Roles of Fe superoxide dismutase and catalase in resistance of Campylobacter coli to freeze-thaw stress

Phylogenetic Association and Genetic Factors in Cold Stress Tolerance in Campylobacter jejuni

Campylobacter jejuni is a major foodborne pathogen transmitted to humans primarily via contaminated poultry meat. Since poultry meat is generally processed, distributed, and stored in the cold chain, the survival of C. jejuni at refrigeration temperatures crucially affects human exposure to C. jejuni. Here, we investigated genetic factors associated with cold stress tolerance in C. jejuni. Seventy-nine C. jejuni strains isolated from retail raw chicken exhibited different survival levels at 4°C for 21 days. Multilocus sequence typing (MLST) clonal complex 21 (CC-21) and CC-443 were dominant among cold stress-tolerant strains, whereas CC-45 was common among cold stress-sensitive strains. Genome-wide average nucleotide identity (ANI) analysis identified a phylogenetic cluster associated with cold stress tolerance. Moreover, a pangenome analysis revealed 58 genes distinctively present in the cold stress-tolerant phylogenetic cluster. Among these 58 genes, cfrA, encoding the ferric enterobactin receptor involved in ion transport and metabolism, was selected for further analysis. Remarkably, the viability of a ΔcfrA mutant at 4°C was significantly decreased, while the levels of total reactive oxygen species and intracellular iron exceeded those of the wild type. Additionally, a knockout mutation of cfrA also significantly decreased the viability of three cold stress-tolerant isolates at 4°C, confirming the role of cfrA in cold stress tolerance. The results of this study demonstrate that unique phylogenetic clusters of C. jejuni associated with cold stress tolerance exist and that cfrA is a genetic factor contributing to cold stress tolerance in C. jejuni. IMPORTANCE The tolerance of foodborne pathogens to environmental stresses significantly affects food safety. Several studies have demonstrated that C. jejuni survives extended exposures to low temperatures, but the mechanisms of cold stress tolerance are not fully understood. Here, we demonstrate that C. jejuni strains in certain phylogenetic groups exhibit increased tolerance to cold stress. Notably, cfrA is present in the phylogenetic cluster associated with cold stress tolerance and plays a role in the survival of C. jejuni at low temperatures by alleviating oxidative stress. This is the first study to discover phylogenetic associations involving cold stress tolerance and to identify genetic elements conferring cold stress tolerance to C. jejuni.

Roles of Aerotolerance, Biofilm Formation, and Viable but Non-Culturable State in the Survival of Campylobacter jejuni in Poultry Processing Environments

Campylobacter jejuni is one of the most common causes of foodborne human gastroenteritis in the developed world. This bacterium colonizes in the ceca of chickens, spreads throughout the poultry production chain, and contaminates poultry products. Despite numerous on farm intervention strategies and developments in post-harvest antimicrobial treatments, C. jejuni is frequently detected on broiler meat products. This indicates that C. jejuni is evolving over time to overcome the stresses/interventions that are present throughout poultry production and processing. The development of aerotolerance has been reported to be a major survival strategy used by C. jejuni in high oxygen environments. Recent studies have indicated that C. jejuni can enter a viable but non-culturable (VBNC) state or develop biofilm in response to environmental stressors such as refrigeration and freezing stress and aerobic stress. This review provides an overview of different stressors that C. jejuni are exposed to throughout the poultry production chain and the genotypic and phenotypic survival mechanisms, with special attention to aerotolerance, biofilm formation, and development of the VBNC state.

Agents of Campylobacteriosis in Different Meat Matrices in Brazil

We aimed to identify the prevalence of thermophilic species of Campylobacter in meats of different species available on the Brazilian commercial market and to determine the genetic diversity, antimicrobial resistance and virulence potential of the isolates. A total of 906 samples, including chicken, beef and pork carcasses and chicken and beef livers, were purchased in retail outlets, and prevalences of 18.7% (46/246), 3.62% (5/138), 10.14% (14/138), 3.62% (5/138) and 4.47% (11/132), respectively, were identified, evidencing the dissemination of genotypes in the main producing macro-regions. Of all isolates, 62.8% were classified as multidrug resistant (MDR), with resistance to amoxicillin-clavulanate (49.4%), tetracycline (51.8%) and ciprofloxacin (50.6%) and co-resistance to macrolides and fluoroquinolones (37.1%). Multivirulent profiles were identified mainly in isolates from chicken carcasses (84.8%), and the emergence of MDR/virulent strains was determined in pork isolates. All isolates except those from chicken carcasses showed a high potential for biofilm formation (71.4% luxS) and consequent persistence in industrial food processing. For chicken carcasses, the general virulence was higher in C. jejuni (54.3%), followed by C. coli (24%) and Campylobacter spp. (21.7%), and in the other meat matrices, Campylobacter spp. showed a higher prevalence of virulence (57.2%). The high rates of resistance and virulence reinforce the existence of strain selection pressure in the country, in addition to the potential risk of strains isolated not only from chicken carcasses, but also from other meat matrices.

Quantification of Campylobacter jejuni gene expression after successive stresses mimicking poultry slaughtering steps

Broiler meat is considered as the most important source of the foodborne pathogen Campylobacter jejuni. Exposure to stress conditions encountered during the slaughtering process may induce bacterial adaptation mechanisms, and enhance or decrease pathogen resistance to subsequent stress. This adaptation may result from changes in bacterial gene expression. This study aims to accurately quantify the expression of selected C. jejuni genes after stresses inspired from the poultry slaughtering process. RT-qPCR was used to quantify gene expression of 44 genes in three strains after successive heat and cold stresses. Main results indicated that 26 genes out of 44 were differentially expressed following the successive thermal stresses. Three clusters of genes were differentially expressed according to the strain and the stress condition. Up-regulated genes mainly included genes involved in the heat shock response, whereas down-regulated genes belonged to metabolic pathways (such as lipid, amino-acid metabolisms). However, four genes were similarly overexpressed in the three strains; they might represent indicators of the thermal stress response at the species scale. Advances in the molecular understanding of the stress response of pathogenic bacteria, such as Campylobacter, in real-life processing conditions will make it possible to identify technological levers and better mitigate the microbial risk.

