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R R Beumer

Publications and source records attributed to R R Beumer.

33 records · Page 2Linked to original sources
PubMed1996

Confirmation and identification of Listeria spp.

All confirmation and identification methods used in this study can be used for the screening of suspected colonies on isolation media for Listeria spp. In traditional enrichment procedures the Microscreen Listeria latex test gives fast results. The DNA probes (Accuprobe and Gene-Trak) are very specific in detecting Listeria monocytogenes. For identification of Listeria spp. both tests (API and Micro-ID) performed equally well. Preference may be given to the API test, since differentiation of L. monocytogenes from L. innocua is based on the absence of arylamidase, through which tests for haemolytic activity and/or CAMP reactions can be omitted. However, the use of Enhanced Haemolysis Agar as isolation medium makes further testing essentially superfluous, since L. monocytogenes strains can be differentiated from L. innocua.

DNA Probes↗
PubMed1995

Antibiotic susceptibility of campylobacter isolates from sewage and poultry abattoir drain water.

In this study, the in vitro susceptibility of 209 campylobacter strains to the quinolones nalidixic acid, flumequine, ciprofloxacin, enrofloxacin, and to ampicillin, tetracycline and erythromycin was tested by the disk diffusion method. The strains were isolated from poultry abattoir effluent (DWA) and two sewage purification plants (SPA and SPB). Sewage purification plant SPA received mixed sewage, including that from a poultry abattoir, whereas SPB did not receive sewage from any meat-processing industry. The quinolone resistance of the DWA isolates ranged from 28% for enrofloxacin to 50% for nalidixic acid. The strains isolated from the sewage purification plants were more susceptible to the quinolones with a range of 11-18% quinolone resistance for SPB isolates to 17-33% quinolone resistance for SPA isolates. The susceptibility criteria as recommended by National Committee Clinical Laboratory Standards (USA) cannot readily be employed for campylobacter isolates. This investigation shows that the resistance of campylobacter bacteria is highest in the plant receiving sewage from a poultry slaughterhouse. Monitoring of antibiotic resistance of aquatic Campylobacter spp. is important, as surface waters are recognized as possible sources of infection.

Abattoirs↗
PubMed1995

Temperature-dependent membrane fatty acid and cell physiology changes in coccoid forms of Campylobacter jejuni.

The effect of temperature and the availability of nutrients on the transition of spiral Campylobacter jejuni cells to coccoid forms was investigated. Ageing of spiral C. jejuni cells in either nutrient-poor or nutrient-rich environments resulted in the formation of nonculturable coccoid cells at 4, 12, and 25 degrees C after different periods, with the cells incubated at 4 degrees C in nutrient-deficient media remaining culturable the longest. To study the phenomenon, ATP levels, protein profiles, and fatty acid compositions were monitored under conditions where the transition from spiral to coccoid cells occurred. During storage, the levels of intracellular ATP were highest in cells incubated at low temperatures (4 and 12 degrees C) and remained constant after a small initial decrease. During the transformation from spiral to coccoid forms, no alteration in protein profiles could be detected; indeed, inhibition of protein synthesis by chloramphenicol did not influence the transition. Furthermore, DNA damage by gamma irradiation had no effect on the process. Membrane fatty acid composition of cocci formed at low temperatures was found to be almost identical to that of spiral cells, whereas that of cocci formed at 25 degrees C was clearly different. Combining these results, it is concluded that the formation of cocci is not an active process. However, distinctions between cocci formed at different temperatures were observed. Cocci formed at 4 degrees C show characteristics comparable to those of spirals, and these cocci may well play a role in the contamination cycle of C. jejuni.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1995

An ATP-dependent L-carnitine transporter in Listeria monocytogenes Scott A is involved in osmoprotection.

