Strep and Staph Flashcards
What are the characteristics of streptococci
- gram (+)
- cocci
- ~<2um
- Singly/pairs/chains
- Faculative anaerobe
- Fastidious
- Commensal in upper resp and low urogenital
Define fastidious
- Fastidious: require additional blood or serum to grow
What are 2 ways to classify streptococci
- Groups
o Hemolysis – alpha, beta, gamma
Beta hemolytic = most pathogenic
o Lancefield group – A, B, C, D
What is the primary pathogenic mechanism of strep? 2 examples
- Pyogenic = abscess and suppuration
- S. suis and pneumoniae
Define Abscess
- Abscess: pus (dead leukocytes and living/dead bacteria) surrounded by intact phagocytes and fibrin
Explain the levels of hemolysis
Hemolysis
* Alpha: incomplete lysis of RBC and oxidation of iron = greenish
o Commensal/opportunistic
* Beta: complete lysis: clear zone of inhibition
o Pathogenic
* Gamma: no ability to lyse RBC
o Non-pathogenic
List 6 virulence factors that strep has. What is their function
- exotoxins: superantigen
- Capsular polysaccharide – prevent phagocytosis
- Hemolysis – cytotoxic
- CAMP – pore forming
- M-protein – antiphagocytic
- Streptokinase – evade host immune system
List the common pathogens causing bovine mastitis
- Common pathogens:
o Strep agalactiae, Staph aureus (contagious)
o Strep dysgalactiae, uberis (environmental or contagious)
o Klebsiella/E. coli (environmental pathogens)
Cause severe mastitis
How to diagnose bovine mastitis
- Use California mastitis test
o Healthy: <200,000 cell/ml
o Allowable: <400,000 cell/ml (in USA <750,000 cell/ml)
What are the clinical signs of bovine mastitis
- Clinically: can be subclinical
o Swelling/heat/red/fever/anorexia/shock - Can cause atrophy of the alveolus
What are the features of Strep. Agalactiae
Strep. Agalactiae: mastitis
* Lancefield group B
* Obligate pathogen of mammary glands in cow
* Commensal in human GI (but it is a different strain than in cows)
* Contagious: direct spread (milking machine)
What is the pathogenesis of Strep. Agalactiae causing mastitis
- Contagious: direct spread (milking machine)
o Milk back flow due to improper use (not complete seal) or teat damage
o Keratin plug expelled in milking so backflow or damage can allow entry
o Bacterial invasion
o Bacteria adhere via pillus
o Colonize teat cistern and ducts – causing inflammation > fibrosis
o Without treatment it can persist in udder
What type of bovine mastitis does Strep. Agalactiae cause
- Causes subclinical mastitis (high SCC/reduced production)
- Can eradicate from herd = low prevalence in CA
What are the virulence factors associated with Strep. Agalactiae and bovine mastitis
- Virulence: type 3 capsular polysaccharide preventing C3 opsonization (avoid phagocytosis) = most important virulence factor
o Toxins: sphingomyelinase/neuramindase/hemolysin/lipoteichoic acid
What are the features of Strep. Uberis and what kind of bovine mastitis does it cause
- Commensal in tonsil and intestine
- Environmental pathogen (enter teat canal and colonize mammary mucosa)
- Clinical mastitis: severity depends on strain and dose
o Migrate to LN
What are the virulence factors associated with Strep. uberis and bovine mastitis
- Virulence: type 3 capsular polysaccharide preventing C3 opsonization (avoid phagocytosis) = most important virulence factor
o Toxins: sphingomyelinase/neuramindase/hemolysin/lipoteichoic acid
What are the subspecies of Strep. dysgalactiae
- Subspecies: dysgalactiae
- Subspecies: equisimilis
What are the features of Strep. dysgalactiae dysgalactiae? What kind of bovine mastitis does it cause
o Lancefield group C
o Alpha hemolytic
o Mastitis in cows
o Contagious and environmental
o Acute and clinical mastitis
o Sporadic in herds
o Associated with teat injury
What are the virulence factors of Strep. dysgalactiae dysgalactiae?
