Role of the GapA and CrmA Cytadhesins of Mycoplasma gallisepticum in Promoting Virulence and Host Colonization

Abstract

bMycoplasma gallisepticum is an important avian pathogen that commonly induces chronic respiratory disease in chicken. To better understand the mycoplasma factors involved in host colonization, chickens were infected via aerosol with two hemadsorption-negative (HA ؊ ) mutants, mHAD3 and RCL2, that were derived from a low passage of the pathogenic strain R (R low ) and are both deficient in the two major cytadhesins GapA and CrmA. After 9 days of infection, chickens were monitored for air sac lesions and for the presence of mycoplasmas in various organs. The data showed that mHAD3, in which the crmA gene has been disrupted, did not promote efficient colonization or significant air sac lesions. In contrast, the spontaneous HA ؊ RCL2 mutant, which contains a point mutation in the gapA structural gene, successfully colonized the respiratory tract and displayed an attenuated virulence compared to that of R low . It has previously been shown in vitro that the point mutation of RCL2 spontaneously reverts with a high frequency, resulting in on-and-off switching of the HA phenotype. Detailed analyses further revealed that such an event is not responsible for the observed in vivo outcome, since 98.4% of the mycoplasma populations recovered from RCL2-infected chickens still display the mutation and the associated phenotype. Unlike R low , however, RCL2 was unable to colonize inner organs. These findings demonstrate the major role played by the GapA and CrmA proteins in M. gallisepticum host colonization and virulence.

Development of Molecular Methods for Rapid Differentiation of Mycoplasma gallisepticum Vaccine Strains from Field Isolates

“…Targeted mutations are located in genes whose significance in virulence has already been investigated. Cytadhesins, encoded by the gapA and crmA genes, play a major role in M. gallisepticum host colonization and virulence (32). The hlp2 gene, similar to hlp3, encodes a cytadherenceassociated protein (high-molecular-weight 2-like protein), while plpA encodes pneumoniae-like protein A, which is capable of binding fibronectin (35).…”

“…Candidate genes were selected according to previous publications (30)(31)(32)(33)(34)(35). The candidate genes were retrieved from the genomes of the M. gallisepticum ts-11, 6/85, and F vaccine strains (GenBank accession number NC_017503.1) and published M. gallisepticum genomes (strain S6, GenBank accession number NC_023030.2; strain R low , GenBank accession number AE015450.2; strain R high , GenBank accession number NC_017502.1; house finch isolates, GenBank accession numbers NC_018412.1, NC_018409.1, NC_018406.1, NC_018407.1, NC_018408.1, NC_018410.1, NC_018411.1, and NC_018413.1; and ts-11 reisolates, GenBank accession numbers MAFU00000000, MAFV00000000, MAFW00000000, MADW00000000, MATM00000000, MATN00000000, MAGQ00000000, and MAGR00000000) and aligned by Geneious (29) (Data Set S1).…”

Identification of Strain-Specific Sequences That Distinguish a Mycoplasma gallisepticum Vaccine Strain from Field Isolates

“…Despite these facts, compared to other pathogens, few virulence-related genes have been identified in M. gallisepticum . GapA (a primary cytadhesin) and CrmA (an accessory cytadhesin) mediate the attachment of this pathogen to the respiratory epithelium of the host (27). VlhA is a surface lipoprotein that undergoes phase variation; changing the bacterial surface architecture and allowing the mycoplasmas to escape immune surveillance (28, 29).…”

Multiple differences in pathogen-host cell interactions following a bacterial host shift

“…Interestingly, Hlp3 and PlpA are fibronectin-binding proteins that bind to the extra-cellular matrix and that have been identified as important determinants of virulence 18 . Similarly, the loss of GapA has been shown to be associated with a loss of cytoadherence 32,33 and recent evidence suggests that GapA may be required for the bacteria to reach, adhere to and persist in host tissue 34 .…”

“…Given that we have no knowledge of the progenitor poultry strain at the origin of the house finch clade of M. gallisepticum, we cannot use R_low (or R_high) as a representative ancestral strain. Rather, R_low and R_high were chosen as references in our experiments because they are well characterised, and many of their virulence related attributes, representing those that we wished to investigate in the house finch strain, have been comprehensively studied 18,22,[34][35][36][37][38][39] . We used the HF_1994 strain to characterise the virulence phenotype at the point of outbreak because it represents the earliest strain collected following first observation of disease in the house finch, and because its genome has been sequenced (GenBank accession number CP003506) 31 .…”