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C B Struijk

Publications and source records attributed to C B Struijk.

At least 19 recordsLinked to original sources
PubMed2001

Advances in the bacteriology of the coliform group: their suitability as markers of microbial water safety.

Advances in the elaboration of novel genomic types of beta-galactosidase-positive Enterobacteriaceae and comprehensive studies of their habitats have resulted in an innovative approach to the assessment of the merits and shortcomings of the thermotrophic and fecal species Escherichia coli and all other coliforms as markers of the microbiological safety of water. As one of the consequences, it is recommended to abolish the "technical" designation fecal coliforms because their current method of detection will result in the isolation of thermotrophic organisms that have been demonstrated, beyond a doubt, to be of environmental, rather than uniquely enteric origin. Additional population studies have demonstrated that none of the coliforms can function as reliable markers for all enteric pathogens (index organisms sensu Ingram), nor be of use in validating adequate processing for safety of raw water, which represents the indicator function of markers, as defined by Ingram. Future studies along these lines will have to provide the data required to assess the suitability of additional markers for the reliable monitoring of drinking water for microbiological safety.

Enterobacteriaceae↗
PubMed2000

Stool microscopy.

Explore the source record for details and available documents.

Diagnosis, Differential↗
PubMed1998

Identification, assessment and management of food-related microbiological hazards: historical, fundamental and psycho-social essentials.

Microbiological risk assessment aimed at devising measures of hazard management, should take into account all perceived hazards, including those not empirically identified. It should also recognise that safety cannot be "inspected into" a food. Rather hazard management should be the product of intervention strategies in accordance with the approach made mandatory in the EU Directive 93/43 and the USDA FSIS Pathogen Reduction HACCP system; Final Rule. It is essential too that the inherent variability of the biological attributes affecting food safety is recognised in any risk assessment. The above strategic principles may be conceptualised as a four-step sequence, involving (i) identification and quantification of hazards; (ii) design and codification of longitudinally integrated ("holistic") technological processes and procedures to eliminate, or control growth and metabolism of, pathogenic and toxinogenic organisms; (iii) elaboration of microbiological analytical standard operating procedures, permitting validation of "due diligence" or responsible care, i.e. adherence to adopted intervention strategies. This should be supported by empirically assessed reference ranges, particularly for marker organisms, while the term "zero tolerance" is refined throughout to tolerable safety limit; (iv) when called for, the need to address concerns arising from lay perceptions of risk which may lack scientific foundation. In relation to infectious and toxic hazards in the practical context the following general models for quantitative holistic risk assessment are presented: (i) the first order, basic lethality model; (ii) a second approximation taking into account the amount of food ingested in a given period of time; (iii) a further adjustment accounting for changes in colonization levels during storage and distribution of food commodities and the effects of these on proliferation of pathogens and toxin production by bacteria and moulds. Guidelines are provided to address: (i) unsubstantiated consumer concern over the wholesomeness of foods processed by an innovative procedure; and (ii) reluctance of small food businesses to adopt novel strategies in food safety. Progress here calls for close cooperation with behavioural scientists to ensure that investment in developing measures to contain risk deliver real benefit.

Animals↗
PubMed1998

Identification, assessment and management of food-related microbiological hazards: historical, fundamental and psycho-social essentials.

