Bacto exam overview

History of Microbiology

• Antonie van Leeuwenhoek, a Dutchman, is considered the "Father of Microbiology" and discovered bacteria, RBC, spermatozoa, muscle fibers, and crystals
• Robert Hooke, an Englishman, was the first to document microorganisms using a microscope and coined the term "cell"
• Edward Jenner, an Englishman, is known as the "Father of Immunology" and developed the concept of vaccines, including the first vaccine against smallpox
• The Golden Age of Microbiology lasted from 1857 to 1910
• Louis Pasteur, a Frenchman, developed the germ theory and vaccination experiments against fowl cholera, anthrax, and rabies
• Robert Koch, a German, discovered the causative agents of many deadly infectious diseases, developed Koch's postulates, and invented the bacterial culture method using agar on glass plates

General Characteristics of Bacteria

• Bacteria are ubiquitous in nature and can be found on body surfaces and in the GI tract, where they help digest nutrients
• Only some bacteria are harmful pathogens, while others are commensals or mutualists
• Bacterial cell types vary in size, shape, and arrangement

Cell Structure

• The cell envelope consists of a phospholipid membrane and a cell wall
• Peptidoglycan/murein is unique to bacterial cell walls
• Gram-positive bacteria have a thicker peptidoglycan layer, while Gram-negative bacteria have a thinner layer and an outer phospholipid membrane with porins
• Exceptions include Mycoplasma, which has no cell wall, and the CMNR group, which has a complex cell wall with mycolic acid

Surface Structures

• Capsules are firmly attached to the cell wall and provide protection and facilitate attachment to hosts
• Slime layers are loosely attached to the cell wall and help with biofilm formation
• Flagella are composed of flagellin and provide motility
• Fimbriae/pili are composed of pilin and facilitate attachment to host cells

Cytoplasmic Structures

• Cytoplasm consists of water, proteins, carbohydrates, lipids, and inorganic ions
• The nucleoid is a single, long, circular DNA molecule
• Plasmids are extrachromosomal DNA molecules that can provide advantages like antimicrobial resistance
• Inclusions are storage granules that store polysaccharides and other nutrients
• Ribosomes are smaller and less dense than those in eukaryotes and consist of 30S and 50S subunits

Criteria for Classification

• Growth on different media
• Growth properties (oxygen, temperature, motility, etc.)
• Microscopy (form, arrangement, size, and staining method)
• Spore production
• Biochemical activity (tests)
• Serological tests (detects antigens/antibodies)
• Genotypic/molecular analysis (MALDI-TOF, PCR, etc.)

Physiology - Metabolism, Growth, and Nutrition

• Main energy production methods: anaerobes via fermentation, aerobes via respiration
• Reproduction via binary fission, with generation time varying among species:
  • E. coli: 20 minutes
  • S. aureus: 27-30 minutes
  • M. bovis: 20 hours
  • M. leprae: 20 days
• Growth phases:
  • Lag phase: dormant, metabolically active, no distinct growth
  • Log phase: exponential growth
  • Stationary phase: population density stabilizes, nutrients run out, toxic waste products build up
  • Death phase: almost as fast as log phase
• Requirements for growth:
  • Oxygen demand: obligate, facultative, microaerophile
  • Carbon dioxide: usually air level, some require higher
  • pH: acidophiles, neutrophiles, alkaliphiles (most are neutrophiles, pH 6.8-7.2)
  • Temperature: psychrophiles (10-15°C), mesophiles (30-37°C), thermophiles (55°C)
  • Osmotic pressure: usually best at physiological saline level
• Nutrients:
  • Macronutrients (95%): components of nutrients, e.g., C, N, K, O, H, and cations for enzymes, cofactors, etc.
  • Micronutrients: vitamins, enzymes, cofactors
  • Growth factors: needed by some for growth, e.g., pyrimidines

