The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Sophia Kathariou - One of the best experts on this subject based on the ideXlab platform.
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conservation and distribution of the benzalkonium chloride resistance cassette bcrabc in listeria monocytogenes
Applied and Environmental Microbiology, 2013Co-Authors: Vikrant Dutta, Driss Elhanafi, Sophia KathariouAbstract:Analysis of a panel of 116 Listeria monocytogenes strains of diverse serotypes and sources (clinical, environment of Food Processing Plants, and Food) revealed that all but one of the 71 benzalkonium chloride-resistant (BCr) isolates harbored bcrABC, previously identified on a large plasmid (pLM80) of the 1998-1999 hot dog outbreak strain H7858. In contrast, bcrABC was not detected among BC-susceptible (BCs) isolates. The bcrABC sequences were highly conserved among strains of different serotypes, but variability was noted in sequences flanking bcrABC. The majority of the BCr isolates had either the pLM80-type of organization of the bcrABC region or appeared to harbor bcrABC on the chromosome, adjacent to novel sequences. Transcription of bcrABC was induced by BC (10 μg/ml) in strains of different serotypes and diverse bcrABC region organization. These findings reveal widespread dissemination of bcrABC across BCr L. monocytogenes strains regardless of serotype and source, while also suggesting possible mechanisms of bcrABC dissemination across L. monocytogenes genomes.
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heavy metal and disinfectant resistance of listeria monocytogenes from Foods and Food Processing Plants
Applied and Environmental Microbiology, 2012Co-Authors: Shakir S Ratani, Vikrant Dutta, Robin M Siletzky, Suleyman Yildirim, Jason A Osborne, Wen Lin, Anthony D Hitchins, Todd J Ward, Sophia KathariouAbstract:The persistence of Listeria monocytogenes in Food Processing Plants and other ecosystems reflects its ability to adapt to numerous stresses. In this study, we investigated 138 isolates from Foods and Food Processing Plants for resistance to the quaternary ammonium disinfectant benzalkonium chloride (BC) and to heavy metals (cadmium and arsenic). We also determined the prevalence of distinct cadmium resistance determinants (cadA1, cadA2, and cadA3) among cadmium-resistant isolates. Most BC-resistant isolates were resistant to cadmium as well. Arsenic resistance was encountered primarily in serotype 4b and was an attribute of most isolates of the serotype 4b epidemic clonal group ECIa. Prevalence of the known cadmium resistance determinants was serotype associated: cadA1 was more common in isolates of serotypes 1/2a and 1/2b than 4b, while cadA2 was more common in those of serotype 4b. A subset (15/77 [19%]) of the cadmium-resistant isolates lacked the known cadmium resistance determinants. Most of these isolates were of serotype 4b and were also resistant to arsenic, suggesting novel determinants that may confer resistance to both cadmium and arsenic in these serotype 4b strains. The findings may reflect previously unrecognized components of the ecological history of different serotypes and clonal groups of L. monocytogenes, including exposures to heavy metals and disinfectants.
