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Flashcards in Microbiology Deck (41)
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1

As an audit task you are asked to obtain data on infective complications for all patients undergoing surgery.
Which of the following operations is likely to be associated with the highest rate of postoperative infection?
(Please select 1 option)
Abdominal hysterectomy
Cholecystectomy
Colonic surgery
Knee replacement
Limb amputation

Limb amputation This is the correct answerThis is the correct answer
According to the National Nosocomial Infections Surveillance Service limb amputation is associated with the highest overall infection rate at 14.8%.

Following amputation was surgery of the bile duct, liver and pancreas at 12.5% then gastric surgery at 11%.

Colonic surgery had an infection rate of 9.7% in the survey, whilst cholecystectomy and hysterectomy were tied at 2.4% and knee replacement surgery recorded the least infections at 1.9%.

Furthermore, 47% of organisms responsible were Staphylococci of which 87% were S. aureus and 62% of these were methicillin-resistant Staphylococcus aureus (MRSA).

2

A young mother is concerned regarding immunising her baby with 'live' viruses.
Which of the following vaccines commonly given in childhood is a live virus?
(Please select 1 option)
Diphtheria
Haemophilus influenzae type B
Measles/mumps/rubella
Pertussis
Tetanus

Measles/mumps/rubella

The measles/mumps/rubella vaccine, given at 12-18 months of age, is an example of a live attenuated vaccine, others being yellow fever and BCG.

Vaccination against diphtheria, pertussis, H. influenzae B and tetanus vaccine is usually administered at 2, 3, and 4 months along with polio in a single vaccine.

The diphtheria and tetanus components are toxoids, the pertussis and polio are inactivated and the H. influenzae B is derived from capsular polysaccharide.

3

A patient who has had a recent below-knee amputation develops an infected wound.
Wound swabs are positive for 'MRSA'.
MRSA is what type of organism?
(Please select 1 option)
A bacillus
A Gram negative organism
A Gram positive organism
A streptococcal organism
An anaerobe

A Gram positive organism

MRSA is a methicillin-resistant Staphylococcus aureus.

During the last 20 years the prevalence of hospital MRSA has fluctuated.

It is spherical in shape (coccus) and a Gram positive aerobe.

MRSA strains produce a variant penicillin-binding protein making them resistant to beta-lactam antibiotics.

4

A patient on the ward with bloody diarrhoea has been diagnosed with Clostridium difficile.
Which of the following is also associated with clostridial infection?
(Please select 1 option)
Anthrax
Diphtheria
Gonorrhoea
Meningitis
Tetanus

Tetanus This is the correct answerThis is the correct answer
Clostridial organisms are responsible for causing a whole host of different infections.

In addition to pseudomembranous colitis caused by Clostridium difficile, Clostridium species also cause:

botulism (Clostridium botulinum)
tetanus (Clostridium tetani)
food poisoning, and
gas gangrene (Clostridium perfringens).

5

Sterilisation can be achieved by using which of the following?
(Please select 1 option)
Alcohol
Chlorhexidine
Ethylene oxide
Glutaraldehyde
Iodine

Ethylene oxide is a highly penetrative gas capable of killing bacteria, spores and viruses.

It is predominantly used for the industrial sterilisation of heat sensitive equipment, such as plastics, as well as sutures and single use equipment.

The other agents listed are all used for disinfection rather than sterilisation and are not capable of removing all micro-organisms.

6

Which of the following is an RNA virus?
(Please select 1 option)
Epstein-Barr
Hepatitis B
Herpes simplex
HIV I
Molloscum contagiosum

HIV I and HIV II are both positive single-stranded RNA viruses with reverse transcriptase. They are known as retroviruses.

The other viruses listed above are all double-stranded DNA viruses.

7

A 34-year-old lady has been admitted as an emergency with abdominal pain. Blood tests have already been performed and show an elevated amylase.
Which of the following disorders is most likely to be the cause of this patient's acute pancreatitis?
(Please select 1 option)
Gallstones
Hypercortisolaemia
Hyperlipidaemia
Mumps
Trauma

Gallstones

Gallstones and alcohol cause 95% of cases of pancreatitis.

Other causes include

Trauma
Metabolic abnormalities (including hypercalcaemia, hypercholesterolaemia and hypercortisolaemia)
Iatrogenic causes (such as drugs and instrumentation of the biliary tract) and
Viruses.

