1-22 Intracellular Bacteria Flashcards
What are the major intracellular bacterial pathogens?
Think “Mademoiselle Arcy’s Five”: MLLE RCCSFIV
- Mycobacteria
- Listeria
- Legionella
- Enterobacteriaceae
- Ricksettial
- Chlamydia
- Cocci
- SFI: systemic fungal infections
- Viruses
Which of the major intracellular bacterial pathogens are obligate-intracellular?
Think “Arcy”: ricksettial and chlamydia.
What is the difference between obligate and factultative intracellular parasites with regard to laboratory diagnosis of infection?
Obligate intracellular parasites can ONLY reproduce within host cells, so they must be provided with host cells to grow in vitro. These plates will be a distinctive pinky-red.
Facultative intracellular parasites can reproduce independently with the right nutrients and do not require host cells, so they can be grown on agar plates or in liquid media. Some, however, like Legionella, may be fastidious.
What are the three major pathways by which intracellular pathogens can survive endocytosis?
- Escape from endosome to replicate in the cytoplasm. Most common.
- Subvert the endosome; prevent it from fusing with the lysosome and hijack it as a growth compartment. Also common.
- Survive endolysosomal fusion by encoding virulence factors that neutralize the acidic lysosomal pH and inactivate lysosomal hydrolytic enzymes. Very rare.
What are the five recurring themes in bacterial intracellular pathogenesis?
- “Trojan Horse”
- Type 3 secretion system
- “Actin rocket”
- Evasion of humoral immune system and surface defenses
- Effective antibiotic treatment for intracellular bacteria requires drugs that can penetrate the human cell membrane
What is the “Trojan Horse” pattern in intracellular pathogenesis?
The use of infected macrophages for transport through the bloodstream/lymphatics to establish additional sites of infection.
- Enterobacteraceae: typhoid fever
- Mycobacteria: extrapulmonary Tb
- Fungi: systemic Histoplasmosis
What is the type 3 secretion system pattern in intracellular pathogenesis?
A variation on hijacking the endosome. Bacteria enhance phagocytosis, then alter the resulting endosome so that lysosomal fusion fails and they can use the endosome as a growth compartment.
- Enterobacteriaceae
- Legionella
- Mycobacter
What is the “actin rocket model” of intracellular pathogenesis?
A variation on escape of the endosome. These bacteria generate an actin “tail” that floats freely behind them in the cytoplasm and eventually can propel them through the cell membrane into the next cell. Virulence factors for these bacteria have names like “ActA.”
- Listeria
- Shigella
What is the pattern of intracellular pathogenesis by which bacteria evade the humoral immune system and surface defenses?
Some bacteria that are especially vulnerable to complement or which produce a lot of surface antigens find it necessary to seek refuge underneath the membrane of a neighboring cell. They can also use actin-based cell-cell spread to infect new cells without exposure to humoral immunity.
- Enterobacteriaceae: use M cells as gateway to exterior intestinal surface, work around colonization resistance and lumenal tight junctions
What is typical of effective antibiotic treatment for intracellular pathogens in the body?
The necessity for drugs that can penetrate the human cell membrane, such as tetracyclines (contraindicated in pregnancy!), azithromycin, and chloramphenicol.
- Ricksettial
- Legionella
- Chlamydia
What is the bacteriology of Listeria monocytogenes?
- Small Gram(+) rod
- Forms Ls and Vs
- Tumbling motility
- β-hemolytic
- Grows well in cold
- Found environmentally: animals, plants, soil
What is the pathogenesis of Listeria monocytogenes?
- Contacts humans through unpasteurized dairy products, undercooked meat, raw vegetables, contact with livestock/manure
- Primarily infects fetus across placenta, newborn during delivery, pregnant women, immunocompromised adults
- Prefers to grow intracellularly; listeriolysin bursts phagosome, allowing bacteria to escape into the cytosol
- Can use actin rocket model
What is the bacteriology of Chlamydia trachomatis?
- Unique life cycle
- Dense, rugged elementary bodies (EBs) attach to cell, survive endocytosis, and “unpack” into RBs
- Larger, delicate reticulate bodies (RBs) replicate, metabolize, “pack” into EBs, and escape the host cell
- Only EBs are infectious; only RBs divide
- RBs require ATP from host
What is the pathogenesis of urogenital chlamydia?
- Can spread sexually or infect newborns at birth
- Often asymptomatic
- Most common STD in U.S.
- Reinfection after antibiotic treatment is common, so treat both partners
