Question book Flashcards
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
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
34 year old with haematuria.
What would be your confirmatory diagnostic finding in schistosomiasis?
Cysts Larvae Ova Adults Microfilariae
Ova
Schistosomiasis species.
Where is the spine present?
S. haematobium
S mansoni
S. japonicum
S. haematobium - terminal spine
S mansoni - lateral spine
S. japonicum - spherical with small knob
Schistosomiasis species.
Where is the spine present?
S. haematobium
S mansoni
S. japonicum
S. haematobium - terminal spine
S mansoni - lateral spine
S. japonicum - spherical with small knob
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
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
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
Bone marrow
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)
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
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
Cary-Blair
Preserves the most common pathogen, including Vibrio spp
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
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
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
It is catalase negative
Almost all of Enterobacteriales, including most Shigella, are catalase pos
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
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)
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
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)
What is meaning of term psychrophilic?
Is same term as Cryophile - can grow in temperatures <15degC
What is the importance of use of XLD agar?
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
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
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
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
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.
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
Calcofluor staining
Mucormycosis causes by Rhizopus/ Mucor species
Broad, ribbon like, with no septate, branches at right angles
What is Albert’s stain used for?
Can be used for identification of pathogenic C. diptheriae
It stains phosphate granules green, which are present in toxin-producing strains
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
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
31 year old female with iron deficiency anaemia. Stool sample examined for OCP.
What is most likely diagnosis?
Ascaris lumbricoides Trichuris Strongyloides Enterobius Ancylostoma
Ancylostoma and Necator appear similarly, and are both Hookworms which cause anaemia and malabsorption
31 year old female with iron deficiency anaemia. Stool sample examined for OCP.
What is most likely diagnosis?
Ascaris lumbricoides Trichuris Strongyloides Enterobius Ancylostoma
Ancylostoma and Necator appear similarly, and are both Hookworms which cause anaemia and malabsorption
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
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
Leishmaniasis
Which species are present in new and old world?
Old world
- Donovani
- Major
- Tropica
New World
- Braziliensis
- Mexicana
- Chagasi
Leishmaniasis
Which species cause visceral Leishmaniasis?
New world/ old world
Old world
- Donovani
New World
- Chagasi
- Infantum
Leishmaniasis
Which species cause cutaneous leishmaniasis?
New world/ Old World
Old world
- Major
- Tropica
New world
- Braziliensis - mucocutaneous
- Mexicana
