Acid and heat tolerance of persistent and nonpersistent Listeria monocytogenes food plant strains

A comparative phenotype analysis of 24 Listeria monocytogenes LO28 stress-resistant variants obtained after high-pressure treatment was performed to assess their robustness and growth performance under a range of food-relevant conditions. In addition, genetic analysis was conducted to characterize the promoter regions and open reading frames of the class I and III transcriptional repressors CtsR and HrcA, which control production of specific sets of stress proteins. Analysis of stress survival capacity, motility, biofilm formation, and growth under various conditions showed all variants to be more resistant to pressure and heat than the wild type; however, differences among variants were observed in acid resistance, growth rate, motility, and biofilmforming capacity. Genetic analysis revealed no variation in the genetic make-up of hrcA and its upstream region, but two variants had deletions in the upstream region of ctsR and seven variants had mutations in the ctsR gene itself. The results of the characterization were cluster analyzed to obtain insight into the diversity of variants. Ten unique variants and three clusters with specific features could be identified: one cluster consisting of seven variants having a mutation in the CtsR regulator gene, one cluster containing two variants with an aerobic biofilm formation capacity similar to that of the wild type, and a cluster composed of five immotile variants. The large population diversity of L. monocytogenes stress-resistant variants signifies the organism's genetic flexibility, which in turn may contribute to the survival and persistence of this human pathogen in food-processing environments.The opportunistic pathogen Listeria monocytogenes causes listeriosis, a serious infection that most commonly affects newborns, pregnant women, seniors, and immune-compromised patients. Because L. monocytogenes is ubiquitous it may be introduced into food-processing plants through many different routes. L. monocytogenes has been shown to colonize processing environments and to contaminate products during processing. Certain strains may become persistent in a plant and cause continuous contamination (18,20,27). The ability of part of a population to survive in a certain environment because of heterogeneity is called persistence. However, there is a difference between survivors that are phenotypically switching between normal cells and persister cells and survivors that are mutated and therefore genetically different (7). Although the origin of persistence can be different, overall persisters can have specific qualities, such as acid and heat tolerance and adherence to surfaces, contributing to the establishment of house strains. A number of studies have shown persistence of L. monocytogenes in various food-processing plants (6,17,19,21,22). Some of these persistent strains dominated and persisted in a plant or production line for years and caused food contamination and human disease. The generation, occurrence, and selection of these persistent strains can have a significan...

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confidence: 99%

Population Diversity of Listeria monocytogenes LO28: Phenotypic and Genotypic Characterization of Variants Resistant to High Hydrostatic Pressure

Boeijen

Chavaroche

Valderrama

et al. 2010

“…Processed foods can be contaminated by contact with equipment, by the handling of raw products by staff, or from postprocessing environmental niches in which L. monocytogenes can survive despite the routine use of thorough disinfection procedures (2, 3). Mechanisms that facilitate the survival of L. monocytogenes in food processing environments include biofilm formation (4, 5), acquisition of antimicrobial resistance (6-10), and stress resistance mechanisms (11,12).…”

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confidence: 99%

The Connection between Persistent, Disinfectant-Resistant Listeria monocytogenes Strains from Two Geographically Separate Iberian Pork Processing Plants: Evidence from Comparative Genome Analysis

