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?