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Papers by Peter van Netten

Research paper thumbnail of The immediate bactericidal effect of lactic acid on meat-borne pathogens

Journal of Applied Bacteriology, 1994

effect of lactic acid decontamination (LAD) o n meat-borne pathogens (Salmonella spp., Campylobac... more effect of lactic acid decontamination (LAD) o n meat-borne pathogens (Salmonella spp., Campylobacter jejuni and Listeria monocytogenes) was studied in a n in-vitro model. T h e bactericidal effect was greatest on organisms in the lactic acid film that replaced the natural fluid on the meat surface during LAD. A stepwise increase in p H from 2.6 to 3-5 and 4.0 progressively reduced the bactericidal effect of decontamination. For treatment with 2% lactic acid for 3@90 s at 21"C, the immediate death of Salmonella spp. decreased from about 0.5-2 loglo cfu at pH 2.6 to an insignificant level at pH 4.0. T h e immediate death for Camp. jejuni decreased from 2.6 to > 5.3 at pH 2-6 to 0-3-1.0 a t pH 4.0. The decrease in bactericidal effect with increasing pH could, however, be countered by an increase in t h e temperature from 21°C t o 37°C. It is suggested that 2% LAD at 37°C for 30-90 s is suitable for elimination of salmonellas on meat but not for L. monocytogenes. Decontamination with 1% lactic acid at pH 3-0 and 21°C for at least 30 s was effective for Camp. jejuni. Mesophilic Enterobacteriaceae were reliable indicators of the LAD-induced bactericidal effect on Salmonella spp. and Camp. jejuni.

Research paper thumbnail of An in-vitro meat model for the immediate bactericidal effect of lactic acid decontamination on meat surfaces

Journal of Applied Bacteriology, 1994

Research paper thumbnail of Psychrotrophic strains of Bacillus cereus producing enterotoxin

Journal of Applied Bacteriology, 1990

Research paper thumbnail of Culture media for the isolation and enumeration of pathogenic Vibrio species in foods and environmental samples

International Journal of Food Microbiology, 1995

The genus Vibrio now includes a large number of species. Clear evidence is only available for the... more The genus Vibrio now includes a large number of species. Clear evidence is only available for the aetiological role of V. cholerae, V. vulnificus and V. parahaemolyticus in foodborne diseases. Until recently, V. cholerae serogroup 0:1 was accepted as the cause of epidemic cholera. However, the designation of outbreaks of diarrhoeal diseases caused by V. cholerae 0:139 as clinical cholera has lead to renewed interest in Non 0:1 serogroups of V. cholerae. A wide range of enrichment and selective media for the isolation of vibrios has been developed. These media are reviewed with respect to their ability to recover and differentiate the target vibrios. Alkaline peptone water (APW) remains the recommended enrichment medium for vibrios in parallel with either salt polymyxin broth (SPB) or glucose teepol (or sodium dodecylsulphate) salt broth (GTSB) when tests for V. parahaemolyticus are required. Thiosulphate citrate bile salt agar (TCBS) in parallel with polymyxin mannose tellurite (PMT) or sodium dodecylsulphate polymyxin sucrose agar (SPS) are the recommended selective plating media.

Research paper thumbnail of The survival and growth of acid-adapted mesophilic pathogens that contaminate meat after lactic acid decontamination

