Micro - Clinical Bacteriology (Gram + Cocci) Flashcards
Pg. 128-129 Sections include: Staphylococcus aureus Staphylococcus epidermidis Streptocococcus pneumoniae Streptococcus bovis (group D streptococci) Streptococcus pyogenes (group A streptococci) Streptococcus agalactiae (group B streptococci) Enterococci (group D streptococci) Streptococcus bovis (group D streptococci)
When you see gram-positive cocci in clusters, what should you think?
Staphylococcus (and be particularly alert to possibility of S. aureus, which is the most important pathogen)
What is the main virulence factor of S. aureus, and how does it function?
PROTEIN A - binds Fc-IgG, inhibiting complement fixation and phagocytosis
What categories of disease does S. aureus cause? Where applicable, specify exotoxins involved.
(1) Inflammatory disease - skin infections, organ abscesses, pneumonia (2) Toxin-mediated disease - toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), & rapid-onset food poisoning (enterotoxins) (3) MRSA (methicillin-resistant S. aureus) = important cause of serious nosocomial and community-acquired infections
What is MRSA? What does it cause? What makes it so uniquely important?
Methicillin-resistant S. aureus; Important cause of serious nosocomial and community-acquired infections; Resistant to methicillin and nafcillin because of altered penicillin-binding protein
To what bacteria does TSST belong? What is TSST? How does it function?
S. aureus; Toxic shock syndrome toxin = superantigen; Binds to MHC II and T-cell receptor, resulting in polyclonal T-cell activation
What causes toxic shock syndrome? How does it present? What predisposes to toxic shock syndrome?
S. aureus’ TSST; Presents as fever, vomiting, rash, desquamation, shock, end-organ failure; Use of vaginal or nasal tampons predisposes to toxic shock syndrome
What causes S. aureus food poisoning? What is the incubation period? What relevance does cooking have in this disease, if any?
Ingestion of preformed toxin (enterotoxin) = short incubation period (2-6 hr). Enterotoxin is heat stable => not destroyed by cooking
What bacteria causes inflammatory disease (skin infections, organ abscesses, & pneumonia) and toxin-mediated disease (toxic shock syndrome, scalded skin syndrome, & rapid-onset food poisoning)? What other prominent diseases does it cause?
S. aureus; Acute bacterial endocarditis, Osteomyelitis
What does S. aureus make that distinguishes it from other Staphylococcus? What is the result of this production?
Bad staph (aureus) make coagulase and toxins. Coagulase = forms fibrin clot around self, which can lead to abscess (Note: It also forms toxins, but the coagulase is what is used in labs to identify S. aureus)
What is Staphylococcus epidermidis known to infect, and how?
Prosthetic devices and intravenous catheters, by producing adherent biofilms
What kind of contamination does S. epidermidis frequently cause, and why does this make sense?
Contaminates blood culture; S. epidermidis = component of normal skin flora
Of what diseases is Streptococcus pneumoniae that most common cause?
(1) Meningitis (2) Ottis Media (3) Pneumonia (4) Sinusitis; For, S. pneumoniae Think: “MOPS are Most OPtochin Sensitive”
What are the defining characteristics that identify S. pneumoniae on gram stain?
Lancet-shaped, gram-positive diplococci
What is S. pneumoniae’s main virulence factor?
IgA Protease
Does S. pneumoniae have a capsule? Why is this important?
Yes, it is encapsulated; No virulence without capsule
With what characteristic clinical presentation is pneumococcus associated? With what condition, and in what particular patient population is it commonly associated?
“Rusty” sputum, sepsis in sickle cell anemia &/or splenectomized patients (due to it being encapsulated)
Compare and contrast Viridans group streptococci with S. pneumoniae.
Both are alpha-hemolytic BUT S. pneumoniae is optochin sensitive and Viridans is optochin resistant
Where are Viridans group streptococci normally found?
Normal flora of oropharynx; Think: Viridans group strep live in the mouth because they are not afraid of-the-chin (op-to-chin resistant)
With what conditions/diseases are Viridans group streptococci associated? What are specific examples of bacteria in Viridans group streptococci that commonly cause each of this?
(1) Dental caries - Streptococcus mutans (2) Subacute bacterial endocarditis - S. sanguis
What kind of bacteria is S. sanguis? What disease does it cause, and how?
