Case31-Salmonelltyphi - Case 31 Lydyard, Peter; Cole,...

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1. What is the causative agent, how does it enter the body and how does it spread a) within the body and b) from person to person? Causative agent The nomenclature of the genus Salmonella has undergone a number of revisions leading to two systems of validly published names, the latest ver- sion of which (post-2002) has the disadvantage of not highlighting impor- tant human pathogens such as Salmonella typhi or Salmonella enteritidis by not giving them succinct names. In the current version of the nomenclature the cause of enteric fever and the organism that is one of the important causes of gastroenteritis would be S. enterica subsp. enterica serovar Typhi and S. enterica subsp. enterica serovar Enteritidis, respectively. For prag- matic reasons, this nomenclature will not be used in this text but will be shortened to Salmonella Typhi. There are only three species of which Salmonella enterica is further subdivided into subspecies and serovars . Salmonella organisms are motile nonsporing gram-negative facultative anaerobic rods measuring 2–3 ¥ 0.4–0.6 m m. The genome of Salmonella Typhi and Salmonella Typhimurium have both been sequenced and contain about 4.8 million base pairs with 4000–5000 coding sequences, of which 98% are homologous between the two strains. Several pathogenicity Case 31 Salmonella typhi A 53-year-old lady returned from a visit to Lahore complaining of feeling generally unwell. She had a temperature and a cough. She attended a clinic where she was seen by a doctor who confirmed that she had a temperature of 38 C and he noticed a rash on the upper chest. She was admitted to hosptial for investigation, which included a thick and thin film for malaria, a full blood count, urea and electrolytes, a chest X-ray, and blood cultures. The malaria investigation was negative, the chest X-ray showed patchy basal consolidation, the full blood count revealed a relative lymphocytosis and gram-negative bacilli were seen in the blood culture (Figure 1). A provisional diagnosis of enteric fever was made and she was started on appropriate antibiotics. The diagnosis was confirmed by isolation of Salmonella typhi from the blood cultures. Figure 1. Gram-negative bacilli in a blood culture. © Lydyard, Peter; Cole, Michael; Holton, John; Irving, Will; Porakishvili, Nino; Venkatesan, Pradhib; Ward, Kate, Jan 01, 201 Garland Science, Hoboken, ISBN: 9780203856871
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islands ( PAIs ) are present in Salmonella enterica (SPI-1, which codes for a type III secretion system and another, SPI-2) and Salmonella Typhi has an additional SPI-7 coding for the Vi antigen. Frequent genome re- arrangements associated with the PAI lead to outgrowth of strains that are better adapted to different environmental circumstances. Horizontal gene transfer is also an important factor in the evolution of the genus. A large plasmid is carried in Salmonella Typhi (pHCM1) that encodes drug resist- ance. Virulence plasmids are also carried in nontyphoidal strains. There are over 2500 serovars in the genus and they are grouped according to the
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This note was uploaded on 09/14/2011 for the course PHARM mb taught by Professor Staff during the Spring '11 term at UCSD.

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Case31-Salmonelltyphi - Case 31 Lydyard, Peter; Cole,...

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