Comparison of Media and Sampling Locations for Isolation of Listeria monocytogenes in Queso Fresco Cheese

2006 ◽  
Vol 69 (9) ◽  
pp. 2151-2156 ◽  
Author(s):  
CHIA-MIN LIN ◽  
LEI ZHANG ◽  
MICHAEL P. DOYLE ◽  
BALA SWAMINATHAN
Keyword(s):  
Listeria Monocytogenes ◽  
Storage Temperature ◽  
Epidemiologic Studies ◽  
Detection Methods ◽  
Health Concern ◽  
Public Health Concern ◽  
Sampling Locations ◽  
Soft Cheese ◽  
Regulatory Analysis ◽  
Storage Temperatures

Listeriosis associated with Hispanic-style soft cheese is an ongoing public health concern. Although rapid detection methods based on molecular and immunological technologies have been applied successfully for detecting Listeria monocytogenes in foods, obtaining isolates of the pathogen is a critical procedure for epidemiologic studies and regulatory analysis. Oxford agar, a medium recommended by the U.S. Food and Drug Administration Bacteriological Analytical Manual (BAM) to isolate L. monocytogenes from cheese, is unable to differentiate L. monocytogenes from other Listeria species. Hence, two selective isolation media, L. monocytogenes blood agar (LMBA) and Rapid 'L. mono agar (RLMA), were compared with Oxford agar for isolating L. monocytogenes from cheese. Queso fresco cheese was inoculated at 100 or 101 CFU/g with a five-strain mixture of L. monocytogenes or with the five-strain L. monocytogenes mixture and Listeria innocua. Cheese samples were stored at 21, 12, and 4°C and Listeria counts were determined at 3, 7, and 10 days; 7, 10, 14, 21 days; and 2, 4, 8, and 12 weeks postinoculation, respectively. Surface and interior cheese samples as well as liquid exudate produced during storage were assayed individually to determine differences in Listeria contamination at different sampling locations. L. monocytogenes was more easily differentiated from L. innocua on RLMA than LMBA and Oxford agar. Similar L. monocytogenes counts (ca. 104 CFU/g) were obtained on the last sampling day on the surface and interior of cheese samples (P > 0.05) for all storage temperatures and both initial inoculation levels, but smaller cell numbers were detected in the exudate produced during storage. In addition, simultaneous inoculation of L. innocua with L. monocytogenes did not affect the final L. monocytogenes counts in the cheese. The amount of exudate released from the cheese and decrease of pH correlated with storage temperature. More exudate was produced and a greater decrease of pH occurred at 21°C than at 12 or 4°C. Our results indicate that RLMA is a suitable medium for isolating L. monocytogenes from queso fresco cheese. Higher counts of L. monocytogenes were obtained from surface and interior samples of cheese than from the exudate of the cheese during storage. In addition, pH may be a useful indicator of improperly stored queso fresco cheese.

Growth Modeling of Listeria monocytogenes in Pasteurized Liquid Egg

2013 ◽  
Vol 76 (9) ◽  
pp. 1549-1556 ◽  
Author(s):  
MIHO OHKOCHI ◽  
SHIGENOBU KOSEKI ◽  
MASAAKI KUNOU ◽  
KATSUAKI SUGIURA ◽  
HIROKAZU TSUBONE
Keyword(s):  
Listeria Monocytogenes ◽  
Specific Growth ◽  
Storage Temperature ◽  
Growth Parameters ◽  
Root Model ◽  
Natural Flora ◽  
Mean Square Errors ◽  
Kinetics Of ◽  
Storage Temperatures ◽  
Maximum Population Density

