Question book Flashcards

1
Q

34 year old haematuria months after swimming in Lake Malawi.

What is optimal sample type for microscopy?

mid-stream urine
terminal void urine
early morning urine
24-hour urinary collection
cystoscopy and biopsy
A

Terminal void urine is best for S. haematobium

24 hour urine is also good sampling method, but more difficult for patient to perform.

Take sample 5 weeks after exposure, as no eggs passed prior to this

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2
Q

34 year old with haematuria.
What would be your confirmatory diagnostic finding in schistosomiasis?

Cysts
Larvae
Ova
Adults
Microfilariae
A

Ova

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3
Q

Schistosomiasis species.

Where is the spine present?

S. haematobium
S mansoni
S. japonicum

A

S. haematobium - terminal spine
S mansoni - lateral spine
S. japonicum - spherical with small knob

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4
Q

Schistosomiasis species.

Where is the spine present?

S. haematobium
S mansoni
S. japonicum

A

S. haematobium - terminal spine
S mansoni - lateral spine
S. japonicum - spherical with small knob

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5
Q

45 year old who keeps reptiles presents with enteritis. Which phenotypic aspects of Salmonella Arizonae must be considered during stool culture?

it does not grow on routine media
it is oxidase positive
it is a lactose fermenter
is it urease positive
it does not grow on XLD
A

it is a lactose fermenter

S. arizonae has a particular association with reptiles, including tortoises and snakes. Can cause enteritis, meningitis and septic arthritis.

Most Salmonella are lactose non-fermenters, so this sub-species can complicate the diagnostics

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6
Q

27 year old with fever after return from India. Which sample would provide highest yield of Salmonella Typhi?

Nasopharyngeal aspirate
Blood
Stool
Bone marrow
Urine
A

Bone marrow

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7
Q

MALDI-TOF suggests blood culture isolate is Salmonella Typhi.

How would you further confirm the isolate identity?

Use biochemical kit
Send it to reference lab
No additional tests needed 
Perform serology (Vi group)
Perform serology (W group)
A

Perform serology (Vi group)

MALDI-TOF and selective media XLD give early identification, but are unreliable in discerning serovar assignment.

Latex agglutination of somatic “O”, flagellar “H” and Vi antigens can provide more specific identification

Vi antigen is capsular antigen which is virulence factor that protects against phagocytosis and complement

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8
Q

Working in refugee camp, outbreak of enteritis. Which is the best transport media for faecal specimens?

Cary-Blair
Amies
Stuart
Alkalne peptone water
Buffered glycerol saline
A

Cary-Blair

Preserves the most common pathogen, including Vibrio spp

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9
Q

27 year old male presents with enteritis and Salmonella Paratyphi grown.

Why is S. paratyphi A notabable among Salmonella spp

Lysine decarboxylase negative
Hydrogen sulphide negative
Gas negative
Urea positive
Phenylalanine deamianse positive
A

Lysine decarboxylase negative - used to identify non-typhoidal salmonella

test also used to identify shigella, which is also negative
S. paratyphi A can occasionally be mis-identified as Shigella

Most other Enterobacteriales are positive - E.coli, Klebsiella, Serratia, Vibrio

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10
Q

What is unique about Shigella dysenteriae serotype 1 compared to other Enterobacteriaeles?

It is oxidase positive
It is catalase positive
It is catalase negative
It does not grow on CLD
It is not a member of the Enterobacteriales
A

It is catalase negative

Almost all of Enterobacteriales, including most Shigella, are catalase pos

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11
Q

27 year old with known HIV presents with enteritis. Which Campylobacter species may not be identified by standard Campylobacter incubation temperatures?

C jejuni
C fetus
C coli
C lari
C ureolyticus
A

C fetus

Campylobacter normally incubated at 42degC for 48 hours microaerobically. This increases rate of growth of Campylobacter, whilst reducing growth of other species. C. fetus does not grow as well at these temps

Campylobacter usually divided in human oral commensals, and those that are zoonotic (C, jejuni, C. coli)

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12
Q
Patient with fever. Blood culture shows:
gram pos cocci
catalase neg
latex agglutination group D
sensitive to penicillin

What is most likely identity?

