Ultrastructural surface alterations of serratia marcescens after exposure to polymyxin B and/or fresh human serum

Area of Science:

• Microbiology
• Cell Biology
• Biochemistry

Background:

• Serratia marcescens is an opportunistic pathogen.
• Polymyxin B is a potent antibiotic targeting Gram-negative bacteria.
• Human serum contains complement proteins and antibodies that can interact with bacterial surfaces.

Purpose of the Study:

• To investigate the ultrastructural effects of polymyxin B and fresh human serum on Serratia marcescens.
• To determine if combined treatment elicits synergistic or distinct alterations.
• To understand the mechanisms of bacterial surface modification by these agents.

Main Methods:

• Exposure of Serratia marcescens cultures to varying concentrations of polymyxin B.
• Incubation of bacterial cells with fresh and heat-inactivated human serum.
• Transmission electron microscopy (TEM) to visualize ultrastructural changes on the bacterial outer cell surface.

Main Results:

• Polymyxin B treatment (10, 5, and 2.5 µg/ml) induced coarse, pleomorphic projections with a double-contoured membrane structure on S. marcescens.
• Fresh human serum, but not heat-inactivated serum, led to the deposition of fine, thread-like aggregates on the bacterial surface.
• Combined exposure to polymyxin B and fresh human serum resulted in ultrastructural alterations characteristic of both treatments.

Conclusions:

• Polymyxin B and fresh human serum induce distinct morphological changes on the Serratia marcescens outer cell surface.
• The observed alterations suggest different interaction mechanisms between the bacteria and each agent.
• These findings contribute to understanding the antibacterial mechanisms and host-pathogen interactions involving S. marcescens.