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comk prophage junction fragments as markers for listeria monocytogenes genotypes unique to individual meat and poultry Processing Plants and a model for rapid niche specific adaptation biofilm formation and persistence
Applied and Environmental Microbiology, 2011Co-Authors: Bindhu Verghese, Sophia Kathariou, Mei Lok, Jia Wen, Valentina Alessandria, Yi Chen, Stephen J KnabelAbstract:Different strains of Listeria monocytogenes are well known to persist in individual Food Processing Plants and to contaminate Foods for many years; however, the specific genotypic and phenotypic mechanisms responsible for persistence of these unique strains remain largely unknown. Based on sequences in comK prophage junction fragments, different strains of epidemic clones (ECs), which included ECII, ECIII, and ECV, were identified and shown to be specific to individual meat and poultry Processing Plants. The comK prophage-containing strains showed significantly higher cell densities after incubation at 30°C for 48 h on meat and poultry Food-conditioning films than did strains lacking the comK prophage (P < 0.05). Overall, the type of strain, the type of conditioning film, and the interaction between the two were all highly significant (P < 0.001). Recombination analysis indicated that the comK prophage junction fragments in these strains had evolved due to extensive recombination. Based on the results of the present study, we propose a novel model in which the concept of defective comK prophage was replaced with the rapid adaptation island (RAI). Genes within the RAI were recharacterized as “adaptons,” as these genes may allow L. monocytogenes to rapidly adapt to different Food Processing facilities and Foods. If confirmed, the model presented would help explain Listeria's rapid niche adaptation, biofilm formation, persistence, and subsequent transmission to Foods. Also, comK prophage junction fragment sequences may permit accurate tracking of persistent strains back to and within individual Food Processing operations and thus allow the design of more effective intervention strategies to reduce contamination and enhance Food safety.
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genetic characterization of plasmid associated benzalkonium chloride resistance determinants in a listeria monocytogenes strain from the 1998 1999 outbreak
Applied and Environmental Microbiology, 2010Co-Authors: Driss Elhanafi, Vikrant Dutta, Sophia KathariouAbstract:Quaternary ammonium compounds such as benzalkonium chloride (BC) are widely used as disinfectants in both Food Processing and medical environments. BC-resistant strains of Listeria monocytogenes have been implicated in multistate outbreaks of listeriosis and have been frequently isolated from Food Processing Plants. However, the genetic basis for BC resistance in L. monocytogenes remains poorly understood. In this study, we have characterized a plasmid (pLM80)-associated BC resistance cassette in L. monocytogenes H7550, a strain implicated in the 1998-1999 multistate outbreak involving contaminated hot dogs. The BC resistance cassette (bcrABC) restored resistance to BC (MIC, 40 μg/ml) in a plasmid-cured derivative of H7550. All three genes of the cassette were essential for imparting BC resistance. The transcription of H7550 BC resistance genes was increased under sublethal (10 μg/ml) BC exposure and was higher at reduced temperatures (4, 8, or 25°C) than at 37°C. The level of transcription was higher at 10 μg/ml than at 20 or 40 μg/ml. In silico analysis suggested that the BC resistance cassette was harbored by an IS1216 composite transposon along with other genes whose functions are yet to be determined. The findings from this study will further our understanding of the adaptations of this organism to disinfectants such as BC and may contribute to the elucidation of possible BC resistance dissemination in L. monocytogenes.
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heavy metal and benzalkonium chloride resistance of listeria monocytogenes isolates from the environment of turkey Processing Plants
Applied and Environmental Microbiology, 2008Co-Authors: S Mullapudi, Robin M Siletzky, Sophia KathariouAbstract:The resistance of Listeria monocytogenes to cadmium and arsenic has been used extensively for strain subtyping. However, limited information is available on the prevalence of such resistance among isolates from the environment of Food-Processing Plants. In addition, it is not known whether the resistance of such isolates to heavy metals may correlate with resistance to quaternary ammonium compounds extensively used as disinfectants in the Food-Processing industry. In this study, we characterized 192 L. monocytogenes isolates (123 putative strains) from the environment of turkey-Processing Plants in the United States for resistance to cadmium and arsenic and to the quaternary ammonium disinfectant benzalkonium chloride (BC). Resistance to cadmium was significantly more prevalent among strains of serotypes 1/2a (or 3a) and 1/2b (or 3b) (83% and 74%, respectively) than among strains of the serotype 4b complex (19%). Resistance to BC was encountered among 60% and 51% of the serotype 1/2a (or 3a) and 1/2b (or 3b) strains, respectively, and among 7% of the strains of the serotype 4b complex. All BC-resistant strains were also resistant to cadmium, although the reverse was not always the case. In contrast, no correlation was found between BC resistance and resistance to arsenic, which overall was low (6%). Our findings suggest that the Processing environment of turkey-Processing Plants may constitute a reservoir for L. monocytogenes harboring resistance to cadmium and to BC and raise the possibility of common genetic elements or mechanisms mediating resistance to quaternary ammonium disinfectants and to cadmium in L. monocytogenes.