Enterococcus faecium
Leuconostoc lactis
Streptococcus gallolyticus
Streptococcus agalactiae
Streptococcus constellatus
A

Streptococcus gallolyticus (previously Strep Bovis)

Enterococcus faecium - also group D, but usually resistant to pencillin

Streptococcus agalactiae - group B
Streptococcus constellatus - Group C or G

Group D - enterococci or Strep bovis (gamma haemolytic unlike other beta haemolytic streptococci)

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13
Q

What is meaning of term psychrophilic?

A

Is same term as Cryophile - can grow in temperatures <15degC

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14
Q

What is the importance of use of XLD agar?

A

XLD agar is selective media, which discerns Salmonella spp. and Shigella spp.

Salmonella appears as red colonies with black centre
Shigella appears as just red colonies

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15
Q

70 year old with COPD exacerbation. Sputum sample grows gram neg cocci, it is oxidase positive.

What further test would you do to identify the organism?

Catalase
DNAse
Coagulase
Oxidase
Indole
A

DNAse - differentiates between moraxella and neisseria

Gram neg causes of COPD exacerbation include oral Neisseria species and Moraxella species. Both are catalase positive.

Moraxella has DNAse

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16
Q

Concern of cleaning of endoscopes.
How would you quantify the number of live bacteria within a broth solution?

Cell count
Flow ctyometry
Miles- Misra method
Optical density
Quantification of DNA
A

Miles-Misra method

Serial dilutions of bacterial suspension, which is inoculated on plates. Number of colonies counted on diluted plates, and used to calculate total colonies in first sample

Other methods do not reliable discern the number of viable colony forming units. For example, optical density can measure number of bacteria, but not necessarily live.

17
Q

61 year old with diabetes presents with severe sinusitis and reduced GCS. What is best laboratory method for rapid identification of fungi responsible for rhinocerebral mucormycosis?

Calcofluor staining
Haematoxylin-eosin staining
Potassium hydroxide staining
Periodic acid-Schiff staining
Methenamine-silver staining
A

Calcofluor staining

Mucormycosis causes by Rhizopus/ Mucor species

Broad, ribbon like, with no septate, branches at right angles

18
Q

What is Albert’s stain used for?

A

Can be used for identification of pathogenic C. diptheriae

It stains phosphate granules green, which are present in toxin-producing strains

19
Q

58 year old with chronic cough has BAL. Filamentous fungi grow on Sabouraud agar. What is most useful method for speciation of filamentous fungi?

Calcofluor white stain
Gram stain
Lactophenol cotton blue stain
Periodic acid-schiff stain
Potassium hydroxide wet preparation
A

Lactophenol cotton blue stain

Calcofluour white and Potassium hydroxide are useful for identifying fungal presence, but do not help with speciation.

Lactophenol cotton blue stain dies fungal wall chitin. Once stained, morphology can be used to help dsicriminate species

20
Q

31 year old female with iron deficiency anaemia. Stool sample examined for OCP.

What is most likely diagnosis?

Ascaris lumbricoides
Trichuris
Strongyloides
Enterobius
Ancylostoma
A

Ancylostoma and Necator appear similarly, and are both Hookworms which cause anaemia and malabsorption

20
Q

31 year old female with iron deficiency anaemia. Stool sample examined for OCP.

What is most likely diagnosis?

Ascaris lumbricoides
Trichuris
Strongyloides
Enterobius
Ancylostoma
A

Ancylostoma and Necator appear similarly, and are both Hookworms which cause anaemia and malabsorption

21
Q

31 year old male with suspected Malaria.
What is most useful method for rapid identification of Plasmodium falciparum?

Thick blood film with Field's stain
Thin blood film with Giemsa stain
Thin blood film with Field's stain
Polymerase chain reaction
Rapid serum agglutination
A

Thin blood film with Giemsa stain

Field’s stain not recommended for thin blood films

Giemsa stain is useful for other parasites e.g Filariaria, Leishmania, Trypanosoma

22
Q

Leishmaniasis

Which species are present in new and old world?

A

Old world

  • Donovani
  • Major
  • Tropica

New World

  • Braziliensis
  • Mexicana
  • Chagasi
23
Q

Leishmaniasis

Which species cause visceral Leishmaniasis?

New world/ old world

A

Old world
- Donovani

New World

  • Chagasi
  • Infantum
24
Q

Leishmaniasis

Which species cause cutaneous leishmaniasis?

New world/ Old World

A

Old world

  • Major
  • Tropica

New world

  • Braziliensis - mucocutaneous
  • Mexicana