One day incubation time for non-invasive urine cultures makes the lab operation and work flow more efficient. However, it has been a matter of debate since striking a balance between potential loss of slow-growing pathogenic organisms weighs heavily over shorter incubation time. Our study at Sutter Health Shared Laboratory (SHSL) evaluated the possibility of significant loss of uropathogens, if cultures incubated for only one day in CO2 and examined using a benchtop magnifier, and compared it with 2 days incubation.
Only routinely collected urine cultures has been included in this study and invasive collection such as nephrostomy, straight or diagnostic catheter collection were excluded. SHSL urine culture procedure defines the workup cut off for uropathognic organisms in a routine culture as 10,000 CFU/mL. Total of 2,709 urine specimens were processed using WASP automated plating system. 1µL sterile loops were used to inoculate BAP/MAC bi-plates. Plates were incubated in 5% CO2 at 35⁰C for at least 18 hours and maximum 24 hours for the first day evaluation. All no-growth plates were examined with a regular bench top magnifier/light for evidence of growth, and if verified, they were incubated for an extra day of incubation. Organism identifications performed by Vitek MS instrument.
Total of 501 out of 2,709 samples were determined No-Growth on the first day examination, and after 2nd day of incubation 435 stayed as No-Growth (86.8%), 66 samples (13.2%) indicate growth of normal Uro-Genital (UG) microbiota, and no uropathognic organisms detected. Among those with growth 54 (10.8%) samples grew <10K, 10 samples (2.0%) grew 10-50K, and 2 samples (0.4% [95% CI= 0.1% - 1.5%]) grew >50K CFU/mL of normal UG microbiota.
Although small percentage with low level urogenital microbiota was missed on the first day of incubation, there were no uropathogenic organisms missed. Therefore the one day incubation of routine urine culture plates in CO2, and careful examination of the plates appeared to have same efficiency of 2 days incubation in pathogen detection. One day incubation can result in workflow efficiency, significant saving in labor and incubation space for large volume laboratories, or labs with total-microbiology-automation.
M. H. Noorbakhsh, None