NonfermentersNonfermenters Gram-Negative Bacilli.
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Transcript of NonfermentersNonfermenters Gram-Negative Bacilli.
NonfermentersNonfermentersNonfermentersNonfermenters
Gram-Negative BacilliGram-Negative Bacilli
Clinically Important Aerobic Gram(-) Bacilli
• 75% = Facultative anaerobic fermenters - Enterobacteriaceae
• 15% = Aerobic nonfermenters – Pseudomonadaceae and related bacteria
• 10% = Pasteurellaceae• <1% = Unusual bacilli
Nonfermenters: Gram(-) Bacilli
• Inhabit soil, vegetation, water; harmless parasites on mucous membranes of human and animals
• Simple growth requirements• Hospital moist reservoirs – food, ice
machine, cut flowers, sinks, toilets, floor mops, disinfectant solutions, respiratory therapy equipment
• Numerous virulence factors• Broad antimicrobial resistance • Infections primarily opportunistic – colonize,
infect immunocompromised; gain access to normally sterile body site through trauma
Nonfermenters: Genera • No family designation• Many genera whose names continually
changing• Do not ferment glucose• Pseudomonas aeroginosa• Acinetobacter baumannii • Stenotrophomonas maltophilia (former
Ps.)• Burkholderia cepacia (former Ps.)• Moraxella catarrhalis
Morphology and Characteristics
• Gram(-) bacilli, coccobacilli
• Obligate aerobes• Most will not grow or
grow poorly under anaerobic conditions
• Some require 48-72 hours for growth
• Grow best at 370 C, but a few grow better at RT (Ps. fluorescens) or tolerate higher (42ºC, Ps. aeruginosa)
Lab Culture Media • Nonfastidious, isolated same as
Enterobacteriaceae• Mac plate – some grow• CBA, MH plate - morphology, size,
hemolytic activity, pigmentation (green, blue) provide valuable information for ID
Lab Test ID
• TSI= K/K - No glucose fermentation
• Oxidase (±)• Mac plate (±) Growth• Unusually resistant to antibiotics
CDC Scheme Nonfermenters (8 Groups)
• Mac plate - Growth, no growth• Oxidase• O/F carbohydrates• Further testing:
– Motility– Nitrate reduction– Urease production– Esculin hydrolysis– Indole production– Rapid amino acid
decarboxylation– Pigment production– Phenylalanine deaminase– Growth at 420 C
Nonfermenters: Lab Unknowns
Oxidase O/F Motile SXT NO3Red
Pseudomonas + +/- + R +
Acinetobacter - +/- - S -Stenotrophomonas - -/- + S -Chyseobacterium + +/- - R -
Pseudomonas aeruginosa• “false unit” – in pairs, resemble single
cell• Numerous virulence factors• Broad-based antimicrobial resistance• Some strains mucoid (CHO capsule),
common in cystic fibrosis patients• Diffusible pigments – pyoverdin
(fluorescein, yellow), pyocyanin (blue), pyorubin (red)
• Tolerate temperatures (4º-42ºC)• Sweet grapelike odor on culture plate
Ps. aeruginosa:Virulence Factors
(Extracellular)• Protease -
– Tissue destruction– Degrade Complement, IgA– Inhibit neutrophil
• Elastase – destroy elastin fiber of lung tissue, blood vessels; hemorrhagic lesions, spreading of infection
• Exotoxin - most toxic product– Cytotoxin lethal for many mammals– LD50 in mice= 60-80 ng– Blocks host cell protein synthesis– Liver is prime target
Virulence Factors (Extracellular)
• Phospholipase C – attack lipid of cell membrane– Hemolysin– Breakdown of phospahtidyl choline, a major
surfactant of the lung; lead to tissue damage, pulmonary collapse
• Leukocidin – cytotoxic• Pyocyanin – secreted pigment
– Toxic– Generate reactive oxygen intermediates
(superoxide radical, hydrogen peroxide)
Ps. aeruginosa:Virulence Factors (Cell
Surface) • Pili and non-pilus adhesions –
attachment respiratory epithelium• LPS – endotoxin; sepsis syndrome, DIC• Iron capturing ability – nutrition, growth• Flagella – motility• Alginate synthesis – forms viscous gel
around MO, function as adhesion, also prevent phagocytosis
• Outer membrane changes - antibiotic unable to enter bacterial cell; drug resistance
Ps. aeruginosa:Respiratory Tract Infection
• Leading cause nosocomial RTI• Range from colonization, benign
tracheobronchitis to severe necrotizing bronchopneumonia
• Seen in patients with: – Cystic fibrosis– Chronic lung diseases– Neutropenia
• Frequently following use of contaminated respiratory therapy equipment
• Severe infections lead to bacteremia and higher mortality
Ps. aeruginosa:Bacteremia, Endocarditis
• Higher mortality rate due to: – Virulence of Pseudomonas strain– Infection in immunocompromised
(neutropenia patient, diabetes mellitis, extensive burns, hematologic cancers)
• Originate from initial infections of LRT, UT, skin & soft tissue (burns, wounds)
• Endocarditis commonly seen in IV drug abusers
Ps. aeruginosa:Ear Infection
• External otitis media:– Swimming a risk factor (swimmer’s ear)– Manage with topical antibiotics, drying agents
• Malignant external otitis media:– More virulent form, invade underlying tissue– Can be life threatening– Require aggressive antimicrobials + surgery
• Chronic otitis media
Ps. aeruginosa:Burn Infection
• Colonize burn wound• Localize vascular damage, tissue
necrosis, bacteremia• Factors predispose patient to infection:
– Moist surface of burn– Absence of neutrophil response
• Limited success treating with topical creams and wound management
Ps. aeruginosa: Other Infections
• GI, UT, CNS, eye, musculoskeletal • Underlying conditions:
– Presence of Pseudomonas in a moist reservoir
– Circumvention or absence of host defense (e.g. cutaneous trauma, elimination of NF by injudicious use of antibiotics, neutropenia)
– Indwelling urinary catheter (best to remove ASAP)
Pseudomonas: Treatment
• Typically resistant to most antibiotics • Difficult to treat patient - often with
compromised host defense, unable to augment antibiotic activity
• Important to isolate MO for antibiotic susceptibility testing
• Requires combined treatment:– Aminoglycoside (tobramycin)– β-lactam antibiotic (ceftaidine, piperacillin).
