It took nearly 2,500 years to get past the cutting edge practice of tasting urine to diagnose diseases. It has taken less than 150 years to advance from tasting urine, to clinical culture, and on to molecular diagnostics.
Hippocrates (460 – 377 BCE) is said to have been the first to diagnose diabetes.1 One of the criteria he used, along with polyuria, polydipsia, and polyphagia, was that the patient’s urine tasted sweet. The word “mellitus” in diabetes mellitus comes from Latin, meaning “flavored with honey.” Flavor wheels were used to allow doctors to diagnose a range of illnesses using the color and taste of urine (you can see an example of one here 2). Rather than taste urine, ants attracted to sugar in urine were used to diagnose diabetes in ancient India.3
“Robert Koch grew bacteria in culture in the 1880s, a virus was first cultured in 1913.„
Development of new technologies led to better tools for urinalysis and diagnosis of disease. Tasting urine to diagnose diabetes began to fall out of favor at about the same time that culture began to be used as a tool for clinical diagnosis, although there was some overlap. Insulin was discovered in 1910 by Sir Edward Albert Sharpey-Schafer. Robert Koch grew bacteria in culture in the 1880s, and a virus was first cultured in 1913.4,5 And notably, pathologists trained in the late 1940s were about diagnosis of diabetes by tasting urine.
“Culture methods continue to be regarded as gold standards for diagnosis of many bacterial and viral infections, even though more sensitive and specific technologies are available.„
Culture methods continue to be regarded as gold standards for diagnosis of many bacterial and viral infections, even though more sensitive and specific technologies are available. This is highlighted by the recent discovery that urine is not sterile. That is, urine samples were previously regarded as sterile if uropathogens failed to grow using standard culture procedures. Thus, the presence of pathogens in a urine sample was interpreted as an infection.6 This began to fall apart with solid evidence of the presence of bacteria in urine samples from both symptomatic and asymptomatic patients who were culture negative.7,8 These findings are now supported by a number of other studies reporting the presence of bacteria in cases where standard culture methods failed to grow bacteria.9–15
“A large number of studies have found that PCR is more sensitive, more specific, and has a more rapid turnaround time than culture methods„
Many of these studies used sequencing of 16S rRNA to identify bacteria in urine, but less expensive and more rapid methods are readily available. A large number of studies have found that PCR is more sensitive, more specific, and has a more rapid turnaround time than culture methods, especially for difficult uropathogens and hemorrhagic cystitis.16–28
PCR can also be used to test for antimicrobial resistance. Does this suggest that there is no place in a clinical laboratory for culture methods? Of course not. A previous study compared molecular methods with culture for prediction of antibiotic resistance in UTI. This study showed that PCR and culture agreed in 77.6% of cases: both positive in 35.2% and both negative in 42.4%. Culture displayed antibiotic resistance in 14.4% of cases in which PCR was negative for resistance genes. This may occur in cases of mutualism, in which one organism confers resistance on another organism that may not carry resistance genes. Conversely, culture was negative for antibiotic resistance in 8.0% of cases where PCR identified the presence of a resistance gene. This can happen in instances of low gene copy number, where the gene may not be expressed, or when the gene product is not fully functional.27
“Thus, while negative culture results should be viewed with caution, a true phenotype identified by culture can be informative with respect to antibiotic resistance.„
It took nearly 2,500 years to get past tasting urine to diagnose diseases. It has taken less than 150 years to advance from tasting urine, to clinical culture, and on to molecular diagnostics.
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