Relapsing Bacillus cereus peritonitis in a patient treated with continuous ambulatory peritoneal dialysis

Unraveling the Role of Vegetables in Spreading Antimicrobial-Resistant Bacteria: A Need for Quantitative Risk Assessment

In recent years, vegetables gain consumer attraction due to their reputation of being healthy in combination with low energy density. However, since fresh produce is often eaten raw, it may also be a source for foodborne illness. The presence of antibiotic-resistant bacteria might pose a particular risk to the consumer. Therefore, this review aims to present the current state of knowledge concerning the exposure of humans to antibiotic-resistant bacteria via food of plant origin for quantitative risk assessment purposes. The review provides a critical overview of available information on hazard identification and characterization, exposure assessment, and risk prevention with special respect to potential sources of contamination and infection chains. Several comprehensive studies are accessible regarding major antimicrobial-resistant foodborne pathogens (e.g., Salmonella spp., Listeria spp., Bacillus cereus, Campylobacter spp., Escherichia coli) and other bacteria (e.g., further Enterobacteriaceae, Pseudomonas spp., Gram-positive cocci). These studies revealed vegetables to be a potential—although rare—vector for extended-spectrum beta-lactamase-producing Enterobacteriaceae, mcr1-positive E. coli, colistin- and carbapenem-resistant Pseudomonas aeruginosa, linezolid-resistant enterococci and staphylococci, and vancomycin-resistant enterococci. Even if this provides first clues for assessing the risk related to vegetable-borne antimicrobial-resistant bacteria, the literature research reveals important knowledge gaps affecting almost every part of risk assessment and management. Especially, the need for (comparable) quantitative data as well as data on possible contamination sources other than irrigation water, organic fertilizer, and soil becomes obvious. Most crucially, dose–response studies would be needed to convert a theoretical “risk” (e.g., related to antimicrobial-resistant commensals and opportunistic pathogens) into a quantitative risk estimate.

Relapsing peritonitis with Bacillus cereus in a patient on continuous ambulatory peritoneal dialysis

We present a case where Bacillus cereus was determined to be the causative agent of relapsing peritonitis in a patient on continuous ambulatory peritoneal dialysis (CAPD). The patient, a 70-year-old man from the Faroe Islands, was admitted with relapsing peritonitis four times over a 3-month period. Peritoneal cultures were positive for growth of B. cereus, a rare bacterial cause of peritonitis. The cultures demonstrated susceptibility to vancomycin, and therefore the patient was treated with intraperitoneal vancomycin, intraperitoneal gentamycin and oral ciprofloxacin. As a result of the relapsing B. cereus peritonitis diagnosis and a CT scan showing contraction of the peritoneum after longstanding inflammation, the peritoneal catheter was removed and the patient converted to haemodialysis. To date, the patient has not been readmitted due to peritonitis. A lack of proper hygiene when changing the dialysis bag was the suspected source of infection with B. cereus.

The Endospore-Forming Pathogen Bacillus cereus Exploits a Small Colony Variant-Based Diversification Strategy in Response to Aminoglycoside Exposure

Bacillus cereus is among the microorganisms most often isolated from cases of food spoilage and causes gastrointestinal diseases as well as nongastrointestinal infections elicited by the emetic toxin cereulide, enterotoxins, and a panel of tissue-destructive virulence factors. This opportunistic pathogen is increasingly associated with rapidly fatal clinical infections especially linked to neonates and immunocompromised individuals. Fatality results from either the misdiagnosis of B. cereus as a contaminant of the clinical specimen or from failure of antibiotic therapy. Here we report for the first time that exposure to aminoglycoside antibiotics induces a phenotype switching of emetic B. cereus subpopulations to a slow-growing small colony variant (SCV) state. Along with altered antibiotic resistance, SCVs showed distinct phenotypic and metabolic properties, bearing the risk of antibiotic treatment failure and of clinical misdiagnosis by standard identification tests used in routine diagnostic. The SCV subpopulation is characterized by enhanced production of the toxin cereulide, but it does not secrete tissue-destructive and immune system-affecting enzymes such as sphingomyelinase and phospholipase. SCVs showed significantly prolonged persistence and decreased virulence in the Galleria mellonella model for bacterial infections, indicating diversification concerning their ecological lifestyle. Importantly, diversification into coexisting wild-type and SCV subpopulations also emerged during amikacin pressure during in vivo infection experiments.

This study shows for the first time that pathogenic spore-forming B. cereus strains are able to switch to a so far unreported slow-growing lifestyle, which differs substantially in terms of developmental, phenotypic, metabolic, and virulence traits from the wild-type populations. This underpins the necessity of molecular-based differential diagnostics and a well-chosen therapeutic treatment strategy in clinical environments to combat B. cereus in a tailored manner. The reported induction of SCV in an endospore-forming human pathogen requires further research to broaden our understanding of a yet unexplored antibiotic resistance mechanism in sporulating bacteria. Our work also raises a general question about the ecological meaning of SCV subpopulation emergence and importance of SCV in sporeformer populations as an alternative route, next to sporulation, to cope with stresses encountered in natural niches, such as soil or host interfaces.