Management Strategies for Prevention of Campylobacter Infections Through the Poultry Food Chain: A European Perspective

Numerous studies point out that at present, a complete elimination of Campylobacter species in the poultry food chain is not feasible. Thus, the current aim should be to establish control measures and intervention strategies to minimize the occurrence of Campylobacter spp. in livestock (esp. poultry flocks) and to reduce the quantitative Campylobacter burden along the food chain in animals and subsequently in foods. The most effective measures to mitigate Campylobacter focus on the primary production stage. Nevertheless, measures applied during slaughter and processing complement the general meat hygiene approaches by reducing fecal contamination during slaughtering and processing and as a consequence help to reduce Campylobacter in poultry meat. Such intervention measures at slaughter and processing level would include general hygienic improvements, technological innovations and/or decontamination measures that are applied at single slaughter or processing steps. In particular, approaches that do not focus on a single intervention measure would need to be based on a thorough process of evaluation, and potential combinatory effects have to be modeled and tested. Finally, the education of all stakeholders (including retailers, food handlers and consumers) is required and will help to increase awareness for the presence of foodborne pathogens in raw meat and meat products and can thus aid in the development of the required good kitchen hygiene.

Stress resistance associated with multi-host transmission and enhanced biofilm formation at 42 °C among hyper-aerotolerant generalist Campylobacter jejuni

One of the emerging conundrums of Campylobacter food-borne illness is the bacterial ability to survive stressful environmental conditions. We evaluated the heterogeneity among 90 C. jejuni and 21 C. coli isolates from different sources in Egypt with respect to biofilm formation capabilities (under microaerobic and aerobic atmosphere) and resistance to a range of stressors encountered along the food chain (aerobic stress, refrigeration, freeze-thaw, heat, peracetic acid, and osmotic stress). High prevalence (63%) of hyper-aerotolerant (HAT) isolates was observed, exhibiting also a significantly high tolerance to heat, osmotic stress, refrigeration, and freeze-thaw stress, coupled with high biofilm formation ability which was clearly enhanced under aerobic conditions, suggesting a potential link between stress adaptation and biofilm formation. Most HAT multi-stress resistant and strong biofilm producing C. jejuni isolates belonged to host generalist clonal complexes (ST-21, ST-45, ST-48 and ST-206). These findings highlight the potential role of oxidative stress response systems in providing cross-protection (resistance to other multiple stress conditions) and enhancing biofilm formation in Campylobacter and suggest that selective pressures encountered in hostile environments have shaped the epidemiology of C. jejuni in Egypt by selecting the transmission of highly adapted isolates, thus promoting the colonization of multiple host species by important disease-causing lineages.

Relationship Between Main Channel Structure of Catalases and the Evolutionary Direction in Cold-Adapted Hydrogen Peroxide-Tolerant Exiguobacteium and Psychrobacter

Catalase has crucial role in adaptive response to H₂O₂. Main channel structure responsible for substrate selectivity was estimated to understand the relationship between the evolutionary direction of catalases from Exiguobacterium oxidotolerans and Psychrobacter piscatorii which survive in cold and high concentration of hydrogen peroxide, and their catalytic property. E. oxidotolerans catalase (EKTA) exhibited a higher ratio of compound I formation rate using peracetic acid (a substrate lager than H₂O₂)/catalase activity using H₂O₂ as the substrate than P. piscatori catalase (PKTA). It was considered that the ratio was attributed to the size of the amino acid residues locating at the bottle neck structure in the main channel. The differences in the ratio of the compound I formation rate with peracetic acid to catalase activity with H₂O₂ between the deeper branches in the phylogenetic tree in both EKTA and PKTA were large. This indicates that catalases from the hydrogen peroxide-tolerant bacteria have evolved in different directions, exhibiting effective catalytic activity and allowing broader substrates size or H₂O₂-specific substrate acceptability in EKTA and PKTA, respectively. It is considered that the main channel structure reflected the difference in the evolutionary direction of clade 1 and clade 3 catalases.

Effect of water temperature on cellular stress responses in meagre (Argyrosomus regius)

Μeagre (Argyrosomus regius) is a newly introduced species in the aquaculture sector characterized by high growth rates and good nutritional value. However, the optimum conditions such as water temperature for the rearing of this species are still under research. The aim of the present study was to investigate several biochemical responses in the heart, muscle, liver, and intestine of meagre reared under different water temperatures (17, 23, and 26 °C) in comparison to the initial acclimation temperature at 20 °C. To assess its cellular stress response, the molecular markers of Hsp70 and Hsp90 induced levels, p38 MAPK and p44/42 MAPK phosphorylated levels, ubiquitin conjugates, and Bcl-2 levels were determined. Moreover, to investigate its antioxidant defense, the activities of superoxide dismutase, catalase, and glutathione reductase were measured. The obtained results in meagre showed a distinct tissue-specific response regarding the variations observed in the studied parameters under different acclimation temperatures. Specifically, most examined tissues presented a decrease in the levels of the examined markers compared to 20 °C, while in the intestine, an increase of Hsp70 and p38 MAPK levels was observed at 23 and 26 °C. However, data on the final weight and length of the fish lead to the conclusion that high water temperatures such as 26 °C might be the best for the rearing of this species. Therefore, it is assumed that the observed differential molecular responses may act in a cell-protective way at all temperatures, irrespectively of the effect of temperature on growth parameters.