Viridans group streptococci (Gram + chains, alpha-hemolytic, optochin resistant); Subacute bacterial endocarditis - S. sanguis sticks to damaged valves by glycocalyx; Think: Sanguis = blood, There is lots of blood in the heart (endocarditis)
What is another name for group A Streptococci?
Streptococcus pyogenes
What categories of disease do S. pyogenes cause? What are examples of specific diseases within each category?
(1) PYOGENIC - pharyngitis, cellulitis, impetigo (2) TOXIGENIC - scarlet fever, toxic shock-like syndrome, necrotizing fasciitis (3) IMMUNOLOGIC - rheumatic fever, acute glomerulonephritis
Is S. pyogenes bacitracin resistant or sensitive? How could this be used to differentiate S. pyogenes from another kind of Strep?
Sensitive; Both Group A and Group B Strep are Beta-hemolytic, but Group A Strep is bacitracin sensitive and Group B Strep is bacitracin resistant
What bacteria causes rheumatic fever? What is the mechanism of disease?
S. pyogenes; Antibodies M protein enhance host defenses against S. pyogenes but can give rise to rheumatic fever
What detects recent S. pyogenes infection?
ASO (i.e., Antistreptolysin O) titer
What are the criteria for diagnosing rheumatic fever collectively called? What are the specific criteria?
JONES criteria; (1) Joints - polyarthritis (2) O (in shape of heart) - carditis (3) Nodules (subcutaneous) (4) Erythema marginatum (5) Sydenham’s chorea
What diseases can follow S. pyogenes pharyngitis?
(1) Rheumatic fever (2) Glomerulonephritis; Think: “PHaryngitis –> rheumatic PHever & glomerulonePHritis”
What is important to remember about impetigo versus pharyngitis in terms of subsequent diseases?
Impetigo more commonly precedes glomerulonephritis than pharyngitis
What signs/symptoms are seen in scarlet fever?
Scarlet rash with sandpaper-like texture, strawberry tongue, circumoral pallor
What is another name for group B streptococci?
Streptococcus agalactiae
Are S. agalactiae bacitracin sensitive or resistant?
Bacitracin resistant
What kind of hemolysis does S. agalactiae display on blood agar? Where in the human body does it colonize?
Beta-hemolytic; Vagina
What diseases does S. agalactiae cause? In what population does it mainly cause them?
Pneumonia, meningitis, & sepsis, mainly in babies; Think: “group B for Babies”
What is the role of CAMP factor as it relates to idenftification of S. agalactiae? What other lab test is positive for S. agalactiae?
S. agalactiae produces CAMP factor, which enlarges the area of hemolysis formed by S. aureus (Note: CAMP stands for the authors of the test, not cyclic AMP); Hippurate test positive
Who should be screened for S. agalactiae, and when? What should be done in cases of positive culture result?
Screen pregnant women at 35-37 weeks; Patients with positive culture receive intrapartum penicillin prophylaxis
What groups are included in Lancefield group D streptococci? What is the basis of Lancefield typing?
(1) Enterococci (2) Nonenterococci; Differences in the C carbohydrate on the bacterial cell wall
What are names of species of enterococci?
(1) E. faecalis (2) E. faecium
Where are enterococci normally found? What conditions/diseases do they cause?
Normal colonic flora; Think: “Entero = intestine, faecalis = feces”; (1) UTI (2) Biliary tract infections (3) Subacute endocarditis
To what antibiotic are enterococci classically resistant?
Penicillin G
What kind of hemolysis do enterococci display?
Variable (alpha or gamma hemolysis)
What kind of enterococci are an important cause of nosocomial infection?
Vancomycin-resistant enterococci
On what lab tested environments can enterococci grow?
(1) 6.5% NaCl (2) Bile
What kind of bacteria is Streptococcus bovis?
Group D streptococci (nonenterococcal)
Where is S. bovis normally found? What diseases can it cause, and in what patient population?
Colonizes the gut; Bacteremia & subacute endocarditis in colon cancer patients; Think: “Bovis in the Blood = Cancer in the Colon”
What is the clinical relevance of Staphylococcus saprophyticus? How is it distinguished from S. epidermidis?
Second most common cause of uncomplicated UTI in young women (first is E.coli). Novobiocin resistant.
