Gram Positive Cocci Flashcards
Catalase Positive Genera
- Micrococcus and related genera
- Staphylococcus
- Rothia (Stomatococcus) mucilaginosus
Staphylococcus genera are primary clinical significance
Micrococcus, Rothia, and related Genera Characteristics
Morph, habitat, transmission, clinical
G+ cocci in tetrads
Grow on routine media
Colonies may be pigmented
Habitat: skin, mucosa, oropharynx
Transmission: endogenous
Clinical significance: rarely complicated, low virulence
Staphylococcus General Characteristics
Morph, atmosphere, habitat, transmission, clinical
G+ cocci in clusters
Grow on routine media
Type: facultative anaerobe
Habitat: nares, axillae, vagina, pharynx, skin surfaces
Transmission: spread of endogenous flora, person to person
Clinical significance: virulence factors, species variation
S. Epidermidis
Predisposing factors? virulence?
Most frequently encountered staph. - moist body surfaces
Predisposing factors: catheters, medical implants, prosthetics, immune status
Major virulence factor: biofilm
Other: a lot are healthcare-acquired, bloodstream, endocarditis
Biofilm
What problems?
- Biofilm cells are more resistant to antibiotics
- More resilient to phagocytosis than free floating bacteria
- Many diseases associated with biofilms
Catheter Associated Infection
- Microbe moves from catheter skin entry side to catheter tip within bloodstream
- Inside the catheter hub into the body
- Hematogenous spread
Staphylococcus lugdunensis
Where, problems, virulence, special test?
- Lower body, axillae
- Community and healthcare infections
- Skin, soft tissue
- Endocarditis, bacteremia, prosthetic devices
Major virulence factor: biofilm
Extracellular clumping factor positive
Staphylococcus saprophyticus
Where, clinical, virulence
GI tract - age season dependent
- UTIs in young, sexually active women
Major virulence factor: adhere to epithelial cells in urogenital tract
Staphylococcus hominis, Staphylococcus haemolyticus
where,what is special about this? Virulence?
Colonize axillae and pubic areas
S. haemolyticus second most common coag- associated with infections: most virulent coag- staphs
Major virulence factor: biofilm or adhesion
Staphylococcus capitis
Where, virulence
Colonize scalp, forehead after puberty
Major virulence factor: biofilm or adhesion
Staphylococcus aureus General
The apex! Raaagh
Most significant staph species
- Mild to life-threatening infections
- Can be on almost any specimen
- Healthcare associated infection
- Increasing antimicrobial resistance problem
S. aureus: Virulence Factors
- Structural components
- Exotoxins
- Enzymes
- Biofilm
S. aureus: Structural Components
Virulence factors, 4 things
Capsule: slime layer, resists chemotaxis, phagocytosis, and facilitates adherence to other bodies
Peptidoglycan: resists phagocytosis
Teichoic acid/lipoteichoic acid: binds to fibronectin, ahesion to human cells
Protein A: binds IgG, inhibits antibody mediated clearance
S. aureus: Exotoxins
Virulence factor, 4 of them
Enterotoxins: superantigens that stimulate T cells and release cytokines, heat stable, involved in food poisoning
- interfere with adaptive immune system, not processed by antigen presenting cell, activates T cell directly, cytokine storm = fever and shock
- Cytolytic toxins: lyses different human cells (RBCS, WBCs, tissue damage)
- Exfoliative toxins: epidermolytic, epidermal cells slough off
- Toxic shock syndrome toxin: superantigen, penetrate mucosal barriers, systemic effects
S. aureus: Enzymes
Hyaluronidase: digest hyaluronic acids in host tissue, spreads microbes
Staphylokinase (fibrinolysin): dissolves fibrin clots, spreads microbes
Lipases: hydrolyzes lipids, microbe can survive in sebaceous areas, spread more
S. aureus Infection: Impetigo
- Intraepidermal vesicles with exudate, leaking and crusting lesion
- Common in children
- Moist areas, warm, highly contagious
- Clears on its own or with antibiotics
S. aureus Infection: Folliculitis
- Inflammation/infection of hair follicles
- Small papule lesions, pustulates with white/yellow centers
- At points of friction like thighs, groin
S. aureus Infection: Furuncles
Boils
- Spreads from follicle to follicle, tissue around it too
- Redness, firm, painful with drainage
- Neck, face, breasts, buttocks, friction and sweat
S. aureus Infection: Carbuncle
Multiple boils
- Infection a lot deeper, into fat, has multiple drainage sites
- Fever and chills maybe
- Don’t really heal by itself, drain and antibiotic treatments
S. aureus Infection: Cellulitis
- Acute inflammatory, subcutaneous tissue, redness, heat, tenderness
- Lower body, legs, skin
- Over 90% of cases are because of S. aureus
- Develop rapidly (24-48 hours) from minor injury to severe septicemia
S. aureus Infection: Scalded Skin Syndrome
Toxin mediated!!
“Ritter disease”
- Abrupt onset, redness, inflammation around mouth and spreads over whole body in 2 days
- Blisters soon after
- Young children, 5% mortality
- Spontaneous recovery, 7 day period of infection
S. aureus Infection: Toxic Shock Syndrome
Toxin mediated!!!
- Rare, may be fatal
- Localized growth in vagina or wound, then releases toxins
- Fever, chills, rash
- 5-65% fatality if incorrect antibiotic is given
S. aureus Infection: Food Poisoning
Toxin mediated!!!!
- Quick onset, 1-6 hours
- Heat stable: reheating food won’t get rid of toxin even after bacteria dies
- Poor food handling
- Vomiting, nausea, cramps, diarrhea
Antibiotic Resistance in S. Aureus
- Methicillin-resistant S. aureus (MRSA)
- Vancomycin-intermediate S. aureus (VISA)
- Vancomycin-resistant S. aureus (VRSA)
- Coag- staphs can be resistant to a variety of antimicrobials
Community Acquired Methicillin Resistant S. aureus (CA-MRSA)
How do you get it?
- Person who hasn’t been recently hospitalized or had a procedure
- Skin infections, otherwise healthy people
- Athletes, military, children, MLM, prisoners
- Skin contact, crowded conditions, openings in skin, bad hygiene
- Contaminated surfaces
- Drug injections
Distinguishing CA-MRSA from Healthcare MRSA
- Location during/before diagnosis (hospital or outpatient?)
- No history of MRSA or colonization
- No medical history recently
- No catheters or things breaking skin
Strain Characteristics of CA-MRSA
Virulence factors:
- susceptible to wider range of antibiotics than HA-MRSA
- Exotoxin Pantone-Valentine leucocidin (PVL) = skin and soft tissue infection and necrotizing pneumonia
Treatment and Prevention
- Antibiotics for Staphylococcs
- Surgical removal
- Good hygiene
- Food safety
- Healthcare precautions
Laboratory Diagnosis
Methods
- Microscopy
- Culture, biochemical
- Instrumentation
Bloodstream Infections: Diagnosis and Results
What to do, diff between contaminant and pathogen?
Collection
- Collection appropriate amount for age
- Prior to antibiotics/at fever spikes
Results
Contaminant: normal skin flora, multiple organisms, blood culture organism not the same as infection site
Pathogen: same organism growing at differen collections, S. aureus, S. pyogenes, S. agalactiae, A. pneumoniae, E. coli, Candida
