A 56-year-old man diagnosed as having acquired immunodeficiency syndrome was admitted to a hospital with fever, progressive cachexia, and multiple skin lesions. He complained of a cough productive of yellow sputum but no hemoptysis. An erythematous fluctuant mass located on the right thigh was aspirated, yielding purulent fluid. A Gram stain of this fluid revealed an abundance of leukocytes but no bacteria. Numerous unstained bacillus footprints or ghost bacilli were noted (figure).
Ghost mycobacteria on Gram stain
Source: Journal of Clinical Microbiology