Bloodstream Infections Flashcards
What is bacteremia vs septicemia?
Bacteremia - Viable bacteria in blood as seen by culture
Septicemia - Bacteremia with signs of multiplication
What facilitates decompensation during septic shock?
Bacterial endotoxins cause:
- Systemic coagulation pathways -> disseminated intravascular coagulation
- Complement activation
- Inappropriate cytokines
- Adult Respiratory Distress Syndrome
What are virulence factors used by Viridans Streptococci to cause blood stream infections?
- Adhesins
2. Fibronectin-binding protein
When do Viridians streptococci enter the bloodstream? How are they identified in the lab?
Normal inhabit the oral cavity, enter during dental procedure or periodontal disease
Lab: No specific cell wall antigens, identified using biochemical tests
What types of heart valves do Viridians streptococci colonize?
Ones with fibrin-platelet vegetations, including congenital heart defect, rheumatic fever, prosthetic valve, or atherosclerotic heart disease
What is the primary virulence factor of Group D Streptococcus / Enterococcus?
Multiple, high-level resistances to a wide variety of antibiotics
Includes VRE
Where do GDS and enterococcus normally live and how are they introduced? How are they identified?
In the intestine or vagina, introduced into bloodstream via surgical procedures, frequent nosocomial infection
Identified as gram + cocci, with Group D antigen
What two fungi can cause endocarditis, especially among immunosuppressed?
- Candida - IV drug users
2. Aspergillus - environmental mold
How is Aspergillus identified in culture?
Branched, septate hyphae (mold form). Blood cultures will be negative, biopsy of infected tissue is necessary (unlike Candida).
What are the four forms of malaria and which is most virulent?
- P. falciparum - most virulent
- P. malariae
- P. vivax
- P. ovale
What is the life cycle of malaria in the human host?
- Sporozoites injected by female Anopheles mosquito into human host
- Parasites travel to liver, form schizonts (dividing merozoite vesicles) in the liver
- Merozoites are released from ruptured liver cells, with P. falciparum being the most
- Merozoites invade RBCs, digest hemoglobin to form trophozoite, schizont, and again merozoites are released
- Gametocytes will differentiate during some cycles to be taken up by mosquitos
What malaria strains can go through hypnozoite stage?
P. vivax and P. ovale can lay dormant in the liver for many years to come and release more parasites from schizonts in liver cells
What is the receptor for P. vivax and P. falciparum on RBCs?
P. vivax - Duffy antigen
P. falciparum - Glycophorin A
Why are P. falciparum adhesions problematic?
- Used to help RBCs adhere (via ICAM-1) to vascular wall to prevent splenic clearance and peripheral detection
Problematic because they can cause occlusion of small vessels (brain aneurysms) - cerebral malaria
What is the mechanism of malaria antigen variation?
- Hypervariability of surface proteins in the schizont stage
- Recombination during sexual reproduction
Why does fever occur in malaria?
When merozoites leaves RBCs in the bloodstream, the released metabolites including hemozoin (broken down heme crystals) are antigenic / pyrogenic, causing IL-1 / TNFa release
Can lead to hypotension / shock
How do bouts of fever become sporadic then cyclical?
Parasite begins to time release of merozoites to invade immune response.
Some species have tertian (48 hour) and quartan (72 hour) cycles
What is the major complication of all malaria?
Anemia
What is Blackwater fever?
Black urine, caused by massive intravascular hemolysis and subsequent hemoglobinuria in malaria
What are a few resistance mechanisms to malaria?
- Lack of Duffy RBC antigen - no P. vivax infection
- Sickle cell -> prevents parasite from using actin to form cell-surface adhesion, and increases splenic clearance this way
- Glucose-6-phosphate dehydrogenase deficiency -> increase free radical killing of parasite
What is ultimately needed to clear the malaria infection? What had the longest infection?
Cell-mediate immunity / intracellular killing mechanisms to kill schizonts, and antibody to bloodstream stages (merozoite, sporozoite)
Natural cure once adequate antibody response, with P. vivax & P. ovale relapsing over 5 year periods.
P. malariae is most persistant (53 year infection)
What is used for malaria prophylaxis?
Atovaquone / Proguanil = Malarone
What are the definitive and intermediate hosts of Babesia microti?
Definitive - Ticks (same tick transmitting Lyme disease, Ixodes)
Intermediate - humans
What are the symptoms of babesiosis? How does it resolve?
Fever, not periodic
Myalgia, anemia, hepatosplenomegaly, renal dysfunction
Resolves spontaneously within a few week
