Screening of Urine Cultures by Three Automated Systems

Abstract

A study was conducted to compare three automated systems and the Gram stain for their ability to detect significant bacteriuria. A total of 1,000 urine specimens were evaluated by Autobac MTS (General Diagnostics), AutoMicrobic system (AMS; Vitek Systems, Inc.), and MS-2 (Abbott Laboratories) and compared with a semiquantitative culture plate method. Two hundred thirty-nine (23.9%) specimens had colony counts of >105 colony-forming units (CFU)/ml by the culture plate method (group I). Of these, 204 (85.3%) were positive by Autobac, 198 (82.8%) were positive by AMS, and 179 (74.9%) were positive by MS-2. When pure cultures of diphtheroids, lactobacilli, and viridans streptococci not group D were considered contaminants and therefore excluded, there were 118 specimens containing pure cultures of probable pathogens. The percentage of significant isolates detected was 97.4% (115 of 118) by the Gram stain, 96.6% (114 of 118) by Autobac, and 95.8% (113 of 118) by AMS and MS-2. The average detection time for all organisms was 2.2 h by Autobac, 6.1 h by AMS, and 1.8 h by MS-2; therefore, all three methods were more rapid than the 18-to 24-h standard plate culture method. One hundred sixty-one (16.1%) specimens had colony counts of 104 to 105 CFU/ml (group II). The probable pathogens not detected in this group were two (1.2%) by Autobac and MS-2 and three by AMS (1.9%). The average detection time for group II was 4.2 h by Autobac, 8.9 h by AMS, and 3.8 h by MS-2. Six hundred specimens had colony counts of <104 CFU/ml. Of these, 188 had colony counts equal to 103 and <104 CFU/ml (group III), and 412 cultures were below detectable limits by the standard plate method (group IV). Less than 37 and 15% of groups III and IV, respectively, were detected by instrumentation. Average detection times for groups III and IV were 4.6 and 4.8 h by Autobac, 10 and 11 h by AMS, and 4.2 and 4.4 h by MS-2. The cost of supplies and technical time with Gram stain, Autobac, and MS-2, when used as screening methods, were comparable and considerably less expensive than for the reference method. The AMS was the least expensive system when the cost for identifying probable pathogens was included.

Rapid detection of bacteriuria by laser nephelometry

“…), and 50% with the Gram range of 106 are sometimes indicative of pyelonephritis (7). stain in the study of Pezzlo et al (10). In the same study, With PT3 it is possible to differentiate these levels.…”

“…Many screening methods have been proposed to detect bacteria in urine on the day of the collection, both to shorten these delays and to lessen the time spent separating negative specimens from those containing more than 104 bacteria per ml. Gram stain (10), measurement of bacterial ATP by luciferase (1), electrochemical (8) and microcalorimetric methods (2), light scatter nephelometry (6), and photometry have been used to test urine specimens, but none of these is fully satisfactory. Laser nephelometry (LM), which is currently used in biochemistry laboratories for rapid determinations of immunoglobulin, inflammation proteins, apolipoproteins, and factor VIII antigens (3)(4)(5)11), was considered as another possible method.…”

Evaluation of Rapid Methods for the Detection of Bacteriuria (Screening) in Primary Health Care

“…Several screening tests of bacteriuria are available (4, 19). The dipslide is a simplified culture test requiring overnight incubation (5,8).…”

Evaluation of three bacteriuria screening methods in a clinical research hospital

“…Although the prevalence of urinary tract infection varies for different patient populations, the majority of urine specimens are culture negative. Due to efforts to reduce the amount of time and money required to process these negative specimens, a variety of methods to screen urine specimens for bacteriuria have become available (5). These include both growth-dependent and growth-independent techniques.…”