Abstract
Micro RNAs (miRNAs) are small noncoding RNAs that regulate gene expression at the post-transcriptional level. The miRNA in the RNA-induced silencing complex acts as a guide strand and binds the target mRNA. Subsequently, the gene is silenced either by cleaving the target mRNA or repressing the translation. Since the discovery of the first miRNA three decades ago, more than 2000 human miRNAs have been discovered. It is known to regulate hundreds of genes in various physiological and pathophysiological processes, including the development and function of immunologically essential cells. miR-155 plays a vital role in the function of T helper 1, 17, and T regulatory cells. miR-24 positively regulates the function of T helper 1, 17, and T regulatory cells, whereas miR-23 and 27 have a negative regulatory effect. miR-223 regulates the differentiation of neutrophils and monocytes. The role of miRNAs in bacterial infections came to light in 2006 after discovering miR-163 as a negative regulator of defense response in Arabidopsis thaliana infected with Pseudomonas syringae. During bacterial infection in the host, aberrant expression of several miRNAs was discovered. miR-155 was found to be the most commonly dysregulated miRNA in bacterial infections such as Helicobacter pylori, Staphylococcus aureus, Listeriamonocytogenes, Mycobacterium tuberculosis, and Chlamydia trachomatis. Therefore, miRNAs can be utilized as a diagnostic and prognostic tool for bacterial infections.

Key words: Bacterial infections, microRNA, miRNA, monocyte, neutrophil, T-cell