Gene expression profile of Campylobacter jejuni in response to growth temperature variation

Prevalence and antimicrobial resistance of Campylobacter jejuni and Campylobacter coli over time in Thailand under a One Health approach: A systematic review and meta-analysis

Campylobacter spp. are major food-borne zoonotic pathogens impacting food safety worldwide. Thailand is one of the countries facing with a significant burden of Campylobacter infections and is recognized as a hotspot of AMR. Our study applied a systematic review and meta-analysis, using a One Health perspective, to investigate the prevalence and AMR of Campylobacter jejuni (C. jejuni) and Campylobacter coli (C. coli) over time in Thailand, from 1985 to 2023. Based on the PRISMA guidelines, a literature search using PubMed, ScienceDirect, and Google Scholar to identify the articles reporting prevalence, sequence types (STs), antimicrobial susceptibility, and resistance genes of Campylobacter spp. in humans, animals, food, and environmental samples was performed. Eighty-one articles were retrieved for systematic review, with 33 reporting Campylobacter spp. prevalence and 20 containing AMR data collected for meta-analysis. The highest prevalence of C. jejuni was found in chickens (43.6 %) and chicken products (31.4 %), followed by ducks (16.7 %), the general human population with diarrhea (15.9 %), children with diarrhea (10.7 %). C. coli was also prevalent in chickens (12.6 %) and chicken products (10.4 %). C. jejuni prevalence decreased by 14.8 % among children with diarrhea (p = 0.006), but increased by 16.7 % in chicken products (p = 0.007). Sixty-two STs were identified, with ST 574, ST 1075, ST 51 being the most prevalent STs recorded. Five STs, including ST 50, ST 51, ST 354, ST 464, and ST 574, were reported in both humans and chickens. The AMR levels were highest against quinolones, ranging 75.4 %-94.8 % in human-related categories and 71.6 %-88.7 % in chicken-related categories. Notably, ciprofloxacin-resistant and nalidixic acid-resistant C. jejuni strains collected from chickens increased by 11.9 % (p = 0.004) and 16.1 % (p = 0.027), respectively. Thirteen resistance genes/mutations were reported, with the phenotypic resistance linked to gyrA mutations and tet(O) genes. The high prevalence and increasing trend of AMR in C. jejuni and C. coli underscore the critical need for One Health surveillance to address the rising AMR challenge posed by these pathogens in Thailand.

ClpB enhances thermotolerance in Campylobacter jejuni through protein disaggregation independent of DnaK

Campylobacter jejuni is a leading cause of foodborne infections worldwide and primarily transmitted to humans through the consumption of contaminated poultry meat. To enhance Campylobacter-associated food safety, it is critical to understand how C. jejuni survives during the thermal processing of poultry products. In this study, we monitored the survival of 86 C. jejuni strains during heat treatment and observed that some strains exhibited elevated heat tolerance. Notably, multilocus sequence typing clonal complex (CC)-443 and CC-607 were dominant among heat-tolerant strains, while the CC-21 strains were mostly heat-sensitive, indicating phylogenetic association with thermotolerance. We also investigated the function of heat shock chaperones in the thermotolerance of C. jejuni. Among several knockout mutants of heat shock chaperones, a mutant lacking clpB exhibited significantly lower survival than the wild type under heat treatment. Moreover, we observed a significantly higher accumulation of protein aggregates in the absence of ClpB, demonstrating that ClpB functions as a disaggregase during heat exposure. Additionally, ClpB from the heat-tolerant CC-443 group possessed distinct amino acid substitutions in the functional nucleotide-binding domain compared to ClpB in other CC groups. Interestingly, despite the well-known interaction of these proteins in many other bacteria, a two-hybrid assay demonstrated that ClpB of C. jejuni does not bind to DnaK, suggesting that C. jejuni may have a distinct mechanism for protein disaggregation and stress tolerance. Our findings demonstrate that ClpB plays a crucial role in the thermotolerance of C. jejuni through unique protein disaggregation mechanisms during poultry processing.IMPORTANCEThis study unveils a distinctive mechanism of thermotolerance involving protein disaggregation in Campylobacter jejuni, a major foodborne pathogen. Understanding C. jejuni's ability to withstand heat stress is crucial for comprehending the occurrence of Campylobacter infections resulting from the consumption of contaminated poultry meat. Our research elucidates the roles of heat shock proteins, particularly ClpB, in the thermotolerance of C. jejuni. These findings significantly contribute to our fundamental understanding of bacterial physiology related to stress tolerance, which has important implications for public health and food safety.

