Gram Negative Rods - Pseudomonads & Vibrio

Question 1

Features of pseudomonads

Answer 1

1. Mostly found in the environment

2. Not normal flora

Question 2

Examples of pseudomonads

Answer 2

1. Pseudomonas aeruginosa (PAE)
2. Stenotrophomonas maltophilia
3. Burkholderia spp
   - Burkholderia cepacia
   - Burkholderia pseudomallei

Question 3

Features of PAE

Answer 3

1. Oxidase positive
2. Non-lactose & non-glucose fermenter
3. Motile
4. Aerobic growth
5. Produce diffusible pigments (commonly green)
6. Found in moist conditions
7. Important cause of opportunistic infections (hospitalised & immunocompromised, on antibiotics, community acquired eg contact lenses, spa baths)

Question 4

Virulence factors of PAE

Answer 4

1. Produces slime/biofilm, allows adherence to implants/lines

Question 5

Clinical presentations of PAE (10)

Answer 5

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

7. Ear infections - malignant otitis externa (spreads to face, neck, bone - req systemic treatment), chronic suppurative otitis meda, esp in elderly diabetes
8. Eye infections - keratitis (corneal ulcer - penetrates/perforates cornea - panophthalmitis), due to contaminated contact lens fluids, ocular medications, minor eye trauma
9. Skin infections - jacuzzi/whirlpool rash (folliculitis)
10. Nail infections

Question 6

Diagnosis of PAE

Answer 6

1. Biochemical tests

2. Mass spectroscopy

Question 7

Treatment of PAE (4)

Answer 7

1. Piperacillin
2. Carbapenems, 3G cephalosporins, aminoglycosides, quinolones
3. HAI usually MDR - check antibiotic sensitivities
4. Severe infection, neutropenia - use 2 antibiotics eg ceftazidime + gentamicin

Question 8

Prevention of PAE

Answer 8

1. Prophylactic ciprofloxacin for neutropenic patients, also prevents septicaemia

Question 9

Treatment of stenotrophomonas maltophilia

Answer 9

• nosocomial pathogen, less common than PAE, MDR
• produces carbapenemases - resistant to carbapenems
  1. Co-trimoxazole, levofloxacin

Question 10

Features of burkholderia cepacia

Answer 10

• 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

Question 11

Epidemiology & transmission of burkholderia pseudomallei

Answer 11

• 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

1. Inhalation & contamination of skin abrasions

Question 12

Clinical presentations of burkholderia pseudomallei (3)

Answer 12

• some show no early signs, but are latently infected & reactive later on (20-80% subclinical)

Melioidosis

1. Pneumonia - CXR w upp lobe disease with cavitation
2. Abscesses - acute/chronic
3. Septicemia

Question 13

Diagnosis of burkholderia pseudomallei (2)

Answer 13

1. Culture - characteristic wrinkled colonies

2. Serology - test for antibodies/observe rise in antibody titre

Question 14

Treatment of burkholderia pseudomallei (3)

Answer 14

1. Ceftazidime/Imipenem (at least 2 weeks IV)
2. Drain abscesses
3. Oral maintenance ≥ 6 months (combination therapy eg doxycycline) - prolonged due to risk of relapse

Question 15

Examples of vibrio

Answer 15

1. Vibrio cholerae
2. Vibrio parahaemolyticus
3. Vibrio vulnificus
4. Vibrio alginolyticus

Question 16

Features of V. cholerae

Answer 16

1. Oxidase positive

2. Sucrose fermenter - produces yellow colonies on TCBS agar

Question 17

Transmission of V. cholerae

Answer 17

Faecal-oral

- esp in disasters when sewage contaminate drinking water, LDCs

Question 18

Virulence factors of V. cholerae (3)

Answer 18

1. 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
2. Motility - non flagellated cells are less virulent
3. Adherence - strains without pili are non virulent

Question 19

Clinical presentations of V. cholerae

Answer 19

Cholera

1. 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

Question 20

Diagnosis of V. cholerae

Answer 20

1. Culture on selective medium (thiosulphate-citrate-bile salts-sucrose agar - TCBS) - characteristic short curved rod with single polar flagellum - rapid motility

Question 21

Treatment of V. cholerae (2)

Answer 21

1. Rehydration
   - ORS - replaces fluid & electrolytes
   - severe cases need IV fluids (potassium, bicarbonate & strict monitoring)
2. Ciprofloxacin/tetracycline
   - reduce period of pathogen excretion & severity of diarrhea

Question 22

Prevention of V. cholerae

Answer 22

1. Vaccine
   - against serotype 01 (inactivated V. cholerae 01 + B subunit of cholera toxin)
   - none against type 0139

Question 23

Features of V. parahaemolyticus

Answer 23

1. Non sucrose fermenter - green colonies on TCBS agar

Question 24

Transmission of V. parahaemolyticus

Answer 24

Contaminated seafood (raw/undercooked shellfish) - thrives in salt water environments

Question 25

Virulence factors of V. parahaemolyticus

Answer 25

Secretes enterotoxin, invasive, primarily affects colon

Question 26

Clinical presentations of V. parahaemolyticus

Answer 26

Food poisoning 1. 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

Question 27

Diagnosis of V. parahaemolyticus

Answer 27

Culture stools

Question 28

Treatment of V. parahaemolyticus

Answer 28

- usually self limiting | - antibiotics do not alter clinical course

Question 29

Transmission of V. vulnificus

Answer 29

1. Contaminated seafood | 2. Contact between sea water & wounds (found in salt water environments)

Question 30

Clinical presentations of V. vulnificus (2)

Answer 30

1. 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 2. Wound infections - cellulitis with edema, erythema & life threatening necrosis - V. alginolyticus - cellulitis & otitis externa (assoc w seawater exposure)

Question 31

Treatment of V. vulnificus

Answer 31

1. Aggressive surgical wound debridement | 2. Combinations of doxycycline/ceftazidine/ciprofloxacin