Gram-Negative Bacilli – Classification Overview

Vocabulary flashcards summarizing the major classification groups mentioned for gram-negative bacilli, emphasizing differences among small pleomorphic bacilli, non-fermenters, non-enteric GI pathogens, and enteric bacilli.

Gram-Negative Bacilli

Rod-shaped bacteria that stain pink on Gram stain due to a thin peptidoglycan layer and outer membrane rich in lipopolysaccharide.

Small Pleomorphic Gram-Negative Bacilli

A subgroup of gram-negative rods that vary in shape and size (pleomorphic); typical examples include Haemophilus species.

Non-Fermentative Gram-Negative Bacilli

Gram-negative rods that do not ferment carbohydrates (e.g., glucose) in standard laboratory media; notable genera include Pseudomonas and Acinetobacter.

Gram-Negative Non-Enteric Gastrointestinal Pathogens

Gram-negative bacteria that can cause gastrointestinal disease but are not classified within the enteric (Enterobacteriaceae) family.

Enteric Bacilli (Enterobacteriaceae)

A large family of facultative anaerobic, gram-negative rods that typically inhabit the intestinal tract; includes Escherichia, Salmonella, Shigella, and Klebsiella.

Enteric vs. Non-Enteric

‘Enteric’ organisms normally reside in or are adapted to the intestinal tract, whereas ‘non-enteric’ organisms do not belong to this natural gut flora despite potentially causing GI disease.