Microbiological risk assessment aimed at devising measures of hazard management, should take into account all perceived hazards, including those not empirically identified. It should also recognise that safety cannot be "inspected into" a food. Rather hazard management should be the product of intervention strategies in accordance with the approach made mandatory in the EU Directive 93/43 and the USDA FSIS Pathogen Reduction HACCP system; Final Rule. It is essential too that the inherent variability of the biological attributes affecting food safety is recognised in any risk assessment. The above strategic principles may be conceptualised as a four-step sequence, involving (i) identification and quantification of hazards; (ii) design and codification of longitudinally integrated ("holistic") technological processes and procedures to eliminate, or control growth and metabolism of, pathogenic and toxinogenic organisms; (iii) elaboration of microbiological analytical standard operating procedures, permitting validation of "due diligence" or responsible care, i.e. adherence to adopted intervention strategies. This should be supported by empirically assessed reference ranges, particularly for marker organisms, while the term "zero tolerance" is refined throughout to tolerable safety limit; (iv) when called for, the need to address concerns arising from lay perceptions of risk which may lack scientific foundation. In relation to infectious and toxic hazards in the practical context the following general models for quantitative holistic risk assessment are presented: (i) the first order, basic lethality model; (ii) a second approximation taking into account the amount of food ingested in a given period of time; (iii) a further adjustment accounting for changes in colonization levels during storage and distribution of food commodities and the effects of these on proliferation of pathogens and toxin production by bacteria and moulds. Guidelines are provided to address: (i) unsubstantiated consumer concern over the wholesomeness of foods processed by an innovative procedure; and (ii) reluctance of small food businesses to adopt novel strategies in food safety. Progress here calls for close cooperation with behavioural scientists to ensure that investment in developing measures to contain risk deliver real benefit.

Consumer Advocacy↗
PubMed1998

Duplex (thermotroph-psychrotroph) quadrant plates: convenient, error-avoiding tools for monitoring of HACCP-contained food lines and for epidemiological investigations under conditions of military or other constraints.

A set of two "two-tier" (thermotroph-psychrotroph) single quadrant plates (QPs) was developed previously to allow convenient enumeration of numbers of colony-forming units of most pertinent pathogenic bacteria or marker bacteria in foods. These include Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, thermotrophic and psychrotrophic Enterobacteriaceae, Clostridium spp., and Enterococcus spp. As the QPs had given excellent results in monitoring samples of marketed food products potentially involved in food-transmitted illnesses, the approach was tested for practicability under military deployment and other constraints. Three approaches were envisaged: (i) validating lapse-free adherence to meticulously codified good military catering practices; (ii) acceptance/rejection testing of locally procured foods or meals; and (iii) employing rapid culture in support of evidence obtained by microscopy in attempts to identify foods involved in infectious or toxic disease outbreaks occurring in the field. The method was found to be elegant, avoiding confusion when larger number of specimens were to be screened, as well as easy to teach to staff with little or no training in microbiology, and it provided entirely reliable results. For use outside the laboratory, preparation of food macerates by use of shake flasks containing glass or plastic beads and peptone saline as a substitute for stomaching was found acceptable, though the shake flask technique led to slightly diminished colony counts. Results obtained with incubation times shortened to ca. 12 h could be relied on only when the results were alarmingly positive, but not when the colony counts at the 12-h point did not yet indicate a reason for concern.

Cheese↗
PubMed1995

Modified methods for the enumeration of spores of mesophilic Clostridium species in dried foods.

Clostridia constitute markers of limited though definite importance for the microbiological integrity of particular foods processed for safety, provided their application and the results obtained are meticulously considered and guided by proper ecological awareness. Their selective diagnostic enumeration in food specimens relies on their ability to reduce sulphite in agar media, visualised by the presence of ferrous cations leading to the production of black colonies. The composition of the medium used substantially affects the productivity of the procedure. We established that (1) the sulphite activity and the ferrous ion should be rigorously standardised; (2) tryptose is one of the appropriate nitrogen sources for a limited number of clostridia; (3) the basal medium should be free of added acetate and lactate. Black colonies obtained in the newly elaborated medium, termed Differential clostridial agar (DCA) should be further examined for morphology and metronidazole sensitivity, since some bacilli might mimic clostridia under the conditions of the procedure. An elegant variant of the technique relies on using a bottom-layer of mannitol/egg yolk/polymyxin/bromocresol purple agar, inoculated with macerates of food in buffered cysteine hydrochloride peptone saline, immediately liberally overlayered with freshly prepared DCA. Plates are incubated and read in tightly closed bags of plastic with a low oxygen permeability coefficient, which eliminates the need for using anaerobic jars. Colony identification is relying on assessment of sulphite reduction, egg yolk dissimilation, the mode of attack on mannitol and when required to be supported by classical other physiological traits. The mandatory precautions to be observed in this procedure call for extreme caution when introducing reference ranges ("standards") for clostridial spores in foods, particularly in the international commerce.