Cultivation

• Process of propagating organisms with proper environmental conditions
• Suitable media need to be sterile and have:
  • Gelling compound: agar-agar
  • Necessary chemical components
  • Certain environmental pH
  • Nutrients
  • Energy source
  • Essential metals and minerals
  • Buffering agents
  • Selective agents, pH indicators
• Agar-agar: polysaccharide from red algae's cell wall, not nutritious, solidifies at 42°C, melts at 97-100°C
• Media types:
  • Chemically defined media: exact amounts of pure components, e.g., citrate broth
  • Complex media: some parts impure digests, exact composition not known, e.g., tryptic soy broth
  • General purpose (basal) media: suitable for all less fastidious bacteria, e.g., nutrient agar
  • Enriched media: basal with additional nutrients, e.g., blood agar
  • Enrichment media: liquid media that permit only certain bacteria to grow, e.g., Fraser broth for Listeria
  • Differential media: pH indicators, e.g., agar color changes with bacterial growth
  • Selective media: inhibitory substances, e.g., 6.5% NaCl broth for enterococci
  • Selective-differential media: combination of selective and differential media, e.g., MSA, BPA
• Other media: semi-solid media for microaerophilic bacteria or motility, assay media for antibiogram
• Unculturable bacteria: don't proliferate on media, e.g., intracellular bacteria like Rickettsia, Coxiella, Chlamydia, Ehrlichia

Haemolysis

• Alpha: greenish color under the colonies, caused by hydrogen peroxide (H2O2) breaking down hemoglobin to methemoglobin
• Beta: light yellow and clear area under and around colonies, caused by complete lysis of RBCs due to exotoxins (streptolysins)
• Double: mix of alpha and beta, wider area, can see two zones
• Gamma: no haemolysis, agar unchanged

Methods of Microbial Control

• Terms:
  • Sterilization: all viable microorganisms eliminated, no levels (0 or 100)
  • Disinfection: significant reduction of vegetative microorganisms on non-living materials
  • Antisepsis: same as disinfection, but on living animals/tissue
  • Asepsis: absence of microorganisms
  • Germicidal/microbicidal: chemical that destroys microorganisms, e.g., bactericidal, virucidal
  • Bacterio-/fungistatic: inhibits proliferation of bacteria/fungi
• Methods can affect cell wall, cell membrane, cytoplasm, enzymes (inactivation), and DNA
• Physical methods:
  • Heat: bacterial spores require >100°C for destruction, most vegetative die in 60-70°C in 10 minutes
  • Dry heat: hot air ovens and flaming (for instruments)
  • Moist heat: pasteurization, boiling water, tyndallization, autoclaving
• Radiation:
  • UV light (non-ionizing): damages DNA by causing bonds between adjacent pyrimidine bases, inhibits DNA replication, and causes death
  • Gamma/X rays (ionizing): with wavelength

Antibiotics

• Antibiotics that inhibit cell wall synthesis: beta-lactam antibiotics (penicillins, cephalosporins), bacitracin, and vancomycin
• Mechanism: bactericidal, better against Gram-positive (G+) bacteria, but also effective against Gram-negative (G-), and anaerobes
• Bacitracin and vancomycin only affect G+ bacteria

Antibiotics that Damage Cell Membrane Functions

• Antibiotics: polymyxins and monensin
• Mechanism: bactericidal, effective against G- aerobes

Antibiotics that Inhibit Nucleic Acid Function

• Antibiotics: nitroimidazoles (metronidazole, dimetridazole), and fluoroquinolones
• Mechanism: bind to inhibit DNA replication or transcription
• Nitroimidazoles: only affect anaerobes and microaerophiles, bactericidal
• Fluoroquinolones: bactericidal, effective against G-

Antibiotics that Inhibit Protein Synthesis

• Antibiotics: tetracyclines, aminoglycosides, chloramphenicol, and macrolides
• Mechanism: affect the 30S or 50S ribosome
• Tetracyclines: bacteriostatic, effective against both G+ and G- and protozoa (broad spectrum)
• Aminoglycosides: bactericidal, effective against G-, mycobacteria, and some mycoplasmas, only affect aerobes
• Chloramphenicol: bacteriostatic, effective against both G+ and G- (broad spectrum)
• Macrolides: bacteriostatic, effective against G+ and mycoplasmas