Tolerance to stress conditions associated with food safety in Campylobacter jejuni strains isolated from retail raw chicken

Campylobacter jejuni is a microaerophilic foodborne pathogen that is sensitive to stress conditions. However, it is not yet understood how this stress-sensitive pathogen may cause a significant number of cases of human gastroenteritis worldwide. In this study, we examined stress tolerance in 70 C. jejuni strains isolated from retail chicken under several stress conditions related to food safety. Compared to oxygen-sensitive (OS) strains of C. jejuni, C. jejuni strains with increased aerotolerance, such as hyper-aerotolerant (HAT) and aerotolerant (AT) strains, were more tolerant to peracetic acid, refrigeration and freeze-thaw stresses. However, the levels of thermotolerance and hyper-osmotolerance were not associated with the aerotolerance level of C. jejuni. The HAT and AT strains of C. jejuni exhibited significantly increased activities of catalase and superoxide dismutase (SOD), compared to the OS strains. Consistently, the HAT and AT strains were highly tolerant to oxidants, such as hydrogen peroxide, cumene hydroperoxide and menadione, compared to the OS strains. The AT and HAT strains that were tolerant to stresses, particularly peracetic acid and refrigeration, predominantly belonged to multilocus sequence typing (MLST) clonal complex (CC)-21. This study shows that oxidative stress resistance plays a role in determining the differential level of aerotolerance in C. jejuni and that AT and HAT strains of C. jejuni are more tolerant to oxidants and low temperatures than OS strains.

Campylobacter jejuni CsrA Regulates Metabolic and Virulence Associated Proteins and Is Necessary for Mouse Colonization

Campylobacter jejuni infection is a leading bacterial cause of gastroenteritis and a common antecedent leading to Gullian-Barré syndrome. Our previous data suggested that the RNA-binding protein CsrA plays an important role in regulating several important phenotypes including motility, biofilm formation, and oxidative stress resistance. In this study, we compared the proteomes of wild type, csrA mutant, and complemented csrA mutant C. jejuni strains in an effort to elucidate the mechanisms by which CsrA affects virulence phenotypes. The putative CsrA regulon was more pronounced at stationary phase (111 regulated proteins) than at mid-log phase (25 regulated proteins). Proteins displaying altered expression in the csrA mutant included diverse metabolic functions, with roles in amino acid metabolism, TCA cycle, acetate metabolism, and various other cell processes, as well as pathogenesis-associated characteristics such as motility, chemotaxis, oxidative stress resistance, and fibronectin binding. The csrA mutant strain also showed altered autoagglutination kinetics when compared to the wild type. CsrA specifically bound the 5' end of flaA mRNA, and we demonstrated that CsrA is a growth-phase dependent repressor of FlaA expression. Finally, the csrA mutant exhibited reduced ability to colonize in a mouse model when in competition with the wild type, further underscoring the role of CsrA in C. jejuni colonization and pathogenesis.

Functions of VPA1418 and VPA0305 Catalase Genes in Growth of Vibrio parahaemolyticus under Oxidative Stress

The marine foodborne enteropathogen Vibrio parahaemolyticus has four putative catalase genes. The functions of two katE-homologous genes, katE1 (VPA1418) and katE2 (VPA0305), in the growth of this bacterium were examined using gene deletion mutants with or without complementary genes. The growth of the mutant strains in static or shaken cultures in a rich medium at 37°C or at low temperatures (12 and 4°C), with or without competition from Escherichia coli, did not differ from that of the parent strain. When 175 μM extrinsic H2O2 was added to the culture medium, bacterial growth of the ΔkatE1 strain was delayed and growth of the ΔkatE1 ΔkatE2 and ΔkatE1 ΔahpC1 double mutant strains was completely inhibited at 37°C for 8 h. The sensitivity of the ΔkatE1 strain to the inhibition of growth by H2O2 was higher at low incubation temperatures (12 and 22°C) than at 37°C. The determined gene expression of these catalase and ahpC genes revealed that katE1 was highly expressed in the wild-type strain at 22°C under H2O2 stress, while the katE2 and ahpC genes may play an alternate or compensatory role in the ΔkatE1 strain. This study demonstrated that katE1 encodes the chief functional catalase for detoxifying extrinsic H2O2 during logarithmic growth and that the function of these genes was influenced by incubation temperature.

Regulation of oxidative stress resistance in Campylobacter jejuni, a microaerophilic foodborne pathogen

Campylobacter jejuni is one of the leading bacterial causes of human gastroenteritis. Due to the increasing rates of human campylobacteriosis, C. jejuni is considered as a serious public health concern worldwide. C. jejuni is a microaerophilic, fastidious bacterium. C. jejuni must overcome a wide range of stress conditions during foodborne transmission to humans, such as food preservation and processing conditions, and even in infection of the gastrointestinal tracts of humans. Particularly, this microaerophilic foodborne pathogen must survive in the atmospheric conditions prior to the initiation of infection. C. jejuni possesses unique regulatory mechanisms for oxidative stress resistance. Lacking OxyR and SoxRS that are highly conserved in other Gram-negative foodborne pathogens, C. jejuni modulates the expression of genes involved in oxidative stress resistance mainly via the peroxide resistance regulator and Campylobacter oxidative stress regulator. Based on recent findings of ours and others, in this review, we described how C. jejuni regulates the expression of oxidative stress defense.

PerR controls oxidative stress defence and aerotolerance but not motility-associated phenotypes of Campylobacter jejuni

The foodborne bacterial pathogen Campylobacter jejuni is an obligate microaerophile that is exposed to atmospheric oxygen during transmission through the food chain. Survival under aerobic conditions requires the concerted control of oxidative stress systems, which in C. jejuni are intimately connected with iron metabolism via the PerR and Fur regulatory proteins. Here, we have characterized the roles of C. jejuni PerR in oxidative stress and motility phenotypes, and its regulon at the level of transcription, protein expression and promoter interactions. Insertional inactivation of perR in the C. jejuni reference strains NCTC 11168, 81-176 and 81116 did not result in any growth deficiencies, but strongly increased survival in atmospheric oxygen conditions, and allowed growth around filter discs infused with up to 30 % H2O2 (8.8 M). Expression of catalase, alkyl hydroperoxide reductase, thioredoxin reductase and the Rrc desulforubrerythrin was increased in the perR mutant, and this was mediated at the transcriptional level as shown by electrophoretic mobility shift assays of the katA, ahpC and trxB promoters using purified PerR. Differential RNA-sequencing analysis of a fur perR mutant allowed the identification of eight previously unknown transcription start sites of genes controlled by Fur and/or PerR. Finally, inactivation of perR in C. jejuni did not result in reduced motility, and did not reduce killing of Galleria melonella wax moth larvae. In conclusion, PerR plays an important role in controlling oxidative stress resistance and aerobic survival of C. jejuni, but this role does not extend into control of motility and associated phenotypes.

