Bert Noseda

Necrotrophic Growth of Legionella pneumophila

ABSTRACT This study examined whether Legionella pneumophila is able to thrive on heat-killed microbial cells (necrotrophy) present in biofilms or heat-treated water systems. Quantification by means of plate counting, real-time PCR, and flow cytometry demonstrated necrotrophic growth of L. pneumophila in water after 96 h, when at least 100 dead cells are available to one L. pneumophila cell. Compared to the starting concentration of L. pneumophila, the maximum observed necrotrophic growth was 1.89 log units for real-time PCR and 1.49 log units for plate counting. The average growth was 1.57 ± 0.32 log units (n = 5) for real-time PCR and 1.14 ± 0.35 log units (n = 5) for plate counting. Viability staining and flow cytometry showed that the fraction of living cells in the L. pneumophila population rose from the initial 54% to 82% after 96 h. Growth was measured on heat-killed Pseudomonas putida, Escherichia coli, Acanthamoeba castellanii, Saccharomyces boulardii, and a biofilm sample. Gram-positive organisms did not result in significant growth of L. pneumophila, probably due to their robust cell wall structure. Although necrotrophy showed lower growth yields compared to replication within protozoan hosts, these findings indicate that it may be of major importance in the environmental persistence of L. pneumophila. Techniques aimed at the elimination of protozoa or biofilm from water systems will not necessarily result in a subsequent removal of L. pneumophila unless the formation of dead microbial cells is minimized.

Effect of O2CO2 enriched atmospheres on microbiological growth and volatile metabolite production in packaged cooked peeled gray shrimp (Crangon crangon)

This study evaluated the effect of modified atmospheres (MAs) with different O(2) concentrations on microbial growth and volatile metabolite production in gray shrimp (Crangon crangon) during storage at 4 °C. Eight MAs were evaluated in total. Four of the MAs evaluated were without CO(2): 0/0/100, 0/10/90, 0/30/70, 0/50/50 (% CO(2)/O(2)/N(2)) whilst the other four MAs all contained 50% CO(2): 50/0/50, 50/10/40, 50/30/20, 50/50/0 (% CO(2)/O(2)/N(2)). Volatile spoilage metabolites were identified by thermal desorption GC-MS and quantified during storage by selective ion flow tube mass spectrometry (SIFT-MS). In comparison to microbial growth observed with an atmosphere of 100% N(2), microbial growth was stimulated by the addition of O(2) in the MAP in the absence of CO(2.) Under these conditions the total psychrotrophic counts exceeded 7 log cfug(-1) after just 3 days of storage. However, in the presence of 50% CO(2) the total psychrotrophic count exceeded 7 log cfug(-1) after 5 days of storage. The combination of 50% CO(2) and 50% O(2) significantly inhibited microbial growth. For this MA condition, a diminishing effect on the production of metabolites was also observed, especially for amines and sulfur compounds, which constituted the major fraction of components causing the offensive odor.

SIFT-MS analysis of Iberian hams from pigs reared under different conditions.

The aim of this study was to investigate the usefulness of a Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS) equipment to tentatively quantify relevant volatile compounds of dry-cured Iberian ham, and to differentiate Iberian hams from pigs reared at four different conditions yielding different commercial grades. The SIFT-MS analysis allowed the rapid quantification of 39 Iberian ham volatile compounds, 16 of them being significantly affected by the rearing conditions of pigs. The full spectra SIFT-MS data allowed the correct classification of 79.2% of hams according to diet, which is a smaller percentage than that obtained using intramuscular fatty acid data (95.8%) obtained by using a gas chromatograph-flame ionization detector after lipid extraction and transesterification. Therefore, the SIFT-MS analysis would be a rapid tool to tentatively quantify some relevant volatile compounds, and also would provide a rapid but rough classification of Iberian ham according to the rearing conditions of pigs.

Evaluation of the microbiological safety and quality of Vietnamese Pangasius hypophthalmus during processing by a microbial assessment scheme in combination with a self-assessment questionnaire

Pangasius hypophthalmus (referred to as Pangasius or tra fish in Vietnam) has become highly appreciated by consumers in the European Union, USA, Japan, etc. and is of worldwide economic importance. Therefore, the microbial quality and safety of Pangasius fish processed for export was assessed by means of a microbial assessment scheme throughout the entire production process. A total of 144 samples were collected from various processing steps and analyzed. It was determined that the microbial safety and quality of the products was not guaranteed as the contamination levels remained high throughout processing. Escherichia coli, Staphylococcus aureus and Vibrio cholerae were present on the hands of food operators, particularly those in the packaging area. Moreover, the presence of Listeria monocytogenes (1 positive out of 9 samples) and V. cholerae (4/9) on the final products was likely a result of inadequate hygiene practices in the processing environment. Also discussed in this paper are the results of a self-assessment questionnaire, which provide insight into the performance of the food safety management system currently implemented at the company. These data are of major importance in order to contribute valuable information to the local and international trade point of view in general and to the intended customers in particular.

Dynamics of microbiological quality and safety of Vietnamese Pangasianodon hypophthalmus during processing

Although the farming of Pangasianodon hypophthalmus is of worldwide economic importance, only little scientific information is currently present on the microbiological quality and safety of these fish fillets throughout the processing chain. This research assessed the microbiological quality and safety of P.hypophthalmus in a Vietnamese Pangasianodon processing company as a case study. The company was initially characterized by a diagnosis of the food safety management system (FSMS) performance by an in-depth interview, which is referred to as a diagnostic instrument. Secondly, a microbiological assessment scheme (MAS), an active and repetitive sampling methodology, was used to evaluate the food safety output and the microbiological quality from raw material until final product. The overall MAS result (level 2) was found to be slightly lower than the company’s food safety performance indicators had indicated (level 2–3). It can be concluded that the microbiological risk of the Vietnamese company and its products is medium high. This is mainly due to the lack of data and knowledge regarding the origin and composition of the microbiological flora present in the fish and in the processing environment. The variability in concentrations of microorganisms also contributed to this lower MAS score and could probably be reduced by improving some specific aspects of the FSMS and the production process.