Evaluation of Petrifilm™ Aerobic Count Plates as an Equivalent Alternative to Drop Plating on R2A Agar Plates in a Biofilm Disinfectant Efficacy Test

Abstract

This paper compares Petrifilm™ aerobic count (AC) plates to drop plating on R2A agar plates as an alternative method for biofilm bacteria enumeration after application of a disinfectant. A Pseudomonas aeruginosa biofilm was grown in a Centers for Disease Control and Prevention biofilm reactor (ASTM E2562) and treated with 123 ppm sodium hypochlorite (as free chlorine) according to the Single Tube Method (ASTM E2871). Aliquots from the same dilution tubes were plated on Petrifilm™ AC plates and drop plated on R2A agar plates. The Petrifilm™ AC and R2A plates were incubated for 48 and 24 h, respectively, at 36 ± 1 °C. After nine experimental runs performed by two technicians, the mean difference in biofilm log densities [log biofilm density (LD) = log10(CFU/cm(2))] between the two methods for control coupons, treated coupons, and log reduction (LR) was 0.052 (p = 0.451), -0.102 (p = 0.303), and 0.152 (p = 0.313). Equivalence testing was used to assess equivalence of the two plating methods. The 90 % confidence intervals for the difference in control and treated mean LDs between methods were (-0.065, 0.170) and (-0.270, 0.064), both of which fall within a (-0.5, +0.5) equivalence criterion. The 90 % confidence interval for the mean LR difference (-0.113, 0.420) also falls within this equivalence criterion. Thus, Petrifilm™ AC plates were shown to be statistically equivalent to drop plating on R2A agar for the determination of control LDs, treated LDs, and LR values in an anti-biofilm efficacy test. These are the first published results that establish equivalency to a traditional plate counting technique for biofilms and for a disinfectant assay.

Interlaboratory study for the evaluation of three microtiter plate-based biofilm quantification methods

“…The ANOVA was followed by Tukeys 95% CIs to determine statistical equivalence at 97.5% confidence for the median responses for ILP and IHP (CFU density for plate counts, resoforin concentration, and crystal violet). For the plate count method the equivalency margin of 0.5 logs was chosen based on previous examples in the literature 24 , 25 . On the other hand, no previous reference was found for establishing an equivalency margin for resazurin and crystal violet method, so the equivalency margin of 0.5 log was used for these methods as well.…”

Preparation of cationic cotton through reaction with different polyelectrolytes

“…Petrifilm AC (3M, USA) is a ready to use product, containing culture media, cold water-soluble gelling agent and triphenyl tetrazolium chloride, an indicator that colors bacterial colonies red. This product can be used for the enumeration of aerobic bacteria growth over a surface (Fritz et al 2015 ; Sjollema et al 2018 ).…”

Moderations in performance, immunity, tissue architecture, and vaccine viability induced by water magnetization in broiler farms

“…Typhimurium were propagated as recommended by Fritz et al . [ 22 ] through the serial passage using MacConkey broth (Thermo Scientific™ Oxoid™ MacConkey Broth, CM0505, 500 g) and tetrathionate broth (Thermo Scientific™ Oxoid™ Tetrathionate Broth Base, CM0029, 500 g) pre-enrichments and were incubated at 44°C/24 h and 37°C/24 h, respectively. The propagation of E. coli O157:H7 and S .…”

“…E. coli O157:H7 suspension (1.5 × 10 5 CFU.mL −1 ) and an S. Typhimurium lyophilized vial (3.4 × 10 2 CFU) were purchased from Animal Health Research Institute, Dokki, Cairo. E. coli O157:H7 and S. Typhimurium were propagated as recommended by Fritz et al [22] through the serial passage using MacConkey broth (Thermo Scientific™ Oxoid™ MacConkey Broth, CM0505, 500 g) and tetrathionate broth (Thermo Scientific™ Oxoid™ Tetrathionate Broth Base, CM0029, 500 g) pre-enrichments and were incubated at 44°C/24 h and 37°C/24 h, respectively. The propagation of E. coli O157:H7 and S. Typhimurium was achieved by transferring 10 µL from positive pre-enrichment MacConkey and tetrathionate broth tubes, which were dropped onto MacConkey agar (Thermo Scientific™ Oxoid™ MacConkey Agar No.3., CM0115, 500 g) and xylose lysine deoxycholate agar (Thermo Scientific™ Oxoid™ X.L.D.…”