Journal of Applied Microbiology, 1998

Lactic acid decontamination (LAD) may adapt pathogens to lactic acid. Such organisms may have an ... more Lactic acid decontamination (LAD) may adapt pathogens to lactic acid. Such organisms may have an increased resistance to acid and can contaminate meat after LAD. The survival and growth of acid adapted Campylobacter jejuni, Salmonella typhimurium. Escherichia coli O157:H7 and Staphylococcus aureus inoculated on skin surface of still warm pork belly cuts 2 h after LAD was examined during chilled (4 degrees C) storage and refrigeration abuse equivalent to 12.5 degrees C. Lactic acid decontamination included dipping in 1, 2 or 5% lactic acid solutions at 55 degrees C for 120 s. Lactic acid decontamination brought sharp reductions in meat surface pH, but these recovered with time after LAD at approximately 1-1.5 pH units below that of water-treated controls. A sharp decrease in the number of cfu of pathogens occurred on chilled 2-5% lactic acid treated pork belly cuts when the skin surface was less than pH 4.8-5.2. The reductions ranged from 0.1-0.3 log10 cfu cm-2 for E. coli O157:H7 to over 1.7-2.4 log10 cfu cm-2 for Camp. jejuni, respectively. Increase in storage temperature from 4 to 12.5 degrees C reduced delayed decrease in numbers of all pathogens except Camp. jejuni by a factor of two. Deaths in Camp. jejuni at 12.5 degrees C slightly exceeded those at 4 degrees C. After the initial sharp decline, the number of cfu of mesophilic pathogens decreased gradually at a rate similar to that on water-treated controls. Growth of all mesophilic pathogens except Camp. jejuni on 2-5% LAD meat occurred during storage at 12.5 degrees C when the meat surface pH exceeded 4.8-5.2, and was slower than on water-treated controls. Low temperature and acid-adapted E. coli O157:H7, Salm. typhimurium and Staph. aureus, and acid adapted Camp. jejuni that contaminate skin surface after hot 2-5% LAD, did not cause an increased health hazard, although microbiota and intrinsic parameters (lactic acid content, pH) were created that could advantage their survival and growth.

Research paper thumbnail of A centrifugation/quadrant plate technique for the simplified differential-bacteriological examination of adequately heat-processed foods

Letters in Applied Microbiology, 1991

ABSTRACT

Research paper thumbnail of Microbiological reference values for foods: a European perspective

Journal - Association of Official Analytical Chemists

Microbiological criteria for food products and meals serve to gauge the results obtained upon mon... more Microbiological criteria for food products and meals serve to gauge the results obtained upon monitoring samples from manufacturing plants or catering units which strictly adhere to good manufacturing practices (GMP). Hazardous practices thus already having been eliminated, the aim of monitoring is to detect and, above all, immediately correct accidental failures in processing or preparation. An essential element of this system of monitoring is that the number of criteria used is kept to a minimum by carefully selecting the criteria of major ecological significance. In view of the sporadic and erratic distribution of pathogenic organisms in foods from well-run manufacturing plants and food service operations, criteria for disease agents are used only occasionally. Where they are used, their selection and detection methodology require intensive and expert scrutiny, including (i) careful designation and precise definition of the relevant agents of disease, toxin formers, or preformed toxins; (ii) prescription of very carefully validated and standardized methods, usually including a resuscitation step; and (iii) mathematically correct interpretation of failure to detect particular infectious or toxinogenic organisms. On the other hand, "marker" organisms ("indicator" and "index" organisms, according to Ingram) are frequently used. These should also be carefully selected by ecological surveys on each specific food product; in particular, their value for reliably revealing deficiencies in hygiene or handling should be assessed. The applicability of the entire group of Enterobacteriaceae (or particular parts of that taxon), Enterococcus species, Staphylococcus aureus, and streptococci of the "mitis-salivarius" group are critically examined. Numerical reference values for microbiological criteria are derived by mathematical treatment from data obtained in surveys of products produced under GMP previously validated by safety analysis. Target values thus derived will include tolerance limits and policies recommended in case high results are obtained. Consequently, "3-class sampling plans" (according to ICMSF) are to be used in most instances.

Research paper thumbnail of A small outbreak of salmonellosis caused by Bologna sausage

Tijdschrift voor diergeneeskunde

Late in August 1985, seventeen subjects in the 3-40 year range contracted salmonellosis which was... more Late in August 1985, seventeen subjects in the 3-40 year range contracted salmonellosis which was associated with the consumption of fermented pork sausage prepared by a butcher. The incubation period varied from 6 to 9 hours, the attack rate was a hundred per cent; there were no deaths or complications. The pH of the incriminated sausage was 5.7 (the pH of controls ranged from 4.5 to 5.0), and the aw was 0.99 (vs. 0.92-0.97 in the controls), a colony count of thermotrophic Enterobacteriaceae was 10(7) per 1 g, including c. 10(6) of Salmonella typhimurium, c. 10(3) Staphylococcus aureus and c. 10(4) cfu of Clostridium perfringes per 1 g. These outbreaks may be prevented by ensuring good practices during production and distribution, supported by monitoring line samples by determining the pH and aw and cfu assessment of Staphylococcus aureus and thermotrophic Enterobacteriaceae.

