Acute inflammatory cells are seen within the tubular epithelium of the epididymis and in the stroma. The tubular architecture may be damaged or destroyed by the inflammatory process. In later stages, regenerative changes and squamous metaplasia may be seen. Acute epididymitis is usually caused by bacteria - coliforms in children, Neisseria gonorrheae and Chlamydia trachomatis in young men, and E. coli and Pseudomonas in older men. Other causative agents include Klebsiella, Staphylococcus, Streptococcus pneumoniae, Neisseria meningitidis, Aerobacter, and Hemophilus influenzae.