B1.2 Staphylococcus aureus Flashcards
What is the coagulase status of Staphylococcus aureus?
True coagulase-positive
Which species of staphylococci is the most virulent?
Staphylococcus aureus.
On which media does Staphylococcus aureus grow well?
Nutrient Agar (NA) and Tryptic Soy Broth (TSB).
Describe the appearance of Staphylococcus aureus colonies on solid media
Round, smooth, opaque, and butyrous
What is the appearance of Staphylococcus aureus colonies on Blood Agar Plate (BAP)?
Golden yellow color and β-hemolytic
What salt concentration is used to cultivate Staphylococcus aureus, and what does this indicate?
7.5 to 10% NaCl; indicates halophilic nature
What infections is Staphylococcus aureus responsible for?
Skin, wound, and deep tissue infections
What type of teichoic acid is present in the cell wall of Staphylococcus aureus?
Ribitol teichoic acid.
Virulence Factors related to staphylococcus aureus
Antigenic Structures
Enzymes
Toxins
Antigenic Structures present in S. aureus
Teichoic Acid
Peptidoglycan
Protein A
Clumping Factor
Capsular Polysaccharide
What is the role of peptidoglycan in Staphylococcus aureus?
Protects from lysis and aids in adherence
What is the unique group-specific antigen in Staphylococcus aureus?
Protein A.
Prevents antibody-mediated phagocytosis by competing for the Fc portion of antibodies
Protein A
Causes clumping of staphylococci in the presence of plasma
clumping factor
What is the role of capsular polysaccharide in Staphylococcus aureus?
Protects from phagocytosis
ENZYMES present in S. aureus
COAGULASE (STAPHYLOCOAGULASE)
HYALURONIDASE (SPREADING FACTOR)
STAPHYLOKINASE (FIBRINOLYSIN)
LIPASE (Fat-splitting Enzyme)
DEOXYRIBONUCLEASE (DNASE) and PHOSPHATASE
PROTEASE
GELATINASE
β-LACTAMASE
Coagulates fibrinogen in plasma to promote fibrin layer formation around abscesses.
coagulase (staphylocoagulase)
Name the two types of coagulase in Staphylococcus aureus
Cell-bound (clumping factor) and unbound (free) coagulase
bound to the cell wall and clots human, rabbit or pig plasma
Cell-bound Coagulase or Clumping Factor
extracellular enzymes not bound to the cell wall and cause clot formation when bacterial cells are incubated with plasma
Unbound or Free Coagulase
Hydrolyzes hyaluronic acid, permitting the spread of infection
hyaluronidase
Dissolves fibrin clots (fibrinolysin)
staphylokinase
Acts on lipids on the skin surface, aiding in the formation of furuncles, carbuncles, and boils
produced by both coagulase (+) and coagulase (-) staphylococci
lipase
Lowers viscosity of exudates and destroys DNA
DNase and phosphatase
Which enzyme in Staphylococcus aureus breaks down β-lactam drugs
β-Lactamase
TOXINS in S. aureus
CYTOLYTIC TOXINS
ENTEROTOXINS
TOXIC SHOCK SYNDROME TOXIN-1(TSST-1)
EXFOLIATIVE TOXIN
CYTOLYTIC TOXINS examples
Hemolysins and Leukocidins
4 Types Hemolysins and the leukocidin found in S. aureus
α-Hemolysin
β-Hemolysin (Sphingomyelinase C)
δ-Hemolysin
γ-Hemolysin
Staphylococcal Leukocidin/ Panton-Valentine leukocidin
Which hemolysin in Staphylococcus aureus causes severe tissue damage
α-Hemolysin
Act as heat-stable exotoxins causing food poisoning
enterotoxins
Which toxin is associated with Toxic Shock Syndrome in Staphylococcus aureus?
Toxic Shock Syndrome Toxin-1 (TSST-1).