Research paper thumbnail of Harmful effects of selective media on stressed micro-organisms: nature and remedies

Society for Applied Bacteriology symposium series

Research paper thumbnail of Chapter 3 Media for the detection and enumeration of Bacillus cereus in foods

Progress in Industrial Microbiology, 1995

ABSTRACT

Research paper thumbnail of Chapter 12 Culture media for the isolation and enumeration of pathogenic vibrio species in foods and environmental samples

Progress in Industrial Microbiology, 1995

The genus Vibrio now includes a large number of species. Clear evidence is only available for the... more The genus Vibrio now includes a large number of species. Clear evidence is only available for the aetiological role of V. cholerae, V. vulnificus and V. parahaemolyticus in foodborne diseases. Until recently, V. cholerae serogroup 0:1 was accepted as the cause of epidemic cholera. However, the designation of outbreaks of diarrhoeal diseases caused by V. cholerae 0:139 as clinical cholera

Research paper thumbnail of Selection, differentiation and counting of haemolytic Listeria spp. on PALCAM medium

Letters in Applied Microbiology, 1991

ABSTRACT

Research paper thumbnail of An improved selective and diagnostic medium for isolation and counting of Listeria spp. in heavily contaminated foods

Letters in Applied Microbiology, 1988

ABSTRACT

Research paper thumbnail of The enumeration of sublethally injured populations of Staphylococcus aureus in foods

Letters in Applied Microbiology, 1990

ABSTRACT

Research paper thumbnail of Rapid Detection of Excessive CFU Counts of Enterobacteriaceae, S. aureus and Yeasts by Nitrate Reduction/Glucose Dissimilation (NGD) Monitoring in Selective Media

Journal of Food Science, 1987

... 6.1 Strep. faecalis Strep. faecium Ps. fluorescens control control 8.1 7.1 6.1 7.3 7.8 8.0 Mi... more ... 6.1 Strep. faecalis Strep. faecium Ps. fluorescens control control 8.1 7.1 6.1 7.3 7.8 8.0 Minced meat Shrimp Minced meat Shrimp Shrimp Shrimp Minced meat Minced meat Minced meat Minced meat Minced meat Shrimp 1.5 ...

Research paper thumbnail of The Effect of Lactic Acid Decontamination on the Microflora on Meat

Journal of Food Safety, 1994

ABSTRACT Meat acquires a characteristic microflora after slaughter and butchering. This normal mi... more ABSTRACT Meat acquires a characteristic microflora after slaughter and butchering. This normal microflora may be beneficial in that it occupies a niche that would otherwise permit unimpeded growth of potential pathogens. Lactic acid decontamination (LAD) is intended to eliminate pathogens but also affects the normal microflora. The immediate effect was studied by means of an in-vitro model. Experiments using this model achieved a reduction in the mesophilic Enterobacteriaceae on meat by 1 to 3 log10 colony forming units and shifted the predominant microflora in the direction of Gram-positive bacteria and yeasts. Colony counts were an unreliable indicator of LAD-induced reductions in Gramnegative foodborne pathogens. Their reduction depended on the ratio of the more lactic acid resistant Gram-positive bacteria to the more sensitive Gram-negative bacteria. The rank order of lactic acid-resistance of nonpathogens present on meat was yeasts = lactobacilli > psychrotrophic Gram-positive bacteria > mesophilic Enterobacteriaceae. Psychrotrophic Gram-negative bacteria were the most sensitive.

