Microbiology of Hematopoietic and Lymphoid System (HLS) Quiz

Salmonellosis and Brucellosis

Objectives of the Lecture

• Define Salmonellosis and Brucellosis
• Describe the causative organisms
• Describe pathogenesis and clinical features of the disease
• Mention diagnostic methods of Salmonellosis and Brucellosis
• State treatment of Salmonellosis and Brucellosis
• Describe prevention and control of the disease

Salmonellosis

• Definition: An infectious disease caused by the bacterium Salmonella typhi (Salmonella enterica Serovar Typhi) and less commonly by Salmonella paratyphi
• Characteristics of Salmonella:
  • Gram-negative enteric bacillus
  • Belongs to the family Enterobacteriaceae
  • Motile with peritrichous flagella
  • Non-sporing, non-capsulated (except S. typhi/paratyphi)
  • Size varies from 2-4 x 0.6 micron
• Cultural Characteristics:
  • Aerobics, facultative anaerobes
  • Grow optimally in temperature of 37°C and pH 6-8
  • Grow on simple media - Nutrient agar, MacConkey medium, and Wilson Blair Bismuth sulphide medium
  • Produce H2S
• Typhoid fever:
  • A systemic bacterial disease caused primarily by Salmonella Typhi
  • Causes:
    • Ingestion of contaminated food or water
    • Contact with an acute case of typhoid fever
    • Water contaminated with inadequate sewerage systems and poor sanitation
    • Contact with a chronic asymptomatic carrier
    • Eating food or drinking beverages handled by a person carrying the bacteria
  • Signs and symptoms:
    • Fever that starts low and increases daily
    • Headache
    • Weakness and fatigue
    • Muscle aches
    • Sweating
    • Dry cough
    • Loss of appetite and weight
    • Abdominal pain
    • Diarrhea or constipation
    • Rash

Paratyphoid Fever

• Caused by Salmonella paratyphi A, B, and C
• Presents with more abrupt onset and mild symptoms compared to typhoid fever
• Features:
  • Fever
  • Headache
  • Abdominal pain
  • Malaise
  • Anorexia
  • Cough
  • Hepatomegaly and splenomegaly
• Paratyphoid A:
  • Causes paratyphoid fever with mild symptoms
• Paratyphoid B:
  • May occur as typhoid-like illness or severe gastroenteritis
  • Cold sores or fever blisters are frequently seen in this infection
• Paratyphoid C:
  • A rare type of infection

Laboratory Diagnosis

• Hematological investigations
• Bacteriological investigations:
  • Blood culture
  • Stool culture
  • Urine culture
  • Duodenal juice or bile culture
• Identifying Enteric Organisms:
  • Non-lactose fermenting
  • Motile
  • Indole positive
  • Urease negative
  • Oxidase negative
  • Ferment Glucose, Mannitol, Maltose
  • Do not ferment Lactose, Sucrose
  • Some Paratyphoid forms acid and gas
  • H2S produced by Salmonella typhi
• Serology:
  • Widal test: detects antibodies in serum against the O&H antigens of Salmonella species

Prevention and Control

• Apply public health and personal hygiene measures
• Proper sewage disposal and proper chlorinated water supply
• Cultures of stool for food handlers to detect carriers
• Pasteurization of milk, proper cooking of poultry, eggs, and meat
• Vaccination:
  • Two vaccines are available, giving 50-80% protection against S. typhi
  • One vaccine consists of acetone-killed S typhi organisms, administered I.M.
  • The other vaccine is a live, attenuated S typhi and is taken orally

Brucellosis

• Definition: A zoonosis primarily of domestic animals, causing a chronic debilitating septicemic disease leading to abortion
• Morphology of Brucella:
  • Small (0.4～0.8 ×0.5～1.5μm)
  • Non-motile
  • Non-capsulate
  • Gram-negative coccobacilli
  • Aerobic
• Growth Characteristics:
  • Nutritional requirements are complex
  • Some strains have been cultivated on defined media containing amino acids, vitamins, salts, and glucose
  • Inoculated on trypticase-soy agar or blood culture media
• Antigenic Structure and Classification:
  • A and M antigens are common to 3 main Brucella spp.
  • B. melitensis has the highest concentration of M antigen and causes the most serious infections
  • The difference between species is related to the amount of the two main antigens
• Spread of Brucella in the body:
  • Mode of transmission:
    • Oral entry - most common route
    • Ingestion of contaminated animal products (often raw milk or its derivatives)
    • Contact with contaminated fingers
    • Aerosols
    • Contamination of the conjunctivae
    • Percutaneous infection through skin abrasions or by accidental inoculation
• Pathogenesis:
  • Incubation period: between 2 and 6 weeks
  • Common route of infection: ingestion of contaminated milk, mucous membrane droplets

This quiz covers microbiology of hematopoietic and lymphoid system, including Salmonella typhi, enteric fever, and Brucella. It is based on the course contents of Medical Microbiology and Prescott's Microbiology.