationship between the evolutionary rate and cellular location of the invasion proteins, possibly reflecting diversifying selection on exported proteins in adaptation to variable host factors in extracellular environments. The SpaO protein, which is hypervariable in S. enterica and exhibits only 24% sequence identity with its homologues in Shigella and Yersinia, is secreted. In contrast, the membrane-associated proteins SpaP, SpaQ, and InvA are weakly polymorphic and have > 60% sequence identity with the corresponding proteins of other enteric bacteria. Acquisition of the inv/spa genes may have been a key event in the evolution of the salmonellae as pathogens, following which the invention of flagellar phase shifting facilitated niche expansion to include warm-blooded vertebrates.

Genetic and redox determinants of nitric oxide cytotoxicity in a Salmonella typhimurium model.

Paradoxically, nitric oxide (NO) has been found to exhibit cytotoxic, antiproliferative, or cytoprotective activity under different conditions. We have utilized Salmonella mutants deficient in antioxidant defenses or peptide transport to gain insights into NO actions. Comparison of three NO donor compounds reveals distinct and independent cellular responses associated with specific redox forms of NO. The peroxynitrite (OONO-) generator 3-morpholinosydnonimine hydrochloride mediates oxygen-dependent Salmonella killing, whereas S-nitrosoglutathione (GSNO) causes oxygen-independent cytostasis, and the NO. donor diethylenetriamine-nitric oxide adduct has no antibacterial activity. GSNO has the greatest activity for stationary cells, a characteristic relevant to latent or intracellular pathogens. Moreover, the cytostatic activity of GSNO may best correlate with antiproliferative or antimicrobial effects of NO, which are unassociated with overt cell injury. dpp mutants defective in active dipeptide transport are resistant to GSNO, implicating heterolytic NO+ transfer rather than homolytic NO. release in the mechanism of cytostasis. This transport system may provide a specific pathway for GSNO-mediated signaling in biological systems. The redox state and associated carrier molecules are critical determinants of NO activity.

Comportamento de Salmonella em ovo em pó em função da atividade de água (Aa) do binômio tempo x temperatura de armazenamento

Salmonella sp. é um dos principais microrganismos causadores de surtos de enfermidades transmitidas por alimentos associados ao consumo de ovos e de alimentos formulados com este ingrediente. Ovos desidratados são largamente utilizados pelas indústrias de alimentos, por oferecer maior praticidade e maior padronização em relação ao produto \"in natura\". Apesar do processo tecnológico de desidratação do ovo incluir uma etapa de pasteurização, existe um risco de haver microrganismos sobreviventes, já que a pasteurização é feita em temperatura branda. Além disso, a pasteurização pode destruir os fatores intrínsecos antimicrobianos presentes na clara, possibilitando a multiplicação de microrganismos que sobreviveram ao processo de pasteurização ou que contaminaram o produto após a pasteurização. O controle da Aa do produto desidratado e o tempo de armazenamento são, portanto, fatores fundamentais para o controle da multiplicação de microrganismos indesejáveis. Nesse estudo, avaliou-se a cinética de multiplicação de Salmonella experimentalmente adicionada a ovo em pó Aa ajustada para 0,4, 0,6, 0,8 e 0,9, durante o armazenamento em quatro temperaturas: 8°C, 15°C, 25°C e 35°C. Os resultados indicaram que S. Enteritidis é capaz de sobreviver por longo tempo (pelo menos 56 dias) em ovo em pó com Aa próximo de 0,4 quando armazenado a 8°C, 15° e a 25°C. Essa sobrevivência é menor (até 28 dias) quando o armazenamento é feito a 35°C. No ovo em pó com Aa em tomo de 0,6 ou 0,8, S. Enteritidis sobrevive por menos tempo do que no produto com Aa de cerca de 0,4, independentemente da temperatura de armazenamento. No produto com Aa de cerca de 0,9, há grande multiplicação de S. Enteritidis quando o armazenamento é feito a 15°C, 25°C ou 35°C. Nesse produto, o armazenamento a 8°C impede a multiplicação do patógeno. Verificou-se também que Salmonella Radar, resistente a diversos antibióticos, apresentou o mesmo comportamento que S. Enteritidis nas amostras de ovo estudadas.

