PubMed Health⌕ Search

Biomedical subjects

M W Griffiths

Publications and source records attributed to M W Griffiths.

At least 55 records · Page 3Linked to original sources
PubMed1998

Rapid monitoring method to assess efficacy of sanitizers against Pseudomonas putida biofilms.

Biofilms of luminescent Pseudomonas putida were developed on rubber surfaces by incubation in brain heart infusion (BHI) broth. Scanning electron microscopy (SEM) and epifluorescence microscopy (EFM) were used to examine biofilm formation. To test the efficacy of two sanitizers commonly employed in dairy plants for CIP (cleaning in place) procedures, a novel bioluminescence method and aerobic plating were used to enumerate cells. Immediately after the sanitizer treatments an apparent 5-log reduction of biofilm-associated cells was determined. However, when the samples were resuscitated for 18 h in BHI broth, high numbers of cells were detected which reached levels close to those of nontreated controls. The results demonstrated that neither sanitizer could completely eliminate biofilm-associated P. putida. The microbial bioluminescence method proved to be the best way for assessing effectiveness of sanitizers against microbial biofilms.

Biofilms↗
PubMed1997

Detection of pathogenic Yersinia enterocolitica in milk and pork using a DIG-labelled probe targeted against the yst gene.

A PCR-amplified, digoxigenin (DIG)-labelled yst probe was evaluated in naturally and artificially contaminated pork and milk samples for its ability to detect and differentiate between pathogenic and nonpathogenic strains of Yersinia enterocolitica following enrichment in irgasan-ticarcillin-chlorate (ITC) enrichment broth. A total of 44 raw pork samples were obtained from one meat-processing factory and two local retail stores. Y. enterocolitica serogroup O:3/biovar 4 was isolated from 6 of the 44 (14%) pork samples tested. The hybridization results were in good agreement when compared with those from standard biochemical and serological tests. The lowest concentration detectable by a colony hybridization technique in the milk samples inoculated with Y. enterocolitica O:8 PA-A corresponded to 10 cfu/ml in the original sample. No pathogenic serovars were detected in 6 raw milk and 3 pasteurized milks tested. The results of this investigation demonstrate that the DIG-labelled yst probe is a reliable tool for rapid detection of pathogenic Y. enterocolitica in naturally and artificially contaminated food samples.

Animals↗
PubMed1997

Infection and removal of L-forms of Listeria monocytogenes with bred bacteriophage.

Phage breeding was employed to produce a bacteriophage (Listeria monocytogenes phage ATCC 23074-B1) which was specific for L-forms of L. monocytogenes. The bred phage was compared to its unbred parent for lytic activity and specificity. It was also tested for its ability to prevent L-form biofilm formation on stainless steel and compared with an organic acid (lactic) at L-form biofilm inactivation on stainless steel. The bred phage lysed only L-forms of L. monocytogenes in broth culture and only plaqued on L-form lawns. Likewise, the unbred phage performed similarly with classical cell-walled culture and lawns. The bred phage successfully inhibited L-form biofilm formation on stainless steel and was as successful as lactic acid (130 ppm) at inactivating pre-formed L-form biofilms. Both reduced viable cell numbers by 3-long cycles over a 6 h period. It appears that phage breeding technology may be an attractive alternative to chemical sanitizers which lack specificity and can be toxic.

Bacteriophages↗
PubMed1997

The determination of efficacy of antimicrobial rinses on turkey carcasses using response surface designs.

Chlorine, lactic acid. TSP (trisodium phosphate) and a commercial phosphate blend (Avgard) were evaluated for their potential bactericidal effects on faecally contaminated turkey carcasses. Carcasses were sprayed for 10 s with each bactericide, at various concentrations and pressure combinations, derived from a response surface central composite design. For all the bactericides, variation in pressure had no significant (P > 0.05) effect in reducing either total or coliform counts. Lactic acid at various concentrations showed a significant effect (P < 0.20) in reducing total and coliform counts. The results indicate that lactic acid at 4.25% (w/w) has the potential for reducing the total microbial load and coliforms by more than 95%. Chlorine, TSP and Avgard concentration did not significantly (P > 0.20) affect the microbial load when compared with a water spray, i.e. no bactericide. Preliminary presumptive testing indicated that lactic acid and Avgard had some effect against Salmonella spp. Chlorine and TSP, irrespective of concentration and pressure, were not effective against Salmonella spp. Overall, these findings suggest that lactic acid was the most effective bactericide for reducing microbial contamination and improving the safety of poultry meat.

