الفهرس 
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Abstract
This investigation was conducted into four phases:
Phase I:
Clinical and field examination
Phase 1 included the study of the frequency and severity of bull semen infection. Also included the investigation of common bacteria isolated from bull semen.
Phase II:
It included the effect of bacteria present in bull semen on some semen parameters as motility and acrosome abnormalities.
Phase III:
It included the effect of bacteria present in bull semen on some immunological parameters in semen as nitric oxide (NO) and DNA integrity by COMET assay.
Phase IV:
It included the investigation of the effect of common bacteria isolated from bull semen on sperm ultra structure by Electron microscopy.
By examining 100 bulls by collecting 2 ejaculates from each one. Bacteriological examination showed that 73 bulls were normal bacteriologically free and 27 bulls infected with different types of bacteria.
from table 7 the results showed that the most common bacteria isolated from bull semen was S. aureus (35.3%) and then followed by E. coli (25.49) and followed by Coagulase negative staphylococci (13.73).
The results showed that, in single infection S. aureus was the predominant (14.82%) then followed by C.N.S and E. coli by the same percentage (11.11%).
In mixed infection, the results showed that S. aureus with E. coli mixture was the predominant (18.53%) and then followed by the mixture of S. aureus with E. coli with Micrococcus Spp with Strep. Faecalis (11.11%) then followed by S. aureus with C.N.S (7.41%) and S. aureus with E. coli with Strep. Faecalis (7.4%).
Also the results showed that the presence of some micro organisms as E. coli and Micrococcus Spp in samples increased after adding diluents. But after making dilution with diluent containing SP, E. coli disappeared from the samples and the percent of S. aureus greatly decreased.
after making dilution with diluent containing GTLS, E. coli and Micrococcus Spp are totally affected by antibiotics combination and did not appeared in bacterial culture. Also, S. aureus and Strep. Faecalis presence in GTLS combination appeared to be less affected than other micro organisms.
when making antibiotic sensitivity test the results showed that S. aureus was sensitive to streptomycin and lincomycin by (100%) also was resistant to Penicillin G by (75%). Also C.N.S was sensitive to Gentamycin by 100% and more resistance to Penicillin G by 60% . E. coli showed sensitivity to streptomycin and lincomycin and also Spectinomycin by (100%) and resistance to Penicillin G by (80%).
the results after 3 hours, there is no difference in motility at the different E. coli total bacterial count. E. coli TBC 10,000 give the highest percentage of acrosome abnormalities especially when increase time of exposure of sample to bacteria. It appear in 3rd hour the percent was 29.4%.
Also when Staphylococcus aureus TBC increased, the motility greatly decreased and this effect increase when the time of exposure increase. The results showed that Staphylococcus aureus TBC 1,000,000 give the high percent of acrosome abnormalities at the different times (21%, 32%, 42%).
The results showed that even adding small amount of Staphylococcus aureus alpha toxin ( 1µ and 2 µ) decrease the motility and with increasing the time of exposure the effect become more great. As the motility reach to 10% after 3 hours. Staphylococcus aureus toxin ( 1µ and 2 µ) made the high percent of acrosome abnormalities more the bacteria itself.
Nitric oxide level in semen samples in special amount increase sperm activity but when increase over the permissible limits it increase metabolic processes and lead to decrease in sperm motility and increase acrosomal abnormalities.
Also increasing TBC in semen samples lead to increase DNA denaturation and this measured by COMET assay.
Electron micrograph for sperm head from semen sample of infected group illustrating swollen, degenerated and vacuolated plasma membrane, segmentation of the outer acrosomal membrane and swollen acrosome (X 12000). In the tail region of sperm from semen of infected group showing severe degeneration of the outer membrane of sperm tail (× 4000). And in the neck region of sperm from semen of infected group showing severe degeneration (marked vacuolation) in the mitochondria that contained electron-translucent spaces with complete absence of the transverse cristae (× 12000).
In conclusion, the results obtained from this study indicate that:
1) Pathological bacterial isolates that contaminate semen samples may directly deteriorate the sperm quality and negatively affect sperm cells.
2) The genital tract infection may be an additional negative factor influencing male fertility and worsening reproductive potential.
3) Microbiological screening should be always performed when investigating male infertility.
4) Must investigate semen samples not only for bacteria but also for its toxic products {toxins}.
5) Should use a combination of antibiotics to get semen samples free from bacteria.
6) Metabolic products as