Microbiology: Pathogen Detection and Culture Characteristics

Practice flashcards covering the culture characteristics, gram stain morphologies, and diagnostic tests for various pathogens across cardiovascular, respiratory, gastrointestinal, genitourinary, and central nervous systems based on lecture notes.

What are the colony characteristics of Staphylococcus aureus on Blood Agar?

Pinpoint colonies that are cream colored, convex, and approximately $2.3\,mm$ in diameter, exhibiting $\beta$-hemolysis.

Which test is used to confirm Staphylococcus aureus after identifying Gram-positive cocci in clusters?

A coagulase test.

How does Streptococcus pneumoniae appear on Blood Agar?

$\alpha$-hemolysis with flattened colonies that have raised edges; some strains may appear mucoid if a capsule is present.

What is the gram stain morphology and Optochin sensitivity for Streptococcus pneumoniae?

Gram-positive diplococci (Lancet shaped) that are Optochin sensitive.

What are the identification features for Enterococcus spp.?

They are Gram-positive cocci in pairs or short chains, often circular and convex on Blood Agar with $\beta$-hemolysis ($E. faecalis$ can show $\alpha$-hemolysis), and are confirmed by Lancefield group D and PYR tests.

What specific agar is required for Haemophilus influenzae and how is it confirmed?

Chocolate agar (CBA), where it grows as greyish colonies; it is confirmed using X and V factors showing pleomorphic Gram-negative coccobacilli.

What unique 'mercury drop' appearance is associated with Bordetella pertussis?

Small, shiny, round colonies with a mercury-silver color on Bordet-Gengou agar.

How can the Viridans group of streptococci be differentiated from Streptococcus pneumoniae?

While both show $\alpha$-hemolysis, Viridans group streptococci are resistant to Optochin, whereas Streptococcus pneumoniae is sensitive.

Describe the appearance of Corynebacterium diphtheriae colonies and its gram stain morphology.

Small grey to black-color colonies; morphologically, it is a Gram-positive rod with a club-shape.

What are the defining characteristics of Streptococcus pyogenes (Group A) on Blood Agar?

Colonies smaller than $1\,mm$ with $\beta$-hemolysis that are sensitive to Bacitracin.

What is the 'safety pin appearance' associated with?

Bipolar staining of Burkholderia pseudomallei, which is a Gram-negative bacilli.

How does Burkholderia pseudomallei appear on Ashdown Agar?

Purple, dry, and wrinkled colonies.

What staining method and media are used for Mycobacterium tuberculosis?

Ziehl-Neelsen stain (acid fast bacilli) and Lowenstein-Jensen or Ogawa medium.

What are the culture characteristics of Klebsiella pneumoniae on MacConkey agar?

Large, pink, mucoid colonies, indicating it is a lactose fermenter.

How do Salmonella Typhi and Shigella dysenteriae appear on MacConkey and DCA agar?

They appear as small to medium-sized colorless colonies because they are non-lactose fermenters.

What is the characteristic appearance of Vibrio cholerae on TCBS agar?

Small to medium-sized, golden yellow colonies.

What type of Gram-stain morphology does Vibrio cholerae exhibit?

Gram-negative bacilli that are curved or comma shaped.

What is the distinguishing growth pattern of Proteus Spp on Blood Agar?

Swarming growth.

What are the characteristics of Neisseria gonorrhoeae on Thayer-Martin Agar?

Colonies vary in diameter from $1-4\,mm$ after $48\,hrs$, are non-pigmented, and appear as kidney-shaped Gram-negative diplococci.

Describe the appearance of Neisseria meningitidis on Thayer-Martin Agar.

Grey, low convex, glistening, smooth, moist colonies with entire edges, appearing as Gram-negative diplococci with flat adjoining sides.

What characterizes Listeria monocytogenes in terms of culture and morphology?

Small, smooth, $\beta$-hemolytic colonies on Blood Agar, appearing as short Gram-positive bacilli.