The growth kinetics of Listeria monocytogenes and natural flora in commercially produced pasteurized liquid egg was examined at 4.1 to 19.4°C, and a growth simulation model that can estimate the range of the number of L. monocytogenes bacteria was developed. The experimental kinetic data were fitted to the Baranyi model, and growth parameters, such as maximum specific growth rate (μmax), maximum population density (Nmax), and lag time (λ), were estimated. As a result of estimating these parameters, we found that L. monocytogenes can grow without spoilage below 12.2°C, and we then focused on storage temperatures below 12.2°C in developing our secondary models. The temperature dependency of the μmax was described by Ratkowsky's square root model. The Nmax of L. monocytogenes was modeled as a function of temperature, because the Nmax of L. monocytogenes decreased as storage temperature increased. A tertiary model of L. monocytogenes was developed using the Baranyi model and μmax and Nmax secondary models. The ranges of the numbers of L. monocytogenes bacteria were simulated using Monte Carlo simulations with an assumption that these parameters have variations that follow a normal distribution. Predictive simulations under both constant and fluctuating temperature conditions demonstrated a high accuracy, represented by root mean square errors of 0.44 and 0.34, respectively. The predicted ranges also seemed to show a reasonably good estimation, with 55.8 and 51.5% of observed values falling into the prediction range of the 25th to 75th percentile, respectively. These results suggest that the model developed here can be used to estimate the kinetics and range of L. monocytogenes growth in pasteurized liquid egg under refrigerated temperature.

Fate of Listeria monocytogenes, Salmonella Typhimurium DT104, and Escherichia coli O157:H7 in Labneh as a Pre- and Postfermentation Contaminant

2000 ◽  
Vol 63 (5) ◽  
pp. 608-612 ◽  
Author(s):  
MOHSEN S. ISSA ◽  
ELLIOT T. RYSER
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Salmonella Typhimurium ◽  
Foodborne Pathogens ◽  
Storage Temperature ◽  
Starter Culture ◽  
Salt Content ◽  
Health Concern ◽  
Escherichia Coli O157 ◽  
E Coli

Commercially pasteurized milk (∼2% milkfat) was heated at 85 to 87°C/30 min, inoculated to contain 2,000 to 6,000 CFU/ml of Listeria monocytogenes, Salmonella Typhimurium DT104, or Escherichia coli O157:H7, cultured at 43°C for 4 h with a 2.0% (wt/wt) commercial yogurt starter culture, stored 12 to 14 h at 6°C, and centrifuged to obtain a Labneh-like product. Alternatively, traditional salted and unsalted Labneh was prepared using a 3.0% (wt/wt) starter culture inoculum, similarly inoculated after manufacture with the aforementioned pathogens, and stored at 6°C and 20°C. Throughout fermentation, Listeria populations remained unchanged, whereas numbers of Salmonella increased 0.33 to 0.47 logs during the first 2 h of fermentation and decreased thereafter. E. coli populations increased 0.46 to 1.19 logs during fermentation and remained that these levels during overnight cold storage. When unsalted and salted Labneh were inoculated after manufacture, Salmonella populations decreased >2 logs in all samples after 2 days, regardless of storage temperature, with the pathogen no longer detected in 4-day-old samples. Numbers of L. monocytogenes decreased from 2.48 to 3.70 to <1.00 to 1.95 logs after 2 days with the pathogen persisting up to 15 days in one lot of salted/unsalted Labneh stored at 6°C. E. coli O157:H7 populations decreased from 3.39 to 3.7 to <1.00 to 2.08 logs during the first 2 days, with the pathogen no longer detected in any 4-dayold samples. Inactivation rates for all three pathogens in Labneh were unrelated to storage temperature or salt content. Unlike L. monocytogenes that persisted up to 15 days in Labneh, rapid inactivation of Salmonella Typhimurium DT104 and E. coli O157:H7 suggests that these emerging foodborne pathogens are of less public health concern in traditional Labneh.

Effect of Native Microflora, Waiting Period, and Storage Temperature on Listeria monocytogenes Serovars Transferred from Cantaloupe Rind to Fresh-Cut Pieces during Preparation†

2012 ◽  
Vol 75 (11) ◽  
pp. 1912-1919 ◽  
Author(s):  
DIKE O. UKUKU ◽  
MODESTO OLANYA ◽  
DAVID J. GEVEKE ◽  
CHRISTOPHER H. SOMMERS
Keyword(s):  
Listeria Monocytogenes ◽  
Storage Temperature ◽  
Plate Count ◽  
Mesophilic Bacteria ◽  
Recent Outbreak ◽  
Plate Count Method ◽  
Fresh Cut ◽  
Native Microflora ◽  
And Storage ◽  
Storage Temperatures