Prevalence and genetic characteristics of Campylobacter jejuni from laying-hens in Hubei Province, China

BACKGROUND

Campylobacter jejuni (C. jejuni), a major global cause of foodborne bacterial diseases, accounts for more than 90% of all reported cases. Poultry is considered a major reservoir for the transmission of Campylobacter to humans. While extensive research has been conducted abroad on the occurrence and epidemiology of C. jejuni in laying hens, there are scant reports on its prevalence in layer chickens in China. The present study was designed to isolate C. jejuni from 482 cloacal swabs collected from seven laying hen farms located in Hubei Province between January and March 2024. Furthermore, the study aimed to explore the genetic diversity, antibiotic resistance, and virulence gene profiles of the isolated strains.

RESULTS

The overall prevalence of C. jejuni amounted to 4.36% (21/482). Whole-genome sequencing of these 21 isolates revealed 11 distinct sequence types (STs) and eight clonal complexes (CCs), with ST-6522 and CC-443 emerging as the predominant genotypes. Antimicrobial susceptibility testing against 11 antibiotics revealed high resistance rates among C. jejuni isolates, particularly towards ceftriaxone and enrofloxacin, where resistance was universal (100%). Similarly, high resistance levels were also observed for doxycycline (95.24%), ceftiofur (80.95%), tilmicosin (76.19%), and amoxicillin-clavulanic acid (57.14%). Through genomic resistance gene prediction, a total of eighteen resistance genes were identified within the 21 C. jejuni isolates. The most frequently occurring resistance genes were the gyrA (T86I) point mutation (95.14%), cmeR (95.14%), and tet(O) (95.14%). Notably, a robust correlation was discernibled between enrofloxacin resistance and the gyrA (T86I) point mutation, as well as between resistance to ceftriaxone and tilmicosin and the presence of the cmeR gene. Conversely, the correlations between other antibiotic resistance phenotypes and their corresponding resistance genes were less robust. A comprehensive analysis of virulence genes isolated from C. jejuni strains revealed a total of 117 virulence genes, categorized according to their functional roles. These categories encompass adhesion (cadF, jlpA, porA, pebA), invasion (ciaB), motility (flaA, flgB, flhB), toxin production (cdtA, cdtB, cdtC), and immune modulation (htrB, wlaN).

CONCLUSIONS

Our results revealed the high resistance rate of C. jejuni from laying-hens in hubei Province, China, which will help the farms take the necessary action to develop effective mitigation strategies for reducing Campylobacter infection in poultry.

High prevalence of antibiotic resistant Campylobacter among patients attending clinical settings in Kigali, Rwanda

BACKGROUND

Thermophilic Campylobacter species are important causes of human gastroenteritis and inappropriate use of antimicrobials has led to the emergence of antimicrobial resistance (AMR). In Rwanda, data is limited on the prevalence and AMR carriage rate of Campylobacter strains. This study aimed at assessing the prevalence and antimicrobial susceptibility profiles of Campylobacter species among isolates obtained from different clinical settings in Kigali city, Rwanda.

METHODS

This cross-sectional study used a purposive sampling method to collect 385 stool samples from consenting patients attending the Microbiology Department at Kigali University Teaching Hospital (CHUK), Nyarugenge District Hospital, Muhima and Biryogo Health Centers (HC). Campylobacter species were isolated using culture and characterized with biochemical tests and multiplex Polymerase Chain Reaction (PCR) for species confirmation. Antimicrobial susceptibility testing (AST) with six antimicrobials [ciprofloxacin (CIP), tetracycline (TET), chloramphenicol (CHL), streptomycin (STR), erythromycin (ERY), and gentamicin (GEN)] was carried out by using Kirby-Bauer disk diffusion.

RESULTS

The overall prevalence of Campylobacter spp. was 7.0% (27/385) and the highest prevalence of 77.8% (21/27) was recorded at Biryogo HC. The prevalence of C. jejuni and C. coli were 92.6% (25/27) and 7.4% (2/27), respectively. Infection was significantly associated with diarrhea (p < 0.0001). Campylobacter isolates showed high resistance to STR (85.2%, 23/27), followed by ERY (66.7%, 18/27), and CIP (37.1%, 10/27). The isolates were sensitive to CHL at 88.9% (24/27), TET at 66.7% (18/27), and GEN at 66.7% (18/27).

CONCLUSION

The prevalence of campylobacteriosis in Kigali City is not negligible and is associated with diarrhea. Campylobacter strains isolated from clinical settings were resistant to commonly used antimicrobials. Larger studies will provide insights into the national status of Campylobacter-related AMR. Routine monitoring of antimicrobial use is recommended to mitigate this public health threat. Molecular analyses of resistant strains are warranted to characterize the genomic drive of antibiotic resistance.

