Opportunistic Features of Non- Strains Containing Gene Cluster.

The cluster of genes determining the production of botulinum toxins is an attribute of not only the species. This cluster is also found in other members of the genus, such as , , and . The occurrence of a botulinum-like cluster has also been recorded in strains of other genera, i.e., , as well as in a Gram-negative species isolated from freshwater sediments; however, the biological activity of -related genes has not been noted. It can be said that the mentioned species have a dual nature. Another species with a dual nature is . This bacterium is a common human and animal gut commensal bacterium and is also frequently found in the environment. Although non-toxigenic strains are currently used as probiotics in Asia, other strains have been implicated in pathological conditions, such as botulism in infants or necrotizing enterocolitis in preterm neonates. Additionally, strains are rare opportunistic pathogens associated with botulism intoxication. They have been isolated from food and soil and can be carried asymptomatically or cause botulism outbreaks in animals and humans. In addition to the mentioned clostridia, the other microorganisms considered as non-toxigenic have also been suspected of carrying botulinum cluster Gram-negative bacteria, such as isolated from freshwater sediments; however, the biological activity of -related genes has not been noted. Additionally, strains have been discovered carrying BoNT-related clusters (BoNT/En). Literature data regarding the heterogeneity of BoNT-producing strains indicate the requirement to reclassify species and other microorganisms able to produce BoNTs or possess botulinum-like gene clusters. This article aims to show the dual nature of strains not belonging to the species that are sporadically able to carry clusters, which are usually considered saprophytic and even probiotic, and -like clusters in microorganisms from other genera. The aim was also to consider the genetic mechanisms of botulinum cluster expression in strains that are considered opportunistic and the microbiological safety aspects associated with their occurrence in the environment.