Mycoplasmas are the smallest and simplest self-replicating bacteria .These microorganisms lack a rigid cell wall and are bound by a single membrane, the plasma membrane. The lack of a cell wall is used to distinguish these microorganisms from ordinary bacteria and to include them in a separate class named Mollicutes. Most human and animal mollicutes are Mycoplasma and Ureaplasma species of the family Mycoplasmataceae. Because mycoplasmas have an extremely small genome, these organisms have limited metabolic options for replication and survival. The smallest genome of a self-replicating organism known at present is the genome of Mycoplasma genitalium (0.58 Mb). Owing to their limited biosynthetic capabilities, most mycoplasmas are parasites exhibiting strict host and tissue specificities. The mycoplasmas enter an appropriate host in which they multiply and survive for long periods of time. These microorganisms have evolved molecular mechanisms needed to deal with the host immune response and the transfer and colonization in a new host. These mechanisms include mimicry of host antigens, survival within phagocytic and nonphagocytic cells, and generation of phenotypic plasticity. The major question is whether mycoplasmas cause damage to the host cells and to what extent the damage is clinically apparent. Mycoplasmas have long resisted detailed analyses because of complex nutritional requirements, poor growth yields, and a paucity of useful genetic tools. Although questions still far outnumber answers, significant progress has been made in identifying the mechanisms by which mycoplasmas interact and damage eukaryotic host cells. Many animal mycoplasmas depend on adhesion to host tissues for colonization and infection. In these mycoplasmas adherence is the major virulence factor, and adherence-deficient mutants are avirulent. 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, and while there are homologs of the characterized adhesins in some other mycoplasmas, it is clear that different molecules and structures may be involved in adhesion in different species.

1. Assignment
On
Mycoplasma: Host-cell interaction

2. 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.

3. PATHOGEN ENVIRONMENT
HOST
DISEASE
TRIAD
OTHER MICROBES
Microbial Interactions
ECOLOGICAL RELATIONSHIPS

4. Health and Disease

5. Equilibrium
Host - Bacteria
IR Virulence
Balance disturbed - Disease

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

8. Mycoplasmas of Humans
• Parasitic
1. 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.

9. 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

10. 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.

11. 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

13. 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

14. 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

15. 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.

17. 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 ).

18. 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

19. Receptors
Receptors for M. pneumoniae
• Host cell surface sialo-glycoconjugates
• Carbohydrate moiety of the glycoprotein
• Sialic acid-free glycoprotein
• Sulfated glycolipids

20. 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

22. 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.

23. 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

24. 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)

25. Superantigen

26. 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 )