Role of alkyl hydroperoxide reductase (AhpC) in the biofilm formation of Campylobacter jejuni

Biofilm formation of Campylobacter jejuni, a major cause of human gastroenteritis, contributes to the survival of this pathogenic bacterium in different environmental niches; however, molecular mechanisms for its biofilm formation have not been fully understood yet. In this study, the role of oxidative stress resistance in biofilm formation was investigated using mutants defective in catalase (KatA), superoxide dismutase (SodB), and alkyl hydroperoxide reductase (AhpC). Biofilm formation was substantially increased in an ahpC mutant compared to the wild type, and katA and sodB mutants. In contrast to the augmented biofilm formation of the ahpC mutant, a strain overexpressing ahpC exhibited reduced biofilm formation. A perR mutant and a CosR-overexpression strain, both of which upregulate ahpC, also displayed decreased biofilms. However, the introduction of the ahpC mutation to the perR mutant and the CosR-overexpression strain substantially enhanced biofilm formation. The ahpC mutant accumulated more total reactive oxygen species and lipid hydroperoxides than the wild type, and the treatment of the ahpC mutant with antioxidants reduced biofilm formation to the wild-type level. Confocal microscopy analysis showed more microcolonies were developed in the ahpC mutant than the wild type. These results successfully demonstrate that AhpC plays an important role in the biofilm formation of C. jejuni.

Starvation and re-feeding affect Hsp expression, MAPK activation and antioxidant enzymes activity of European sea bass (Dicentrarchus labrax)

In the context of food deprivation in fish (wild and farmed), understanding of cellular responses is necessary in order to develop strategies to minimize stress caused by starvation in the aquaculture section. The present study evaluates the effects of long term starvation (1F-3S: one-month feeding-three-month starvation) and starvation/re-feeding (2S-2F: two-month starvation-two-month re-feeding) compared to the control group (4F-0S: four-month feeding-zero month starvation) on cellular stress response and antioxidant defense in organs, like the intestine, the liver, the red and white muscle of European sea bass Dicentrarchus labrax. Molecular responses were addressed through the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases and particularly p38 mitogen-activated protein kinase (p38 MAPK) and the extracellular signal-regulated kinases (ERK-1/2). For the determination of the effect of the oxidative stress caused by food deprivation and/or re-feeding, the (maximum) activities of antioxidant enzymes such as glutathione peroxidise (GPx), catalase (CAT) and superoxide dismutase (SOD) as well as the determination of thiobarbituric acid reactive substances (TBARS) were studied. The experimental feeding trials caused a tissue distinct and differential response on the cellular and antioxidant capacity of sea bass not only during the stressful process of starvation but also in re-feeding. Specifically, the intestine phosphorylation of ERKs and antioxidant enzymatic activities increased in the 2S-2F fish group, while in the 1F-3S group an increase was detected in the levels of the same proteins except for GPx. In the liver and the red muscle of 2S-2F fish, decreased Hsp70 and phosphorylated p38 MAPK levels and increased Hsp90 levels were observed. Additionally, SOD activity decreased in the red muscle of 2S-2F and 1F-3S groups. In the liver and red muscle of 1F-3S group Hsp70 levels increased, while the activation of p38 MAPK in the liver decreased. In the white muscle, Hsp90 levels decreased and the phosphorylation of p38 MAPK increased in both feeding regimes compared to control. In the same tissue, GPx and catalase levels were decreased in 2S-2F regime, while SOD levels were decreased in 1F-3S regime.

The Campylobacter jejuni transcriptional regulator Cj1556 plays a role in the oxidative and aerobic stress response and is important for bacterial survival in vivo

Campylobacter jejuni is the leading bacterial cause of human gastroenteritis worldwide. Despite stringent microaerobic growth requirements, C. jejuni is ubiquitous in the aerobic environment and so must possess regulatory systems to sense and adapt to external stimuli, such as oxidative and aerobic (O(2)) stress. Reannotation of the C. jejuni NCTC11168 genome sequence identified Cj1556 (originally annotated as a hypothetical protein) as a MarR family transcriptional regulator, and further analysis indicated a potential role in regulating the oxidative stress response. A C. jejuni 11168H Cj1556 mutant exhibited increased sensitivity to oxidative and aerobic stress, decreased ability for intracellular survival in Caco-2 human intestinal epithelial cells and J774A.1 mouse macrophages, and a reduction in virulence in the Galleria mellonella infection model. Microarray analysis of gene expression changes in the Cj1556 mutant indicated negative autoregulation of Cj1556 expression and downregulation of genes associated with oxidative and aerobic stress responses, such as katA, perR, and hspR. Electrophoretic mobility shift assays confirmed the binding of recombinant Cj1556 to the promoter region upstream of the Cj1556 gene. cprS, which encodes a sensor kinase involved in regulation of biofilm formation, was also upregulated in the Cj1556 mutant, and subsequent studies showed that the mutant had a reduced ability to form biofilms. This study identified a novel C. jejuni transcriptional regulator, Cj1556, that is involved in oxidative and aerobic stress responses and is important for the survival of C. jejuni in the natural environment and in vivo.

