Bacterial Infections of Humans

• Introduction


  1. How do Bacteria Cause Disease?

  2. Bacterial Infections of the Skin

  3. Bacterial Infections of the Ears

  4. Bacterial Infections of the Eyes

  5. Bacterial Infections of the Respiratory System

  6. Bacterial Infections of the Oral Region

  7. Bacterial Infections of the Gastrointestinal Tract

  8. Bacterial Infections of the Genitourinary System

  9. Bacterial Infections of the Circulatory System

  10. Bacterial Infections of the Central Nervous System

  11. Diseases Caused by Anaerobic Bacteria

  12. Diseases Associated With Biofilms

  13. Recap of Major Bacterial Infections of Humans

  14. Recap of Major Bacterial Pathogens of Humans

  15. Appropriate Therapy for Bacterial Infections
• How Do Bacteria Cause Disease?


  • Adherence and colonization factors
  • Factors that prevent activation of complement
  • Factors that enable escape from phagocytosis by white blood cells
  • Factors that prevent destruction within phagocytes
  • Factors that suppress the host immune system (i.e., factors that cause immunosuppression)
  • Endotoxin (a component of the cell walls of Gram-negative bacteria)
  • Production of exotoxins (e.g., cytotoxins, enterotoxins, neurotoxins)
  • Production of necrotic and other types of destructive enzymes
• Acne


  Caused by Propionibacterium acnes and other Propionibacterium spp.; anaerobic Gram-positive bacilli
• Anthrax, Woolsorter Disease


  Caused by Bacillus anthracis; a spore-forming, Gram-positive bacillus
• Gas gangrene (myonecrosis)


  Caused by anaerobic bacteria in the genus Clostridium, especially C. perfringens
• Leprosy (Hansen disease)


  Caused by Mycobacterium leprae; an acid-fast bacillus
• Staphylococcal skin infections (folliculitis, furuncles, abscesses, etc.)

  Caused by Staphylococcus aureus, a Gram-positive coccus
• Streptococcal skin infections (scarlet fever, erysipelas, etc.)


  Caused by Streptococcus pyogenes, a Gram-positive coccus
• Diseases Caused by Staphylococcus aureus

  • Folliculitis
  • Furuncles
  • Abscesses
• Diseases Caused by Streptococcus pyogenes

  • Scarlet fever
  • Erysipelas
• Wound infections


  • Result when protective skin barrier is broken as a result of burns, punctures, surgical procedures, or bites
  • Opportunistic indigenous microbiota and environmental bacteria can invade and cause local or deep tissue infections
  • Pathogens may spread through blood or lymph, causing serious systemic infections
• Otitis externa (external otitis, ear canal infection, swimmer's ear)

  Caused by Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Staphylococcus aureus; less commonly caused by a fungus such as Aspergillus
• Otitis media (middle ear infection)

  • Bacterial causes: Streptococcus pneumoniae, a Gram-positive diplococcus; Haemophilus influenzae, a Gram-negative bacillus; and Moraxella catarrhalis, a Gram-negative diplococcus
  • Viral causes: measles, parainfluenza, and respiratory syncytial viruses (RSV)
• Bacterial conjunctivitis (pink eye)


  Caused by Haemophilus influenzae biogroup aegyptius and Streptococcus pneumoniae
• Chlamydial conjunctivitis (inclusion conjunctivitis, paratrachoma)


  Caused by certain serotypes (serovars) of Chlamydia trachomatis
• Trachoma (chlamydia keratoconjunctivitis)


  Caused by certain serotypes of Chlamydia trachomatis
• Gonococcal conjunctivitis (gonorrheal ophthalmia neonatorum)


  Caused by Neisseria gonorrhoeae; a Gram-negative diplococcus; also called gonococcus or GC
• Infections Caused by Haemophilus influenzae

  • Otitis media
  • Conjunctivitis
• Gonococcal Ophthalmia Neonatorum


  • Conjunctivitis
• Diphtheria


  • Caused by Corynebacterium diphtheriae; a pleomorophic, Gram-positive bacillus
  • Transmission occurs via airborne droplets, direct contact, contaminated fomites, and raw milk
• Streptococcal pharyngitis (strep throat)


  • Caused by Streptococcus pyogenes; beta-hemolytic, catalase-negative, Gram-positive cocci in chains
  • Transmission is human-to-human by direct contact, usually hands; also via aerosol droplets
• Pneumonia


