Gram stain and shape
Gram-negative coccobacilli
Short, plump rods that blur toward cocci: fastidious respiratory organisms and the classic zoonotic bacteria.
How this group is recognized
Coccobacilli sit between cocci and rods: short, rounded rods that can be hard to call on shape alone, which is why the label itself is the study clue. On a Gram stain they read pink like other gram-negative organisms.
The group divides naturally by story: fastidious respiratory organisms such as Haemophilus and Bordetella that need enriched media, and the zoonotic bacteria such as Brucella, Francisella, and Pasteurella that are anchored to animal exposure in most course vignettes.
PetriKey lists 10 gram-negative coccobacilli. Shape is read from each organism's classification; organisms whose card does not state a shape stay on the main Gram-negative page.
All 10
Organisms and their lab clues
Acinetobacter baumannii Healthcare-associated nonfermenting coccobacillus
Oxidase-negative nonfermenter contrast. Coccobacillus morphology.
Bordetella pertussis Small respiratory coccobacillus with toxin vocabulary
PCR vocabulary. Special media terms to recognize.
Brucella species Undulant fever, unpasteurized dairy zoonosis
Slow-growing, fastidious vocabulary. Facultative intracellular survival concept.
Coxiella burnetii Q fever, aerosol zoonosis, no vector needed
Obligate intracellular growth vocabulary. Spore-like environmental resistance concept.
Francisella tularensis Tularemia, rabbit/tick zoonosis, cysteine need
Cysteine-requiring growth vocabulary. Fastidious, slow-growing concept.
Haemophilus influenzae Small Gram-negative coccobacillus with X/V factors
Chocolate agar vocabulary. X factor and V factor terms.
Kingella kingae Fastidious HACEK coccobacillus of young children
Recovery improved by inoculating aspirates into blood-culture bottles. NAAT/PCR of joint fluid concept.
Pasteurella multocida Cat/dog bite coccobacillus, rapid cellulitis
Oxidase positive vocabulary. Catalase positive concept.
Yersinia enterocolitica Cold-tolerant enteric rod, pseudoappendicitis
Cold enrichment growth vocabulary. Motile at 25C, non-motile at 37C concept.
Yersinia pestis Flea-borne plague, safety-pin bipolar rod
Bipolar 'safety-pin' staining with Giemsa/Wayson vocabulary. F1 capsular antigen concept.