[Bacteriological analysis of semen samples from sperm donors]

To explore the distribution and characteristics of semen bacteria in sperm donors.

For lack of the reference value for semen bacterial culture and colony count, we referred to the existing criteria for the diagnosis of male urinary tract infection (urine bacterial colonies >105 cfu/ml for infection, <104 cfu/ml for possible bacterial contamination, and 104－105 cfu/ml for suspected infection) and set the threshold value for unqualified semen culture at bacterial colonies ≥104cfu/ml. We performed bacterial culture of the semen samples from 3 160 sperm donors in the Chongqing Human Sperm Bank from April 2015 to November 2019, counted the bacterial colonies using the British Synbiosis automatic colony counter, and identified the bacterial species in the samples with bacterial colonies ≥104cfu/ml with the automatic microbial identification instrument.

Of the 3 160 semen samples, 456 (14.43%) were found without bacterial growth, and the other 2 704 (85.57%) with bacterial growth, which included 143 (4.53%) with miscellaneous bacteria contamination and 2 561 (81.04%) positive for bacterial culture but not contaminated, the latter including 2 305 (72.94%) with bacterial colonies <104cfu/ml and 256 (8.10%) with bacterial colonies ≥104cfu/ml. Bacterial identification showed that 87.89% of the bacteria were Gram-positive (G+) and 12.11% Gram-negative (G－), mainly including Staphylococcus epidermidis (26.95%), Hemolytic staphylococcus (16.40%), Corynebacterium (13.28%), Enterococcus faecalis (6.64%) and Staphylococcus aureus (5.86%).

Semen samples from sperm donors have a high rate of bacteria-carriers, and the bacteria vary widely in strain, with G+ bacteria as the main type.