bacillary

Bacillary is an adjective relating to bacilli, the rod-shaped form of bacteria. The term is also used to indicate diseases or infections caused by bacteria. In microbiology, bacillary distinguishes rod-shaped bacteria from cocci (spherical) or spirilla (spiral).

Bacilli are a morphological category of bacteria that are typically rod-shaped; some are straight, others curved or slightly elongated. They can be Gram-positive or Gram-negative. Notable genera include Bacillus (Gram-positive, spore-forming), Listeria (Gram-positive, non-spore-forming), Escherichia and Salmonella (Gram-negative rods), Bordetella, Pseudomonas, and Corynebacterium. Some bacteria are described as coccobacilli, a short rod-like form intermediate between cocci and bacilli.

In clinical usage, bacillary infections refer to bacterial infections. Bacillary dysentery historically describes dysentery caused by enteric bacteria such as Shigella. Bacillary angiomatosis is a vascular lesion associated with Bartonella infection in immunocompromised patients. The term is broad and emphasizes bacterial etiology rather than viral or fungal origins.

Diagnosis and laboratory identification of bacillary infections typically rely on specimen staining, culture and isolation of organisms, and molecular methods. Gram staining differentiates Gram-positive versus Gram-negative bacilli; some bacteria are acid-fast and require special staining. Antibiotic susceptibility testing guides appropriate therapy.

Etymology: bacillus means a small staff or rod in Latin, with the plural bacilli. The adjective bacillary has long been used in microbiology to describe rod-shaped bacteria or infections caused by them.