Genus including many species of Gram negative, non-fermenting, aerobic bacilli
Natural Habitat of Pseudomonas: soil, water, plants, a common human saprophyte (necroparasite; an organism that grows on dead organic matter, plant or animal.) Stedman’s Medical Dictionary
Pseudomonas aeruginosa
most common pseudomonas human pathogen
0.5-0.8 by 1.5-3.0
m m
motile with polar monotrichous flagella
an obligate aerobe except in the presence of nitrate (can use over 30 organic compounds for growth)
does not ferment CHO, oxidizes Glucose, Xylose, but not Maltose
has a characteristic sweet grape-like odor in culture
grows in moist areas, even in distilled water
produces pigments; most are piliated and have flagella
contains LPS with stain-specific O side chain
Pathogenicity
P. aeruginosa
is both invasive and toxigenic
Three stages:
(1) bacterial attachment and colonization
Þ produces a mucoid exopolysaccharide (especially in cystic fibrosis)
(2) local invasion
Þ produce toxins, proteases, and hemolysins Þ degrade local tissue
(3) disseminate and systemic disease
Þ LPS and exotoxin A
Prior cellular insult (e.g. viral infection, endotracheal intubation, etc) can play a role in the initial attachment.
Pilli
bind to receptors on the host cell
Exoenzyme (exotoxin) S
three effects: 1) serves as adhesion for glycosphingolipids on respiratory cells 2) ribosylates GTP-binding proteins in the ras gene superfamily 3) appears to have immuno-suppressive function too.
Under certain conditions P. aeruginosa produces a mucoid exoploysaccharide (MEP)
MEP
– forms a matrix bridging sister cells to host
protects from the mucocilliary mechanism of the respiratory tract as well as from phagocytes, Ab’s, and complement
Proteases
two types – both are necrotizing in skin, lung, and cornea; they destroy connections between cells to make nutrients available to the bacteria.
(1) Elastase
– capable of producing hemorrhage and destruction of lung tissue; degrades the lamin and elastin in vascular tissue; proteolytically inactivates INF-
g and TNF.
(2) Alkaline Protease
– acts like plasmin anticoagulant and hydrolyzes fibrin and fibrinogen.
Lipid A
(LPS)– moiety of P. aeruginosa endotoxin that activates clotting, fibrinolysis, kinin, and complement. Also stimulates production of prostaglandins, leukotrienes, and cytokines such as TNF Þ septic shock.
Exotoxin A
– a "potent inhibitor of mammalian protein synthesis" Like Diphtheria, this toxin catalyzes the transfer of the ribose moiety of NAD into a covalent linkage with Elongation Factor 2 (EF-2) inhibiting EF-2. Looks different, gets into cell differently than Diphtheria; having toxin Ý virulence
Clinical Epidemiology
Patients debilitated in the ICU (can be spread by respiratory equipment)
Granulocytopenia – patients with Neutropenia (loss of PMN’s) due to cancer chemotherapy
Burn Wounds – the larger the burn, the larger the chance of going septic.
Ý mortality
IDU’s (Injectable Drug Users) – use tap water (home of Pseudomonas) to shoot. Only IDU’s show up with Pseudomonas endocarditis.
CF – all get Pseudomonas, host/parasite relationship develops.
HIV – poorly understood correlation but there is an increase in infection with the immuno-compromised.
In the Normal Host
opportunistic pathogen (except in CF)
UTI’s (urinary tract infections) – "Apollo 13", an astronaut had a Pseudomonas UTI in outer space. PMN’s do not migrate properly in microgravity
Severe eye infections – "fishhook in the eye" can result in the loss of an eye. Osteochondritis of the foot – results from a nail through a sweaty sneaker into bone.
Dermatitis from the hot tub – rash the next day. Folliculitis (Pseudomonas grows in high temperatures, one needs to hyperchlorinate those hot tubs!)
Burns – when there is damage to the integument. If it gets into the bloodstream
Þ high mortality.
Cystic Fibrosis
Provides a unique lung environment
Pseudomonas
converts to a mucoid phenotype
Results in a high bacterial burden (108 cfu/mL of sputum) cfu = colony forming units
MEP prevents normal opsonization and killing
Almost never invades the blood stream
Most CF patients die from Pseudomonas pneumonia in their early thirties
Young CF patients get Staphlococcus aureus first, which clears up. However by age 10 CF patients are colonized by Pseudomonas. (they will always have Pseudmonas)
Osteochondritis of foot
all shoes nowadays have water trapping synthetics in them.
Nail
Þ foam Þ into bone = infection
very aggressive destruction, a surgical disease.
Þ Treatment: debridement and 2wk antibiotics
loss of bone density
Þ abscess "pus-pocket" in the metatarsal
Corneal Ulcer –
"fishhook eye"
trauma to the eye (wet branch scrapping eye, etc), needs surgical drainage
Ulcer
raised red rim with necrotic tissue center. Infarcted skin. This is why neutropenic patients need a daily head-to-toe exam when they have a fever. Treatment: pull catheter, and IV antibiotics targeted at Pseudomonas.
Endocarditis
fibrosis of the tricuspid valve; seen in IDU’s (Injectable Drug Users)
Non-aeruginosa pseudmonas species
*
aerobic gram-negative bacilli (non-fermentative) but now given new names (based on RNA homology):
Burkholderta cepacia
(used to be Pseudomonas cepacia)
a plant pathogen that infects CF patients (pulmonary pathogen)
an opportunist seen in long term indwelling catheters, seen in the ICU
high fever, severe progressive respiratory failure
fail to respond to treatment with aminoglycosides, ureidopenicillins and 3rd generation cephlosporins (antibiotics)
Burkholderia pseudomallei
(used to be Pseudomonas pseudomallei)
A soil saprophyte found especially in Southeast Asia
Very long latency (inoculate skin Þ sits in lymph nodes)
Vietnam vets and Peace Corp workers can get this
Usually chronic ulcers with swollen lymph nodes (lymphangitis); also pneumonia
Relapses common
Burkholderia mallei
(used to be Pseudomonas mallei) DO NOT CONFUSE WITH Ý
A veterinary disease- causes "Glanders" (swollen glands) in horses and mules; lymphatic disease with pulmonary involvement
Do not confuse with pseudomallei
Septicemic form is fatal in 7 –10 days
occasional transmission to humans
Stenotrophomonas maltophilia
(previously Pseudomonas and Xanthomas maltophilia)
Uncommon in the normal host – a very resistant nosocomial, water-loving bacteria