Research paper thumbnail of Fate of low temperature and acid-adapted Yersinia enterocolitica and Listeria monocytogenes that contaminate lactic acid decontaminated meat during chill storage

Journal of Applied Microbiology, 1997

Pathogens found in the environment of abattoirs may become adapted to lactic acid used to deconta... more Pathogens found in the environment of abattoirs may become adapted to lactic acid used to decontaminate meat. Such organisms are more acid tolerant than non-adapted parents and can contaminate meat after lactic acid decontamination (LAD). The fate of acid-adapted Yersinia enterocolitica and Listeria monocytogenes, inoculated on skin surface of pork bellies 2 h after LAD, was examined during chilled storage. LAD included dipping in 1%, 2% or 5% lactic acid solutions at 55 degrees C for 120 s. LAD brought about sharp reductions in meat surface pH, but these recovered with time after LAD at approximately equal to 1-1.5 pH units below that of water-treated controls. Growth permitting pH at 4.8-5.2 was reached after 1% LAD in less than 0.5 d (pH 4.8-5.0), 2% LAD within 1.5 d (pH 4.9-5.1) and after 5% LAD (pH 5.0-5.2) within 4 d. During the lag on 2% LAD meat Y. enterocolitica counts decreased by 0.9 log10 cfu per cm2 and on 5% LAD the reduction was more than 1.4 log10 cfu per cm2. The reductions in L. monocytogenes were about a third of those in Y. enterocolitica. On 1% LAD the counts of both pathogens did not decrease significantly. The generation times of Y. enterocolitica and L. monocytogenes on 2-5% LAD meats were by up to twofold longer than on water-treated controls and on 1% LAD-treated meat they were similar to those on water-treated controls. Low temperature and acid-adapted L. monocytogenes and Y. enterocolitica that contaminate skin surface after hot 2-5% LAD did not cause an increased health hazard, although the number of Gram-negative spoilage organisms were drastically reduced by hot 2-5% LAD and intrinsic (lactic acid content, pH) conditions were created that may benefit the survival and the growth of acid-adapted organisms.

Research paper thumbnail of A note on catalase enhanced recovery of acid injured cells of Gram negative bacteria and its consequences for the assessment of the lethality of L-lactic acid decontamination of raw meat surfaces

Journal of Applied Microbiology, 1984

Addition of catalase (150 units/ml) to a rich infusion agar used for solid medium repair of acid ... more Addition of catalase (150 units/ml) to a rich infusion agar used for solid medium repair of acid injured pathogenic Enterobacteriaceae increased the recovery of such populations by 1-2 log cycles entailing an equal size reduction in the true lethality of this mode of processing for safety.

Research paper thumbnail of A selective and diagnostic medium for use in the enumeration of Listeria spp. in foods

International Journal of Food Microbiology, 1988

A new medium, called RAPAMY agar, has been elaborated for the isolation from and the enumeration ... more A new medium, called RAPAMY agar, has been elaborated for the isolation from and the enumeration of Listeria spp. in foods. It is based on Ralovich's nalidixic acid-trypaflavin-agar with the following modifications: (i) the slight inhibitory properties of that medium were overcome by the use of Columbia Blood agar base instead of tryptose agar and the addition of 0.05% ferric ammonium citrate and 2.5% egg yolk emulsion; (ii) selectivity was improved by the addition of 0.25% 2-phenyl ethanol and incubation under microaerobic conditions; (iii) the medium was provided with two diagnostic traits by the addition of (a) aesculin + ferric ammonium citrate; and (b) D-mannitol and phenol red. The growth of Enterococcus spp., the only organisms other than Listeria spp. which grow on RAPAMY agar, was not inhibited by the addition of 20 microgram.ml-1 Cefoxitin (Moxolactam). Higher levels inhibited some Listeria spp., but not the enterococci. The medium recovered Listeria spp. quantitatively and allowed recovery from foods colonized by Enterococcus spp. at levels upto 10(2) per g.

Research paper thumbnail of Media for the detection and enumeration of Bacillus cereus in foods: a review

International Journal of Food Microbiology, 1992

Bacillus cereus is an established cause of food poisoning in addition to being a troublesome and ... more Bacillus cereus is an established cause of food poisoning in addition to being a troublesome and persistent contaminant, responsible for a variety of spoilage defects in processed foods and dairy products. A range of diagnostic and selective media has been developed to facilitate the detection and enumeration of B. cereus in routine surveillance situations and food poisoning investigations. These media are reviewed with respect to the selective and diagnostic systems they employ, their ability to recover and differentiate the target organism, and their advantages and limitations in particular applications.