The most recent outbreak of listeriosis linked to consumption of fresh-cut cantaloupes indicates the need to investigate the behavior of Listeria monocytogenes in the presence of native microflora of cantaloupe pieces during storage. Whole cantaloupes were inoculated with L. monocytogenes (108-CFU/ml suspension) for 10 min and air dried in a biosafety cabinet for 1 h and then treated (unwashed, water washed, and 2.5% hydrogen peroxide washed). Fresh-cut pieces (~3 cm) prepared from these melons were left at 5 and 10°C for 72 h and room temperature (20°C) for 48 h. Some fresh-cut pieces were left at 20°C for 2 and 4 h and then refrigerated at 5°C. Microbial populations of fresh-cut pieces were determined by the plate count method or enrichment method immediately after preparation. Aerobic mesophilic bacteria, yeast and mold of whole melon, and inoculated populations of L. monocytogenes on cantaloupe rind surfaces averaged 6.4, 3.3, and 4.6 log CFU/cm2, respectively. Only H2O2 (2.5%) treatment reduced the aerobic mesophilic bacteria, yeast and mold, and L. monocytogenes populations to 3.8, 0.9, and 1.8 log CFU/cm2, respectively. The populations of L. monocytogenes transferred from melon rinds to fresh-cut pieces were below detection but were present by enrichment. Increased storage temperatures enhanced the lag phases and growth of L. monocytogenes. The results of this study confirmed the need to store fresh-cut cantaloupes at 5°C immediately after preparation to enhance the microbial safety of the fruit.

scholarly journals Differential Listeria monocytogenes Strain Survival and Growth in Katiki, a Traditional Greek Soft Cheese, at Different Storage Temperatures

2009 ◽  
Vol 75 (11) ◽  
pp. 3621-3626 ◽  
Author(s):  
Dafni-Maria Kagkli ◽  
Vassilios Iliopoulos ◽  
Virginia Stergiou ◽  
Anna Lazaridou ◽  
George-John Nychas
Keyword(s):  
Listeria Monocytogenes ◽  
Pulsed Field Gel Electrophoresis ◽  
Temperature Dependent ◽  
Protected Designation Of Origin ◽  
Soft Cheese ◽  
Different Temperatures ◽  
The Subject ◽  
Survival And Growth ◽  
Different Strains ◽  
Storage Temperatures

ABSTRACT Katiki Domokou is a traditional Greek cheese, which has received the Protected Designation of Origin recognition since 1994. Its microfloras have not been studied although its structure and composition may enable (or even favor) the survival and growth of several pathogens, including Listeria monocytogenes. The persistence of L. monocytogenes during storage at different temperatures has been the subject of many studies since temperature abuse of food products is often encountered. In the present study, five strains of L. monocytogenes were aseptically inoculated individually and as a cocktail in Katiki Domokou cheese, which was then stored at 5, 10, 15, and 20°C. Pulsed-field gel electrophoresis was used to monitor strain evolution or persistence during storage at different temperatures in the case of the cocktail inoculum. The results suggested that strain survival of L. monocytogenes was temperature dependent since different strains predominated at different temperatures. Such information is of great importance in risk assessment studies, which typically consider only the presence or absence of the pathogen.

Growth ofListeria monocytogenesin Camembert and other soft cheeses at refrigeration temperatures

1993 ◽  
Vol 60 (3) ◽  
pp. 421-429 ◽  
Author(s):  
Jonathan P. Back ◽  
Sarah A. Langford ◽  
Rohan G. Kroll
Keyword(s):  
Listeria Monocytogenes ◽  
Temperature Dependent ◽  
Ripening Process ◽  
Significant Growth ◽  
Soft Cheese ◽  
French And English ◽  
Dependent Growth ◽  
Rates Of Growth ◽  
Storage Temperatures

SummaryListeria monocytogenessurvived and, under most conditions, multiplied when inoculated directly into the cheese milk of laboratory made Camembert cheeses. The rate and extent of growth was reduced at lower storage temperatures. Significantly higher rates of growth occurred at the surface compared with the centre of the cheeses, and these were probably associated with increased pH and proteolysis at the cheese surface due to the mould ripening process. Similar results were obtained with Camembert cheeses surface inoculated after manufacture. There was also temperature-dependent growth of List, monocytogenes on a range of inoculated commercially manufactured soft cheeses. Significant growth occurred in Cambazola, French and English Brie, blue and white Lymeswold, French Camembert and Brie with garlic. Little if any growth occurred in blue and white Stilton, Mycella, Chaume and full fat soft cheese with garlic and herbs at the temperatures examined.

