AssignmentOn

Mycoplasma: Host-cell interaction

Presented By:Dr. Rajat VarshneyPhD ScholarRoll no. 1772

DIVISION OF VETERINARY BACTERIOLOGY AND MYCOLOGY, IVRI

Introduction• Mycoplasmas (class Mollicutes) are the smallest and simplest

self-replicating bacteria.

• Mycoplasmas have an extremely small genome.

• These organisms have limited metabolic options for replication and survival.

• Most mycoplasmas are parasites exhibiting strict host and tissue specificities.

PATHOGEN ENVIRONMENT

HOST

DISEASE

TRIAD

Host-P

aras

ite

Inte

racti

ons

OTHER MICROBES

Microbial Interactions

ECOLOGICAL RELATIONSHIPS

Health and Disease

Equilibrium

Host - Bacteria

IR Virulence

Balance disturbed - Disease

Mycoplasma species of veterinary significance, the disease conditions which they cause and their geographical distribution

Mycoplasmas of Humans• Parasitic1. Established pathogens: M. pneumoniae

2. Presumed pathogens: M. hominis,U. urealyticum

3. Non pathogenic: M. orale, M. buccale, M. genitalium, M. fermentans

• Saprophytic – present mainly on skin & in mouth.

Virulence factors Adhesins

Attachment Organelle

Ciliary Adhesin of Mycoplasma hyopneumoniae

Adhesins of Other Species of Mycoplasma

Hydrogen Peroxide

Biofilm Formation

Capsules

Sialidase

Superantigens and Lipoproteins

Other Virulence Factors

Contd…Adhesins

Adherence of organism to host tissue is a major pre-requisite for pathogenicity.

Non pathogenic mycoplasma adhere to mucosa or epithelium of host???

Primary interactions between the host and mycoplasma cells occur through cell surface adhesins produced by the mycoplasma.

The adhesins have been characterized in only a limited number of mycoplasmas.

It is clear that different molecules and structures may be involved in adhesion in different species.

Identification of the adhesin proteins of mycoplasmas-

Inhibition of cytadhesion with specific antibodies Selection of spontaneous or transposon - induced mutants deficient or reduced

in their capacity to attach to cells.

Contd..Attachment Organelle of Mycoplasma pneumoniae

Possesses a specialized tip or terminal organelle that functions in adherence and motility.

Several components are required for the correct assembly and function of the major adhesins P1 and P30, with at least eight accessory proteins involved in the assembly (Krause and Balish 2004 ).

The P1 protein clusters at the tip organelle enabling attachment between the tracheal cilia

Adherence of Mycoplasma pneumoniae to host cells. A: scanning electron microscopy of filamentous M. pneumoniae grown in broth medium. (Micrograph courtesy of S. Razin, The Hebrew University-Hadassah Medical School.)B: transmission electron microscopy of flask-shaped M. pneumoniae (M) attached by the terminal tip organelle (arrow) to ciliated mucosal cells. (Micrograph courtesy of A. M. Collier, The University of North Carolina School of Medicine.) Magnification: A, ×10,000; B, ×36,000

Schematic diagram of the location of the major cytadherence and accessory proteins in M. pneumoniae. [Modified from Balish and Krause (4).].

Rottem S Physiol Rev 2003;83:417-432

©2003 by American Physiological Society

Contd..Attachment Organelle Mycoplasma gallisepticum Also possesses a tip structure or bleb.

The P1 homolog (GapA) and several accessory proteins (Goh et al. 1998 ; Papazisi et al. 2003 ).

The cytadhesin VlhA, previously referred to as pMGA (Markham et al. 1992 ).

The pvpA gene of M. gallisepticum encodes an additional putative cytadhesin (Yogev et al. 1994 ; Boguslavsky et al. 2000 ).

VlhA is also found in the phylogenetically unrelated poultry pathogen Mycoplasma synoviae (Noormohammadi et al. 1997 ), and its presence in M. gallisepticum and M. imitans is probably the result of past horizontal gene transfer.

Contd..Ciliary Adhesin of Mycoplasma hyopneumoniae The causative agent of porcine enzootic pneumonia

Possesses the cell surface ciliary adhesin P97.

