Environmental factors influencing Listeria monocytogenes survival and attachment on surfaces inoculated with droplets

Authors: IONITA, CLAUDIA - PURDUE UNIVERSITY; Annous, Bassam; NIVENS, DAVID - PURDUE UNIVERSITY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2008
Publication Date: 6/28/2008
Citation: Ionita, C., Annous, B.A., Nivens, D. 2008. Environmental factors influencing Listeria monocytogenes survival and attachment on surfaces inoculated with droplets. [Abstract]. Institute of Food Technologies. p. 1.

Interpretive Summary:

Technical Abstract: Pathogenic microorganisms residing on food or food contact materials are important sources of food-borne microbial contamination. The objective of this study is to explore factors responsible for Listeria monocytogenes survival and colonization on surfaces when bacteria are inoculated from drying droplets. Listeria monocytogenes F4244 and its green fluorescence protein derivative, L. monocytogenes pNF9 were grown in Tryptic Soy Broth and Modified Welshimer’s Broth. In this study we use atomic force microscopy and epi-fluorescence microscopy to assess (i) spatial distribution of bacteria as they dry from droplets (ii) bacterial survival within the droplet area and (iii) bacterial attachment to the surface. Environmental factors were considered such as temperature, presence of nutrients and relative humidity. In order to reduce the amount of medium components, cultures were dialyzed against sterile water and approximately 2 x 106 CFU/ml were spotted on hydrophobic glass slides. The drying pattern showed different areas with clumped cells and cells within a medium component-based matrix. To confirm cell viability, agar plugs were place on the surface and upon growth, viable cells formed patterns similar to those observed in the dried spots. Moreover, in similar experimental conditions of relative humidity and temperature rich media allowed bacterial survival after 84 hours of drying, whereas minimal media-grown bacteria survived for 72 hours. Similar bacterial preparations regarding available nutrients but stored at refrigeration temperature and higher relative humidity survived for more than 10 days. A majority of the bacterial survival was found within dried medium-based matrices. When washed with a peristaltic pump at a flow rate of 5 ml per minute for 1 minute, re-examination of the surfaces shows that cell-clumps were preferentially retained. Our results demonstrate that droplet inoculums are dramatically affected by environmental conditions and result in mixed distribution of microenvironments, with some of which promote adhesion and/or survival.