Validation of the Hygicult (R) E dipslides method in surface hygiene control: A Nordic collaborative study

A collaborative study with Enterobacteriaceae was conducted to validate Hygicultr E dipslides by comparison with violet red bile glucose agar (VRBGA) contact plates and swabbing, using stainless steel surfaces artificially contaminated with microbes at various levels. Twelve laboratories participated in the validation procedure. The total number of collaborative samples was 108. The microbial level in each sample was assessed in triplicate by using the 3 above-mentioned methods. No Enterobacteriaceae were used at the low inoculation level. At the middle inoculation level, the percentages detached from the test surfaces were 16.6 with the Hygicult E method, 15.3 with the contact plate method, and 14.6 with swabbing; at the high innoculation level, the percentages were 14.5, 15.8, and 9.8, respectively. The percentage of acceptable results after the removal of outliers was 97.2. Repeatability relative standard deviations ranged from 33.4 to 44.9%; reproducibility relative standard deviations ranged from 45.2 to 77.1%. The Hygicult E dipslide, VRBGA contact plate, and swabbing methods gave similar results at all 3 microbial levels tested: <1.0 colony-forming units (CFU)/cm2 at the low level, 1.2-1.3 CFU/cm2 at the middle level (theoretical yield 8.0 CFU/cm2), and 1.2-2.0 CFU/cm2 at the high level (theoretical yield 12.5 CFU/cm2).