[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/) › Haemophilus ducreyi

[Microbiology](https://durgical.com/en/microbiology/) · [Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/)

# Haemophilus ducreyi

- Bacterium
- Gram-negative
- For completeness

A sexually transmitted bacterium that causes chancroid: painful genital ulcers with inguinal lymph nodes that suppurate.

Updated 2026-11-01

Also called: soft chancre

## Key points

- Chancroid: PAINFUL ulcer with a bubo; syphilis gives a PAINLESS ulcer.
- Gram stain: coccobacilli in a "school of fish".
- Needs X factor to grow.
- The genital ulcer raises the risk of acquiring and passing on HIV.

## At a glance

**Gram**
Gram-negative

**Shape**
Coccobacillus

**Oxygen**
Facultative anaerobe, grows best with CO2

**Family**
Pasteurellaceae

**Stain**
Coccobacilli in parallel chains ("school of fish")

## Morphology

- Small Gram-negative coccobacillus
- Lines up in parallel rows on smears
- Fastidious: needs X factor (haemin) and enriched media

## Transmission

- Sexual contact with the ulcer
- Small breaks in genital skin or mucosa

**Reservoir:** Humans only

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Cytolethal distending toxin damages epithelial cells and delays healing
- Adhesins fix it to damaged skin and ulcer tissue
- Resists phagocytosis and complement

## Diseases it causes

- Chancroid (soft chancre) [Chancroid →](https://durgical.com/en/conditions/chancroid/)

## Clinical picture

- One or more deep, painful genital ulcers with ragged edges and a dirty base
- Tender inguinal bubo that may drain; present in fewer than half of cases
- Facilitates HIV transmission

## Diagnosis

- Culture of the ulcer base on special enriched media (rarely available, low sensitivity)
- Validated PCR in some laboratories
- Probable diagnosis: typical painful ulcer, syphilis ruled out and herpes testing negative
- Test everyone with chancroid for HIV and syphilis

## Treatment

Macrolides (azithromycin or erythromycin), third-generation cephalosporins (ceftriaxone) or fluoroquinolones (ciprofloxacin). People with HIV and uncircumcised men respond less well. Sex partners are evaluated and treated.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Azithromycin](https://durgical.com/en/pharmacology/azithromycin/)
- [Ceftriaxone](https://durgical.com/en/pharmacology/ceftriaxone/)
- [Ciprofloxacin](https://durgical.com/en/pharmacology/ciprofloxacin/)
- [Erythromycin](https://durgical.com/en/pharmacology/erythromycin/)

## Prevention

- Condoms
- Treatment of sex partners
- HIV and syphilis screening

## Memory aid

"You do cry with ducreyi": a genital ulcer that hurts with a node that drains is the soft chancre, not the treponeme.

## Test yourself

Think of the answer, then tap the question to see it.

## What key clinical difference separates chancroid from the syphilitic chancre?

Chancroid hurts and has ragged edges; the syphilitic chancre is painless with a clean, indurated base.

## How does H. ducreyi look on a Gram stain of the ulcer base?

As Gram-negative coccobacilli in parallel rows, described as a "school of fish".

## Which other tests are ordered for a person with chancroid?

HIV and syphilis tests, because they share the route and the ulcer facilitates HIV.

## Which antibiotic families are used against chancroid?

Macrolides, third-generation cephalosporins and fluoroquinolones.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/haemophilus-ducreyi/)

## Related

- [Treponema pallidum](https://durgical.com/en/microbiology/treponema-pallidum/)
- [Chlamydia trachomatis](https://durgical.com/en/microbiology/chlamydia-trachomatis/)
- [Herpes simplex virus 2](https://durgical.com/en/microbiology/herpes-simplex-virus-2/)

## Related conditions

- [Chancroid](https://durgical.com/en/conditions/chancroid/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Other clinically important bacteria](https://durgical.com/en/microbiology/groups/other-clinically-important-bacteria/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Chancroid - STI Treatment Guidelines](https://www.cdc.gov/std/treatment-guidelines/chancroid.htm) (CDC, 2021); Jawetz, Melnick & Adelberg's Medical Microbiology, 26th ed., chapter 18: Haemophilus, Bordetella, Brucella, and Francisella (McGraw-Hill, 2013).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/haemophilus-ducreyi/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/haemophilus-ducreyi/