Bacillus cereus bacteremia in a preterm infant caused by consumption of contaminated breastmilk

Investigating environmental transmission to resolve a Bacillus cereus group outbreak in a neonatal intensive care unit using core genome multilocus sequence typing

BACKGROUND

We analyzed an outbreak of Bacillus cereus group (Bcg) at a single-center neonatal intensive care unit level IV by conducting comprehensive sampling of both patients and the environment.

METHODS

Between 06/2020 and 10/2021, all Bcg isolates identified by both regular colonization screening and additional sampling of the environment were subjected to whole-genome sequencing, followed by in vitro extraction of MLST ST, resistance genes and virulence factors. Using publicly available genome sequences, we defined an ad hoc core genome multilocus sequence typing (cgMLST) scheme comprising 2759 target genes for Bcg typing, which we applied to the detected isolates. We have compared the results with a stable cgMLST that was published in the meantime and completed the investigation with a SNP analysis.

RESULTS

We analyzed 28 Bcg isolates from patient and environmental samples using MLST and cgMLST. This revealed multiple sequence types, with ST127 being the most common (n = 13). Both cgMLST schemes grouped ten of the 13 ST127 isolates into a cluster, including two invasive isolates from two different patients and several environmental samples. SNP analysis postulated a screen from a ventilation machine as a possible reservoir.

CONCLUSION

In sensitive settings such as neonatal intensive care units, considering the environment in outbreak analyses is crucial, especially when investigating potential transmission routes through shared devices. When dealing with widespread bacteria such as Bcg, high-resolution typing techniques are necessary. In this study, we successfully resolved an outbreak of Bcg infections using a custom cgMLST scheme combined with a SNP analysis.

Microbiological Screening of Donor Human Milk

Mother's own milk is recognized as the optimal feeding not only for term but also for preterm infants. In addition to risk reduction for sepsis, necrotizing enterocolitis, bronchopulmonary dysplasia, and retinopathy of prematurity in the early infancy, feeding preterm infants with mother's own milk is also associated with a better neurodevelopmental outcome; lower rates of otitis media, gastroenteritis, and respiratory infections; and a reduced risk of cardiovascular disease, obesity, and diabetes later in life. Donor human milk is the best alternative if mother's own milk is not available or with short supply. There is growing evidence that the benefits of human milk are mediated by the human milk microbiota and by human milk oligosaccharides through their influence on the infant's gut microbiota. Unfortunately, although human milk contains beneficial bacteria, it may also contain pathogenic bacteria. The antimicrobial properties of human milk protect those infants fed with their own mother's raw milk. In donor human milk, however, the antimicrobial activity is diminished due to storage and in particular by pasteurization, hereby lowering the resistance against bacterial infections. Subsequently, microbiological screening of donor human milk might enhance its safety for preterm infants. Up to date, a consensus on recommendations for the microbiological testing of donor human milk is lacking. Existing local and national guidelines for the microbiological screening vary significantly in terms of timing and frequency of testing as well as their specific acceptance and discard criteria. We reviewed the literature about microbiological testing of donor human milk to provide evidence-based recommendations for donor human milk.

Bacillus cereus strains from donor human milk and hospital environment: uncovering a putative common origin using comparative analysis of toxin and infra-red spectroscopy profiles

Bacillus cereus is reported as a common cause of toxin-induced food poisoning and of contamination in pasteurized human milk donations. As various toxins can be produced by B. cereus, the aim of this work was first to investigate the toxigenic potential and profiles of 63 B. cereus isolates from Amiens Picardie human milk bank. A comparison to the toxigenic profiles of 27 environmental B. cereus isolates harvested in the hospital in which this human milk bank is situated was performed. Toxin gene prevalences were the highest for nhe (ABC) and entFM followed by cytK and hbl(ACD). A 27% prevalence was found for ces human milk isolates, which is higher than previous works reporting on pasteurized milk and dairy products. No significant differences could be found between human milk and environmental isolates regarding toxin gene prevalences and/or toxin gene profiles. The second aim was to establish whether a B. cereus cross-contamination between human milk and the environment could occur. This was achieved with the help of Fourrier-transform infra-red spectroscopy which enabled the discrimination of 2 main clusters of 11 and 8 isolates, each containing human milk and Amiens Picardie human milk bank environmental isolates. For these two clusters, the time sequence showed that human milk isolates were the first to occur and might have contaminated the milk bank environment as well as other human milk donations. Routinely used on B. cereus isolates, Fourrier-transform infra-red spectroscopy could help in rapidly detecting such clusters and in limiting the spread of a B. cereus strain that might generate rejection of pasteurized donation by the human milk bank.

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.