Bacillus: An Environmental Contaminant or Misunderstood Pathogen?

Review Article

J Bacteriol Mycol. 2019; 6(6): 1117.

Bacillus: An Environmental Contaminant or Misunderstood Pathogen?

Ravine TJ*

Department of Biomedical Sciences, University of South Alabama, Mobile, AL, USA

*Corresponding author: Ravine, TJ. Department of Biomedical Sciences, University of South Alabama, USA

Received: November 02, 2019; Accepted: December 09, 2019; Published: December 16, 2019


For many years, Bacillus species (spp.) recovered from patient samples were mostly considered as environmental contaminants and not agents of disease. Then came the current era when Bacillus anthracis, the bacterium responsible for anthrax, became listed as a potential bioterrorism agent. This ignited great interest in quickly identifying B. anthracis, which has translated into newer identification methods that also allow for classification of other Bacillus spp. There have been several reports of B. cereus in medical literature as the source of human disease, including its relationship to hospital-acquired infections. However, the actual role of Bacillus spp. other than B. anthracis and B. cereus as agents of human disease remains in question. A body of accumulating evidence from case reports to original research papers appears to indicate that several other Bacillus spp. have been implicated in severe and sometime life-threatening infections. In many cases these infections are seen to involve debilitated patients with a weaken immune response. This review collects a sampling of this literature to advance a greater understanding of the role of less frequently encountered Bacillus spp. in human infections. It by no means suggests that these findings are the only reports of esoteric Bacillus spp. infections. However, the relatively low number of reports may represent an unintentional underreporting of these species due to their ubiquitous nature in environments inside and outside of healthcare facilities. In words attributed to Sophocles - ‘Look and you will find it - what is unsought will go undetected.’

Keywords: Bacillus; Hospital-acquired infections; Immunosuppression


Much attention has been given to the genus Bacillus in recent years. This is primarily due to the genus member Bacillus anthracis, the causative agent of anthrax. Extensive study of B. anthracis characteristics has been completed primarily due to its potential use as a bioterrorism agent. This research has sparked some renewed interest in several other Bacillus species (spp.). This would include like B. cereus and B. subtilis both confirmed agents of human disease. These two bacilli, or rod-shaped bacteria, have become recognized as opportunistic human pathogens. Other Bacillus spp. recovered from patient samples are less well characterized in their ability to cause human disease. They are most likely considered an environmental contaminant. Traditional methods of Bacillus identification rely mostly upon extensive biochemical testing along with an examination of colony morphology on nutrient agar and Gram stain characteristics. Newer identification methods used in clinical microbiology laboratories such a real-time Polymerase Chain Reaction (PCR); [1] and (Matrix Assisted Laser Desorption/ Ionization-Time of Flight (MALDI-TOF); [2] have afforded greater opportunities to investigate more esoteric Bacillus species associated with patient samples.

Immunosuppressed Patient Population

A question remains as to whether a Bacillus species recovered from a patient sample is a true pathogen or an environmental contaminant. Up until a few years ago, most Bacillus spp. were considered as environmental contaminants rarely being associated with disease when recovered from patient samples [3]. Today, Bacillus is classified as an opportunistic pathogen that is gaining increasing notoriety as a cause of severe infections in immunocompromised patients. B. cereus infections seen in this patient population include brain abscesses, coagulopathies, colitis, endocarditis, hemolysis, meningitis, respiratory tract infections, and septic shock [4]. Consequently, special consideration may be warranted to Bacillus species recovered in samples from debilitated patients with a depressed immune system response [5]. This would include cancer patients receiving either chemotherapy treatment alone or in conjunction with radiation therapy. It would similarly apply to patients receiving immunosuppressive drugs as a recipient of a transplanted organ (e.g. kidney) or from an acquired immunodeficiency. Since the 1980’s, the immunosuppressed patient population has increased and may continue to increase, or at least remain steady, in the near future. These individuals are at increased risk of infections by microorganisms, bacterial, fungal, or viral that may be fatal [6,7]. Going forward, Bacillus spp. recovered from these patient samples deserve greater attention as agents of Healthcare-Acquired Infections (HAIs).


HAIs are infections that are not present upon patient entry into a healthcare environment. They are a direct result of patient treatment occurring in a healthcare facility. Worldwide, HAIs are the most frequent adverse event in health-care delivery affecting hundreds of millions of patients. HAIs cause significant sickness (morbidity) and death (mortality) in both developing and developed countries. For every 100 hospitalized patients, 1 out of 7 patients (14.3%) in developed countries and 1 out of 10 (10.0%) patients in developing countries will be afflicted with at least one HAI at any one time [8]. HAIs are usually thought to be associated with treatment received in an inpatient setting. Diagnosis of HAIs are more difficult to establish for outpatients. The lack of hospital confinement makes it hard to distinguish between an infection caused by a contaminated medical device and an infection acquired by a patient while in a public venue (e.g., shopping center), which is referred to as community-acquired infection.

Bacillus Characteristics

The genus Bacillus represents a large group of aerobic grampositive rods (Figure 1) belonging to the bacterial Phylum Firmicutes. Most Bacillus species are nonpathogenic bacteria feeding off dead or decaying organic matter [3]. They are a source of antibiotics including the topical ointment bacitracin, which is effective in preventing minor skin infections [9]. Bacillus spp. are ubiquitous in nature being found in a variety of land and water environments. They are very hardy microbes capable of withstanding a wide range of acidic-toalkaline, low-to-high saline, and hot-to-cold conditions. Bacillus spp. can produce dormant endospores (spores) upon nutrient depletion or other unfavorable conditions. Their ability to form spores makes them resistant to effects of drying, heat, ultraviolet radiation, many disinfectants, and several other environmental stressors [9,10]. Bacillus spores are easily spread by a variety of means into man-made environments, including hospital operating rooms [3].

Citation: Ravine TJ. Bacillus: An Environmental Contaminant or Misunderstood Pathogen?. J Bacteriol Mycol. 2019; 6(6): 1117.