What does exfoliative toxin cause in Staphylococcus aureus infections
Staphylococcal Scalded Skin Syndrome (Ritter’s disease) and bullous impetigo
damage RBC, platelets and macrophages and cause severe tissue damage
Predominant hemolysin
α-Hemolysin
acts on sphingomyelin in the plasma membrane of RBC
β-Hemolysin (Sphingomyelinase C)
aka“hot-cold” lysine : enhanced hemolytic activity on incubation at 37° C (heat labile) and subsequent exposure to cold (4° C)
β-Hemolysin (Sphingomyelinase C)
exhibited in the CAMP test
lethal and dermonecrotic
β-Hemolysin (Sphingomyelinase C)
less toxic to cells than either α-hemolysin or β-hemolysin
produced by all S. aureus strain that cause RBC injury in culture and produce edematous lesions
δ-Hemolysin
associated with Panton-Valentine leukocidin (PVL)
γ-Hemolysin
exotoxin lethal to polymorphonuclear leukocytes
Pore forming exotoxin that suppress phagocytosis and associated with severe cutaneous infections and necrotizing pneumonia
associated with community-acquired staphylococcal infections
Staphylococcal Leukocidin/ Panton-Valentine leukocidin
heat-stable exotoxin: 100° C for 30 minutes
resistant to hydrolysis by gastric and jejunal enzymes
act as neurotoxins that stimulate vomiting through the vagus nerve
ENTEROTOXINS
Enterotoxins are produced by _____% of S. aureus isolates
30% to 50%
Enterotoxins A, B, and D causes
Staphylococcal food poisoning
Enterotoxins B and C and sometimes G and I causes
TSS
Enterotoxin B causes
Staphylococcal Pseudomembranous Enterocolitis (contaminated milk products)
TOXIC SHOCK SYNDROME TOXIN-1(TSST-1) is also known as
ENTEROTOXIN F or PYROGENIC EXOTOXIN C
menstruating-associated TSS= TSS associated with tampon use
chromosomal-mediated toxin
SUPERANTIGEN stimulating T-cell proliferation and production of a large amount of cytokines
TOXIC SHOCK SYNDROME TOXIN-1(TSST-1)
TOXIC SHOCK SYNDROME TOXIN-1(TSST-1) low concentrations=
higher concentrations=
low concentrations= leakage by endothelial cells;
higher concentrations= cytotoxic
EXFOLIATIVE TOXIN aka
EPIDERMOLYTIC TOXIN A and B or EXFOLIATIN
serotypes A and B
Serine protease that divides the intrcellular bridges of the epidermis and causes excessive sloughing of the epidermis (stratum granulosum)
causes STAPHYLOCOCCAL SCALDED SKIN SYNDROME referred to as RITTER’S DISEASE
implicated in BULLOUS IMPETIGO
EXFOLIATIVE TOXIN
RELATED INFECTIONS AND DISEASES S. aureus
Cutaneous Infections
Toxic Shock Syndrome
Food Poisoning
Staphylococcal Bacteremia
Staphylococcal Osteomyelitis
Staphylococcal Pneumonia
Septic Arthritis
Acute Bacterial Endocarditis
UTI
Cutaneous Infections caused by S. aureus
Folliculitis
Furuncles (Boils)
Carbuncles
Bullous Impetigo
Scalded Skin Syndrome
Toxic Epidermal Necrolysis (TEN)
mild inflammation of a hair follicle or oil gland; infected area is raised and red
Folliculitis
focal suppurative lesions which has resulted from an infection (folliculitis) that extend into subcutaneous tissue; large, raised, superficial abscesses
Furuncles (Boils)
larger, more invasive lesions develop from multiple furuncles, which can progress into deeper tissues; present with fever and chills, indicating systemic infection
Carbuncles
larger pustules surrounded by a small zone of erythema
highly contagious infection that spread by direct contact, fomites, or autoinoculation
Bullous Impetigo
superficial cutaneous infection commonly seen in newborns and young children characterized by the formation of encrusted pustules surrounded by red border
Impetigo
