FASTIDIOUS GRAM EGATIVE RODS.2 DUCREYI

Question 1

What disease is caused by haemophilus ducreyi

Answer 1

Chancroid (Chancroid is a sexually transmitted infection (STI) caused by the bacterium Haemophilus ducreyi)

Question 2

what are the symptoms of chancroid

Answer 2

Painful ulcers that are shallow and bleed easly

Question 3

What specimens should be collected for laboratory diagnosis of chancroid?

Answer 3

1. Specimens should be collected from the base of the lesion after cleansing with a saline swab (excluding necrotic tissue).
2. These specimens are then inoculated directly onto enriched media and held for 5 days.

Question 4

What does the Gram stain reveal about H. ducreyi?

Answer 4

1. Under the Gram stain, H. ducreyi appears as groups of coccobacilli that resemble a school of fish.
2. The staining is pale, so Gram smears should be counterstained with dilute carbol fuchsin to enhance visibility

Question 5

Where can H. ducreyi be found in smears?

Answer 5

1. In smears, H. ducreyi may be found within pus cells or extracellularly.
2. It often appears in loose clusters, strands, or parallel chains.

Question 6

What is the sensitivity and specificity of a Gram smear for H. ducreyi?

Answer 6

1. The sensitivity and specificity of a Gram smear for H. ducreyi are low.
2. Therefore, isolation of the organism by culture is required for a definitive diagnosis of chancroid.

Question 7

What specific growth factors does H. ducreyi require?

Answer 7

H. ducreyi requires factor X but not factor V for growth. (The text doesn’t specify what these factors are, but the answer focuses on the specific requirement mentioned).

Question 8

Describe the recommended culture media for H. ducreyi.

Answer 8

Chocolate agar containing 1% Isovitalex and vancomycin (3 µg/ml) is recommended for culturing H. ducreyi. The chocolate agar provides nutrients, while Isovitalex and vancomycin suppress the growth of Gram-positive bacteria that might contaminate the culture.

Question 9

What are the ideal incubation conditions for H. ducreyi cultures?

Answer 9

H. ducreyi cultures require a moist environment with CO2 enrichment and incubation at a temperature between 32-35°C

Question 10

How long does it typically take for H. ducreyi colonies to appear on culture plates?

Answer 10

H. ducreyi grows slowly, and colonies usually appear within 2-4 days.

Question 11

Describe the typical appearance of H. ducreyi colonies

Answer 11

H. ducreyi colonies are small, grey-yellow, or brown. They are difficult to emulsify (suspend in liquid) and can be easily pushed across the agar surface.

Question 12

Explain the biochemical test results of haemophilia ducreyi

Answer 12

1. Slowly oxidase positive (colour develops after 15–20 seconds).
2. Catalase, urease, and indole negative.
3. Ornithine decarboxylase (ODC) negative.
4. delta-Aminolevulinic acid (ALA), negative (showing requirement for factor
   X).

Question 13

What is the treatment of haemophilia dureyi

Answer 13

1. Azithromycin 1 g orally in a single dose or
2. Ceftriaxone 250 mg intramuscularly in a single dose or
3. Ciprofloxacin 500 mg orally 2 times a day for 3 days, or
4. Erythromycin base 500 mg orally 3 times a day for 7 days