Chapter 9: Bacterial Diseases

Chapter 9: Bacterial Diseases

Organized by type of transmission:

  • Foodborne and/or Waterborne
  • Airborne
  • STDs
  • Contact Diseases (other than STDs)
  • Soilborne
  • Arthropod-borne

Foodborne and Waterborne Bacterial Diseases

  • Food Intoxication (Food Poisoning):

    • Involves the ingestion of bacterial toxins, which may occur with or without the microbe's presence.
    • Symptoms involve gastrointestinal disturbances due to enterotoxins, including nausea, vomiting, diarrhea, and possibly bloody stools.

  • Foodborne Infection:

    • Bacteria multiply in the intestinal tract, secrete enterotoxins, and may invade intestinal cells.
    • Source: 2009 Report by the Center for Science in the Public Interest (CSPI), Washington D.C.

  • Common Sources of Bacterial Contamination:

    • Monroy’s 3Bs:
    1. Bottle Water
    2. Bananas
    3. Beer
Specific Foodborne Intoxications

  1. Botulism:

    • Caused by the botulinum neurotoxin produced by Clostridium botulinum, a G(+) spore-forming bacillus found primarily in soil.
    • Commonly linked to improperly canned foods, such as:
      • String beans
      • Peppers
      • Asparagus
      • Sausage and cured pork
      • Smoked fish and canned salmon
    • Therapy: Antitoxin and mechanical ventilation.
    • Botox: Utilized to remove wrinkles and reduce muscle overactivity.

  2. Staphylococcal Food Poisoning:

    • Caused by Staphylococcus aureus, a G(+) coccus and the most common type of food poisoning.
    • Found in human nasal passages.
    • Produces a heat-stable enterotoxin.
    • Symptoms include:
      • Abdominal cramps
      • Nausea
      • Vomiting
      • Diarrhea
    • Symptoms appear within a few hours and are very severe but short-lived.

  3. Cholera Intoxication:

    • Caused by the exotoxin secreted by Vibrio cholerae, a G(-), curved rod.
    • Transmission occurs primarily through the consumption of fecally contaminated water or food, including raw shellfish.
    • Characterized by a voluminous "rice-water" diarrhea, necessitating quick rehydration to prevent death.
    • Oral rehydration therapy can save lives.
    • Conditions favoring cholera: Poverty, overcrowding, and poor sanitation.

  4. Salmonellosis:

    • Caused by several G(-) bacilli species within the genus Salmonella.
    • Symptoms include nausea, vomiting, abdominal cramps, diarrhea, and possibly fever.
    • Salmonella enteritidis infects eggs retained in healthy hens and can also contaminate meats, seafood, fresh fruits, and vegetables.
    • Zoonosis: Species such as iguanas, lizards, snakes, and turtles may carry various Salmonella species.

  5. Typhoid Fever:

    • Caused by Salmonella typhi.
    • Primarily occurs in less developed countries.
    • Transmission occurs via fecally-contaminated food, hands, and frequently by flies and fomites.
    • The organism invades small intestine cells, causing ulcers, bloody stools, fever, and potentially delirium.

  6. E. coli O157:H7 (Entrohemorrhagic E. coli, EHEC):

    • Commonly contaminates undercooked meat (particularly hamburgers), fresh spinach, and sprouts.
    • Present as normal flora in cattle, it produces Shiga enterotoxin acquired from Shigella dysenteriae (via lysogenic phage).
    • Can lead to Hemolytic Uremic Syndrome (HUS), resulting in kidney failure and potentially death in children under five.

  7. Enterotoxigenic E. coli (ETEC):

    • The most common cause of traveler’s diarrhea.
    • E. coli is easy to culture and detect—serving as an indicator of fecal contamination.
    • Present as O antigen (part of LPS) and H antigen (flagella).

  8. Pseudomembranous Colitis:

    • Caused by Clostridium difficile (C. dif), a G(+), spore-forming bacillus.
    • Spread via fecal–oral route and fomites.
    • Major nosocomial infection caused frequently by patients on antibiotics, often due to depletion of normal flora.
    • Treatment may involve fecal transplantation.
Traveler’s Diarrhea (TD)
  • Between 20% and 56% of international travelers can expect to develop TD during travels under 100 days.
  • Characterized by 7 to 13 watery stools over 2 days, possibly accompanied by additional enteric symptoms.
  • Often self-limiting, TD on average lasts 4 days.
  • Enterotoxigenic Escherichia coli (ETEC) and enteroaggregative E. coli (EAEC) are responsible for 80% of cases, while invasive bacteria such as Shigella and Campylobacter contribute 4%-20% of TD.
  • Prophylactic treatment with rifaximin 600 mg/day for 14 days can be implemented.

Airborne Bacterial Diseases

Upper Respiratory Tract Infections

  1. Diphtheria:

    • Caused by an exotoxin produced by Corynebacterium diphtheriae, a G(+) bacillus.
    • Toxin kills epithelial cells, forming a leathery pseudomembrane leading to suffocation.
    • Toxin diffuses into the bloodstream, causing widespread damage, particularly to the heart (myocarditis).
    • Immunization programs are vital for disease control, especially in underdeveloped areas.
    • Extreme lymph node swelling can result in a "bull neck" appearance.

  2. Whooping Cough:

    • Caused by Bordetella pertussis, a G(-) coccobacillus.
    • Humans are the sole reservoir; particularly threatens children under age 4.
    • Transmitted via contaminated droplets (talking, coughing, sneezing).
    • Exotoxin damages ciliated epithelial cells, leading to characteristic deep inspirations ("whoop").
    • B. pertussis is endemic in the U.S., with epidemics occurring every 3-5 years.

  3. Streptococcus Infections:

    • A large genus of G(+) cocci; S. pyogenes is the most virulent.
    • Commonly resides in the nose and throat and spreads via respiratory droplets or contact.
    • Common childhood affliction: streptococcal pharyngitis (tonsillitis).
    • Long-term complications of repeated infections include:
      • Glomerulonephritis (kidney disease)
      • Rheumatic fever (heart and joint involvement).
    • Streptococcal toxic shock syndrome and necrotizing fasciitis are severe invasive infections.
    • Erythrogenic toxin-producing strains of S. pyogenes cause scarlet fever and a