Antimicrobial Resistance

• Main mechanisms: reducing penetration, using efflux pumps, modifying/degrading antibiotics, modifying/protecting targets, and developing alternate pathways
• Intrinsic resistance: chromosomally encoded, natural to the taxonomic group
• Extrinsic resistance: acquired through mutation or transfer of genetic material
• Transfer of genetic material: vertical transmission, transformation, transduction, and conjugation
• Over-reliance/usage of antibiotics contributes to resistance

Pathogenicity and Virulence Factors

• Identifying pathogenic bacteria: Koch's postulates
• Infection: multiplication of an infectious agent within the body
• Types of transmission: exogenous, endogenous, contact, vectors, iatrogenic, vertical, ingestion, inhalation, and inoculation
• Most frequent transmission routes: damaged skin, mucous membranes, injuries, surgical sites, teats, and umbilicus
• Definitions: bacteremia, septicemia, sepsis, pathogenicity, and virulence
• General characteristic of pathogenesis: transmission, adherence, persistence, invasion, toxigenicity, evasion, and survival abilities

Virulence Factors

• Adherence factors: pili, fimbriae, lipoteichoic acid, protein F, etc.
• Invasion factors: hyaluronidase, collagenase, fibrinolysin, lecithinase, coagulase, and DNAse
• Evasion factors: modulate cell surfaces, release proteins to inhibit/degrade host immune factors, and mimic host molecules
• Toxigenicity factors: enzymes, exotoxins, and endotoxins

Animal Microflora

• ~500-1000 bacterial species on all surfaces exposed to the environment
• Vital functions: synthesize vitamins, ferment indigestible carbohydrates, and convert lactose to lactic acid
• Presence inhibits growth of pathogenic bacteria and trains host immunity
• Most are anaerobes, and also includes fungi and protozoa

Staphylococcus aureus Virulence Factors

• Cell wall-associated structures: MSCRAMM, peptidoglycan, capsule, and capsular polysaccharides for attachment, colonization, and invasion
• Protein A: biofilm formation, binds to immunoglobulins, evading immune recognition and opsonization
• Clumping factor: bound coagulase
• Exotoxins:
  • Hemolysins: α, β, γ, and δ
  • Leukocidins: LukMF, LukPQ, and LukSF-I
  • Enterotoxins: induce vomiting and cause food poisoning
  • Superantigens: stimulate T-cell proliferation and massive cytokine release
  • Exfoliating toxins: break intercellular adhesion molecules, causing blisters and skin peeling
• Enzymes:
  • Staphylokinase: breaks down fibrin clots
  • DNAse: degrades DNA
  • Lipase and phospholipase: enzymatic activity
  • Hyaluronidase: breaks down hyaluronic acid in connective tissue
  • Coagulase: converts fibrinogen to fibrin, creating clots that coat bacterial cells, resisting opsonization and phagocytosis
  • Protease: causes proteolysis

Bacillus anthracis Virulence Factors

• Two toxins: lethal factor (LEF) and edema factor (EF)
• Enzymes encoded in pXO1 plasmid
• LEF: causes major cytokine release, apoptosis, cell necrosis, and hypoxia
• EF: adenylyl cyclase, converting ATP to cAMP, causing upset water homeostasis and edema
• EF also inactivates phagocytes
• Capsule: encoded in pXO2 plasmid, providing strong antiphagocytic protection
• Secondary virulence factors:
  • Peptidases: affect proteins
  • Phospholipases: hydrolyze phospholipids
  • Hemolysins: α, β, γ, and δ