The adhesin was identified through monoclonal antibody inhibition assays (Zhang et al. 1995 ),

Subsequent analysis revealed two amino acid repeat sequences, R1 and R2, in the predicted sequence of the protein (Hsu et al. 1997 ).

The R1 amino acid repeat promotes adhesion to porcine tracheal cilia (Minion et al. 2000 ).

Although the P97 paralog Mhp493, which lacks the R1 repeat, binds to tracheal cilia and heparin in a dose-dependent manner (Wilton et al. 2009 ).

Both P97 and Mhp493 are subject to posttranslational proteolytic cleavage.

P159, which has also been implicated in binding to porcine cells and to heparin (Burnett et al. 2006 ).

Contd..Adhesins of Other Species of Mycoplasma• Mycoplasma bovis an emerging pathogen in Europe, pneumonia, mastitis and arthritis . • Mycoplasma agalactiae the cause of contagious agalactia in sheep and goats, possesses a 40 - kDa lipoprotein (P40) that mediates attachment to lamb synovial

cells (Fleury et al. 2002 ).

• Both M. bovis and M. agalactiae possess a family of antigenically and phase variable cell surface lipoproteins, the Vsps and Vpmas, respectively

• The 150 - kDa protein LppS has been identified as being involved in adherence to lamb synovial cells by Mycoplasma conjunctivae , a primary cause of infectious keratoconjunctivitis in domestic sheep and goats and wild Caprinae

Receptors

Receptors for M. pneumoniae

• Host cell surface sialo-glycoconjugates

• Carbohydrate moiety of the glycoprotein

• Sialic acid-free glycoprotein

• Sulfated glycolipids

Schematic diagram of the fusion of a mycoplasma with a eukaryotic cell.

Rottem S Physiol Rev 2003;83:417-432

©2003 by American Physiological Society

Contd..Biofilm Formation The pathogenic mycoplasmas M. bovis , M. agalactiae, Mycoplasma pulmonis ,

and M. mycoides subsp. mycoides small colony type are all capable of forming biofilms in vitro , increasing their resistance to desiccation, heat, and complement mediated lysis (McAuliffe et al. 2006, 2008 ; Simmons and Dybvig 2007 ).

The formation of biofilms is a two – step process, with initial binding of the organisms to a suitable substrate followed by further accumulation of organisms on these. The length of the tandem repeat region in Vsas of M. pulmonis is associated with biofilm formation (Simmons et al. 2007 ), and the Vsps of M. bovis may play a similar role.

Contd..Capsules The capsule of M. mycoides subsp. mycoides small colony type is composed of

galactan. (Buttery et al. 1976 ).

It has a dramatic toxic effect in calves that are injected intravenously (Buttery et al. 1976 ).

Their presence might be expected to aid –

The formation of biofilms

Impede host defenses,

Improve persistence in the environment

Contd..Sialidase The role sialidase and hyaluronidase play in the pathogenicity of

Mycoplasma alligatoris has been investigated in alligator pulmonary fi broblast cultures (Hunt and Brown 2007 ).

Inhibition of sialidase with 2,3 - didehydro - 2 - deoxy - N – acetylneuraminic acid in infected cultures reduced apoptosis in a dose - dependent manner.

As sialidase alone could not induce apoptosis, it has been hypothesized that sialidase acts in concert with hyaluronidase to cause apoptosis, although the presence of a virulence cofactor other than hyaluronidase cannot be ruled out.

There are sialidase genes in M. synoviae (Vasconcelos et al. 2005 ) and M. gallisepticum (Papazisi et al. 2003)

Superantigen

Contd..Superantigens and Lipoproteins The arthritogenic pathogen of mice and rats, M. arthritidis , produces a

superantigen known as MAM ( M. arthritidis mitogen).

Together with MAM of M. arthritidis , mycoplasma lipoproteins have been identified as nonspecific mediators of immune responses through activation of Toll - like receptor (TLR) - 2 (Hasebe et al. 2007 ).

The diacylated forms of lipoproteins appear to be potent stimulators of this response and these forms are major components of mycoplasma cell membranes

Other Virulence Factors The p65 antigen of M. hyopneumoniae is a cell surface lipoprotein with lipolytic

enzymatic activity with a preference for long - chain fatty acids

In addition to its probable role in catabolism to supply nutrients, it may play a role in disease by damaging lung surfactant (Schmidt et al. 2004 )

Thank you