Applied Microbiology

When bacteria are subjected to acidic pH of the gastric environment they may enter the viable but non culturable (VBNC) state of survival. In this state, bacteria cannot be cultured on solid media and still exhibit signs of metabolic activity. The response of pathogenic Vibrio cholerae O1 and O139 to low pH simulated environments of the human stomach was evaluated for their survival by culturability (plate count) and viability (flow cytometry-FC) assays. Bacteria were acid challenged with simulated gastric fluid (SGF) at varying acidic pH over 180 minutes. We established that exposure to the acidic SGF for a limited period of time increased acid tolerance of the pathogenic Vibrio up to pH 3.5 with acid challenge occurring at pH 4.5. Bacteria were culturable from pH 2.5-4.5 up to 60 min SGF exposure. Stationary phase Vibrio cultures survived SGF at all pH in an ‘injured’ state with FC. This could mean that the bacteria have entered the VBNC stage of survival. The minimal number of ingested Vibrio pathogens necessary to inflict disease still remains a controversial issue and in this study we established that low numbers of Vibrio were able to survive the acidic conditions of SGF without pre-adaptation. This study foresees the potential increase of waterborne diseases in immune-compromised individuals that depend on the gastric fluid barrier as protection against bacterial pathogens. This is a worrying public health concern due to the fact that once favorable conditions arise (intestines) these Vibrio can change back to an infectious state and cause disease.