Escherichia coli Virulence Factors

• Adhesins: mediate attachment to host tissues
• Capsule: K antigen, made of polysaccharides, protecting from phagocytosis
• Cell wall: lipopolysaccharides
• Lipid A (endotoxin): activates cytokine release from immune cells
• O-antigen layer: protects against phagocytosis and the membrane attack complex
• Toxins:
  • Enterotoxins: disturb intestinal fluid metabolism
  • Heat-stable toxins: low molecular weight, poorly antigenic
  • Heat-labile toxins: high molecular weight, highly antigenic
  • Shiga toxins (Stx)/verotoxins: inhibit protein synthesis, inducing apoptosis
  • Hemolysins: α-hemolysin, enterohemolysin, and cytolysin A
  • Cyclomodulins: stimulate or inhibit the eukaryotic cell cycle
• Secretion systems:
  • T1SS: hemolysin secretion
  • T2SS: mediates transport of nutrient acquisition enzymes and exports some toxins
  • T3SS: injects virulence factors into host cells
  • T4SS: transports effector proteins to host and DNA to other bacteria
  • T5SS: autotransporters, promoting adherence, aggregation, and proteolytic activity
  • T6SS: against other bacteria, secreting antibacterial proteins directly into the periplasm of target bacteria
• Iron transport/uptake: siderophores take iron from host's lactoferrin and transferrin

Action Mechanism of Clostridial Toxins

• Done by the light (L) chain of the toxin molecule
• Both cleave one of the three SNARE complex proteins that would normally connect the neurotransmitter vesicles with the neuron's synaptic membrane
• C.botulinum: produces botulinum toxin, inhibiting the release of acetylcholine neurotransmitter containing vesicles in neuromuscular junctions, resulting in flaccid paralysis
• C.tetani: produces tetanospasmin, preventing the release of glycine and GABA neurotransmitters in the central inhibitory interneurons, resulting in spasmic paralysis

Dermonecrotic Toxin

• Affects cell-signaling pathways, increasing levels of inflammatory cytokines and proliferation of osteoclasts, and deficiency of osteoblasts, leading to distortion of nasal turbinate bones
• Bordetella bronchiseptica first attaches to nasal mucosa, causing nasal irritation and making the nasal turbinates susceptible to DMT, which mildly damages the epithelium
• Pasteurella multocida then attaches to damaged epithelium and secretes PMT, destroying the nasal turbinates

Mastitis

• Caused by Staphylococcus aureus, Bacillus licheniformis, and Bacillus subtilis in ruminants, and Staphylococcus aureus, Streptococcus agalactiae, Streptococcus uberis, Streptococcus dysgalactiae, Corynebacterium bovis, and Bacillus cereus (rarely) in bovines.
• Transmission occurs primarily from udder to udder during milking via contaminated milking machines or farmer's hands/other equipment, and also from the environment.
• Clinical signs include:
  • Subclinical: elevated somatic cell count in milk
  • Clinical: swollen, firm, warm, and tender udder, and visually changed milk
  • More severe and peracute: onset of hyperthermia, reduced eating, rapid heart rate, and depression

Exudative Epidermitis (Greasy Pig Disease)

• Caused by Staphylococcus hyicus, a natural commensal of pig's skin, nose, and ears.
• Disease occurs worldwide in piglets up to 3 months of age.
• Transmission occurs through skin contact or vertical transmission (from vaginal mucosa at or shortly after birth).
• Disease-causing strains produce exfoliative toxins, while commensals in healthy pigs do not.
• Clinical signs include:
  • Lethargy, depression, anorexia, and reddened skin
  • Lesions progress over time, with skin covered in sebum, serum, and sweat, giving a greasy feel
  • Microscopically: superficial and deep pyoderma with brownish exudate

Strangles

• Caused by Streptococcus equi equi in solipeds (horses).
• Highly contagious infection in nasopharynx and associated lymph nodes, leading to abscess formation.
• Clinical signs include:
  • Fever, nasal discharge, lassitude, difficult swallowing, mild cough, and swollen mandibular lymph nodes
  • Sometimes, abscesses also form in lungs, abdomen, and brain (metastases)
  • Most recover quickly and uneventfully, but sometimes the infection stays in the guttural pouch after clinical recovery, leading to empyema (pus collection in a natural cavity) and chondroids (pus "stones")

Neonatal Septicemia and Juvenile Streptococcosis

• Caused by Streptococcus canis in cats.
• Neonatal septicemia: transmission from vaginal secretion or mouth of queen to kitten, leading to local abscess, spread, and death within a week.
• Juvenile streptococcosis: infection in 2-4 month old kittens, with S. canis invading tonsils and cranial lymphatics, leading to purulent lymphadenitis.

