Motility and Hemolytic Activity in E. coli
No, motile strains of E. coli are not consistently more hemolytic; in fact, the evidence suggests an inverse relationship where lower-motility strains tend to have higher prevalence of certain virulence factors including hemolytic activity.
The Relationship Between Motility and Virulence Factors
The interplay between bacterial motility and hemolytic activity in E. coli is complex and appears to be inversely related:
Lower-motility E. coli strains demonstrate a higher prevalence of virulence factors, including a significantly higher prevalence of ompT genes (p = 0.0497), which are associated with virulence mechanisms 1.
Hemolysin production (25.8%) was documented in uropathogenic E. coli strains, but this was not specifically correlated with increased motility 2.
Higher-motility strains were more common in spontaneous bacterial peritonitis (59%) but required fewer additional virulence factors to cause infection, suggesting that motility itself serves as a primary virulence mechanism rather than being coupled with hemolytic activity 1.
Why Lower Motility May Associate with More Virulence Factors
The evidence reveals a compensatory mechanism:
E. coli isolates with lower motility require more bacterial virulence factors to develop extraintestinal infections, suggesting that when motility is reduced, strains compensate by expressing other virulence mechanisms including potential hemolytic activity 1.
Different phylogenetic groups show varying motility patterns, with higher-motility strains showing lower prevalence of phylogenetic groups A and B1, which are typically associated with different virulence factor profiles (p = 0.018) 1.
Trade-offs Between Motility and Other Virulence Mechanisms
There is a functional trade-off between different virulence factors:
Constitutive expression of type 1 fimbriae significantly decreases motility and flagellin expression (P < 0.0001), demonstrating that expression of certain virulence factors directly suppresses motility 3.
Flagellum-mediated motility contributes to fitness and pathogenesis by enabling bacterial dispersal and immune evasion, but this is a distinct mechanism from hemolytic activity 4.
Clinical Implications
The key takeaway is that motility and hemolytic activity represent different virulence strategies rather than co-occurring traits. Strains may rely primarily on one mechanism or the other depending on their genetic background and the type of infection they cause 1, 5.