Enumeration of micro-organisms in food: a comparative study of five methods

Kramer, John M.; Gilbert, R. J.

doi:10.1017/s0022172400053857

Cited by 25 publications

(11 citation statements)

References 21 publications

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“…Counts obtained in two successive experiments of 2-s duration with a sampling speed of five tubes/s had a CV of 1% (data not shown). This variation is considered normal in microbiological counts (24). Therefore, this sampling method should not influence precision of results.…”

Section: Resultsmentioning

confidence: 99%

Influence of Temperature and Pressure on the Lethality of Ultrasound

Raso

Pagán

Condón

et al. 1998

Appl Environ Microbiol

208

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A specially designed resistometer was constructed, and the lethal effect on Yersinia enterocolitica of ultrasonic waves (UW) at different static pressures (manosonication [MS]) and of combined heat-UW under pressure treatments (manothermosonication [MTS]) was investigated. During MS treatments at 30°C and 200 kPa, the increase in the amplitude of UW of 20 kHz from 21 to 150 μm exponentially decreased decimal reduction time values (D MS) from 4 to 0.37 min. When pressure was increased from 0 to 600 kPa at a constant amplitude (150 μm) and temperature (30°C),D MS values decreased from 1.52 to 0.20 min. The magnitude of this decrease in D MS declined progressively as pressure was increased. The influence of pressure onD MS values was greater with increased amplitude of UW. Pressure alone of as much as 600 kPa did not influence the heat resistance of Y. enterocolitica(D 60 = 0.094; z = 5.65). At temperatures of as much as 58°C, the lethality of UW under pressure was greater than that of heat treatment alone at the same temperature. At higher temperatures, this difference disappeared. Heat and UW under pressure seemed to act independently. The lethality of MTS treatments appeared to result from the added effects of UW under pressure and the lethal effect of heat. The individual contributions of heat and of UW under pressure to the total lethal effect of MTS depended on temperature. The inactivating effect of UW was not due to titanium particles eroded from the sonication horn. The addition to the MS media of cysteamine did not increase the resistance of Y. enterocolitica to MS treatment. MS treatment caused cell disruption.

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Section: Resultsmentioning

confidence: 99%

Influence of Temperature and Pressure on the Lethality of Ultrasound

Raso

Pagán

Condón

et al. 1998

Appl Environ Microbiol

208

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“…2000; Cullison and Jaykus 2002), differences in recoveries based on direct plating of the pellet were more variable and statistically different than if recoveries were calculated based on the percent loss to supernatant. When recovery results based on direct plating of the pellet were transformed to log format, the counts never varied by more than 0·5 log 10 , an acceptable within‐method degree of variability (Kramer and Gilbert 1978; Alonso‐Calleja et al. 2002).…”

Section: Resultsmentioning

confidence: 99%

Direct detection of bacterial pathogens in representative dairy products using a combined bacterial concentration-PCR approach

Stevens

Jaykus

2004

J Appl Microbiol

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Aims: To develop a simple, rapid method to concentrate and purify bacteria and their nucleic acids from complex dairy food matrices in preparation for direct pathogen detection using polymerase chain reaction (PCR). Methods and Results: Plain non-fat yogurt and cheddar cheese were each seeded with Listeria monocytogenes or Salmonella enterica serovar. Enteritidis in the range of 10 1 -10 6 CFU per 11-g sample. Samples were then processed for bacterial concentration using high-speed centrifugation (9700 g) followed by DNA extraction, PCR amplification, and amplicon confirmation by hybridization. Bacterial recoveries after centrifugation ranged from 53 to >100% and 71 to >100% for serovar. Enteritidis and L. monocytogenes, respectively, in the non-fat yogurt samples; and from 77 to >100% and 69 to >100% for serovar. Enteritidis and L. monocytogenes, respectively, in the cheddar cheese samples. There were no significant differences in recovery efficiency at different inocula levels, and losses to discarded supernatants were always <5%, regardless of dairy product or pathogen. Conclusions: When followed by pathogen detection using PCR and confirmation by amplicon hybridization, detection limits of 10 3 and 10 1 CFU per 11-g sample were achieved for L. monocytogenes and serovar. Enteritidis, respectively, in both product types and without prior cultural enrichment. Significance and Impact of the Study: This study represents progress toward the rapid and efficient direct detection of pathogens from complex food matrices at detection limits approaching those that might be anticipated in naturally contaminated products.

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“…Previous comparison between methods of enumeration of micro-organisms have been carried out under strictly controlled conditions on pure cultures of bacteria, spore suspensions, or relatively small numbers of food samples (Jarvis, Lach & Wood, 1977;Hedges, Shannon & Hobbs, 1978;Kramer & Gilbert, 1978, Kramer, Kendall & Gilbert, 1979. These workers showed a good correlation between the methods tested.…”

Section: Discussionmentioning

confidence: 99%

The microbiology of selected retail food products with an evaluation of viable counting methods

Greenwood

Coetzee²,

Ford

et al. 1984

J. Hyg.

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SUMMARYIn an inter-laboratory survey, the pour plate, surface spread, agar.droplet and spiral plate methods were used in parallel with the surface drop method for enumeration of micro-organisms in foods. Good agreement was obtained between all surface methods of enumeration, but there was poor agreement between molten agar methods and the surface drop method.A total of 1143 samples of food that were ready for consumption at the point of retail sale were examined. Eight types of food products were chosen: meat pasties, sausage rolls, real-cream slices, synthetic-cream slices, mayonnaise-based coleslaws, faggots, pates and continental sausages. The results ofthis survey suggest that the upper limit for an acceptable viable count should vary according to the food product. Salmonellae were not isolated on any occasion. Potentially harmful organisms were not isolated at levels expected to constitute a public health hazard.

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Enumeration of micro-organisms in food: a comparative study of five methods

Cited by 25 publications

References 21 publications

Influence of Temperature and Pressure on the Lethality of Ultrasound

Influence of Temperature and Pressure on the Lethality of Ultrasound

Direct detection of bacterial pathogens in representative dairy products using a combined bacterial concentration-PCR approach

The microbiology of selected retail food products with an evaluation of viable counting methods

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