The Efficacy of a Ferric Sillen Core-Linked Polymer in Suppressing the Pathogenicity of Campylobacter jejuni

Campylobacter spp. are considered the leading bacterial cause of human gastroenteritis in the world. The development of effective intervention strategies aimed at limiting C. jejuni infections has encountered various challenges, including a lack of an appropriate animal model. Nevertheless, recent advancements in research have clarified the molecular mechanisms underlying C. jejuni's pathogenicity, potentially opening new avenues for targeted interventions. This study evaluated the efficacy of a ferric sillen core-linked polymer (FSCLP) in lowering the proliferation and gene expression of C. jejuni virulence factors in vitro. Furthermore, this study sought to examine the impact of this FSCLP in an ex vivo environment by investigating its ability to influence the attachment to and invasion of porcine jejunal epithelial (IPEC-J2) cells by C. jejuni. Findings show that the FSCLP exhibits significant inhibitory effects on the growth of C. jejuni (p < 0.001) and decreases gene expression related to both virulence and colonisation in C. jejuni. Moreover, supplementation with the FSCLP significantly reduced the attachment of C. jejuni to IPEC-J2 cells (p < 0.01) when compared to the control. Thus, this water-soluble product presents a potential management strategy for Campylobacter infections in poultry, potentially impeding colonisation, reducing transmission, and ultimately mitigating the incidence of human campylobacteriosis.

Effects of in-package cold plasma treatment on poultry breast meat packaged in high CO2 atmosphere

High CO2 in packages significantly extends microbiological shelf life of poultry meat. Cold plasma is an emerging antimicrobial treatment, which generates various reactive gas species and inactivates microbials effectively. The objective of this study was to explore the potential effects of combining high CO2 package and in-package cold plasma (IPCP) treatments on the quality and safety of raw chicken breast meat. Noninoculated samples and samples inoculated with Campylobacter jejuni and Salmonella Typhimurium were packaged in 0, 30, 70, or 100% CO2 (with make-up gas N2) and treated with IPCP at 70 kV for 3 min. Ozone formation, microbial counts, drip loss, pH, and color were measured. There was no interaction effect between high CO2 package and IPCP on microbial counts, drip loss, and color measurements. IPCP reduced spoilage microbial growth by 0.43 log (from 7.00 log to 6.57 log, P = 0.033) and C. jejuni populations by 0.67 log (from 4.82 log to 4.15 log, P < 0.001) on meat surface but did not affect S. Typhimurium (P = 0.206). Increased CO2 in packages had more effect on spoilage microbial growth (more than 1.5 log from 8.08 log to 6.35 log, P < 0.001) and S. Typhimurium populations (more than 0.5 log from 4.94 log to 4.39 log, P = 0.004) than IPCP but did not affect C. jejuni (P = 0.163). IPCP resulted in increases in changes in L* by 1.67 units (0.70 vs. 2.37, P = 0.016) and a* values by 0.56 units (0.73 vs. 1.29, P < 0.001) and decreases in b* values by 0.91 units (0.46 versus -0.45, P = 0.015). High CO2 levels caused increases in changes in L* values by 4.35 units (-0.82 versus 3.53, P < 0.001) with no effects on a* and b* values (P > 0.05). Data demonstrate that there are no combined effects by high CO2 package and IPCP on meat quality and safety of raw chicken breast meat under our experimental conditions. Either high CO2 package or IPCP can retain microbial quality and safety, even though they may cause changes in appearance of stored chicken breast meat.

Interplay of two small RNAs fine-tunes hierarchical flagella gene expression in Campylobacter jejuni

Like for many bacteria, flagella are crucial for Campylobacter jejuni motility and virulence. Biogenesis of the flagellar machinery requires hierarchical transcription of early, middle (RpoN-dependent), and late (FliA-dependent) genes. However, little is known about post-transcriptional regulation of flagellar biogenesis by small RNAs (sRNAs). Here, we characterized two sRNAs with opposing effects on C. jejuni filament assembly and motility. We demonstrate that CJnc230 sRNA (FlmE), encoded downstream of the flagellar hook protein, is processed from the RpoN-dependent flgE mRNA by RNase III, RNase Y, and PNPase. We identify mRNAs encoding a flagella-interaction regulator and the anti-sigma factor FlgM as direct targets of CJnc230 repression. CJnc230 overexpression upregulates late genes, including the flagellin flaA, culminating in longer flagella and increased motility. In contrast, overexpression of the FliA-dependent sRNA CJnc170 (FlmR) reduces flagellar length and motility. Overall, our study demonstrates how the interplay of two sRNAs post-transcriptionally fine-tunes flagellar biogenesis through balancing of the hierarchically-expressed components.

