flexneri, boydii, sonnei, flexneri, boydii, sonnei,

Shiga toxin Shiga toxin  enterotoxic enterotoxic  cytotoxic cytotoxic  inhibits protein synthesis inhibits protein synthesis – lysing 28S rRNA Shigella Shigella attachment and penetration attachment and penetration  W W ithin 2-3 days ithin 2-3 days  E E pithelial cell damag pithelial cell damag e e Clinical significance Clinical significance  man only reservoir man only reservoir  mostly young children mostly young children – fecal to oral contact fecal to oral contact – children to adults children to adults  transmitted by adult food handlers transmitted by adult food handlers – unwashed hands unwashed hands Clinical significance Clinical significance  The infective dose required to cause infection is ver y low 10-200 organisms.  There is an incubation of 1-7 days followed by fever , cramping, abdominal pain, and watery diarrhea due to the toxinfor 1-3 days.  This may be followed by frequent, scant stools with blood, mucous, and pus due to invasion of intestina l mucosa.  Is is rare for the organism to disseminate.  The severity of the disease depends upon the specie s one is infected with. S. dysenteria is the most path ogenic followed by S. flexneri, S. sonnei and S. boydi i. Immunity Immunity  SIgA. Diagnosis of Shigella infection Diagnosis of Shigella infection  Specimen: stool.  Culture and Identification  Quick immunological methods: 1. Immunofluorescent “ball” test; 2. Coagglutination . Prevention Prevention  streptomycin dependent SD dysentery vaccine. Treating shigellosis Treating shigellosis  manage dehydration  patients respond to antibiotics , P roblem of drug-resistance – disease duration diminished Shigella  Shigella 4 species; S. flexneri, S. boydii, S. sonnei, S. dysenteriae all cause bac illary dysentery or shigellosis, bloody feces associated with intestinal pain. T he organism invades the epithelial lining layer, but does not penetrate. Usually , within 2-3 days, dysentery results from bacteria damaging the epithelium lini ng layers of the intestine often with release of mucus and blood found in the f eces and attraction of leukocytes also found in the feces as pus. Shiga toxi n chromosomally encoded is neurotoxic, enterotoxic and cytotoxic plays a ro le. The toxin inhibits protein synthesis acting on the 80S ribosome and lysing 28S rRNA. This is primarily a disease of young children occurring by fecal-o ral contact. Adults can catch this disease from children. However it can be tra nsmitted by infected adult food handlers, contaminating food. The source in e ach case is unwashed hands. Man is the only reservoir.  Patients with severe dysentery are usually treated with antibiotics e.g. ampici llin. In contrast to salmonellosis, patients respond to antibiotic therapy and di sease duration is diminished. Salmonella Salmonella  Salmonellosis may pres ent as one of several sy ndromes including gast roenteritis, enteric typ hoid fever or septicemi a. The antigenic structures of salmonellae The antigenic structures of salmonellae used in serologic typing used in serologic typing Salmonella Salmonella  2000 antigenic types” 2000 antigenic types”  disease category disease category – S. enteritidis S. enteritidis – many serotypes many serotypes – S. cholerae-suis S. cholerae-suis – S. typhi S. typhi Virulence factors Virulence factors  Endotoxin – may play a role in intracellular survival  Capsule for S. typhi and some strains of S. paratyphi  Adhesions – both fimbrial and non-fimbrial  Type III secretion systems and effector molecules – 2 different sy stems may be found: – One type is involved in promoting entry into intestinal epithelial cel ls – The other type is involved in the ability of Salmonella to survive ins ide macrophages  Outer membrane proteins - involved in the ability of Salmonella t o survive inside macrophages  Flagella – help bacteria to move through intestinal mucous  Enterotoxin - may be involved in gastroenteritis  Iron capturing ability  Enteric or typhoid fever occurs when the bacteria l Enteric or typhoid fever occurs when the bacteria l eave the intestine and multiply within cells of the r eave the intestine and multiply within cells of the r eticuloendothelial system. eticuloendothelial system.  The bacteria then re-enter the intestine, causing ga The bacteria then re-enter the intestine, causing ga strointestinal symptoms. strointestinal symptoms.  Typhoid fever has a 10-14 day incubation period a Typhoid fever has a 10-14 day incubation period a nd may last for several weeks. nd may last for several weeks.  Salmonella typhi is the most common species isolat Salmonella typhi is the most common species isolat ed from this salmonellosis. ed from this salmonellosis.  H H uman reservoir uman reservoir : :carrier state common  C C ontaminated food ontaminated food : : water supply water supply  P P oor sanitary conditions oor sanitary conditions Typhoid Typhoid • acute phase, gastroenteritis acute phase, gastroenteritis gall bladder gall bladder – shedding, weeks shedding, weeks Septicemia Septicemia -occurs 10-14 days -occurs 10-14 days – lasts 7 days lasts 7 days gastrointenteritis gastrointenteritis