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Susceptibility of Listeria monocytogenes-containing Biofilms to Chemical Disinfectants and Potential Transfer of Listeria from Soil to Produce at Refrigerated Temperature.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Susceptibility of Listeria monocytogenes-containing Biofilms to Chemical Disinfectants and Potential Transfer of Listeria from Soil to Produce at Refrigerated Temperature./
Author:	Hardy, Quincy T.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2019,
Description:	93 p.
Notes:	Source: Masters Abstracts International, Volume: 81-03.
Contained By:	Masters Abstracts International81-03.
Subject:	Food science. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=13865764
ISBN:	9781085639873

Susceptibility of Listeria monocytogenes-containing Biofilms to Chemical Disinfectants and Potential Transfer of Listeria from Soil to Produce at Refrigerated Temperature.
Hardy, Quincy T.

Susceptibility of Listeria monocytogenes-containing Biofilms to Chemical Disinfectants and Potential Transfer of Listeria from Soil to Produce at Refrigerated Temperature. - Ann Arbor : ProQuest Dissertations & Theses, 2019 - 93 p.

Source: Masters Abstracts International, Volume: 81-03.

Thesis (M.S.)--University of Delaware, 2019.

This item must not be sold to any third party vendors.

Listeria monocytogenes (Lm) contamination has caused over 30 recalls of produce and produce-related items in 2018 and contributed to substantial amounts of economic loss. This pathogen can be found attached to surfaces in food processing environments and such attached cells are known to be less susceptible to antimicrobial agents than cells growing in suspension. Therefore, it was of interest to determine if cells released from surfaces retained the level of tolerance to antimicrobials they exhibited when attached to surfaces. Since processing of produce takes place in many cases under refrigeration temperatures, studies were conducted with Lm growing at 4°C on polystyrene surfaces or on stainless steel (SS), high density polyethylene (HDPE), and polyvinyl chloride (PVC), surface materials frequently encountered in produce processing environments. Two biofilm types were cultured on the processing surfaces, a mixture of six Lm strains (pure mono-species biofilm) or a mixture of these strains plus a Pseudomonas sp. and a Flavobacterium sp. strain (mixed-species biofilm) isolated from a produce-processing facility operating at refrigeration temperature.In the first phase of the study, the susceptibility of mono- and mixed-species biofilms to antimicrobials commonly used for produce washes or process surface sanitation was assayed using MBECTM microtiter plate pegs. The cells attached to the pegs were exposed to sodium hypochlorite (NaOCl), peroxyacetic acid (PAA), and Madison-75, a quaternary amine commercial sanitizer. The estimated minimum concentrations of sodium hypochlorite for inactivation of Lm in both biofilm types after 5 min was 500-ppm and 100-ppm for a 45-min exposure. Inactivation by peroxyacetic acid required a concentration greater than 1000-ppm for 5 min and less than 50-ppm for 45 min. Madison-75 required up to 150-ppm for complete inactivation within 5 min and 75-ppm for a 45-min exposure.In the second phase of the study, the susceptibility of Lm biofilm cells released from processing surfaces into wash water and treatment solutions containing antimicrobial agents was tested. When three coupons carrying mono- or mixed-species biofilms were subjected to water agitation by a magnetic stirrer, the numbers of Lm cells released into the water after 1, 2, 5, 10 and 15 min ranged between 105 to 107 CFU/mL from all surface material coupons. When the coupons were submerged in wash solutions containing antimicrobials, the number of cultured Lm cells released from the coupons fell below the limit of detection after 2 min of exposure to 18.75-ppm Madison-75 and after 5 min of 25-ppm NaOCl and PAA, regardless of the coupon material. These data indicated that Lm cells released from surfaces can be inactivated by concentrations of antimicrobials that are below those recommended for application.In the third phase of the study, mixed-specie biofilms were cultivated in sterile soil particles suspended in R2B or water mediums at 4℃ for 5 days. The soil particles were washed to remove unattached cells, sterile tap water was adjusted to low (25-ppm), moderate (125-ppm) and high (250-ppm) concentrations of antimicrobial agents and 2.5 ml or 500 ml of the solutions were combined with mung beans or spinach leaves, respectively. During 15 min of agitation, samples were removed for Lm enumeration in the water and treatment solutions, in the soil and on each produce commodity. Lm counts in soil were greater than 8 log/g. The highest concentrations of each antimicrobial agent were insufficient at eradicating all Lm from soil, counts ranged from 6.0 to 7.5 log CFU/g after treatment. In treatment solutions to which mung beans were added low, moderate, and high concentrations of antimicrobials, could not prevent transfer of Lm from the soil to the beans, as counts ranged from 2.5 to 4 logs CFU/bean were detected. Results indicated that under conditions where particulate and organic matter are present, transfer of Lm within soil to produce being washed even in the presence of antimicrobials, is feasible.The experiments with spinach leaves were carried out with 10 g of Lm-containing soil and 500 mL of water or anti-microbial solutions. While Lm released from soil was able to attach to spinach leaves during agitation in water at a level of 4 log CFU per leaf, spinach leaves agitated in solutions with a low concentration (25-ppm) of the antimicrobial agent, achieved undetectable limits of Lm within 2 and 5 min of exposure to all antimicrobials. The high concentration (250-ppm) reduced cultured Lm counts to below detectable levels in all antimicrobials after 1 min of exposure in all treatments.

