Gram Positive Cocci and Gram Negative Cocci Flashcards
Which genera are in the Micrococcaeceae Family?
Staphylococcus, Micrococcus, and Stomatococcus
Staphylococci characteristics:
Part of normal skin flora and mucous membranes; facultative anaerobic GPC that tend to form clusters on gram stain
Micrococcus characterisitics:
Often appear as tetrads and produce lemon-yellow colonies; normal on skin and mucous membranes; rarely cause disease
Stomatococcus mucilaginosus
Rarely causes disease; normal oral cavity flora; catalase negative, modified oxidase negative, resistant to bacitracin, susceptible to furazolidone, and encapsulated
How are Staphylococcus and Micrococcus differentiated from each other?
Both are catalase positive unlike Stomatococcus; Staphylococcus is susceptible to furazolidone and lysostaphin but resistant to bacitracin; whereas, Micrococcus is the opposite. Micrococcus is also modified oxidase positive while the other two are negative.
Mannitol Salt Agar (MSA)
a selective and differential media used for staph (the high salt concentration inhibits most GNRs and other GPs). When mannitol is fermented, the pH indicator (phenol red) turns from red to yellow.
Staphylococcus aureus diseases:
- Invasive diseases: skin infections (folliculitis), abscesses, wound infections, osteomyelitis, pneumonia, and endocarditis
- Toxigenic: Food poisoning, Scalded Skin Syndrome, Toxic Shock Syndrome
Coagulase Negative Staph Diseases:
- Associated with indwelling medical devices
- UTIs (S. saprophyticus is a leading cause of UTIs in young, sexually active females)
- Immunocompromised individuals
Staphylococcus aureus biochemicals
Tube coagulase positive and mannitol salt agar positive (yellow); Subspecies aureus is D-mannose positive while subspp. anaerobius is negative
Coagulase Negative Staphylococcus biochemicals
S. saprophyticus- Resistant to novobiocin
S. lugdunesis- ODH positive
S. schleiferi- DNase positive
Streptococcus Characteristics:
Catalase negative, facultative anaerobic GPC that form chains; four naming systems for species
Four naming systems for streptococci
- Serogrouping/ Lancefield grouping: based on cell wall antigens (group A, B, etc)
- Physiological properties: based on biochemical reactions
- Hemolytic activity: alpha, beta, and gamme hemolysis groups
- Common names: ex- B strep or pneumococci
Group A Streptococcus (GAS)/ S. pyogenes Diseases
Not part of the normal flora for humans although some may be asymptomatic carriers; suppurative (pus forming); pharyngitis (strep throat), scarlet fever, bacteremia, skin infections (cellulitis, erypsipelas, pyoderma), toxic shock syndrome
Group B Streptococcus (GBS)/ S. agalactiae Diseases
normal genitourinary tract flora; most common cause of neonatal sepsis and meningitis; can cause UTIs, skin and soft tissue infections, postpartum fever, and sepsis
Group C, F, and G Streptococci Diseases
normal respiratory, gastrointestinal, and vaginal flora; can cause bacteremia, endocarditis, and wound infections
Group D Streptococcus/ S. bovis Diseases
normal GI tract inhabitant; associated with colon cancer (Biotype 1) and gall bladder disease (Biotype 2); can cause bacteremia and endocarditis;
Streptococcus pneumoniae Diseases
normal habitat is the upper resp. tract; causes pneumonia (most common cause of community bacterial pneumonia), bacteremia, meningitis, and otitis media
Viridans Streptococci Diseases
inhabit resp. tract, GI tract, and skin; cause endocarditis in patients with artificial heart valves, dental carries, wound infections, and brain abscesses
Streptococcus-Like Bacteria Diseases
found on mucous membranes; infections are rare, but includes endocarditis, bacteremia, osteomyelitis, and wound infections
Which Streptococcus species has a rapid antigen test?
GAS has a rapid antigen detection test for pharyngitis
GAS Identification
large B hemolytic zone, susceptible to bacitracin, resistant to SXT, PYR positive;
B hemolysis is caused by two toxins (Streptolysin S and streptolysin O) - SLS is oxygen stable and SLO is not, so organisms with only SLO will not be Beta aerobically unless the agar is stabbed to create an anaerobic environment
GBS Identification
small zone of B hemolysis (some are nonhemolytic), CAMP positive, hippurate positive, carrot broth positive, and resistant to both bacitracin and SXT
Large colony vs small colony Group C and G
Large colony are VP negative whereas small colony are part of the S. anginosus group and are VP positive
Group D Identification
alpha or gamma hemolytic, bile esculin positive, NaCl negative, PYR negative, resistant to bacitracin; Biotype 1 produces glucan and ferments mannitol (Biotype 2 does not)