Matthew J Stasiewicz - One of the best experts on this subject based on the ideXlab platform.
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classification of listeria monocytogenes persistence in retail delicatessen environments using expert elicitation and machine learning
Risk Analysis, 2014Co-Authors: Pajau Vangay, Martin Wiedmann, Jon Arni Steingrimsson, Matthew J StasiewiczAbstract:Increasing evidence suggests that persistence of Listeria monocytogenes in Food Processing Plants has been the underlying cause of a number of human listeriosis outbreaks. This study extracts criteria used by Food safety experts in determining bacterial persistence in the environment, using retail delicatessen operations as a model. Using the Delphi method, we conducted an expert elicitation with 10 Food safety experts from academia, industry, and government to classify L. monocytogenes persistence based on environmental sampling results collected over six months for 30 retail delicatessen stores. The results were modeled using variations of random forest, support vector machine, logistic regression, and linear regression; variable importance values of random forest and support vector machine models were consolidated to rank important variables in the experts’ classifications. The duration of subtype isolation ranked most important across all expert categories. Sampling site category also ranked high in importance and validation errors doubled when this covariate was removed. Support vector machine and random forest models successfully classified the data with average validation errors of 3.1% and 2.2% (n = 144), respectively. Our findings indicate that (i) the frequency of isolations over time and sampling site information are critical factors for experts determining subtype persistence, (ii) Food safety experts from different sectors may not use the same criteria in determining persistence, and (iii) machine learning models have potential for future use in environmental surveillance and risk management programs. Future work is necessary to validate the accuracy of expert and machine classification against biological measurement of L. monocytogenes persistence.
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listeria monocytogenes persistence in Food associated environments epidemiology strain characteristics and implications for public health
Journal of Food Protection, 2014Co-Authors: Vânia Ferreira, Martin Wiedmann, Paula Teixeira, Matthew J StasiewiczAbstract:Over the last 10 to 15 years, increasing evidence suggests that persistence of Listeria monocytogenes in Food Processing Plants for years or even decades is an important factor in the transmission of this Foodborne pathogen and the root cause of a number of human listeriosis outbreaks. L. monocytogenes persistence in other Food-associated environments (e.g., farms and retail establishments) may also contribute to Food contamination and transmission of the pathogen to humans. Although L. monocytogenes persistence is typically identified through isolation of a specific molecular subtype from samples collected in a given environment over time, formal (statistical) criteria for identification of persistence are undefined. Environmental factors (e.g., facilities and equipment that are difficult to clean) have been identified as key contributors to persistence; however, the mechanisms are less well understood. Although some researchers have reported that persistent strains possess specific characteristics that may facilitate persistence (e.g., biofilm formation and better adaptation to stress conditions), other researchers have not found significant differences between persistent and nonpersistent strains in the phenotypic characteristics that might facilitate persistence. This review includes a discussion of our current knowledge concerning some key issues associated with the persistence of L. monocytogenes, with special focus on (i) persistence in Food Processing Plants and other Food-associated environments, (ii) persistence in the general environment, (iii) phenotypic and genetic characteristics of persistent strains, (iv) niches, and (v) public health and economic implications of persistence. Although the available data clearly indicate that L. monocytogenes persistence at various stages of the Food chain contributes to contamination of finished products, continued efforts to quantitatively integrate data on L. monocytogenes persistence (e.g., meta-analysis or quantitative microbial risk assessment) will be needed to advance our understanding of persistence of this pathogen and its economic and public health impacts.
