5.1 Gram + cocci Flashcards
3 major genera of gram + cocci, and their results on the catalase test:
Staphylococcus - positive
Streptococcus - negative
Enterococcus - negative
what is the catalase test? what does it tell us?
Catalase: an enzyme breaking down hydrogen peroxide (H2O2) into water (H2O) and oxygen (O2).
It is a virulence factor for some pathogens (helps resist the oxidative burst in phagocytes)
staphylococcus characteristics. morphology of populations? where are they found? do they survive in environment? are they commonly pathogenic? host specificity? what kind of infections do they cause?
- Grape-like clusters (in vivo→in clinical samples, not in cultures)
- Commensals of skin and exposed mucosae of animals and humans
- Survive well in environment
- Numerous species, but most are non-pathogenic
- Some host-specificity (but not as strong as for streptococci)
- Opportunist pathogens
- Typically cause purulent infections
3 important staphylococcus spp. in animals, and the species they infect commonly
S. aureus: Human, numerous animal species
S. pseudintermedius, SIG: Dogs, cats (others, humans from animals)
S. hyicus: Pigs
What are opportunistic pathogens?
Normally commensal in the body but can cause disease when the host’s resistance is altered.
diseases caused by staphylococcus aureus
Causes several diseases:
* Pus and local necrosis
* Localized infections (abscess)
* Tendency to bacteremia (blood)
* Skin and wound infections
* Urinary tract infections (humans, dogs, cats)
* Bovine mastitis (other animal species)
* Bumblefoot in chickens (foot abscess)
* “contagious”, cause of hospital-acquired infections
* Methicillin-resistant S. aureus (MRSA)
what is MRSA? how do its properties arise, genetically/mechanistically?
methicillin-resistant staphylococcus aureus
>cause of staph infections that is difficult to treat due to resistance to some antibiotics
> Resistant to all β-lactams because of the presence of mecA, a gene that produces a penicillin binding protein (PBP2a) with low affinity for β-lactam antibiotics
What species can be infected by/transmit MRSA?
cats, pigs, dogs, horses, humans…
what type of animals does staphylococcis pseudointermedius commonly infect? what tyope of pathogen is it?
- Opportunist pathogen of dogs and cats
what issues can staphylococcus pseudointermedius cause in dogs?
-UTI
-reproductive tract infections
-resp tract infections
-otitis externa
-canine pyoderma
what is MRSP? what species is it a problem in?
- Methicillin-resistant S. pseudintermedius = MRSP
- Relatively recent emergence of MRSP
- A more important problem in dogs than MRSA
>otitis externa, pyoderma - Often multiresistant
what is Staphylococcus hyicus? what species/animals does it commonly infect and what disease does it cause? Symptoms?
Exudative epidermitis: “Greasy pig disease”
- Under 7 weeks old
- Reddening of the skin, erosions at the coronary band, anorexia
- Systemic involvement and it can be fatal
- Death in 3-5 days in acute disease
- Reddened areas of skin turn into brown spots, producing serum exudates
Staphylococcus spp.: laboratory diagnosis strategies
- Smear and Gram stain of clinical material
- Culture and identification (1 day)
- Antimicrobial susceptibility testing (1 day)
- Molecular methods: mecA for MRSA and MRSP
Staphylococcus spp.: treatment and prevention
- Treatment with antimicrobials and elimination of primary cause (opportunistic pathogen!)
- Mastitis: prevention by detection of subclinical infections, hygiene, milking equipment, treatment with antimicrobials
- Frequent antimicrobial resistance ➔ Susceptibility testing
- No vaccine available
streptococcus spp. general characteristics: morphology of colonies, habitat, envrionmental survival, infection types caused, host specificity?
