[Microbiological diagnosis of urinary tract infections].

Definitive diagnosis of urinary tract infection (UTI) is performed through quantitative urine culture. Traditionally the presence of 100,000 or more bacteria/ml in urine has been considered to represent significant bacteriuria, indicating UTI. However, this criterion is only applicable to certain population groups and cannot currently be considered an absolute criterion. The "real" presence of any number of bacteria in urine can represent a UTI when there are specific symptoms and pyuria. In the last few years various automatic systems have been introduced onto the market which, by adapting classical diagnostic techniques, allow the presence of a UTI to be rapidly ruled out, although their clinical utility is controversial. In addition, the new chromogenic culture media allow direct identification of uropathogens and, in particular, are of enormous help in the detection of polymicrobial cultures. Likewise, automatic systems can provide results on identification and sensitivity to be obtained in a single day. However, because new phenotypes of resistance are continually appearing, the antibiogram model used with classical uropathogens has had to be modified, requiring special techniques for pathogen detection and characterization. Correct interpretation of the antibiogram in these cases is essential to detect these phenotypes and achieve therapeutic success.