In vitro investigation of antibacterial activity against fecal bacteria infecting wounds

Background

Fecal bacterial wound infection is common in both gastrointestinal surgery and decubitus ulcers. Various approaches have been developed to suppress bacterial growth. Antibacterial activity shown by the conventional assays using a few representative strains may not necessarily be similar to in vitro activity at infection sites.

Purpose

The purpose of the present study was to develop a simple and easy in vitro assay system to investigate antibacterial activity against fecal bacteria and to evaluate its validity.

Methods

The cultures contained Hank’s balanced salt solution containing 10% fetal calf serum as a culture medium and were incubated at 37 °C with constant stirring in room air. Fecal bacterial growth was evaluated by several methods, including optical density at 600 nm, analysis of bacterial DNAs, real time-polymerase chain reaction, and terminal restriction fragment length polymorphism. Four methods were investigated for inhibiting fecal bacterial growth.

Results

Facultative anaerobes, including E. coli, Enterococcus faecaliss, and Lactobacillus species, increased after culture in contrast to the decrease in obligate anaerobes, Clostridium coccoides, Clostridium leptum, Bactroides fragilis, Prevotella, and Bifidobacterium species. The addition of 5 mM EDTA, activated carbons, maintenance of the medium pH at 4.4, and the combination of the above inhibited the increase in optical density.

Conclusion

This in vitro assay is easy to use, partly simulates fecal bacterial growth in vivo, and can be used to measure fecal bacterial growth inhibition.