ObjectiveTo investigate bacterial infection and the distribution of different bacterial species in the donor semen and the influence of different bacterial counts on semen quality.

METHODSBacterial colonies in the semen samples from 1 126 donors were counted with the Synbiosis Protocol 3 Automatic Colony Counter and the bacterial species with a colony count ≥10⁴ cfu/ml identified with the VITEK2 Compact Automatic Biochemical Analyzer. The Makler Sperm Counting Board was used to examine the semen quality of the semen samples with a colony count = 0 cfu/ml (n = 22, group A), those with a colony count <10⁴ cfu/ml (n = 22, group B) and those with a colony count ≥10⁴ cfu/ml (n = 22, group C). Univariate analysis was employed for comparison of semen quality among different groups.

RESULTSAmong the 1 126 donor semen samples cultured, 5 (0.44%) showed mixed bacterial contamination and 993 (88.58%) showed none but with growth of a certain species of bacteria, 2.22% (22/993) with a colony count ≥10⁴ cfu/ml, mainly including Streptococcus bovis, tiny bacilli, Staphylococcus epidermis, and Staphylococcus aureus, among which gram-positive and gram-negative bacteria accounted for 95.45% (21/22) and 4.54% (1/22), respectively. Compared with group A, groups B and C manifested significantly reduced total sperm count (［567.5 ± 327.6］ vs ［421.9 ± 155.9］ and ［389.9 ± 110.6］ × 106 per ejaculate, P <0.05) and percentage of progressively motile sperm (［65.0 ± 6.5］ vs ［61.0 ± 3.5］ and ［61.6 ± 4.3］ %, P <0.05). There were no statistically significant differences among the three groups in the semen liquefaction time, semen pH value, total sperm motility or percentage of morphologically normal sperm (P > 0.05). Of the 284 randomly selected semen samples, 34 (11.97%) were found positive for Ureaplasma urealyticum (UU) and no significant difference was observed in the semen quality between the UU-positive and UU-negative samples (P> 0.05).

CONCLUSIONSThe bacteria-positive rate is high in the donor semen and the bacterial species are varied, mainly including gram-positive bacteria. Semen quality is reduced with the increased number of bacterial colonies.