Listeria monocytogenes is a gram-positive, psychotrophic, food-borne pathogen which is able to grow in osmotically stressful environments. Carnitine (beta-hydroxy-L-tau-N-trimethyl aminobutyrate) can contribute significantly to growth of L. monocytogenes at high osmolarity (R. R. Beumer, M. C. te Giffel, L. J. Cox, F. M. Rombouts, and T. Abee, Appl. Environ. Microbiol. 60:1359-1363, 1994). Transport of L-[N-methyl-14C]carnitine in L. monocytogenes was shown to be energy dependent. Analysis of cell extracts revealed that L-carnitine was not further metabolized, which supplies evidence for its role as an osmoprotectant in L. monocytogenes. Uptake of L-carnitine proceeds in the absence of a proton motive force and is strongly inhibited in the presence of the phosphate analogs vanadate and arsenate. The L-carnitine permease is therefore most likely driven by ATP. Kinetic analysis of L-carnitine transport in glucose-energized cells revealed the presence of a high-affinity uptake system with a Km of 10 microM and a maximum rate of transport (Vmax) of 48 nmol min-1 mg of protein-1. L-[14C]carnitine transport in L. monocytogenes is significantly inhibited by a 10-fold excess of unlabelled L-carnitine, acetylcarnitine, and tau-butyrobetaine, whereas L-proline and betaine display, even at a 100-fold excess, only a weak inhibitory effect. In conclusion, an ATP-dependent L-carnitine transport system in L. monocytogenes is described, and its possible roles in cold adaptation and intracellular growth in mammalian cells are discussed.

Adenosine Triphosphate↗
PubMed1994

Effect of exogenous proline, betaine, and carnitine on growth of Listeria monocytogenes in a minimal medium.

Three Listeria monocytogenes strains isolated from food or food-processing environments were used to assess the response of this species to salinity in a chemically defined minimal medium. Growth in a minimal medium containing five essential amino acids and glucose as a carbon and energy source was comparable to growth in a rich medium (brain heart infusion broth). In the absence and presence of 3% NaCl the final cell numbers reached in minimal medium were 10(9) and 10(7) CFU/ml, respectively. Growth under the latter conditions could not be detected by spectrophotometry by measuring A660. Apparently, this technique was not suitable for these experiments since the detection level was > 10(7) CFU/ml. Exogenously added proline (10 mM), trimethylglycine (betaine) (1 mM), and beta-hydroxy-gamma-N-trimethyl aminobutyrate (carnitine) (1 mM) significantly stimulated growth under osmotic stress conditions in minimal medium at both 37 and 10 degrees C. Betaine and carnitine are present in foods derived from plants and animals, respectively. Therefore, these compounds can contribute significantly to growth of L. monocytogenes in various foods at high osmolarities.

Amino Acids↗
PubMed1992

Isolation of salmonellas by immunomagnetic separation.

Magnetisable particles, coated with anti-salmonella serum, were used to isolate Salmonella livingstone from pure cultures, mixed cultures and food samples. Beads (10(7] were generally incubated with 10(4) Salm. livingstone cells/ml for 60 min at room temperature. The incubation and washing medium (0.01 mol/l phosphate-buffered saline; PBS) contained 0.1% bovine serum albumin (BSA) and 0.1% Tween 20, respectively. This method gave a recovery for Salm. livingstone of 51.0 +/- 7.8%. However, other micro-organisms such as Aeromonas hydrophila interfered with this test because of non-specific reactions (recovery 50.9 +/- 12.7%). These non-specific reactions could be decreased by using 4% skim milk instead of 0.1% BSA in the incubation medium. The ratio of the recovery of Salm. livingstone relative to the recovery of Aer. hydrophila changed from 0.9 when PBS with 0.1% BSA was used, to 13.4 when PBS with 4% skim milk was used. Immunomagnetic separation of Salmonella spp. from food samples offers good prospects for concentrating salmonella cells from heterogeneous bacterial suspensions, such as enrichment broths.

Culture Media↗
PubMed1991

Enzyme-linked immunoassays for the detection of Salmonella spp.: a comparison with other methods.

The first enzyme immunoassay for Salmonella was reported in 1977 and since that time several enzyme-linked immuno assays (ELISAs) have been developed, using either polyclonal or monoclonal antibodies that will detect most Salmonella serotypes. Two of these kits have been declared official first status by the Association of Official Analytical Chemists (AOAC). In comparison with a culture method used in collaborative studies, the total assay time is reduced by 2 days and statistical analysis of the data indicated no significant difference. The main problem related to all methods other than traditional culture methods is the occurrence of false-positive and/or false-negative results. False-positive ELISA results can be eliminated by using (combinations of) highly specific monoclonal antibodies. Good enrichment procedures are very important to be sure that the detection limit of approx. 10(5) cells/ml will be reached. In the future even better limits of detection may be achieved by using enzyme amplification or chemiluminescence to decrease the number of false-negative results.

