Gram stain and shape
Gram-negative curved rods
Comma-shaped and gently spiraled rods: the vibrios, Campylobacter, and Helicobacter.
How this group is recognized
Curved rods are a distinct branch of the gram-negative workup because the comma shape is visible on the stain itself, before any biochemical testing. The classic members are the Vibrio species, Campylobacter, and Helicobacter.
Growth conditions do much of the separating here: the vibrios are associated with water and salt tolerance in lab teaching, while Campylobacter and Helicobacter are the classic microaerophiles of the group.
PetriKey lists 5 gram-negative curved rods. Shape is read from each organism's classification; organisms whose card does not state a shape stay on the main Gram-negative page.
All 5
Organisms and their lab clues
Campylobacter jejuni Curved motile Gram-negative rod
Curved morphology. Motility vocabulary.
Helicobacter pylori Curved urease-positive gastric rod
Urease test vocabulary. Stool antigen/urea breath test terms.
Vibrio cholerae Comma-shaped oxidase-positive rod
Curved rod morphology. Oxidase positive.
Vibrio parahaemolyticus Salt-loving seafood gastroenteritis vibrio
Oxidase positive vocabulary. Green colonies on TCBS (sucrose non-fermenter).
Vibrio vulnificus Marine vibrio, wound and shellfish sepsis
Oxidase positive vocabulary. Lactose fermenter (unusual for vibrios) concept.