Animals↗
PubMed1997

Development of a highly specific assay for rapid identification of pathogenic strains of Yersinia enterocolitica based on PCR amplification of the Yersinia heat-stable enterotoxin gene (yst).

The chromosomal gene yst, which encodes a heat-stable enterotoxin of Yersinia enterocolitica, is a useful diagnostic marker because it occurs only in invasive strains of this species. A homologous gene also occurs in some strains of Yersinia kristensenii. Sequence analysis of the yst genes from two different strains of Y. enterocolitica and from Y. kristensenii revealed a substantial number of mismatches at the 3' ends of the yst genes of the so-called American and European biotypes of Y. enterocolitica. Moreover, several mismatches and a deletion of 5 codons were found in the yst of Y. kristensenii. These findings were used to develop a PCR-based assay for yst of Y. enterocolitica which yielded a detectable product in as little as 50 min. The assay was 100% specific in terms of its ability to identify potentially pathogenic strains of Y. enterocolitica regardless of biotype or serotype. The PCR yielded an amplicon that was visible on agarose gel electrophoresis from as few as 100 CFU, or 10 CFU when the PCR was combined with dot blot hybridization with a digoxigenin-labeled oligonucleotide probe that corresponded to an internal sequence of yst. These results establish the value of the yst gene as a target for the identification of pathogenic bioserotypes of Y. enterocolitica and the usefulness of PCR for this purpose.

Amino Acid Sequence↗
PubMed1996

Luminescent Salmonella strains as real time reporters of growth and recovery from sublethal injury in food.

LuxA and luxB genes from V. harveyi carried by a Tn-5 containing plasmid were introduced into S. enteritidis by either conjugation or electroporation. Lux genes were used as a reporter to indicate the effects of heat treatment (50 degrees C, 55 degrees C and 65 degrees C) and pH (from 1 to 7) on the survival, growth and recovery of Salmonella cells. When a luminescent S. enteritidis strain, obtained by electroporation, was subjected to a plasmid curing procedure, the resulting culture lost the plasmid but remained luminescent. Southern hybridization was performed to determine the location of lux genes in S. enteritidis cells. The light output from recombinant cultures with different gene locations was compared and found to be higher for strains in which the luciferase was plasmid-mediated. The luminescent Salmonella culture was inoculated in food samples such as homogenized chicken meat, whole liquid eggs and fluid milk and development of luminescence with time was monitored. The minimum number of Salmonella cells required for positive observation was approximately 1 x 10(2) CFU/ml in broth and homogenized meat cultures, 2 x 10(3) CFU/ml in fluid milk and 7 x 10(3) CFU/ml in whole liquid egg.

Food Microbiology↗
PubMed1996

Prevalence, detection and control of Cryptosporidium parvum in food.

The role of Cryptosporidium parvum as a foodborne pathogen has not been well documented. Epidemiological features of this parasitic protozoon lead to the assumption that the incidence of cryptosporidiosis due to contaminated food is under-estimated. The high prevalence of C. parvum among dairy herds has increased the spread of oocysts in the farm environment, and their potential presence in raw milk and other raw foods. In October 1993, the first well-documented foodborne outbreak was reported in Maine, USA, and was caused by contaminated hand-pressed apple cider. Although various cases of cryptosporidiosis among humans have pointed to raw milk and other raw foods as possible sources of infection, a conclusive demonstration of foodborne cryptosporidiosis has rarely been established. The limited numbers of oocysts in the suspected samples and the lack of sensitive detection methods adapted for oocyst detection in food contribute to this under-reporting. This review paper discusses various aspects of Cryptosporidium spp. and cryptosporidiosis, including the routes of transmission, the control of oocysts in food, and the available detection methods. The polymerase chain reaction (PCR) combined with DNA probe hybridization is a promising detection method. Recent knowledge on the molecular biology of the parasite for the development of new PCR assays and their potential use in the detection of C. parvum in food are described.