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listeria monocytogenes persistence in Food associated environments epidemiology strain characteristics and implications for public health
Journal of Food Protection, 2014Co-Authors: Vânia Ferreira, Martin Wiedmann, Paula Teixeira, Matthew J StasiewiczAbstract:Over the last 10 to 15 years, increasing evidence suggests that persistence of Listeria monocytogenes in Food Processing Plants for years or even decades is an important factor in the transmission of this Foodborne pathogen and the root cause of a number of human listeriosis outbreaks. L. monocytogenes persistence in other Food-associated environments (e.g., farms and retail establishments) may also contribute to Food contamination and transmission of the pathogen to humans. Although L. monocytogenes persistence is typically identified through isolation of a specific molecular subtype from samples collected in a given environment over time, formal (statistical) criteria for identification of persistence are undefined. Environmental factors (e.g., facilities and equipment that are difficult to clean) have been identified as key contributors to persistence; however, the mechanisms are less well understood. Although some researchers have reported that persistent strains possess specific characteristics that ...
Martin Wiedmann - One of the best experts on this subject based on the ideXlab platform.
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classification of listeria monocytogenes persistence in retail delicatessen environments using expert elicitation and machine learning
Risk Analysis, 2014Co-Authors: Pajau Vangay, Martin Wiedmann, Jon Arni Steingrimsson, Matthew J StasiewiczAbstract:Increasing evidence suggests that persistence of Listeria monocytogenes in Food Processing Plants has been the underlying cause of a number of human listeriosis outbreaks. This study extracts criteria used by Food safety experts in determining bacterial persistence in the environment, using retail delicatessen operations as a model. Using the Delphi method, we conducted an expert elicitation with 10 Food safety experts from academia, industry, and government to classify L. monocytogenes persistence based on environmental sampling results collected over six months for 30 retail delicatessen stores. The results were modeled using variations of random forest, support vector machine, logistic regression, and linear regression; variable importance values of random forest and support vector machine models were consolidated to rank important variables in the experts’ classifications. The duration of subtype isolation ranked most important across all expert categories. Sampling site category also ranked high in importance and validation errors doubled when this covariate was removed. Support vector machine and random forest models successfully classified the data with average validation errors of 3.1% and 2.2% (n = 144), respectively. Our findings indicate that (i) the frequency of isolations over time and sampling site information are critical factors for experts determining subtype persistence, (ii) Food safety experts from different sectors may not use the same criteria in determining persistence, and (iii) machine learning models have potential for future use in environmental surveillance and risk management programs. Future work is necessary to validate the accuracy of expert and machine classification against biological measurement of L. monocytogenes persistence.
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listeria monocytogenes persistence in Food associated environments epidemiology strain characteristics and implications for public health
Journal of Food Protection, 2014Co-Authors: Vânia Ferreira, Martin Wiedmann, Paula Teixeira, Matthew J StasiewiczAbstract:Over the last 10 to 15 years, increasing evidence suggests that persistence of Listeria monocytogenes in Food Processing Plants for years or even decades is an important factor in the transmission of this Foodborne pathogen and the root cause of a number of human listeriosis outbreaks. L. monocytogenes persistence in other Food-associated environments (e.g., farms and retail establishments) may also contribute to Food contamination and transmission of the pathogen to humans. Although L. monocytogenes persistence is typically identified through isolation of a specific molecular subtype from samples collected in a given environment over time, formal (statistical) criteria for identification of persistence are undefined. Environmental factors (e.g., facilities and equipment that are difficult to clean) have been identified as key contributors to persistence; however, the mechanisms are less well understood. Although some researchers have reported that persistent strains possess specific characteristics that may facilitate persistence (e.g., biofilm formation and better adaptation to stress conditions), other researchers have not found significant differences between persistent and nonpersistent strains in the phenotypic characteristics that might facilitate persistence. This review includes a discussion of our current knowledge concerning some key issues associated with the persistence of L. monocytogenes, with special focus on (i) persistence in Food Processing Plants and other Food-associated environments, (ii) persistence in the general environment, (iii) phenotypic and genetic characteristics of persistent strains, (iv) niches, and (v) public health and economic implications of persistence. Although the available data clearly indicate that L. monocytogenes persistence at various stages of the Food chain contributes to contamination of finished products, continued efforts to quantitatively integrate data on L. monocytogenes persistence (e.g., meta-analysis or quantitative microbial risk assessment) will be needed to advance our understanding of persistence of this pathogen and its economic and public health impacts.
