Comparison of Oxygen Scavengers for Their Ability to Enhance Resuscitation of Heat-injured Listeria monocytogenes

1995 ◽  
Vol 58 (3) ◽  
pp. 244-250 ◽  
Author(s):  
J. R. PATEL ◽  
C.-A. HWANG ◽  
L. R. BEUCHAT ◽  
M. P. DOYLE ◽  
R. E. BRACKETT
Keyword(s):  
Listeria Monocytogenes ◽  
Incubation Time ◽  
Skim Milk ◽  
Oxygen Scavengers ◽  
Sodium Pyruvate ◽  
Percentage Recovery ◽  
Cysteine Hydrochloride ◽  
Whole Milk ◽  
Conventional Methods ◽  
Optimal Incubation

The recovery of heat-injured Listeria monocytogenes Scott A in Fraser broth (FB) supplemented with sodium thioglycolate, sodium pyruvate, L-(+)-cysteine hydrochloride, catalase or Oxyrase? was studied. After 3 h of incubation at 30°C, recovery was enhanced by all oxygen scavengers except sodium pyruvate. Oxyrase? (0.005 U ml−1) promoted the highest recovery (34%) compared to recovery in control broth (19%). All oxygen scavengers enhanced the recovery of injured L. monocytogenes in FB within 6 h of incubation. After 6 h at 30°C, 49 and 55% of injured cells underwent resuscitation in FB containing 2.5 mg of sodium pyruvate ml−1 and 400 μg of catalase ml−1, respectively, compared to 24% resuscitation in FB not supplemented with oxygen scavengers. The percentage recovery was increased as the incubation time was extended to 6 and 24 h. Nearly all injured cells were recovered within 24 h of incubation, regardless of supplementation of FB with oxygen scavengers. Fraser broth containing 2.5 mg of sodium pyruvate ml−1, 400 μg of catalase ml−1 or 0.01 U of Oxyrase? ml−1 were tested to determine the optimal incubation time and temperature for recovering heat-injured L. monocytogenes. Percentage recovery of injured cells increased with an increase in temperature from 25 to 30°C and from 30 to 35°C. The highest percentage of injured cells recovered was observed in FB containing 400 μg of catalase ml−1 (67%) and 0.01 U of Oxyrase? ml−1 (68%) within 6 h of incubation at 35°C. Catalase (400 μg ml−1) and Oxyrase? (0.01 U ml−1) in FB resulted in significantly higher recovery of injured cells from heated whole milk; however, recovery of injured cells from heated skim milk was not significantly higher. Enrichment in FB containing catalase or Oxyrase? has potential for recovering heat-injured L. monocytogenes cells within 6 h compared to 24 h required in conventional methods.

Thermal Resistance of Listeria monocytogenes Scott A in Ultrafiltered Milk as Related to the Effect of Different Milk Components

2010 ◽  
Vol 73 (11) ◽  
pp. 2110-2115 ◽  
Author(s):  
KINGA SZLACHTA ◽  
SUSANNE E. KELLER ◽  
ARLETTE SHAZER ◽  
STUART CHIRTEL
Keyword(s):  
Listeria Monocytogenes ◽  
Thermal Resistance ◽  
Milk Fat ◽  
Milk Powder ◽  
Skim Milk ◽  
Skim Milk Powder ◽  
Single Measure ◽  
Total Solids ◽  
Whole Milk ◽  
Milk Components

Pasteurization parameters for grade A milk are well established and set by regulation. However, as solids levels increase, an increased amount of heat is required to destroy any pathogens present. This effect is not well characterized. In this work, the effect of increased dairy solids levels on the thermal resistance of Listeria monocytogenes was examined through the use of ultrafiltered (UF) milk, reconstituted milk powder, and the milk components lactose and caseinate. From the results obtained, lactose and caseinate did not appear to affect thermal resistance. In addition, the level of milk fat, up to 10% of the total solids in UF whole milk, did not result in statistically significant changes to thermal resistance when compared with UF skim milk. Reconstituted skim milk powder at 27% total solids (D62-value = 1.16 ± 0.2 [SD] min, z = 5.7) did result in increased thermal resistance, as compared with reconstituted skim milk powder at 17.5% (D62-value = 0.86 ± 0.02 min, z = 5.57) and UF whole milk at 27% total solids (D62-value = 0.66 ± 0.07 min, z = 5.16). However, that increase appeared to be due to the increase in salt levels, not to increases in caseinate, fat, or lactose. Consequently, total solids, as a single measure, could not be used to predict increased thermal resistance of L. monocytogenes in concentrated milk.

