By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

SYNOPSIS: Bacillus cereus group organisms may cause a rapidly fatal pulmonary infection consistent with anthrax.

SOURCE: Dawson P, Schrodt CA, Feldmann K, et al. Notes from the field: Fatal anthrax pneumonia in welders and other metalworkers caused by Bacillus cereus group bacteria containing anthrax toxin genes — U.S. Gulf Coast States, 1994–2020. MMWR Morb Mortal Wkly Rep 2021;70:1453-1454.

In 2020, a 34-year-old man in Texas died as the result of a rapidly progressive pulmonary infection caused by an organism identified as Bacillus cereus. In that same year, a 39-year-old man survived a similar infection, also due to B. cereus. That patient was given anthrax antitoxin. Five additional cases, four of which were fatal, were identified by the Centers for Disease Control and Prevention (CDC) from 1994-2011.

In each of the seven cases, the patients were metalworkers (five were welders) in Texas or Louisiana. Their ages ranged from 39 to 56 years, and only one was female. In one case, a soil sample from the patient’s work site yielded a bacterium that genetically matched a clinical isolate from the patient.

COMMENTARY

Organisms of the B. cereus group are gram-positive, spore-forming facultative anaerobes that are widespread within the environment, with their dominant reservoir in soil and dust. They may contaminate food and cause acute vomiting and diarrhea. In addition, they may cause ocular and cutaneous infections, as well as bacteremia and endocarditis, with the latter two most often associated with injection drug use and central venous access infection.1 Taxonomic studies indicate that B. cereus (now termed the B. cereus group) should be subdivided into nine species. Whole-genome sequence analysis identified the isolates from these patients as Bacillus tropicus.2

The strains causing severe disease, such as those reported by the CDC, have acquired plasmids encoding virulence factors closely associated with those of Bacillus anthracis, which carries a tripartite toxin comprised of protective antigen (PA), lethal factor (LF), and edema factor (EF).3 PA forms membrane pores, facilitating the entrance of the other two, with LF then inhibiting protein kinase activity and inducing apoptosis, while EF also interferes with cell signaling. Also required for full virulence of B. anthracis is an exopolysaccharide capsule. Additional toxins have been identified in B. cereus strains causing lethal infection.

The reason why all the cases reviewed here occurred in only Texas and Louisiana is unknown. However, metalworking is associated with various respiratory illnesses, including an increased risk of lower tract infections and pneumonia, as well as hypersensitivity pneumonitis. The latter is believed to be caused by contamination of metalworking fluid with rapidly growing mycobacteria, such as Mycobacterium abscessus.4

REFERENCES

  1. McDowell RH, Sands EM, Friedman H. Bacillus cereus. 2021; Sep 16. StatPearls [Internet]. StatPearls Publishing; 2021.
  2. Liu Y, Du J, Lai Q, et al. Proposal of nine novel species of the Bacillus cereus group. Int J Syst Evol Microbiol 2017;67:2499-2508.
  3. Baldwin VM. You can’t B. cereus — A review of Bacillus cereus strains that cause anthrax-like disease. Front Microbiol 2020;11:1731.
  4. Kapoor R, Yadav JS. Expanding the mycobacterial diversity of metalworking fluids (MWFs): Evidence showing MWF colonization by Mycobacterium abscessus. FEMS Microbiol Ecol 2012;79:392-399.