bullous exfoliative dermatitis that occurs primarily in newborns and previously healthy young children
Scalded Skin Syndrome
localized skin lesion SSS:
few blisters,
pemphigus neonatorum,
Ritter disease
generalized form of SSS:
cutaneous erythema, profuse peeling of the epidermis
clinical manifestation with multiple causes; symptoms are due to hypersensitivity reaction
Toxic Epidermal Necrolysis (TEN)
rare but potentially fatal, multisystem disease characterized by sudden onset of fever, chills, vomiting, diarrhea, muscle aches, and rash, which can quickly progress to hypotension and shock
Toxic Shock Syndrome
Food Poisoning caused by
Enterotoxins A (78%), D (38%), and B (10%)
intoxication resulting from ingestion of a toxin formed outside the body
symptoms appear rapidly (2 to 8 hours after ingestion) and resolve within 24 to 48 hours: nausea, vomiting, abdominal pain, and severe cramping, diarrhea
Food Poisoning
perfuse and watery diarrhea due to water and electrolyte loss
FOOD POISONING
- Food won’t appear or taste tainted
- Death: Intoxication rather than infection
- Reheating the food – kills the bacteria, but not
inactivate the heat stable toxin
FOOD POISONING
ENTEROCOLITIS caused by
Enterotoxin A and (leukocidins) LukE
and LukP
leads to secondary pneumonia and endocarditis observed among IV drug users
Staphylococcal Bacteremia
secondary to bacteremia
Staphylococcal Osteomyelitis
secondary to influenza virus infection
multiple abscesses and focal lesions in the pulmonary parenchyma
Staphylococcal Pneumonia
frequent in children and occur in patients with a history of rheumatoid arthritis or IV drug abuse
Septic Arthritis
JOINT INFECTIONS/SEPTIC ARTHRITIS found in
Both Adults and Neonates/Children
S. aureus
S. agalactiae
S. pyogenes
Enterobacteriaceae
JOINT INFECTIONS/SEPTIC ARTHRITIS found in
Neonates/Children
only
H. influenzae type b (Hib)
Kingella kingae
JOINT INFECTIONS/SEPTIC ARTHRITIS found in
Sexually Active
N. gonorrhoea
Specimen of choice for testing S. aureus
Pus,
Purulent Fluids,
Sputum,
Urine,
Blood
Gram Stain results of S. aureus
Gram(+) cocci in irregular clusters
Culture Media used for S. aureus
BAP, PEA, MSA, CNA, Chapman Stone Agar, Vogel-Johnson Medium
Columbia Colistin–Nalidixic acid (CNA)
MSA and PEA
CHROM Agar
media used for purulent exudates
Columbia Colistin–Nalidixic acid (CNA)
Media used for heavily contaminated specimen
MSA and PEA
Media used for selective-differential for MRSA
CHROM Agar
Biochemical Tests used for S. aureus
Catalase Test
Coagulase Test
Mannitol Fermentaion Test
Growth on Tellurite Glycine Agar
Polymyxin B Sensitivity
Lysostaphin Sensitivity Test (2ug/ml)
Voges-Proskauer (VP) Test
Deoxyribonuclease (Dnase) Test
Pyrrolidonyl Arylamidase (PYR) Test
Rapid Methods of Identification
Molecular Methods
What reagent is used in the aerobic catalase test?
3% H2O2
What reagent is used in the anaerobic catalase test?
15% H2O2
What is the catalase reaction result for Staphylococcus?
Catalase positive
What is the catalase reaction result for Streptococcus?
Catalase negative
best single criterion of recognition and pathogenicity of S. aureus
Coagulase Test
What reagent is used in the coagulase test?
Rabbit plasma with EDTA
Methods for coagulase test
Slide Method
Tube Method
rapid screening test
detects cell-bound coagulase or clumping factor
Other Slide Coagualse Positive: S. lugdunensis and S. schleiferi
Slide Method
sensitive but definitive; confirm all slide negative results
detects extracellular or free coagulase
Tube Method
What does the slide coagulase test detect?
