Introduction of urine culture and sensitivity
A urine culture test is useful to grow and identify organisms, mainly bacteria, and fungi that may cause a Urinary Tract Infection (UTI). Bladder urine is normally sterile and free from any organisms. UTIs are common in females and children than in adult males. The antibiotic sensitivity test (AST) helps to select an appropriate antibiotic that is effective against specific types of bacteria or fungi causing any infection.
When need Urine Culture and sensitivity Test?
Following conditions that are useful for culture and sensitivity are-
- when you’ve experienced pain during urinating, less urine, and also frequent urine symptoms.
- When this is prolonged for some time ( 3-4 days) and if the symptoms do not subside, the doctor would then suggest a Urine Culture and Sensitivity test to determine if there is an infection and to what extent.
- In many cases, if the urine infection levels have increased, the person may also experience high fever and sudden chills in the body. This may go up to 5-6 days as well, if not detected and cured on time.
- Urine culture and sensitivity are used to diagnose, and screen for diseases or medical conditions related to urinary tract infection for persons experiencing symptoms such as frequent and painful urination.
General symptoms of UTIs
- Painful or difficult urination with a burning sensation
- Increased urination frequency
- Urine that smells bad or appears cloudy or reddish
- Pain and pressure in the lower abdomen (belly) and back
- Feeling Chills
- Unexpected fever
- Malaise
- Tiredness
Why does the urine culture report take 3 days?
No all reports take 3 days. Only positive i.e. growth of organism takes 3 days due to following reasons-
- On the first day inoculation of urine on culture media and then incubated for 24 hours.
- If the growth of organisms, on the second day perform biochemical tests as well as AST.
- On 3 days, report for isolation of bacteria/organism and AST pattern.
Urine collection for culture
Collect Mid-Stream Urine (MSU). Clean the genitals before collection, following these steps to get the sample:
- Initial or the first few drops of the urine should be discarded in the toilet.
- MSU samples should be collected in the sterile container provided.
- The end of the urine should not be collected. Cap the container.
- If delay in test processing, keep it in the refrigerator or a cool place during the collection period.
Test procedure of Urine culture and sensitivity
On the first day
Culture urine Specimens
Blood agar
Incubate aerobically
MacConkey agar
Incubate aerobically
Or alternate of these two, you can use CLED agar
Day 2 and Onwards
Examine and Report Cultures of Urine Specimens
Blood agar and MacConkey agar cultures
Look particularly for:
- E. coli
- Proteus species
- Klebsiella species
- Enterococcus species
- S. saprophyticus (10-30% of young women)
- Pseudomonas
- Providentia
- Citrobacter
- Serratia
Biochemical tests
Depending on the nature of organisms
Antimicrobial susceptibility test
Antimicrobial sensitivity pattern also depends on the nature of organism involvement
On 3rd day
Organism isolated
Antimicrobial sensitivity pattern
Sensitive (S)
Resistant (R)
Intermediate (I)
Result and interpretation
No growth after 24 hours of incubation at 37°C.
or > 105 CFU/ml of organism (E. coli) isolated
AST pattern
Antibiotic – Sensitive
Antibiotic- Intermediate
Antibiotic-Resistant
Reference Range
>100,000 colonies/ml : Positive
10,000-100,000 colonies/ml: Indeterminate
<10,000 colonies/ml: Negative
Positive means that there is a certain amount of bacteria or organisms that have been found in the Urine Sample and that the infection is certainly because of these bacteria. The Culture report not only detects the various types of germs present but also shows its sensitivity to various Antibiotics. This means you can gauge from this report itself that which antibiotics would provide maximum benefit.
Possible pathogens of urine
Bacteria
Gram-positive
- Staphylococcus saprophyticus
- Enterococcus species
Gram-negative
- Escherichia coli
- Proteus species
- Klebsiella species
- Pseudonomas aeruginosa
- Providentia
Citrobacter
Serratia - Fungi
Candida albicans
Parasites - Trichomonas vaginalis (trophozoite)
- Enterobius vermicularis (Ova)
- Schistosoma hematobium (ovum)
Commensals
Any commensal organisms found in urine are usually those that have contaminated the specimen from the urethra and they are-
Micrococci
Diphtheroids
Candida species
Mycoplasma species
Mycobacterium smegmatis
Acinetobacter species
Bibliography
- Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
- Clinical Microbiology Procedure Handbook Vol. I & II, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
- Colour Atlas and Textbook of Diagnostic Microbiology. Editors: Koneman E.W., Allen D.D., Dowell V.R. Jr, and Sommers H.M.
- Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.
- Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmons, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Francisco 1996.
- Manual of Clinical Microbiology. Editors: P.R. Murray, E. J. Baron, M. A. Pfaller, F. C. Tenover and R. H. Yolken, 7th ed 2005, Publisher ASM, USA
- Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
- Topley & Wilsons Principle of Bacteriology, Virology and immunology Vol I, II, III, IV & V. Editors: M.T. Parker & L.H. Collier, 8th ed 1990, Publisher Edward Arnold publication, London.
- Medical Microbiology-The Practice of Medical Microbiology Vol-2-12th Edn. –Robert Cruickshank
- District Laboratory Practice in Tropical Countries – Part-2- Monica Cheesebrough- 2nd Edn Update
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2082698/
- https://www.scielo.br/scielo.php?script=sci_arttext&pid=S1413-86702008000400020
- https://academic.oup.com/jtm/article/14/5/334/1808850