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listeria monocytogenes persistence in Food associated environments epidemiology strain characteristics and implications for public health
Journal of Food Protection, 2014Co-Authors: Vânia Ferreira, Martin Wiedmann, Paula Teixeira, Matthew J StasiewiczAbstract:Over the last 10 to 15 years, increasing evidence suggests that persistence of Listeria monocytogenes in Food Processing Plants for years or even decades is an important factor in the transmission of this Foodborne pathogen and the root cause of a number of human listeriosis outbreaks. L. monocytogenes persistence in other Food-associated environments (e.g., farms and retail establishments) may also contribute to Food contamination and transmission of the pathogen to humans. Although L. monocytogenes persistence is typically identified through isolation of a specific molecular subtype from samples collected in a given environment over time, formal (statistical) criteria for identification of persistence are undefined. Environmental factors (e.g., facilities and equipment that are difficult to clean) have been identified as key contributors to persistence; however, the mechanisms are less well understood. Although some researchers have reported that persistent strains possess specific characteristics that ...
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salt stress induced transcription of σb and ctsr regulated genes in persistent and non persistent listeria monocytogenes strains from Food Processing Plants
Foodborne Pathogens and Disease, 2012Co-Authors: Daina L Ringus, Martin Wiedmann, Reid A Ivy, Kathryn J BoorAbstract:Abstract Listeria monocytogenes is a Foodborne pathogen that can persist in Food Processing environments. Six persistent and six non-persistent strains from fish Processing Plants and one persistent strain from a meat plant were selected to determine if expression of genes in the regulons of two stress response regulators, σB and CtsR, under salt stress conditions is associated with the ability of L. monocytogenes to persist in Food Processing environments. Subtype data were also used to categorize the strains into genetic lineages I or II. Quantitative reverse transcriptase–polymerase chain reaction (qRT-PCR) was used to measure transcript levels for two σB-regulated genes, inlA and gadD3, and two CtsR-regulated genes, lmo1138 and clpB, before and after (t=10 min) salt shock (i.e., exposure of exponential phase cells to BHI+6% NaCl for 10 min at 37°C). Exposure to salt stress induced higher transcript levels relative to levels under non-stress conditions for all four stress and virulence genes across all...
Hannu Korkeala - One of the best experts on this subject based on the ideXlab platform.
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human listeriosis outbreaks linked to dairy products in europe
Journal of Dairy Science, 2004Co-Authors: Janne Lunden, Riina Tolvanen, Hannu KorkealaAbstract:Abstract Dairy products have been associated with approximately half of the reported listeriosis outbreaks in Europe. The listeriosis outbreaks have mostly been linked to consumption of raw milk or products made of unpasteurized milk. Outbreaks, such as in Switzerland in 1983 to 1987 caused by unpasteurized soft cheese, in Austria in 1986 by unpasteurized milk, and in France in 1995 by a Brie-type cheese made of unpasteurized milk demonstrate the risks involved in the consumption of raw milk or soft cheeses made of unpasteurized milk. The pasteurization of raw milk, which destroys Listeria monocytogenes , does not eliminate later risk of L. monocytogenes contamination in dairy products. The outbreak in Finland from 1998 to 1999, with butter as the source, shows that dairy products made of pasteurized milk may become contaminated in subsequent stages of production with L. monocytogenes . Extensive work has been ongoing in several European countries during the last decade to prevent outbreaks and decrease the incidence of listeriosis. This work has included preventive measures in Food Processing Plants, consumer education, and early detection of outbreaks. A marked reduction has occurred in the incidence of listeriosis in some of these countries during the 1990s, suggesting a relationship between preventive measures and reduction in listeriosis.