Cell-bound coagulase (clumping factor)
Which species are slide coagulase positive besides S. aureus?
S. lugdunensis and S. schleiferi
What does the tube coagulase test detect?
Extracellular (free) coagulase
Name other tube coagulase-positive species besides S. aureus
S. hyicus,
S. intermedius,
S. lutrae,
S. delphini, and
S. schleiferi subsp. coagulans
At what temperature should the tube coagulase test be incubated initially?
35°C–37°C
How long should the tube coagulase test be incubated before reading the result?
1-4 hours
During a coagulase test, if no clot forms after 4 hours what should you do
reincubate at room temperature for additional 20 hours
What is the significance of reading the tube coagulase test result within 4 hours?
To prevent false negatives due to fibrinolysin activity
Coagulase plasma is not suitable with
Citrate
These species use citrate and release calcium forming clot in the absence of coagulase causing a false positive result for Coagulase test
Pseudomonas and Enterococci
What medium is used for the mannitol fermentation test?
Mannitol Salt Agar (MSA)
S. aureus can ferment mannitol and can tolerate high salt concentrations of what percent
(7.5-10%)
What is the pH indicator used in the mannitol fermentation test
Phenol Red
What is the positive result for mannitol fermentation on MSA?
Yellow-colored colonies with a yellow halo
What colonies does S. aureus produce on tellurite glycine agar?
Jet-black colonies
What is the reaction of S. aureus to polymyxin B?
Resistant
What is the reaction of other staphylococci to polymyxin B?
Susceptible
What is the reaction of S. aureus in the lysostaphin sensitivity test?
Sensitive
What is the reaction of micrococci in the lysostaphin sensitivity test?
Resistant
What is the culture medium for the Voges-Proskauer (VP) test?
VP broth with 5% glucose
used to differentiate S. aureus (+) from S. intermedius (-)
Voges-Proskauer (VP) Test
What reagents are used in the Voges-Proskauer (VP) test?
α-naphthol and KOH
Name VP-positive species besides S. aureus
S. lugdunensis, S. haemolyticus, and S. schleiferi
What culture medium is used in the DNase test?
DNA-methyl green agar
What is the DNase result for S. aureus?
DNase positive
What substrate is used in the PYR test?
Pyroglutamyl-β-naphthylamide (PYR)
(Lpyrrolidonyl-β-naphthylamide; PYR)
differentiates coagulase(+) staphylococci by slide method
Pyrrolidonyl Arylamidase (PYR) Test
What reagent is used in the PYR test?
p-dimethylaminocinnamaldehyde
What is the end product of the PYR test?
L-pyrrolidone and β-naphthylamine
What is the positive result for the PYR test?
Cherry red color
Name PYR-positive species
S. lugdunensis,
S. intermedius,
S. schleiferi,
S. haemolyticus
Rapid Methods of Identification
Particle Agglutination Test
Staphyloslide use sensitized sheep RBC
Staphaurex
BACTiStaph
Staphylochrome
Sero-STAT
Bacto Staph Latex
Accu-Staph
Hemostaph
Staphylatex
plasma-coated carrier particles (latex)
plasma detects both clumping factor (with fibrinogen) and protein A in the cell wall of S. aureus (with IgG)
Staphylatex
What does plasma-coated carrier particles in rapid tests detect?
Clumping factor (fibrinogen) and Protein A (IgG)
Molecular Methods used in the detection of S. aureus
Real-time PCR
Qualitative Nucleic Acid Hybridization
Assays
What molecular method is used to detect MRSA and MSSA?
Real-time PCR
staphylococci from prepared smears in
blood cultures
identification of mecA gene
Qualitative Nucleic Acid Hybridization
Assays
What gene is identified by molecular methods in S. aureus?
mecA gene
What specimen is used for molecular testing for S. aureus?
Anterior nares swabs
Advantage of Qualitative Nucleic Acid Hybridization Assays
rapid detection test for MRSA