  • May be caused by Gram-positive or Gram-negative bacteria, mycoplasmas, chlamydias, viruses, fungi, or protozoa
  • Community-acquired bacterial pneumonia is most frequently caused by Streptococcus pneumoniae
  • Hospital-acquired pneumonia is most frequently caused by Staphylococcus aureus
  • Transmission, in most cases, occurs via infected humans
• Gram-Positive Streptococcus pneumoniae in a Gram-Stained Smear of a Purulent Sputum


  • Note the diplococci
• Legionellosis (Legionnaires' disease, Pontiac fever)


  • Caused by Legionella pneumophila, a poorly staining, Gram-negative bacillus
  • Transmission is via environmental water sources, ponds, air-conditioning systems, hot tubs, etc.
• Mycoplasmal pneumonia (primary atypical pneumonia)


  • Caused by Mycoplasma pneumoniae, tiny bacterium lacking cell wall
  • Transmission occurs via droplet inhalation, direct contact with an infected person, or contaminated articles
• Tuberculosis (TB)


  • Primarily caused by Mycobacterium tuberculosis (a slow-growing, acid-fast bacillus), occasionally other Mycobacterium spp.
  • Transmission occurs primarily via infected humans (airborne droplets)
• Whooping cough (pertussis)


  • Caused by Bordetella pertussis, a small, encapsulated, nonmotile, Gram-negative coccobacillus that produces endotoxin and exotoxins
  • Transmission occurs via infected humans (i.e., droplets by coughing)
• Acute necrotizing ulcerative gingivitis (ANUG); also known as Vincent's angina and trench mouth


  A synergistic infection involving two or more species of anaerobic bacteria of the indigenous oral microbiota; most commonly, Fusobacterium nucleatum and Treponema vincentii
• Bacterial gastritis and ulcers


  • Caused by Helicobacter pylori, a curved, microaerophilic, capnophilic, Gram-negative bacillus
  • Transmission occurs via infected humans; probably by ingestion; presumed to be either oral–oral or fecal–oral

  
• Campylobacter enteritis


  • Caused by Campylobacter jejuni (less common, C. coli), curved, S-shaped or spiral Gram-negative bacillus
  • Transmission occurs via animals, including poultry, cattle, sheep, swine, rodents, birds, kittens, puppies, and other pets
• Cholera


  • Caused by certain biotypes of Vibrio cholerae serogroup 01 & O139, curved, Gram-negative bacillus that secretes enterotoxin
  • Transmission occurs via infected humans and aquatic reservoirs; fecal–oral route
• Salmonellosis


  • Caused by Salmonella spp.; members of the family Enterobacteriaceae, Gram-negative bacilli that invade intestinal cells, release endotoxin, and produce cytotoxins and enterotoxins
  • Transmission occurs via domestic and wild animals; contaminated food, fecal–oral, food handlers, contaminated water
• Typhoid fever (enteric fever)

  • Caused by Salmonella typhi, a Gram-negative bacillus that releases endotoxin and produce exotoxins
  • Transmission occurs via infected humans for typhoid and paratyphoid; some people become carriers after infection (e.g., "Typhoid Mary")
• Shigellosis (bacillary dysentery)


  • Caused by Shigella dysenteriae, S. flexneri, S. boydii, and S. sonnei; nonmotile, Gram-negative bacilli, members of the family Enterobacteriaceae
  • Transmission occurs via infected humans. Fecal/oral route
• Clostridium difficile-associated disease (CDAD)
• Enterobacteriaceae


  Gram-negative bacilli that invade intestinal cells, release endotoxin, and produce cytotoxins and enterotoxins
• Transmission of Enterobacteriaceae


  1. Domestic and wild animals

  2. Contaminated food

  3. Fecal–oral

  4. Food handlers

  5. Contaminated water
• Typhoid fever (enteric fever)


  Salmonella typhi, a Gram-negative bacillus that releases endotoxin and produce exotoxins
• Transmission of typhoid fever

  1. Infected humans

  2. Some people become carriers after infection (e.g., "Typhoid Mary")
• Shigellosis (bacillary dysentery)


  Shigella dysenteriae, S. flexneri, S. boydii, and S. sonnei; nonmotile, Gram-negative bacilli, members of the family Enterobacteriaceae