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.

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.

Pathogenicity of Food and Clinical Listeria monocytogenes Isolates in a Mouse Bioassay

2003 ◽  
Vol 66 (12) ◽  
pp. 2362-2366 ◽  
Author(s):  
KAZUE TAKEUCHI ◽  
MARY ALICE SMITH ◽  
MICHAEL P. DOYLE
Keyword(s):  
Listeria Monocytogenes ◽  
Raw Milk ◽  
The United States ◽  
Clinical Samples ◽  
Mouse Bioassay ◽  
Factors Affecting ◽  
Serotype 1 ◽  
Horse Blood ◽  
Serotype 4B ◽  
Immunocompromised Mice

Serotype distributions of Listeria monocytogenes in clinical samples and foods often differ. It is unknown whether such differences reflect a variation in the virulence of strains or are due to other factors that are not directly related to the strains' ability to cause illnesses. Fifty-two food and eight clinical isolates of L. monocytogenes were obtained from France, Japan, and the United States. Their pathogenicity in nonimmunocompromised female ICR mice was determined by intraperitoneal (i.p.) injection of the mice with test strains at 108 to 109 CFU per mouse. Five mice were injected with each Listeria strain and observed for 5 days. Listeria isolates that caused at least one death in 5 days were considered pathogenic. Isolates that caused no deaths in 5 days were considered nonpathogenic. All strains except Listeria innocua and one L. monocytogenes serotype 4b strain (RM3-1) isolated from bovine raw milk were pathogenic to nonimmunocompromised mice. Three food isolates of L. monocytogenes serotype 1/2c were weakly pathogenic to nonimmunocompromised mice, killing a maximum of 50% of mice at 108 CFU. Strains with no pathogenicity or reduced pathogenicity were further tested for their pathogenicity to immunocompromised mice. Each strain was inoculated i.p. into five mice at 103 to 1010 CFU per mouse. No deaths of immunocompromised mice inoculated with 108 CFU were observed, but 20 to 40% of the mice died when inoculated with 109 CFU of L. monocytogenes RM3-1. The three L. monocytogenes serotype 1/2c isolates were also weakly pathogenic to immunocompromised mice, with two of the three isolates killing ≤60% of mice at doses of ≤108 CFU. The hemolytic activity of the three weakly pathogenic serotype 1/2c isolates was similar to that of pathogenic strains. However, the nonpathogenic strain RM3-1 was not found to be hemolytic on horse blood agar. We have identified several L. monocytogenes strains with reduced virulence levels. Further characterization of such isolates may aid in understanding factors affecting the variation in virulence among strains.

Behavior of Listeria monocytogenes during the Manufacture, Ripening, and Cold Storage of Afuega'l Pitu Cheese

1997 ◽  
Vol 60 (6) ◽  
pp. 689-693 ◽  
Author(s):  
ABELARDO MARGOLLES ◽  
ANA RODRÍGUEZ ◽  
CLARA G. de los REYES-GAVILÁN
Keyword(s):  
Listeria Monocytogenes ◽  
Lactococcus Lactis ◽  
Cell Damage ◽  
Salt Content ◽  
Northern Spain ◽  
Growth And Survival ◽  
Lactococcus Lactis Subsp ◽  
Whole Milk ◽  
Serotype 1 ◽  
Serotype 4B

Afuega'l Pitu is an artisanal acid-coagulated cheese manufactured in Asturias (northern Spain) and mainly consumed between the 3rd and the 30th day of ripening. Six cheese-making trials were performed in a pilot plant by using pasteurized whole milk inoculated with Listeria monocytogenes (strain L2 [serotype 1/2a], L39, or L41 [serotype 4b]) to ca. 2.7 log CFU/ml. A starter containing three strains, Lactococcus lactis subsp. lactis IPLA 947, Lactococcus lactis subsp. lactis biovar diacetylactis IPLA 838, and Leuconostoc citreum IPLA 616, grown separately in milk and combined in the volumetric proportion 3:1:1.3 was used. During the acidification L. monocytogenes counts increased 2.78- to 7.03-fold, depending on the strain, and remained within the curd; from this time counts decreased abruptly and were not detected in cheeses beyond the 7th day. The average pH in the curd was 4.43, and it decreased to around 4.0 in 5- to 7-day-old cheeses. These pH values were near the tolerance limit for L. monocytogenes and probably caused cell damage. Although moisture, aw, and NaCl levels were not limiting for the growth and survival of L. monocytogenes, salt content must be considered as a contributing factor in L. monocytogenes inactivation. Finally, the L2 strain grew better in curd and was slightly more resistant to low pH and refrigeration than strain L39 or L41. The manufacture of Afuega'l Pitu cheese from pasteurized milk and the design of a specific starter from the autochthonous lactic microbiota can lead to a safer product that can be consumed after very short ripening periods.

