Bacteriology 7: Staphylococcus Flashcards
Morphology of staphylococcus
-S.aureus
-S.epidermidis
-S.saprophyticus
Gram (+) cocci and arrange in clusters
Some have capsules (inhibits phagocytosis)
-S.aureus often appear as yellow “golden” colonies in the mannitol salt test
-S.aureus is B-hemolytic
Physiology of staphylococcus
facultative anaerobe
Diagnosis of staphylococcus aureus
catalase test (common) and salt tolerance test are ways to distinguish staphylococci from streptococci
Mannitol-salt agar used for the isolation of Staphylococcus species, particularly Staphylococcus aureus. It is designed to select for salt-tolerant organisms and differentiate those capable of fermenting mannitol.
catalase test is used to identify organisms that produce the enzyme catalase, which breaks down **hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂).
Why is Staphylococcus aureus producing bubbles in the catalase test?
-the catalase test is used to identify organisms that produce the enzyme catalase, which breaks down hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen (O₂).
test to differentiate catalase-positive organisms, such as Staphylococci (e.g., Staphylococcus aureus), from catalase-negative organisms like Streptococci
-Immediate production of bubbles (O₂ gas), indicating the presence of catalase when H2O2 is added
-benefit = they can survive b/c they can convert toxic chemicals into O2
There are 2 tests to distinguish Staphylococcus aureus from other staphylococcal species
-the coagulase test
-mannitol salt fermentation
Mannitol-salt agar used for the isolation of Staphylococcus species, particularly Staphylococcus aureus. It is designed to select for salt-tolerant organisms and differentiate those capable of fermenting mannitol.
Staphylococcus epidemiology and what are they the common cause of?
Staphylococci are ubiquitous and all humans are colonized w/ CNS on the skin and mucosal surfaces.
S.aureus are common colonizer in the nares (nose). (CPS)
S.aureus and the CNS can be found in the oropharynx, skin, GI tract, GU tract.
Staphylococci are common causes of nosocomial infections in surgical and burn patients.
The most common CNS species is Staphylococcus epidermidis, which is part of the normal skin flora.
Diagnosis of Staphylococcus aureus
-growth
-fermentation
Specimen collection: Pus, purulent fluids, sputum, urine
Catalase test and MSA= (growth) to distinguish staphylococcus (+) from streptococcus (-)
Coagulase and MSA = (fermentation) to distinguish staphylococcus aureus (+) from other staphylococcus species
Latex agglutination: protein A from S.aureus binds to Fc fragment of IgG
Treatment for staphylococcus aureus
-MRSA
-non-MRSA
MRSA and non-MRSA strains refer to two categories of Staphylococcus aureus bacteria, distinguished by their susceptibility or resistance to certain antibiotics, specifically methicillin which are beta-lactam antibiotics.
Antibiotics
MRSA (penicillin):
A. erythromycin = macrolides = 50S
B. 5th gen cephalopsorins
C. I.V. Vancomycin (serious infections) = inhibit PG’S synthesis
Non-MRSA strains:
A. Beta-lactamase-resistant penicillin
B. Pen G = intramuscular = natural pen’s
C. 1st gen cephalopsorins
Staphylococcus aureus Virulence factors
-alpha-toxin
Alpha-toxin is secreted by most strains of S.aureus
Pore-forming toxin that affects RBC’s and more leukocytes (Not neutrophils) causing lysis
Alpha-toxin lyses red blood cells (hemolysis), which can be observed in blood agar as a zone of beta-hemolysis (clear area around S. aureus colonies).
b/c of this alpha-toxin that S.aureus as a virulence factor they are Beta-hemolytic
Staphylococcus aureus Virulence factors
-toxic shock syndrome toxin-1 (TSST-1)
-clinical manifestations
Staphylococcus aureus toxic shock syndrome toxin-1 (TSST-1) is a superantigen produced by certain strains of S. aureus. It is responsible for causing toxic shock syndrome (TSS), a severe and life-threatening condition characterized by high fever, rash, desquamation of the skin (palms and soles), low blood pressure (hypotension), multi-organ failure (w/n 48hrs), and shock.
bacteria remain local while the toxin enters the bloodstream and becomes systemic
-super antigen that causes capillary leakage and hypotension
-produced by 15% of S.aureus strains
Superantigen Activity: TSST-1 acts as a superantigen, meaning it bypasses the normal antigen processing and presentation pathways.
It binds directly to MHC class II molecules on antigen-presenting cells (APCs) and simultaneously to T-cell receptors (TCRs).
This cross-linking results in the non-specific activation of a large number of T-cells, leading to the release of massive amounts of cytokines, a phenomenon called a cytokine storm.
Toxic shock syndrome (TSS) epidemiology
Use of highly absorbent tampons
Nasal surgery patients
Skin wounds
Postpartum wound infections
Staphylococcus aureus toxic shock syndrome toxin-1 (TSST-1) is a superantigen produced by certain strains of S. aureus. It is responsible for causing toxic shock syndrome (TSS),
Toxic shock syndrome (TSS)
Treatment
MSSA: clindamycin + nafcillin
MRSA: vancomycin
Supportive care
Staphylococcus aureus Virulence factors
-exfoliative toxin
-clinical manifestations
Staphylococcus aureus Exfoliative toxin is a virulence factor produced by certain strains of S. aureus. It is primarily responsible for staphylococcal scalded skin syndrome (SSSS), a condition characterized by widespread skin damage and peeling, resembling scalded skin (separation/desquamation of the epidermis)
This toxin is produced by 5% of S.aureus strains
staphylococcal scalded skin syndrome (SSSS) mechanism of action and caused by?
Caused by staphylococcus aureus exfoliative toxin (superantigen)
Mechanism of Action:
Targeting Desmosomes: Exfoliative toxins specifically target desmoglein-1 (Dsg-1), a linker protein found in desmosomes. Desmosomes are structures that hold epithelial cells together, providing skin integrity.
Cleavage of Desmoglein-1: By cleaving desmoglein-1, exfoliative toxins disrupt the connection between skin cells (keratinocytes) in the upper epidermis.
Skin Separation: The breakdown of cell-cell adhesion causes the skin to separate at the epidermal level, resulting in the characteristic skin peeling and blister formation seen in staphylococcal scalded skin syndrome. induces desquamation
staphylococcal scalded skin syndrome (SSSS)
Clinical manifestations and cause by
S.aureus exfoliative toxin (superantigen)
(SSSS) a condition characterized by widespread skin damage and peeling, resembling scalded skin (separation/desquamation of the upper epidermis)
-no scaring- body can restore epidermis and the affected skin peels off
-large blisters with clear fluid
-most common in infants
