Pathogenic Bacteria Associated with Urinary Tract Infections in Men

Urinary tract infections are among the most common diseases in humans. Uncomplicated and complicated infections can occur in both male and female patients, but they are much less common in men. Although the signs and symptoms of UTIs in men are similar to those in women, they are most often due to anatomical abnormalities, prostatic hyperplasia, or insertion of a catheter. In addition to causing inflammation of the urethra, bladder, and kidneys, bacterial infections in men may also cause prostatitis. This review focuses on UTIs in males with the goals of determining whether there are unique features of the pathogenic bacteria that cause them and stimulating further research in this area. The normal urinary microbiome in males is different from that in females and contains several urotypes. Among the most common urinary tract pathogens are the Gram-negative bacteria Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Pseudomonas aeruginosa, along with the Gram-positive bacteria Enterococcus faecalis and Staphylococcus saprophyticus. These bacteria produce a large number of virulence factors, including adhesive pili, various surface proteins, metal ion acquisition systems, and flagella. The ability of many pathogens to form biofilms on host cells or urinary catheters may contribute to both uncomplicated and complicated UTIs. Uropathogenic E. coli (UPEC) is the most common and best-studied cause of both uncomplicated and complicated UTIs. While no specific strain of this bacterium appears to cause UTIs in men, combinations of virulence factors in certain clonal groups are found more often in male patients. Other less well-studied bacteria, including some corynebacteria, Francisella species, mycoplasmas, campylobacteria, and streptococci, may be more frequently associated with UTIs in men than in women and deserve further analysis. In addition to more microbiological studies, specific research on the cell biology and immunology of the male urinary system would be helpful in understanding the unique features of UTIs in men.