Ortiz

López-Alonso

Rodríguez³

et al. 2016

100

The aim of this study was to investigate the basis of the putative persistence of Listeria monocytogenes in a new industrial facility dedicated to the processing of ready-to-eat (RTE) Iberian pork products. Quaternary ammonium compounds, which included benzalkonium chloride (BAC), were repeatedly used as surface disinfectants in the processing plant. Clean and disinfected surfaces were sampled to evaluate if resistance to disinfectants was associated with persistence. Of the 14 isolates obtained from product contact and non-product contact surfaces, only five different pulsed-field gel electrophoresis (PFGE) types were identified during the 27-month study period. Two of these PFGE types (S1 and S10-1) were previously identified to be persistent and BAC-resistant (BAC r ) strains in a geographically separate slaughterhouse belonging to the same company. The remaining three PFGE types, which were first identified in this study, were also BAC r . Whole-genome sequencing and in silico multilocus sequence typing (MLST) analysis of five BAC r isolates of the different PFGE types identified in this study showed that the isolate of the S1 PFGE type belonged to MLST sequence type 31 (ST31), a low-virulence type characterized by mutations in the inlA and prfA genes. The isolates of the remaining four PFGE types were found to belong to MLST ST121, a persistent type that has been isolated in several countries. The ST121 strains contained the BAC resistance transposon Tn6188. The disinfection-resistant L. monocytogenes population in this RTE pork product plant comprised two distinct genotypes with different multidrug resistance phenotypes. This work offers insight into the L. monocytogenes subtypes associated with persistence in food processing environments. Listeria monocytogenes is a Gram-positive bacterium of the phylum Firmicutes. Often found in raw foods, L. monocytogenes bacteria can cause the life-threatening disease listeriosis. Most cases of human listeriosis appear to be caused by ready-to-eat (RTE) foods, and the risk of illness increases with the number of cells ingested and with RTE foods that support the growth of L. monocytogenes (1). Processed foods can be contaminated by contact with equipment, by the handling of raw products by staff, or from postprocessing environmental niches in which L. monocytogenes can survive despite the routine use of thorough disinfection procedures (2, 3). Mechanisms that facilitate the survival of L. monocytogenes in food processing environments include biofilm formation (4, 5), acquisition of antimicrobial resistance (6-10), and stress resistance mechanisms (11,12).L. monocytogenes is capable of colonizing food production plants with certain subtypes that are found only in specific sections of the plants (13, 14). Furthermore, some of these subtypes may persist in food processing environments for years (15-17). Persistent strains have been identified to be major postprocessing contaminants of RTE foods, and in many cases, listeriosis outbreaks have been associated with cases of p...

“…These differences may affect the incidence of the strains in the environment, including the food supply chain (39), and their presence in human clinical samples (23). Differences in inactivation rates among serotype groups have been previously observed following exposure to dry coleslaw mix at pH 3.5 (20).…”

Section: Resultsmentioning

confidence: 99%

“…To accelerate the processing time and maintain acceptable flavors, meat products are often dipped into lactate and acetate mixtures. There is a possibility that transient exposures to organic acids may contribute to survival and potential persistence of L. monocytogenes strains in factory environments by selecting for acid-resistant strains (39,56,62).…”

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confidence: 99%

Transcriptomic and Phenotypic Responses of Listeria monocytogenes Strains Possessing Different Growth Efficiencies under Acidic Conditions

Bowman

Chang

Pinfold

et al. 2010

In an experiment delineating aciduric strains, food and clinical Listeria monocytogenes isolates tended to produce the most biomass whereas ovine and avian strains produced comparatively less biomass when exposed to high levels of sodium diacetate (SD) and potassium sorbate. Compared to reference strains that exhibited greater acid sensitivity, representative food isolates with comparatively good growth capacities in the presence of 21 mM SD at pH 5.0 accumulated reduced levels of acetate anion and K ؉ ion. The aciduric nature of SD-resistant strains was also reflected by comparatively high tolerance to pH 2.4 (HCl) acid challenges, a property boosted by the presence of SD. Exposure to elevated levels of SD (21 mM SD at pH 5.0) was found to have broad effects on gene expression, as differentiated from effects caused by mildly acidic conditions (pH 5.0). SD-resistant strain FW04/0025 was more responsive to elevated SD, increasing the expression of 222 genes (>2-fold change [P < 0.05]), compared to the more sensitive EGD reference strain, which exhibited increases in expression of 112 genes. Key differences between the strains in relation to SD-enhanced transcripts were notably associated with the cell envelope, oxidative stress management, and intermediary metabolism. SD thus appears to differentially influence growth efficiency and survival of strains, under conditions relevant to acidic foods, that could be due to altered cell wall and metabolic phenotypes.