Pseudomonas, Legionella, Moraxella and Other Gram Negative Bacilli Flashcards
Psedomonas genus
- Gram -
- bacilli
- obligate aerobe
- blue/green
- P. aeruginosa
P. aeruginosa
- Among the most deadly of bacterial infections
- Opportunistic infection at variable sites
- Confined to the immunocompromised and debilitated
- High level of resistance to antimicrobials
- Aerobic, oxidase and catalase positive
- Pigments (yellow, blue, rust, fluorescent) – Pyocyanin (blue) unique to P. aeruginosa
- Exopolysaccharide (alginate) polymer can form glycocalyx
P. aeruginosa Exotoxins
•Exotoxin A or ExoA (can be induced by low iron levels)
-ADP-ribosylates Elongation Factor-2 (same mechanism as in DT, but much different in manefestation)
•Other enzymes (toxins)
-Phospholipase, collegenase, elastase (a protease)
P. aeruginosa Epidemiology
- Extremely hardy -free-living in water, soil, plants
- Survives at 42 oC (High GC content)
- Throat, stool microbiota – up to 10%
- Colonizes patients with cystic fibrosis (CF)
- Contaminates medical environment
– Respirators
– Contact lens solutions
– Medications
– Even some disinfectants
P. aeruginosa Pathogenesis
- Access via contamination of vulnerable site, solution
- Immune compromise + antimicrobial resistance
- ExoA – no systemic action like DT
- Quorum-sensing
– Bacteria secrete signal chemicals
– ExoA produced when critical mass reached
P. aeruginosa CF
Alginate biofilm/glycocalyx
- Regulatory gene mutations allow overproduction of polymer
- Limits access of complement, phagocytes, antimicrobials
- Quorum-sensing activated by high osmolarity of CF secretions
P. aeruginosa Manifestations
- Wound, burn, UTI, eye, hot tubs, swimmers’ ear
- Environmental contamination
- Immunocompromised
- CF
- Vascular –> Necrotic lesions (ecthyma gangrenosum)
P. aeruginosa Diagnosis
• Culture
P. aeruginosa Treatment
- “Wild type” multiresistant to most antimicrobial classes
- Outer membrane porins are relatively impermeable
- Anti-pseudomonas drugs are prized (newer aminoglycosides, cephalosporins, etc.)
Legionella genus
- Gram -
- bacilli
- aerobic
- oxidase and catalase +
- fastidious
- Require L-cysteine, ferric ions (fastidious)
- pH optimum 6.9
•doesn’t Gram stain well (prefer environment inside human macrophages or amoebas!)
- use Silver stain
•L. pneumophila
-multiple serogroups (16)
– Serogroup 1 (Philadelphia strain) still most common
Legionnaires’ Disease Epidemiology
• Legionella widely present in domestic and wild aquatic environments
– Live in association with algae and inside amoebae
– Dormant states occur in environment
• Aerosol production allows transmission to humans by inhalation
– Cooling towers
– Grocery market mist sprayers
- Human-human transmission not demonstrated
- Attack rate <5% of those exposed
- Immunocompromised patients
- Faucets, showers, etc.
- Biofilms, dormant nutrientrestricted organisms
- Institutional disinfection
– Old pipes, scale, etc.
– Hot water, chlorine
– Silver, copper ions
Legionnaires’ Disease Pathogenesis
Legionnaires’ Disease Manifestations
- Severe toxic pneumonia
- Dry cough, scant sputum
- Confined to lung Pontiac fever
- Self-limiting febrile illness
- Probably endotoxin or immune
Legionnaires’ Disease Diagnosis
Legionnaires’ Disease Treatment
- Beta-lactamase producer
- Erythromycin – original outbreak
- Also - azithromycin, fluoroquinolones
Moraxella
- Moraxella is another genus of Gram-negative with variable shapes that include coccobacilli to diplococcus.
- Some species require enriched media, such as blood or chocolate agar.
- Their morphology, fastidious growth, and positive oxidase reaction can result in confusion with Neisseria in the laboratory.
- A medically important member is Moraxella catarrhalis.
-Moraxella catarrhalis, a Gram-negative diplococcus, is found in the oropharyngeal microbiota, and it is an occasional cause of lower respiratory tract infection, acute or subacute sinusitis, otitis media (typically beta lactamase-producing) and community acquired suppurative pneumonia.
Burkholderia
•Burkholderia pseudomallei is a saprophyte in soil, ponds, rice paddies, and vegetables located in Southeast Asia, the Philippines, Indonesia, and other tropical areas.
- Infection is acquired by direct inoculation or by inhalation of aerosols or dust containing the bacteria.
- The disease, melioidosis, is usually an acute pneumonia; however, it is sufficiently variable that subacute, chronic, and even relapsing infections may follow systemic spread.
•B. cepacia complex is a group of opportunistic species that have been found to contaminate reagents, disinfectants, and medical devices in much the same manner as does P. aeruginosa.
Acinetobacter
- The genus Acinetobacter comprises Gram-negative coccobacilli that occasionally appear sufficiently round on Gram smears to be confused with Neisseria.
- They are most frequently found as contaminants of almost anything wet, including soaps and some disinfectant solutions.
- Pneumonia is the most common infection, followed by urinary tract and soft tissue infections.
- Nosocomial respiratory infections have been traced to contaminated inhalation therapy equipment, and bacteremia to infected intravenous catheters.
Aeromonas and Plesiomonas
- The genera Aeromonas and Plesiomonas have bacteriologic features similar to those of the Enterobacteriaceae, Vibrio, and Pseudomonas.
- Their habitat is basically environmental (water and soil), but they can occasionally be found in the human intestinal tract.
- Aeromonas is an uncommon, but highly virulent cause of wound infections acquired in fresh or saltwater. The onset can be as rapid as 8 hours after the injury, and the cellulitis can progress rapidly to fasciitis, myonecrosis, and bacteremia in less than a day.