Research paper thumbnail of The immediate bactericidal effect of lactic acid on meat-borne pathogens

Journal of Applied Bacteriology, 1994

effect of lactic acid decontamination (LAD) o n meat-borne pathogens (Salmonella spp., Campylobac... more effect of lactic acid decontamination (LAD) o n meat-borne pathogens (Salmonella spp., Campylobacter jejuni and Listeria monocytogenes) was studied in a n in-vitro model. T h e bactericidal effect was greatest on organisms in the lactic acid film that replaced the natural fluid on the meat surface during LAD. A stepwise increase in p H from 2.6 to 3-5 and 4.0 progressively reduced the bactericidal effect of decontamination. For treatment with 2% lactic acid for 3@90 s at 21"C, the immediate death of Salmonella spp. decreased from about 0.5-2 loglo cfu at pH 2.6 to an insignificant level at pH 4.0. T h e immediate death for Camp. jejuni decreased from 2.6 to > 5.3 at pH 2-6 to 0-3-1.0 a t pH 4.0. The decrease in bactericidal effect with increasing pH could, however, be countered by an increase in t h e temperature from 21°C t o 37°C. It is suggested that 2% LAD at 37°C for 30-90 s is suitable for elimination of salmonellas on meat but not for L. monocytogenes. Decontamination with 1% lactic acid at pH 3-0 and 21°C for at least 30 s was effective for Camp. jejuni. Mesophilic Enterobacteriaceae were reliable indicators of the LAD-induced bactericidal effect on Salmonella spp. and Camp. jejuni.

Research paper thumbnail of An in-vitro meat model for the immediate bactericidal effect of lactic acid decontamination on meat surfaces

Journal of Applied Bacteriology, 1994

Research paper thumbnail of Psychrotrophic strains of Bacillus cereus producing enterotoxin

Journal of Applied Bacteriology, 1990

Research paper thumbnail of Culture media for the isolation and enumeration of pathogenic Vibrio species in foods and environmental samples

International Journal of Food Microbiology, 1995

The genus Vibrio now includes a large number of species. Clear evidence is only available for the... more The genus Vibrio now includes a large number of species. Clear evidence is only available for the aetiological role of V. cholerae, V. vulnificus and V. parahaemolyticus in foodborne diseases. Until recently, V. cholerae serogroup 0:1 was accepted as the cause of epidemic cholera. However, the designation of outbreaks of diarrhoeal diseases caused by V. cholerae 0:139 as clinical cholera has lead to renewed interest in Non 0:1 serogroups of V. cholerae. A wide range of enrichment and selective media for the isolation of vibrios has been developed. These media are reviewed with respect to their ability to recover and differentiate the target vibrios. Alkaline peptone water (APW) remains the recommended enrichment medium for vibrios in parallel with either salt polymyxin broth (SPB) or glucose teepol (or sodium dodecylsulphate) salt broth (GTSB) when tests for V. parahaemolyticus are required. Thiosulphate citrate bile salt agar (TCBS) in parallel with polymyxin mannose tellurite (PMT) or sodium dodecylsulphate polymyxin sucrose agar (SPS) are the recommended selective plating media.

Research paper thumbnail of The survival and growth of acid-adapted mesophilic pathogens that contaminate meat after lactic acid decontamination

