NON FERMENTATIVE

• Relevance of isolation of nonfermentative bacilli


  Differs depending on patient risk factors and clinical condition
• Gram-negative bacilli are divided into at least two large groups: fermentative and nonfermentative organisms
• Fermentative organisms


  Catabolize carbohydrates anaerobically, using inorganic ions other than oxygen as the final electron acceptor, or by both aerobic and anaerobic pathways
• Nonfermentative organisms


  Do not ferment carbohydrates. Some use carbohydrates aerobically to derive energy (oxidizers), others do not break down carbohydrates at all (nonoxidizers or asaccharolytic)
• This module unit discusses the nonfermentative gram-negative bacilli (NFGNB)
• Nonfermentative gram-negative bacilli


  • Ubiquitous and found in moist environments, typically in soil and water, on plants and decaying vegetation, and in many foodstuffs
  • Can colonize hospitalized patients, especially those who are immunocompromised
  • Account for about 15% of all gram-negative bacilli isolated from clinical specimens
• Four groups of nonfermenters that make up most isolates routinely seen in clinical laboratories


  • Pseudomonas aeruginosa
  • Burkholderia spp.
  • Acinetobacter spp.
  • Stenotrophomonas maltophilia
• Pseudomonas


  The genus that accounts for the largest percentage of all nonfermenters isolated from clinical specimens
• Pseudomonads


  • Classified based on rRNA/DNA homology and common culture characteristics
  • Each of the five rRNA groups represents taxonomically distinct genetic groups, with different genus names assigned to each
• Pseudomonas species


  • Members of the fluorescent group, including P. aeruginosa, produce pyoverdin, a yellow-green pigment that fluoresces white to blue-green under long-wavelength (400-nm) ultraviolet light
• Pseudomonas aeruginosa


  • Gram-negative bacilli, motile, non-spore-forming, strict aerobe, grows well at 37-42°C, oxidase-positive, nonfermentative, oxidative
  • Produces pigments like pyocyanin (blue), pyoverdin (green or yellow-green), pyorubin (red), or pyomelanin (black)
• Habitat and transmission of P. aeruginosa


  • Occurs widely in soil, water, plants, and animals, and grows to very high numbers in moist environments
  • Uncommon part of the normal flora of the colon in about 10% of humans, gets on the skin from fecal organisms
  • Sources of infections include contaminated catheters, humidifiers, ventilators, intravenous solutions, anesthesia and resuscitation equipment in hospitals, raw vegetables, cut and potted flowers, sink drains, pools, and hot tubs
• Pathogenesis of P. aeruginosa


  Primarily an opportunist, unlikely to cause infections in healthy people with intact anatomical barriers, severe infections occur in people with weakened host defenses, primarily a nosocomial pathogen
• Diseases caused by P. aeruginosa


  • Bacteremia/septicemia
  • Pneumonia
  • Infection of wounds and burns
  • Urinary tract infection
  • Meningitis
  • Otitis externa
  • Eye infections
• Virulence factors of P. aeruginosa


  • Alginate (capsular polysaccharide that allows biofilm formation)
  • Pili (surface appendages for adherence)
  • Neuraminidase (removes sialic acid from host cell receptors)
  • Lipopolysaccharide (endotoxic properties)
  • Exotoxin A (inhibits protein synthesis)
  • Enterotoxin (disrupts gastrointestinal activity)
  • Exoenzyme S (inhibits protein synthesis)
  • Phospholipase C (destroys host cell membranes)
  • Elastase (cleaves immunoglobulins and complement, disrupts neutrophil activity)
  • Leukocidin (inhibits neutrophil and lymphocyte function)
  • Pyocyanins (suppress other bacteria, disrupt respiratory ciliary activity, cause oxidative damage)
• Since most common nosocomial Pseudomonas infections occur in compromised hosts, scrupulous attention to disinfection and hand washing, especially among health care workers, is crucial for prevention and control
• Entry into the cytoplasm of the host cell


  Facilitated by a Type III secretion system of the organism
• Phospholipase C


  A heat-labile hemolysin that degrades lipids thereby destroying the host cell cytoplasmic membrane; which favors spread of the organism to contiguous tissues
• Phospholipase C


  • Destroys pulmonary surfactant and inactivates opsonins
• Elastase


  Cleaves immunoglobulins and complement components, and disrupts neutrophil activity
• Elastase


  • Degrades proteins that allow the organism to acquire nutrients from the host and disseminate from the local site
• Leukocidin


  Inhibits neutrophil and lymphocyte function
• Pyocyanins


  • Suppress other bacteria and disrupt respiratory ciliary activity
  • Cause oxidative damage to tissues, particularly oxygenated tissues such as that of the lungs
• Since most common nosocomial Pseudomonas infection occur in compromised hosts, scrupulous attention to disinfection and hand washing, especially among health care workers, is necessary to prevent infections caused by this ubiquitous pathogen
• Because pseudomonas thrives in moist environments, special attention should be paid to sinks, water baths, showers, hot tubs, and other wet areas
• P. aeruginosa binds and secretes the A-B Exotoxin A (ExoA)