8

Which of the following micro-organisms is the commonest cause of haematogenous osteomyelitis?
(Please select 1 option)
H.influenzae
Salmonella
Staphylococcus aureus
Streptococcus

Staph A

In persons with haematogenous osteomyelitis, when infection penetrates the periosteal membrane, a cloaca may form and extend into the adjacent soft tissues. Cortical sequestration can subsequently appear.

In infants and young children, a suppurative process of the metaphysis may extend into the epiphysis and also lead to involucrum formation. Other abnormalities include single or multiple Brodie's abscesses usually of staphylococcal origin. On radiographs these abscesses appear as areas of radiolucency with adjacent sclerosis.

In the metaphysis, the lucent region may connect with the growth plate by a tortuous channel (that is, channel or tract sign)
In the diaphysis, the radiolucent abscess cavity can be located in central or subcortical areas or in the cortex itself and may contain a central sequestrum
In an epiphysis, a circular, well-defined osteolytic lesion is seen.
A cortical abscess simulates the appearance of an osteoid osteoma or a stress fracture.

9

Associated with severe periodontal disease.

Porphyromonas gingivalis
Porphyromonas gingivalis causes severe periodontal disease.

10

Overgrows in the intestine after antibiotic treatment and produces two toxins, which cause antibiotic associated diarrhoea and pseudomembranous colitis.

Clostridium difficile
Stool cultures should be sent on patients who develop antibiotic-associated diarrhoea. Treatment is with metronidazole.

11

Implanted in dirty wounds and produces an exotoxin that causes hypereflexic spasm.

Clostridium tetani
The clinical manifestations of the disease are due to the potent neurotoxin, tetanospasmin.

12

Associated with necrobacillosis; a severe tonsillitis with septicaemia and metastatic abscesses.

Fusobacterium necrophorum

13

Grows in anaerobic foods and produces a toxin that blocks neuromuscular transmission causing paralysis.

Clostridium botulinum
In botulism, neurological symptoms dominate the clinical picture and include blurred vision and diplopia.

14

A 54-year-old alcoholic presents with weight loss, fever and abdominal swelling. On examination he has signs of chronic liver disease, is pyrexial and has ascites. An ascitic tap confirms a diagnosis of spontaneous bacterial peritonitis.

Cefotaxime

With regard to spontaneous bacterial peritonitis associated with alcoholic liver disease, enteric organisms are usually responsible (50% Escherichia coli). More recently, the third-generation cephalosporin, cefotaxime has been demonstrated to be as efficacious as the ampicillin/aminoglycoside combination, and it does not carry the increased risk of nephrotoxicity in cirrhotic patients.

15

A 45-year-old male presents with pain and tenderness at a venflon site. On examination there is redness, swelling and pain overlying the antecubital vein.

Flucloxacillin
This man has a thrombophlebitis post venflon insertion. The most likely organism is S. aureus and the most appropriate treatment is flucloxacillin. Alternatives in penicillin allergic patients include erythromycin.

16

A 73-year-old male presents one week post operatively with a pyrexia. On examination he has a right basal pneumonia and blood cultures reveal methicillin resistant Staphylococcus aureus (MRSA).

Vancomycin
The third case has a nosocomial MRSA sepsis and requires vancomycin therapy. Other agents that can be used in MRSA infection includes teicoplanin and linezolid.

17

An 82-year-old male presents three days after being treated for a chest infection with watery diarrhoea. Investigations confirm the presence of Clostridium difficile toxin.

Metronidazole
This patient has pseudomembranous colitis and, bearing in mind the symptomatology of the patient, he requires treatment with metronidazole. Another appropriate therapy is vancomycin.

18

A 17-year-old male is admitted with abdominal pain and fever. Examination reveals a pyrexia of 38.3°C, tender cervical and inguinal lymphadenopathy. Blood cultures are negative and a full blood count shows atypical lymphocytes.

No treatment required
This case of a young male with temperature, lymphadenopathy and atypical lymphocytes suggests a diagnosis of glandular fever. No treatment is required as it is usually self limiting. Ampicillin will induce a rash. Mesenteric adenitis may produce the abdominal pain and unnecessary laparotomies have been performed.