Proteome profiling of Campylobacter jejuni 81-176 at 37 °C and 42 °C by label-free mass spectrometry

BACKGROUND

The main natural reservoir for Campylobacter jejuni is the avian intestinal tract. There, C. jejuni multiplies optimally at 42 °C - the avian body temperature. After infecting humans through oral intake, the bacterium encounters the lower temperature of 37 °C in the human intestinal tract. Proteome profiling by label-free mass spectrometry (DIA-MS) was performed to examine the processes which enable C. jejuni 81-176 to thrive at 37 °C in comparison to 42 °C. In total, four states were compared with each other: incubation for 12 h at 37 °C, for 24 h at 37 °C, for 12 h at 42 °C and 24 h at 42 °C.

RESULTS

It was shown that the proteomic changes not only according to the different incubation temperature but also to the length of the incubation period were evident when comparing 37 °C and 42 °C as well as 12 h and 24 h of incubation. Altogether, the expression of 957 proteins was quantifiable. 37.1 - 47.3% of the proteins analyzed showed significant differential regulation, with at least a 1.5-fold change in either direction (i.e. log2 FC ≥ 0.585 or log2 FC ≤ -0.585) and an FDR-adjusted p-value of less than 0.05. The significantly differentially expressed proteins could be arranged in 4 different clusters and 16 functional categories.

CONCLUSIONS

The C. jejuni proteome at 42 °C is better adapted to high replication rates than that at 37 °C, which was in particular indicated by the up-regulation of proteins belonging to the functional categories "replication" (e.g. Obg, ParABS, and NapL), "DNA synthesis and repair factors" (e.g. DNA-polymerase III, DnaB, and DnaE), "lipid and carbohydrate biosynthesis" (e.g. capsular biosynthesis sugar kinase, PrsA, AccA, and AccP) and "vitamin synthesis, metabolism, cofactor biosynthesis" (e.g. MobB, BioA, and ThiE). The relative up-regulation of proteins with chaperone function (GroL, DnaK, ClpB, HslU, GroS, DnaJ, DnaJ-1, and NapD) at 37 °C in comparison to 42 °C after 12 h incubation indicates a temporary lower-temperature proteomic response. Additionally the up-regulation of factors for DNA uptake (ComEA and RecA) at 37 °C compared to 42 °C indicate a higher competence for the acquisition of extraneous DNA at human body temperature.

The characterization and correlation between the phenotypic and genotypic resistance of Campylobacter spp. isolates from commercial broilers and native chickens in the south of Thailand

RESEARCH HIGHLIGHTS

High Campylobacter prevalence in chickens; C. jejuni more prevalent than C. coli.Susceptibility to macrolides but resistance to quinolones/tetracyclines in isolates.Homogeneous resistance patterns within farms; higher in broilers than in native birds.Partial association between phenotypic and genotypic resistance among isolates.

Unravelling the transcriptome response of Enterobacter sp. S-33 under varying temperature

Enterobacter genus includes the bacteria occupying every aspect of environment, however, their adaptability at varying temperature is not clear. In the present study, we analyzed the transcriptome response of Enterobacter sp. S-33 and their functional genes under various temperatures (30-45 ℃) that were expressed and accumulated in cells under temperature-stress. During a temperature shift from 37 to 45 ℃, 165 genes showed differential expression including 112 up-regulated and 53 down-regulated. In particular, heat-shock genes such as CspA, 16 kDa heat shock protein A/B and transcriptional regulators such as LysR, TetR, and LuxR were differentially expressed, indicating the role of complex molecular mechanism of Enterobacter adapting to temperature stress. Similarly, genes associated to signal transduction, ABC transporters, iron homeostasis, and quorum sensing were also induced. The Gene ontology enrichment analysis of differentially expressed genes (DEGs) were categorized into "transmembrane transport", "tRNA binding", "hydrogen sulfide biosynthetic process" and "sulfate assimilation" terms. In addition, Kyoto Encyclopedia of Genes and Genomes pathways showed that ABC transporter as well as quorum sensing pathways were significantly enriched. Overall, current study has contributed to explore the adaptive molecular mechanisms of Enterobacter spp. upon temperature change, which further opens new avenues for future in-depth functional studies.

