Neuroinvasive Bacillus cereus Infection in Immunocompromised Hosts: Epidemiologic Investigation of 5 Patients With Acute Myeloid Leukemia

Background

Bacillus cereus is a ubiquitous gram-positive rod-shaped bacterium that can cause sepsis and neuroinvasive disease in patients with acute leukemia or neutropenia.

Methods

A single-center retrospective review was conducted to evaluate patients with acute leukemia, positive blood or cerebrospinal fluid test results for B cereus, and abnormal neuroradiographic findings between January 2018 and October 2022. Infection control practices were observed, environmental samples obtained, a dietary case-control study completed, and whole genome sequencing performed on environmental and clinical Bacillus isolates.

Results

Five patients with B cereus neuroinvasive disease were identified. All patients had acute myeloid leukemia (AML), were receiving induction chemotherapy, and were neutropenic. Neurologic involvement included subarachnoid or intraparenchymal hemorrhage or brain abscess. All patients were treated with ciprofloxacin and survived with limited or no neurologic sequelae. B cereus was identified in 7 of 61 environmental samples and 1 of 19 dietary protein samples-these were unrelated to clinical isolates via sequencing. No point source was identified. Ciprofloxacin was added to the empiric antimicrobial regimen for patients with AML and prolonged or recurrent neutropenic fevers; no new cases were identified in the ensuing year.

Conclusions

B cereus is ubiquitous in the hospital environment, at times leading to clusters with unrelated isolates. Fastidious infection control practices addressing a range of possible exposures are warranted, but their efficacy is unknown and they may not be sufficient to prevent all infections. Thus, including B cereus coverage in empiric regimens for patients with AML and persistent neutropenic fever may limit the morbidity of this pathogen.

Bacillus cereus Invasive Infections in Preterm Neonates: an Up-to-Date Review of the Literature

Bacillus cereus group species are widespread, Gram-positive, spore-forming environmental bacteria. B. cereus sensu stricto is one of the major causes of food poisoning worldwide. In high-risk individuals, such as preterm neonates, B. cereus infections can cause fatal infections. It is important to note that the phenotypic identification methods commonly used in clinical microbiology laboratories make no distinction between B. cereus sensu stricto and the other members of the group (Bacillus anthracis excluded). As a result, all the invasive infections attributed to B. cereus are not necessarily due to B. cereus sensu stricto but likely to other closely related species of the B. cereus group. Next-generation sequencing (NGS) should be used to characterize the whole genome of the strains belonging to the B. cereus group. This could confirm whether the strains involved in previously reported B. cereus invasive infections preferentially belong to formerly known or emerging individual species. Moreover, infections related to B. cereus group species have probably been overlooked, since their isolation in human bacteriological samples has for a long time been regarded as an environmental contaminant of the cultures. Recent studies have questioned the emergence or reemergence of B. cereus invasive infections in preterm infants. This review reports our current understanding of B. cereus infections in neonates, including taxonomical updates, microbiological characteristics, bacterial identification, clinical features, host-pathogen interactions, environmental sources of contamination, and antimicrobial resistance.

Bacillus cereus Induces Severe Infections in Preterm Neonates: Implication at the Hospital and Human Milk Bank Level

Human breast milk (HBM) is a source of essential nutrients for infants and is particularly recommended for preterm neonates when their own mother's milk is not available. It provides protection against infections and decreases necrotizing enterocolitis and cardiovascular diseases. Nevertheless, HBM spoilage can occur due to contamination by pathogens, and the risk of a shortage of HBM is very often present. B. cereus is the most frequent ubiquitous bacteria responsible for HBM being discarded. It can contaminate HBM at all stages, from its collect point to the storage and delivery. B. cereus can induce severe infection in newborns with very low birth weight, with sometimes fatal outcomes. Although the source of contamination is rarely identified, in some cases, HBM was suspected as a potential source. Even if the risk is low, as infection due to B. cereus in preterm infants should not be overlooked, human milk banks follow strict procedures to avoid contamination, to accurately identify remaining bacteria following pasteurization and to discard non-compliant milk samples. In this review, we present a literature overview of B. cereus infections reported in neonates and the suspected sources of contamination. We highlight the procedures followed by the human milk banks from the collection of the milk to its microbiological characterization in Europe. We also present improved detection and decontamination methods that might help to decrease the risk and to preserve the public's confidence in this vital biological product for infants whose mothers cannot breastfeed.

Bacillus cereus and severe intestinal infections in preterm neonates: Putative role of pooled breast milk

BACKGROUND

Bacillus cereus is an environmental pathogen whose spores resist the usual cleaning procedure applied by the food industry and hospitals. We reported a cluster of severe intestinal infections due to B cereus in 2 very low birth weight neonates from a neonatal intensive care unit.

METHODS

Environmental sampling and bacteriological analysis of pooled breast milk (PBM) were performed. Practices for preparation and administration of milk were observed and additional laboratory experiments performed. Strains were typed using M13-polymerase chain reaction and their virulence tested using cellular and insect models.

RESULTS

B cereus strains were exclusively isolated from intestinal tracts and PBM. No environmental culture yielded any viable B cereus. Although genotypically diverse, both clinical and food strains exhibited high virulence potency. These findings pointed out the pathogenic potency of B cereus in neonates; the putative role of PBM as a reservoir for pathogenic B cereus and the triggered effect of a defective care procedure, which allowed the growth of bacteria in pasteurized PBM. Well described from dried formula, the presence of pathogenic B cereus strains in PBM was not previously reported.

CONCLUSIONS

Careful monitoring of conditions during collection, conservation, and administration of PBM should be implemented in high-risk populations such as premature neonates.