A fastidious gram-negative bacillus with gliding motility observed in darkfield is most likely which genus?

A fastidious gram-negative bacillus with gliding motility observed in darkfield is most likely which genus?

• A. Capnocytophaga
• B. Chromobacterium
• C. Kingella
• D. Plesiomonas

Answer: (A)

Gliding motility in a fastidious, gram-negative bacillus points strongly to Capnocytophaga. These organisms are slender, often fusiform gram-negative rods that require enriched growth conditions and CO2 to grow well. A hallmark behavior is their ability to glide smoothly along surfaces rather than using flagella, which is why you’d observe their movement as they spread across a medium. This combination of being fastidious and displaying gliding motility is characteristic and helps distinguish Capnocytophaga from other gram-negative rods that may be motile by flagella or simpler to culture. The other genera listed do not typically show this same pattern: they may be motile or non-motile and do not exhibit the distinctive gliding on surfaces seen with Capnocytophaga.