Chapter 11 - Intravascular Infection Flashcards
(27 cards)
Definition of Endocarditis
- Inflammation or infection of the endocardium, which is the inner lining of the heart muscle and most commonly the heart valves.
- Infective endocarditis (IE) denotes infection of the endocardial surface of the heart and implies the physical presence of microorganisms in the lesion.
- Although the heart valves are affected most commonly, the disease also may occur within septal defects or on the mural endocardium.
- Infection of intravascular devices: pacemakers, central vein catheters. The introduction of pacemakers is an invasive procedure that leads to nosocomial infections, which are extremely dangerous since the patient’s immune system is already compromised and becomes prone to infections by pathogens that have serious virulence properties due to exchanges that occur in the hospital.
Clinical Manifestations of Endocarditis
- Osler nodes: painful, red, raised lesions found on the hands and feet, caused by immune complex deposition.
- Janeway lesion: a few mm of non-tender, small erythematous hemorrhagic macular or nodular lesions on the palms or soles.
- Roth spots: retinal hemorrhages with white or pale centers composed of coagulated fibrin.
- Splinter hemorrhages.
Name of the Criteria for Endocarditis Diagnosis and Requirements for Definite Diagnosis
DUKE CRITERIA
Major:
* Blood cultures positive (more than 1)
* Evidence of endocardial involvement through Serology/PCR or Echocardiography
Minor:
* Predisposing factor
* T > 38C
* Vascular phenomena
* Immunologic phenomena
* Microbiologic evidence
Requirements:
* 2 major
* 1 major 3 minor
* 5 minor
PVE and PMIE
- The risk of infection for infection of prosthetic valve endocarditis (PVE) is the same for mechanical of biologic valves, with the highest risk within 6 months of the operation.
- In the first month the infection is often nosocomial bacteria like S. aureus or in late PVE (more than 1 year) due to streptococci.
- The treatment consists of 4-6 weeks including an empirical treatment of Vancomycin and aminoglycoside, and the possibility of surgery to remove the infected material.
- The pacemaker infection endocarditis (PMIE) have the same etiology of PVE
.
Staphylococci Identification
Coagulase-negative Staphylococci:
* Normal commensals of the skin, anterior nares, and ear canals of humans.
* They were rarely the cause of significant infections in the past, but emerged as important agents of nosocomial infections with the increasing use of implanted catheters and prosthetic devices.
* Immunosuppressed or neutropenic patients and premature infants have been particularly affected.
Staphylococci Culture Media
Enriched media containing broth and/or blood
Properties of Staphylococcus Epidermis
- Present in large numbers as part of the normal flora of the skin. As such, frequently recovered from blood cultures act generally as contaminant from the skin.
- Despite its low virulence, a common cause of infection of implants (such as heart valves and catheters).
Pathogenesis of Staphylococcus Epidermis
- It produces an extracellular polysaccharide material, a polysaccharide intercellular adhesin called slime or biofilm, facilitating adherence to bioprosthetic material surfaces and is an important virulence factor acting as a barrier to antimicrobial agents, protecting bacteria.
- The production of a biofilm is depicted as a 5-stage process:
1. Initial attachment of cells to surface.
2. Production of the extracellular exopolysaccharide matrix.
3. Early development of biofilm architecture.
4. Maturation of biofilm architecture.
5. Dispersion of bacterial cells from the biofilm. - Chemotaxis leads to a multispecies biofilm; for example, normal flora in teeth could attract other virulent species, leading to infections.
Properties of Staphylococcus Saprophyticus
part of the normal vaginal flora and frequent cause of cystitis (UTI – inflammation of the bladder) in women.
Laboratory Identification of Staphylococcus Aureus
Common, coagulase+, yellow/golden colonies, novobiocin sensitivity
Laboratory Identification of Staphylococcus Saprophyticus
Occasional, coagulase-, variable colored colonies, novobiocin resistance
Laboratory Identification of Staphylococcus Epidermis
Common, coagulase-, white colonies, novobiocin sensitivity
Properties of Leptospira Interrogans
they can survive for several weeks in stagnant water, but are sensitive to heat and highly sensitive to a wide range of disinfectants.
Patogenesis of Leptospira Interrogans
- A number of wild and domestic animals serve as reservoirs, as Leptospirosis is essentially an animal disease.
- It is coincidentally transmitted to humans by water or food contaminated with animal urine, via small skin abrasions, or via the conjunctiva.
Clinical Significance of Leptospira Interrogans
- Fever occurs 1 to 2 weeks after infection, at which time spirochetes (Leptospira with spiral shape) appear in the blood. Symptoms then decrease after about 1 week.
- In cases of biphasic disease, spirochetes reappear, accompanied by invasion of the liver, kidneys and CNS. This results in jaundice, hemorrhage, tissue necrosis or aseptic meningitis; this stage lasting 3 or more weeks.
- In severe cases, mortality can be as high as 10%.
Laboratory Identification of Leptospira Interrogans
- Primarily serologic.
- Standard test is limited to reference laboratories.
- Organisms can be isolated (from the blood, CSF, or urine) but culture is rarely attempted because the organisms take week to grow in a special medium that few laboratories bother to stock.
What does HACEK stand for?
- Haemophilus species
- Actinobacillus actinomycetemcomitans
- Cardiobacterium hominis
- Eikenella corrodens
- Kingella species
Characteristics of HACEK Group
Organisms found as part of the normal human oral flora with an enhanced capacity to produce endocardial infections (infective endocarditis). Complications may include massive arterial emboli and congestive heart failure.
Other Infections of HACEK Group
- Periodontal infections
- Bacteremia
- Abscesses
- Peritonitis
- Otitis media
- Conjunctivitis
- Pneumonia
- Septic arthritis
- Osteomyelitis
- UTI
- Wound infections
- Brain abscess
Haemophila Characteristics
Pleomorphic, non-motile, Gram-, facultative anaerobes, oxidase+, obligate parasite, requiring factor X (hemin) and/or V (NAD+) for growth, chocolate agar containing hemin and NAD+
Actinobacillus actinomycetemcomitans
Currently known as Aggregatibacter actinomycetemcomintans, it was first isolated in 1912 from skin lesions. It is the etiologic agent of localized juvenile periodontitis, one manifestation of early-onset periodontitis. Growth occurs in trypticase soy broth (TSB), where it forms granules that float on top.
Eikenella corrodens
- It takes its name from its ability to corrode (or pit) the agar during growth; Gram- pleomorphic, often coccobacillary, rod exuding a chlorine bleach odor.
- It is part of the oral flora and many other mucosal surfaces and is facultatively anaerobic.
- It is a well-recognized cause of cellulitis resulting from human bites and clenched-fist injuries. It is also found to be a common cause of soft-tissue infections and endocarditis in intravenous drug users.
- These infections are often complicated by osteomyelitis of the underlying bone.
Define Plasmodium
Clinically relevant protozoa, classified according to site of infection.
Properties of Plasmodium
Sexual & asexual cycles of reproduction are completed in ≠ host species:
i. Sexual phase: gametocytes motile zygote = ookinete oocyste (gut of
mosquitoes).
ii. Asexual phase: oocyste sporozoites (mosquitoes: body cavity to salivary
glands; to humans).
iii. Then, sporozoites merozoites (liver); merozoites trophozoites
(erythrocytes).
iv. Parasites eventually burst from the erythrocyte & invade other uninvolved RBCs.
Causes malaria in the host, characterized by periodic fever & anemia.
