Showing papers by "Frank Devlieghere published in 2012"

Strain-specific transfer of antibiotic resistance from an environmental plasmid to foodborne pathogens.

Abstract: Pathogens resistant to multiple antibiotics are rapidly emerging, entailing important consequences for human health. This study investigated if the broad-host-range multiresistance plasmid pB10, isolated from a wastewater treatment plant, harbouring amoxicillin, streptomycin, sulfonamide, and tetracycline resistance genes, was transferable to the foodborne pathogens Salmonella spp. or E. coli O157:H7 and how this transfer alters the phenotype of the recipients. The transfer ratio was determined by both plating and flow cytometry. Antibiotic resistance profiles were determined for both recipients and transconjugants using the disk diffusion method. For 14 of the 15 recipient strains, transconjugants were detected. Based on plating, transfer ratios were between 6.8 × 10−9 and 3.0 × 10−2 while using flow cytometry, transfer ratios were between <1.0 × 10−5 and 1.9 × 10−2. With a few exceptions, the transconjugants showed phenotypically increased resistance, indicating that most of the transferred resistance genes were expressed. In summary, we showed that an environmental plasmid can be transferred into foodborne pathogenic bacteria at high transfer ratios. However, the transfer ratio seemed to be recipient strain dependent. Moreover, the newly acquired resistance genes could turn antibiotic susceptible strains into resistant ones, paving the way to compromise human health.

The spoilage microbiota of ray (Raja sp.) during ice storage under different conditions: Molecular identification and characterisation of the spoilage potential

Abstract: The dominant microbiota of ray stored on ice was systematically identified. Isolates grown on various media were identified by partial 16S rRNA, gyrB and rpoB gene sequencing. Microbiological shifts were observed during storage, ending in a dominance of especially members of the genera Pseudomonas and Psychrobacter. Most isolates could be identified by rpoB (Pseudomonas spp.) or gyrB gene sequencing as Pseudomonas fluorescens, Pseudomonas fragi, Pseudomonas psychrophila, Psychrobacter cibarius, Psychrobacter cryohalolentis, Psychrobacter glacincola and Psychrobacter immobilis. Also species from the genera Arthrobacter, Flavobacterium, Pseudoalteromonas, Shewanella and Staphylococcus were detected during storage of ray. Subsequently, the spoilage potential of six selected isolates (Flavobacterium tegetincola, Pseudomonas fluorescens, Pseudomonas psychrophila, Psychrobacter cibarius, Psychrobacter cryohalolentis and Shewanella frigidimarina) was determined and quantified based on the presence of VOCs. Additionally, API ZYM and urease analyses determined the species’ enzymatic capacity to contribute to spoilage by degrading lipids, amino acids and proteins and breaking down urea to ammonia. The six isolates were inoculated separately as pure cultures on gamma-sterilised ray. The inoculated samples were stored at 4°C and the production of VOCs by the pure strains on the ray matrix was identified via gas chromatography coupled to mass spectrometry (GC-MS). VOC production was quantified by selected ion flow tube mass spectrometry (SIFT-MS). The sensory profile of the selected species revealed that especially Psychrobacter cibarius and Pseudomonas psychrophila were able to produce higher concentrations of VOCs and might be responsible for the off-odours produced during spoilage of ray.

A predictive model for the growth/no growth boundary of Zygosaccharomyces bailii at 7°C and conditions mimicking acidified sauces

Abstract: The spoilage potential of Zygosaccharomyces bailii has been widely recognized within the food industry. However, few data are available on the growth characteristics of this yeast at low temperature and in the absence of chemical preservatives. In this study, the growth/no growth boundary of Z. bailii was defined at refrigeration temperature (7 °C) and at conditions relevant to high-sugar, low-pH foods (such as ketchup and salad dressing), i.e. pH 3.0–5.0 (five levels), a w 0.93–0.97 (five levels) and acetic acid concentration 0–2.5% (v/v; six levels). Yeast growth was followed during 90 days by optical density measurements, and logistic regression models were used to describe the data. Acetic acid had a significant effect on the relation between a w and NaCl concentration and this interaction had important consequences for the model development. When data were modelled as a function of a w or NaCl concentration, a stimulatory effect by acetic acid was observed. In contrast, as a function of (toxic) Na+ ions, no evidence was found of such a phenomenon. These results indicate that in cases where the relationship between a w and solute concentration is not straightforward such as in the presence of acid preservatives, one must be critical towards the interpretation of data and correspondingly, the development of predictive models. On a practical note, the developed models, especially the one incorporating Na+ ions, may be used (1) to assess the stability of shelf-stable acidified foods stored under chilled conditions after opening or (2) to formulate new additive-free products intended for storage at 7 °C.

Analysis of Intracellular pH in Escherichia coli O157:H7 to Determine the Effect of Chlorine Dioxide Decontamination

Abstract: The aim of this study was to investigate the response of Escherichia coli O157:H7 when exposed to different concentrations of sanitation agent chlorine dioxide (ClO2) by determining intracellular pH (pHi). For this purpose, fluorescence ratio imaging microscopy was used together with pH-sensitive, ratiometric green fluorescent protein that was introduced in E. coli O157:H7 cells. Along with pHi, colony counts were determined during the treatment with ClO2. Results revealed several post-treatment subpopulations with different physiological states, as judged by their pHi. The fraction of cells with no pH gradient increased, and the colony count decreased as the concentration of ClO2 increased.