Evaluation of different surface sampling methods to assess the presence of biofilm in the food processing industry

Maes, S.1, Heyndrickx, M.1, Steenackers, H.2, Vanderleyden, J.2, De Reu, K.1 1Institute for Agricultural and Fisheries Research (ILVO), Technology & Food Science Unit, Brusselsesteenweg 370, B-9090 Melle, Belgium 2Catholic University of Louvain, Department of Microbial and Molecular Systems, Centre of Microbial and Plant Genetics, Kasteelpark Arenberg 20, B-3001 Louvain, Belgium Introduction Biofilms play an important role in several ecological niches including food industry. The importance and role of biofilms in persistent infections with for example spoilage organisms and pathogenic bacteria is however insufficiently known. The aim of this study was to evaluate different surface sampling methods to assess the presence of biofilms in different food processing companies. Material and methods In seven different food processing companies (producing oven foods, dairy products, meat products, baker’s yeast, sauces and egg products) different surfaces were sampled after cleaning and disinfection using 2 methods of sampling. The first method was scraping with a cell scraper(VWR) followed by swabbing with a floqswab(Copan). Simultaneous a second method, swabbing using a spongestick(3M) hydrated with 10ml of ¼ ringers solution(Oxoid), was performed on a nearby surface. Sampled areas differed from 20cm² to 600cm² but were similar between the two sampling methods. Different microbiological analyses were performed on both types of samples. Only samples with a minimum of 10² CFU/100cm² were taken into account for the comparison of the two sampling methods for biofilms. Statistical analyses on the obtained results were carried out with Statistical Analysis System software (SAS®, version 9.4, SAS Institute Inc., Cary, NC, USA). Mean with standard deviation are given for counts that were normally distributed and median with first and third quartile (indicated in parentheses) are given for counts that didn’t follow this distribution. Results Results for total aerobic plate count (TAC) and Pseudomonas spp. were normally distributed, while enumerations of lactic acid bacteria (LAB) were not normally distributed. The average count for TAC (n=34) using the scraper/floqswab was 2,68±1,30 log CFU/100cm² while 3,38±1,24 log CFU/100cm² when sampling with the spongestick (p=0,0251). For Pseudomonas spp. (n=9) enumeration with the scraper/floqswab and spongestick were 2,52±1,21 and 3,58±0,67 log CFU/100cm² respectively (p=0,0504). The average count of LAB (n=7) with the scraper/floqswab was 3,08 [0,48-4,18] log CFU/100cm² and 2,91 [2,34-3,88] log CFU/100cm² with the spongestick (p=0,8982). Discussion Results showed that using spongesticks higher counts were obtained for TAC and Pseudomonas spp. moreover this difference was significant. This gives preference to sampling with a spongestick if only microbiological yield is considered. On the other hand, scientific research showed that the spongestick (composed by cellulose) gives interference in the chemical analysis of the extracellular polymeric substance (EPS) of the biofilm, making the sampling method less suitable for chemical analysis of biofilms. When chemical analysis of the biofilm is required cell scraper combined with a floqswab, which is more labour intensive and provides lower recovery of the bacteria from biofilms, is recommended.