ISBN: 9781085639873Subjects--Topical Terms:

3173303
Food science.

Susceptibility of Listeria monocytogenes-containing Biofilms to Chemical Disinfectants and Potential Transfer of Listeria from Soil to Produce at Refrigerated Temperature.
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520 $a Listeria monocytogenes (Lm) contamination has caused over 30 recalls of produce and produce-related items in 2018 and contributed to substantial amounts of economic loss. This pathogen can be found attached to surfaces in food processing environments and such attached cells are known to be less susceptible to antimicrobial agents than cells growing in suspension. Therefore, it was of interest to determine if cells released from surfaces retained the level of tolerance to antimicrobials they exhibited when attached to surfaces. Since processing of produce takes place in many cases under refrigeration temperatures, studies were conducted with Lm growing at 4°C on polystyrene surfaces or on stainless steel (SS), high density polyethylene (HDPE), and polyvinyl chloride (PVC), surface materials frequently encountered in produce processing environments. Two biofilm types were cultured on the processing surfaces, a mixture of six Lm strains (pure mono-species biofilm) or a mixture of these strains plus a Pseudomonas sp. and a Flavobacterium sp. strain (mixed-species biofilm) isolated from a produce-processing facility operating at refrigeration temperature.In the first phase of the study, the susceptibility of mono- and mixed-species biofilms to antimicrobials commonly used for produce washes or process surface sanitation was assayed using MBECTM microtiter plate pegs. The cells attached to the pegs were exposed to sodium hypochlorite (NaOCl), peroxyacetic acid (PAA), and Madison-75, a quaternary amine commercial sanitizer. The estimated minimum concentrations of sodium hypochlorite for inactivation of Lm in both biofilm types after 5 min was 500-ppm and 100-ppm for a 45-min exposure. Inactivation by peroxyacetic acid required a concentration greater than 1000-ppm for 5 min and less than 50-ppm for 45 min. Madison-75 required up to 150-ppm for complete inactivation within 5 min and 75-ppm for a 45-min exposure.In the second phase of the study, the susceptibility of Lm biofilm cells released from processing surfaces into wash water and treatment solutions containing antimicrobial agents was tested. When three coupons carrying mono- or mixed-species biofilms were subjected to water agitation by a magnetic stirrer, the numbers of Lm cells released into the water after 1, 2, 5, 10 and 15 min ranged between 105 to 107 CFU/mL from all surface material coupons. When the coupons were submerged in wash solutions containing antimicrobials, the number of cultured Lm cells released from the coupons fell below the limit of detection after 2 min of exposure to 18.75-ppm Madison-75 and after 5 min of 25-ppm NaOCl and PAA, regardless of the coupon material. These data indicated that Lm cells released from surfaces can be inactivated by concentrations of antimicrobials that are below those recommended for application.In the third phase of the study, mixed-specie biofilms were cultivated in sterile soil particles suspended in R2B or water mediums at 4℃ for 5 days. The soil particles were washed to remove unattached cells, sterile tap water was adjusted to low (25-ppm), moderate (125-ppm) and high (250-ppm) concentrations of antimicrobial agents and 2.5 ml or 500 ml of the solutions were combined with mung beans or spinach leaves, respectively. During 15 min of agitation, samples were removed for Lm enumeration in the water and treatment solutions, in the soil and on each produce commodity. Lm counts in soil were greater than 8 log/g. The highest concentrations of each antimicrobial agent were insufficient at eradicating all Lm from soil, counts ranged from 6.0 to 7.5 log CFU/g after treatment. In treatment solutions to which mung beans were added low, moderate, and high concentrations of antimicrobials, could not prevent transfer of Lm from the soil to the beans, as counts ranged from 2.5 to 4 logs CFU/bean were detected. Results indicated that under conditions where particulate and organic matter are present, transfer of Lm within soil to produce being washed even in the presence of antimicrobials, is feasible.The experiments with spinach leaves were carried out with 10 g of Lm-containing soil and 500 mL of water or anti-microbial solutions. While Lm released from soil was able to attach to spinach leaves during agitation in water at a level of 4 log CFU per leaf, spinach leaves agitated in solutions with a low concentration (25-ppm) of the antimicrobial agent, achieved undetectable limits of Lm within 2 and 5 min of exposure to all antimicrobials. The high concentration (250-ppm) reduced cultured Lm counts to below detectable levels in all antimicrobials after 1 min of exposure in all treatments.
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