Micrococcaceae Flashcards
Micrococcaceae
staphylococcus and micrococcus
Staphylococcus species
S. aureus, S. epidermidis, S. hemolyticus, S. saprophyticus, S. intermedius
Micrococcaceae general characteristics
- Gram-positive cocci, catalase positive, singly, pairs or in clusters
- Colony morphology: cream-colored, buttery on BA or CNA, some produce Beta hemolysis
- aerobic or falcultative anaerobes, non motile, non spore forming, non encapsulated
exceptions to general characteristics
S. saprophyticus is an obligate anaerobe
Micrococcus luteus
- Gram-positive, catalase positive, coagulase negative
- morphology: distinct yellow colony
- non-pathogen
coagulase
staphylocoagulase enzyme clots plasma
coagulase positive staphylococci
- S. aureus (human pathogen)
- S. delphini, S. intermedius, S. lutrae, S. hyicus (animal pathogens)
coagulase negative staphylococci (CoNS)
- S. epidermidis (nosocomial infections)
- S. saprophyticus (UTI’s in young, sexually active females)
Staphylococcus aureus
- exist in carrier state in 20-30% of population
- most virulent staph species
- superficial to systemic infections
Virulence factors of S. aureus
- enzymes: coagulase, hyaluronidase, lipase
- enterotoxins, toxins A-E and G-I, exfoliative toxins, cytolytic toxin
- Protein A
hyaluronidase
hydrolyzes the hyaluronic acid present in connective tissue and helps spread infection
lipase
breaks down the fats and oil created by sebaceous glands on skin surfaces
enterotoxins
heat-stable exotoxins that cause diarrhea and vomiting
toxins A-E and G-I
- resistant to gastric acid and associated with food poisoning
- A, B, and D associated with staph food poisoning
- toxic shock syndrome toxin-1 (TSST-1)
- TSST-1, B, C, G, and I are superantigens
- causes toxic shock syndrome
exfoliative toxin (epidermolytic toxin)
causes epidermal layer of skin to slough off; causes Scalded Skin Syndrome and bullous impetigo
cytolytic toxins
alpha, beta, and gamma hemolysin
alpha hemolysin
destroys platelets and tissues
beta hemolysin
- acts on the sphingomyelin of RBC membranes, causing lysis
- hot-cold lysin because works at 37 and 4 degrees C
gamma hemolysin
- also called Panton-Valentine leukocidin (PVL)
- exotoxin kills polymorphonuclear leukocytes to help prevent phagocytosis
- typically associated with community-acquired infections
Protein A
- binds the fragment crystallizable (Fc) portion of an antibody to avoid phagocytosis by masking it immunogenic proteins with host proteins to look like “self”
- negates the protective effects of IgG
Transmission of Staph. aureus
- colonizes nares (20-30% carriers)
- axillae, vagina, pharynx, other skin surfaces
- nosocomial
- fomites, poor hygiene
Clinical cases of Staph. aureus include
localized (pyogenic) skin infections, impetigo
Scalded Skin Syndrome
- extensive exfoliative dermatitis, most likely to occur in renal failure patients and ICP’s
- localized lesion to profuse peeling
- 2-4 days, can be fatal in adults, spontaneous recovery in children
toxic shock syndrome
- associated with super-absorbent tampons
- high fever, rash of the trunk/extremeties, watery diarrhea, vomiting, dehydration, leads to hypotension
- Disseminated intravascular coagulation (DIC),
- increase in blood urea nitrogen (BUN) and creatinine
toxic epidermal necrolysis (TEN)
- causes: drug induced, infections, vaccines
- similar to Staph. Scaleded Skin Syndrome (SSSS), except steroids can be effective
- high mortality rate
- Gram-positive cocci, catalase positive, singly, pairs or in clusters
- Colony morphology: cream-colored, buttery on BA or CNA, some produce Beta hemolysis
- aerobic or falcultative anaerobes, non motile, non spore forming, non encapsulated
Micrococcaceae general characteristics
- Gram-positive, catalase positive, coagulase negative
- morphology: distinct yellow colony
- non-pathogen
Micrococcus luteus
- exist in carrier state in 20-30% of population
- most virulent staph species
- superficial to systemic infections
Staphylococcus aureus
hydrolyzes the hyaluronic acid present in connective tissue and helps spread infection
hyaluronidase
breaks down the fats and oil created by sebaceous glands on skin surfaces
lipase
heat-stable exotoxins that cause diarrhea and vomiting
enterotoxins
causes epidermal layer of skin to slough off; causes Scalded Skin Syndrome and bullous impetigo
exfoliative toxin (epidermolytic toxin)
destroys platelets and tissues
alpha hemolysin
- acts on the sphingomyelin of RBC membranes, causing lysis
- hot-cold lysin because works at 37 and 4 degrees C
beta hemolysin
- also called Panton-Valentine leukocidin (PVL)
- exotoxin kills polymorphonuclear leukocytes to help prevent phagocytosis
- typically associated with community-acquired infections
gamma hemolysin
- binds the fragment crystallizable (Fc) portion of an antibody to avoid phagocytosis by masking it immunogenic proteins with host proteins to look like “self”
- negates the protective effects of IgG
Protein A
- extensive exfoliative dermatitis, most likely to occur in renal failure patients and ICP’s
- localized lesion to profuse peeling
- 2-4 days, can be fatal in adults, spontaneous recovery in children