Clostridium↗
PubMed1995

[Escherichia coli, other Enterobacteriaceae and additional indicators as markers of microbiologic quality of food: advantages and limitations].

The 93/43 European Union directive assigns to the food and catering industries the main responsibility for an integrated safety and quality assurance strategy in the food chain. Relying on hazard analysis, followed by design and adoption of control of all critical points and practices ("HACCP"). Hiatus-free compliance with such HACCP-based Codes of Good Practices is to be assessed by monitoring, recording results on process performance charts and gauging such data against experimentally established, attainable and maintainable references ranges ("standards"). Marker microorganisms are a major analytical tool for validating compliance in the sense of the EU directive. They should be expertly chosen amongst microbes usually present in food so that their, whose presence in quantities exceeding predetermined levels point to a lack of microbiological integrity of a food product. This may encompass (i) the potential presence of taxonomically, physiologically and ecologically related pathogens, markers are called index organisms; or else (ii) a lack of process integrity; in this case, markers are termed indicator organisms. The classical index organism was E. coli, introduced in the 1980's to monitor drinking water supplies. It is still used as an appropriate marker to assess the bacteriological safety of raw foods. In the 1920's the coli-aerogenes ("coliform") group was adopted as an indicator to validate the adequate processing, i.e. pasteurization of dairy products. Since the 1950's the entire Enterobacteriaceae taxon is preferred for the latter purpose because it is better defined in determinative sense and includes more organisms of significance. In some food and water supplies, processed for safety, more vigorous or more resistant organisms than the Gram-negative rods are reliable supplementary markers. These include Enterococcus spp., spores of the Clostridium genus, and bacteriophages of E. coli and Bacteroides fragilis mimicking the fate of enteric viruses under particular ecological conditions. Population surveys conducted by the authors provided ranges for epsilon-factors. Those factors were defined as the proportion between colony forming units (cfu) numbers of index organisms and the pathogenic agent to whose potential occurrence they are expected to point. Epsilon factor values obtained for thermotropic Enterobacteriaceae in relation to Salmonella spp. allow the calculation of the probability that the pathogen has been reliably eliminated by the processing of initially contaminated raw materials, when cfu's of the marker organisms remain below a reference range previously fixed.

Enterobacteriaceae↗
PubMed1991

Public health implication of refrigerated pasteurized ('sous-vide') foods.

Food that upon pasteurization is stored in hermetically sealed containers at food temperatures not exceeding 3 degrees C could be designated by the generic term Refrigerated Pasteurized Foods of Extended Durability, REPFEDs. If not properly processed or protected against recontamination, or if temperature-abused, REPFEDs may present serious health risks. However, control is readily available. Sound microbial ecology, supported by expert risk assessment, allows the design and introduction of longitudinally integrated manufacture, distribution, handling by outlets and consumers and culinary preparation, which result in the assurance of the wholesomeness of the commodity as eaten. Recent progress, including intrinsic preservation by the incorporation of starter cultures, bacteriocins or particular enzymes, opens vistas for attractive future developments. Once microbiological safety has been built into the REPFED-line, monitoring can be limited to (i) real-time tests particularly applied to the factory environment; and (ii) rapid, simple examination for marker organisms of freshly manufactured products versus those approaching expiration dates. Such audits will allow rapid retrieval of incidental process failure and its rectification. It also serves to substantiate measurements of food temperature and spot checks on intrinsic inhibitory attributes. The application of scientific knowledge and technological expertise should primarily be entrusted to the industry itself, heeding Lord Plumb's strategy of "partnership along the food production chain from farm to fork." It should be supported and validated by Public Health Authorities. At all stages safety communication with the public should be ensured.

Bacteria↗