Gpos
Gram Positive Bacteria AGR 329
Gram Positive Cocci
Key Points:
Comparison of Staphylococcus vs Streptococcus
Use of Sheep Blood Agar for hemolysis testing
Gram Positive Cocci Staphylococcus species
Macroscopic Appearance
On Sheep Blood Agar (SBA):
Appearance: white/cream, smooth, butter-like, round
Microscopic Appearance
Gram Stain: cocci in grape-like clusters
Metabolic Properties
Oxygen Respiration: facultative anaerobe
Catalase: positive
Oxidase: negative
Hemolysis: varies on species
Motility: non-mobile
Clinical Importance
Zoonotic: MRSA (Methicillin Resistant Staphylococcus aureus)
Common Commensal: skin and mucous membranes
Diseases:
Pyogenic/Suppurative infections (pus-forming) in various species
Specific conditions in dogs/cats: conjunctivitis, ear infections, skin infections, uterine infections, bladder infections
Mastitis in ruminants and horses, trauma-induced abscesses in horses
Bumblefoot in poultry
Gram Positive Cocci Staphylococcus aureus
Characteristics
Associated with MRSA and antibiotic resistance (oxacillin, penicillin, amoxicillin)
Diseases Associated
Botryomycosis: chronic granulomatous lesions in various animals
Scirrhous Cord: enlargement of spermatic cord in castrated horses
Bumblefoot: in poultry
Omphalitis: bacterial infection in feet of poultry and guinea pigs
Symptoms: suppurative wounds, septicemia, pyogenic urinary tract infections (UTI), pyoderma in dogs/horses, lameness and bacteremia in lambs
Gram Positive Cocci Staphylococcus hyicus
Commonly infects swine
Clinical Disease: exudative epidermitis (greasy pig disease)
Symptoms: sebaceous secretions, anorexia, depression, arthritis
Gram Positive Cocci Staphylococcus pseudintermedius
Found in dogs and cats
Infections: pyoderma, endometritis, cystitis, otitis externa
Staphylococcus -> Micrococcus
Nine species, biochemically different
Aerobic: oxidase positive, catalase positive
Staphylococci resistant to bacitracin, while Micrococcus is not
Gram Positive Cocci Streptococcus sp.
Macroscopic Appearance
Appearance: mucoid, round, smooth
Microscopic Appearance
Gram Stain: medium cocci in chains, can also appear as singles or pairs
Metabolic Properties
Oxygen Respiration: facultative anaerobe/aerobic
Catalase: negative
Oxidase: negative
Hemolysis: differentiates Streptococcus species
Beta: pathogenic
Tests: CAMP test for recognizing Staphylococcus agalactiae
Groups of Strep:
Streptococcus
Enterococcus
Peptoniphilus (mostly anaerobic, not commonly seen)
Gram Positive Cocci Streptococcus species
Streptococcus pyogenes: human strep throat
Streptococcus agalactiae: bovine contagious mastitis
Streptococcus equi: equine strangles
Streptococcus zooepidemicus: genital infections in horses, mastitis in cattle, septicemia in swine
Streptococcus bovis: lactic acidosis in ruminants
Streptococcus suis: meningitis, septicemia, pneumonia, arthritis in swine
Streptococcus porcinus: causes jowl abscess/cervical lymphadenitis in swine
Streptococcus pneumoniae: pneumonia in cavies and humans
Gram Positive Cocci Enterococcus faecalis
Naturally found in GI tract of humans and animals, causing UTIs
Appearance: cocci in pairs, chains, facultative anaerobe
Pathogenicity: pathogenic in urinary or wound infections, resistant to antibiotics
Review Questions
Differentiating Staphylococcus vs Streptococcus: Catalase test
Staphylococcus under microscope: grape-like clusters
Streptococcus under microscope: chains
Gram Positive Rods
Gram Positive Rods Actinomyces
Macroscopic Appearance
Gram Stain: branching rods resembling fungi
Metabolic Properties
Oxygen: microaerophilic/anaerobic
Catalase: negative
Oxidase: negative
Hemolysis: gamma
Motility: non-motile
Normal Flora: opportunistic pathogens
Clinical Relevance
Species Examples:
Actinomyces viscosus & Actinomyces hordevulneris: associated with puncture wounds in dogs
Actinomyces suis: causes mastitis, cystitis, pyelonephritis in sows
Actinomyces bovis: causes lumpy jaw in cattle due to wounds in the oral mucosa
