12- Microbiology MSQs Only

Question 1

2 of 53

What is the mechanism of action of macrolides?

Answer 1

Inhibits protein synthesis

Macrolides act by inhibiting bacterial protein synthesis. If pushed to give an answer they are bacteriostatic in nature, but in reality this depends on the dose and type of organism being treated. Erythromycin was the first macrolide used clinically. Newer examples include clarithromycin and azithromycin.
Adverse effects of erythromycin gastrointestinal side-effects are common cholestatic jaundice: risk may be reduced if erythromycin stearate is used P450 inhibitor

Question 2

3 of 53

An enthusiastic watercress farmer is admitted with a protracted history of severe abdominal pain, fevers and progressive jaundice. Imaging with ultrasound shows mildly dilated bile ducts with hyperechoic areas within them. What is the most likely cause?

Answer 2

Fasciola hepatica

The watercress history is important here as fasicola hepatica is most classically transported to humans through eating watercress. The USS finding of luminal parasites is classical and its this that contributes to jaundice.

Question 3

4 of 53

A 21 year old man is admitted with crampy abdominal pain and diarrhoea. He attended a large wedding earlier in the day. Several other guests are also affected with the same illness. Which of the organisms is likely to be accountable?

Answer 3

Clostridium perfringens

C. Perfringens is a common cause of food borne illness and its ability to form spores may make it relatively resistant to cooking. The timing of onset would favor C. Perfringens which typically evolves over several hours, rather than staphylococcus aureus poisoning which may occur sooner.

Question 4

6 of 53

A 68 year old man with diabetes presents with an area of necrosis of the perineum at the base of the scrotum, there is some surrounding erythema. He is systemically unwell and hypotensive. Which of the following organisms is likely to be accountable?

Answer 4

E-coli and bacteroides

This is likely to be Fournier’s Gangrene. A number of agents are implicated. E-coli and bacteroides are the most commonly isolated organisms. The key point is that both aerobic and anaerobic organisms must be present.

Question 4

7 of 53

A 34 year old homosexual is admitted with diarrhoea of 3 months duration. He is found to be HIV positive with a CD4 count <50. Which of the organisms listed below is most likely to be responsible?

Answer 4

Cryptosporidium

Although a self limiting diarrhoea is the norm, this is not the case in immunocompromised individuals who can develop severe illness. Other organisms may include Salmonella, Shigella, and Campylobacter.

Question 5

5 of 53

A 58 year old man undergoes a difficult colonoscopy for assessment of a caecal cancer. 48 hours after the procedure he is admitted with septicaemia. His abdomen is soft and non tender. Blood cultures grow gram positive cocci. What is the most likely underlying organism?

Answer 5

Streptococcus bovis

Streptococcus bovis septicaemia is associated with carcinoma of the colon. It can also cause endocarditis.

Question 6

8 of 53

A 62 year old lady is unwell following a difficult acute cholecystectomy for acute cholecystitis. Her gallbladder spilled stones intraoperatively and she has been on ciprofloxacin intravenously for this for the past 4 days. She now has colicky abdominal pain and profuse, foul smelling diarrhoea. Which of the organisms below is likely to account for this illness?

Answer 6

Clostridium difficile

C. difficile may complicate administration of broad spectrum antibiotics.

Question 7

9 of 53

A 30 year old aid worker becomes unwell whilst helping at the scene of a recent earthquake. He develops vomiting and soon afterwards a diarrhoea that is loose and extremely watery. What is the most likely infective organism?

Answer 7

Vibrio cholera

The passage of very loose and watery stools distinguishes cholera. Most gastroenteric infections do not produce such watery motions.

Question 8

10 of 53

A 45 year old man is recovering in hospital following a total hip replacement. He develops a profuse and watery diarrhoea. Several other patients have been suffering from similar symptoms. Infection with which of the following is the most likely underlying cause?

Answer 8

Clostridium difficile

Clostridium difficile can spread rapidly on surgical wards. The use of broad spectrum prophylactic antibiotics during arthroplasty surgery can increase the risk.

Question 9

11 of 53

A 22 year old man presents with a painless penile ulcer and marked inguinal lymphadenopathy. Some of the exudate from the lesion is sent for microscopy. What organism is most likely to be visualized?

Answer 9

Treponema pallidum

A hard painless ulcer affecting the genital area of a young male is likely to be the primary lesion of syphilis and that is caused by treponema pallidum. It would be unusual for actinomycosis to affect this area.

