Lab 9- Post Lab Quiz: Staph, Strep, Water Quality,

Streptococci

• Gram positive, Mostly Pathogens

Hemolysis

is the breakdown of red blood cells to obtain iron within
using hemolysins which are considered virulence factors

3 types of hemolytic organisms

1. Alpha

2. Beta

3. Gamma

Alpha hemolysis

is the incomplete lysis which produces a greenish zone around the colony S. pneumoniae some other normal flora also do this

Beta (β) hemolysis

gets a clearing around the colonies due to compete lysis, S.
pyogenes which causes strep throat- it is a group A strep because it has the A carbohydrate

Gamma (γ) hemolysis

non-hemolytic - Streptococci that do not lyse red blood cells

Medium used for looking at hemolytic patterns

• Blood agar

Streptococci Sampling Procedure

You are going to take your own throat culture as close to tonsils as
possible make sure to roll swab around to get fully covered
– AVOID touching your teeth or tongue
• First quadrant streak the blood agar with the individually wrapped
swabs then finish quadrants 2-4 with loop
• Next week determine pattern of hemolysis and gram stain an
isolated colony

Staphylococci

• Gram-Positive, mostly pathogens

• gram positive organisms that tolerate high salt
  concentrations and are frequent pathogens

Two main staphylococci

1. Staphylococcus aureus

2. Staphylococcus epidermidis

S. aureus

is frequently in the nose and there are many methicillin
resistant strains that cause nosocomial (hospital acquired) infections

S. epidermidis

is more of an opportunistic pathogen and infects burns sites, joint replacement site, and other human/medical device surfaces

Staphylococci 3 Media used

Staphylococci Medium 110 (SM110)
• Selective due to high salt concentration of ~7.5% due to NaCl
• Clear medium color allows us to observe colony color
– Mannitol Salts Agar (MSA)
• Selective due to high salt concentration of ~7.5% due to NaCl
• Differential for mannitol fermentation due to phenol red pH
indicator
– Fermenters turn plate yellow due to production of acid
– Rabbit Plasma- (Small foam stoppered tubes)
• Differential for coagulase production
– Enzyme produced by some organisms to clot blood
– Indicated by the medium solidifying after inoculation

Staphylococci Medium 110 (SM110)

• Selective due to high salt concentration of ~7.5% due to NaCl

• Clear medium color allows us to observe colony color

Mannitol Salts Agar (MSA)

• Selective due to high salt concentration of ~7.5% due to NaCl
• Differential for mannitol fermentation due to phenol red pH
indicator
– Fermenters turn plate yellow due to production of acid

Rabbit Plasma- (Small foam stoppered tubes

Differential for coagulase production
– Enzyme produced by some organisms to clot blood
– Indicated by the medium solidifying after inoculation

Staphylococcus aureus characteristics

• + plasma (solid)

• + (yellow plate)

• Yellow colony

Staphylococcus epidermidis characteristics

• - plasma (runny)

• - Red plate)

• White colony