Impact of growth temperature and agar versus liquid media on freeze-thaw tolerance of Yersinia enterocolitica

Yersinia enterocolitica is a foodborne pathogen well known for its ability to grow at low temperatures. Recent studies with another psychrotrophic foodborne pathogen, Listeria monocytogenes, revealed that temperature of growth had pronounced impact on survival following repeated freezing and thawing (cryotolerance). Listerial cryotolerance was significantly more pronounced when bacteria were grown at 37 degrees C than following growth at either 4 degrees C or 25 degrees C. However, it is not known whether such impact of growth temperature is a general adaptation shared with other foodborne pathogens. In this study, we investigated the impact of growth temperature (4 degrees C, 25 degrees C, and 37 degrees C) on cryotolerance of Y. enterocolitica. In strong contrast to findings previously obtained with Listeria spp., cryotolerance of Y. enterocolitica was impaired following growth in liquid media at 37 degrees C, with cell concentration dropping to undetectable levels (<10(1) colony forming unit/mL) following as few as six freeze-thaw cycles. On the other hand, when the bacteria were grown at 4 degrees C, cryotolerance was significantly higher (p < 0.05), and substantial survival was maintained even after 18 cycles (2-5 log reduction, depending on strain). Enhanced cryotolerance was also observed with cultures grown at 25 degrees C. Bacteria grown at 37 degrees C on agar were significantly more cryotolerant than following growth at 37 degrees C in liquid media (p < 0.05). The data suggest species-specific impact of growth temperature and liquid versus agar medium on cryotolerance of cold-tolerant bacteria.

Temperature-dependent requirement for catalase in aerobic growth of Listeria monocytogenes F2365

Listeria monocytogenes is a Gram-positive, psychrotrophic, facultative intracellular food-borne pathogen responsible for severe illness (listeriosis). The bacteria can grow in a wide range of temperatures (1 to 45°C), and low-temperature growth contributes to the food safety hazards associated with contamination of ready-to-eat foods with this pathogen. To assess the impact of oxidative stress responses on the ability of L. monocytogenes to grow at low temperatures and to tolerate repeated freeze-thaw stress (cryotolerance), we generated and characterized a catalase-deficient mutant of L. monocytogenes F2365 harboring a mariner-based transposon insertion in the catalase gene (kat). When grown aerobically on blood-free solid medium, the kat mutant exhibited impaired growth, with the extent of impairment increasing with decreasing temperature, and no growth was detected at 4°C. Aerobic growth in liquid was impaired at 4°C, especially under aeration, but not at higher temperatures (10, 25, or 37°C). Genetic complementation of the mutant with the intact kat restored normal growth, confirming that inactivation of this gene was responsible for the growth impairment. In spite of the expected impact of oxidative stress responses on cryotolerance, cryotolerance of the kat mutant was not affected.

Inactivation of a cold-induced putative rna helicase gene of Listeria monocytogenes is accompanied by failure to grow at low temperatures but does not affect freeze-thaw tolerance

Freeze-thaw tolerance (cryotolerance) of Listeria monocytogenes is markedly influenced by temperature of growth of the bacteria, and may involve responses to low-temperature stresses encountered during freezing and thawing. A cold-sensitive mariner-based transposon mutant of L. monocytogenes F2365 was found to harbor a single insertion in LMOf2365_1746, encoding a putative RNA helicase, and earlier shown by other investigators to be induced during 4 degrees C growth of L. monocytogenes. The mutant had normal growth at 37 degrees C but completely failed to grow at either 4 or 10 degrees C, and had impaired growth and reduced swarming on soft agar at 25 degrees C. However, the mutation had no discernible influence on the ability of the bacteria to tolerate repeated freezing and thawing after growth at either 25 or 37 degrees C. The findings suggest that the transposon insertion in the putative helicase gene, in spite of the severely cold-sensitive phenotype that accompanies it, does not affect the ability of the bacteria to cope with cold-related stresses encountered during repeated freezing and thawing.

Survival of Campylobacter jejuni and Campylobacter coli on retail broiler meat stored at -20, 4, or 12 degrees C and development of Weibull models for survival

Survival of Campylobacter jejuni and Campylobacter coli isolated from broiler meat was investigated and modeled on retail breast meat. Meat portions were inoculated with C. jejuni or C. coli at 6.4 to 6.8 log CFU/g followed by storage at -20 degrees C for 84 days or at 4 or 12 degrees C for 14 days. Kinetic data within a species and temperature were fitted to the Weibull model. When >or=70% of the residuals were in an acceptable prediction zone from -1 (fail-safe) to 0.5 (fail-dangerous) log units, the model was considered to have acceptable performance. Survival of Campylobacter was highest at 4 degrees C, lowest at 12 degrees C, and intermediate at -20 degrees C. Survival of C. jejuni and C. coli was similar at -20 degrees C but was lower (P<0.05) for C. jejuni than for C. coli at 4 and 12 degrees C. The Weibull model provided acceptable predictions for four of six sets of dependent data with unacceptable performance for survival of C. jejuni at -20 and 12 degrees C. A difference in survival was observed between the two strains of C. jejuni tested. Comparison of Weibull model predictions with data for C. jejuni archived in ComBase revealed mostly unacceptable performance, indicating that C. jejuni and C. coli survival on raw broiler breast meat differs from published results for other strains and growth media. Variation in Campylobacter survival among replicate storage trials was high, indicating that performance of the models can be improved by collection of additional data to better define the survival response during storage at temperatures from -20 to 12 degrees C.

Selection of low-temperature resistance in bacteria and potential applications

Microbial consortia may harbour an array of resistance mechanisms that facilitate survival under harsh conditions, including antifreeze and ice-nucleation proteins. Antifreeze proteins lower freezing points as well as inhibit the growth of large, potentially damaging ice crystals from small ice embryos. In contrast, ice-nucleation proteins prevent supercooling and allow ice formation at high, sub-zero temperatures. Psychrophiles and psychrotolerant microbes are typically sought in extremely cold environments. However, given that geography is unlikely to present an insurmountable barrier to microbial dispersal, we reasoned that species with low-temperature adaptations should also be present, although rare, in more temperate environments. In consequence, the challenge then becomes one of selecting for rare microbes present in a larger community. Following the introductory commentary, we demonstrate that both freeze-thaw survival and ice-affinity selection can be used to identify microbes, which demonstrate low-temperature resistance, from enrichments derived from temperate environments. Selection resulted in a drastic decrease in cell abundance and diversity, allowing the isolation of a subset of resistant microbes. Depending on the origin of the consortia, these resistant microbes demonstrated cross-tolerance to osmotic stress, or a high proportion of antifreeze and/or ice-nucleation protein activities. Both types of ice-associating proteins presumably facilitate microbial survival at low temperatures. These proteins, as well as molecules that maintain osmotic balance, are also of commercial interest, with applications in the food, energy and medical industries. In addition, the resistant phenotypes described here provide a glimpse into the breadth of strategies microbes use to survive and thrive at low temperatures.