Vegetais minimamente processados prontos para o consumo: influência da etapa de desinfecção na inativação de Salmonella Typhimurium, na ocorrência da contaminação cruzada e na avaliação quantitativa de risco microbiológico em relação a este patógeno

Dados mundiais apontam haver uma associação entre o aumento do comércio de vegetais minimamente processados prontos para o consumo (VPC) e o aumento da ocorrência de surtos de enfermidades transmitidas por alimentos. Durante o processamento industrial de VPC, a desinfecção é a principal etapa de inativação de micro-organismos patogênicos presentes, mas nessa etapa também pode ocorrer contaminação cruzada, com transferência de contaminantes de produtos contaminados para não-contaminados. Neste trabalho, foram coletadas informações sobre as práticas empregadas na etapa de desinfecção em dez importantes indústrias produtoras de VPC no Estado de São Paulo, avaliando-se, em seguida, a influência dessas práticas na qualidade microbiológica dos produtos e na inativação de Salmonella Typhimurium, bem como na ocorrência de contaminação cruzada por este patógeno. Um modelo de avaliação quantitativa de risco microbiológico foi elaborado para estimar o impacto da contaminação cruzada durante a etapa de desinfecção no risco de infecção por Salmonella devido ao consumo de VPC. Observou-se que, em todas as indústrias visitadas, a desinfecção dos vegetais era feita com produtos à base de cloro em concentrações de 50 a 240 mg/L, que resultava em redução de até 1,2 log na carga microbiana dos vegetais que entravam na linha de processamento. Ao avaliar a influência das características da água de processamento (pH, temperatura, concentração de matéria orgânica e concentração de dicloroisocianurato de sódio) e do tempo de contato entre a água clorada e os vegetais na redução de Salmonella, observou-se que a concentração do produto à base de cloro foi o parâmetro que apresentou maior influência (p<0.05). Concentrações de dicloroisocianurato de sódio acima de 10 mg/L foram necessárias para controle da contaminação cruzada durante a etapa de lavagem. O modelo de avaliação de risco construído indicou quantitativamente haver uma relação entre a concentração de dicloroisocianurato de sódio na água de desinfecção e o risco de ocorrência de surtos causados por Salmonella em VPC. Cenários simulando uso de dicloroisocianurato de sódio em concentrações abaixo de 5 mg/L indicaram que mais de 96% dos casos preditos de infecção por Salmonella poderiam ser atribuídos à ocorrência de contaminação cruzada, enquanto que em cenários com concentrações acima de 50 mg/L, casos de infecção devidos à contaminação cruzada não foram preditos. Estes resultados mostram que o controle da qualidade da água e o monitoramento da concentração de sanitizante na etapa de desinfecção são essenciais para evitar a ocorrência de contaminação cruzada e garantir a produção de VPC seguros para o consumo.

Complete protection against P. berghei malaria upon heterologous prime/boost immunization against circumsporozoite protein employing Salmonella type III secretion system and Bordetella adenylate cyclase toxoid

Sterile immunity against malaria can be achieved by the induction of IFNgamma-producing CD8(+) T cells that target infected hepatocytes presenting epitopes of the circumsporozoite protein (CSP). In the present study we evaluate the protective efficacy of a heterologous prime/boost immunization protocol based on the delivery of the CD8(+) epitope of Plasmodium berghei CSP into the MHC class I presentation pathway, by either a type III secretion system of live recombinant Salmonella and/or by direct translocation of a recombinant Bordetella adenylate cyclase toxoid fusion (ACT-CSP) into the cytosol of professional antigen-presenting cells (APCs). A single intraperitoneal application of the recombinant ACT-CSP toxoid, as well as a single oral immunization with the Salmonella vaccine, induced a specific CD8(+) T cell response, which however conferred only a partial protection on mice against a subsequent sporozoite challenge. In contrast, a heterologous prime/boost vaccination with the live Salmonella followed by ACT-CSP led to a significant enhancement of the CSP-specific T cell response and induced complete protection in all vaccinated mice.