Inhibition of Listeria monocytogenes and Salmonella by Natural Antimicrobials and High Hydrostatic Pressure in Sliced Cooked Ham

2005 ◽  
Vol 68 (1) ◽  
pp. 173-177 ◽  
Author(s):  
TERESA AYMERICH ◽  
ANNA JOFRÉ ◽  
MARGARITA GARRIGA ◽  
MARTA HUGAS
Keyword(s):  
Listeria Monocytogenes ◽  
Hydrostatic Pressure ◽  
High Hydrostatic Pressure ◽  
Storage Temperature ◽  
Detection Methods ◽  
Most Probable Number ◽  
Probable Number ◽  
Cooked Ham ◽  
Potassium Lactate ◽  
Microbial Enumeration

The effectiveness of nisin, lactate salts, and high hydrostatic pressure to inhibit the growth of Listeria monocytogenes and Salmonella in sliced cooked ham was studied through a combination of PCR-based detection methods, most probable number, and classical microbial enumeration techniques (International Organization for Standardization protocols). A synergistic effect to inhibit a cocktail of Listeria monocytogenes CTC1010, CTC1011, and CTC1034 was observed between potassium lactate, high hydrostatic pressure (400 MPa, 17°C, 10 min), and low storage temperature when sliced cooked ham was stored for 84 days at 1°C. The high hydrostatic pressure treatment also proved to be useful to inhibit a cocktail of Salmonella enterica serotypes London CTC1003, Schwarzengrund CTC1015, and Derby CTC1022.

Modeling the Growth of Listeria monocytogenes in Pasteurized White Asparagus

2007 ◽  
Vol 70 (3) ◽  
pp. 753-757 ◽  
Author(s):  
A. VALERO ◽  
E. CARRASCO ◽  
F. PÉREZ-RODRÍGUEZ ◽  
R. M. GARCÍA-GIMENO ◽  
G. ZURERA
Keyword(s):  
Listeria Monocytogenes ◽  
Food Processing ◽  
Goodness Of Fit ◽  
Microbial Population ◽  
Storage Temperature ◽  
Arrhenius Model ◽  
Microbial Risks ◽  
The Relationship ◽  
And Storage ◽  
Storage Temperatures

Growth of Listeria monocytogenes in pasteurized white asparagus was monitored at different storage temperatures (4, 10, 20, and 30°C). Among the main microbial kinetic parameters, growth rate (μ) per hour was calculated at each temperature using the Baranyi-Roberts model. L. monocytogenes was able to grow at all temperatures, although at 4°C only a slight increment of the microbial population was observed (∼1 log CFU/g) after 300 h of storage. Subsequently, two different secondary modeling approaches were proposed to study the relationship between μ and storage temperature: the Arrhenius and Ratkowsky models. Although both models properly described the data observed, smaller values of root mean square error (RMSE) and standard error of prediction (SEP) were obtained with the Ratkowsky model, providing a better goodness of fit (Ratkowsky model: RMSE = 0.010, SEP = 21.23%; Arrhenius model: RMSE = 0.026, SEP = 54.37%). The maximum population density (MPD) was calculated at each temperature studied. A clear dependence between MPD and temperature was found; lower temperatures produced lower values of MPD. This finding confirmed the Jameson effect, indicating that multiple hurdles in the food-processing chain plus lower temperatures reduced L. monocytogenes growth. Predicting the growth of L. monocytogenes along the food chain will help to reduce microbial risks associated with consumption of pasteurized white asparagus.

scholarly journals Isolation and Molecular Characterization of Mycobacterium Africanum from the Sputum of Butchers in a Municipal Abattoir in