Journal of Applied Microbiology, 1998

Lactic acid decontamination (LAD) may adapt pathogens to lactic acid. Such organisms may have an ... more Lactic acid decontamination (LAD) may adapt pathogens to lactic acid. Such organisms may have an increased resistance to acid and can contaminate meat after LAD. The survival and growth of acid adapted Campylobacter jejuni, Salmonella typhimurium. Escherichia coli O157:H7 and Staphylococcus aureus inoculated on skin surface of still warm pork belly cuts 2 h after LAD was examined during chilled (4 degrees C) storage and refrigeration abuse equivalent to 12.5 degrees C. Lactic acid decontamination included dipping in 1, 2 or 5% lactic acid solutions at 55 degrees C for 120 s. Lactic acid decontamination brought sharp reductions in meat surface pH, but these recovered with time after LAD at approximately 1-1.5 pH units below that of water-treated controls. A sharp decrease in the number of cfu of pathogens occurred on chilled 2-5% lactic acid treated pork belly cuts when the skin surface was less than pH 4.8-5.2. The reductions ranged from 0.1-0.3 log10 cfu cm-2 for E. coli O157:H7 to over 1.7-2.4 log10 cfu cm-2 for Camp. jejuni, respectively. Increase in storage temperature from 4 to 12.5 degrees C reduced delayed decrease in numbers of all pathogens except Camp. jejuni by a factor of two. Deaths in Camp. jejuni at 12.5 degrees C slightly exceeded those at 4 degrees C. After the initial sharp decline, the number of cfu of mesophilic pathogens decreased gradually at a rate similar to that on water-treated controls. Growth of all mesophilic pathogens except Camp. jejuni on 2-5% LAD meat occurred during storage at 12.5 degrees C when the meat surface pH exceeded 4.8-5.2, and was slower than on water-treated controls. Low temperature and acid-adapted E. coli O157:H7, Salm. typhimurium and Staph. aureus, and acid adapted Camp. jejuni that contaminate skin surface after hot 2-5% LAD, did not cause an increased health hazard, although microbiota and intrinsic parameters (lactic acid content, pH) were created that could advantage their survival and growth.

Research paper thumbnail of A centrifugation/quadrant plate technique for the simplified differential-bacteriological examination of adequately heat-processed foods

Letters in Applied Microbiology, 1991

ABSTRACT

Research paper thumbnail of Microbiological reference values for foods: a European perspective

Journal - Association of Official Analytical Chemists

Microbiological criteria for food products and meals serve to gauge the results obtained upon mon... more Microbiological criteria for food products and meals serve to gauge the results obtained upon monitoring samples from manufacturing plants or catering units which strictly adhere to good manufacturing practices (GMP). Hazardous practices thus already having been eliminated, the aim of monitoring is to detect and, above all, immediately correct accidental failures in processing or preparation. An essential element of this system of monitoring is that the number of criteria used is kept to a minimum by carefully selecting the criteria of major ecological significance. In view of the sporadic and erratic distribution of pathogenic organisms in foods from well-run manufacturing plants and food service operations, criteria for disease agents are used only occasionally. Where they are used, their selection and detection methodology require intensive and expert scrutiny, including (i) careful designation and precise definition of the relevant agents of disease, toxin formers, or preformed toxins; (ii) prescription of very carefully validated and standardized methods, usually including a resuscitation step; and (iii) mathematically correct interpretation of failure to detect particular infectious or toxinogenic organisms. On the other hand, "marker" organisms ("indicator" and "index" organisms, according to Ingram) are frequently used. These should also be carefully selected by ecological surveys on each specific food product; in particular, their value for reliably revealing deficiencies in hygiene or handling should be assessed. The applicability of the entire group of Enterobacteriaceae (or particular parts of that taxon), Enterococcus species, Staphylococcus aureus, and streptococci of the "mitis-salivarius" group are critically examined. Numerical reference values for microbiological criteria are derived by mathematical treatment from data obtained in surveys of products produced under GMP previously validated by safety analysis. Target values thus derived will include tolerance limits and policies recommended in case high results are obtained. Consequently, "3-class sampling plans" (according to ICMSF) are to be used in most instances.

Research paper thumbnail of A small outbreak of salmonellosis caused by Bologna sausage

Tijdschrift voor diergeneeskunde

Late in August 1985, seventeen subjects in the 3-40 year range contracted salmonellosis which was... more Late in August 1985, seventeen subjects in the 3-40 year range contracted salmonellosis which was associated with the consumption of fermented pork sausage prepared by a butcher. The incubation period varied from 6 to 9 hours, the attack rate was a hundred per cent; there were no deaths or complications. The pH of the incriminated sausage was 5.7 (the pH of controls ranged from 4.5 to 5.0), and the aw was 0.99 (vs. 0.92-0.97 in the controls), a colony count of thermotrophic Enterobacteriaceae was 10(7) per 1 g, including c. 10(6) of Salmonella typhimurium, c. 10(3) Staphylococcus aureus and c. 10(4) cfu of Clostridium perfringes per 1 g. These outbreaks may be prevented by ensuring good practices during production and distribution, supported by monitoring line samples by determining the pH and aw and cfu assessment of Staphylococcus aureus and thermotrophic Enterobacteriaceae.