  Acts on protein synthesis by the same mechanism as diphtheria toxin
• Type III injection secretion system


  1. Delivers Exoenzyme S (ExoS) to the cell cytoplasm

  2. Elastase is secreted extracellularly
• All toxins act to destroy the cell and the bacteria may enter the blood
• Oxidizers


  Produce acid only in the open tube exposed to atmospheric oxygen
• Fermenters


  Produce acid in both tubes
• Nonsaccharolytic bacteria


  Inert in this medium, which remains at an alkaline pH after incubation
• Genus Burkholderia includes species that were formerly placed in the genus Pseudomonas
• B. mallei


  An obligate parasite of animals (primarily horses, mules, and donkeys) causing a respiratory tract infection known as glanders or farcy
• B. mallei human disease


  • Extremely rare; from an animal source, B. mallei can be transmitted to humans either by entry of the organism through an abrasion or break on the skin, or by inhalation of the organisms
  • Human infections can be fatal which usually begins as an ulcer of the skin or mucous membranes followed by lymphangitis and sepsis
  • Inhalation of the organisms may lead to primary pneumonia
• B. pseudomallei


  • An environmental organism found in soil, streams, surface water, such as rice paddies
  • Causes infection in sheep, goats, swine, horses, and other animals, although animals do not appear to be a primary reservoir for the organism
  • Human infections can occur by inhalation of dust, ingestion of contaminated water, and contact with contaminated materials (e.g., soil)
  • Causes melioidosis, a disease that is clinically and pathologically similar to glanders
  • Endemic in areas with tropical climates such as that of Southeast Asia (including Vietnam and Thailand), northern Australia, and Mexico
  • Incubation period is not clearly defined but may range from 2 days to many years
• B. pseudomallei and B. mallei are considered potential agents for biologic warfare and biologic terrorism
• B. cepacia complex


  • Consists of the prototypic species Burkholderia cepacia plus at least 18 other genomospecies which have been isolated in humans
  • An environmental organism able to grow in water, soil, plants, animals, and decaying vegetable materials
  • Human transmission is by exposure of medical devices and solutions contaminated from the environment
  • People with cystic fibrosis (CF) and those patients with chronic granulomatous disease are particularly vulnerable to infection with bacteria in this complex
  • They may have asymptomatic carriage, progressive deterioration over a period of months, or rapidly progressive deterioration with necrotizing pneumonia and bacteremia
  • It is likely that B. cepacia can be transmitted from one CF patient to another by close contact
  • In addition, members of this complex have been reported to cause endocarditis (specifically in intravenous drug abusers), pneumonitis, UTIs, osteomyelitis, dermatitis, and other wound infections resulting from the use of contaminated water
• Acinetobacter species


  • Opportunists, and they are second to P. aeruginosa in frequency of isolation of all nonfermenters in the clinical microbiology laboratory
  • A. baumannii is the species most commonly isolated
  • A. lwoffii and other species are isolated occasionally
  • Widely distributed in soil and water and can occasionally on the skin and mucous membranes (.e.g, pharynx) of healthy people
  • In the hospital environment, they have been associated with ventilators, humidifiers, catheters, and other devices
  • Transmission in health care settings is usually aided by instrumentation
  • Infections primarily affect patients with weakened immune systems and coexisting diseases
  • These infections usually occur in areas with a high fluid content such as the urinary tract and respiratory tract, and in peritoneal fluids
  • Diseases with which they have been associated include UTIs; pneumonia, tracheobronchitis, or both; endocarditis; septicemia; meningitis, often as a complication chemotherapy; and cellulitis, usually as a result of contaminated indwelling catheters, trauma, burns, or introduction of a foreign body
• Acinetobacter species are usually coccobacillary or coccal in appearance, and they resemble neisseriae on smears, because diplococcal forms predominate in body fluids and on solid media
• Stenotrophomonas maltophila


  • The third most common nonfermentative, gram-negative bacillus isolated in the clinical laboratory
  • Ubiquitous in the environment, being found in water, sewage, and plant materials
  • A significant nosocomial pathogen; it is very common in the hospital environment, where they can be found contaminating blood-drawing equipment, disinfectants, transducers, and other equipment
  • Risk factors for colonization or infection with this organism are mechanical ventilation, use of broad-spectrum antibiotics, catheterization, and neutropenia
  • Diseases attributed to this organism includes endocarditis, especially in a setting of prior intravenous drug abuse or heart surgery; wound infections, including cellulitis and ecthyma gangrenosum; bacteremia; and, rarely, meningitis, cholangitis, and UTIs