Antibiotics modulates the virulence of N. meningitidis by regulating capsule synthesis

Environmental desiccation stress induces viable but non culturable state in Neisseria meningitidis

Environmental factors play a crucial role in bacterial virulence. During transmission, in a non-host environment bacteria are exposed to various environmental stress which could alter bacterial physiology and virulence. N. meningitidis is transmitted from person to person through direct contact. However, the role of environmental desiccation in the virulence of bacterial pathogens is not clearly understood. Therefore, the effect of environmental desiccation on survival, transmission, and virulence needs further investigation. We demonstrate that N. meningitidis was sensitive to desiccation stress. The viable counts reduced significantly (p < 0.05) after desiccation. It was found that desiccation induces a viable but non-culturable state (VBNC) in N. meningitidis. We considered cells to be in VBNC when no viable counts were obtained on growth media and live cells were detected after live-dead staining. After resuscitation, N. meningitidis retained virulence characteristics which indicate that it can transit between the host in VBNC state. Furthermore, the relative expression of capsule increased significantly after 12 and 24 h of desiccation. The observations indicate that the environmental desiccation might induce capsule biosynthesis in N. meningitidis, leading to enhanced virulence and survival in macrophages.

Evaluation of the in vitro effects of concentrations of antibiotics on three Enterobacteriaceae isolates

Due to the misuse and overuse of antibiotics, bacteria are now exposed to sub-minimum inhibitory concentrations (sub-MICs) of antibiotics in various environments. In recent years, exposure of bacteria to sub-MICs of antibiotics has led to the widespread emergence of antibiotic-resistant bacteria. In this study, three bacterial species from the Enterobacteriaceae family (Raoultella ornithinolytica, Pantoea agglomerans and Klebsiella quasivariicola) were isolated from water. The antibiotic susceptibility of these bacteria to 16 antibiotics was then investigated. The effects of sub-MICs of four selected antibiotics (kanamycin, chloramphenicol, meropenem, and ciprofloxacin) on the growth, biofilm formation, surface polysaccharide production, siderophore production, morphology, and expression of the translational/transcriptional regulatory transformer gene rfaH of these bacteria were analysed. The MICs of kanamycin, chloramphenicol, meropenem, and ciprofloxacin were determined to be 1, 2, 0.03 and 0.03 µg/mL for R. ornithinolytica; 0.6, 6, 0.03 and 0.05 µg/mL for P. agglomerans; and 2, 5, 0.04 and 0.2 µg/mL for K. quasivariicola. The growth kinetics and biofilm formation ability decreased for all three isolates at sub-MICs. The surface polysaccharides of R. ornithinolytica and P. agglomerans increased at sub-MICs. There was no significant change in the siderophore activities of the bacterial isolates, with the exception of MIC/2 meropenem in R. ornithinolytica and MIC/2 kanamycin in K. quasivariicola. It was observed that the sub-MICs of meropenem and ciprofloxacin caused significant changes in bacterial morphology. In addition, the expression of rfaH in R. ornithinolytica and K. quasivariicola increased with the sub-MICs of the selected antibiotics.