- Chains of cocci
- Commensals of mucous membranes of animals and humans (usually not skin)
- Does not survive well in environment
- Relatively “fastidious”
- Pyogenic infections+++
- Strong host-specificity
Virulence factors of streptococci
- Capsule (antiphagocytic)
- Antiphagocytic surface proteins (M-proteins)
- Toxins (β-haemolysin)
- Superantigens (Strep toxic shock toxins, cytokine storm)
virulence factors of staphylococci
Variable virulence factors arsenal, depending on strain.
eg. Hemolysins, Leucocidins, Enterotoxins, etc.
- Fibronectin-binding proteins: Adhesin, colonization of wound
- DNAse, lipase, elastase, hyaluronidase: Host tissue penetration
- Hemolysins: Damage cell membranes, necrosis
- Leucocidins: Cytolysis of leucocytes
- Enterotoxins: Diarrhea
- Toxic shock syndrome toxin: Superantigen, shock
- Coagulase: Fibrin protects from phagocytosis
- Biofilm: Shielding from host defenses and antibiotics
Some important Streptococcus spp.
S. equi subsp. zooepidemicus
S. equi subsp. equi
S. suis
S. canis
S. agalactiae
S. equi subsp. zooepidemicus: what type of pathogen is it? what species does it infect? what type of infections?
- Important opportunist pathogen of horses (and
other species) - “The” cause of purulent infections in horses
- Diverse infections: Upper respiratory tract infections, “mild strangles”, pneumonia, abscesses, wounds, urogenital tract, mastitis, etc
- Foal septicemia and its sequelae (if no colostrum)
- Zoonosis (uncommon in humans)
what type of disease does S equi subsp. equi cause? how is it transmitted?
streptococcus equi subsp. equi
>strangles in horses, commonly infect upper airway and lymph nodes of the head and neck
- Highly contagious, severe pharyngitis and associated
lymphadenitis of lymph nodes of head and neck - Transmitted by discharges of disease and infected guttural pouch carriers
how can we treat/prevent S. equi subsp. equi infections?
- Treatment/prevention: Isolation and quarantine (until 3 negative PCR results), cleaning and disinfection, early treatment with penicillin (before abscesses)
- Vaccines available, none perfect. Long-lasting but not always complete immunity after infection
what are the properties of S. canis infection? what species? what symptoms?
– Opportunistic purulent infections (dog, cat)
– Minor pathogen, variety of infections: urogenital infections, mastitis, wound infections, otitis externa
– Toxic shock syndrome and necrotizing fasciitis
what disease is caused by S. agalactiae?
highly contagious, subclinical mastitis (cows)
what disease is caused by S. suis? what species?
-septicemia and meningitis/encephalitis (death)
-is zoonotic
-commonly in pigs
Streptococcus spp.: laboratory diagnosis strategies
- Smear and Gram stain of clinical material
- Culture and identification
- Antimicrobial susceptibility testing ? Usually not necessary
-can look for Hemolysis (β-hemolysis and pyogenic species)
Streptococcus spp.: treatment and prevention
- Neonatal septicemia: foals require colostrum!
- Treatment of cuts, wounds, predispositions
- Antimicrobial treatment: Penicillin G for pyogenic streptococci. Resistance to penicillin still rare (in animals, but different in humans)
- Mastitis: hygiene, antimicrobial treatment
- Vaccination:
– Strangles (i.m., intranasal, lip)
– S. suis: not yet available
enterococci characteristics: type of bacteria, habitat, type of pathogen, infections caused…
- Gram positive cocci
- Normal intestinal flora
- Numerous species (major: E.faecalis, E.faecium)
- Low grade pathogens, true opportunists (predisposing factors +++)
- Diverse types of infections
- Mastitis, wound infections, UTI, secondary infection; Nosocomial +++++
enterococci antibiotic resistance profile and consequences
- Naturally resistant to many antimicrobial agents, especially E. faecium
- Frequent acquired resistance
- Major problem in human hospitals and some veterinary hospitals
- “Vancomycin Resistant Enterococci”: Superbugs; part of the ESKAPE group of hospital-acquired infections