Research paper thumbnail of Harmful effects of selective media on stressed micro-organisms: nature and remedies

Society for Applied Bacteriology symposium series

Research paper thumbnail of Chapter 3 Media for the detection and enumeration of Bacillus cereus in foods

Progress in Industrial Microbiology, 1995

ABSTRACT

Research paper thumbnail of Chapter 12 Culture media for the isolation and enumeration of pathogenic vibrio species in foods and environmental samples

Progress in Industrial Microbiology, 1995

The genus Vibrio now includes a large number of species. Clear evidence is only available for the... more The genus Vibrio now includes a large number of species. Clear evidence is only available for the aetiological role of V. cholerae, V. vulnificus and V. parahaemolyticus in foodborne diseases. Until recently, V. cholerae serogroup 0:1 was accepted as the cause of epidemic cholera. However, the designation of outbreaks of diarrhoeal diseases caused by V. cholerae 0:139 as clinical cholera

Research paper thumbnail of Selection, differentiation and counting of haemolytic Listeria spp. on PALCAM medium

Letters in Applied Microbiology, 1991

ABSTRACT

Research paper thumbnail of An improved selective and diagnostic medium for isolation and counting of Listeria spp. in heavily contaminated foods

Letters in Applied Microbiology, 1988

ABSTRACT

Research paper thumbnail of The enumeration of sublethally injured populations of Staphylococcus aureus in foods

Letters in Applied Microbiology, 1990

ABSTRACT

Research paper thumbnail of Rapid Detection of Excessive CFU Counts of Enterobacteriaceae, S. aureus and Yeasts by Nitrate Reduction/Glucose Dissimilation (NGD) Monitoring in Selective Media

Journal of Food Science, 1987

... 6.1 Strep. faecalis Strep. faecium Ps. fluorescens control control 8.1 7.1 6.1 7.3 7.8 8.0 Mi... more ... 6.1 Strep. faecalis Strep. faecium Ps. fluorescens control control 8.1 7.1 6.1 7.3 7.8 8.0 Minced meat Shrimp Minced meat Shrimp Shrimp Shrimp Minced meat Minced meat Minced meat Minced meat Minced meat Shrimp 1.5 ...

Research paper thumbnail of The Effect of Lactic Acid Decontamination on the Microflora on Meat

Journal of Food Safety, 1994

ABSTRACT Meat acquires a characteristic microflora after slaughter and butchering. This normal mi... more ABSTRACT Meat acquires a characteristic microflora after slaughter and butchering. This normal microflora may be beneficial in that it occupies a niche that would otherwise permit unimpeded growth of potential pathogens. Lactic acid decontamination (LAD) is intended to eliminate pathogens but also affects the normal microflora. The immediate effect was studied by means of an in-vitro model. Experiments using this model achieved a reduction in the mesophilic Enterobacteriaceae on meat by 1 to 3 log10 colony forming units and shifted the predominant microflora in the direction of Gram-positive bacteria and yeasts. Colony counts were an unreliable indicator of LAD-induced reductions in Gramnegative foodborne pathogens. Their reduction depended on the ratio of the more lactic acid resistant Gram-positive bacteria to the more sensitive Gram-negative bacteria. The rank order of lactic acid-resistance of nonpathogens present on meat was yeasts = lactobacilli > psychrotrophic Gram-positive bacteria > mesophilic Enterobacteriaceae. Psychrotrophic Gram-negative bacteria were the most sensitive.

