Pseudomonas Gram negative bacteria Rod-shaped, polar flagella (hence, motile) Inhabit the soil and water Pseudomonas aeruginosa is the most prevalent opportunistic pathogen Intrinsically resistant to many antibiotics  nosocomial infection combinations >2 drugs (eg. Penicillin + aminoglycoside)

P. aeruginosa Obligate aerobe Produce a sweet or grape-like smell Colonies with a fluorescent greenish colour, nonfluorescent bluish pigment pyocyanin greenish pigment pyoverdin dark red pigment pyorubin black pigment pyomelanin

Pathogenesis Pili (fimbriae) – promote attachment Exotoxin A – causes necrosis, blocks protein synthesis ( DTx) P. aeruginosa is only pathogenic when introduced into areas of devoid normal defenses

A 48 year old Caucasian male presented to the emergency room after a progressive history of left foot ‘cellulitis’. The patient works as an oil-field worker and began experiencing left foot erythema and blisters. -- progressed to increased erythema and a green-yellowish drainage from the digits and in between the toes. Medical history. abuse alcohol ,drug abuse when he was in his 20’s. His family history includes diabetes mellitus. His x-ray report reveals no signs of gas in the tissue and no signs of osteomyelitis. His culture report revealed +3 tiny gram negative rods and +1 gram positive cocci. On day 1, presumptive +4 Pseudomonas aeruginosa was identified. Diptheroids and coagulase negative staphylococcus species were also identified. His aerobic and anaerobic blood cultures were negative.In the photo on left, it is interesting how just his left foot is infected and his right foot is completely spared.   Discussion and Treatment host does not initially appear to be immunocompromised. However, he has a history of drug use and consumes alcohol quite heavily during the week. His work conditions are also conducive to these type of infections; wears steel toe type boots and rubber-type boots in the field. Soil contaminates and moisture would play an important role in pathogenesis of this infection. The patient also had exposure to Bactrim early in his treatment which may have played a role in the ability of his immune system to fight the infection in its early stage. Two extracellular proteases and extracellular protein toxins are produced in the initial infective stage. Elastin protease and alkaline protease destroy the cells ground substance and lysis its supporting structure of fibrin and elastin. Exotoxin A has a tissue necrotizing effect and has the same mechanism of action as the diphtheria toxin. Exoenzyme S is also thought to be a tissue destructive exoenzyme that is commonly seen during pseudomonas colonization on burn wounds.

The picture at left represents local colonization of pseudomonal infection of the foot. Here, the skin is erythematous and has a scalded-skin type appearance. This is likely due to extracellular toxins and proteases causing local ground substance disruption. You can also readily see the alginate slime layer that forms a matrix of the pseudomonas biofilm. This alginate biofilm is representative of pseudomonas colonization and the bacterial attempt at protecting the colony from host defenses. Treatment should include primary coverage for pseudomonal infection. Sensitivity reports revealed bacteriocidal activity using Ciprofloxacin.

Burkholderia pseudomallei Small, motile, aerobic Gram-negative bacillus Colonies are mucoid and smooth to rough and wrinkled in cream to orange colour. Melioidosis of humans, in SE Asia and northern Australia high mortality rate if untreated surgical drainage of localised infection may be necessary