**3. The types of urinary tract infections**

There are different types of UTIs including acute and/or chronic, asymptomatic and/or symptomatic (mild/moderate and/or severe), complicated and/or uncomplicated, and community and/or nosocomial acquired infections. If the UTIs occur ≥ three times in a year or ≥ two times continuously after disappearance (treatment) of the first infection in a half year, they are recognized as recurrent UTIs (rUTIs). In addition to this diversity, as the human's urinary tract (UT) is divided into two parts of lower and upper sections, the UTIs may occur in the lower part of the UT (known as cystitis) and/or upper part of the UT (known as nephritis). These characteristics are in association with microbial pathogenomics, duration of infection, and the abilities of human host. The threshold of microbial population for UTIs is reported as ≥100,000 living cells or colony-forming unit (CFU) per urine milliliter (ml); however, it varies from 100 to 1000 to 100,000 CFU/ml. Of course, the UTIs without syndromes and with syndromes are recognized as asymptomatic and symptomatic UTIs, respectively [1, 2, 4, 7–10, 12, 19–22].