Research paper thumbnail of Fate of low temperature and acid-adapted Yersinia enterocolitica and Listeria monocytogenes that contaminate lactic acid decontaminated meat during chill storage

Journal of Applied Microbiology, 1997

Pathogens found in the environment of abattoirs may become adapted to lactic acid used to deconta... more Pathogens found in the environment of abattoirs may become adapted to lactic acid used to decontaminate meat. Such organisms are more acid tolerant than non-adapted parents and can contaminate meat after lactic acid decontamination (LAD). The fate of acid-adapted Yersinia enterocolitica and Listeria monocytogenes, inoculated on skin surface of pork bellies 2 h after LAD, was examined during chilled storage. LAD included dipping in 1%, 2% or 5% lactic acid solutions at 55 degrees C for 120 s. LAD brought about sharp reductions in meat surface pH, but these recovered with time after LAD at approximately equal to 1-1.5 pH units below that of water-treated controls. Growth permitting pH at 4.8-5.2 was reached after 1% LAD in less than 0.5 d (pH 4.8-5.0), 2% LAD within 1.5 d (pH 4.9-5.1) and after 5% LAD (pH 5.0-5.2) within 4 d. During the lag on 2% LAD meat Y. enterocolitica counts decreased by 0.9 log10 cfu per cm2 and on 5% LAD the reduction was more than 1.4 log10 cfu per cm2. The reductions in L. monocytogenes were about a third of those in Y. enterocolitica. On 1% LAD the counts of both pathogens did not decrease significantly. The generation times of Y. enterocolitica and L. monocytogenes on 2-5% LAD meats were by up to twofold longer than on water-treated controls and on 1% LAD-treated meat they were similar to those on water-treated controls. Low temperature and acid-adapted L. monocytogenes and Y. enterocolitica that contaminate skin surface after hot 2-5% LAD did not cause an increased health hazard, although the number of Gram-negative spoilage organisms were drastically reduced by hot 2-5% LAD and intrinsic (lactic acid content, pH) conditions were created that may benefit the survival and the growth of acid-adapted organisms.

Research paper thumbnail of A note on catalase enhanced recovery of acid injured cells of Gram negative bacteria and its consequences for the assessment of the lethality of L-lactic acid decontamination of raw meat surfaces

Journal of Applied Microbiology, 1984

Addition of catalase (150 units/ml) to a rich infusion agar used for solid medium repair of acid ... more Addition of catalase (150 units/ml) to a rich infusion agar used for solid medium repair of acid injured pathogenic Enterobacteriaceae increased the recovery of such populations by 1-2 log cycles entailing an equal size reduction in the true lethality of this mode of processing for safety.

Research paper thumbnail of A selective and diagnostic medium for use in the enumeration of Listeria spp. in foods

International Journal of Food Microbiology, 1988

A new medium, called RAPAMY agar, has been elaborated for the isolation from and the enumeration ... more A new medium, called RAPAMY agar, has been elaborated for the isolation from and the enumeration of Listeria spp. in foods. It is based on Ralovich's nalidixic acid-trypaflavin-agar with the following modifications: (i) the slight inhibitory properties of that medium were overcome by the use of Columbia Blood agar base instead of tryptose agar and the addition of 0.05% ferric ammonium citrate and 2.5% egg yolk emulsion; (ii) selectivity was improved by the addition of 0.25% 2-phenyl ethanol and incubation under microaerobic conditions; (iii) the medium was provided with two diagnostic traits by the addition of (a) aesculin + ferric ammonium citrate; and (b) D-mannitol and phenol red. The growth of Enterococcus spp., the only organisms other than Listeria spp. which grow on RAPAMY agar, was not inhibited by the addition of 20 microgram.ml-1 Cefoxitin (Moxolactam). Higher levels inhibited some Listeria spp., but not the enterococci. The medium recovered Listeria spp. quantitatively and allowed recovery from foods colonized by Enterococcus spp. at levels upto 10(2) per g.

Research paper thumbnail of Media for the detection and enumeration of Bacillus cereus in foods: a review

International Journal of Food Microbiology, 1992

Bacillus cereus is an established cause of food poisoning in addition to being a troublesome and ... more Bacillus cereus is an established cause of food poisoning in addition to being a troublesome and persistent contaminant, responsible for a variety of spoilage defects in processed foods and dairy products. A range of diagnostic and selective media has been developed to facilitate the detection and enumeration of B. cereus in routine surveillance situations and food poisoning investigations. These media are reviewed with respect to the selective and diagnostic systems they employ, their ability to recover and differentiate the target organism, and their advantages and limitations in particular applications.