Microbiology Cases for Midterm Flashcards
What is the significance of M protein?
Protein that is harmful in untreated streptococcal pharyngitis.
- Patients can develop a cross-reactive antibody against heart tissue (meromyosin).
- Glomerulonephritis of IE –> can come from pharyngitis or skin infections
What is a typical course of untreated Rheumatic Heart Disease?
- Exposure to group A streptococcus
- Group A streptococcal upper respiratory tract infection
- Acute rheumatic fever (flu-like)
- Recurrent acute rheumatic fever
- Rheumatic heart disease (RHD)
- Can lead to heart failure or stroke endocarditis –> surgery/disability/death
What are the vascular phenomena classified by the Duke Criteria?
- Arterial emboli
- Janeway lesions
- -Usually non-tender, small hemorrhagic lesions on palms and soles
- -Last days to weeks
- -Commonly seen in acute IE
- -Histology consistent with septic micro-emboli (bacteria in lesion)
What are the immunological phenomena classified by the Duke Criteria?
- Rheumatoid factor
- Roth’s spots
- Osler’s nodes
What is rheumatoid factor?
- Antibody that can bind the constant region of IgG.
- Antibody against antibody that leads to immune complexes, deposition, inflamed joints, etc.
- Antibody against antibody–binds Fc portion of IgG antibody
What are osler’s nodes?
- Red-purple, tender, slightly raised lumps with pale center on pads of fingers and toes
- Pain precedes development of lesion (~24 hrs)
- Stays for hours-days
- Can occur at any time with endocarditis
- Immunological cause (inflam.) but bacteria also isolated from lesions (early on)
- Type II hypersensitivity!! (cytotoxic- antibody mediated)
What is an example of Type II hypersensitivity?
RHD - antibodies bind to M protein on the tissue but then start to confuse the M protein for meromyosin in the heart tissue. Then the antibodies start attacking meromyosin.
What are the three mechanisms of Type II hypersensitivity?
- Opsonization and phagocytosis
- Complement-and Fc receptor-mediated inflammation
- Antibody-mediated cellular dysfunction
What happens in Type II hypersensitivity?
Cytotoxic - IgM and IgG bind to fixed antigen on “enemy” cell –> cellular destruction
What are examples of Type III hypersensitivity?
Roths spots
Osler nodes
What is type III hypersensitivity?
Immune complexes - antigen-antibody (IgG) complexes activate complement, which attracts neutrophils, neutrophils release lysosomal enzymes
(antigen-antibody-complement)
What infections lead to hemolytic anemia?
CMV EBV Malaria Hepatitis Streptococcal infections Typhoid fever etc.
How can you get anemia in acute and subacute endocarditis?
Clots on the heart disrupt and destroy RBCs passing through.
-Probably causes spherocytes
What are the most important virulence factors in CV disease?
Factors used for attachment!
Being able to establish infection on heart tissue is KEY.
What are 2nd most important virulence factors in CV disease?
Factors involved in invasion and multiplication
What VF are associated with Streptococcus species (viridians)?
- Dextran production/glycocalyx formation
- Surface adhesion proteins (FimA, GspB)
- these help it adhere to valve and colonize
What VF are associated with Streptococcus pneumoniae?
Capsule
-Helps it evade host defenses and neutralize the ability of antibodies to attach to bacteria
What VF are associated with Streptococcus pyogenes?
Capsule
-Helps it evade host defenses and neutralize the ability of antibodies to attach to bacteria
M Protein
What VF are associated with Neisseria meningitidis?
Capsule
-Helps it evade host defenses and neutralize the ability of antibodies to attach to bacteria
What VF is associated with Enterococcus species?
Biofilm formation (various proteins)
What VF are associated with Staph. aureus?
- Capsule
- Biofilm formation (various proteins)
- Elastin, Collagen, & Fibronectin (FnbpA) binding proteins*
- Coagulase
- Leukocidin
What VF are associated with Staph. epidermis?
- SD-repeat containing protein-G (SdrG)*
- Biofilm formation (various proteins)
What virulence factors are associated with Coxsackie A, Coxsackie B and Adenovirus?
Coxsackie-Adenovirus cellular receptor (CAR) binding proteins
What is the significance of CAR binding proteins?
They are cellular receptors that allow COXA, COXB, and adenovirus to bind directly to heart tissue!
What VF are associated with Rickettsia rickettsia?
- OmpA and OmpB (attachment)
- Type 4 Secretion System (T4SS) (host cell entry)
What is the T4SS?
Type 4 Secretion System:
- Look like needle in syringe
- Helps it to deposit stuff into the cell
- Can induce the cell to do something for it
- Once Rickettsia binds to a cell it injects molecules that tricks the host cell into engulfing it
- Then it can infect the host cell
What type of pathogen is Rickettsia?
Obligate intracellular pathogen that requires host cell machinery!
What is the name for the wide variety of attachment proteins used by strep and staph to form infections?
MSCRAMMs:
Microbial Surface Components Recognizing adhesive matrix molecules
What is likely sufficient to diagnose RMSF?
Clinical diagnosis - classic triad: fever, headache, rash
How to diagnose RMSF with tests?
- Indirect immunological assay (fluorescence/agglutination)
- Skin biopsy
- PCR for R. Rickettsii DNA
What is used to treat RMSF?
Doxycycline
What can you use to diagnose Coxsackievirus A or B or Echovirus infection?
RT-PCR
How do you treat a viral pericarditis?
Give supportive treatment
Fever 104F Chills Severe headache Muscle aches Pulse = 110 bpm Resp. Rate = 28 bpm BP = 100/60 mmHg Rash - palms and soles, extremities What does he have? How to confirm?
RIckettsia Rickettsii - RMSF -Indirect immunological assay -Skin biopsy -PCR for RR DNA Clinical diagnosis: classic triad
What infectious microorganisms cause rash on palms of hands and soles of feat?
- Syphyllus
- Rickettsia Rickettsii
- Coxsackie Viruses
- T. pallidum
-102.2F
-11 yr old
-Joint pain, swelling
-SOB upon exertion & laying down
-Sore throat improved with penicillin G four weeks ago
-HR: 160 bpm
-RR: 32 bpm
-BP: 100/60 mmHg
-O2: 94%
-Holosystolic murmur 3/6 heard at apex with radiation to axilla
-Cardiomegaly on X-ray
-EKG = prolonged PR interval
What does he have? What organism caused it?
Rheumatic fever
Streptococcus pyogenes
What will follow a rheumatic fever infection in genetically predisposed individuals?
RHD - Type II hypersensitivity with M protein
-Summer!
-Severe chest pain
-Arrhythmias
-104F
-Extreme fatigue
What inf. agents? What does he have?
Coxsackievirus A or B, Echovirus, Pericarditis
How do infectious agents reach the heart?
- Oral cavity
- Skin
- Upper respiratory tract
Why does endocardium become enflamed in endocarditis?
Immune response to the valve colonization