Animals↗
PubMed1996

In vivo bioluminescence to detect the attachment of L-forms of Listeria monocytogenes to food and clinical contact surfaces.

A bioluminescent phenotype of Listeria monocytogenes was employed to study the adhesion and biofilm formation of both classical and L-forms to relevant food and clinical contact surfaces. Attachment of both parental (cell-walled) and L-forms to intravenous tubing and stainless steel was compared using viable counts and bioluminescence. Both cell types attached themselves to intravenous tubing and stainless steel. Parental cell numbers attached to intravenous tubing were 1 log higher than L-form numbers, and on stainless steel, attached L-form numbers were 1 log higher. Bioluminescence measurements yielded a pattern similar to viable count measurements. There was a clear relationship between light output of attached bacteria and their viability and, thus, a bioluminescent phenotype provides a rapid monitor of both microbial viability and biofilm formation by L-forms.

Bacterial Adhesion↗
PubMed1996

Epidemiological typing of Bacillus spp. isolated from food.

Biotypes, fatty acid profiles, and restriction fragment length polymorphisms of a PCR product (PCR-RFLP of the cereolysin AB gene) were compared for 62 isolates of the Bacillus cereus group. Eleven isolates originated from various foods, and 51 isolates were obtained from pasteurized milk which had been processed by two different dairies. The isolates were clustered into 6 biotypes, 10 fatty acid groups, or 7 PCR-RFLP clusters. Isolates with mesophilic or psychrotrophic characteristics were preferentially distributed into specific fatty acid or PCR-RFLP groups (P = 0.004). Unique fatty acid clusters were predominantly found in milk samples of each dairy (P < 0.0001), suggesting that certain dairy plants may harbor plant-specific B. cereus which might constantly contribute to postpasteurization contamination.

Animals↗
PubMed1996

Detection of Cryptosporidium parvum in raw milk by PCR and oligonucleotide probe hybridization.

Cryptosporidium spp. are potential contaminants of food. Suspected cases of food-borne cryptosporidiosis are rarely confirmed because of the limited numbers of oocysts in the samples and the lack of sensitive detection methods adaptable to food. PCR was investigated as a means of overcoming this problem. A PCR assay was designed for the specific amplification of a previously sequenced portion of an oocyst protein gene fragment of Cryptosporidium parvum (N. C. Lally, G. D. Baird, S. J. McQuay, F. Wright, and J. J. Oliver, Mol. Biochem. Parasitol. 56:69-78, 1992) and compared with the primer set of Laxer et al. (M. A. Laxer, B. K. Timblin, and R. J. Patel, Am. J. Trop. Med. Hyg. 45:688-694, 1991). The PCR products were hybridized with digoxigenin-labeled internal probes and detected by chemiluminescence to enhance sensitivity. The two sets of primers were compared with regard to their sensitivity and specificity by using a variety of human and animal isolates of C. parvum and related parasites. Both assays enabled the detection of 1 to 10 oocysts in 20 ml of artificially contaminated raw milk. The assay based on the PCR set and probe of Laxer et al. detected DNAs from Eimeria acervulina and Giardia intestinalis. The new assay has good specificity for C. parvum bovine isolates and hence has a better potential for monitoring the prevalence of C. parvum in raw milk and other environmental samples.

Animals↗
PubMed1995

Specific oligonucleotide primers for detection of lecithinase-positive Bacillus spp. by PCR.

An assay based on the PCR has been developed to facilitate detection and identification of Bacillus cereus in foods. Three primers for the PCR have been designed within the sequence for cereolysin AB, a cytolytic determinant that encodes lecithin-hydrolyzing and hemolytic activities of B. cereus. With the PCR and hybridization, the specificity of the primers was tested with 39 isolates of the B. cereus group, with 17 other Bacillus spp., and with 21 non-Bacillus strains. Results demonstrate a high specificity of the three oligonucleotides for isolates of the B. cereus group. With a combined PCR-hybridization assay, the detection limit for B. cereus in artificially contaminated milk was 1 CFU/ml of milk.

