Staphylococcus Flashcards
How does staphylococci gram stian?
Gram Positive
Cocci in grape like clusters
What are the general characteristics of staphylococci?
Non-motile
Non Spore Forming
Catalase Positive
Facultative Anaerobes (except: S.Anaerobius and Saccharolyticus)
What are the important species of staphylococci?
S. Aureus
S. Epidermidis
S.Saprophyticus
S.Lugdunensis
What are some characteristics of S.Aureus when grown on agar plates?
Off-white cream color
Zone of B-hemolysis
Where are S.Aureus found?
Environment
SKin/Mucous membranes (Especially anterior nares)
What can predispose to S.Aureus infections?
Leukocyte Chemotaxis defects Opsonization defects Acquired Hypogammaglobulinemia Complement defect Defective intracellular killing of bacteria (Inability to activate membrane bound oxidase system) Skin Injuries (Burns, incisions, sports injuries) Presence of foreign bodies Viral infections Chronic Underlying Diseases
Where are the usual sites of infections for S.Aureus?
Skin: Impetigo, Furuncles, Carbuncles, Post Surgical wound infections
Nose and Throat
GI Tract
Urethra/Vagina
What is pyoderma and what causes it?
Pyogenic skin disease caused by infections (ex: S.Aureus), or autoimmune (ex: pyoderma gangrenosum)
What are furuncles?
Boils on skin caused by infeciton of hair follicles leading to localized accumulation of pus and dead tissue with white head in center of lump later
What are carbuncles?
Abscess larger than a boil with one or more openings that drain pus onto skin
Most common on back and nape of neck
What are the toxin mediated infections caused by S.Aureus?
Scalded Skin Syndrome: neonates and children
What can happen when S.Aureus disseminates in blood?
Pneumonia Bacteremia Endocarditis Osteomyelitis Septic Arthritis Septic Embolization Metastatic Infections
What are the virulence factors of S.Aureus that interfere with phagocytosis? What do they do?
Capsules:prevent ingestion by PMNs
Protein A: binds Fc region of IgG -> prevent opsonizaiton and ingestion by PMNs
PVL: enzyme that alters cation permeability of leukocytes-> WBC destruction
Coagulase: binds prothrombin-> catalyze fibrinogen to fibrin -> coat bacterial cells wiht fibrin -> resistance to opsonization and phagocytosis
What are virulence factors causing hemolysis?
a-hemolysin: lyse RBCS and leukocyte toxicity
B-hemolysin: shows clearning around colony on agar plate due to killing of RBCs (Seen with S.Aureus)
d-hemolysin: Surfactant that disrupts cell membrane and forms channels to leak cellular contents
y-hemolysin: lysis of cells
What are Exofliatins?
Epidermolytic toxins that cause staphylococcal scalded skin syndrome
Dissolves mucopolysachardie matrix of epidermis -> separation of skin layers
Mostly neonates and children
What are enterotoxins?
Causes staphylococcal food poisoning
Toxins produced causes sickness within 2-8 hours => most likely staph aureus
Resolution within 24-48 horus
What are the enzymatic virulence factors of S.Aureus?
Fibrinolysins: break down fibrin clots -> infection to tissues
Hyaluronidase: hdyrolyze matrix of mucopolysaccharides-> promote spread
PLC: Make tissue more susceptible to damage and destruction by complement components
What are superantigens?
Pyogenic Toxin superantigens that induce polyclonal T cell proliferation and are pyrogenic
What are the superantigen virulence factors?
TSST-1 (S.Aureus)
SPE (Streptococcal pyrogenic exotoxins)
Streptococcal superantigens
What does it mean in a lab if a bacteria strain with serum and plasma causes clots?
Coagulase + (Improtnatn for determining S.Aureus)
What is the latex agglutination test?
Alternative Coagulase test
Fibrinogen bound to latex to detect clumping factor
Smooth suspension: coag neg
Clumping: Coag pos
What is staph epidermidis?
Coagulase Negative
Novobiocin Sensitive
Associated with infections of indwelling devices
Biofilm production and adherence to surfaces of foreign bodies
What are the characteristics of Staph Saprophyticus?
Cause of acute UTI infection in sexually active young woemn
2nd most common cause of uncomplicated cystitis in child bearing age women
Coagulase Negative
Novobiocin Resistant
What are hte unique characteristics of Staph Lugdunensis?
Similar disease problems of S.Aureus
PYR and Ornithine positive
Coagulase Neg
Who gets staph/MRSA most often?
Patient si hospitals or healthcare facilities iwth weakened immune systems
What are the most important reservoirs of MRSA in hospitals?
Colonized/Infected patients
How do hospital personnel play a role in MRSA transmission?
Serve as a link for transmission between colonized/infected patients
What are community acquired MRSA?
MRSA infections acquired by people who have not been recently hospitalized or had an invasive medical procedure
What is the mecA gene?
Encodes for ALTERED PBP2a
How does mecA play a role wiht MRSA?
altered PBP2a -> decreased binding affinity for B-lactam abx -> allows peptidoglycan synthesis even with abx
S.Aureus wiht mecA gene -> resistance to B-lactam drugs like Penicillin
What are SSTI?
Skin and soft tissue infections
When shoudl MRSA be considered in the differential diagnosis?
Sepsis Osteomyelitis Necrotizing Pneumonia/Fascitis Septic Arthritis SSTI
What can be done to control MRSA?
Hand hygiene for all patient interactions Standard contact/droplet precautions Effective cleaning of patient rooms Clean equipment Appropriate use of abx
How do we screen for MRSA?
Screen everyone on admission via swab on both nostrils on anterior nares -> LAB (Culture, RT-PCR)
What is the most important reservoir of MRSA in hospitals?
A.Colonized or infected pts
B. Colonized or infected medical staff
C. Clothing worn by patient care personnel
D.Child visitors who attend day care centers
E. Medical Equipment
A
An organism identified as gram-positive cocci in
clusters is isolated from the urine of a 21 year
female with symptoms of acute cystitis. The
laboratory reports that the organism is coagulasenegative,
furozolidone susceptible and novobiocin
resistant. What is the most likely identification of
this bacterium?
A Staphylococcus aureus
B Staphylococcus epidermidis
C Staphylococcus lugdunensis
D Staphylococcus pyogenes
E Staphylococcus saprophyticus
E