Atypical roles for Campylobacter jejuni amino acid ATP binding cassette transporter components PaqP and PaqQ in bacterial stress tolerance and pathogen-host cell dynamics

Campylobacter jejuni is a human pathogen causing severe diarrheal disease; however, our understanding of the survival of C. jejuni during disease and transmission remains limited. Amino acid ATP binding cassette (AA-ABC) transporters in C. jejuni have been proposed as important pathogenesis factors. We have investigated a novel AA-ABC transporter system, encoded by cj0467 to cj0469, by generating targeted deletions of cj0467 (the membrane transport component) and cj0469 (the ATPase component) in C. jejuni 81-176. The analyses described here have led us to designate these genes paqP and paqQ, respectively (pathogenesis-associated glutamine [q] ABC transporter permease [P] and ATPase [Q]). We found that loss of either component resulted in amino acid uptake defects, most notably diminished glutamine uptake. Altered resistance to a series of environmental and in vivo stresses was also observed: both mutants were hyperresistant to aerobic and organic peroxide stress, and while the DeltapaqP mutant was also hyperresistant to heat and osmotic shock, the DeltapaqQ mutant was more susceptible than the wild type to the latter two stresses. The DeltapaqP and DeltapaqQ mutants also displayed a surprising but statistically significant increase in recovery from macrophages and epithelial cells in short-term intracellular survival assays. Annexin V, 4',6-diamidino-2-phenylindole (DAPI), and Western blot analyses revealed that macrophages infected with the DeltapaqP or DeltapaqQ mutant exhibited transient but significant decreases in cell death and extracellular signal-regulated kinase-mitogen-activated protein kinase activation compared to levels in wild-type-infected cells. The DeltapaqP mutant was not defective in either short-term or longer-term mouse colonization, consistent with its increased stress survival and diminished host cell damage phenotypes. Collectively, these results demonstrate a unique correlation of an AA-ABC transporter with bacterial stress tolerances and host cell responses to pathogen infection.

Role of growth temperature in freeze-thaw tolerance of Listeria spp

The food-borne pathogen Listeria monocytogenes can grow in a wide range of temperatures, and several key virulence determinants of the organism are expressed at 37 degrees C but are strongly repressed below 30 degrees C. However, the impact of growth temperature on the ability of the bacteria to tolerate environmental stresses remains poorly understood. In other microorganisms, cold acclimation resulted in enhanced tolerance against freezing and thawing (cryotolerance). In this study, we investigated the impact of growth temperature (4, 25, and 37 degrees C) on the cryotolerance of 14 strains of L. monocytogenes from outbreaks and from food processing plant environments and four strains of nonpathogenic Listeria spp. (L. welshimeri and L. innocua). After growth at different temperatures, cells were frozen at -20 degrees C, and repeated freeze-thaw cycles were applied every 24 h. Pronounced cryotolerance was exhibited by cells grown at 37 degrees C, with a <1-log decrease after 18 cycles of freezing and thawing. In contrast, freeze-thaw tolerance was significantly reduced (P < 0.05) when bacteria were grown at either 4 or 25 degrees C, with log decreases after 18 freeze-thaw cycles ranging from 2 to >4, depending on the strain. These findings suggest that growth at 37 degrees C, a temperature required for expression of virulence determinants of L. monocytogenes, is also required for protection against freeze-thaw stress. The negative impact of growth at low temperature on freeze-thaw stress was unexpected and has not been reported before with this or other psychrotrophic microorganisms.

Role of oxidative stress in C. jejuni inactivation during freeze-thaw treatment

Campylobacter jejuni represents one of the leading causes of bacterial enteritis throughout the world. Poultry is an important source of C. jejuni. Despite hygiene measures taken in the production chain, C. jejuni is frequently isolated from poultry meat. C. jejuni is a microaerophilic pathogen, affected by oxidative stress. Freeze-thaw treatment induces cell death by several mechanisms, including oxidative stress. In this article, we investigate the role of oxidative stress in C. jejuni sensitivity during and after a freeze-thaw treatment. This treatment results in dead and sublethally injured cells. The latter population might have an increased sensitivity to oxidative stress. To test this, cells were stored for another 24 h at 4 degrees C under aerobic conditions and compared to cells that were not treated. C. jejuni survival was measured in different media (water, BHI broth, chicken juice, and chicken fillets) to test the environment protective effect. Different strains were tested, including sodB (encoding the superoxide dismutase) and cj1371 (encoding a periplasmic protein) mutants. Cell death was particularly important in water but similar in BHI, chicken juice, and chicken fillets. The sodB mutant was more sensitive to freeze-thaw treatment, suggesting that the killing mechanism involves production of superoxide anions. On the contrary, the cj1371 mutant was more sensitive to storage at 4 degrees C, suggesting that it does not play a role in the detoxification of reactive oxygen species. Storage at 4 degrees C after freeze-thaw treatment increases cell death of oxidative stress-sensitive populations. Sensitization to oxidative stress, freeze-thaw treatment, and further storage at 4 degrees C could be a way to reduce C. jejuni populations on carcasses.