Zoonotic Bacteria in Anolis sp., an Invasive Species Introduced to the Canary Islands (Spain)

Lizards belonging to the genus Anolis are native to America and have been introduced in many parts of the world. In this work, a gastrointestinal microbiological analysis from Anolis sp. introduced to Tenerife, Canary Island, was carried out. A total of 74 individuals were analyzed by culture and molecular tools. Pseudomonas spp. was the most prevalent bacteria isolated (64.3%), followed by enteropathogenic Escherichia coli with at least one of the investigated virulent genes (stx1, stx2, and eae) (44.6%). The stx2 gene was more prevalent which differs to that reported in other reptiles, probably due to wastewater transmission. Campylobacter spp. was detected in 32.4% of the animals, highlighting the detection of C. jejuni and C. fetus by their relevance to public health. The zoonotic Staphylococcus lugdunensis, found in 14.9% of the animals, was firstly detected in reptiles. Vibrio sp. which is more associated with aquatic environments was found in 10.8% of the lizards in this study, with Vibrio cholerae being found in two of the animals. The prevalence of Salmonella sp. (5.4%) was low, compared with other studies carried out in reptiles. These results indicate that Anolis sp. in Tenerife could be playing a role in the maintenance and spread of the pathogens detected, being a possible risk factor for public health and biodiversity conservation.

Survival of Campylobacter jejuni 11168H in Acanthamoebae castellanii Provides Mechanistic Insight into Host Pathogen Interactions

Campylobacter jejuni is the leading cause of bacterial foodborne gastroenteritis worldwide but is rarely transferred between human hosts. Although a recognized microaerophile, the majority of C. jejuni are incapable of growing in an aerobic environment. The persistence and transmission of this pathogen outside its warm-blooded avian and mammalian hosts is poorly understood. Acanthamoebae species are predatory protists and form an important ecological niche with several bacterial species. Here, we investigate the interaction of C. jejuni 11168H and Acanthamoebae castellanii at the single-cell level. We observe that a subpopulation of C. jejuni cells can resist killing by A. castellanii, and non-digested bacteria are exocytosed into the environment where they can persist. In addition, we observe that A. castellanii can harbor C. jejuni 11168H even upon encystment. Transcriptome analyses of C. jejuni interactions revealed similar survival mechanisms when infecting both A. castellanii and warm-blooded hosts. In particular, nitrosative stress defense mechanisms and flagellum function are important as confirmed by mutational analyses of C. jejuni 11168H. This study describes a new host–pathogen interaction for C. jejuni and confirms that amoebae are transient hosts for the persistence, adaptability, and potential transmission of C. jejuni.

Quantitative Assessment of First Nations Drinking Water Distribution Systems for Detection and Prevalence of Thermophilic Campylobacter Species

Water is considered a major route for transmitting human-associated pathogens. Although microbial water quality indicators are used to test for the presence of waterborne pathogens in drinking water, the two are poorly correlated. The current study investigates the prevalence of thermophilic DNA markers specific for Campylobacter spp. (C. jejuni and C. coli) in source water and throughout the water distribution systems of two First Nations communities in Manitoba, Canada. A total of 220 water samples were collected from various points of the drinking water distribution system (DWDS) between 2016 and 2018. Target Campylobacter spp. were always (100%) detected in a home with a fiberglass (CF) cistern, as well as the community standpipe (SP). The target bacteria were also frequently detected in treated water at the Water Treatment Plant (WTP) (78%), homes with polyethylene (CP) (60%) and concrete (CC) (58%) cisterns, homes with piped (P) water (43%) and water truck (T) samples (20%), with a maximum concentration of 1.9 × 10³ cells 100 mL^-1 (C. jejuni) and 5.6 × 10⁵ cells 100 mL^-1 (C. coli). Similarly, target bacteria were detected in 68% of the source water samples with a maximum concentration of 4.9 × 10³ cells 100 mL^-1 (C. jejuni) and 8.4 × 10⁵ cells 100 mL^-1 (C. coli). Neither target Campylobacter spp. was significantly associated with free and total chlorine concentrations in water. The study results indicate that there is an immediate need to monitor Campylobacter spp. in small communities of Canada and, particularly, to improve the DWDS in First Nations communities to minimize the risk of Campylobacter infection from drinking water sources. Further research is warranted in improving/developing processes and technologies to eliminate microbial contaminants from water.

