Gram + Cocci Flashcards
Describe the morphology of cocci
Spherical cells Purple beadies - grape like clusters due to pattern of cell division Gram positive Non motile Non spore forming
Describe the metabolic characteristics of cocci
Facultative anaerobes (can use oxygen or not) Catalase positive (make catalysts... It bubbles! Not really doing anything...) Ferment sugars
Describe characteristics of staphylococcus aureus in micro lab
Golden pigment (Aureus = gold) Coagulase positive (unique to staph aureus!)
Virulence factors of staph. Aureus
Protein A - binding antibodies the WRONG way which coats the bacterial cell in immunoglobulin making it hard to identify (Master in Disguise!)
Exotoxins - don’t memorize all 4 (alpha, beta, delta, gamma)
Leukocidins
TSST**
Enterotoxin - if present on consumed food (heat-stable)
Exfoliatin - scalded skin syndrome
What is toxic shock syndrome toxin?
A super antigen causing massive release of cytokines (cytokine Storm) causing drastic drop in blood pressure and kidney failure!
Powerful exotoxin that stimulates tumor necrosis factor leading to necrosis
Stimulates interleukin leading to fever, rash
Originally associated with tampon use BUT also affect men and non-menstruating women
Name the Extracellular enzymes utilized by staphylococcus aureus
Coagulase
Catalase
Where is Staphylococci found?
Found as part of the normal flora and are the leading cause of wound infection (surgical and accidental)
Skin
Upper respiratory tract
Gastrointestinal tract
What is osteomyelitis?
Bone infection from staph. Aureus and commonly follows trauma
Most common in boys under 12
What is MRSA?
Staph aureus that is methicillin resistant
Hospital Acquired - pt had surgery and got wound infection or admitted for something else and since they had a weakened immune system, acquired this bacteria
Community Acquired - acquire at gym, supermarket, etc. No medical record of MRSA infection or surgeries
What are skin pathologies that can be caused by staph aureus?
Furuncles (boils) and carbuncles
Impetigo
Folliculitis
Scalded skin syndrome
What are characteristics of staphylococcus epidermis?
Coagulase negative
Opportunistic pathogen
Catheters, prosthetic joints and artificial heart valves can cause it
Frequent contaminant in blood draws because it lives on the skin
How do you tell the difference between staphylococcus and streptococcus?
Staphylococcus is catalase positive (bubbles under hydrogen peroxide) and strep will not
How can you isolate staphylococcus aureus?
Mannitol fermentation agar will ferment in the presence of staphylococcus aureus which will change the colour of the agar from red to yellow
What would you see with alpha hemolysis?
Partial hemolysis with greenish cast around colonies
What would you see with Beta hemolysis on an agar plate?
Complete lysis of blood cells creating a clear area around colonies
What would gamma hemolysis look like on a agar plate?
No lysis of blood cells
What was Rebecca Lancefield for?
Lancefield Groups that divide strep by serological testing of extractable carbohydrate
Characteristics of lactic streptococci
Non pathogenic
No hemolysis (gamma)
Found in milk!
What are characteristics of enterococcus
Lancefield group D
Normal flora of intestinal tract (in our poop)
Different hemolysis patterns
Clinically commonly cause urinary tract infections
Non beta-hemolytic streptococci characteristics
Large group of heterogenous group
No Lancefield antigen
Alpha hemolysis
May cause tooth decay
May enter bloodstream and infect a weakened heart during dental cleaning
Normal flora of the mouth and resp. Tract
Beta hemolytic cocci characteristics
Lancefield groups A and B
What are virulence factors of Lancefield Group A (streptococcus pyogenes or beta hemolytic streptococci)
M proteins
Hyaluronic acid capsule (sneaky)
Progenitor exotoxins - fever
Extracellular products (hyaluronidase, streptokinase, leukocidin, proteinase)
What are pathologies that can be caused by Group A?
Streptococcal pharyngitis (can lead to middle ear infections and meningitis)
Streptococcal impetigo (co-infection w/staph. Aureus)
Cellulitis
Erysipelas (St. Anthony’s Fire)
Scarlet fever
List 2 post stretococcal diseases
Rheumatic fever
Glomerulonephritis
How would you treat Group A infections?
Penicillin for 8-10 days
Benzylpenicillin
What are pathologies from Lancefield Group B (beta-hemolytic streptococci, s. Agalactiae)
Neonatal meningitis, pneumonia, sepsis in first week of life
How would you diagnose Lancefield a group B? What would it look like on an agar plate?
CAMP test: weak beta hemolysis of Group B strep combines and grows with beta hemolysis of staph aureus strain
Positive test products arrow shape of strong beta hemolysis
Where is Lancefield Group B found normally?
Normal flora of the female genital tract
What makes the streptococcus pneumoniae so virulent?
Polysaccharide capsule
Where does s. Pneumoniae live normally?
It’s part of the normal body flora
How does infection of s. Pneumoniae begin?
When an invasive strain moves to the lower lungs
(Follows viral flu often and is Common in alcoholics and elderly)
Also causes meningitis in adults and osteomyelitis in children
How would you diagnose s. Pneumoniae?
Gram stain sputum sample
How would you treat s. Pneumoniae?
Early treatment = rapid recovery!
Penicillin
Vancomycin
Your patient is a teacher and requires vaccinations to protect herself and her students. She asks you how to avoid getting pneumonia. What do you suggest for her?
PCV13 vaccination which contains 7 capsular polysaccharide antigens that account for most of the disease
Describe the morphology of streptococci
Spherical cells Found in chains Gram positive Non-motile Non-endospore forming