Gram Positive Rods Bacillus
Macroscopic Appearance
Gram Stain: large rods in chains or pairs, with a medusa head appearance
Metabolic Properties
Oxygen: facultative anaerobe/aerobe
Catalase: positive
Oxidase: positive
Hemolysis: beta or gamma
Motility: motile
Spore forming: capable of endospore formation
Clinical Relevance
Bacillus anthracis: bioterrorism agent associated with anthrax
Transmission: inhalation, ingestion, wounds, direct contact
Symptoms: respiratory failure, septicemia, often fatal
Recommendations: cremation or deep lime burial; necropsy should not be performed (no rigor mortis)
Bacillus cereus: foodborne illness in humans, gangrenous bovine mastitis, abortion in cows and ewes
Gram Positive Rods Listeria monocytogenes
Macroscopic Appearance
Gram Stain: short chains, medium clear/white, round
Metabolic Properties
Oxygen: facultative anaerobe
Catalase: positive
Oxidase: negative
Hemolysis: beta
Motility: motile at 20 °C
Clinical Relevance
Causes Listeriosis: meningitis, encephalitis, uterine infections, abortions, stillbirths
Sources: soil, feces, food
Two Forms:
Neural: circling disease in ruminants
Visceral: affects monogastric species with sepsis
Gram Positive Rods Corynebacterium
Macroscopic Appearance
Gram Stain: small pleomorphic rods/club-shaped
Metabolic Properties
Oxygen: facultative anaerobe/aerobe
Catalase: positive
Oxidase: negative
Hemolysis: weak beta
Motility: non-motile
Clinical Relevance
Species Examples:
Corynebacterium diptheriae: human diphtheria
Corynebacterium renale: opportunistic in the lower urinary tract
Corynebacterium pseudotuberculosis: causes caseous lymphadenitis in small ruminants, often seen in distinct palisades under the microscope
Gram Positive Rods Dermatophilus congolensis
Macroscopic Appearance
Gram Stain: branching filamentous rods resembling train tracks
Metabolic Properties
Oxygen: aerobe
Catalase: positive
Oxidase: negative
Hemolysis: beta
Motility: through zoospores
Clinical Relevance
Diseases: Lumpy Wool or Strawberry Foot Rot in sheep, often spreading in rain and wet conditions
Gram Positive Rods Erysipelothrix rhusiopathiae
Macroscopic Appearance
Gram Stain: small short rods, gray/white
Metabolic Properties
Oxygen: facultative anaerobe
Catalase: negative
Oxidase: negative
Hemolysis: alpha
Motility: non-motile
Clinical Relevance
Causes Erysipelas, affecting swine, turkeys, and humans, characterized by skin lesions, fever, and joint issues
Review Questions
Identify causative agents for specific conditions (e.g., lumpy jaw, anthrax, listeriosis, etc.)
Acid Fast Rods
Definition
Acid Fastness: Bacteria resistant to decolorization by acids during staining
Examples
Bacillus: Rhodococcus equi, Mycobacterium sp., Nocardia sp.
Acid Fast – Gram Positive Rhodococcus equi
Macroscopic Appearance
Microscopic: coccobacillus, mucoid colonies with gray/white coloration
Metabolic Properties
Oxygen: aerobic
Catalase: positive
Oxidase: negative
Hemolysis: gamma
Motility: non-motile
Clinical Relevance
Causes Foal Pneumonia: transmitted via manure and nasal discharge; at risk foals under 6 months
Acid Fast – Gram Positive Mycobacterium sp.
Macroscopic Appearance
Gram Stain: medium rods, small yellow/cream round colonies
Metabolic Properties
Oxygen: aerobic
Catalase: positive
Oxidase: negative
Hemolysis: varies by species
Motility: non-motile
Clinical Relevance
Causes granulomas; notable zoonotic species include Mycobacterium tuberculosis (TB), Mycobacterium bovis (bovine TB), and Mycobacterium leprae (leprosy)
Acid Fast – Gram Positive Nocardia asteroides
Macroscopic Appearance
Gram Stain: branching rods, pleomorphic, small yellow colonies
Metabolic Properties
Oxygen: aerobic
Catalase: positive
Oxidase: positive
Hemolysis: gamma
Clinical Relevance
Infects dogs, cattle, swine, sheep; known for causing lesions in thoracic cavity and skin
Review Questions
Identify causative agents for various bacterial infections (e.g., foal pneumonia, tuberculosis, Johne's disease, leprosy).