Introduction

Bacillus cereus is a gram positive, facultatively anaerobic, spore-forming rod widely distributed environmentally, with no substantial pathogenic potential despite its great capacity of surviving adverse conditions¹. This microorganism is frequently associated with gastrointestinal infections, mostly related to rice ingestion, and is characterized by vomiting and diarrhea in the immunocompetent host^1,3. It belongs to the genus Bacillus that comprises seven closely related species: Bacillus cereus sensu lato, Bacillus anthracis, Bacillus thuringiensis, Bacillus mycoides, Bacillus pseudomycoides, Bacillus weihenstephanensis and Bacillus cytotoxicus. These strains share a highly conserved genome, and their 16S rRNA gene sequences show high levels of similarity². Extraintestinal infections due to B. cereus are rare; however, when present they could manifest as bacteremia, endocarditis, meningitis, endophthalmitis, pneumonia, and soft tissue infections³. Therefore, the isolation of this microorganism from blood culture samples is often regarded as contamination, which delays diagnosis and the choice of appropriate treatment⁴.

There have been many reports of hospitals outbreaks of B. cereus bacteremia, mainly among immunocompromised patients attributable to contaminated medical equipment, alcohol-based hand wash solutions, linens, reused towels, intravenous catheters and other implantable devices^4,8,5.

We present here a case of B. cereus bacteremia due to an abdominal stab wound. This work was approved by the Research and Teaching Committee of the Eva Perón Hospital.

Case report

An otherwise healthy 32 year-old- female was admitted to the intensive care unit (ICU) after exploratory laparotomy for a penetrating abdominal stab wound and hepatic lesion. Remarkable laboratory findings included, white cell blood count 16900 (91% neutrophils), pH 7.19 (PCo₂ 42 Hco₃ 19) and ASAT 378mUI/ml ALAT 388mUI/ml. As the patient reached a temperature of 38.6(C in the next 48h, blood, urine and BAL cultures were taken.

A computerized tomography (CT) was performed revealing bilateral pulmonary consolidation, in addition to a segment IV hepatic fluid collection. CT-guided percutaneous drainage was performed and treatment with ampicillin/sulbactam was initiated. Blood samples were processed with the BacT/ALERT 3D automated microbial detection system for five days. These samples became positive after 8h of incubation showing gram positive bacilli. A small volume of this material was inoculated onto blood, chocolate, Cysteine Lactose Electrolyte Deficient (CLED) agar, and thioglycolate broth. Blood agar with hemin and vitamin K1 was the non-selective medium used for anaerobic bacteria and Wilking-Chagren agar was chosen as selective medium. A gram positive bacillus surrounded by wide beta hemolysis was isolated from blood on the fourth day, and from the hepatic samples after 24h of incubation. After micro and macro observation of the morphological characters, the microbe was assumed to belong to the Bacillus spp. and finally the isolate was finally confirmed as B. cereus using MALDI-TOF mass spectrometry (Bruker, Daltonics) with a score value 2.

This Bacillus spp. was susceptible to vancomycin assessed by the Etest according to the Clinical and Laboratory Standards Institute (CLSI) guidelines (M45, 3rd Edition) obtaining a MIC value of 2(g/ml.

Samples from the liver abscess were obtained during CT-guided drainage and were again inoculated onto blood, chocolate, Cysteine Lactose Electrolyte Deficient (CLED) AGAR, a selective medium for anaerobic bacteria and thioglycolate broth. Again, abundant gram positive bacilli developed.

MiniBAL cultures and the urine sample turned negative by using quantitative methods.

Vancomycin was added to the antibiotic treatment, and since the patient’s condition failed to improve, surgical removal of the remaining liver collection was performed.

The patient had a favorable clinical evolution after fourteen days of regular dose of intravenous ampicillin/sulbactam plus vancomycin treatment, and required vasopressors for three days and twelve days of mechanical ventilation. She was discharged from hospital after 24 days.

Discussion

Bacillus spp. bacteremia in the immunocompetent host is mostly transient and resolves spontaneously, which is perhaps the reason why most Bacillus species (except B. anthracis) isolated from blood cultures are often considered contaminants⁹.

There are many case reports of severe infections caused by B. cereus in the literature^1,4,9, the majority of which take place in immunocompromised patients, intravenous drug addicts, or are associated with neoplastic processes or hospital outbreaks^8-10. There are only a few reports of severe infection by this microorganism linked to trauma despite of the environmental ubiquity of this bacteria¹.

Our search only found one case report of Bacillus spp. bacteremia developed after trauma, and it occurred in patients who had suffered gunshot wounds⁷. We could not find infections associated with stab wounds, which gives relevance to our report, since it implies a young immunocompetent patient, without previous gastrointestinal symptoms, in whom the bacteremia could be secondary to the abdominal stab wound. Nevertheless, it is still possible that the infection had occurred during the surgical act, although this option was dismissed given the absence of similar cases at the time of the microorganism isolation.

The study published by Ikeda et al.⁶ attempted to characterize the antibiotic susceptibility and the impact of the correct treatment choice and showed that all the isolates of B. cereus were sensitive to gentamicin, carbapenems and vancomycin, according to Walkaway system and the standard criteria of CLSI guidelines. Between 48.3% and 100% of isolates were resistant to cephalosporins, 65.5% were resistant to clindamycin, and 10.3% were resistant to levofloxacin⁶. In the mentioned study the appropriateness of the empirical antibiotic therapy was not related to survival. However, it was still beneficial because early defervescence was significantly linked to the correct choice of empirical antibiotic treatment⁶.

In the case we present in this study, the antibiotic treatment was adjusted 72h after the patient developed a fever, in accordance with the microbiological findings, with a favorable outcome.

In the article written by Veysseyre et al. presenting 57 cases of B. Cereus infection, the presence of bacteremia was identified as a factor related to poor prognosis, contrary to our results, although it was a single patient¹⁰.

We finally insist on highlighting the importance of considering B. cereus as a pathogen capable of causing severe infections in all types of patients, due to its extensive environmental presence, multiple and complex virulence factors and resistance mechanisms. It is worth insisting on the fact that this microorganism should not be considered a simple contaminant, a situation that continues to occur despite the ongoing documentation of cases of extraintestinal infection^3,10,6.

Conflict of interest

The authors declare that they have no conflicts of interest.