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18 terms

Lecture 12a: Gram Negative Rods (not Enterobacteriaceae)

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Gram negative bacilli, not Enterobacteriaceae? (5)
Pseudomonas aeruginosa
Legionella pneumophila
Vibrio cholerae
Helicobacter pylori
Campylobacter jejuni

All aerobic
Medically important Pseudomonads? Why such a problem?
**Pseudomonas aeruginosa
(also P. fluorescens, P. putida, P. stutzeri but RARE)

Problem bc can grow on basically anything where there's moisture
- think faucets and drains in hospitals
--> never wash respiratory equiptment in tap water***
- soil, water, man-made solutions
- even in IV bags and disinfectants
- artificial nails

Can use many different organic compounds for growth

--> notorious hospital acquired infections
**OPPORTUNISTIC PATHOGEN
Previously classified as Pseudomonas? Clinical disease?
Burkholderia cepacia
- respiratory colonization in CF

Stenotrophomonas maltophila
- hospital acquired pathogen
- resistant to most common Abx
Which species has associated parts/toxins? Function?
Pili
Exotoxin A
Alginate
LasA and LasB
Endotoxin
Pseudomonas aeruginosa

Pili --> adherence
Exotoxin A --> ADP-ribosylates EF2

Alginate
- exopolysaccharide
- mucoidy phenotype in CF
- antiphagocytic

LasA +LasB = elastase
- degrade elastin

Endotoxin = LPS
- all gram negative bacteria
- TLR 4 trigger
Mechanism of quorum sensing?
Way for bacteria to sense their numbers

- Bacteria express QS autoinducer and R' for autoinducer
- if only a few bacteria, small concentration of autoinducer
--> keep virulence low bc if trigger immune system, bacteria will lose

If numbers high
- high concentration of autoinducer
--> increase virulence factors
- power in numbers
Pseudomonas aeruginosa clinical disease? (5)
**OPPORTUNISTIC
- copious purulent secretions

CF patients
--> repeated bouts of respiratory infections
- cannot eradicate

Nosocomial pneumonia
- esp mechanically ventilated patients***
- may cause necrotizing pneumonia (remember have elastase proteins - LasA, LasB)

Cancer patients
- bacteremia, sepsis

Hot tub folliculitis
Skin lesions
- ecthyma gangrenosum**
How dx pseudomonas aeruginosa? Tx?
- produces grape like odor

- produces fluorescent pigments
- blue/pyocanin and yellow/pyoverdin --> blue-green pigment
- can sometimes see in infected skin (remember foot pic)

- Oxidase positive (from electron transport chain - must be aerobic)

Tx:
- intrinsic and acquired resistance
to penicillins, cephalosporins

- use 2 Abx at once
- Aminoglycosides and a cell wall agent (piperacillin, ceftazidime, imipenem, aztreonam)
Medically important Legionella and disease they cause?
**Legionella pneumophila

17 other spp can infect humans
- most common of these --> L. micdadei

Cause pneumonia
- Legionairre's disease
Additional symptoms
- headache, change in mental status
- nausea, V/D
- hyponatremia*** (low blood Na)
Transmission of Legionella pneumophila? Who at risk?
Aspiration of contaminated water
Inhalation of aerosol
-think vegetable mister at grocery store

Natural bodies of water
Cooling towers, water distribution systems
- parasitize ameobae

***NO human to human transmission
yet get nosocomial and community outbreaks

Risk groups:
IC, elderly
smokers, COPD
Alcoholics
- people more prone to aspirate
Legionella unique mech of infection?
**facultative intracellular pathogen (like Listeria)
- primarily infect macs (Listeria does epithelial cells)

Coiling phagocytosis
- thin pseudopod from mac
- engulfs in coiled vesicle

Fusion with lysosome to make a phagolyzosome blocked
- ER membranes with ribosomes are recruited to the phagosome

- bacteria survive and multiply WITHIN the phagosome
- eventually lyses cell
Factors associated with which species? Function?
dot locus
Phospholipase C
Legionella pneumophila
- facultative intracellular pathogen
- lives and divides INSIDE phagosome

dot locus
--> defect in organelle trafficking
--> blocks phagolysosome fusion
--> ribosome recruitment
(type IV secretion system - function same as type III)

phospholipase C
- hydrolyze phosphatidyl choline in eukaryotic membranes
How dx Legionella pneumophila?
- poorly stained by gram stain
--> use silver staining

- grows on buffered charcoal-yeast extract agar (needs L-cysteine)
- need Abx bc grows so slowly
**ex of selective agar

Ab test, urinary antigen test
Clinical: low Na
- maybe not typical pneumonia

Tx with Abx
Vibrios spp and associated diseases? Transmission? (3)
Vibrio cholerae
- comma shaped
- cholera = severe diarrhea
- salt and fresh water

Vibrio parahemolyticus
- gastroenteritis
- from raw/undercooked seafood

Vibrio vulnificus
- gastroenteritis
- wound infections that are exposed to seawater** (think step on clam shell)
- life threatening bacteremia (liver disease pts, iron overload pts)
Helicobacter pylori disease? Risk factor for?
Peptic ulcer disease
- grows in mucus of gastric mucosa

Infection usually asymptomatic even with gastric inflammation (30% of pop infected)

Risk factor for adenocarcinoma, non-Hodgkin's lymphoma, low-grade B cell mucosa-associated lymphoid tissue (MALT) lymphoma of the stomach
**ex. of cancer that can treat with Abx

Grows best in microaerophilic conditions
- slender spiral shape
Factors associated with which bacteria spp? Function?
Urease
flagella and curved shape
VacA
Type IV secretion system
Helicobacter pylori

urease
- splits urea into ammonia
--> alkaline environment so can survive in acid stomach

flagella and curved shape
- allows motility through mucus lining (burrowing)
- adherance to gastric epith cells

VacA
- cytotoxin
--> vacuolation of epith cells (in culture)
- may contribute to ulcer formation

Type IV secretion
- secrete in toxins
- stimulates inflammation
H. pylori tx?
PPI - facilitates healing
amoxicillin
clarithromycin or metronidazole
How dx H. pylori?
Endoscopy
- Giemsa stain (same as Y. pestis)or
- silver stain (same as Legionella)

Urease test - in bx
Urea breath test
- exhale radio labeled CO2 (liberated by urease)

Blood IgG test
- do not decrease for 6 months after successful Abx therapy
- not good for monitoring tx

Ab tests that measure antigens in stool
Disease caused by Camylobacter?
Gastroenteritis that leads to diarrhea

Curved gram-neg rod (similar shape as Helicobacter pylori)