Spore-forming bacterial species pose a serious threat to food plants and healthcare facilities that use high-temperature processing and sterilizing techniques to sanitize medical equipment and food items. These severe processing conditions trigger sporulation, which is the process by which spore-forming bacteria, such as those of the Bacillus and Clostridium species, begin to produce spores, which are extremely resilient entities capable of withstanding adverse environmental circumstances. Additionally, these spores are resistant to a wide range of disinfectants and antibacterial therapies, such as hydrolytic enzymes, radiation, chemicals, and antibiotics. Because of their ability to combat bacteria through several biological pathways, selenium nanoparticles (SeNPs) have emerged as an effective method for either eliminating or preventing the formation of spore-forming bacteria. This review aims to investigate every potential pathway of entry and mechanism by which SeNPs impact bacterial species that produce spores. Additionally, SeNPs’ antibacterial efficacy against several infections is reviewed. To precisely explain the antibacterial mechanism of SeNPs and the various factors that can affect their effectiveness, more research is necessary.

The present study aimed to unveil the phenotypic heterogeneity and heteroresistance of P. aeruginosa to acidic stress and imipenem. Furthermore, the growth, morphology, and potential for biofilm formation of the subject isolates at different pHs were assessed. Isolates of P. aeruginosa were recovered from juice samples and confirmed by molecular analysis. Antibiotics sensitivity was evaluated using the Kirby–Bauer-disk diffusion method, and the MIC for imipenem was determined, followed by a biofilm formation assay and population analysis. Scanning electron microscopy (SEM) was used to visualize biofilm formation. The subject isolates persisted in an acidic environment and adopted a biofilm lifestyle. The population analysis assay indicated the presence of two distinct phenotypes, i.e., a normal colony phenotype (NCP) and slow growing colony phenotype (SGCP). NCP showed visible colonies after 48 h, while SGCP colonies appeared after 72 h of incubation. Both displayed heteroresistance to imipenem and susceptibility to other antibiotics. Biofilm formation at acidic pH was observed in both phenotypes. Interestingly, the recovery of SGCP was increased in an acidic environment. Biofilm consortia were highly resistant to imipenem. The present study indicated that P. aeruginosa persisted for a long time in an acidic environment, through phenotypic alteration. The subject isolates adopted a biofilm lifestyle and reduced metabolism, to neutralize the effects of acidic pH and imipenem toxicity. Interestingly, the biofilm consortia harbored metabolically active (NCP), as well as inactive populations, of (SGCP), to maintain an active growth and persistency. SGCP retained the potential to revert to NCP upon subsequent sub-culturing in plentiful nutrients and optimum conditions.

The present study discusses a biofilm-positive P. aeruginosa isolate that survives at pH levels ranging from 4.0 to 9.0. The biofilm consortia were colonized with different phenotypes i.e., planktonic, slow-growing and metabolically inactive small colony variants (SCVs). The lower base of the consortia was occupied by SCVs. These cells were strongly attached to solid surfaces and interconnected through a network of nanotubes. Nanotubes were observed at the stationary phase of biofilm indwellers and were more prominent after applying weight to the consortia. The scanning electron micrographs indicated that the nanotubes are polar appendages with intraspecies connectivity. The micrographs indicated variations in physical dimensions (length, width, and height) and a considerable reduction in volume due to weight pressure. A total of 35 cells were randomly selected. The mean volume of cells before the application of weight was 0.288 µm³, which was reduced to 0.144 µm³ after the application of weight. It was observed that a single cell may produce as many as six nanotubes, connected simultaneously to six neighbouring cells in different directions. The in-depth analysis confirmed that these structures were the intra-species connecting tools as no free nanotubes were found. Furthermore, after the application of weight, cells incapable of producing nanotubes were wiped out and the surface was covered by nanotube producers. This suggests that the nanotubes give a selective advantage to the cells to resist harsh environmental conditions and weight pressure. After the removal of weight and proper supply of nutrients, these phenotypes reverted to normal planktonic lifestyles. It is concluded that the nanotubes are not merely the phenomenon of dying cells; rather they are a connectivity tool which helps connected cells to tolerate and resist environmental stress.