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typing of listeria monocytogenes isolates originating from the Food Processing industry with automated ribotyping and pulsed field gel electrophoresis
Journal of Food Protection, 2003Co-Authors: K Aarnisalo, Tiina Autio, Annamaija Sjoberg, Janne Lunden, Hannu Korkeala, Maijaliisa SuihkoAbstract:A total of 486 Listeria monocytogenes isolates originating from 17 Finnish Food Processing Plants (representing meat, poultry, fish, and dairy production) were collected and typed by automated ribotyping using EcoRI as the restriction enzyme. The isolates were divided into 16 different ribotypes (RTs). Some of these isolates (121), representing all EcoRI types and 16 Food Plants, were subjected to ribotyping with the PvuII enzyme, to pulsed-field gel electrophoresis (PFGE) typing with AscI and SmaI restriction enzymes, and to serotyping with O-antigen antisera. Nineteen ribotypes were generated with PvuII, 42 macrorestriction patterns were generated with AscI and 24 with SmaI, and three serotypes were generated with antisera. When the results were combined, the overall number of RTs was 23, and that of the PFGE types was 46. Thus, the overall discrimination power of PFGE was higher (discrimination index [DI] 0.966) than that of ribotyping (DI 0.906). The most common serotype (90.1% of the isolates) was 1/...
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transfer of persistent listeria monocytogenes contamination between Food Processing Plants associated with a dicing machine
Journal of Food Protection, 2002Co-Authors: Janne Lunden, Tiina Autio, Hannu KorkealaAbstract:: The possibility of the transfer of persistent Listeria monocytogenes contamination from one plant to another with a dicing machine was evaluated, and possible reasons for persistent contamination were analyzed. A dicing machine that diced cooked meat products was transferred from plant A to plant B and then to plant C. After the transfer of the dicing machine, L. monocytogenes PFGE type I, originally found in plant A, was soon also found in Plants B and C. This L. monocytogenes PFGE type I caused persistent contamination of the dicing lines in Plants B and C. The persistent L. monocytogenes strain and three nonpersistent L. monocytogenes strains found in the dicing line of plant C were tested for adherence to stainless steel surfaces and minimal inhibitory concentrations of a quaternary ammonium compound and sodium hypochlorite, disinfectants widely used in the dicing lines. The persistent strain showed significantly higher adherence to stainless steel surfaces than did the nonpersistent strains. The minimal inhibitory concentrations of sodium hypochlorite were similar for all strains, and the minimal inhibitory concentrations of the quaternary ammonium compound for three of the L. monocytogenes PFGE types, including the persistent PFGE type, were high. All persistent L. monocytogenes PFGE type I isolates were found in an area with high hygienic standards, with the dicing machine being the first point of contamination. These observations show that the dicing machine sustained the contamination and suggest that the dicing machine transferred the persistent L. monocytogenes PFGE type from one plant to another.
Vikrant Dutta - One of the best experts on this subject based on the ideXlab platform.