Erysipelas

• Caused by Erysipelothrix rhusiopathiae.
• Ubiquitous in nature, affecting many species, but most common in swine.
• Found in tonsils and intestinal lymphoid tissues.
• Transmission occurs through:
  • Shedding in feces, contaminated food, water, and soil
  • Arthropod bites and wound infections
• 3m-3y old pigs are most susceptible.
• Forms of swine erysipelas include:
  • Septicemic (peracute/acute): high mortality, febrile and depressed pigs, abortions, skin lesions during septicemia or after recovery
  • "Diamond skin" (acute): febrile pigs with different skin lesions (small, light pink, purple, raised areas, many pink/purple diamond-shaped when severe)
  • Chronic arthritis: infection localizes in joint, leading to synovium thickening and joint deterioration for years
  • Vegetative endocarditis (chronic): masses most commonly on the mitral valves of the heart, often asymptomatic, sometimes with signs of congestive heart failure or sudden death

Listeriosis

• Caused by Listeria monocytogenes/ivanovii.
• Widely distributed in environment, mostly in soil and decaying plants, also in GI tract, feces, silage, sewage, and bodies of fresh water.
• Transmission occurs mainly through:
  • Contaminated feed, especially silage with pH > 5.5
  • Inhalation and mucous membrane wounds
• Forms of listeriosis include:
  • Septicemic or "visceral" (mainly in monogastric animals): affects organs other than the brain, especially liver, with small necrotic foci
  • Meningoencephalitis or "neural" (affects RU and sometimes SU): localized asymmetric infection of the brain stem, with clinical signs including depression, confusion, drooping ears, head tilt, salivation, tongue sticking out of the mouth, facial paralysis, food impaction, and circling movement
  • Abortions: L. monocytogenes invades fetoplacental tissue, leading to abortion usually during the 3rd trimester
  • Mastitis and lymphadenitis

Caseous Lymphadenitis

• Caused by Corynebacterium pseudotuberculosis (also Streptococcus canis in kittens).
• The genus is part of the CMNR group with a mycolic acid layer on the cell wall.
• Found on skin, nasopharynx mucous membranes, and intestinal tract.
• Transmission occurs through superficial wounds, spreading via the lymphatic system.
• Forms of caseous lymphadenitis include:
  • Granulomatous form: necrosis of superficial lymph nodes and subcutaneous tissue
  • Visceral form: lesions in internal organs and lymph nodes
  • Ulcerative lymphadenitis: in EQ, rare, ulcerative form: cellulitis that ascends the lymphatics, affected sites swell, abscesses rupture, and ulcers form
  • External form (pigeon fever/breast bone fever): single, large, thick-capsuled abscess under the abdomen or pectoral region

Bovine Pyelonephritis

• Caused by Corynebacterium renale and cystitidis + pilosum (less pathogenic - mild cystitis).
• Shed in urine, contaminating soil, and attaching to urogenital tract mucosa, producing urease that hydrolyzes urea, damaging the tract and kidneys, leading to hemorrhagic cystitis, urethritis, and pyelonephritis.
• Clinical signs include:
  • Fever, anorexia, arched back, frequent urination of small amounts (containing leukocytes, fibrin, and blood clots)

