Expanded Quantitative Urine Culture (EQUC)

Increasingly used in research studies investigating the urinary microbiome and how it influences recurrent and chronic UTI, Expanded Quantitative Urine Culture (EQUC) is a new technology using a used a modified culture protocol from that of the standard urine analysis laboratory method.  This includes analysing larger volumes of urine (10–100 mL instead of 1 mL for a standard mid stream urine culture), the incubation of samples using differing atmospheric conditions to cultivate bacteria that may not grow on standard urine culture and longer times for incubation where the urine sample is incubated in a special liquid broth.  If no growth is seen after 3 days, the incubation is extended for another 3 days. For slower growing bacteria or those where different methods of development other than standard agar plate are needed, EQUC is a useful tool.

A study by Loyola University Chicago, published in the American Journal of Microbiology in 2014 comparing the standard urine culture against EQUC noted that the EQUC analysis method found bacteria in 92% of samples tested compared against the same samples analysed via standard methods which showed negative growth for bacteria. With this, bacterial presence as low as 10 colony forming units (CFU) per mL could be detected; indeed, Lactobacillus, Corynebacterium, and multiple other genera were isolated using this EQUC. The authors proposed a “streamlined” version of this EQUC, which specified using a higher volume of 100 mL of urine on MacConkey, blood, and colisitin-nalidixic acid (CNA) agars in a 5% CO2 incubator for 48 h to yield 84% sensitivity relative to the extended spectrum protocol. This protocol has been utilized by several investigators since.

A further study of 150 women published in the Journal of Clinical Microbiology in 2016, patients were grouped by whether or not they had self-reported UTI-like symptoms and performed the aforementioned streamlined EQUC on catheterized urine specimens; while they did not find a difference in the number of isolated uropathogens, they did find a reduced species richness and diversity in patients who did have clinical UTI symptoms. About half of the uropathogens in the UTI cohort were missed by standard urine culture; additionally, the threshold of 105 CFU/mL would not report a predominant organism in numerous patients with a clinical UTI in this cohort.

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