Question 10

12 of 53

What is the risk of wound infection occurring in a 43 year old woman who is undergoing a laparoscopic cholecystectomy for uncomplicated biliary colic?

Answer 10

5%

The incidence is higher because it is a clean contaminated wound. If there is a bile spill the risks increase and intravenous antibiotics should be given perioperatively.

Question 11

13 of 53

Which statement relating to actinomycosis is false?

Answer 11

They are gram positive bacilli
They are strict aerobes (Right)
It may be a cause of chronic multiple abscesses
Abdominal cases may develop in the appendix
Open biopsy of the lesions is the best diagnostic test
…………………………………………………………….
They are facultative anaerobes and may be difficult to culture. Direct visualisation of organisms and sulphur granules from lesions themselves is the easiest way to make a diagnosis. It remains a differential of conditions such as hydradenitis supprativa, particularly if it is occurring in odd locations and with deeper abscesses than usual.

Question 12

14 of 53

A 25 year old man returns from a backpacking holiday in India. He presents with symptoms of coughing and also of episodic abdominal discomfort. Peri anal examination is normal. Stool microscopy demonstrates both worms and eggs within the faeces. What is the most likely infective organism?

Answer 12

Ascaris lumbricoides

Infection with Ascaris lumbricoides usually occurs after individuals have visited places like sub Saharan Africa or the far east. Unlike ancylostoma duodenale infection there is usually evidence of both worms and eggs in the stool. The absence of pruritus makes enterobius less likely. The presence of coughing may be due to the migration of the larva through the lungs.

Question 13

15 of 53

A 22 year old man returns to the UK from holiday in India. He presents with painless jaundice. On examination he is not deeply jaundiced and there is no organomegaly. What is the most likely cause?

Answer 13

Hepatitis A infection

Infective hepatitis is the most likely cause. In the UK, foreign travel is a common cause of developing infectious hepatitis, of which hepatitis A is the most common.

Question 14

16 of 53

What is the risk of a wound infection in a male undergoing a Hartmanns procedure for perforated sigmoid diverticular disease?

Answer 14

35%

These infected cases carry a high risk of wound infection. In really heavily contaminated cases, some surgeons do not close the skin at all. Even if antibiotics are given in this case, the infection rate will still be very high.

Question 15

17 of 53

A young woman is admitted to hospital with E-coli 0157 after visiting Germany during an outbreak. Which of the following is not true of the condition?

Answer 15

It may be complicated by micro-angiopathic haemolytic anaemia.
Adults typically develop haemolytic uraemic syndome.(Right)
It is most commonly transmitted by consumption of contaminated food.
Plasmids typically confer antibiotic resistance.
E-Coli is a gram negative organism.
…………………………………………………………….
Children typically develop this complication.

Question 16

18 of 53

Which virus is implicated in cervical carcinoma?

Answer 16

Human papilloma virus 16

Question 17

19 of 53

A 72 year old man with peripheral vascular disease develops a gangrenous toe. This becomes infected and there is evidence of infection in the surrounding tissues. On clinical palpation there is crepitus present within the tissues. What is the most likely infective organism?

Answer 17

Clostridium perfringens

Clostridium perfringens is the most likely pathogen to be associated with gangrene.

Question 18

20 of 53

A 23 year old man is readmitted following a difficult appendicectomy. His wound is erythematous and, on incision, foul smelling pus is drained. Which of the organisms listed below is responsible?

Answer 18

Bacteroides fragilis

Bacteroides is commonly present in severe peritoneal infections and as it is facultatively anaerobic may be present in pus. It has a pungent aroma.

Question 19

21 of 53

What is the commonest cause of an amoebic liver abscess?

Answer 19

Entamoeba histolytica

Enamoeba histiolytica is the only agent on the list that would produce an amoebic abscess.

Question 20

22 of 53

A surgical trainee is incising a groin “abscess” in an intravenous drug abuser. Unfortunately the “abscess” is a false aneurysm and torrential bleeding ensues. In the panic of the situation the doctor then stabs himself in the finger. It transpires that the patient is a Hepatitis B carrier and the doctor is not immunised! What type of virus is Hepatitis B?

Answer 20

Double stranded DNA virus

Question 21

23 of 53

Which of the following statements related to necrotising fasciitis is false?