Production of a New Extracellular Cytotoxin from Listeria monocytogenes Serotype 4b and ATCC 15313 Serotype 1/2a in Relation to Growth Stage and Growth Temperature

1992 ◽  
Vol 55 (4) ◽  
pp. 252-255 ◽  
Author(s):  
DIRK VAN DER KELEN ◽  
JAMES A. LINDSAY
Keyword(s):  
Listeria Monocytogenes ◽  
Stationary Phase ◽  
Growth Medium ◽  
Growth Temperature ◽  
Growth Stage ◽  
Skim Milk ◽  
Broad Temperature Range ◽  
Temperature Range ◽  
Serotype 1 ◽  
Serotype 4B

Both virulent (4b) and avirulent (ATCC 15313:l/2a) strains of Listeria monocytogenes synthesize a previously unrecognized extracellular cytotoxin over a broad temperature range of 4–37°C. The highest level of cytotoxin production was observed during stationary phase; however, for all growth temperatures cytotoxin production was detected in early to mid-log phase. The cytotoxin was stable in the growth medium at both 37 and 4°C. Both strains synthesized the cytotoxin at 4 and 10°C in either whole or skim milk, at the same rate as in the semisynthetic growth medium.

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.

Gene Transcription Patterns of pH- and Salt-Stressed Listeria monocytogenes Cells in Simulated Gastric and Pancreatic Conditions

2014 ◽  
Vol 77 (2) ◽  
pp. 254-261 ◽  
Author(s):  
MARIOS MATARAGAS ◽  
ANNA GREPPI ◽  
KALLIOPI RANTSIOU ◽  
LUCA COCOLIN
Keyword(s):  
Life Cycle ◽  
Listeria Monocytogenes ◽  
Reference Strain ◽  
Expression Patterns ◽  
Wild Strain ◽  
Hostile Environment ◽  
Fermented Sausage ◽  
Laboratory Reference ◽  
Serotype 1 ◽  
Serotype 4B

A Listeria monocytogenes subgenomic array, targeting 54 genes involved in the adhesion, adaptation, intracellular life cycle, invasion, and regulation of the infection cycle was used to investigate the gene expression patterns of acid- and salt-stressed Listeria cells after exposure to conditions similar to those in gastric and pancreatic fluids. Three L. monocytogenes strains, one laboratory reference strain (EGDe) and two food isolates (wild strain 12 isolated from milk and wild strain 3 isolated from fermented sausage), were used during the studies. Differences in the expressed genes were observed between the gastric and pancreatic treatments and also between the serotypes. Increased transcripts were observed of the genes belonging to the adaptation and regulation group for serotype 4b (strain 12) and to the invasion and regulation group for serotype 1/2a (strain EGDe). Interestingly, no significantly differentially expressed genes were found for serotype 3c (strain 3) in most cases. The genes related to adaptation (serotype 1/2a) and to intracellular life cycle and invasion (serotype 4b) were down-regulated in order to cope with the hostile environment of the gastric and pancreatic fluids. These findings may provide experimental evidence for the dominance of serotypes 1/2a and 4b in clinical cases of listeriosis and for the sporadic occurrence of serotype 3c.

