Frequency among Enterobacteriaceae of the DNA sequences encoding type 1 pili

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Type 1 pili are surface appendages found in the Enterobacteriaceae family, characterized by mannose-inhibitable hemagglutination.
• These pili play roles in bacterial adhesion and colonization, but their genetic basis across different genera is not fully understood.

Purpose of the Study:

• To investigate the distribution of the Type 1 pil operon within the Enterobacteriaceae family.
• To determine the genetic location (chromosomal vs. plasmid) of the Type 1 pil operon.

Main Methods:

• Preparation of a radiolabeled DNA probe from the Escherichia coli pil operon.
• Hybridization assays using the probe to detect homologous DNA sequences in 236 bacterial isolates from 11 Enterobacteriaceae genera.
• Analysis of restriction nuclease-digested whole-cell DNA from E. coli and Shigella isolates.

Main Results:

• Homologous DNA sequences for the pil operon were exclusively detected in Escherichia coli and Shigella species.
• Mannose-sensitive hemagglutination, a characteristic of Type 1 pili, was observed in nine different genera, indicating functional pili without the specific DNA sequence detected.
• The pil operon was confirmed to be located on the chromosome, not on plasmids, in the strains examined.

Conclusions:

• The genetic determinant for Type 1 pili, the pil operon, is highly conserved within Escherichia coli and Shigella but absent in other Enterobacteriaceae genera that exhibit Type 1 pilus-like activity.
• Variations in flanking chromosomal sequences of the pil operon are common among E. coli and Shigella strains.