Answer 21

Mainly polymicrobial.
A feature may include ‘dirty dishwater fluid’ in the wound.
The presence of crepitus is needed to make the diagnosis.
Further surgery is mandatory 24-48h after initial surgery to review extension of infection. (Right)
The muscles are relatively spared.
…………………………………………………………….
Never attempt primary closure after the initial debridement of necrotising fasciitis.

Crepitus may be present in only 35% of cases, therefore its absence should not exclude a diagnosis of necrotising fasciitis.

Question 22

24 of 53

A 53-year-old woman is diagnosed with cellulitis surrounding her leg ulcer. A swab is taken and oral flucloxacillin is started. The following result is obtained:
Skin swab: Group A streptococcus
How should the antibiotic therapy be adjusted?

Answer 22

Add penicillin

Penicillin is the antibiotic of choice for group A streptococcal infections. The BNF suggests stopping flucloxacillin if streptococcal infection is confirmed in patients with cellulitis, due to the high sensitivity. This should be balanced however with the variable absorption of phenoxymethylpenicillin.

Question 23

25 of 53

A 68 year old women with previous rheumatic fever is admitted with pyrexia of unknown origin. Her blood cultures are unhelpful but transoesophageal echocardiography reveals vegetations on the mitral valve. Infection with which of the following organisms is most likely?

Answer 23

Streptococcus viridans

This is the most common organism affecting previously abnormal heart valves.

Question 24

26 of 53

Which of the following is not a feature of Campylobacter jejuni infection?

Answer 24

Infection may present in a similar manner to acute appendicitis
Pyrexia is unusual (Right)
They are gram negative organisms
Infection accounts for 26% case of Guillain-Barre syndrome
It is the commonest cause of infective diarrhoea arising from non viral causes
…………………………………………………………
A prodromal period of fever and generalised malaise precedes abdominal pain (which may mimic appendicitis) and diarrhoea.

Question 24

28 of 53

A 6 year old boy presents with symptoms of recurrent pruritus ani. On examination, there is evidence of a small worm like structure protruding from the anus. What is the most likely infective organism?

Answer 24

Enterobius vermicularis

Infection with enterobius is extremely common. Pruritus is the main symptom, as there is a lack of tissue invasion it is rare for individuals to have any signs of systemic sepsis.

Question 24

27 of 53

A 54-year-old female is admitted one week following a cholecystectomy with profuse diarrhoea. Apart from a minor intra-operative bile spillage incurred during removal of the gallbladder, the procedure was uncomplicated. What is the most likely diagnosis?

Answer 24

Clostridium difficile infection

This is a complex question, read the explanation below carefully. It tests two domains, firstly that bile spill is an indication for broad spectrum intravenous antibiotics and that this is a risk factor for clostridium difficile (which explains the diarrhea post antibiotic administration)

Antibiotics are not routinely administered during an uncomplicated cholecystectomy. Indications for administration of broad spectrum antibiotics include intraoperative bile spillage. Delayed pelvic abscesses following bile spills are extremely rare since most surgeons will manage these intra-operatively.

Question 25

29 of 53

A 22 year old man presents with crampy abdominal pain diarrhoea and bloating. He has just returned from a holiday in Egypt. He had been swimming in the local pool a few weeks ago. He reports that he is opening his bowels 5 times a day. The stool floats in the toilet water, but there is no blood. What is the most likely cause?

Answer 25

Giardia lamblia

Giardia causes fat malabsorption, therefore greasy stool can occur. It is resistant to chlorination, hence risk of transfer in swimming pools.

Question 26

30 of 53

A 50-year-old female with a history of rheumatoid presents with a suspected septic knee joint. A diagnostic aspiration is performed and sent to microbiology. Which of the organisms below is most likely to be responsible?

Answer 26

Staphylococcus aureus

Septic arthritis - most common organism: Staphylococcus aureus

Question 27

31 of 53

A 48 year old lady is admitted with crampy abdominal pain and diarrhoea. She has been unwell for the past 12 hours. In the history she complains that her milk bottles have been pecked repeatedly by birds, she otherwise has had no dietary changes. Which of the following is the most likely causative organism?

Answer 27

Campylobacter jejuni

Birds are a recognised reservoir of campylobacter.

Question 28

32 of 53

A 32 year old woman undergoes mastectomy and latissimus dorsi flap reconstruction for breast cancer, to provide optimal cosmesis a McGhan implant is placed under the myocutaneous flap. Three weeks post operatively the patient continues to suffer from recurrent wound infections that have proved resistant to multiple courses of antibiotics. Which of the organisms listed below is most likely to be responsible?

