Interface effect of natural precipitated dust on the normal flora of Escherichia coli and Staphylococcus epidermidis

This study aimed to evaluate the interface effect between five types of natural precipitated dust and two normal floras. Five kinds of natural dust (FC-1^#, FC-2^#, FC-15^#, FC-18^#, and FC-21^#) were collected, and particle size and chemical components were detected by laser particle size analyzer and X-ray fluorescence (XRF). The elements, bacterial count, glucose (GLU) consumption, pH, and three biochemical indicators were measured after being co-cultured with Escherichia coli and Staphylococcus epidermidis in vitro. In addition, the changes of bacterial morphology were observed by scanning electron microscopy (SEM). Results showed that most particles contained a high level of SiO₂, which diameter ranged from 0.3 to 1.0 μm. The concentration of Ca showed s significant increase upon interaction with E. coli and S. epidermidis in all dusts (p < 0.01). Moreover, FC-1^# and FC-21^# induced obvious growth in bacterial count, glucose consumption, and pH after they reacted with two normal floras (p < 0.05). Besides, the results also showed an apparent increase in the concentration of pyruvate, β-galactosidase, and alkaline phosphatase (AKP) after being co-cultured with E. coli and S. epidermidis, in which FC-1^# is enhanced in the most obvious. The E. coli interacted with dust made more indentations in surface, and the configuration became thin and long. Some broken bacteria were present, and bacterial wreckage was visible. Plenty of S. epidermidis interacted with dust gathered in the indentations of dust, particularly in pleated surfaces. Further, these findings demonstrated that the alkaline dust with higher Ca content stimulated the growth of bacteria, and irregularly shaped or thin dust would be easier to combine with bacteria and conduct interface effect.