Pathogenic Bacteria

Defining Pathogenic Bacteria

• Pathogen: Infectious agent that can cause disease upon colonization of the host.

  • Virulence Genes: Required for infection (e.g. adherence, invasion, evasion of immune system, and/or toxins).

• Types of Pathogens:

  • Obligate Pathogen: Must infect a host and cause disease to multiply.

  • Facultative Pathogen: Can multiply in the environment and also in hosts.

  • Opportunistic Pathogen: Normally does not cause disease but becomes pathogenic under certain conditions (e.g., impaired host immunity).

Types of Intracellular Pathogens

• Obligate Intracellular Pathogens: Must reproduce inside the host cell (e.g. Rickettsia, Ehrlichia, Mycoplasma, Chlamydia).

• Facultative Intracellular Pathogens: Can survive and multiply both intra- and extracellularly (e.g. Mycobacterium, Salmonella).

• Extracellular Pathogens: Can survive and multiply outside of host cells (e.g. Streptococcus group A).

Gram Staining

• Gram-Negative: Pink color in staining process.

• Gram-Positive: Purple color in staining process.

Types of Bacteria by Shape

• Cocci: Spherical bacteria.

• Bacilli: Rod-shaped bacteria.

• Important Pathogen Groups:

  • Extracellular & Facultative: Includes various bacterial types.

  • Obligate Intracellular: E.g., Rickettsia, Chlamydia, etc.

  • Gram-positive and Gram-negative: Mycobacteria, Spirochetes, etc.

Gram-Positive Bacteria: Cocci

• Reservoir Locations:

  • Skin and mucous membranes of animals and humans

  • Upper respiratory tract, lower urogenital tract, gastrointestinal tract

• Species of Clinical Importance:

  • Staphylococcus aureus: Humans & animals

  • Staphylococcus pseudintermedius: Dogs & cats

  • Staphylococcus hyicus: Pigs

• Infections:

  • Pyogenic infections (pus-filled lesions) caused by S. aureus

Gram-Positive Bacteria: Staphylococcus

• Common Infections:

  • Pyoderma: Local suppurative skin infections

  • Otitis Externa: Ear infections, often secondary to parasites, allergies, or foreign bodies.

Bovine Staphylococcal Mastitis

• Causative Agent: S. aureus

• Hosts: Cattle, small ruminants

• Clinical Significance: Leads to production losses due to chronic mastitis.

Gram-Positive Bacteria: Streptococcus

• Common Species:

  • Streptococcus pyogenes: Humans

  • Streptococcus agalactiae: Contagious mastitis in cattle

  • Streptococcus dysgalactiae: Environmental mastitis in cattle

  • Streptococcus equi: Causes strangles in horses

• Clinical Effects: Suppurative infections, septicemia, and localized infections in various hosts.

Strangles in Equines

• Causative Agent: Streptococcus equi subsp. equi

• Characteristics: Highly contagious febrile disease leading to lymph node abscessation.

Gram-Positive Rods/Bacilli

• Listeria monocytogenes:

  • Reservoir: Ubiquitous in the environment, can grow in refrigeration.

  • Clinical Syndromes: Septicemia, abortion, encephalitis.

Clostridium Bacteria

• Pathogenic Types:

  • Neurotoxic (C. tetani, C. botulinum)

  • Histotoxic (e.g., C. chauvoei for blackleg)

  • Enteropathogenic (C. perfringens for enterotoxaemia).

• C. tetani: Causes tetanus via neurotoxin production.

• C. botulinum: Causes botulism through neurotoxin ingestion.

Gram-Negative Rods/Bacilli

• Enterobacteriaceae:

  • Escherichia coli, Salmonella spp. - Major pathogens.

  • Opportunistic Pathogens: e.g., Klebsiella pneumoniae.

Zoonotic Pathogens

• Brucella spp.:

  • Clinical Impacts: Causes abortion in livestock and reproductive issues in dogs and pigs.

• Transmission: Direct contact with infected animal secretions, raw milk.

Canine Cough and Other Infections

• Bordetella bronchiseptica: Causes kennel cough, can facilitate other infections.

Spirochetes and Associated Diseases

• Leptospira: Causes reproductive failure in livestock and flu-like symptoms in humans.

• Borrelia burgdorferi: Causes Lyme disease, transmitted by ticks.

Mycoplasma and Rickettsiales

• Mycoplasma spp.: Smallest prokaryotes without cell walls, causing various infections in livestock.

• Rickettsiales: Obligate intracellular bacteria that target blood cells, transmitted through ticks.

Conclusion

• Memorization Emphasis: Important for exams and understanding the pathogens and their impacts on veterinary medicine.