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Urine culture is quantitative and very reliable, but can take at least one day to obtain a result and it is expensive. [8] [14] Miniaturization of bacterial culture within dipstick format, Digital Dipstick, [15] allows bacterial detection, identification and quantification for bacteriuria within 10–12 hours at the point-of-care.
In some cases, urine samples or positive blood culture samples are applied directly to the test medium, bypassing the preliminary step of isolating the organism. [15] If the antibiotic inhibits microbial growth, a clear ring, or zone of inhibition, is seen around the disc.
Normal urine pH is slightly acidic, with usual values of 6.0 to 7.5, but the normal range is 4.5 to 8.0. A urine pH of 8.5 or 9.0 is indicative of a urea-splitting organism, such as Proteus, Klebsiella, or Ureaplasma urealyticum; therefore, an asymptomatic patient with a high pH means UTI regardless of the other urine test results.
CLED agar (cystine–lactose–electrolyte-deficient agar or medium) is a valuable non-inhibitory growth medium used in the isolation and differentiation of urinary microbes. It contains cystine and lactose and is electrolyte-deficient; the latter trait prevents the swarming of Proteus species. Cystine promotes the formation of cystine ...
It normally ranges from 1.003 to 1.035; lower values indicate that the urine is dilute, while higher values mean that it is concentrated. A urine specific gravity that consistently remains around 1.010 (isosthenuria) can indicate kidney damage, as it suggests that the kidneys have lost the ability to control urine concentration. [39]
While the MIC is the lowest concentration of an antibacterial or antifungal agent necessary to inhibit visible growth, the minimum bactericidal concentration (MBC) is the minimum concentration of an antibacterial agent that results in bacterial death. It is defined by the inability to re-culture bacteria, and the closer the MIC is to the MBC ...
An alkaline urine sample is a possible sign of P. mirabilis. It can be diagnosed in the lab due to characteristic swarming motility, and inability to metabolize lactose (on a MacConkey agar plate, for example).
Inoculating from a broth culture is not recommended because the inoculum would be too heavy. If the organism has the ability to use citrate, the medium usually changes its color from green to blue, though growth on the medium even without colour change is considered a positive result. [1] An observation of no growth is a negative result.