Anthrax is a serious infectious disease caused by the bacterium Bacillus anthracis. Understanding this microorganism often begins with observing it under a microscope. Microscopy provides initial insights into its structure and helps distinguish it from other bacteria.
Visualizing Bacillus anthracis
When observed under a microscope, Bacillus anthracis has a distinctive appearance. These rod-shaped bacteria typically measure about 1.0 to 1.2 micrometers in width and 3.0 to 5.0 micrometers in length. They are often found arranged in long chains, which can resemble a “bamboo pole” or “boxcar” appearance. This chain-like arrangement helps differentiate it from other bacteria.
The vegetative cells of Bacillus anthracis are Gram-positive, staining purple or blue due to their cell wall structure. The presence of a capsule, a protective outer layer, can also be observed in many strains, contributing to their virulence.
The Resilient Anthrax Spore
Distinct from vegetative cells, Bacillus anthracis forms highly resilient spores. These oval-shaped structures are highly refractile, appearing bright and shiny under a light microscope. Spores are located centrally or subterminally within the bacterial cell and do not cause it to swell.
The spore form allows Bacillus anthracis to survive harsh environmental conditions like extreme temperatures, dehydration, and chemical disinfectants. This resistance enables the bacterium to persist for extended periods, potentially decades or even centuries. Spores are the primary infectious agent for all forms of anthrax, germinating into vegetative cells once they enter a hospitable host environment.
Microscopic Identification and Significance
Microscopic examination plays a role in the presumptive identification of Bacillus anthracis from various samples. Gram staining is a common technique used to observe the bacterium’s morphology and arrangement. The presence of large, Gram-positive rods arranged in chains, often described as “boxcar-shaped,” is a strong indicator.
Special stains, such as spore stains, can be employed to visualize the highly resistant spores, appearing as bright, unstained ovals within the stained bacterial cells. The India ink stain can be used to visualize the capsule, appearing as a clear zone around the bacterial cell, especially in clinical specimens. While microscopic examination provides a rapid preliminary diagnosis, further laboratory tests are needed for definitive identification due to the close resemblance to other Bacillus species. Laboratories handling suspected anthrax samples must adhere to strict biosafety precautions.