Objective To study the relationship between Escherichia coli (E.coli.) phylogenetic groups and the antimicrobial resistance in elderly patients with urinary tract infections.Methods 133 Escherichia coli were collected from elderly patients with urinary tract infections in 3 general hospitals in Tianjin.Kirby Bauer method was used to test susceptibility of E.coli.to four antibiotics.Escherichia coli DNA was extracted by boiling method.Phylogenetic groups (A,B1,B2 and D) of the E.coli was isolated by the two-step triplex-PCR.Results In all the strains,levofloxacin resistance rate was the highest (54.1％,72 strains),piperacillin/tazobactam resistance rate was the lowest (15.0％,20 strains) (Z=51.57,P＜0.01).The detection rates of Escherichia coli phylogenetic group A,B1,B2 and D were 24.8％ (33 strains),15.0％ (20 strains),18.0％ (24 strains),42.1％(56 strains) (Z=31.2,P＜0.01).Levofloxacin-sensitive strains were more common in Escherichia coli phylogenetic group B2 strains,and there was a significant difference in the strain number between the resistant and sensitive strains [29.5％ (18/61) vs.8.3％ (6/72),x2 =10.01,P＜0.01].Levofloxacin-resistant strains were more common in Escherichia coli phylogenetic group D strains,and there was a significant difference in the strain number between the resistant and sensitive strains [31.1％ (19/61) and 51.4 ％ (37/72),x2 =5.55,P＜0.05].There was no significant relationship between the Escherichia coli phylogenetic groups and the other three antibiotic resistance (all P＞0.05).Conclusions The detection rates of group D are the highest in the Escherichia coli phylogenetic groups,and it has a relationship with levofloxacin resistant.The antimicrobial resistance can be estimated by phylogenetic analysis in elderly patients with E.coli urinary tract infections.

0.05).Thirty genotypes were got from 54 strains by ERIC-PCR.CONCLUSIONS There isn′t significant difference on the absence rate of oprD2 gene in Tianjin and it gives us a hint that other factors can also result in the prevalence of IRPA.The existence of prevalence of IRPA clone in some departments advises us to effectively control the IRPA in hospital.