The diagnosis of Salmonella types

Includes bibliographical references

Proceedings of the 3rd International Symposium on the Epidemiology and Control of Salmonella in Pork : Renaissance Mayflower Hotel, Washington, D.C., August 5 to 7, 1999 /

Includes bibliographical references.

Isolation and identification of Salmonella [and] Shigella /

Tables.

Quantification and prevalence of Salmonella in beef cattle presenting at slaughter

Aims: A survey to determine the prevalence and numbers of Salmonella in beef cattle presented for slaughter at abattoirs across Australia was conducted between September 2002 and January 2003. Methods and Results: Automated immunomagnetic separation (AIMS) was used for detection and isolation of Salmonella enriched from cattle faeces. Salmonella were enumerated from positive samples using a combination of the Most Probable Number (MPN) technique and AIMS. A total of 310 faecal samples were tested, 155 were from lot-fed cattle and 155 from grass-fed cattle. Salmonella spp. were isolated from 21 (6.8%) of the cattle and the prevalence amongst grass-fed cattle (4.5%) was not significantly different to that found in lot-fed cattle (9%). Counts of Salmonella in positive faeces varied from

Investigation of ansB and sspA derived promoters for multi- and single-copy antigen expression in attenuated Salmonella enterica var. typhimurium

Five candidate promoters were examined to determine their utility in directing immunogenic levels of expression of the C fragment from tetanus toxin in attenuated S. enterica used as an oral vaccine in mice. Promoters derived from the genes encoding the stringent starvation protein (sspA) from E. coli and S. enterica, but not ansB derived promoters, expressed immunogenic levels of C fragment from multi-copy plasmids in attenuated S. enterica in vivo and, following oral immunization, induced high titre specific anti-tetanus toxoid serum antibodies. We also demonstrate that not only the choice of promoter, replicon and growth conditions but also how expression constructs are assembled in the chosen plasmid is critical for the successful development of plasmid-based antigen delivery systems using attenuated S. enterica. In addition, the S. enterica sspA promoter is able to elicit anti-tetanus toxoid antibodies in mice when the psspA-tetC expression cassette is integrated in single copy on the S. enterica chromosome.

Long-term persistence of multi-drug-resistant Salmonella enterica serovar Newport in two dairy herds

Objective - To evaluate the association between maintaining joint hospital and maternity pens;and persistence of multi-drug-resistant (MDR) Salmonella enterica serovar Newport on 2 dairy farms. Design - Observational study. Sample Population - Feces and environmental samples from 2 dairy herds. Procedure - Herds were monitored for fecal shedding of S enterica Newport after outbreaks of clinical disease. Fecal and environmental samples were collected approximately monthly from pens housing sick cows and calving cows and from pens containing lactating cows. Cattle shedding the organism were tested serially on subsequent visits to determine carrier status. One farm was resampled after initiation of interventional procedures, including separation of hospital and maternity pens. Isolates were characterized via serotyping, determination of antimicrobial resistance phenotype, detection of the CMY-2 gene, and DNA fingerprinting. Results - The prevalence (32.4% and 33.3% on farms A and B, respectively) of isolating Salmonella from samples from joint hospital-maternity pens was significantly higher than the prevalence in samples from pens housing preparturient cows (0.8%, both farms) and postparturient cows on Farm B (8.8%). Multi-drug-resistant Salmonella Newport was isolated in high numbers from bedding material, feed refusals, lagoon slurry, and milk filters. One cow excreted the organism for 190 days. Interventional procedures yielded significant reductions in the prevalences of isolating the organism from fecal and environmental samples. Most isolates were of the C2 serogroup and were resistant to third-generation cephalosporins. Conclusions and Clinical Relevance - Management practices may be effective at reducing the persistence of MDR Salmonella spp in dairy herds, thus mitigating animal and public health risk.