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 0.288µm3, 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.

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Background The growing interest on usage of probiotic lactobacilli in maintaining oral health has posed number of questions on its probable side effects. One such consideration could be an increased acid production in dental plaque, in turn leading to dental caries. Thus, the aim of this study was to comparatively evaluate the lactic acid producing ability of L. acidophilus and L. plantarum with and without dental plaque. Material and Methods The study consisted of five groups: 3 control groups ( Supragingival plaque, L. acidophilus and L. plantarum ) and 2 test groups (Supragingival plaque with L. acidophilu s and Supragingival plaque with L. plantarum ). 26 samples for each group were collected and their baseline spectrophotometric values were recorded. The acid production was initiated by adding 25?l fructose (10%) and stopped by centrifugation for 2 min. The concentration of the lactic acid produced was determined with the aid of COBAS INTEGRA 400 plus. Results On comparison of Lactic Acid estimation in mg/dl, the mean values of Plaque group was the highest followed by Plaque +L acidophilus, Plaque +L plantarum, L acidophilus and least in L plantarum. The posthoc analysis shows that the comparison of Group 1 (Plaque) and Group 2 (Plaque +L acidophilus) is statistically Significant results between all the groups except between the Plaque +L acidophilus and Plaque +L plantarum group. Conclusions The lactic acid producing ability of pure suspensions of L.acidophilus and L.plantarum and the lactic acid producing efficiency becomes more when they are added to the supragingival plaque. Key words: Probiotic, lactic Acid, plaque.

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.