Answer 28

Staphylococcus epidermidis

This tends to colonise plastic devices and forms a biofilm which allows colonisation with other bacterial agents. It is notoriously difficult to eradicate once established and the usual treatment is removal of the device.

Question 28

34 of 53

A 22 year old man presents with a 5 day history of sore throat, malaise and fatigue. On examination, he has a large peritonsillar abscess. What is the most likely underlying infective organism?

Answer 28

Streptococcus pyogenes

Quinsy usually occurs as a result of bacterial tonsillitis and the most common cause of bacterial tonsillitis is streptococcal organisms.

Question 29

33 of 53

Which of the following statements relating to osteomyelitis is false?

Answer 29

Is the result of haematogenous spread in most cases
Is due to Staphylococcus aureus in 50% cases
Should be treated by aggressive surgical debridement initially(Right)
Plain radiographs may be normal in the early stages
The presence of associated septic joint involvement will significantly alter management
………………………………………………………..
It is managed medically in the first instance (with an antistaphylococcal antibiotic).
This differs from the situation in septic joints where early joint washout is mandatory.

Question 30

35 of 53

A 27-year-old male presents to urology for investigation of pyelonephritis. He reports malaise, pyrexia, lymphadenopathy and a maculopapular rash. The Monospot test is negative. Given a history of recent high-risk sexual behaviour you are asked to exclude a HIV seroconversion illness. What is the most appropriate investigation?

Answer 30

p24 antigen test

Question 31

36 of 53

In a 72 year old man undergoing a sigmoid colectomy for diverticular disease, which of the following interventions is most likely to reduce his risk of developing a post operative wound infection?

Answer 31

Administration of single dose of broad spectrum antibiotics prior to the procedure

Administration of prophylactic antibiotics will reduce the risk of wound infection. Plain incise drapes increase the risk of wound infections and should not be used. Iodophor impregnated drapes have been demonstrated to reduce the risk of wound infection. Shaving one day prior to surgery will increase the risk.

Question 32

37 of 53

A 48 year old lady undergoes an ERCP for jaundice. 36 hours following the procedure she develops a fever and rigors. A blood culture is taken, which of the following organisms is most likely to be cultured?

Answer 32

Escherichia coli

Charcots triad = Surgical emergency.
Patients need: Biliary decompression and broad spectrum antibiotics.

E Coli is the most common organism implicated in cholangitis infections. Whilst enterobacter is occasionally cultured it is not the most common organism.

Question 33

38 of 53

A 77-year-old female presents with a non-healing ulcer on her right foot. Blood cultures grow MRSA. Which antibiotic would you consider in addition to vancomycin to cover this?

Answer 33

Rifampicin

The MRSA would or may be resistant to Other antibiotics. Rifampicin is normally given in combination with another antibiotic.

Question 34

39 of 53

Which of the following is true regarding the Salmonella species?

Answer 34

A relative bradycardia is often seen in typhoid fever

Question 35

40 of 53

A 58 year old man is reviewed in the clinic following a successful cadaveric renal transplant the previous year. He has been able to return to work as a swimming instructor. Over the past week he reports that he has been suffering from recurrent episodes of diarrhoea. It has made him feel lethargic and exhausted. Stool microscopy shows evidence of cysts. What is the most likely source of infection?

Answer 35

Cryptosporidium

Cryptosporidium is associated with infection, particularly in those who are immunocompromised. Diarrhoea is the main disease. The cysts are typically identified on stool microscopy.

Question 36

41 of 53

A 22 year old lady is breastfeeding her first child. One week post partum she presents with a tender indurated mass in the right breast. Infection with which of the following is most likely?

Answer 36

Staphylococcus aureus

Staphylococcus aureus is the commonest cause of lactational mastitis.

Question 37

44 of 53

A 22 year old man has undergone an inguinal hernia repair. Seven days later he presents with an erythematous and tender wound that is discharging a purulent material. What is the most likely cause?

Answer 37

Infection with Staphylococcus aureus

In this setting Staphylococcus aureus Infection is the most likely cause. In the UK between 2010 and 2011 the commonest cause of wound infection was enterobacter infections (usually following cardiac or colonic surgery). 23% of infections were due to Staph aureus, which fits the scenario above. Infection with the other organisms including strep pyogenes was much rarer.

