If gram-positive (or gram-variable) bacilli contain spores, Clostridium or Bacillus species are likely [T1] [I1d]. ... Although the Gram stain is used for detection and differentiation of bacteria, other microorganisms, most frequently yeasts and fungi, can be seen on a Gram-stained smear.

Does Bacillus appear gram-variable?

Gram-variable: bacteria that partially retain the purple color of the crystal violet in the Gram stain; most com- monly seen with Bacillus spp., Clostridium spp., Acineto- bacter spp., Streptococcus pneumoniae.

What are gram-variable bacilli?

Gram-negative bacilli. Gram-variable organisms are those that cannot be grouped as either negative or positive. The appearance of organisms that stain gram-positive or -negative means that the smear contains organisms. These organisms may be pathogenic or nonpathogenic.