Optimising the viability during storage of freeze-dried cell preparations of Campylobacter jejuni

Freeze-dried cultures of Campylobacter jejuni are used in the food and microbiological industry for reference materials and culture collections. However, C. jejuni is very susceptible to damage during freeze-drying and subsequent storage and it would be useful to have longer-lasting cultures. The survival of C. jejuni during freeze-drying and subsequent storage was investigated with the aim of optimising survival. C. jejuni was freeze-dried using cultures of different age (24-120 h), various lyoprotectants (10% phytone peptone, proteose peptone, peptonized milk, trehalose, soytone and sorbitol), various storage (air, nitrogen and vacuum) and re-hydration (media, temperature and time) conditions. One-day-old cultures had significantly greater survival after freeze-drying than older cultures. The addition of trehalose to inositol broth as a lyoprotectant resulted in almost 2 log(10) increase in survival after 2 months storage at 4 degrees C. Storage in a vacuum atmosphere and re-hydration in inositol broth at 37 degrees C increased recovery by 1-2 log(10) survival compared to re-hydration in maximal recovery diluent (MRD) after storage at 4 degrees C. Survival during storage was optimal when a one-day-old culture was freeze-dried in inositol broth plus 10% (w/v) trehalose, stored under vacuum at 4 degrees C and re-hydrated at the same incubation temperature (37 degrees C) in inositol broth for 30 min. The results demonstrate that the survival of freeze-dried cells of C. jejuni during storage can be significantly increased by optimising the culture age, the lyoprotectant, and the storage and re-hydration conditions. The logarithmic rate of loss of viability (K) followed very well an inverse dependence on the absolute temperature, i.e., the Arrhenius rate law. Extrapolation of the results to a more typical storage temperature (4 degrees C) predicted a very low K value of 1.5 x 10(-3). These results will be useful to the development of improved reference materials and samples held in culture collections.

Stress Response of Campylobacter spp. and its Role in Food Processing

In many temperate countries Campylobacter spp. are the most common bacterial causes of human infectious intestinal disease. Yet the aetiology of this infection has only partly been described. A majority of human campylobacteriosis cases are associated with food of animal origin. Despite being very sensitive to environmental stressors Campylobacter spp. are able to persist in the food chain and can pose a threat to the consumer. In this review, the survival potential and stress response of Campylobacter spp. in food will be summarized and the importance of food preservation technologies will be discussed.

The influence of freezing and duration of storage on Campylobacter and indicator bacteria in broiler carcasses

In total, 215 commercially processed broiler carcasses were examined to determine optimum cultural enumeration, the effects of freezing, method of thawing, and duration of frozen storage on levels of Campylobacter spp. and fecal coliforms. Enumeration studies compared MPN procedures to direct plating onto selective mCCDA agar and indicated equivalency for quantitation of Campylobacter spp. Levels of Campylobacter and fecal coliforms were subsequently estimated by direct plating of carcass rinses. Freezing of naturally contaminated carcasses followed by storage at -20 degrees C for 31, 73, 122 and 220 days showed statistically significant (P< or =0.05) reductions in Campylobacter counts initially as compared with counts found on fresh product. Among 5 lots of broilers, levels of Campylobacter on carcasses were reduced by log mean values ranging from 0.65 to 2.87 after freezing and 31 days of storage. Similar reductions due to freezing were not observed for fecal coliforms counts. The level of Campylobacter was reduced by approximately one log immediately after freezing, and remained relatively constant during the 31-220 days of frozen storage. The levels were constant during 7 days of refrigerated storage. After 31 days of frozen storage there was a reduced rate in reduction of counts among broilers thawed at 7 degrees C as compared to thawing at 22 degrees C with either cultural method (MPN and mCCDA). These findings warrant consideration of the public health benefits related to freezing contaminated poultry prior to commercial distribution to reduce Campylobacter exposure levels associated with contaminated carcasses.

The nature of plant growth-promoting effects of a pseudoalteromonad associated with the marine algae Laminaria japonica and linked to catalase excretion

AIMS

The goal of this study was to identify a marine algae-associated bacterium isolated from Laminaria japonica and investigate this microorganism's growth-promoting effects on plants.

METHODS AND RESULTS

The bacterium, identified as Pseudoalteromonas porphyrae, was determined to display a biostimulatory activity for seed germination and shoot growth in several agricultural plants and also for growth in ginseng callus cell culture. This biostimulatory activity was linked to a catalase enzyme that was excreted in the maximal amount during the transition from logarithmic growth phase to stationary growth phase. In addition, selected shifts in growth temperature and medium salinity affected the amount of enzyme excreted. The purified catalase was determined to be composed of identical subunits. The catalase of interest displayed significantly higher biostimulatory activity than the catalase from bovine liver.

CONCLUSIONS

The catalase investigated in this study is unique in that it promotes growth in and possibly contributes to stress tolerance of plants.

SIGNIFICANCE AND IMPACT OF THE STUDY

The catalase of interest has the potential for use in treatments that aim to improve percent seed germination as well as obtaining tall shoots in a shorter time period.

Environmental survival mechanisms of the foodborne pathogen Campylobacter jejuni

Campylobacter spp. continue to be the greatest cause of bacterial gastrointestinal infections in humans worldwide. They encounter many stresses in the host intestinal tract, on foods and in the environment. However, in common with other enteric bacteria, they have developed survival mechanisms to overcome these stresses. Many of the survival mechanisms used by Campylobacter spp. differ from those used by other bacteria, such as Escherichia coli and Salmonella spp. This review summarizes the mechanisms by which Campylobacter spp. adapt to stress conditions and thereby increase their ability to survive on food and in the environment.

The Campylobacter jejuni stringent response controls specific stress survival and virulence-associated phenotypes

Campylobacter jejuni is a highly prevalent food-borne pathogen that causes diarrhoeal disease in humans. A natural zoonotic, it must overcome significant stresses both in vivo and during transmission despite the absence of several traditional stress response genes. Although relatively little is understood about its mechanisms of pathogenesis, its ability to interact with and invade human intestinal epithelial cells closely correlates with virulence. A C. jejuni microarray-based screen revealed that several known virulence genes and several uncharacterized genes, including spoT, were rapidly upregulated during infection of human epithelial cells. spoT and its homologue relA have been shown in other bacteria to regulate the stringent response, an important stress response that to date had not been demonstrated for C. jejuni or any other epsilon-proteobacteria. We have found that C. jejuni mounts a stringent response that is regulated by spoT. Detailed analyses of a C. jejuni delta spoT mutant revealed that the stringent response is required for several specific stress, transmission and antibiotic resistance-related phenotypes. These include stationary phase survival, growth and survival under low CO2/high O2 conditions, and rifampicin resistance. A secondary suppressor strain that specifically rescues the low CO2 growth defect of the delta spoT mutant was also isolated. The stringent response additionally proved to be required for the virulence-related phenotypes of adherence, invasion, and intracellular survival in two human epithelial cell culture models of infection; spoT is the first C. jejuni gene shown to participate in longer term survival in epithelial cells. Microarray analyses comparing wild-type to the delta spoT mutant also revealed a strong correlation between gene expression profiles and phenotype differences observed. Together, these data demonstrate a critical role for the C. jejuni stringent response in multiple aspects of C. jejuni biology and pathogenesis and, further, may lend novel insight into unexplored features of the stringent response in other prokaryotic organisms.