o Virulence factors
Hyaluronidase – spreading factor
M-like protein/fibrinolysin – colonization
Lipoteichoic acid
capsule
What are the features of Strep. dysgalactiae equisimilis ? What kind of disease does it cause
o Lancefield group A, C, G, or L
o Beta hemolytic
o Disease in many species
o Clinically:
Puppy and kitten pneumonia
Horse: metritis and placentitis
Piglet: septicemia/arthritis/meningitis/endocarditis
o Not zoonotic – species specific strain
What are the virulence factors of Strep. dysgalactiae equisimilis ?
o Virulence: streptokinase (convert plasminogen to plasmin = break fibrin)
Prevent walling off of bacteria
What is the pathogenesis of Strep. dysgalactiae equisimilis in pigs
o Pigs: commensal in tonsil and repro – shed in nasal cavity/mammary gland/vaginal and preputial secretions
Common to infect piglet during birth = bacteremia/septicemia
What are the features of Strep suis? What species? What bacterial type?
- Lancefield group D
- Pigs: spread in resp secretions
o Common in weaners and growing pigs - Many serotypes = many pathogenicity
o Serotype 2 most pathogenic - Zoonotic
What are the virulence factors of Strep suis?
- Virulence: capsular polysaccharide (block opsonization) + suilysin (cytotoxic exotoxin = create hole in target cell membrane)
What are the gross lesions of Strep suis in pigs and humans? how do humans get it?
- Gross:
o Swollen hock
o Lung petechiae
o Polyserositis - In humans: sepsis/meningitis/hearing loss/renal failure/endocarditis/pneumonia
o Via eating contaminated/raw pork, pork blood oral or skin infections
What are the features of Strep. Equi subsp. Equi? What does it cause? What are the clinical signs
- Lancefield group C – beta hemolytic
- Obligate pathogen
- Clinically: strangles (high morbidity/low mortality)
o Clinical signs within 3-11d
Fever > lymphoid abscess
Can cause dyspnea or guttural pouch empyema/chondroids (dry pus) - Very contagious
- Mainly only horses
- Can survive in environment: water trough reservoir (live up to 6wks)
What is the pathogenesis of Strep. Equi subsp. Equi?
o Inhale/ingest from acutely infected or carrier horse
o Strep equi M-proteins. = adhesions that attach to lingual tonsils
o access LN (sublingual and retropharyngeal)
o proliferate in LN
o enlarge LN
What is the virulence factors of Strep. Equi subsp. Equi?
o Hyaluronic acid capsule – prevent phagocytosis
o Iron acquisition – equibactin / heme binding system
o Streptolysin S – cytotoxic exotoxin
o Streptokinase- invasion
o IgG endopeptidase – interfere with Ig binding
o M protein – antiphagocytic
o SeeI/SeeL/SeeM (+/-SeeM) = superantigen (pyrogenic mitogens)
Stimulate overzealous immune reaction – draw a large number of neutrophils
What are 4 complications of strangles
o Guttural pouch disease
o Persistent carriers
o Metastatic abscessation: bastard strangles
o Purpura hemorrhagic
Explain persistence carriers of strangles
o Persistent carriers
Rupture of retropharyngeal LN into guttural pouch = guttural pouch empyema = chondroid formation = aspiration pneumonia
Can be clinically normal and shed
Require culture or PCR
Can be carriers for years if chondroids present
Explain metastatic abscessation of strangles
o Metastatic abscessation: bastard strangles
Colonize any other organ
Clinically: depend on where they colonize
* Abdomen – peritonitis/colic
* Brain – neuro
2-20% cases
Explain Purpura hemorrhagic of strangles
o Purpura hemorrhagic
Type 3 HS: immune mediated vasculitis
Rarely after vaccination for strangles or exposed to disease
Petechiae or ecchymosis hemorrhage on skin/mucosa/kidney
What are the features of Strep. Equi subsp. zooeepidemicus? What species does it affect? What does it cause?
- Commensal
- Opportunistic
- Zoonotic
- Horse: joint infection/lymphadentitis/pneumonia/metrtritis/mastitis
- Pig: septicemia
What are the virulence factor of Strep. Equi subsp. zooeepidemicus?