Scalded Skin Syndrome
- associated with super-absorbent tampons
- high fever, rash of the trunk/extremeties, watery diarrhea, vomiting, dehydration, leads to hypotension
- Disseminated intravascular coagulation (DIC),
- increase in blood urea nitrogen (BUN) and creatinine
toxic shock syndrome
- causes: drug induced, infections, vaccines
- similar to Staph. Scaleded Skin Syndrome (SSSS), except steroids can be effective
- high mortality rate
toxic epidermal necrolysis (TEN)
food poisoning
- enterotoxins A, B, and D, from enterotoxin-producing strains contaminating rich foods and inadequate refrigeration
- toxin causes the sickness, 2-8 hrs after ingestion, lasts 24-48 hrs, nausea, vomiting, abdominal pain, cramping
- enterotoxins A, B, and D, from enterotoxin-producing strains contaminating rich foods and inadequate refrigeration
- toxin causes the sickness, 2-8 hrs after ingestion, lasts 24-48 hrs, nausea, vomiting, abdominal pain, cramping
food poisoning
Other infections caused by staph species
secondary pneumonia, bacteremia and endocarditis, osteomyelitis, arthritis (if bacteria in joints)
- predominately nosocomial infections (skin flora introduced in catheters, CSF shunts and heart valves)
- produces a slime layer to adhere to prosthetics and avoid phagocytosis
- common cause of hospital-acquired UTI’s
Staph. epidermidis
- causes UTI’s in young, sexually active females
- increased adherence to epithelial cells of urogenital tract
- found in urine cultures
S. saprophyticus
- coagulase negative staph that mimics S. aureus infection
- pathogen of infective endocarditis, septicemia, meningitis, skin and soft tissue infections, UTI’s, and septic shock
Staph. lugdunensis
Opportunistic staphs
- S. warneri, S. capitis, S. simulans, S. hominis, S. schleiferi
- normal flora that can cause endocarditis and septicemia
- CoNS
- common CoNS found in wounds, bacteremia, endocarditis and UTI’s
- may have resistance to vancomycin
S. haemolyticus
Isolation of Staphs
- grow well on blood agar and thioglycolate
- if contaminated specimen, can be selected for on mannitol salt agar, Columbia colistin-nalidixic acid agar (CNA), PEA, CHROMagar
Thioglycolate broth
- pancreatic digest of casein, soy broth and glucose
- supports anaerobes, aerobes, microaerophilic and fastidious organisms
- colistin, nalidixic acid, and 5% sheep blood
- selects for isolation of gram-positive cocci
Columbia colistin-nalidixic acid agar (CNA)
- peptone base, mannitol, 7.5% salt, phenol red indicator
- selective isolation for staph.
- turns yellow if mannitol is hydrolyzed (S. aureus)
Mannitol salt agar
CHROMagar
MRSA colonies show up magenta
Identification methods
oxidative-fermentative glucose medium, modified oxidase, catalase, coagulase, PYR, Bacitracin disk test, Novobiocin, antimicrobial susceptibility
Oxidative-fementative glucose medium
most Staph. ferment glucose, while Micrococci don’t
modified oxidase
microdase disk will be positive for Micrococci and negative for most Staphylococci
Catalase test
- hydrogen peroxide becomes water and oxygen gas in the presence of enzyme catalase
- bubbling is positive, staph. are positive
coagulase
clumping factor that causes agglutination in plasma
coagulase test
- mix water or saline with organism and rabbit plasma
- if it clumps, it’s positive
- if negative, tube test must be run
- hallmark test for S. aureus (other staph can be pos. too)
extracellular free coagulase
- extracellular enzyme that clots plasma
- tube test: check for clotting 4 hrs and 24 hrs after inoculation
PYR
negative for S. aureus, but positive for other coagulase positive staph
Groups of Coagulase-positive staph
S. aureus group, S. hyicus group, S. intermedius group
PYR test
- detection of pyrrolidonyl arylamidase helps differentiate streptococci and enterococci
- color change to red if positive
Bacitracin disk test
- differentiates Micrococcus from CoNS
- Micrococcus luteus is susceptible
- CoNS are resistant (sapro, epidermidis)
Novobiocin test
- presumptive differentiation of CoNS
- if resistant, S. saprophyticus
- if susceptible, likely S. epidermidis
Rapid Identification
BBL staphloslide, Staphaurex, Bactistaph, Plasma-carrier coated particles detect clumping factor and protein A, PCR for MRSA and MSSA, qualitative nucleic acid hybridization assays, MALDI-TOF mass spectrometry
antimicrobial susceptibility
- most S. aureus are resistant, so you need to do Beta-lactamase test
MRSA
- community-acquired MRSA, health care-associated/community onset MRSA, hospital associated MRSA
- infection control by barrier protection, contact isolation and handwashing
- treat w/ vancomycin (susceptibility test with cefoxitin disk)
Borderline oxacillin-resistant S. aureus (BORSA)
can separate from MRSA on oxacillin salt agar plate
mecA gene
gene in MRSA that encodes penicillin-binding proteins (PBPs); very few express phenotype
Gold standard
mecA gene detected by PCR
VRSA
Vancomycin resistant staph. aureus
Macrolide resistance
- resistance to clindamycin may not be obvious
- if resistance to clindamycin and erythromycin are not the same, do a D test
- induced resistance if forms a D (on clindamycin side)
