Biofilm Structure and Formation in Haemophilus ducreyi

By: Delaney Lacey

Biofilms are of particular interest to the scientific and clinical community due to the variety of biotic and abiotic surfaces they can colonize. Teeth, surgical instruments, and organs (such as the lungs of cystic fibrosis patients) can all be colonized by a bacterial biofilm. Biofilm formation is characterized by the following steps: signaling by an environmental cue, attachment of cells to a surface, growth and aggregation of cells into microcolonies, maturation and maintenance of architecture, detachment, and dispersal. Progression from a microcolony to a biofilm is mediated by the secretion of extracellular polymeric substances (EPS), a conglomerate of DNA, carbohydrates, lipids, and proteins that enclose the cells in a 3D matrix and contribute to the biofilm structure and function. When grown in a biofilm, bacteria collectively shift their phenotype as a result of differential gene regulation. This shift can lead to pathogenicity, increased virulence, and increased resistance to antibiotics. 65-80% of all infections and 60% of chronic wound infections are associated with biofilm formation. Identifying infections caused by biofilms and characterizing genes required for biofilm formation will better inform the development of treatments for and prevention of infectious disease.

Haemophilus ducreyi, the causative agent of chancroid, a sexually transmitted genital ulcer disease, as well as a non-sexually transmitted chronic limb ulceration syndrome, forms microcolonies in the presence of HFF cells and thus engages in the first two stages of biofilm formation. However, secretion of EPS and the formation of a 3D matrix has yet to be documented. Our long term goal is to understand the mechanism by which biofilm formation occurs in H. ducreyi and assess the influence of biofilm formation on virulence in vivo. The overall objective of this proposal is to identify genes that may affect biofilm formation in H. ducreyi. The rationale that supports the proposed research is that by characterizing biofilm formation in H. ducreyi in vitro, the effect of H. ducreyi biofilms in vivo on virulence and antibiotic resistance can be assessed. Furthermore, by investigating putative biofilm genes, the pathway for biofilm formation in H. ducreyi can be further characterized, aiding in the development of treatments for and prevention of H. ducreyi and other infectious diseases.

We plan to test our central hypothesis and achieve the objective of this proposal by pursuing two specific aims:
1) Examine class I, II, and ulcer strain H. ducreyi via confocal imaging for EPS components (extracellular DNA and carbohydrates).
2) Determine the effect of surface appendage and sensory regulatory gene disruption on biofilm formation in H. ducreyi.

The expected outcomes of this proposal include the characterization of the capacity of H. ducreyi to form a biofilm. In addition, we also will complete the identification of genes crucial for formation of these biofilms.

Leave a Reply