Urine culture

Direct Gram Stained Smear
If a direct Gram stain is ordered, make a smear of one drop of unspun urine. Large numbers of squamous epithelial cells indicate a "dirty-catch". WBC's indicate inflammation and possible infection. Report types of cells seen and relative cell quantitation. Report morphological types, relative numbers of bacteria seen, and Gram reactions. If bacteria are seen, there are at least 10/5 org/ml in the urine.

Useful Urinalysis Results.
“Culture if Indicated” and “Dirty Catch” Criteria
Since Gram stained direct smears of urine are not done routinely, the standardized "microscopic “done as part of urinalysis in the Clinical lab, provides similar information. Look at WBC, epithelial cell and bacterial quantity estimations and also nitrate and leukocyte esterase results. If an order is written, “culture if indicated”, a urine qualifies for culture if there are >5WBCs/HPF and <7-10>10 epithelial cells/LPF is a "dirty" catch. Even if there are >5WBCs/HPF, recollection prior to culture is suggested..

Urines Held for Possible Culture
All urines which qualify for culture according to the above criteria have a comment entered as part of the urinalysis which reads "Held for possible culture". The Clinical lab follows up on urines held for possible culture.

Culture Inoculation
Media: SBA incubated : 35 C CO2 incubator
MAC 35 C ambient air

SBA and MAC are inoculated with 0.001ml of well-mixed urine.

Examination of Cultures
Colony Count. The number of colonies growing on the SBA plate are counted or estimated to one significant number. As the plates were inoculated with 0.01 ml of urine, multiply the count by 1000 to obtain the count per ml. of urine.
10 colonies = 104 organisms/ml or 10,000 organisms/ml
confluent growth = more than 105 org/ml or more than 100,000 org/ml

MAC and SBA Plate Exam : After the total number of organisms grown is determined, then a breakdown quantitation is made for the various organisms growing using the quantitation terms “rare”, “few”, “moderate” and “many”.
"rare" Fewer than 103 (1000) org./ml. No significant growth. Minimal vaginal, urethral or fecal contamination unless the urine was a cath spec.

"few" 103 to 104 org./ml. (1000 to 10,000) No significant growth Probable low number vaginal, urethral or fecal contamination, especially if multiple organisms grown.

"moderate" 104 to 5.0 x 104 (10,000 to 50,000) Possible infection, especially if a pure culture. Growth if 3 or more organisms indicates probable urine contamination.

"many" 5.0 x 104 to >105 more ( 50,000 to >100,000) probable infection unless multiple normal flora genital organisms such as Lactobacillus or Gardnerella are grown.

Use "No significent growth", to report mixed culture growth of 2 or more organisms for clean catch urines with <10,000>10,000 organisms/ml for a clean catch urine. Assume that organisms grown from a cath urine are significent unless the specimen was taken from an indwelling or Foley catheter. The final decision whether to identify all organisms and/or to do susceptibility testing is the physician or caregivers.

If more three or more organisms are isolated, and the organisms are a mixture of skin flora or normal genital/vaginal flora organisms, do preliminary ID of organisms by plate examination and Gram stain if necessary, record morphotypes on logcard and report as "Three or more organisms grown indicates contamination at time of collection" . If a mixture of organisms is grown which are likely urinary pathogens - mixture of GNR, enterococci, yeast, staphylococci - consult with the physician before setting up the MIC susceptibilities or completely identifying the isolates.

Susceptibility Tests
A pure culture of 100,00 organisms/ml of an organism is indicative of a urinary tract infection. Lactobacilli, "diphtheroids”, or Gardnerella vaginalis MAY be pathogens. See Antimicrobial Susceptibility manual section for method for each organism. See also “Antimicrobial Susceptibility Codes” in benchtop flip charts. Set up susceptibility tests as directed in the Antimicrobial Susceptibility section of this manual.

Culture Interpretation

The most frequent contaminants are:
Staphylococcus epidermidis and other coagulase-negative staphylococci
streptococci - alpha and non-hemolytic, Group D/ not Group D
Gardnerella vaginalis

The most common organisms causing infection include:
Escherichia coli Streptococcus agalactiae
Proteus mirabilis Staphylococcus aureus
Klebsiella pneumoniae Staphylococcus epidermidis
any enterobacteriaceae Staphylococcus saprophyticus
Pseudomonas aeruginosa Candida albicans
other Pseudomonas sp. Neisseria gonorrhoeae
Acinetobacter sp.

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