Epigenetics of Haemophilus influenzae

Pathogenic bacterial strains that have adapted to solely infect humans need to go through a constant cycle of host changing, colonization, and transmission. Any population incapable of doing this might be experiencing an evolutionary dead end. An enormous amount of pressure has been placed on the creation of extraordinarily effective methods to circumvent the human innate and adaptive immunity by the ongoing selection process that occurs across several distinct cycles of transmission via various human hosts. Bacteria that have evolved to live in human surroundings as pathogens frequently exhibit the phase variation of virulence-linked genes. While homologous recombination is one possible method for this kind of random, high-frequency switching of gene expression, simple tandem DNA repeating sequences are also capable of mediating phase variation. Because of the innate instability of these DNA repeats, individuals within the bacterial population showed diversity in the expressing virulence-associated genes as a result of the regular loss or gain of repeated units in the promoter regions or the open reading frames of these genes. A population of bacteria with a diverse range of cells that have already reacted to various environmental, intra-, and inter-host constraints can be produced using a very effective contingency method called phase variation. More studies have been done on restriction modification systems with phase-variable expression. Global modifications in DNA methylation result from phase variation in these systems. Multiple human-adapted bacterial diseases have Type III restriction-modification systems, which show how global alterations in methylation affect numerous gene expressions. Phasevarion switching aids infections in evading the human immune system by altering virulence features. The most prominent human Haemophilus influenzae bacterial infection is examined in this chapter with regard to the significance of phasevarions in pathogenesis and immunological resistance.