Enzyme-Linked Immunosorbent Assay↗
PubMed1988

The occurrence of Campylobacter jejuni in raw cows' milk.

Faeces and raw milk from individual cows were examined for the presence of Campylobacter jejuni. After drawing milk, the lactoperoxidase system was inactivated by raising the pH to 7.5. The organism was isolated from 22% of 904 faecal samples and from 4.5% of 904 milk samples. From laboratory experiments it could be concluded that inactivation of the lactoperoxidase system resulted in a better isolation of C. jejuni from raw cows' milk.

Animals↗
PubMed1982

[Microbiological studies of beef tartar].

Two hundred lots of 'filet américain' (a mixture of minced meat, acid sauce, condiments, salt, etc., meant to be eaten raw) were sampled from retailers and examined for several types of micro-organism; 185 lots had been prepared by the retailer, fifteen on an 'industrial' scale. Pork had been used in seventy-three lots (including fourteen 'industrial' lots); beef was present in all lots, horse meat in none of them. On the whole, the bacterial state of the meats in which pork had been used was found to be considerably inferior to that of samples not containing this ingredient. The aerobic bacterial count and number of yeasts, as well as Enterobacteriaceae and group D. streptococci were at least 10 times higher on an average in this case than they were in lots not containing pork. In the case of Lactobacillus, Staphylococcus aureus and Clostridium perfringens the picture was similar, though the counts of the two lastnamed species were smaller. Salmonella was detected in 84 per cent of the pork-containing lots and in 13 per cent of the other lots. For Yersinia enterocolitica, these figures were 44 per cent and 5 per cent, and for Campylobacter fetus, subsp, jejuni 18 per cent and 6 per cent. The pH varied from 5 to 6. Lots containing pork averaged a higher pH. Addition of acid sauce had only a slight effect on pH levels. A number of these results were related to each other. It is concluded that the use of raw pork in meat products meant for raw consumption should be avoided.

Animals↗
PubMed1982

Microbiological studies on hamburgers.

One hundred and eighty-two raw, 112 pre-cooked and 750 cooked hamburgers composed mainly of beef or beef and pork were subjected to microbiological examination.Raw hamburgers gave total bacterial counts from 10(6) to 10(8) per g, counts of Enterobacteriaceae from 10(4) to 10(6) per g, of Escherichia coli from 10(3) to 10(5), of group D streptococci from 10(2) to 10(4), of Staphylococcus aureus from 3 to 10(2) and of Clostridium perfringens less than 10 bacteria per g. Of the samples, 32% contained salmonellas; the highest most probable number was 10(2) per g but most estimates were below 1 per g. Corresponding figures for the pre-cooked samples were 2-3 log cycles lower, and only one sample contained salmonella. Yersinia enterocolitica was not isolated from any raw or pre-cooked sample.Three hundred and ninety-five of the cooked hamburgers were prepared by grilling raw hamburgers for between 2 and 5.5 min. These gave total bacterial counts from 10(5) to 10(7) per g, and counts of Enterobacteriaceae from 10(2) to 10(5) per g. Of the samples, 9.4% contained salmonellas, always in numbers below 1 per g. The remaining 355 cooked hamburgers were prepared from samples pre-cooked for 10 min at 80 degrees C. Some were grilled and some fat fried. The total bacterial counts were from 10(3) to 10(5) per g, and counts of Enterobacteriaceae below 10(2) per g. Salmonellae, again in small numbers only, were recovered from 3.5% of samples.When hamburgers were artificially contaminated with Salmonella typhimurium it took 5.5 min on a commercial grill, 2.25 min frying in a frying pan and 1.75 min on a household grill to reliably reduce the salmonella count one hundredfold. This means that at many vending places hamburgers are often cooked for too short a time.D-values were determined for S. typhimurium in hamburger meat at 50, 55, 60, 65 and 70 degrees C, these values were 7.1, 5.1, 1.2, 0.9 and 0.6 min respectively. It can be concluded that the heating action in the centre of the hamburgers will take place more slowly than in the hamburger as a whole, and that the time between cooking and consumption is very important in reducing the microbial load to acceptable levels.Pre-cooking (10 min at 80 degrees C in a water bath) gives a reduction in the numbers of salmonella of about 4 x 10(3), after which cooking gives a further reduction as mentioned above.