- Virulence factors: protase
o No M protein/variable capsule/less superantigen
What are the features of Strep. canis? What species does it affect? What does it cause?
- Lancefield group G
- Beta hemolytic
- Colonize mucus membranes
- Opportunistic
- Cause skin infection/LN abscess/metritis/kitten septicemia
What are the characterisitics of staphylococci
- Gram (+) cocci
- 0.8-1um
- Single/pair/tetrad/irregular or grape clusters
- Facultative anaerobes
- Main organism of microflora = opportunistic
List 3 main staphylococci infections. List the species and main clinical manifestation for each
- 3 main:
o S. aureus
Rabbit: pododermatitis
Chicken: pododermatitis
Cow: mastitis
o S. pseudointermedius
Dog: pyoderma
o S. hyicus
Pig: exudative epidermitis
What is the pathogenesis of staphylococci infections
- Pyogenic = suppurative lesion
- More virulent strains = invasive causing bacteremia/hematogenous spread
- Require predisposing factors for infection
List the virulence factors of staphylococci infections
- Coagulase = most important
- Enterotoxins
- Clumping factor
- catalase
- Exfoliatins – skin damage
- Hemolysins – lyse RBC
- Toxic shock – inflammation
How does coagulase act as a virulence factors? Provide examples
- Coagulase = most important
o Associated with virulence/pathogenicity
o Adherence to prothromobin – transforms fibrinogen to fibrriin
o Coag (+) = S. aureus/pseudointermedius
o Coag (-) = opportunisitic
o S. hyicus has variable coagulase
How does hemolysins act as a virulence factors?
- Hemolysins – lyse RBC
o Alpha toxin: pore forming
o Beta toxin: sphingomyelinase = damage cell membrane
o Gamma toxin = pore forming
o Delta toxin = cytolytic (promote pro-inflam cytokines)
How does Toxic shock act as a virulence factors?
- Toxic shock – inflammation
o Emesis – due to mast cell degranulation
o Infectious disease – due to superantigens
What does S. aureus cause in cattle
- Chronic/subclinical infection
- Contagious
- Colonize mammary epithelium due to teat injury
- Gangrenous/necrotizing mastitis
- Can also cause metritis/abscess/pneumonia/umbilical infection
What does S. aureus cause in poutlry
- Poultry
o Commensal on skin and mucous membranes
o Septicemia in joints/tendon sheaths
o Clinical: arthritis/synovitis/chondronecrosis/osteomyelitis
Gangrenous dermatitis
Omphalitis
Lameness/fever
Pododermatitis – abscesses covered by scab
What does S. aureus cause in horse
- Horse
o Neonatal septicemia
o Secondary: wound/surgical site infection/tenosynovitis/septic arthritis
What does S. hyicus cause? What are the manifestations
- Pig
- Commensal
- Exudative epidermitis: greasy pig disease
o Acute to chronic
o Young pig – generalized dermatitis with sebaceous secretion/exudate/exfoliation
o Death if lots of exudation and dehydration
What is the pathogenesis of S. hyicus in pigs?
- Pathogenesis: damage skin = exfoliative toxin = epidermal necrolysis
- Typically you see pigs up to 7 weeks with brown/black scab on shoulder/neck – spread
- Transmit: contact with older pigs
What are the virulence factors of S. hyicus in pigs?
- Virulence
o Exotoxin
o Adhesion
o Capsular polysaccharide/protein A
What does S. psuedointermedius cause? What are the manifestations
- Dog
- Skin and ear infection
- Opportunistic – predisposing factors
- Clinically: pyoderma
o UTI/surgical site infection/orthopedic implants/discospondylitis
What is a relevant AMR mechanism for staph
Antibiotic Resistance: Methicillin (MRSA/MRSP)
* Common in: surgical site infection/pyoderma/otitis/UTI
* Due to mecA gene = general beta lactam resistance
* Transmissible between pets and humans
What type of sample should you take
Specimens
* Depend on pathological condition
o Exudate/aspirate/pus/milk/skin scraping/CSF/urine/tissue
How do you isolate and identify the pathogen
- Isolate and ID
o Direct microscopy (diffQuik/gram)
o Culture
Blood agar
o PCR – Strep equi - Abx susceptibility testing
