The Waxy Cell Envelope of Pathogenic and Non-Pathogenic Mycobacteria: Resistance to Antibiotics and Protection against Host Response. An Overview

Tuberculosis, an ancient infectious disease caused by Mycobacterium tuberculosis (MTb), a Gram-positive bacillus, is a public health problem because 95% of infected people develop latent tuberculosis, while 5% develop active disease.The situation is worsen by the increase in multidrug resistance (MDR), co-morbidities and the lack of a more effective vaccine, which prolongs and induces longlasting memory immune responses in young older adults.The development of pharmacological and immunotherapies depends on an understanding the spectrum of the disease, the genetic susceptibility to mycobacterial infection and evasion the mechanisms developed by Mtb against the microbicide action of the host.The three-layered mycobacterial envelope is roughly seen from the outside to the inside: -A surface layer, -the capsule, composed of polysaccharides and proteins, present only in the pathogenic species.The mycomembrane (MM), composed of proteins and long fatty acids (long chain mycolic acids from C60-C90) with free intercalated glycolipids and covalently linked to arabinogalactan and peptidoglycan layer, similar to those of Gram-negative bacteria, and the phospholipid bilayer inner classical plasma membrane.These components are pathogen-associated molecular patterns (PAMPs) that are recognized by patterns of receptor recognition (PPRs) on the surface of antigen-presenting cells (macrophages, dendritic cells).This is the first interaction between host and pathogen that results in effective activation and immune modulation of the host response.The pathways involved in the biosynthesis of the outer and inner membranes, including the waxy cell wall of the mycomembrane, represent immunological or pharmacological targets for diagnosis and treatment.Here is an overview of the characteristics of the mycobacterial cell envelope.