AUTHOR=Si Wei , Wang Liangliang , Usongo Valentine , Zhao Xin 

TITLE=Colistin Induces S. aureus Susceptibility to Bacitracin

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.02805

DOI=10.3389/fmicb.2018.02805

ISSN=1664-302X

ABSTRACT=<p>Bacitracin has been used in topical preparations with polymyxin B for bacterial infections. Colistin belongs to the polymyxin group of antibiotics and is effective against most Gram-negative bacilli. This study investigated whether colistin could affect the susceptibility of <italic>S. aureus</italic> to bacitracin. <italic>S. aureus</italic> isolates were first incubated with colistin and the susceptibility of <italic>S. aureus</italic> to bacitracin was increased. The effect of the combination of colistin and bacitracin on <italic>S. aureus</italic> was then confirmed by the checkerboard assay and the time-kill kinetics. The Triton X-100-induced autolysis was significantly increased after <italic>S. aureus</italic> was exposed to colistin. Exposure to colistin also led to a less positive charge on the cell surface and a significant leakage of Na<sup>+</sup>, Mg<sup>2</sup>, K<sup>+</sup>, Ca<sup>2+</sup>, Mn<sup>2+</sup>, Cu<sup>2+</sup>, and Zn<sup>2+</sup>. Finally, disruptions on the cell surface and an irregular morphology were observed when the bacteria were exposed to colistin and bacitracin. Bacitracin had a stronger antibacterial activity against <italic>S. aureus</italic> in the presence of colistin. This could be due to the fact that colistin damaged the bacterial membrane. This study suggests that combination of colistin with bacitracin has a potential for treating clinical <italic>S. aureus</italic> infections.</p>