Analysis identifying common and distinct sequences among Texas clinical strains of Mycoplasma genitalium

Abstract

Mycoplasma genitalium is a human bacterial pathogen linked to urethritis and other sexually transmitted diseases. Here, we assessed the incidence of M. genitalium infection in patients attending a sexually transmitted disease clinic in San Antonio, TX, by use of diagnostic real-time PCR. Overall, 16.8% of women and 15.1% of men were found M. genitalium positive. Regions of the mgpB gene, which encodes the MgPa adhesin, were amplified from positive clinical specimens and evaluated for sequence variability, which demonstrated transmission of the pathogen between sexual partners. Follow-up analysis of a subset of patient specimens revealed reinfection by a different strain of M. genitalium, indicating the absence of protective immunity. Eighteen DNA sequence variants were obtained and compared with all other available clinical sequences. Detailed analysis revealed silent mutations of six amino acid residues within the encoded region of the MgPa adhesin in numerous clinical strains. In addition, missense mutations of limited numbers of amino acids were observed. Alignment of putative amino acid sequences revealed the simultaneous occurrence of several mutations and the existence of identical or similar protein variants in strains from different locations.

FIG. 1.

Predicted phylogenetic tree. Reference strain G37 and 73 distinct clinical sequences obtained in this study or previously (14, 17, 21) were aligned by CLUSTALW. The sequence of the corresponding region of the M. pneumoniae adhesin P1 gene (MPN141) was included as an outlier.

FIG. 2.

Comparison of MgPa-13 nucleotide and deduced amino acid sequences. The region of F⁷⁵ (extreme left) to N¹³⁶ (extreme right) of the MgPa protein in reference strain G37 is presented. Percentages of mutated codons (striped bars) and of detected missense mutations (black bars) are shown. Percentages represent the fraction of the 73 aligned clinical sequences that contained a codon/amino acid different from that of the G37 sequence. Recurrent silent mutations of six amino acid residues are indicated (asterisks).

FIG. 3.

Alignment of deduced amino acid sequence from F⁷⁵ to N¹³⁶ of reference strain G37-MgPa with sequences of clinical strains. Amino acids identical to those of G37 are presented as dots (•); missense mutations are highlighted with gray (hydrophobic amino acid) or black (hydrophilic amino acid). Amino acid deletions compared with those of G37-MgPa are indicated (−). Positions of the majority of silent mutations are indicated (asterisks). Sequences were grouped to demonstrate existence of observed protein variants. Seventy-three distinct clinical sequence variants were obtained previously (14, 17, 21) and in this study.