Intracellular bacteria Flashcards
Major intracellular pathogens
- Cocci: Neisseria
- Enterics: Shigella, E.coli, Salmonella, Yersinia
- Mycobacter
- Rickettsial: Rickettsia, Ehrlichia, Anaplasma, C. burnetti
- Listeria
- Some Bacilli (B. anthracis)
- Legionella
- Chlamydia
- Some fungal infections
- Viruses
Obligate intracellular parasites
- Can only reproduce within host cells
- Must be provided with host cells to grow in vitro
- Rickettsial
- Chlamydia
- Viruses
Facultative intracellular parasites
- Can replicate independently when they have the right nutrients
- May be fastidious but can grow on agar plates
- Cocci
- Enterics
- Mycobacteria
- Bacilli
- Listeria
- Legionella
- Fungi
Three methods of establishing infection
- Most common: escape the endosome, replicate in the cytoplasm
- Also common: subvert the endosome, prevent it from fusing with the lysosome and use it as a growth compartment
- Rare: survive endolysosomal fusion, encode virulence factors for neutralizing the acidic lysosomal pH and inactivating the lysosomal hydrolytic enzymes
Recurring themes in bacterial intracellular pathogenesis
- Use of infected macrophage for transport to target site of infection
- Type 3 secretion systems
- Actin-based motility and cell-cell spread
- Intracellular lifestyle evades humoral immune system
- Effective antibiotic treatment for bacteria that are primarily intracellular in the body requires drugs that can penetrate the host cell membrane (not just circulate in the blood)
Examples of use of infected macrophage for transport to target site of infection
- Enterics: typhoid fever
- Mycobacter: Tb
- Fungi: Histoplasma
Examples of type 3 secretion systems
- Enterics, legionella, mycobacter
- Enhance phagocytosis by target cell type
- Alter endosome so that lysosomal fusion fails
Actin-based motility and cell-cell spread examples
- Listeria, shigella
- Virulence factors with names like ActA
- Generate an actin “tail” behind bacteria free in the cytoplasm
- Bacteria can eventually ram through cell membrane into next cell
Intracellular lifestyle evades humoral immune system examples
- Enterics: use of M cells as gateway to exterior surface of intestine, works around colonization resistance and tight junctions on interior surface
- Actin based cell-cell spread allows infection of new cells without exposure to humoral immunity
- CMI required to clear infection (like viruses)
Effective antibiotic treatment for bacteria that are primarily intracellular in the body require drugs that can penetrate the host cell membrane examples
- Rickettsial, legionella, chlamydia
- Doxycycline, tetracycline
Listeria monocytogenes bacteriology
- Small gram + rod
- Forms Ls and Vs
- Tumbling motility
- Beta-hemolytic
- Grows well in cold
- Environmental
Listeria monocytogenes pathogenesis
- Human contact through unpasteurized dairy, undercooked meat, raw veggies, contact with livestock and manure
- Primarily infects: fetus across placenta, newborn during delivery, pregnant women, immunocompromised adults
- Prefers to grow intracellularly
- Pops phagosome using listeriolysin and bacteria escape into cytosol
Rickettsia rickettsiae bacteriology
- Very short rods
- Hard to gram stain -
- Vectored by ticks
- Obligate intracellular parasites
Rickettsia rickettsiae pathogenesis
- Rocky mountain spotted fever
- Bacteremia
- Invade and multiply in vascular endothelium
- Blood vessels leak ad infected cells die, causes rash
Urogenital Chlamydia trachomatis bacteriology
- Unique life cycle: dense rugged elementary bodies (EBs) attach to cell and “unpack” into reticulate bodies (RBs). Larger, delicate RBs replicate, metabolize, pack into EBs and escape the host cell
- Only EBs are infections, only RBs divide
Pathogenesis of Serovars D-K: genital chlamydia
- Most common STD in US
- Often asymptomatic
- May spread sexually or infect newborns at birth