Foal Rhodococcosis

• Caused by Rhodococcus hoagii.
• Natural habitat is soil, coprophilic (grow in herbivore feces and foal LI).
• Transmission occurs through contaminated soil, inhalation of dust particles, and ingestion.
• Forms include:
  • Multifocal purulent bronchopneumonia with abscesses: most common form, symptoms seen in 4-12 weeks old foals
  • Ulcerative typhlocolitis and mesenteric lymphadenitis: in 50% of foals with rhodococcal pneumonia
  • Other less common manifestations: osteomyelitis, purulent arthritis, ulcerative lymphangitis, reactive arthritis, and ocular inflammatory processes

Rhodococcosis in Other Animals

• SU and BO: pyogranulomatous lesions in lymph nodes, often found at slaughter and confused with tuberculosis
• Goats: can have severe systemic form, with abscesses in lungs, liver, etc.

Anthrax

• Caused by Bacillus anthracis, an obligate pathogen.
• Spores are ubiquitous in soils, and the vegetative form is only found in hosts.
• Most commonly affects ungulate herbivores.
• Transmission occurs through:
  • Skin
  • Ingestion
  • Inhalation
• Forms of anthrax include:
  • Cutaneous: local growth, leading to localized edema, necrotic, black lesions, rare in animals, mostly in pigs
  • Intestinal: subclinical to fatal, gas build-up, mucosal edema, necrotic lesions, leading to regional hemorrhagic lymphadenitis, septicemia, toxemia, shock, and death
  • Pulmonary: most severe form, rapid spread to regional lymph nodes, leading to same as above, most common form in RU

Anthrax in RU

• Typical case: sudden and unanticipated death, minor anorexia and reduced milk yield are common, rapid rise of temperature (41.5C), staggering, dyspnea, trembling, and collapse with a few convulsive movements, and bleeding from orifices at death

Anthrax in EQ

• Clinical signs: fever, chills, severe colic, anorexia, depression, weakness, bloody diarrhea, ventral edema, death within 2-3 days

Anthrax in SU and CAR

• Acute form: oropharyngitis that can lead to suffocation
• Chronic form: anorexia, vomiting, diarrhea/sometimes constipation, getting better with treatment

Control and Prevention of Anthrax

• Safe disposal of all carcasses and infected animals - culling and burning
• Surveillance of in-contact animals
• Blood samples for bacteriological examination without opening carc

Botulism and Tetanus

• Botulism: caused by Clostridium botulinum, found in soils and lake/sea sediments, transmission through ingestion of spores or wound contamination, mostly affects RU and EQ.
• Clinical signs: progressive and symmetrical flaccid paralysis, limb weakness, breathing difficulties, recumbency, and death by respiratory arrest.
• Tetanus: caused by Clostridium tetani, ubiquitous in soil worldwide, transmission through wound contamination with spores from soil, feces, dust, etc., mostly affects EQ and OV.
• Clinical signs: hyperactivity of voluntary muscles, rigidity, tetanic spasms, and localized or systemic disease.

Gas Gangrene and Malignant Edema

• Caused by: Clostridium septicum, histotoxic infection, bacteria destroy and ingest host tissues, damage by enzymes and toxins.
• Transmission: contaminated wounds, ingestion of contaminated soil, and colonization of intestinal tract.
• Clinical signs: kill the animal, and environment is contaminated with spores, leading to spread.
• Braxy: abomasitis in sheep after eating frozen root crops/grass, especially during winter.
• Malignant edema: caused by introduction of the pathogen into a wound, produces alpha and beta toxins.

Blackleg

• Caused by: Clostridium chauvoei, histotoxic infection in BO, bacteria destroy and ingest host tissues, damage by enzymes and toxins.
• Transmission: ingestion of spores, colonization of intestinal tract, and spread to muscle tissues via blood/lymphatics.
• Clinical signs: remains dormant in muscle tissues.

Salmonellosis

• Caused by: different serotypes of Salmonella enterica subsp. Enterica, natural habitat in the intestinal tract of warm and cold-blooded animals.
• Transmission: fecal-oral, contaminated food and water, host-specific serotypes.
• Clinical signs: depression, fever, and death in 24-48 hours, neurologic signs in calves and pigs, mortality may reach 100%.
• Enteritis: without septicemia, same fever, severe watery diarrhea, sometimes dysentery, and tenesmus.