Competitive Growth of Listeria monocytogenes and Yersinia enterocolitica in Milk

1993 ◽  
Vol 56 (6) ◽  
pp. 528-532 ◽  
Author(s):  
EBO BUDU-AMOAKO ◽  
SYED TOORA ◽  
RICHARD F. ABLETT ◽  
JIM SMITH
Keyword(s):  
Listeria Monocytogenes ◽  
Yersinia Enterocolitica ◽  
Skim Milk ◽  
Competitive Growth ◽  
No Inhibition ◽  
Whole Milk ◽  
Uninoculated Control ◽  
Control Samples

Sterile whole milk and skim milk were inoculated with cultures of Yersinia enterocolitica (10 CFU/ml) and Listeria monocytogenes (15 CFU/ml) either separately or together and incubated at 4, 10, and 22°C. Unlike uninoculated control samples, growth of Y. enterocolitica with or without L. monocytogenes in whole milk or skim milk at 22°C and in whole milk at 10°C led to the development of off-odors with coagulation after heating to 80°C. Growth of Y. enterocolitica alone in whole milk and in skim milk at 4°C and in skim milk at 10°C did not result in any odor changes or coagulation. Similar or lower populations did not result in any character changes in trials with L. monocytogenes. In the presence of Y. enterocolitica, the growth of L. monocytogenes was found to be competitively inhibited in whole milk at temperatures of 10 and 22°C, but not at 4°C, whereas in skim milk no inhibition was observed at all the temperatures investigated.

Attachment of Listeria monocytogenes and Salmonella typhimurium to Stainless Steel and Buna-N in the Presence of Milk and Individual Milk Components

1993 ◽  
Vol 56 (6) ◽  
pp. 479-484 ◽  
Author(s):  
DAVID M. HELKE ◽  
EILEEN B. SOMERS ◽  
AMY C. L. WONG
Keyword(s):  
Stainless Steel ◽  
Listeria Monocytogenes ◽  
Salmonella Typhimurium ◽  
Dairy Industry ◽  
Skim Milk ◽  
Whole Milk ◽  
Milk Components ◽  
Phosphate Buffered Saline ◽  
Β Lactoglobulin

The effects of milk and individual milk components on the attachment of Listeria monocytogenes and Salmonella typhimurium to two commonly used materials in the dairy industry were studied. Attachment of both organisms to stainless steel and Buna-N was significantly inhibited by the presence of skim, 2%, whole, or chocolate 2% milk compared to the phosphate-buffered saline (PBS) control. The addition of individual milk components, casein, α-lactalbumin, and β-lactoglobulin to the attachment menstruum significantly reduced attachment. Pretreating surfaces with milk and milk components for 1 h prior to attachment in PBS gave similar results. The presence of lactose did not affect attachment of either organism; however, attachment of S. typhimurium was significantly decreased on pretreated Buna-N. Cells of either organism pretreated with skim milk or β-lactoglobulin prior to attachment in PBS showed significantly less attachment than untreated cells. Pretreating S. typhimurium cells with casein had no effect on attachment to stainless steel. Pretreatment of S. typhimurium with lactose increased attachment to both surfaces while pretreatment had no effect on L. monocytogenes. Attachment of both organisms was significantly reduced in diluted whole milk. Both organisms attached significantly less to surfaces soiled with one or more layers of whole milk.

Psychrotrophic Growth and Thermal Inactivation of Listeria monocytogenes as a Function of Milk Composition

1986 ◽  
Vol 49 (12) ◽  
pp. 994-998 ◽  
Author(s):  
CATHERINE W. DONNELLY ◽  
ELIZABETH H. BRIGGS
Keyword(s):  
Listeria Monocytogenes ◽  
Thermal Resistance ◽  
Thermal Inactivation ◽  
Skim Milk ◽  
Raw Milk ◽  
Milk Composition ◽  
Cellular Growth ◽  
Whole Milk ◽  
Serotype 1 ◽  
Serotype 4B

Listeria monocytogenes strains 19111, 19113, 19115, F5027 and F5069 were grown in 11% nonfat milk solids, skim milk and whole milk at 4, 10, 22, and 37°C to determine the influence of temperature and milk composition on growth and thermal resistance. Milk composition affected cellular growth. The psychrotrophic growth of L. monocytogenes serotype 4b strains was enhanced in whole milk when compared to skim milk or 11% NFMS. This enhancement of psychrotrophic growth was not observed for serotype 1 or 3 strains. The stimulatory effect of whole milk on serotype 4b L. monocytogenes strains was most dramatic at 10°C where cells increased from 7.9 × 10° to 5.8 × 106 CFU/ml within 48 h. Milk composition did not affect the thermal resistance of L. monocytogenes. All strains used in this study had a D62.7°C value of 1.0 min or less, therefore, pasteurization as defined by current FDA guidelines should eliminate this organism from raw milk with a large margin of safety. Post-pasteurization contamination of dairy products with L. monocytogenes must be eliminated since the psychrotrophic nature of this organism ensures survival and proliferation during refrigerated storage.

