Microbiology

Question 1

Features of Campylobacter jejuni

Answer 1

• Most common cause of acute infective diarrhoea
• Spiral, gram negative rods
• Usually infects caecum and terminal ileum. Local lymphadenopathy is common
• May mimic appendicitis as it has marked right iliac fossa pain
• Reactive arthritis is seen in 1-2% of cases

Question 2

Feature of shigella spp

Answer 2

Members of the enterobacteriaceae
Gram negative bacilli
Clinically causes dysentery
Shigella soneii is the commonest infective organism (mild illness)
Usually self limiting, ciprofloxacin may be required if individual is in a high risk group

Question 3

Features of salmonella

Answer 3

Facultatively anaerobic, gram negative, enterobacteriaceae
Infective dose varies according to subtype
Salmonellosis: usually transmitted by infected meat (especially poultry) and eggs

Question 4

Features of e coli

Answer 4

Enteropathogenic
Enteroinvasive: dysentery, large bowel necrosis/ulcers
Enterotoxigenic: small intestine, travelers diarrhoea
Enterohaemorrhagic: 0157, cause a haemorrhagic colitis, haemolytic uraemic syndrome and thrombotic thrombocytopaenic purpura

Question 5

Features of Yersinia enterocolitica

Answer 5

Gram negative, coccobacilli
Typically produces a protracted terminal ileitis that may mimic Crohns disease
Differential diagnosis acute appendicitis
May progress to septicaemia in susceptible individuals
Usually sensitive to quinolone or tetracyclines

Question 6

Features of cholera

Answer 6

Short, gram negative rods
Transmitted by contaminated water, seafood
Symptoms include sudden onset of effortless vomiting and profuse watery diarrhoea
Correction of fluid and electrolyte losses are the mainstay of treatment
Most cases will resolve, antibiotics are not generally indicated

Question 7

Define diarrhoea, acute and chronic diarrhoea

Answer 7

Diarrhoea: > 3 loose or watery stool per day
Acute diarrhoea < 14 days
Chronic diarrhoea > 14 days

Question 8

Causes of chronic diarrhoea?

Answer 8

IBS, UC, Crohns, AssCa, Coeliac disease, thyrotoxicosis, appendicitis with pelvic abscess

Question 9

What is Malignant otitis externa

Answer 9

Uncommon type of otitis externa that is found in immunocompromised individuals (90% cases found in diabetics)
Infective organism is usually Pseudomonas aeruginosa
Infection commences in the soft tissues of the external auditory meatus, then progresses to involve the soft tissues and into the bony ear canal
Progresses to temporal bone osteomyelitis

Question 10

What is necrotising fascitis

Answer 10

Advancing soft tissue infection associated with fascial necrosis
Uncommon, but can be fatal
In many cases there is underlying background immunosuppression e.g. Diabetes
Caused by polymicrobial flora (aerobic and anaerobic) and MRSA is seen increasingly in cases of necrotising fasciitis
Streptococcus is the commonest organism in isolated pathogen infection (15%)

Question 11

Describe Giardiasis

Answer 11

Diarrhoeal infection caused by Giardia lamblia (protozoan)
Infections occur as a result of ingestion of cysts
Symptoms are usually gastrointestinal with abdominal pain, bloating and passage of soft or loose stools
Diagnosis is by serology or stool microscopy
First line treatment is with metronidazole

Question 12

Describe Cryptosporidium

Answer 12

Protozoal infection
Organisms produce cysts which are excreted and thereby cause new infections
Symptoms consist of diarrhoea and cramping abdominal pains. Symptoms are worse in immunosuppressed people
Cysts may be identified in stools
Treatment is with metronidazole

Question 13

Describe Strongyloidiasis

Answer 13

Due to infection with Strongyloides stercoralis
Rare in west
Organism is a nematode living in duodenum of host
Initial infection is via skin penetration. They then migrate to lungs and are coughed up and swallowed. Then mature in small bowel are excreted and cycle begins again
An auto infective cycle is also recognised where larvae will penetrate colonic wall
Individuals may be asymptomatic, although they may also have respiratory disease and skin lesions
Diagnosis is usually made by stool microscopy
In the UK mebendazole is used for treatment

Question 14

Describe Ascariasis

Answer 14

Due to infection with roundworm Ascaris lumbricoides
Infections begin in gut following ingestion, then penetrate duodenal wall to migrate to lungs, coughed up and swallowed, cycle begins again
Diagnosis is made by identification of worm or eggs within faeces
Treatment is with mebendazole

Question 15

Describe Ancylostoma duodenale

Answer 15

Hookworms that anchor in proximal small bowel
Most infections are asymptomatic although may cause iron deficiency anaemia
Larvae may be found in stools left at ambient temperature, otherwise infection is difficult to diagnose
Infection occurs as a result of cutaneous penetration, migrates to lungs, coughed up and then swallowed
Treatment is with mebendazole

Question 16

Describe Enterobiasis

Answer 16

Due to organism Enterobius vermicularis
Common cause of pruritus ani
Diagnosis usually made by placing scotch tape at the anus, this will trap eggs that can then be viewed microscopically
Treatment is with mebendazole