Genomic Analysis Reveals That Isolation Temperature on Selective Media Introduces Genetic Variation in Campylobacter jejuni from Bovine Feces

Campylobacter jejuni is commonly isolated on selective media following incubation at 37 °C or 42 °C, but the impact of these temperatures on genome variation remains unclear. Previously, Campylobacter selective enrichments from the feces of steers before and after ceftiofur treatment were plated on selective agar media and incubated at either 37 °C or 42 °C. Here, we analyzed the whole genome sequence of C. jejuni strains of the same multilocus sequence typing (MLST)-based sequence type (ST) and isolated from the same sample upon incubation at both temperatures. Four such strain pairs (one ST8221 and three ST8567) were analyzed using core genome and whole genome MLST (cgMLST, wgMLST). Among the 1970 wgMLST loci, 7-25 varied within each pair. In all but one of the pairs more (1.7-8.5 fold) new alleles were found at 42 °C. Most frameshift, nonsense, or start-loss mutations were also found at 42 °C. Variable loci CAMP0575, CAMP0912, and CAMP0913 in both STs may regularly respond to different temperatures. Furthermore, frameshifts in four variable loci in ST8567 occurred at multiple time points, suggesting a persistent impact of temperature. These findings suggest that the temperature of isolation may impact the sequence of several loci in C. jejuni from cattle.

Feeling the Heat: The Campylobacter jejuni HrcA Transcriptional Repressor Is an Intrinsic Protein Thermosensor

The heat-shock response, a universal protective mechanism consisting of a transcriptional reprogramming of the cellular transcriptome, results in the accumulation of proteins which counteract the deleterious effects of heat-stress on cellular polypeptides. To quickly respond to thermal stress and trigger the heat-shock response, bacteria rely on different mechanisms to detect temperature variations, which can involve nearly all classes of biological molecules. In Campylobacter jejuni the response to heat-shock is transcriptionally controlled by a regulatory circuit involving two repressors, HspR and HrcA. In the present work we show that the heat-shock repressor HrcA acts as an intrinsic protein thermometer. We report that a temperature upshift up to 42 °C negatively affects HrcA DNA-binding activity to a target promoter, a condition required for de-repression of regulated genes. Furthermore, we show that this impairment of HrcA binding at 42 °C is irreversible in vitro, as DNA-binding was still not restored by reversing the incubation temperature to 37 °C. On the other hand, we demonstrate that the DNA-binding activity of HspR, which controls, in combination with HrcA, the transcription of chaperones' genes, is unaffected by heat-stress up to 45 °C, portraying this master repressor as a rather stable protein. Additionally, we show that HrcA binding activity is enhanced by the chaperonin GroE, upon direct protein-protein interaction. In conclusion, the results presented in this work establish HrcA as a novel example of intrinsic heat-sensing transcriptional regulator, whose DNA-binding activity is positively modulated by the GroE chaperonin.

Proteomic insights into Lysinibacillus sp.-mediated biosolubilization of manganese

There has been alarming depletion of manganese (Mn) reserves owing to the ongoing extensive mining operations for catering the massive industrial demand of this element. Moreover, the mining operations have been leading to the generation of Mn-rich waste, thereby contaminating both terrestrial and aquatic bodies. The current scenario necessitates the development of alternative processes for bioremediation as well as economic recovery of Mn from mining wastes. The present investigation aims to report the bioleaching of Mn by Lysinibacillus sp. from mining waste residues in the context of mine waste remediation. Results confirmed that the native isolate had a high Mn biosolubilization potential with a solubilizing efficiency of 84% at the end of a 21-day study under optimized conditions of pulp density 2% (< 150-μm particle size), pH 6.5, and temperature 30 °C. Fourier transform infrared spectroscopy (FTIR) studies followed by liquid chromatography mass spectrometry (LC-MS) analysis were used to ascertain the change in microbial protein conformation, configuration, and protein identification. The results revealed the expression of heat shock proteins (HSP) from the family HSP which is predominantly expressed in bacteria during stress conditions. This study represents the application of native bacterial strain in Mn biosolubilization. We foresee the utility of proteomics-based studies to provide a methodological framework to the underlying mechanism of metal solubilization, thereby facilitating the two-tier benefit of recovery of Mn from alternative sources as well as bioremediation of waste having high manganese content.

Staphylococcus aureus enhances biofilm formation, aerotolerance, and survival of Campylobacter strains isolated from retail meats

In retail meat products, Campylobacter jejuni, C. coli, and Staphylococcus aureus have been reported in high prevalence. The polymicrobial interaction between Campylobacter and other bacteria could enhance Campylobacter survival during the adverse conditions encountered during retail meat processing and storage. This study was designed to investigate the potential role of S. aureus from retail meats in enhancing the survival of Campylobacter exposed to low temperature, aerobic conditions, and biofilm formation. Results indicated that viable S. aureus cells and filter-sterilized cell-free media obtained from S. aureus prolonged the survival of Campylobacter at low temperature and during aerobic conditions. Biofilm formation of Campylobacter strains was significantly enhanced in the presence of viable S. aureus cells, but the results were inconclusive when extracts from cell-free media were used. In conclusion, the presence of S. aureus cells enhances survivability of Campylobacter strains in adverse conditions such as low temperature and aerobic conditions. Further investigations are warranted to understand the interaction between Campylobacter and S. aureus, and effective intervention strategies are needed to reduce the incidence of both foodborne pathogens in retail meat products.

