Gram Negative Rods - Pseudomonads & Vibrio Flashcards
Features of pseudomonads
- Mostly found in the environment
2. Not normal flora
Examples of pseudomonads
- Pseudomonas aeruginosa (PAE)
- Stenotrophomonas maltophilia
- Burkholderia spp
- Burkholderia cepacia
- Burkholderia pseudomallei
Features of PAE
- Oxidase positive
- Non-lactose & non-glucose fermenter
- Motile
- Aerobic growth
- Produce diffusible pigments (commonly green)
- Found in moist conditions
- Important cause of opportunistic infections (hospitalised & immunocompromised, on antibiotics, community acquired eg contact lenses, spa baths)
Virulence factors of PAE
- Produces slime/biofilm, allows adherence to implants/lines
Clinical presentations of PAE (10)
Hospital acquired
- infects areas with abnormal stasis of body fluids, exposed wounds or penetrated by poorly maintained instruments/fluids
1. UTI - related to catheterisation, instrumentation, surgery, residual bladder urine, common after multiple recurrent inf
2. Pneumonia - diffuse bronchopneumonia or rapidly progressing multi-focal necrotising pulmonary lesions (& bacteremia) esp in cystic fibrosis patients
3. Septicaemia - esp in neutropenic patients, classically assoc w ecthyma gangrenosum (small skin nodules that hemorrhage, necrose, ulcerate)
4. GI infection - necrotising enterocolitis, esp in young infants & neutropenic cancer patients, 2 to gut colonisation
5. SSTI - hemorrhage, necrosis, esp in burns/wounds
6. Bone & joint infections, meningitis, endocarditis
Community acquired
- Ear infections - malignant otitis externa (spreads to face, neck, bone - req systemic treatment), chronic suppurative otitis meda, esp in elderly diabetes
- Eye infections - keratitis (corneal ulcer - penetrates/perforates cornea - panophthalmitis), due to contaminated contact lens fluids, ocular medications, minor eye trauma
- Skin infections - jacuzzi/whirlpool rash (folliculitis)
- Nail infections
Diagnosis of PAE
- Biochemical tests
2. Mass spectroscopy
Treatment of PAE (4)
- Piperacillin
- Carbapenems, 3G cephalosporins, aminoglycosides, quinolones
- HAI usually MDR - check antibiotic sensitivities
- Severe infection, neutropenia - use 2 antibiotics eg ceftazidime + gentamicin
Prevention of PAE
- Prophylactic ciprofloxacin for neutropenic patients, also prevents septicaemia
Treatment of stenotrophomonas maltophilia
- nosocomial pathogen, less common than PAE, MDR
- produces carbapenemases - resistant to carbapenems
1. Co-trimoxazole, levofloxacin
Features of burkholderia cepacia
- rare in healthy people, usually after prolonged antimicrobial therapy or in cystic fibrosis patients
- causes serious & terminal lung infections - poor drainage of respiratory secretions leads to repeated infections & antibiotics that select for resistant organisms
Epidemiology & transmission of burkholderia pseudomallei
- endemic in SEA & northern australia
- found in soil & surface waters (esp rainy season)
- immunocompromised eg diabetics & exposure to soil, water eg rice farmers are at risk
- Inhalation & contamination of skin abrasions
Clinical presentations of burkholderia pseudomallei (3)
- some show no early signs, but are latently infected & reactive later on (20-80% subclinical)
Melioidosis
- Pneumonia - CXR w upp lobe disease with cavitation
- Abscesses - acute/chronic
- Septicemia
Diagnosis of burkholderia pseudomallei (2)
- Culture - characteristic wrinkled colonies
2. Serology - test for antibodies/observe rise in antibody titre
Treatment of burkholderia pseudomallei (3)
- Ceftazidime/Imipenem (at least 2 weeks IV)
- Drain abscesses
- Oral maintenance ≥ 6 months (combination therapy eg doxycycline) - prolonged due to risk of relapse
Examples of vibrio
- Vibrio cholerae
- Vibrio parahaemolyticus
- Vibrio vulnificus
- Vibrio alginolyticus
Features of V. cholerae
- Oxidase positive
2. Sucrose fermenter - produces yellow colonies on TCBS agar
Transmission of V. cholerae
Faecal-oral
- esp in disasters when sewage contaminate drinking water, LDCs
Virulence factors of V. cholerae (3)
- Cholera toxin
- A subunit crosse membrane, activates adenylate cyclase - cAMP - inhibits active absorption of electrolytes & osmotic reabsorption of water by enterocytes - increases anion extrusion & decreases Na/H2O uptake + increases Na outflow & H2O secretion - vast fluid loss – causes diarrheal disease
- B subunit binds to ganglioside receptors on enterocyte membrane – immunogenic - Motility - non flagellated cells are less virulent
- Adherence - strains without pili are non virulent
Clinical presentations of V. cholerae
Cholera
- Profuse watery diarrhea
- rice water stools with fish odour
- no abdominal pain & fever, sometimes vomiting
- results in severe dehydration, can cause death <1 day
- epidemic strains are serotype 01 & 0139, the other non-epidemic strains are usually less severe
Diagnosis of V. cholerae
- Culture on selective medium (thiosulphate-citrate-bile salts-sucrose agar - TCBS) - characteristic short curved rod with single polar flagellum - rapid motility
Treatment of V. cholerae (2)
- Rehydration
- ORS - replaces fluid & electrolytes
- severe cases need IV fluids (potassium, bicarbonate & strict monitoring) - Ciprofloxacin/tetracycline
- reduce period of pathogen excretion & severity of diarrhea
Prevention of V. cholerae
- Vaccine
- against serotype 01 (inactivated V. cholerae 01 + B subunit of cholera toxin)
- none against type 0139
Features of V. parahaemolyticus
- Non sucrose fermenter - green colonies on TCBS agar
Transmission of V. parahaemolyticus
Contaminated seafood (raw/undercooked shellfish) - thrives in salt water environments
Virulence factors of V. parahaemolyticus
Secretes enterotoxin, invasive, primarily affects colon
Clinical presentations of V. parahaemolyticus
Food poisoning
- Acute onset explosive watery diarrhea/frank dysentery-like syndrome
- seldom causes severe fluid loss/significant intestinal tissue damage
- associated with cramping abdominal pain, low grade fever
Diagnosis of V. parahaemolyticus
Culture stools
Treatment of V. parahaemolyticus
- usually self limiting
- antibiotics do not alter clinical course
Transmission of V. vulnificus
- Contaminated seafood
2. Contact between sea water & wounds (found in salt water environments)
Clinical presentations of V. vulnificus (2)
- Food poisoning (ingestion of contaminated seafood)
- self-limiting diarrhea
- immunocompromised: acute septicaemia w high fever, hypotension, 50% mortality, multiple erythematous skin lesions (turn hemorrhagic, necrotic then ulcerating)
- high risk in elderly males with alcoholic liver damage - Wound infections
- cellulitis with edema, erythema & life threatening necrosis
- V. alginolyticus - cellulitis & otitis externa (assoc w seawater exposure)
Treatment of V. vulnificus
- Aggressive surgical wound debridement
2. Combinations of doxycycline/ceftazidine/ciprofloxacin
