Microorganisms/gram Stain List

Question 1

Staphylococcus species

Answer 1

Gram positive cocci
Clumps like grapes
Normal flora of skin
Facultative anaerobe
Non motile, non spore forming, can be in high salt environment 
Catalase positive

Question 2

Staphylococcus aureus

Answer 2

Aureus = golden (colony color)
Found on skin, in nose, axillae and groin (normal flora) but also highly virulent
Number 1 suspect in wound infections
Breaks down lipids in skin, intracellular matrix of tissues, and the protein that clots plasma.
Enterotoxin causes GI symptoms
Exotoxins (leukocidin) kills WBCs
Disease: skin infections like impetigo and scalding skin syndrome
Osteomyelitis (bone inflammation)
Pneumonia
Food poisoning
Gastroenteritis
TSS
MRSA resistance:
Strains resistant to penicillin so methicillin is used more

Question 3

Staphylococcus epidermis

Answer 3

Inhabits skin, low virulence

Diseases usually have to do with foreign bodies (IVs, prosthetics, endocarditis, etc) bc it can form a biofilm

Question 4

Staphylococcus saprophyticus

Answer 4

Associated with UTIs in young sexually active females

Resistant to some antibiotics

Question 5

Streptococcus

Answer 5

Gram positive cocci, often in chains
Normal flora in mouth, nose, intestines 
Most facultative anaerobes
Catalase negative
Non motile
Non spore forming
Grouped according to colonies and hemolytic reaction on sheep blood agar

Question 6

Alpha hemolysis

Answer 6

Partial destruction of RBCs around colony, green to brown discoloration of media

Streptococcus pneumoniae
Streptococcus bovis
Enterococcus
Viridians streptococcus group

Question 7

Beta hemolysis

Answer 7

RBCs completely lysed giving clear zone around colonies. Weak strains may have pink zone under the colony. Two toxins produce this: streptolysin O (only produced without oxygen present); streptolysin S (works with or without oxygen)

Strep. Pyogenes
agalactiae

Very rare beta hemolytic organisms: enterococcus and strep bovis