Basilli

Basilli, or bacilli, is a term used for a broad category of rod-shaped bacteria. They can be Gram-positive or Gram-negative and include many genera with diverse lifestyles. Morphologically, bacilli are elongated cells, typically 0.5 to 5 micrometers long; some species are curved or filamentous. A notable feature is that many Gram-positive bacilli form endospores under nutrient stress; this spore formation is common among Bacillus and Clostridium species and helps survival in harsh environments.

Taxonomy and identification: The bacilli comprise several major lineages. Clinically relevant examples include Bacillus species (such as B. anthracis and B. cereus), Listeria monocytogenes, and a wide array of Gram-negative rods such as Escherichia coli, Klebsiella, Salmonella, and Pseudomonas. Bacilli may be aerobic, anaerobic, or facultatively anaerobic. Spore-forming bacilli belong primarily to Bacillus and Clostridium; non-spore-forming bacilli include Listeria and many Gram-negative rods. They range from harmless environmental organisms to pathogens.

Ecology and relevance: Bacilli are common in soil, water, and the intestinal tracts of animals. Some cause disease in humans or animals, including anthrax (Bacillus anthracis), botulism and tetanus (Clostridium botulinum and Clostridium tetani), and listeriosis (Listeria monocytogenes). Others have important industrial or research roles; Bacillus subtilis is widely used in biotechnology and as a model organism for studying bacterial physiology.

In microbiology, bacilli are identified through microscopy, Gram staining, spore staining, culture characteristics, and a battery of biochemical tests. The term “bacilli” is a descriptive category rather than a strict taxonomic group, capturing the common rod-shaped form shared by many distinct bacteria.