Thermal resistance of Listeria monocytogenes in inoculated and naturally contaminated raw milk

1988 ◽  
Vol 7 (4) ◽  
pp. 277-286 ◽  
Author(s):  
J.M. Farber ◽  
G.W. Sanders ◽  
J.I. Speirs ◽  
J.-Y. D'Aoust ◽  
D.B. Emmons ◽  
...  
Keyword(s):  
Listeria Monocytogenes ◽  
Thermal Resistance ◽  
Raw Milk

scholarly journals Construction, Characterization, and Use of Two Listeria monocytogenes Site-Specific Phage Integration Vectors

2002 ◽  
Vol 184 (15) ◽  
pp. 4177-4186 ◽  
Author(s):  
Peter Lauer ◽  
Man Yin Nora Chow ◽  
Martin J. Loessner ◽  
Daniel A. Portnoy ◽  
Richard Calendar
Keyword(s):  
Listeria Monocytogenes ◽  
Lethal Dose ◽  
Attachment Site ◽  
Donor Cell ◽  
Single Copy ◽  
Cell Extract ◽  
Site Specific ◽  
Specific Phage ◽  
Serotype 1 ◽  
Serotype 4B

ABSTRACT Two site-specific shuttle integration vectors were developed with two different chromosomal bacteriophage integration sites to facilitate strain construction in Listeria monocytogenes. The first vector, pPL1, utilizes the listeriophage U153 integrase and attachment site within the comK gene for chromosomal insertion. pPL1 contains a useful polylinker, can be directly conjugated from Escherichia coli into L. monocytogenes, forms stable, single-copy integrants at a frequency of ∼10−4 per donor cell, and can be used in the L. monocytogenes 1/2 and 4b serogroups. Methods for curing endogenous prophages from the comK attachment site in 10403S-derived strains were developed. pPL1 was used to introduce the hly and actA genes at comK-attBB′ in deletion strains derived from 10403S and SLCC-5764. These strains were tested for second-site complementation in hemolysin assays, plaquing assays, and cell extract motility assays. Unlike plasmid-complemented strains, integrated pPL1-complemented strains were fully virulent in the mouse 50% lethal dose assay. Additionally, the PSA phage attachment site on the L. monocytogenes chromosome was characterized, and pPL1 was modified to integrate at this site. The listeriophage PSA integrates in the 3′ end of an arginine tRNA gene. There are 17 bp of DNA identity between the bacterial and phage attachment sites. The PSA prophage DNA sequence reconstitutes a complete tRNAArg gene. The modified vector, pPL2, was integration proficient at the same frequency as pPL1 in common laboratory serotype 1/2 strains as well as serotype 4b strains.

Fluorometric Determination of Alkaline Phosphatase in Fluid Dairy Products: Collaborative Study

1990 ◽  
Vol 73 (6) ◽  
pp. 842-849 ◽  
Author(s):  
Richard M Rocco
Keyword(s):  
Alkaline Phosphatase ◽  
Dairy Products ◽  
Collaborative Study ◽  
Skim Milk ◽  
Raw Milk ◽  
Chocolate Milk ◽  
Phenyl Phosphate ◽  
Whole Milk ◽  
Standard Deviations

Abstract Official methods for the measurement of alkaline phosphatase (ALP) in dairy products use either phenyl phosphate or phenolphthaleln monophosphate as substrate. Quantitation of results requires butanol extraction of the Indophenol (Scharer) or 3-h dialysis of the liberated phenolphthaleln (Rutgers). The Advanced Fluorophos® assay Is based on a self-indicating substrate which, when acted upon by ALP, loses a phosphate radical and becomes a highly fluorescent compound. The rate of fluorophore formation Is monitored for 3 mln In a fluorometer and the enzyme activity In mU/L Is calculated. Eight laboratories participated in a collaborative study to evaluate the Fluorophos® assay for determining ALP activity In whole milk, skim milk, chocolate milk, and cream (half and half). The comparative method was the AOAC quantitative phenyl phosphate method, 16.121-16.122 (14th Ed.). Mixed herd raw milk was added to pasteurized samples at 0.05, 0.1, and 0.2% (v/v). Method performance at 0.1% (v/v) added raw milk as measured by repeatability and reproducibility standard deviations (sr and sR) and relative standard deviations (RSDr and RSDR), respectively, were: whole milk, sr = 21.7%, sR = 34.6%, RSDr = 4.4%, RSDR = 7.0%; skim milk, sr = 19.2%, sR = 31.4%, RSDr = 3.8%, RSDR = 6.2%; chocolate milk, sr = 27.6%, sR = 45.8%, RSDr = 5.3%, RSDR = 8.8%. The method has been adopted official first action by AOAC for determination of alkaline phosphatase in whole milk, skim milk, and chocolate milk.

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