2021 ◽  
Vol 40 (4) ◽  
pp. 306-314
Author(s):  
C.A. Agada ◽  
I.F. Ijabone ◽  
D. Igwe ◽  
S.I.B. Cadmus
Keyword(s):  
Public Health ◽  
Molecular Characterization ◽  
Physical Contact ◽  
High Rate ◽  
Health Concern ◽  
Public Health Concern ◽  
Soft Cheese ◽  
Occupationally Exposed ◽  
Mycobacterium Africanum ◽  
High Level

Tuberculosis (TB) caused by the Mycobacterium tuberculosis complex (MTC) remains a major public health concern due to its high rate of person to person transfer as well as a high level of morbidity and mortality. The risk factors for transmission of zoonotic TB to humans are close physical contact with cattle, consumption of unpasteurised milk and milk products and unhealthy meat processing by butchers are common in developing countries like Nigeria. However, the circulating MTC among the occupationally exposed are unknown therefore the need to determine the prevalence of tuberculosis and to characterize the mycobacterial species in them. A crosssectional study was conducted among butchers, cattle traders and herders in Bodija Municipal Abattoir, Akinyele International Cattle Market and some herds respectively. Using systematic random sampling, 93 sputum samples were collected and analyzed by culture, Mycobacterium Genus Typing as well as Deletion Typing (Multiplex Polymerase Chain Reaction (PCR)). Of the 93 sputa collected, two (2.2%) were positive for mycobacteria by culture which were confirmed to be Mycobacterium africanum by molecular characterization. These bacilli were isolated from two butchers; one of which had the habit of eating raw meat and cherish ‘wara’ (a local soft cheese made from milk). The isolation of M. africanum from butchers in this study raises public health concern on the contamination of the meat processed as well as highlights its importance in the epidemiology of tuberculosis in Nigeria.

Effect of Salt, Smoke Compound, and Storage Temperature on the Growth of Listeria monocytogenes in Simulated Smoked Salmon†

2007 ◽  
Vol 70 (10) ◽  
pp. 2321-2328 ◽  
Author(s):  
CHENG-AN HWANG
Keyword(s):  
Listeria Monocytogenes ◽  
Storage Temperature ◽  
Control Measures ◽  
Lag Phase ◽  
Phase Duration ◽  
Liquid Smoke ◽  
Smoked Salmon ◽  
And Storage ◽  
Storage Temperatures ◽  
Maximum Population Density

Smoked salmon can be contaminated with Listeria monocytogenes. It is important to identify the factors that are capable of controlling the growth of L. monocytogenes in smoked salmon so that control measures can be developed. The objective of this study was to determine the effect of salt, a smoke compound, storage temperature, and their interactions on L. monocytogenes in simulated smoked salmon. A six-strain mixture of L. monocytogenes (102 to 103 CFU/g) was inoculated into minced, cooked salmon containing 0 to 10% NaCl and 0 to 0.4% liquid smoke (0 to 34 ppm of phenol), and the samples were stored at temperatures from 0 to 25°C. Lag-phase duration (LPD; hour), growth rate (GR; log CFU per hour), and maximum population density (MPD; log CFU per gram) of L. monocytogenes in salmon, as affected by the concentrations of salt and phenol, storage temperature, and their interactions, were analyzed. Results showed that L. monocytogenes was able to grow in salmon containing the concentrations of salt and phenol commonly found in smoked salmon at the prevailing storage temperatures. The growth of L. monocytogenes was affected significantly (P < 0.05) by salt, phenol, storage temperature, and their interactions. As expected, higher concentrations of salt or lower storage temperatures extended the LPD and reduced the GR. Higher concentrations of phenol extended the LPD of L. monocytogenes, particularly at lower storage temperatures. However, its effect on reducing the GR of L. monocytogenes was observed only at higher salt concentrations (>6%) at refrigerated and mild abuse temperatures (<10°C). The MPD, which generally reached 7 to 8 log CFU/g in salmon that supported L. monocytogenes growth, was not affected by the salt, phenol, and storage temperature. Two models were developed to describe the LPD and GR of L. monocytogenes in salmon containing 0 to 8% salt, 0 to 34 ppm of phenol, and storage temperatures of 4 to 25°C. The data and models obtained from this study would be useful for estimating the behavior of L. monocytogenes in smoked salmon.

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