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.

Optimal reference genes for real-time quantitative PCR and the expression of sigma factors in Acidithiobacillus caldus under various conditions

AIMS

Acidithiobacillus caldus is an important sulphur-oxidizing bacterium that plays crucial roles in the bioleaching industry. This study aims to analyse the optimal reference gene for real-time quantitative PCR (RT-qPCR) under different conditions and investigate the transcription levels of the sigma factor genes in the stress response.

METHODS AND RESULTS

We selected six housekeeping genes and analysed them via RT-qPCR using two energy resources, under four stress conditions. Three statistical approaches BestKeeper, geNorm, and NormFinder were utilized to determine transcription stability of these reference genes. The gapdH gene was the best internal control gene using elemental sulphur as an energy resource and under heat stress, map was the best internal control gene under pH and osmotic stress, era was the best internal control gene for the K₂ S₄ O₆ energy resource, and rpoC was the best internal control gene under Cu²⁺ stress. Furthermore, the expressional levels of 11 sigma factors were analysed by RT-qPCR in the stress response.

CONCLUSIONS

Stable internal control genes for RT-qPCR analysis of A. caldus were determined, and the expression patterns of sigma factor genes of A. caldus were investigated.

SIGNIFICANCE AND IMPACT OF THE STUDY

The identification of the optimal reference gene and analysis of transcription levels of sigma factors in A. caldus can provide clues for reference gene selection and the study of sigma factor function.

Functional analysis and cryo-electron microscopy of Campylobacterjejuni serine protease HtrA

Campylobacter jejuni is a predominant zoonotic pathogen causing gastroenteritis and other diseases in humans. An important bacterial virulence factor is the secreted serine protease HtrA (HtrA _Cj ), which targets tight and adherens junctional proteins in the gut epithelium. Here we have investigated the function and structure of HtrA _Cj using biochemical assays and cryo-electron microscopy. Mass spectrometry analysis identified differences and similarities in the cleavage site specificity for HtrA _Cj by comparison to the HtrA counterparts from Helicobacter pylori and Escherichia coli. We defined the architecture of HtrA _Cj at 5.8 Å resolution as a dodecamer, built of four trimers. The contacts between the trimers are quite loose, a fact that explains the flexibility and mobility of the dodecameric assembly. This flexibility has also been studied through molecular dynamics simulation, which revealed opening of the dodecamer to expose the proteolytically active site of the protease. Moreover, we examined the rearrangements at the level of oligomerization in the presence or absence of substrate using size exclusion chromatography, which revealed hexamers, dodecamers and larger oligomeric forms, as well as remarkable stability of higher oligomeric forms (> 12-mers) compared to previously tested homologs from other bacteria. Extremely dynamic decay of the higher oligomeric forms into lower forms was observed after full cleavage of the substrate by the proteolytically active variant of HtrA _Cj . Together, this is the first report on the in-depth functional and structural analysis of HtrA _Cj , which may allow the construction of therapeutically relevant HtrA _Cj inhibitors in the near future.

Zoonotic and Public Health Implications of Campylobacter Species and Squamates (Lizards, Snakes and Amphisbaenians)

Campylobacter spp. is one of the most widespread infectious diseases of veterinary and public health significance. Globally, the incidence of campylobacteriosis has increased over the last decade in both developing and developed countries. Squamates (lizards, snakes and amphisbaenians) are a potential reservoir and source of transmission of campylobacteriosis to humans. This systematic review examined studies from the last 20 years that have reported squamate-associated human campylobacteriosis. It was found that C. fetus subsp. testudinum and C. fetus subsp. fetus were the most common species responsible for human campylobacteriosis from a squamate host. The common squamate hosts identified included bearded dragons (Pogona vitticeps), green iguana (Iguana iguana), western beaked gecko (Rhynchoedura ornate) and blotched blue-tongued skink (Tiliqua nigrolutea). People with underlying chronic illnesses, the immunocompromised and the elderly were identified as the most vulnerable population. Exposure to pet squamates, wild animals, consumption of reptilian cuisines and cross contamination with untreated water were risk factors associated with Campylobacter infections. Proper hand hygiene practices, responsible pet ownership, ‘One Health’ education and awareness on zoonotic diseases will help reduce the public health risks arising from Campylobacter exposure through squamates. Continued surveillance using molecular diagnostic methods will also enhance detection and response to squamate-linked campylobacteriosis.

