An etiological diagnosis of bacterial urinary tract infection by quantitative cultivation of the Urine with identification and susceptibility test of the isolated bacteria
Types of specimen
Urine (Midstream urine), suprapubic aspiration, catheterized urine.
Criteria of specimen rejection
Un-refrigerated specimen older than 2 hours may be subject to overgrowth and may not yield valid results; unlabeled specimen; mislabeled specimen; specimen in expired transport container; 24 hours urine specimens.
Common pathogens
Neisseria gonorrhoeae E. coli and other Enterobacteriaceae
Enterococcus spp Staphylococcus aureus
Staph saprophyticus Corynebacterium jeikeium
Acinetobacter spp Pseudomonas spp
Gardnerella vaginalis β-haemolytic streptococci
Salmonella spp (early stage of infection)
Commensal flora
Diphtheroid bacilli Lactobacillus sp
Coagulase negative Staphylococci α Haemolytic Streptococci
Bacillus spp Non-pathogenic Neisseria spp.
Anaerobic cocci Commensal Mycobacterium
Commensal Mycoplasma spp.
Parasites
Schistosoma haemetobium Trichomonas vaginalis
First morning specimens yield highest bacterial counts from overnight incubation in the bladder, and are the best specimens. Colony count interpretation standards are based on controlled studies from first early morning collections. Forced fluids or random specimens dilute the urine and may cause reduced colony counts. Hair from perineum will contaminate the specimen. The stream from a male may be contaminated by bacteria from beneath the prepuce. Bacteria from vaginal secretions, vulva or distal urethra may contaminate transport. Organisms from hands or clothing might contaminate. Receptacle must be sterile.
Time relapse before processing the sample
The maximum time allowed for processing a urine sample is 2 hours from the time of collection
Storage
At room temperature unless delay is inevitable; it must be refrigerated
Specimen processing
Media
1. Blood Agar,
2. MacConkey Agar
3. Nutrient Agar
Culturing procedure
Mix the urine sample to re-suspend microorganism present. Dip a 1 μl calibrated loop in vertical position in the urine and remove the loop and use the collected fluid to inoculate a Nutrient Agar Plate that will be used for urine plate count.
Take another loop to streak Blood agar and another loop to streak MacConkey agar plates. Streak the Nutrient agar plate to cover all surface area.
A plate count of 10,000 CFU/ml of pure culture should be considered positive and isolated organism should be identified and sensitivity test will be performed.
Post specimen processing
Interfering factors:
Patient on antibiotic therapy.
Improper sample collection.
Result reporting:
Report wet mount as an initial report.
Report the isolated pathogen and its sensitivity pattern as a final report.
Turn around time:
Wet mount results should be available 1 hour after specimen receipt. Isolation of a possible pathogen can be expected after 2-3 days. Negative culture will be reported out 1-2 days after the receipt of the specimen.
