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IntroductionThe Bacillus cereus group encompasses a complex group of closely related pathogenic and non-pathogenic bacterial species. Key members include B. anthracis, B. cereus, and B. thuringiensis organisms that, despite genetic proximity, diverge significantly in morphology and pathogenic potential. Taxonomic challenges persist due to inconsistent classification methods, particularly for B. cereus isolates that resemble B. anthracis in genetic clustering.MethodsThis study investigated B. cereus group isolates from blood smears of animal carcasses in Kruger National Park, uncovering an unusual isolate with B. cereus features based on classical microbiological tests yet B. anthracis-like genomic similarities with an Average Nucleotide Identity (ANI) of ≥95%. Using comparative genomics, pan-genomics and whole genome Single Nucleotide Polymorphism (wgSNP) analysis, a total of 103 B. cereus group genomes were analyzed, including nine newly sequenced isolates from South Africa and a collection of isolates that showed some classification discrepancies, thus classified as “anomalous.”Results and discussionOf the 36 strains identified as B. anthracis in GenBank, 26 clustered phylogenetically with the four confirmed B. anthracis isolates from South Africa and shared 99% ANI. Isolates with less than 99% ANI alignment to B. anthracis exhibited characteristics consistent with B. cereus and/or B. thuringiensis, possessing diverse genetic profiles, insertion elements, resistance genes, and virulence genes features, contrasting with the genetic uniformity of typical B. anthracis. The findings underscore a recurrent acquisition of mobile genetic elements within B. cereus and B. thuringiensis, a process infrequent in B. anthracis.ConclusionThis study highlights the pressing need for standardized taxonomic criteria in B. cereus group classification, especially as anomalous isolates emerge. This study supports the existing nomenclature framework which offers an effective solution for classifying species into genomospecies groups. We recommend isolates with ANI ≥99% to standard reference B. anthracis be designated as typical B. anthracis in GenBank to maintain taxonomic clarity and precision.

In this paper we describe the transmission of a multi-drug resistant Klebsiella pneumoniae ST101 clone from hospital to wastewater and its persistence after chlorine treatment. Water samples from influents and effluents of the sewage tank of an infectious diseases hospital and clinical strains collected from the intra-hospital infections, during a period of 10 days prior to wastewater sampling were analyzed. Antibiotic resistant K. pneumoniae strains from wastewaters were recovered on selective media. Based on antibiotic susceptibility profiles and PCR analyses of antibiotic resistance (AR) genetic background, as well as whole-genome sequencing (Illumina MiSeq) and subsequent bioinformatic analyses, 11 ST101 K. pneumoniae strains isolated from hospital wastewater influent, wastewater effluent and clinical sector were identified as clonally related. The SNP and core genome analyses pointed out that five strains were found to be closely related (with ≤18 SNPs and identical cgMLST profile). The strains belonging to this clone harbored multiple acquired AR genes [blaCTX–M–15, blaOXA–48, blaOXA–1, blaSHV–106, blaTEM–150, aac(3)-IIa, aac(6′)-Ib-cr, oqxA10, oqxB17, fosA, catB3, dfrA14, tet(D)] and chromosomal mutations involved in AR (ΔmgrB, ΔompK35, amino acid substitutions in GyrA Ser83Tyr, Asp87Asn, ParC Ser80Tyr). Twenty-nine virulence genes involved in iron acquisition, biofilm and pili formation, adherence, and the type six secretion system – T6SS-III were identified. Our study proves the transmission of MDR K. pneumoniae from hospital to the hospital effluent and its persistence after the chlorine treatment, raising the risk of surface water contamination and further dissemination to different components of the trophic chain, including humans.