Bacillus cereus↗
PubMed1994

Predictive modelling: applications in the dairy industry.

Predictive modelling has been used in the dairy industry for determining the keeping quality of raw milk and pasteurized products. More recently, predictive equations describing growth and toxin production for a number of bacteria of concern to dairy microbiologists have been developed. A more mathematical approach is also being adopted for determining effective pasteurization conditions for organisms present in milk.

Animals↗
PubMed1994

Psychrotrophs in dairy products: their effects and their control.

Health concerns and technological effects of psychrotrophic bacteria in dairy products are reviewed, as well as methods to control their presence and development. The various Gram-negative and Gram-positive psychrotrophic species are listed and, with respect to pathogenic psychrotrophs, emphasis is given on Listeria monocytogenes, Yersinia enterocolitica, and Bacillus cereus. The influence of psychrotrophic bacteria on the quality of raw milk, pasteurized and UHT milks, butter, ice cream, cheese, and powders is examined. Public health considerations of Listeria monocytogenes, Yersinia enterocolitica, and Bacillus cereus of these various dairy products are also presented. Methods that can be used to eliminate or control the development of psychrotropic bacteria include low or high temperatures, chemicals, gases, the lactoperoxidase system, lactic acid bacteria, microfiltration, bactofugation, lactoferrin-related proteins, sanitation, flavors, and naturally occurring spore germinants.

Animals↗
PubMed1994

Adenosine triphosphate bioluminescence as a method to determine microbial levels in scald and chill tanks at a poultry abattoir.

According to Hazard Analysis of Critical Control Points (HACCP) programs developed for the poultry industry, poultry processing waters should be actively monitored to minimize cross-contamination between chicken carcasses. In order to monitor HACCP programs, a test is required that provides results on a real time basis. A modified adenosine triphosphate (ATP) bioluminescence test has been developed that can assess microbial levels in poultry processing waters within 15 min. A study was conducted to determine the effectiveness of this test for examining scald, prechill, and chill tank waters. The results showed that the modified ATP bioluminescence method gave results comparable to plate counts. The microbial levels were dependent on the tank and the time of sampling. The highest microbial levels were detected in the scald tank. In all three tanks, the microbial levels increased over time during the day.

Abattoirs↗
PubMed1993

Applications of bioluminescence in the dairy industry.

Several applications of ATP bioluminescence of relevance to the dairy industry have been proposed. This paper reviews some of the major benefits of the technology. New developments in bioluminescence research have made the simple, rapid, sensitive detection of foodborne pathogens a distinct possibility.

Adenosine Triphosphate↗
PubMed1987

A note on the use of the Catalasemetre in assessing the quality of milk.

The Catalasemetre, for assessing the quality of raw and pasteurized milk, has been studied. No correlation was found between catalase activity and bacterial counts for farm bulk tank milks within the range 5.2 X 10(2)-5.4 X 10(5) cfu/ml. Similarly, no relation was observed between catalase activity and somatic cell counts of milk (range of counts from 0.08 to 3.5). However, the catalase activity and bacterial count of pasteurized milks which had been pre-incubated at 21 degrees C for 25 h in the presence of crystal violet-penicillin-nisin to inhibit Gram-positive bacterial growth were significantly related. Thus, the use of this pre-incubation procedure coupled with the Catalasemetre to estimate bacterial growth, has potential in assessing the keeping quality of pasteurized milk samples within 25.5 h of production. Results on the thermostability of native milk catalase are also presented.

Animals↗
PubMed1986

Estimation of gram-negative bacteria in milk: a comparison of inhibitor systems for preventing gram-positive bacterial growth.

A number of inhibitor systems which have been reported to allow selection of Gram-negative bacteria were tested against Gram-positive and Gram-negative isolates of dairy origin. No one system worked perfectly. A mixture of crystal violet-penicillin-nisin or monensin had least inhibitory effect on Gram-negative isolates whereas Selectocult (a commercially available mixture of Benzalkon A 50% and crystal violet) and sodium deoxycholate were the most effective inhibitors of Gram-positive bacteria. Cetrimide-fucidin-cephaloridine solutions, which have been reported as allowing selective growth of pseudomonads, were not so specific when applied to milk systems.

Animals↗