Pseudomonas: Prevention
• Hospital Infection Control– Avoid contamination of sterile equipment
such as respiratory therapy machine– Prevent cross-contamination of patient by
medical personnel; i.e. hand washing, fomites
• Avoid inappropriate use of broad-spectrum antibiotics that kill and suppress host NF
Acinetobacter • “unable to move” • A. baumannii (oxidizer = saccharolytic)• A. lwoffii (nonoxidizer = inert)• Found in soil, water; NF skin,
oropharyngeal• Common colonizer, cause of nosocomial
respiratory infection• Thrive in moist environments, found as
contaminants in respiratory equipment and monitoring devices
• Resistant to many antibiotics; use aminoglycosides and broad-spectrum cephalosporins
Stenotrophomonas maltophilia
• “narrow, feed, unit”; “malt lover” • Second most frequently isolated
nonfermenter• Nosocomial - transient NF of patients• Opportunist – especially debilitated
patient, impaired host-defense• Variety of infections – bacteremia,
pneumonia, meningitis, wounds, UTIs• Resistant to commonly used antibiotics• Treat with trimethoprim-sulfmethaxazole
(SXT)
Burkholderia cepacia• “onion”• Low level virulence, nosocomial pathogen• Respiratory Tract infection:
– Range from colonization to broncopneumonia– Patients with cystic fibrosis, chronic
granulomatous disease
• Opportunistic infection:– Patient with urinary catheter– Immunocompromised patient with
intravascular catheter
Burkholderia pseudomallei: Melioidosis
• Disease primarily SE Asia, India, Africa, Australia; normal inhabitant of soil, water
• Acquired via contamination of wounds, inhalation, ingestion
• Range of infection:– Most unapparent, asymptomatic– Cutaneous, localized suppurative infection,
lymphadenopathy, fever, malaise; resolves or progress to sepsis
– Chronic or acute pulmonary infection, overwhelming septicemia with multiple abscesses in many organs
Burkholderia mallei: Glanders
• “mallei” glanders• Equine infection, humans occasionally
acquire disease• Contact with infected nasal secretions
of horses; through skin abrasions, occasionally inhalation
• A problem in military when horses were commonly used
• Disease may manifest as:– Chronic pulmonary disease– Multiple abscesses of skin, subcutaneous
tissue, lymphatics– Acute, fatal septicemia
• Potential bioterrorist agent
Moraxella catarrhalis• “downflowing, inflammation” • Oropharyngeal NF• Previously healthy patient, also
hospitalized patient• Bronchitis, bronchopneumonia in
patient with chronic pulmonary disease• Sinusitis• Otitis media• Most penicillin-resistant, susceptible to
erythromycin
Class Assignment• Textbook Reading: Chapter 21
Nonfermenting Gram-Negative Bacilli (Omit: Less Commonly Encountered Nonfermentive GNB)
• Key Terms• Learning Assessment Questions
Case Study 4 – Pseudomonas
• A 63-year-old man has been hospitalized for 21 days for the management of newly diagnosed leukemia.
• Three days after the patient entered the hospital, a urinary tract infection with Escherichia coli developed.
• He was treated for 14 days with broad-spectrum antibiotics.
• On day 21 of his hospital stay the patient experienced fever and shaking chills.
Case Study 4 - Pseudomonas
• Within 24 hours he became hypotensive, and ecthymic skin lesions appeared.
• Despite aggressive therapy with antibiotics, the patient died.
• Multiple blood cultures were positive for P. aeruginosa.
Case Study - Questions• 1. What factors put this man at increased
risk for infection with P. aeruginosa?• 2. What virulence factors possessed by
the organism make it a particularly serious pathogen? What are the biologic effects of these factors?
• 3. What antibiotics can be used to treat P. aeruginosa?
• 4. What diseases are caused by S. maltophila? A. baumanni? M. catarrhalis?