Question 37

42 of 53

A group of consultant surgeons are meeting at a symposium. The chef preparing the canapes has an infection on his finger. Approximately 40 minutes after eating the canapes the group are struck down with severe vomiting. What is the most likely underlying explanation for this process?

Answer 37

Presence of enterotoxin from Staphylococcus aureus in the food

Staphylococcus aureus may release an enterotoxin, this is preformed and thus will typically result in rapid onset of symptoms in affected individuals.

Question 37

43 of 53

A 22 year old female is admitted to A&E with a splenic rupture. She has not been involved in any trauma. What infection can cause spontaneous splenic rupture?

Answer 37

Epstein-Barr virus

Epstein - Barr Virus may cause generalised lymphadenopathy. This may be associated with splenomegaly. This enlargement has been associated with spontaneous rupture.

Question 38

45 of 53

A 28 year old lady is breast feeding her first child. She presents with discomfort of the right breast. Clinical examination demonstrates erythema and an area that is fluctuant. Aspiration and culture of the fluid is most likely to demonstrate infection with which of the following organisms?

Answer 38

Staphylococcus aureus

Staphylococcus aureus is the commonest cause. The infants mouth is usually the source as it damages the nipple areolar complex allowing entry of bacteria.

Question 39

46 of 53

Which of the following is not associated with Epstein-Barr virus?

Answer 39

Burkitt’s lymphoma
Post-transplantation lymphoma
Hodgkin’s lymphoma
Nasopharyngeal carcinoma
Mycosis fungoides(Right)

Question 40

47 of 53

Which of the following cancers is not associated with the human papillomavirus?

Answer 40

Anal cancer
Oropharyngeal cancer
Tracheal cancer(Right)
Vulval cancer
Penile cancer
……………………………………………….
HPV is associated with:
1. Cervical cancer (HPV 16/18 most common)
2. Anal cancer
3. Penile cancer
4. Vulval cancer
5. Oropharyngeal cancer

Question 41

48 of 53

A 29 year old female undergoes a sub total thyroidectomy. Five days post operatively the wound becomes erythematous and discharges pus. What is the most likely causative organism?

Answer 41

Staphylococcus aureus

In this setting Staphylococcus aureus Infection is the most likely cause. In the UK between 2010 and 2011 the commonest cause of wound infection was enterobacter infections (usually following cardiac or colonic surgery). 23% of infections were due to Staph aureus, which fits the scenario above. Infection with the other organisms including strep pyogenes was much rarer.

Question 42

49 of 53

A 53 year old man presents with an ulcerated mass at the anal verge. A biopsy is taken and the histology demonstrates as squamous cell carcinoma. Infection with which of the viruses below is most likely to have contributed to the development of the condition?

Answer 42

Human papillomavirus 16

Infection with human papilloma virus 16 is a risk factor for the development of intra epithelial dysplasia of the anal skin with subsequent increased risk of invasive malignancy.

Question 43

50 of 53

What is the likely risk of surgical wound infection in a 23 year old male undergoing an elective inguinal hernia repair?

Answer 43

Less than 5%

This is a clean procedure and carries the lowest risk of SSI. That is why it is safe to use meshes in these settings.

Question 44

52 of 53

A 23 year old woman is admitted with sepsis and right loin pain. She has a history of a UTI that was treated by the GP with a course of trimethoprim that was commenced 24 hours previously. Which of the organisms listed below is the most likely cause?

Answer 44

E-Coli

Ascending infection of the genitourinary tract is most commonly caused by E-Coli.
Other organisms may be accountable, however, these are less common

Question 44

51 of 53

A 28 year old chef presents to the medical team with profuse bloody diarrhoea. On further questioning he describes tenesmus. They arrange a sigmoidoscopy which reveals necrosis and ulceration of the descending colon mucosa. What is the most likely cause?

Answer 44

Infection with entero invasive E Coli

Necrosis and ulcers of the large bowel are a feature of enteroinvasive E.coli. It presents with a dysentery type illness similar to shigellosis.

Question 44

53 of 53

A 68 year old man with poorly controlled diabetes presents with severe otalgia and headaches. On examination, there is granulation tissue within the external auditory meatus. What is the most likely underlying infective agent?

Answer 44

Pseudomonas aeruginosa
…………………………………………..
Malignant otitis externa is caused by Pseudomonas aeruginosa

Severe pain, headaches and granulation tissue within the external auditory meatus are key features of malignant otitis externa. Diabetes mellitus is one of the commonest risk factors.