Background Mycoplasma pneumoniae is a common pathogen that caused community-acquired pneumonia (CAP).P1 protein served as major adhesion and immunodominant protein in Mycoplasma pneumoniae,but little about P1 gene was leed and the relationship between P1 genotype and macrolide resistance has yet to be explored.Methods The DNA sequence of the entire P1 gene from 35 strains isolated from clinical specimens collected in Beijing,China,in 2010 was determined.The resulting sequences were checked for known macrolide resistance mutations,such as A2063G,A2064G,C2617G in domain V of 23S rRNA.Antibiotic susceptibility test was done to further identify macrolide resistant strains.Results Thirty-four clinical strains were type 1,and were identical to type 1 reference strain MP129.Only one clinical strain,MpYYM22,was type 2,and proved to be variant 2c.One synonymous point mutation in the P1 type 1 gene from two isolates was identified relative to the MP129 P1 sequence at nucleotide position (nt) 552 (C＞A),while another two isolates had missense mutations at nt 2504 (G＞A).This point mutation caused an amino acid change from glycine to glutamic acid.An AGT tri-nucleotide variable-number tandem repeat (VNTR),coding for serine and repeating 6-11 times,up to 15-16 times,was found in the region between the RepMP4 and RepMP2/3 elements in the 35 isolates examined.All 35 clinical strains,including MpYYM22,demonstrated macrolide resistance with the range of minimum inhibitory concentration (MIC) of erythromycin from 64 to 256 μg/ml,having an A2063G transition in domain V of the 23S rRNA gene.Conclusions P1 type 1 was the dominant type of Mycoplasma pneumoniae in Beijing in 2010,although variant 2c strains were present.More samples are needed to determine whether there is a relationship between the P1 genotype and macrolide resistance,as the 35 strains examined did not allow a conclusive result.However,the AGT tri-nucleotide VNTR may be a more informative locus for multi-locus VNTR analysis.