Growth of Listeria monocytogenes at 10°C in Milk Preincubated with Selected Pseudomonads1

1988 ◽  
Vol 51 (4) ◽  
pp. 277-282 ◽  
Author(s):  
DOUGLAS L. MARSHALL ◽  
RONALD H. SCHMIDT
Keyword(s):  
Listeria Monocytogenes ◽  
Skim Milk ◽  
Growth Curves ◽  
Milk Composition ◽  
Pseudomonas Fragi ◽  
Pseudomonas Spp ◽  
Generation Times ◽  
Whole Milk ◽  
Dry Milk ◽  
Stimulation Of

Preliminary studies involving co-inoculation of Listeria monocytogenes with Pseudomonas fragi into whole or skim milk demonstrated that neither inhibition nor stimulation of growth occurred for either organism. Additional investigations involved preincubation of whole milk, skim milk, and 10% reconstituted nonfat dry milk (NDM) for 3 d at 10°C with P. fragi, Pseudomonas fluorescens P26, P. fluorescens T25, or P. fluorescens B52, followed by inoculation with L. monocytogenes and further incubation at 10°C. Growth curves of L. monocytogenes were constructed for each treatment combination and generation times were statistically compared for differences. Results indicated that L. monocytogenes did not affect growth or survival of the preincubated Pseudomonas spp. However, growth rates of L. monocytogenes were significantly (P<0.05) enhanced in milks preincubated with pseudomonads. Doubling times of L. monocytogenes were reduced by up to 3 h when grown in milk preincubated with Pseudomonas spp. Three strains of P. fluorescens showed more stimulation of the growth rate of L. monocytogenes compared to P. fragi in preincubated whole or skim milk but not in preincubated NDM. Milk composition had little effect on growth of either genus when incubated alone. Results of this study indicate that L. monocytogenes can grow in the presence of Pseudomonas spp. either as a co-inoculant or following preincubation in milk at 10°C. Furthermore, data suggest that the presence of the pseudomonads may enhance growth of L. monocytogenes in milk.

Growth of Listeria monocytogenes in the Presence of Pseudomonas fluorescens at 7 or 13°C in Skim Milk

1989 ◽  
Vol 52 (12) ◽  
pp. 852-855 ◽  
Author(s):  
SEHAM A. FARRAG ◽  
ELMER H. MARTH
Keyword(s):  
Listeria Monocytogenes ◽  
Pseudomonas Fluorescens ◽  
Incubation Period ◽  
Skim Milk

Autoclaved samples of skim milk were inoculated with Listeria monocytogenes (strain Scott A, California or V7), Pseudomonas fluorescens (strain P26 or B52), or a combination of L. monocytogenes plus P. fluorescens, and incubated at 7 or 13°C for 8 weeks. McBride Listeria Agar was used to determine populations of L. monocytogenes (at 0, 7, 14, 28, 42, or 56 d), and Pseudomonas isolation agar to enumerate P. fluorescens. Growth of L. monocytogenes was somewhat enhanced after 7 d of incubation at 7 but not at 13°C in the presence of pseudomonads. However, after 14 d and until the end of the incubation period (56 d), slight inactivation of L. monocytogenes in the presence of P. fluorescens was observed. L. monocytogenes did not affect growth or survival of P. fluorescens; also, no marked changes in pH of the milk were caused either by L. monocytogenes alone or by L. monocytogenes plus P. fluorescens.

Inactivation of Surface-adherent Listeria monocytogenes Hypochlorite and Heat

1991 ◽  
Vol 54 (1) ◽  
pp. 4-6 ◽  
Author(s):  
SHIN-HO LEE ◽  
JOSEPH F. FRANK
Keyword(s):  
Stainless Steel ◽  
Listeria Monocytogenes ◽  
Cell Population ◽  
Incubation Time ◽  
Cell Populations ◽  
Adherent Cell ◽  
Adherent Cells ◽  
D Cells

Inactivation by hypochlorite of Listeria monocytogenes cells adherent to stainless steel was determined. Adherent cell populations were prepared by incubating stainless steel slides with a 24 h culture of L. monocytogenes for 4 h at 21°C. Adherent microcolonies were prepared by growing L. monocytogenes on stainless steel slides submerged in a 1:15 dilution of tryptic soy broth at 21°C. The slides were then rinsed and transferred to fresh sterile broth every 2 d with a total incubation time of 8 d. Although the 4 h and 8 d adherent populations were at similar levels, 8 d adherent cells were over 100 times more resistant than the 4 h adherent cell population when exposed to 200 ppm hypochlorite for 30 s. When stainless steel slides containing adherent cells were heated at 72°C both adherent cell populations were inactivated after 1 min. Detectable numbers of L. monocytogenes remained on stainless steel slides after treatment at 65°C for 3 min when adherent 8 d cells were tested but not when adherent 4 h cells were used.