19

A 72-year-old male with diabetes who originally was admitted with urinary retention and was catheterised presents during the second week of his admission with fever and suprapubic discomfort. He has successfully undergone trial without catheter but his urine culture grows Pseudomonas aeruginosa.

Ciprofloxacin
This patient has a pseudomonas urinary tract infection (UTI) that requires treatment with an agent such as ciprofloxacin. Although gentamicin is an alternative, ciprofloxacin would be preferred based on renal function and no requirement to check levels.

20

A 20-year-old male is to undergo splenectomy due to Hodgkin's lymphoma.

One month before surgery

21

A 21-year-old female is to undergo cervical lymph node excision for suspected Hodgkin's disease.

Not required

Immunocompromised individuals particularly those without a spleen are very susceptible to capsulated bacteria such as Pneumococcus which may cause a fulminant septicaemia. Pneumovax may provide some protection for these patients.

Indications for pneumovax include:

Splenectomised patients
Functional asplenia
HIV positive, or
Immunocompromised patients.
Pneumovax should be administered at least two weeks prior to surgery to maximise its effects.

Hodgkin's disease confined to the cervical region does not itself require vaccination.

22

A patient requires a blood transfusion following joint replacement surgery. They ask you about the risks of acquiring a transfusion-related infection.
Which of the following infections is currently tested for?
(Please select 1 option)
Hepatitis A
Human T-cell leukaemia virus (HTLV)
Malaria
Syphilis
Variant Creutzfeldt-Jakob disease (vCJD)

Syphillis

In the United Kingdom every blood donation is screened for evidence of hepatitis B, hepatitis C, HIV I, HIV II and syphilis.

Donor selection is designed to exclude potentially infectious individuals from donating blood, but there is no testing for malaria.

Some countries exclude donors who lived in the United Kingdom over the period of the bovine spongiform encephalopathy (BSE) epidemic, but blood is not screened for vCJD in this country.

23

Which of the following cutaneous manifestations is correctly paired with its underlying disease?
(Please select 1 option)
Erythema chronicum migrans and Lyme disease
Erythema infectiosum and tuberculosis
Erythema marginatum and parvovirus B19
Erythema multiforme and sarcoidosis
Erythema nodosum and orf

Erythema chronicum migrans and Lyme disease

Erythema infectiosum, which is also referred to as 'slapped cheeks', is caused by parvovirus B19.

Erythema marginatum is a non-itchy, pale red, macular eruption. It is a major criterion for the diagnosis of rheumatic fever but is also seen in acute glomerulonephritis and drug reactions.

Erythema chronicum migrans is an expanding annular lesion occurring in Lyme disease.

Erythema nodosum is characterised by tender red swellings usually over the shins. The most common cause is streptococcal infection. Tuberculosis, sarcoidosis, leprosy, sulphonamides and inflammatory bowel disease are other important causes.

Erythema multiforme is characterised by cutaneous 'target' lesions and mucosal involvement. Children and young adults are more commonly affected. Orf, mycoplasma, and herpes simplex are among the known causes.

Erythema gyratum repens is an erythema forming repeated concentric rings; often there is an underlying malignancy.

Erythema induratum is a persistent or recurring cutaneous condition associated with past or active tuberculosis.

24

Disinfectant solutions may become contaminated with which of the following?
(Please select 1 option)
Escherichia coli
Pseudomonas aeruginosa
Salmonella species
Staphylococcus pyogenes
Streptococcus species

Pseudomonas aeruginosa

Disinfectant solutions have variable bactericidal and fungicidal properties but there are reports of contamination with:

Pseudomonas spp.
Enterobacter
Serratia
Actinomyces, and
fungi.
Bacterial spores may also survive.

25

Which of the following is true of Actinomyces israelii?
(Please select 1 option)
Colonies appear as sulphur granules
Is a fast growing organism
Is a frequent cause of urinary tract infection
Is an aerobic organism
Is Gram negative

Colonies appear as sulphur granules

Actinomyces israelii species is a Gram positive, cast-forming, non-acid-fast, non-spore-forming anaerobic bacillus that is difficult to isolate and identify. Its filamentous growth and mycelia-like colonies have a striking resemblance to fungi.

It is primarily a commensal microbe found in normal oral cavities, in tonsillar crypts, in dental plaques, and in carious teeth.

Pathologically it can cause a keratitis, skin disease, tooth disease and wound infections.

