Differences in biofilm development and antibiotic susceptibility among clinical Ureaplasma urealyticum and Ureaplasma parvum isolates

Objectives: The aim of this work was to study the ability of clinical isolates of Ureaplasma spp. to form biofilms in vitro and to compare the antibiotic susceptibility of sessile cells and their planktonic counterparts. Methods: A total of nine Ureaplasma spp. isolates recovered from unrelated male patients diagnosed with urethritis or chronic prostatitis and two isolates isolated from the urine of two healthy volunteers were included. Ureaplasma species identification was performed by 16S rDNA gene amplification and sequencing. Conventional antibiotic susceptibility tests were carried out by the broth microdilution method. Biofilm susceptibility assays were performed following the method proposed by Moskowitz using 10C urea broth medium and confirming bacterial growth by colour shift of the medium. The x 2 test was applied to analyse the statistical differences between the MIC and the minimal biofilm inhibitory concentration. Results: Isolates were identified as Ureaplasma urealyticum serovar 7 (five isolates), U. urealyticum serovar 13 (four isolates) and Ureaplasma parvum serovar 3 (two isolates). Biofilm formation was observed in 9 out of the 11 strains studied (82%); two isolates of U. urealyticum serovar 13 were non-biofilm formers. Global resistance percentages of planktonic cells compared with sessile cells were different for erythromycin (0% versus 44%, P = 0.02), telithromycin (22% versus 77%, P 5 0.02), ciprofloxacin (66% versus 100%), levofloxacin (0% versus 33%) and tetracycline (0% versus 33%). All nine biofilm-forming strains were fully susceptible to clarithromycin in both planktonic and biofilm types of growth. Conclusions: These results indicate that biofilm formation can protect mycoplasma cells from antibiotics and host defences, favouring their persistence in chronically infected or colonized patients while increasing resistance to antimicrobial agents. Therefore, the capacity to form biofilms by Ureaplasma spp. isolates should be considered when antibiotic treatments are required.