Antimicrobial Effects of d-3-Phenyllactic Acid on Listeria monocytogenes in TSB-YE Medium, Milk, and Cheese

1998 ◽  
Vol 61 (10) ◽  
pp. 1281-1285 ◽  
Author(s):  
VIRGINIE DIEULEVEUX ◽  
MICHELINE GUÉGUEN
Keyword(s):  
Listeria Monocytogenes ◽  
Growth Phase ◽  
Physiological State ◽  
Geotrichum Candidum ◽  
Bactericidal Effect ◽  
Exponential Growth Phase ◽  
Bacteriostatic Effect ◽  
Experimental Conditions ◽  
Phenyllactic Acid ◽  
Whole Milk

d-3-Phenyllactic acid is a compound with anti-Listeria activity which is produced and secreted by the yeastlike fungus, Geotrichum candidum. This compound has a bactericidal effect independent of the physiological State of Listeria monocytogenes when added at a concentration of 7 mg/ml to tryptic soy broth supplemented with yeast extract (TSB-YE). An initial L. monocytogenes population of 105 CFU/ml was reduced 100-fold (2 log) after 4 days of culture at 25 °C in TSB-YE containing d-3-phenyllactic acid. The Listeria population was reduced 1,000-fold (3 log) when the compound was added during the exponential growth phase, and was reduced to less than 10 CFU/ml when it was added during the stationary phase. d-3-Phenyllactic acid had a bacteriostatic effect in UHT whole milk, reducing the population by 4.5 log, to give fewer cells than in the control after 5 days of culture. The results obtained with L. monocytogenes at concentrations of 105 and 103 CFU/ml in cheese curds were less conclusive. d-3-Phenyllactic acid was 10 times less active than nisin in our experimental conditions (TSB-YE at 25°C).

Fate of Listeria monocytogenes During the Manufacture and Ripening of Camembert Cheese

1987 ◽  
Vol 50 (5) ◽  
pp. 372-378 ◽  
Author(s):  
ELLIOT T. RYSER ◽  
ELMER H. MARTH
Keyword(s):  
Listeria Monocytogenes ◽  
Fold Increase ◽  
Original Sample ◽  
Cheese Making ◽  
Penicillium Camemberti ◽  
Shaped Surface ◽  
Standard Procedures ◽  
Whole Milk ◽  
Camembert Cheese ◽  
Made In

The ability of Listeria monocytogenes to survive the Camembert cheese-making process and grow during ripening of the cheese was examined. Pasteurized whole milk was inoculated to contain about 500 L. monocytogenes [strain Scott A, V7, California, (CA) or Ohio (OH)] CFU/ml and made into Camembert cheese according to standard procedures. All wheels of cheese were ripened at 6°C following 10 d of storage at 15–16°C to allow proper growth of Penicillium camemberti. Duplicate wedge (pie-shaped), surface and interior cheese samples were analyzed for numbers of L. monocytogenes by surface-plating appropriate dilutions made in Tryptose Broth (TB) on McBride Listeria Agar (MLA). Initial TB dilutions were stored at 3°C and surface-plated on MLA after 2, 4, 6 or 8 weeks if the organism was not quantitated in the original sample. Selected Listeria colonies from duplicate samples were confirmed biochemically. Results showed that numbers of Listeria in cheese increased 5- to 10-fold 24 h after its manufacture. Listeria counts for strains Scott A, CA and OH decreased to <10 to 100 CFU/g in all cheese samples taken during the first 18 d of ripening. In contrast, numbers of strain V7 remained unchanged during this period. All L. monocytogenes strains initiated growth in cheese after 18 d of ripening. Maximum Listeria counts of ca. 1 × 106 to 5 × 107 CFU/g were attained after 65 d of ripening. Generally, a 10- to 100-fold increase in numbers of Listeria occurred in wedge or surface as compared to interior cheese samples taken during the latter half of ripening. During this period, Listeria growth paralleled the increase in pH of the cheese during ripening.

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