Buponic Plague (Black Death)

• Caused by: Yersinia pestis, facultative intracellular bacteria, primary reservoir in tolerant mice and rats.
• Transmission: mostly through the oriental rat flea, inhalation of droplets from infected animals, and rarely through raw meat.
• Clinical signs: regional lymphadenitis, fever, depression, anorexia, sneezing, coughing, and CNS disturbances in cats, mostly fatal.

Shipping Fever/BRDC

• Caused by: Pasteurella multocida and Mannheimia haemolytica, commensal of upper respiratory and GI tracts of mammals, birds, reptiles.
• Transmission: inhalation, bites, open wounds, contact with contaminated feces/carcasses.
• Clinical signs: fever, inappetence, listlessness, inconsistent respiratory signs, leading to pneumonia.

Atrophic Rhinitis

• Caused by: Bordetella bronchoseptica and Pasteurella multocida, chronic, synergetic infection of the nasal cavity.
• Affects: 3-7 month old pigs, clinical signs include sneezing, epistaxis, tear leakage, deviation of the nose, and secondary pneumonia.

Hemorrhagic Septicemia

• Caused by: Pasteurella multocida, acute, systemic infection in RU.
• Clinical signs: high fever, depression, subcutaneous edema, hypersalivation, diarrhea, and sudden death.

Other Diseases

• Glanders: caused by Burkholderia mallei, facultative intracellular bacteria, transmission through ingestion, aerosols, fomites, and skin lesions.
• Melioidosis: caused by Burkholderia pseudomallei, naturally found in soil and water, transmission through direct contact, inhalation, ingestion, and wound infections.
• Calf Diphtheria: caused by Fusobacterium necrophorum, obligate anaerobe, transmission through the mouth, GI, and urogenital tracts.
• Tuberculous Infections: caused by different Mycobacterium, transmission through aerosol inhalation, unpasteurized milk, and damaged skin barrier.
• Johne's Disease: caused by Mycobacterium avium paratuberculosis, obligate pathogen, transmission through fecal-oral route.
• Feline Leprosy: caused by Mycobacterium lepraemurium, skin nodules, ulceration, and lymph node involvement.
• Swine Dysentery: caused by Brachyspira hyodysenteriae, transmission through fecal-oral route, multiplications in the large intestine lead to disease.
• Lyme Disease: caused by Borrelia burgdorferi, transmission through Ixodes species ticks, clinical signs include high fever, lameness, swollen joints, and swollen lymph nodes.
• Leptospirosis: caused by different Leptospira serovars, widespread zoonotic disease, transmission through contact with urine/tissues from infected animals, contaminated water, and soil.

Mycoplasmal Diseases

• Mycoplasmas are ubiquitous parasites in animals and plants, causing chronic endemic diseases in many domestic mammals.
• They can be transmitted through various routes, including aerosols, milk, reproductive secretions, and eggs.
• Infections can lead to septicemia, multiple system diseases, and polyarthritis.

Specific Mycoplasma Species

• M. mycoides ssp. capri: causes septicemia in young goats, characterized by polyarthritis, pneumonia, and lesions in multiple organs.
• M. capricolum ssp. Capricolum: causes acute and severe, generalized infections in goats and sheep, leading to fatal septicemia or polyarthritis.
• M. hyorhinis: colonizes the upper respiratory tract of pigs, causing pleuritis, pericarditis, peritonitis, and polyarthritis.
• M. bovis: causes pneumonia, followed by arthritis and polyarthritis.
• M. agalactiae: causes mastitis in goats and sheep, leading to septicemia or polyarthritis.

Hemotrophic Infections

• Mycoplasmas are epicellular parasites of red blood cells, causing hemolytic anemia.
• M. haemofelis: infects cats, causing hemolytic anemia.
• M. ovis: infects lambs, causing hemolytic anemia.
• M. suis: infects pigs, causing hemolytic anemia.

