Effects of pH and incubation time on the susceptibility of Ureaplasma urealyuticum to erythromycin,azithromycin and josamycin in vitro

Objective To determine the effects of pH and incubation time on the susceptibility of Ureaplasma urealyticum(Uu)to erythromycin,azithromycin and josamycin in vitro.Methods With different pH at 6.0,6.5,7.0 and different incubation time for 24,36,48,60 hours,multiple-proportional broth microdilution method was applied to detect the MICs of 35 clinical specimens isolated from patients with nongonococcal urethritis.Results The MICs were found unchanged when incubation time was prolonged from 48 to 60 hours.But within 48 hours,as pH increased from 6.0 to 7.0,the MICs of pH 7.0 of erythromycin,azithromycin and josamycin decreased markedly by 1～16,2～32 and 2～32 times respectively(P0.005) and the MIC_(90) decreased by 4～8 and 2～4 times respectively(P0.005),compared to that of pH6.0.When the incubation time was prolonged from 24 to 48 hours,the MICs of 48 hours increased by 1～32,1～8 and 1～16 times,compared to that of 24 hours for erythromycin,azithromycin and josamycin respectively(P0.005).MIC_(90) increased by 4～8? 2～4 and 2～4 times respectively(P0.005).Conclusion The study suggests that the MICs of erythromycin,azithromycin and josamycin to Uu decreased markedly as the culture medium pH increased from 6.0 to 7.0 and increased significantly as the incubation time was prolonged from 24 hours to 48 hours.As compared with the MICs incubated for 48 hours,the MICs for more than 48 hours were the same.For detecting MIC,48 hours for culture is the endpoint.