Download CHAPTER 35 Pseudomonas and Other Opportunistic Gram

CHAPTER 35
Pseudomonas and Other Opportunistic Gramnegative Bacilli
A number of opportunistic Gram-negative rods of several genera not considered in other
chapters are included here. With the exception of Pseudomonas aeruginosa, they rarely
cause disease, and all are frequently encountered as contaminants and superficial
colonizers. The significance of their isolation from clinical material thus depends on the
circumstance and site of culture and on the clinical situation of the patient.
Pseudomonas aeruginosa
I. BACTERIOLOGY
1. P. aeruginosa most important Pseudomonas species
2. Other Pseudomonas species cause opportunistic infection
3. Pigment-producing rod is resistant to many antimicrobics
4. Grows aerobically with minimal requirements
5. Colonies are oxidase positive
6. Blue pyocyanin produced only by P. aeruginosa
7. Yellow fluorescin and pyocyanin combine for green color in culture and
sometimes clinical exudates
8. Outer membrane protein porins are relatively impermeable
9. Secreted alginate forms a slime layer
10. Alginate overproduction is due to regulatory mutations
11. Multiple extracellular enzymes are produced
12. Exotoxin A (ExoA) action same as diphtheria toxin
13. Exoenzyme S (ExoS) injected by secretion system
II. P. aeruginosa DISEASE
A. EPIDEMIOLOGY
1. Primary habitat is environmental
2. Colonizes humans
3. Multiplies in humidifiers, solutions, and medications
4. Risk for immunocompromised persons is high
5. Respiratory colonization of cystic fibrosis (CF) patients becomes chronic
B. PATHOGENESIS
1. Needs break in first-line defenses
2. Pili, flagella, and slime mediate adherence
3. ExoA secreted through quorum-sensing system in which chemicals (lactones,
quinolones) signal cell-to-cell
4. ExoA correlates with invasion, destruction
5. Elastin is attacked in lung and blood vessels
6. Injected ExoS disrupts cells
a. P. aeruginosa and Cystic Fibrosis
1. P. aeruginosa colonization may be aided by the fact that cells from CF
patients are less highly sialylated than normal epithelial cells
2. Mutants overproduce alginate polymer
3. Alginate biofilm protects bacteria
III. P. aeruginosa DISEASE: CLINICAL ASPECTS
A. MANIFESTATIONS
1. Infects burns and environmentally contaminated wounds
2. Pneumonia is aggressive in the immunocompromised and chronic in CF
Common cause of otitis externa
3. Contamination of contact lenses leads to keratitis
4. Bacteremia may cause ecthyma gangrenosum
B. DIAGNOSIS
1. P. aeruginosa is readily grown in culture
2. Pigments typically demonstrated in culture
C. TREATMENT
1. Of the pathogenic bacteria, P. aeruginosa is the most consistently resistant to
many antimicrobials
2. Multiresistance is primarily by restricting entry
3. Resistance to penicillins and aminoglycosides is common
4. Third-generation cephalosporins are often active
5. Effective oral agents are scarce
BURKHOLDERIA
1. Burkholderia pseudomallei is a saprophyte in soil, ponds, rice paddies and
vegetables located in Southeast Asia, the Philippines, Indonesia, and other
tropical areas
2. Melioidosis is a tropical pneumonia that relapses
3. B. cepacia is a nosocomial, CF pathogen
ACINETOBACTER
1. Gram-negative coccobacilli that occasionally are morphologically confused with
Neisseria
2. Resemble the Enterobacteriaceae in growth pattern and colonial morphology
3. Respiratory and urinary infection come from soil and water
4. Treatment is complicated by frequent resistance to penicillins, cephalosporins,
and occasionally aminoglycosides.
MORAXELLA
1. Moraxella are Gram-negative rods that are usually paired end to end
2. M. catarrhalis is an occasional cause of otitis media and lower respiratory tract
infection
3. Bronchitis and otitis come from presence in normal respiratory flora
AEROMONAS AND PLESIOMONAS
1. Resemble other enteric bacteria
2. Rapid cellulitis follows injury in fresh or saltwater
3. Diarrheas relate to enterotoxin production