Animals↗
PubMed1978

The hygienic quality of vegetables grown in or imported into the Netherlands: a tentative survey.

Samples of 61 home grown and 199 imported vegetables of different varieties were examined for Escherichia coli, faecal streptococci and, when E. coli was present, for salmonellas. Eleven per cent of samples contained greater than 10(4) E. coli per 100 g, and 14% greater than 10(6) faecal streptococci per 100 g. Salmonellas were isolated from 23 out of 103 samples examined. Salmonellas were isolated from 8% of 76 samples with E. coli less than 10(4)/100 g, but from 63% of 27 samples with E. coli exceeding 10(4)/100 g; from 6% of 65 samples containing less than 10(6) faecal streptococci/100 g but from 51% of 37 samples containing more than 10(6)/100 g. S. typhi was isolated from one sample of vegetables imported from the tropics. To our knowledge this is the first isolation of S. typhi from food in the Netherlands. Products from tropical countries were found to present the highest level of contamination. The hygienic quality of Dutch products is sometimes inferior to that of similar imported products, although the different seasons of sampling may have influenced the result. For the prevention of risk to the consumer of vegetables, good kitchen hygiene would appear to be the most important factor.

Escherichia coli↗
PubMed1977

Survival of Salmonella eastbourne and Salmonella typhimurium in milk chocolate prepared with artificially contaminated milk powder.

Milk chocolate mass containing salmonellas was prepared by mixing artificially contaminated milk powder with the other ingredients at a temperature of about 40 degrees C. From this mass bars were made. Two series were prepared, with S. eastbourne and S. typhimurium respectively. The number of surviving salmonellas was counted after various periods of storage, up to 19 months. S. eastbourne was reduced in numbers during 19 months from an initial count of ca. 3 x 10(4) to ca. 3 x 10(2) per 100 g of chocolate. S. typhimurium died off more rapidly, and was not detectable in about 55 g after 15 months, in spite of an initial count of ca. 10(5) per 100 g.In these experiments the salmonellas in the milk powder had had to survive the spraying procedure and the adverse conditions in the dried powder. This may be the reason why S. eastbourne showed a distinctly better survival on storage than the same serotype showed in previous experiments in which the organism was added as a broth culture to the chocolate mix. With S. typhimurium, however, such a difference was hardly detectable.Possible explanations of these results are discussed.

Animals↗
PubMed1976

Survival of Salmonella east bourne and Salmonella typhimurium in chocolate.

Experiments were carried out to assess the reduction rate of two salmonella strains (S. eastbourne and S. typhimurium) in chocolate bars. After artificial contamination of chocolate, after 'conching', with about 10(6) S. eastbourne/g. this organism was still recovered after 9 months storage. The strain of S. typhimurium was less resistant. Both serotypes died off more rapidly in bitter chocolate than in milk chocolate. After contamination with a smaller dose (about 10(3)/g.) with these two serotypes, similar differences were observed.

Cacao↗
PubMedDate not supplied

Campylobacter jejuni non-culturable coccoid cells.

The behaviour of Campylobacter jejuni in the environment is poorly documented. Rapid loss of viability on culture media is reported. This phenomenon is associated with the development of so-called coccoid cells. It has been suggested that these cells can be infective to animals and man. Results obtained with ATP-measurements of coccoid cells and Direct Viable Count (DVC) support this hypothesis. Introduction of coccoid cells into simulated gastric, ileal and colon environments did not result in the presence of culturable cells. Oral administration to laboratory animals and volunteers caused no typical symptoms of campylobacteriosis. Until 30 days after uptake of the cells antibodies against C. jejuni could not be detected in the blood, and the presence of this microorganism in stool samples could not be demonstrated.

Adenosine Triphosphate↗