Iron acquisition and regulation in Campylobacter jejuni

Iron affects the physiology of bacteria in two different ways: as a micronutrient for bacterial growth and as a catalyst for the formation of hydroxyl radicals. In this study, we used DNA microarrays to identify the C. jejuni genes that have their transcript abundance affected by iron availability. The transcript levels of 647 genes were affected after the addition of iron to iron-limited C. jejuni cells. Several classes of affected genes were revealed within 15 min, including immediate-early response genes as well as those specific to iron acquisition and metabolism. In contrast, only 208 genes were differentially expressed during steady-state experiments comparing iron-rich and iron-limited growth conditions. As expected, genes annotated as being involved in either iron acquisition or oxidative stress defense were downregulated during both time course and steady-state experiments, while genes encoding proteins involved in energy metabolism were upregulated. Because the level of protein glycosylation increased with iron limitation, iron may modulate the level of C. jejuni virulence by affecting the degree of protein glycosylation. Since iron homeostasis has been shown to be Fur regulated in C. jejuni, an isogenic fur mutant was used to define the Fur regulon by transcriptome profiling. A total of 53 genes were Fur regulated, including many genes not previously associated with Fur regulation. A putative Fur binding consensus sequence was identified in the promoter region of most iron-repressed and Fur-regulated genes. Interestingly, a fur mutant was found to be significantly affected in its ability to colonize the gastrointestinal tract of chicks, highlighting the importance of iron homeostasis in vivo. Directed mutagenesis of other genes identified by the microarray analyses allowed the characterization of the ferric enterobactin receptor, previously named CfrA. Chick colonization assays indicated that mutants defective in enterobactin-mediated iron acquisition were unable to colonize the gastrointestinal tract. In addition, a mutation in a receptor (Cj0178) for an uncharacterized iron source also resulted in reduced colonization potential. Overall, this work documents the complex response of C. jejuni to iron availability, describes the genetic network between the Fur and iron regulons, and provides insight regarding the role of iron in C. jejuni colonization in vivo.

Freezing: an underutilized food safety technology?

Freezing is an ancient technology for preserving foods. Freezing halts the activities of spoilage microorganisms in and on foods and can preserve some microorganisms for long periods of time. Frozen foods have an excellent overall safety record. The few outbreaks of food-borne illness associated with frozen foods indicate that some, but not all human pathogens are killed by commercial freezing processes. Freezing kills microorganisms by physical and chemical effects and possibly through induced genetic changes. Research is needed to better understand the physical and chemical interactions of various food matrices with the microbial cell during freezing and holding at frozen temperatures. The literature suggests that many pathogenic microorganisms may be sublethally injured by freezing, so research should be done to determine how to prevent injured cells from resuscitating and becoming infectious. Studies on the genetics of microbial stress suggest that the induction of resistance to specific stresses may be counteracted by, for example, simple chemicals. Research is needed to better understand how resistance to the lethal effect of freezing is induced in human pathogens and means by which it can be counteracted in specific foods. Through research, it seems possible that freezing may in the future be used to reliably reduce populations of food-borne pathogens as well as to preserve foods.

Improvement of the Resistance of Lactobacillus delbrueckii ssp. bulgaricus to Freezing by Natural Selection

Lactic acid bacteria are often produced as frozen or freeze-dried cultures that can be used for the direct inoculation of milk in cheese and fermented milk production processes. The objective of this study was to investigate whether the resistance of Lactobacillus delbrueckii ssp. bulgaricus to freezing could be improved by natural selection. Three parallel cultures of strain CFL1 were propagated for 30 cycles in which each cycle involved three serial transfers through milk, one freezing step, and one thawing step. The concentration in viable cells after thawing as well as the acidifying activity of the thawed cultures increased dramatically throughout the experiment. This may be explained by the random appearance of better-adapted mutants that can outcompete the other genotypes. However, after 30 cycles of subcultivation, freezing, and thawing, all the cultures contained subpopulations having different survival rates to freezing. Our results show that serial transfer culture experiments may be used to improve technological properties of lactic acid bacteria. Furthermore, investigation of the mutations that are responsible for an increased cryotolerance may help to define new targets for improving the resistance of lactic acid bacteria to several stresses.

Effect of paraquat on cellular defense enzymes and glutathione level of Funalia trogii

The effect of paraquat on the activities of antioxidant defense and detoxifying enzymes of the white-rot fungus Funalia trogii was determined. Paraquat increased the activities of glutathione reductase (GR), glutathione transferase (GT) and superoxide dismutase at 1 mmol/L, while at 0.1 mmol/L it did not affect the activity of GR and GT. It depressed the catalase activity and the amount of glutathione at all concentrations used. Paraquat treatment probably depresses antioxidant defense components such as catalase and glutathione.

The physiology of Campylobacter species and its relevance to their role as foodborne pathogens

Campylobacter jejuni and C. coli are recognised as the leading causes of bacterial foodborne diarrhoeal disease throughout the development world. While most foodborne bacterial pathogens are considered to be relatively robust organisms, as a consequence of the necessity to survive the inimical conditions imposed by food processing and preservation, Campylobacter species have uniquely fastidious growth requirements and an unusual sensitivity to environmental stress. Campylobacters also lack many of the well characterised adaptive responses that can be collated with resistance to stress in other bacteria. The aim of this review is to outline the unusual physiology of campylobacters (C. jejuni and C. coli) and to describe how this influences their role as foodborne pathogens.