Bacterial prostatitis often results from gram-negative Enterobacteriaceae (Escherichia coli, Proteus mirabilis, Klebsiella species, Enterobacter species, Pseudomonas aeruginosa, and Serratia marcescens). Anaerobic bacteria and gram-positive bacteria other than enterococci rarely cause acute bacterial prostatitis. Staphylococcus aureus infection can occur due to prolonged catheterization in hospital settings. Other organisms include Neisseria gonorrhoeae, Mycobacterium tuberculosis, Salmonella species, Clostridium species, and parasitic or mycotic organisms. Infection spreads from infected urine by reflux into the prostate gland, by the hematogenous route, from ascending urethral infection, or by invasion of rectal bacteria via the lymphatic vessels. Infection may also result from urethral procedures performed with instruments, such as cystoscopy and catheterization, or sexual intercourse. Chronic prostatitis usually results from bacterial invasion from the urethra, whereas granulomatous prostatitis occurs secondary to spread of M. tuberculosis. Nonbacterial prostatitis produces symptoms of prostatitis without bacterial infection.

UTI is the most common complication of prostatitis. An untreated infection can progress to prostatic abscess, acute urine retention from prostatic edema, pyelonephritis, and epididymitis.

The patient with acute prostatitis may report sudden fever, chills, low back pain, myalgia, perineal fullness, perineal pain, arthralgia, frequent urination, urinary urgency, dysuria, nocturia, and transient erectile dysfunction. Some degree of urinary obstruction can occur, and the urine may appear cloudy. On palpation, the bladder may feel distended, swollen, firm, warm, and tender. Patients with chronic bacterial prostatitis may be asymptomatic or have milder symptoms of the acute version. Other symptoms include hemospermia, persistent urethral discharge, and painful ejaculation. The prostate may feel soft, and crepitation may be evident if prostatic calculi are present. Digital examination in granulomatous prostatitis may reveal a stony, hard induration of the prostate, and there is often a history of pulmonary or GI tuberculosis or receiving intravesical therapy for superficial bladder cancer. With nonbacterial prostatitis, the patient usually complains of dysuria, mild perineal or low back pain, and frequent nocturia.