Staphylococcus, Micrococcus, and Similar Organisms Flashcards
General characteristics of Staphylococcus
- Catalase-producing gram (+) cocci
- Nonmotile, non–spore-forming
- Aerobic or facultative anaerobic except for S. aureus subsp. anaerobius and S. sacchrolyticus
- Spherical cells (0.5 to 1.5 μm) that appear singly, in pairs, and in clusters
- Normal inhabitants of skin, mucous membranes and intestines
- On BAP, the colonies are medium sized (4 to 8 mm) and appear cream-colored, white or rarely light gold, and “buttery-looking”
- Other spp. may have gray colonies; some may be β-hemolytic (S. aureus)
A biochemical test used to separate Staphylococci (+), Micrococci (+), and Streptococci (-)
Catalase Test
Positive result of Catalase Test
Vigorous bubbling
Concentration of Hydrogen Peroxide (H2O2) used in Catalase Test for Staphylococci and Micrococci
3% H2O2
15% H2O2 used in anaerobes
30% H2O2 used in Mycobacterium and Neisseria
Why can’t we use colonies from BAP when performing Catalase Test?
BAP is positive for hemoglobin; hgb + H2O2 = bubbles (False positive)
Staphylococci are able to grow in what concentration of NaCl?
7.5-10% NaCl
Staphylococci are resistant in how many units of Bacitracin?
0.04 units
S. pyogenes is susceptible
Hemolytic pattern of Staphylococci on BAP
Beta-hemolytic
The most virulent species of staphylococci encountered
Staphylococcus aureus
General characteristics of Staphylococcus aureus
Most virulent
Normal flora of anterior nares and nasopharynx
Facultative anaerobe
Colony appearance of SAU in BAP
Creamy, white with pinhead colonies
Colony appearance of SAU in Tellurite agar/Vogel Johnson Medium
Jet-black colonies
Staphylococcus aureus is a true coagulase positive. True or False?
True
Appearance of SAU on solid media
Colonies are round, smooth, opaque and butyrous
Contain ribitol teichoic acid in cell wall
Teichoic Acid
Together with teichoic acid, it protects the bacteria from lysis and
probably aids in adherence
Peptidoglycan
Group specific antigen unique to S. aureus
Protein A
Prevents antibody-mediated phagocytosis by PMN—competes for the Fc portion
Protein A
Component on cell wall responsible for clumping of the whole
staphylococci in the presence of plasma
Clumping Factor
Protects SAU from phagocytosis
Capsular Polysaccharide
Coagulates fibrinogen in the plasma
Coagulase (Staphylocoagulase)
Promotes fibrin layer formation around the staphylococcal abscess protecting the bacteria from phagocytosis
Coagulase (Staphylocoagulase)
Two types of Coagulase (Staphylocoagulase)
Cell-bound Coagulase or Clumping Factor: bound to the cell wall and clots human, rabbit or pig plasma
Unbound or Free Coagulase: extracellular enzymes not bound to the cell wall and cause clot formation when bacterial cells are incubated with plasma
Hydrolyzes hyaluronic acid present in the intracellular ground substance, permitting the spread of infection
Hyaluronidase (Spreading Factor)
Hyaluronidase (Spreading Factor) is also known as
T Factor or DUran-Raynal Factor
Fibrinolytic activities by dissolving fibrin clot and may enable infection to spread once the clot is dissolved
Staphylokinase (Fibrinolysin)
Act on lipids present on the surface of the skin, particularly fats and oil
secreted by the sebaceous glands
Lipase (Fat-splitting Enzyme)
Important in the formation of furuncles, carbuncles and boils
Lipase (Fat-splitting Enzyme)
Lipase (Fat-splitting Enzyme) is produced by both coagulase (+) and coagulase (-) staphylococci. True or False?
True
Destroys DNA and lowers viscosity of exudates giving the pathogen more mobility
Deoxyribonuclease (DNAse) and Phosphatase
Deoxyribonuclease (DNAse) is also known as
Thermonuclease
Breaks down Penicillin and β-lactam drugs
β-Lactamase
Breaks down gelatin to produce an and-product amino acid
Gelatinase
Breaks down peptide bonds in proteins
Protease
Cytolytic toxins produced by SAU
Hemolysin
Leukocidins
4 types of hemolysin
α-Hemolysin
β-Hemolysin (Sphingomyelinase C)
δ-Hemolysin
γ-Hemolysin
Hemolysin that disrupts the smooth muscle in blood vessels and is toxic to erythrocytes, leukocytes, hepatocytes, and platelets
α-Hemolysin
Predominant hemolysin
α-Hemolysin
A heat-labile sphingomyelinase, which catalyzes the hydrolysis of membrane phospholipids resulting in cell lysis
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)
Hemolysin which is cytolytic to erythrocytes and demonstrates nonspecific membrane toxicity to other mammalian cells
δ-Hemolysin
Produced by all S. aureus strain that cause RBC injury in culture and produce edematous lesions
δ-Hemolysin
Hemolysin associated with Panton-Valentine leukocidin (PVL)
γ-Hemolysin
Exotoxin lethal to polymorphonuclear leukocytes
Staphylococcal Leukocidin/ Panton-Valentine leukocidin
Pore forming exotoxin that suppress phagocytosis and associated with severe cutaneous infections and necrotizing pneumonia
Staphylococcal Leukocidin/ Panton-Valentine leukocidin
Characteristics of SAU enterotoxins
- Heat-stable exotoxin at 100° C for 30 minutes
- Resistant to hydrolysis by gastric and jejunal enzymes
- Act as neurotoxins that stimulate vomiting through the vagus nerve
- Produced by 30% to 50% of S. aureus isolates
Toxic Shock Syndrome Toxin-1 (TSST-1) is also known as
Enterotoxin F
Pyrogenic Exotoxin C
TSS associated with tampon use
Menstruating-associated TSS
Serine protease that divides the intercellular bridges of the epidermis and causes excessive sloughing of the epidermis (stratum granulosum)
Exfoliative Toxin
Causes Staphylococcal scalded skin syndrome/Ritter’s disease
Exfoliative Toxin
Exfoliative Toxin is also known as
Epidermolytic toxin A and B or Exfoliatin serotypes A and B
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
Bullous Impetigo
