Shigella and salmonella

Transcription

1 Sulaimani University College of Pharmacy Microbiology Lec. 9 & 10 Shigella and salmonella Dr. Abdullah Ahmed Hama PhD. Microbiology/Molecular Parasitology abdullah.hama@spu.edu.iq 1

2 Shigella Shigella species are closely related to E coli. All species are non-motile. Most of them are fail to produce gas when fermenting glucose and not ferment lactose. Their antigenic makeup has been characterized in a manner similar to that of E coli with the exception that they lack flagella (H antigens). The genus is divided into four species: S. dysenteriae (Group A) S. flexneri (Group B) S. boydii (Group C) S. sonnei (Group D)

3 shigellosis Shigellosis: is a type of food poisoning caused by infection with the shigella bacterium. Shigella pathogens cause an acute inflammatory colitis and bloody diarrhea, which in the most characteristic state presents as a dysentery syndrome clinical manifistation: cramps, painful straining to pass stools (tenesmus), and a frequent, small-volume, bloody, mucoid fecal discharge with fever. Which is typically spread person to person under poor sanitary conditions. This spread by person-to-person contact is so effective because the infecting dose is extremely low (fecal-oral).

4 Pathogenesis Shigella, unlike Vibrio cholerae and most Salmonella species, is acidresistant and survives passage through the stomach to reach the intestine. Shigellae, which cause disease almost exclusively in the gastrointestinal tract, produce bloody diarrhea (dysentery) by invading the cells of the mucosa of the distal ileum and colon. Local inflammation accompanied by ulceration occurs, but the organisms rarely penetrate through the wall or enter the bloodstream, unlike salmonellae. Although some strains produce an enterotoxin (called Shiga toxin), invasion is the critical factor in pathogenesis.

5 Shigella Toxin mechanism of action

6 Laboratory Diagnosis: All Shigella species are readily isolated using selective media (eg, Hektoen enteric agar). Shigellae form non-lactose-fermenting (colorless) colonies on MacConkey's or EMB agar. Treatment: The main treatment for shigellosis is fluid and electrolyte replacement. In severe cases, a fluoroquinolone (e.g., ciprofloxacin) is the drug of choice.

7 Salmonella spp. Large and complex group of organisms; grouped by O, H, and Vi (for virulence) antigens. Salmonellae possess multiple types of pili and flagella. Transmission is by the fecal oral route. Clinical infection: The clinical patterns of salmonellosis can be divided into gastroenteritis, bacteremia with and without focal extraintestinal infection and enteric fever. 1. S. enterica : Salmonella Gastroenteritis and bacteremia 2. Salmonella Typhi: enteric fever(typhoid fever)

8 Pathogenesis Pathogenic salmonellae ingested in food,survive passage through the gastric acid barrier and invade the mucosa of the small and large intestine and produce toxins. Invasion of epithelial cells stimulates the release of Pro-inflammatory cytokines which induce an inflammatory reaction. The acute inflammatory response causes diarrhea and may lead to ulceration and destruction of the mucosa. The bacteria can disseminate from the intestines to cause systemic disease.

9 S. enterica : Salmonella Gastroenteritis S. enterica gastroenteritis is predominantly a disease associated with improper food handling, which allows the transmission from the animal reservoir to humans. Modern delivery systems can spread disease efficiently. The typical example of Salmonella "food poisoning" is the community picnic or bazaar, in which volunteers prepare poultry, salads, and other potential culture media to be eaten later in the day. One to two days after eating, a significant portion of the revelers develop abdominal pain, nausea, vomiting, and diarrhea lasting for 3 or 4 days

10 Bacteremia The acute gastroenteritis caused by S. enterica can be associated with transient or persistent bacteremia. Salmonella Serovar Typhi: enteric fever(typhoid fever) Typhoid fever has a slow, insidious onset, and if untreated, lasts for weeks. The pathogen can be transmitted in the water supply due to contamination of drinking water. Enteric fever is a multi-organ system Salmonella infection characterized by prolonged fever, sustained bacteremia, and profound involvement of the mesenteric lymph nodes, liver, and spleen

11 Laboratory Diagnosis: Culture of Salmonella from the blood or feces is the primary diagnostic method. Salmonellae form non-lactose-fermenting (colorless) colonies on McConkey's or EMB agar.. Treatment: The primary therapeutic approach to Salmonella gastroenteritis consists of fluid and electrolyte replacement and the control of nausea and vomiting. Antimicrobial therapy is clearly indicated in typhoid fever, The treatment of choice is either ceftriaxone or ciprofloxacin.

12 Yersinia Infections Lecture -10- Morphologically, Yersinia tend to be coccobacillary. Growth and metabolic characteristics are the same as those of other Enterobacteriaceae, although some strains grow more slowly or have optimal growth temperatures lower than 37 C. The genus includes 11 species, of which Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica are the pathogens for humans. Yersinia are primarily animal pathogens, with occasional transmission to humans through direct or indirect contact.

13 Yersinia Infections Y. enterocolitica and Y. pseudotuberculosis are most common species of Yersinia Both Y. enterocolitica and Y. pseudotuberculosis cause acute mesenteric lymphadenitis, a syndrome involving fever and abdominal pain that often mimics acute appendicitis. Yersinia pestis Causes plague, which is a disease primarily of rodents; transmitted by fleas

14 Epidemiology: The portal of entry for humans is the gastrointestinal tract, by consumption of contaminated food or water. In most cases, animals, including wild animals, are the most likely source of infection, but the exact mode of transmission is unknown. Treatment: The role of antimicrobial therapy in the enteric Yersinia infections is uncertain, because they are usually self-limiting. Y pseudotuberculosis is susceptible to ampicillin, cephalosporins, aminoglycosides, and tetracyclines, but Y enterocolitica is usually resistant to penicillins and cephalosporins through the production of beta-lactamases.

15 Klebsiella The most distinctive bacteriologic features of the genus Klebsiella are the absence of motility and the presence of a polysaccharide capsule. K. pneumoniae has a very large capsule, which gives its colonies a striking mucoid appearance. Several types of pili are also present on the surface and probably aid in adherence to respiratory and urinary epithelium.