Detection of agents that alter the bacterial cell surface

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Antimicrobial Resistance

Background:

• Proteus mirabilis exhibits resistance to polymyxin B, normal serum, and sodium deoxycholate independently.
• Current antibiotic screening methods may overlook agents that enhance susceptibility to other treatments or host defenses.

Purpose of the Study:

• To investigate the synergistic effect of polymyxin B on the susceptibility of Proteus mirabilis to normal serum and sodium deoxycholate.
• To highlight the limitations of conventional in vitro antibiotic screening.
• To introduce a novel method for detecting cell surface-modifying antimicrobial agents.

Main Methods:

• Exposure of Proteus mirabilis to polymyxin B.
• Assessment of bacterial susceptibility to normal serum and sodium deoxycholate post-exposure.
• Development and description of a new screening assay for cell surface-modifying agents.

Main Results:

• Proteus mirabilis, resistant to polymyxin B, normal serum, and sodium deoxycholate alone, becomes susceptible to serum and deoxycholate after polymyxin B exposure.
• This observed synergism is attributed to polymyxin B-induced alterations in the bacterial cell surface.
• Existing antibiotic screening assays failed to identify polymyxin B's potentiating effect.

Conclusions:

• Polymyxin B can induce surface changes in Proteus mirabilis, rendering it susceptible to host defense mechanisms and other antimicrobials.
• There is a critical need for improved antibiotic screening methods capable of detecting agents that modify bacterial susceptibility.
• A new method has been developed to identify such crucial cell surface-modifying agents.