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conservation and distribution of the benzalkonium chloride resistance cassette bcrabc in listeria monocytogenes
Applied and Environmental Microbiology, 2013Co-Authors: Vikrant Dutta, Driss Elhanafi, Sophia KathariouAbstract:Analysis of a panel of 116 Listeria monocytogenes strains of diverse serotypes and sources (clinical, environment of Food Processing Plants, and Food) revealed that all but one of the 71 benzalkonium chloride-resistant (BCr) isolates harbored bcrABC, previously identified on a large plasmid (pLM80) of the 1998-1999 hot dog outbreak strain H7858. In contrast, bcrABC was not detected among BC-susceptible (BCs) isolates. The bcrABC sequences were highly conserved among strains of different serotypes, but variability was noted in sequences flanking bcrABC. The majority of the BCr isolates had either the pLM80-type of organization of the bcrABC region or appeared to harbor bcrABC on the chromosome, adjacent to novel sequences. Transcription of bcrABC was induced by BC (10 μg/ml) in strains of different serotypes and diverse bcrABC region organization. These findings reveal widespread dissemination of bcrABC across BCr L. monocytogenes strains regardless of serotype and source, while also suggesting possible mechanisms of bcrABC dissemination across L. monocytogenes genomes.
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heavy metal and disinfectant resistance of listeria monocytogenes from Foods and Food Processing Plants
Applied and Environmental Microbiology, 2012Co-Authors: Shakir S Ratani, Vikrant Dutta, Robin M Siletzky, Suleyman Yildirim, Jason A Osborne, Wen Lin, Anthony D Hitchins, Todd J Ward, Sophia KathariouAbstract:The persistence of Listeria monocytogenes in Food Processing Plants and other ecosystems reflects its ability to adapt to numerous stresses. In this study, we investigated 138 isolates from Foods and Food Processing Plants for resistance to the quaternary ammonium disinfectant benzalkonium chloride (BC) and to heavy metals (cadmium and arsenic). We also determined the prevalence of distinct cadmium resistance determinants (cadA1, cadA2, and cadA3) among cadmium-resistant isolates. Most BC-resistant isolates were resistant to cadmium as well. Arsenic resistance was encountered primarily in serotype 4b and was an attribute of most isolates of the serotype 4b epidemic clonal group ECIa. Prevalence of the known cadmium resistance determinants was serotype associated: cadA1 was more common in isolates of serotypes 1/2a and 1/2b than 4b, while cadA2 was more common in those of serotype 4b. A subset (15/77 [19%]) of the cadmium-resistant isolates lacked the known cadmium resistance determinants. Most of these isolates were of serotype 4b and were also resistant to arsenic, suggesting novel determinants that may confer resistance to both cadmium and arsenic in these serotype 4b strains. The findings may reflect previously unrecognized components of the ecological history of different serotypes and clonal groups of L. monocytogenes, including exposures to heavy metals and disinfectants.
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genetic characterization of plasmid associated benzalkonium chloride resistance determinants in a listeria monocytogenes strain from the 1998 1999 outbreak
Applied and Environmental Microbiology, 2010Co-Authors: Driss Elhanafi, Vikrant Dutta, Sophia KathariouAbstract:Quaternary ammonium compounds such as benzalkonium chloride (BC) are widely used as disinfectants in both Food Processing and medical environments. BC-resistant strains of Listeria monocytogenes have been implicated in multistate outbreaks of listeriosis and have been frequently isolated from Food Processing Plants. However, the genetic basis for BC resistance in L. monocytogenes remains poorly understood. In this study, we have characterized a plasmid (pLM80)-associated BC resistance cassette in L. monocytogenes H7550, a strain implicated in the 1998-1999 multistate outbreak involving contaminated hot dogs. The BC resistance cassette (bcrABC) restored resistance to BC (MIC, 40 μg/ml) in a plasmid-cured derivative of H7550. All three genes of the cassette were essential for imparting BC resistance. The transcription of H7550 BC resistance genes was increased under sublethal (10 μg/ml) BC exposure and was higher at reduced temperatures (4, 8, or 25°C) than at 37°C. The level of transcription was higher at 10 μg/ml than at 20 or 40 μg/ml. In silico analysis suggested that the BC resistance cassette was harbored by an IS1216 composite transposon along with other genes whose functions are yet to be determined. The findings from this study will further our understanding of the adaptations of this organism to disinfectants such as BC and may contribute to the elucidation of possible BC resistance dissemination in L. monocytogenes.