Date of Award


Degree Type


Degree Name

Master of Science (MS)


Microbiology and Immunology


Lactobacillus species are widely accepted as beneficial bacteria of the human microbiota1-8. Lactobacilli spp. are well documented to inhibit pathogens by production and secretion of hydrogen peroxide (H2O2), organic acids, and/or proteinaceous bacteriocins into their environment. Most research attributes bactericidal activity of cell free supernatant (CFS) to H2O2 and/or lactic acid. Here, I demonstrate that CFS from a clinical isolate of Lactobacillus crispatus contains a molecule(s) that inhibits uropathogenic Escherichia coli (UPEC) colony formation independently of H2O2 and organic acids. Physiologic concentrations of H2O2 and organic acids produced by L. crispatus do not inhibit UPEC colony formation. Incubation of UPEC with L. crispatus CFS has a bactericidal effect on UPEC that begins at about 4 hours and results in undetectable CFUs by 16 hours, apparently the result of severe plasmolysis. Bactericidal activity of this CFS is effective against some Gram-negative and Gram-positive species including multidrug resistant (MDR) E. coli. The broad-spectrum activity shows CFS may have applicability as future therapeutic for treatment of various bacterial infections including MDR infections.

The active molecule(s) present in CFS is stable over a wide temperature range and can be stored for at least 3 months while retaining full bactericidal activity. The active molecule(s) is sensitive to dilution and increased salt concentrations. The active molecule(s) from CFS can be isolated via organic extraction. Based on the extraction profile, the molecule is predicted to be a dipolar organic molecule(s). The majority of proteins and tri-peptides are removed during organic extraction yet extracts retain full bactericidal activity. I conclude that L. crispatus produces a very stable potentially novel dipolar, organic molecule with broad-spectrum activity that is concentration-dependent and salt-sensitive, and which results in plasmolytic activity against its target. Isolation and identification of this molecule(s) could lead to application as a decontaminant or therapeutic.

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Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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