The organism is difficult to eradicate with surgery and extended penicillin-based therapy required.

26

Which of the following is true of exotoxins?
(Please select 1 option)
Are derived only from Gram positive bacteria
Are less toxic than endotoxins
Are neutralised by their homologous antitoxin
Cannot be converted to a toxoid
Have a generalised action

Are neutralised by their homologous antitoxin

Toxigenesis, or the ability to produce toxins, is an underlying mechanism by which many bacterial pathogens produce disease.

At a chemical level, there are two types of bacterial toxins

Lipopolysaccharides, which are associated with the cell walls of Gram negative bacteria, and
Proteins, which are released from bacterial cells and may act at tissue sites removed from the site of bacterial growth.
The lipopolysaccharide toxins are referred to as endotoxins and the extracellular diffusible toxins are referred to as exotoxins.

Exotoxins are soluble proteins produced by the living bacteria and are generally specific for the pathogenic bacteria involved (can be produced by both Gram positive and Gram negative bacteria, for example, enterotoxigenic Escherichia coli).

Bacterial protein toxins are the most powerful human poisons known and retain high activity at very high dilutions.

Their effect may be neutralised by the antitoxin and this is used as a treatment (toxoid).

27

Regarding bacterial plasmids, which of the following statements is true?
(Please select 1 option)
Always contain genes for enzymes that modify antibiotics
Are responsible for endotoxaemic shock
Are responsible for transferring resistance to macrolids
May be transferred by conjugation between different strains
May consist of a circular molecule of double-stranded RNA

May be transferred by conjugation between different strains

Plasmids comprise a group of extra-chromosomal, usually circular, molecules of double-stranded DNA, and may contain genetic information for various bacterial characteristics, for example, toxin production, adhesins, etc. as well as enzymes.

They can replicate autonomously (that is independently from the bacterial chromosome), and larger plasmids are transferred naturally by conjugation between bacterial strains.

DNA transferred between bacteria can be integrated into the recipient host chromosome or maintained as a plasmid.

28

Which of the following is correct concerning bacterial capsules?
(Please select 1 option)
Are associated with endotoxic shock
Are typical of Mycobacterium tuberculosis
Can transfer antibiotic resistance to other bacteria
Enhance bacterial resistance to dehydration and phagocytosis
Reduce bacterial resistance to antibiotics

Enhance bacterial resistance to dehydration and phagocytosis

Bacterial capsules are usually composed of polysaccharide and may be associated with mucoid colonial morphology. The slimy material functions as an anti-phagocytic agent and also protects the bacterial cell from the environment, for example, dehydration, and antibiotics which may be present.

However, many important bacterial pathogens do not rely on capsules, for example, M. tuberculosis.

Endotoxic shock is associated with the biological activity of Gram negative cell wall lipopolysaccharide (LPS), not capsules. Capsulated bacteria include Strep. pneumoniae and Pseudomonas.

Although capsules may help to protect against antibiotics they do not transfer antibiotic resistance.

29

Regarding necrotising fasciitis, which of the following statments is correct?
(Please select 1 option)
Conservative excision of the necrotic fascia and skin and muscle should be carried out within 24 hours
It can be treated with high dose antibiotic therapy alone
It is a severe infective process, but the skin initially appears normal
It is not common after minor trauma
Spread is limited by hyperbaric oxygen therapy

It is a severe infective process, but the skin initially appears normal

In order to limit infection spread wide surgical excision is preferred to conservative excision.

Benzylpenicillin is active against the main causative group of organisms, namely Streptococci. Antibiotics and supportive therapy are also administered.

The skin initially appears normal as the pathology lies within the subcutaneous tissue and deep fascia.

Necrotising fasciitis can arise without any history of injury, but can also follow operations or more localised infections.

30

Which one of the following is an example of a DNA virus?
(Please select 1 option)
Cystovirus
Enterovirus
Herpes simplex virus
Influenza virus
Rotavirus

Herpes simplex virus

The Herpesviridae family of viruses are dsDNA viruses that include herpes simplex, Varicella zoster, cytomegalovirus (CMV) and Epstein-Barr virus (EBV).

The influenza virus belongs to the Orthomyxoviridae family, and enteroviruses belong to the Picornaviridae family. Both are ssRNA viruses.

Rotavirus and cystovirus are dsRNA viruses.