Salmonella

• Salmonellosis


  A gram-negative motile bacilli belonging to the family Enterobacteriaceae

  
• Salmonellae species


  • Defined by different combinations of somatic O, surface Vi, and flagellar H antigens

  
• Bacteria of the genus Salmonella are highly adapted for growth in both humans and animals and cause a wide spectrum of disease
• S. Typhi & S. Paratyphi

  Their growth is restricted to human hosts, in whom they cause enteric (typhoid) fever
• Nontyphoidal salmonella


  Can colonize the GIT of a broad range of animals, including mammals, birds, and insects. More than 200 serotypes are pathogenic to humans, in whom they often cause gastroenteritis and can be associated with localized infections and/or bacteremia
• Most commonly, food-borne or waterborne transmission of enteric fever results from fecal contamination by ill or asymptomatic chronic carriers
• Sexual transmission between male partners has been described for enteric fever
• Health care workers occasionally acquire enteric fever after exposure to infected patients or during processing of clinical specimens and cultures
• It is estimated that enteric fever occurs in about 6,000 people per year in the United States
• In 2013 enteric fever resulted in about 161,000 deaths
• The risk of death from enteric fever may be as high as 25% without treatment while with treatment it is between one and four percent
• Pathophysiology of enteric fever

  1. Bacteraemia

  2. Localization in lymphoid tissue of small intestine (distal ilium)

  3. Lesions in Peyer's patches and follicles

  4. Chronic carrier state with bacilli living in gallbladder
• Clinical features of enteric fever

  • Fever in stepladder fashion for 4-5 days
  • Headache
  • Myalgia
  • Relative bradycardia
  • Constipation
  • Diarrhoea and vomiting in children
  • Epistaxis
  • Rose spots on trunk
  • Splenomegaly
  • Cough and basal ronchi
  • Abdominal distension and tenderness
  • Diarrhoea
  • Positive Widal test
• Rose spots in enteric fever

  • Salmon-colored, blanching, truncal, maculopapules usually 1-4 cm wide and fewer than 5 in number
  • Resolve within 2-5 days
  • Bacterial emboli to the dermis
  • May develop in shigellosis or nontyphoidal salmonellosis
  • Cultures of punch-biopsy samples have 63% sensitivity
• Complications of enteric fever


  • Intestinal haemorrhage
  • Intestinal perforation
  • Delirium, coma and death (if untreated)
  • Extra-intestinal complications including endocarditis, vascular infections, cholecystitis, hepatic and splenic abscesses, nephritis, pneumonia, meningitis, septic arthritis, osteomyelitis, and reactive arthritis
• Paratyphoid fever


  • Shorter and milder course than typhoid fever
  • More abrupt onset with acute enteritis
  • More abundant rash
  • Less frequent intestinal complications
• Investigations for enteric fever

  1. Blood culture (80% sensitivity in first week)

  2. Bone marrow culture (90% sensitivity)

  3. Stool and urine culture (30-40% sensitivity in third week)

  4. WBC count (may be normal, leukopenia, neutropenia, eosinopenia and relative lymphocytosis)

  5. Widal test (negative in first week, positive in second week with 4-fold rise in antibodies)
• Polymerase chain reaction and DNA probe assays to detect S. Typhi in blood are being developed
• Empirical antibiotic therapy for enteric fever

  • Macrolides and 3rd generation cephalosporins are preferred
  • Ceftriaxone, cefotaxime, and cefixime are effective
  • Oral azithromycin is also effective
  • Fluoroquinolones are most effective but resistance is increasing
• Other antibiotics for enteric fever

  Chloramphenicol, ampicillin and co-trimoxazole are losing effectiveness due to resistance
• Steroid therapy for severe enteric fever

  1. Dexamethasone 3 mg/kg initially, followed by 1 mg/kg every 6 hours for 48 hours

  2. Steroids should not be continued for more than 48 hours as they can mask signs of complications
• Even with effective chemotherapy, there is still a danger of complications, relapse of the disease and the development of a carrier state
• Treatment of chronic carrier state

  1. Oral antibiotics like amoxicillin, TMP-SMX, ciprofloxacin or norfloxacin for 4-6 weeks

  2. Surgical correction of anatomical abnormalities may also be required
• Before antibiotics, typhoid fever had a mortality rate of 20-25%, which has been reduced to less than 1% in industrialized countries, but remains as high as 30-50% in some developing countries
• Relapses were more common with older antibiotics like chloramphenicol, ampicillin and TMP-SMX, but are less frequent with ceftriaxone and fluoroquinolones (less than 5%)
• Untreated survivors of typhoid fever may shed the bacterium in the feces for up to 3 months, so 3 stool cultures in one-month intervals should be performed to rule out a carrier state
• Brucellosis


  A major zoonotic disease worldwide, particularly in the Mediterranean, Africa, Middle East, and Latin America. Caused by gram-negative intracellular coccobacilli of the genus Brucella
• Brucella species and their reservoir hosts

  • B. abortus - Cattle
  • B. Melitensis - Sheep, goats, cattle (causes most severe disease)
  • B. Suis - Swine
  • B. Canis - Canine
• Routes of transmission of brucellosis to humans include direct contact with infected animals or their products, ingestion of contaminated food or water, and inhalation of infectious aerosols
• hoxazole but seemed to be much less frequent in those treated with ceftriaxone and fluoroquinolones (<5%).
• Untreated survivors of typhoid fever may shed the bacterium in the feces for up to 3 months. Therefore, after disease resolution, 3 stool cultures in one-month intervals should be performed to rule out a carrier state. Concurrent urinary cultures should be considered.
• Brucellosis


  Worldwide a major source of disease in domestic animals and humans
• Brucellosis


  • Major zoonotic disease worldwide particularly Mediterranean, Africa, Middle East, Latin America
  • Gram negative intracellular coccobaceli
  • Other names for human disease: undulant fever, Malta fever, Mediterranean fever
• Brucella species


  • Brucella abortus (Cattle)
  • Brucella Melitensis (Sheep, goats, cattle - causes the most severe disease)
  • Brucella Suis (Swine)
  • Brucella Canis (Canine)
• Routes of transmission to human

  1. Direct contact with animals or their secretions, through cuts and skin abrasions

  2. Infected aerosols inhaled or inoculated into eye or conjunctival sac

  3. Ingestion of unpasteurized dairy products (milk and soft cheeses)
• Brucellosis constitutes occupational risk for: farmers, veterinarians, abattoirs and Laboratory personnel.
• Pathogenesis


  1. After penetrating the epithelial cells, Brucella organisms induce an excess polymorphonuclear neutrophil response

  2. Ingestion of organisms by neutrophils and tissue macrophages, spread to regional lymph nodes

  3. If host defenses within the lymph nodes are overwhelmed, bacteremia follows
• Incubation period


  1½ to 3 weeks between infection and bacteremia
• Bacteremia is accompanied by phagocytosis of free Brucella organisms by neutrophils and localization of bacteria primarily to the spleen, liver, and bone marrow, with the formation of granulomas
• Clinical Manifestations


  • Subclinical illness
  • Acute or subacute disease
  • Localized disease
  • Complications
  • Relapsing infection
  • Chronic disease