Gram-negative bacilli

Question 1

What is E.Coli?

Answer 1

facultative anaerobic, lactose-fermenting, Gram negative rod which is a normal gut commensal

Part of the enterobacteriacea family

Question 2

What diseases does E.Coli cause?

Answer 2

Intestinal disease:

• Enterotoxigenic: a major cause of traveller’s diarrhoea
• Enterohaemorrhagic e.g. O157:H7: severe, haemorrhagic, watery diarrhoea. It has a high mortality rate and can be complicated by HUS. It is often spread by contaminated ground beef.
• Enteropathogenic: infants in areas of poor sanitation
• Enteroinvasive: dysentery-like syndrome.
• Enteroadherent: traveller’s diarrhoea, chronic diarrhoea in children/hiv.

Extra-intestinal disease (from own flora that is not pathogenic in the intestine causing disease elsewhere):

• UTI
• Neonatal meningitis
• Nosocomial infection
• Pneumonia
• Meningitis
• Sepsis

Question 3

What is Klebsiella pneumonia?

Answer 3

Gram-negative rod that is part of the normal gut flora, mouth and skin

Question 4

What can Klebsiella cause?

Answer 4

• Pneumonia (usually following aspiration) –> 50% mortality
• UTI
• Necrotizing disease and sepsis if immunosuppressed
• Nasopharyngeal inflammation
• Associated with antibiotic exposure, in-dwelling catheters, immunosuppression

Question 5

What is Proteus mirabilis?

Answer 5

Gut commensal

Question 6

What does Proteus mirabilis cause?

Answer 6

UTI (very fishy odor, struvite stonesm urease +++

NB: struvite stones –> from urease production that breaks down urea to make ammonia and then these stones form in the presence of magnesium, calcium, and phosphate

Question 7

What is pseudomonas aeruginosa?

Answer 7

Aerobic gram-negative rod found in environment.

Spread by contact/ingestion.

Important cause of nosocomial infection

Question 8

What does pseudomonas aeruginosa cause?

Answer 8

Causes infection in compromised tissue:

• chest infections (especially in cystic fibrosis or ventilation)
• skin: burns, wound infections, ‘hot tub’ folliculitis
• otitis externa (especially in diabetics who may develop malignant otitis externa)
• UTI with catheterization
• Septicaemia if immunosuppressed

Question 9

What are the features of pseudomonas aeruginosa?

Answer 9

• Characteristic blue-green pigment
• Gram-negative rod
• Non-lactose fermenting
• Oxidase positive

Question 10

How do you treat P. aeruginosa?

Answer 10

Resistant to many antibiotics (specific to cover) –> from Impermeability of membrane and biofilm colonization

Options include ceftazidime/carbapenem, aminoglycoside, colistin

Combination may be needed.

Question 11

What is the pathophysiology of P.aeruginosa?

Answer 11

Produces both an endotoxin (causes fever and shock) and exotoxin A (inhibits protein synthesis by catalyzing ADP-ribosylation of elongation factor EF-2)

Question 12

What is H.influenza?

Answer 12

Divided into encapsulated, typeable forms (a-f); and unencapsulated, non-typeable forms.

Upper respiratory tract carriage, transmitted by droplets

Question 13

What does Hib cause?

Answer 13

• Meningitis
• Epiglottitis, otitis media
• Pneumonia, cellulitis
• Septic arthritis
• Bacteraemia.
• Fatal in ~5%. Routine immunization in childhood and splenectomy/hyposplenism.

Question 14

What is the treatment of Hib?

Answer 14

Non-typeable forms cause pneumonia and sinusitis.

Treatment: amoxicillin, macrolide, cephalosporin, chloramphenicol, rifampicin.

Question 15

What does bordetella pertussis present?

Answer 15

• Catarrhal phase (coryza, fever) 1–2wk
• Then paroxysmal coughing (1pp days)
• ‘Whoop’ is a breath through partially closed vocal cords, seen mainly in children. Infants have ↑complications/mortality.

Question 16

How do you diagnose bordetella pertussis?

Answer 16

PCR nasal/throat swab. Culture sensitivity 10–60%.

Question 17

How do you treat bordotella pertussis?

Answer 17

• Macrolides (erythromycin) ↓infectivity but may not alter disease course
• Routine childhood vaccination
• Vaccination in pregnancy ↑placental antibody transfer to protect neonate