Karmakar, Sushmita and Roychoudhury, K.
E.coli and B. Cereus were induced to Viable but Non Culturable State by starvation and temperature upshift to 50°C. The change in osmolarity by addition of more than 10% NaCl also resulted into induction of VBNC state of both B.cereus and E.coli. In the VBNC state the cultures lost their capacity to reduce nitrate B.cereus also lost the capacity to ferment maltose, fructose, hydrolysis of starch and citrate utilization. On the other hand for E.coli the capacity to ferment arabinose, sorbitol and sucrose was lost. While serum and egg yolk could not help the resuscitation of the cultures but favourable temperature between 35° C -40°C and enrichment of media could help in resuscitation of these cultures. There were distinct differences in the VBNC state with respect to enzyme activity.
Keywords: E. Coli | B. cereus | Culture
Introduction
It is not necessary for all living systems to be in an environment which favours their survival. Various types of stress conditions may be experienced by microbes in different living conditions. The adaptability of the microbes to such stress conditions depends on various factors. A bacterial cell may enter into a starvation mode or enter into a physiological stress , wherein it is viable but not dead but multiplies by such a low rate that a visible colony is not formed . Such a state wherein the bacteria are viable but are not in a condition to grow well and hence non culturable can be defined as Viable but Non Culturable State or simply VBNC state. Conditions such as temperature, osmolarity, nutrient availability, pH and hydration are common factors leading to induction in the VBNC state.
Once a bacterial cell enters into VBNC state the question remains to be answered is that whether the state is a permanent state or the state can be reverted back to a culturable state.The change of non culturable bacteria back to culturable state is known as ‘Resuscitation.’ This has been observed in many pathogens like Mycobacterium tuberculosis (Laam li et al., 2014) Legionella sps (Steinert et al., 1997; Al Bana et al., 2013). Vibrio sps. (Baffone et al., 2003; Sun et al., 2008) When VBNC cells in the latent phase of a disease gets resuscitated the culturable cells then retain their virulence potential. A number of virulence and toxin genes are expressed even in the VBNC state.(Vora et al., 2005).
Sinc many of the common pathogens including food pathogens are known to enter into the non culturable VBNC state and later resuscitate in the host body. It is important to have a detailed investigation of the various stress responses of the commonly known pathogens.