Co-effect of Leached Metals and pH of Simulated Gastric Fluid on the Survival of Microorganisms in Geophagic Clays

In this study, the bacterial activity was investigated following exposure of geophagic clays to simulated gastric fluid. The inhibitory effects of either acidity or metals released were considered. The geophagic clay samples were characterized using XRD and XRF techniques, the bacteria were identified using 16S rDNA sequencing and their survival in simulated gastric overtime was monitored using plate count. The results showed that heavy metals were released in the gastric fluid overtime while the pH remained acid over the same period of time. The mobility of the metals from the geophagic clays decreased in the order Pbgreater thanNigreater than Cogreater thanFegreater thanCrgreater thanCugreater thanZn. The count of cell number under such conditions showed that both acidity and metal concentrations had contributed to the decrease of cell number in the simulated gastric fluid. Total metal concentration increase from 25 to 35 mg/L contributed to a two folds decrease of bacterial number after 150 min, a decrease of bacteria count overtime was observed in samples containing mostly Gram-negative bacteria, while no significant change was observed in samples dominated by Gram-positive bacteria. The results have shown the decrease of bacterial activity and increase of metals released at low pH. The acidity inhibits the growth of bacteria and also increases metal release which further enhances bacteria inhibition.