Uptake and levels of the antibiotic berberine in individual dormant and germinating Clostridium difficile and Bacillus cereus spores as measured by laser tweezers Raman spectroscopy

Shiwei Wang, Barbara Setlow, Peter Setlow and Yong-qing Li

Spores of Clostridium difficile and Bacillus cereus are major causes of nosocomial diarrhoea and foodborne disease. Our aim was to measure the dynamics of the uptake of the antibiotic berberine by individual germinating spores and the levels of berberine accumulated in germinated spores. Laser tweezers Raman spectroscopy (LTRS) and differential interference contrast microscopy were used to measure levels of berberine accumulated in single germinating spores and to monitor berberine uptake and germination of individual C. difficile and B. cereus spores. MIC values of berberine for C. difficile and B. cereus spores were 640 and 256 mg/L, respectively. Levels of berberine accumulated at the berberine MICs in individual germinated spores were heterogeneous, with values of 17.1 ± 5.4 and 12.7 ± 5.5 g/L for C. difficile and B. cereus spores, respectively. These values were 25–50-fold higher than the MIC values. However, berberine did not affect the germination of C. difficile and B. cereus spores, but did block germinated spores' outgrowth. Berberine uptake kinetics were similar for these two kinds of spores. After the addition of germinants, berberine began to enter germinating spores at the time (Tlag) when rapid release of the spore core's large depot of the 1:1 chelate of Ca2+ with dipicolinic acid began, and the level of berberine taken up was maximal shortly after spore cortex lysis was completed (Tlysis). LTRS can be used to measure uptake and levels of berberine in single cells. High levels of berberine can enter spores of C. difficile and B. cereus soon after germination is initiated, thus inhibiting spore outgrowth and minimizing hazards posed by germinated spores.

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