Localized Infections

• Respiratory tract infections: cause bronchitis, bronchiolitis, and pneumonia in various animals, including calves, lambs, pigs, dogs, mice, and rats.
• Pleuropneumonia: caused by M. mycoides ssp. Mycoides, resulting in mortality rates of up to 50%.
• Conjunctivitis: caused by various mycoplasma species, including M. gallisepticum, M. bovoculi, and M. felis.
• Mastitis: caused by M. bovis and other species, leading to swollen udders, reduced milk production, and fibrin deposits.

E. coli Infections

• Diarrheagenic strains: cause diarrhea in various animals, including pigs, calves, lambs, and poultry.
• Enteric colibacillosis: causes severe, watery diarrhea, often leading to mortality.
• EPEC: causes diarrhea in all animals, including humans, characterized by attaching and effacing lesions.
• STEC: causes diarrhea, often with bloody stools, and can lead to hemolytic uremic syndrome (HUS) in humans.
• ExPEC: causes a range of extraintestinal infections, including septicemia, meningitis, and urinary tract infections.

Other Pathogens

• Streptococcus equi zooepidemicus: causes mucosal commensal infections in various animals, including horses, cattle, and humans.
• Streptococcus canis: causes infections in dogs, cats, and other animals, including otitis externa, pneumonia, and endocarditis.
• Streptococcus suis: causes septicemia, meningitis, and endocarditis in pigs, and can be transmitted to humans.
• Enterococcus spp.: causes infections in various animals, including otitis externa, urinary tract infections, and bacterial endocarditis.
• Trueperella pyogenes: causes pyogenic infections in various animals, including mastitis, arthritis, and pneumonia.
• Klebsiella pneumoniae: causes opportunistic infections in various animals, including pneumonia, suppurative conditions, and urinary tract infections.
• Yersinia pseudotuberculosis: causes mesenteric lymphadenitis, terminal ileitis, and acute gastroenteritis in various animals, including birds and rodents.
• Yersinia enterocolitica: causes infections in domestic animals and primates, including diarrhea, mastitis, and abortion.
• Yersinia ruckeri: causes enteric red mouth disease in freshwater fish, particularly rainbow trout.
• Campylobacter spp.: causes reproductive and intestinal diseases in various animals, including abortions, diarrhea, and asymptomatic infections.

Chlamydia

• Obligate intracellular parasites: no environmental reservoir.
• Gram negative: no peptidoglycan layer.
• Worldwide distribution: asymptomatic and persistent infections in the GI tract.
• Transmission: mainly fecal-oral, also droplet inhalation and interpersonal contact.
• Biphasic development: elementary bodies and reticulate bodies.

Specific Chlamydia Species

• Chlamydia abortus: causes ovine enzootic abortions globally.
• Chlamydia psittaci: causes avian chlamydiosis in over 500 species, especially pigeons and parrots.
• Chlamydia felis: causes acute to chronic conjunctivitis, rhinitis, and respiratory disease in cats.

Coxiella burnettii

• Gram negative, obligate intracellular pathogen: causes coxiellosis (Q fever) worldwide.
• Biphasic development: replicative large-cell variant and metabolically dormant, spore-like small cell variant.
• Transmission: aerosols, ingestion, or tick bites.

Rickettsiales

• Gram negative, obligate intracellular bacteria: worldwide distribution.
• Infections in livestock and companion animals: include genus Anaplasma, Ehrlichia, and Rickettsia.

Lawsonia intracellularis

• Gram negative, obligately intracellular bacterium: causes proliferative enteropathy.
• Found in the apical cytoplasm of infected enterocytes: wide host range, including pigs, sheep, dogs, birds, and marsupials.
• Transmission: feces or direct contact with infected pig.
• Two major clinical forms in pigs: acute hemorrhagic diarrhea and chronic mild diarrhea and reduced performance.