Biofilm formation and extracellular microvesicles-The way of foodborne pathogens toward resistance

Almost all known foodborne pathogens are able to form biofilms as one of the strategies for survival under harsh living conditions, to ward off the inhibition and the disinfection during food production, transport and storage, as well as during cleaning and sanitation of corresponding facilities. Biofilms are communities where microbial cells live under constant intracellular interaction and communication. Members of the biofilm community are embedded into extracellular matrix that contains polysaccharides, DNA, lipids, proteins, and small molecules that protect microorganisms and enable their intercellular communication under stress conditions. Membrane vesicles (MVs) are produced by both Gram positive and Gram negative bacteria. These lipid membrane-enveloped nanoparticles play an important role in biofilm genesis and in communication between different biofilm members. Furthermore, MVs are involved in other important steps of bacterial life like cell wall modeling, cellular division, and intercellular communication. They also carry toxins and virulence factors, as well as nucleic acids and different metabolites, and play a key role in host infections. After entering host cells, MVs can start many pathologic processes and cause serious harm and cell death. Prevention and inhibition of both biofilm formation and shedding of MVs by foodborne pathogens has a very important role in food production, storage, and food safety in general. Better knowledge of biofilm formation and maintaining, as well as the role of microbial vesicles in this process and in the process of host cells' infection is essential for food safety and prevention of both food spoilage and host infection.

Variability in lag-duration of Campylobacter spp. during enrichment after cold and oxidative stress and its impact on growth kinetics and reliable detection

Campylobacter jejuni and Campylobacter coli continue to be the leading cause of zoonotic gastroenteritis in the European Union, making reliable detection in food important. Low storage temperatures and atmospheric oxygen concentrations during food production can cause sub-lethal damage or transient non-culturability which is why ISO 10272-1:2017 includes an enrichment step to repair cell damage and increase cell concentrations, thereby supporting detection of campylobacters from foods. The aim of this study was to assess the variability in lag-duration of C. jejuni and C. coli during enrichment after different food-relevant stress treatments and evaluate its impact on growth kinetics and reliability of detection outcomes. Therefore, 13 C. jejuni and 10 C. coli strains were subjected to cold stress during refrigerated and frozen storage. Refrigerated storage did not significantly reduce culturability, but frozen storage reduced cell concentrations by 1.6 ± 0.1 log₁₀cfu/ml for both species. Subsequently, cells were enriched following ISO 10272-1:2017-A and cell concentrations were determined over time and lag-duration and growth rate were determined by fitting the Baranyi-model. Without prior stress treatment, mean lag-duration for C. jejuni and C. coli was 2.5 ± 0.2 h and 2.2 ± 0.3 h, respectively. Refrigerated storage increased lag-duration for C. jejuni to 4.6 ± 0.4 h and for C. coli to 5.0 ± 0.4 h and frozen storage increased lag-duration to 5.0 ± 0.3 h and 6.1 ± 0.4 h for C. jejuni and C. coli, respectively. Comparison of strain- and biological variability showed that differences in recovery after cold stress can be attributed mainly to strain variability since strain variability after refrigeration and freeze stress increased respectively 3-fold and 4-fold while biological variability remained constant. A subset of strains was also subjected to oxidative stress that reduced cell concentrations by 0.7 ± 0.2 log₁₀ cfu/ml and comparison of recovery patterns after oxidative and freeze stress indicated that recovery behaviour was also dependent on the stress applied. A scenario analysis was conducted to evaluate the impact of heterogeneity in outgrowth kinetics of single cells on the reliability of detection outcomes following ISO protocol 10272-1:2017. This revealed that a 'worst-case'-scenario for successful detection by a combination of the longest lag-duration of 7.6 h and lowest growth rate of 0.47 h^-1 still resulted in positive detection outcomes since the detection limit was reached within 32.5 h. This suggests that other factors such as competitive microbiota can act as a causative factor in false-negative outcomes of tested food samples.

Differences in the Transcriptomic Response of Campylobacter coli and Campylobacter lari to Heat Stress

Campylobacter spp. are one of the most important food-borne pathogens, which are quite susceptible to environmental or technological stressors compared to other zoonotic bacteria. This might be due to the lack of many stress response mechanisms described in other bacteria. Nevertheless, Campylobacter is able to survive in the environment and food products. Although some aspects of the heat stress response in Campylobacter jejuni are already known, information about the stress response in other Campylobacter species are still scarce. In this study, the stress response of Campylobacter coli and Campylobacter lari to elevated temperatures (46°C) was investigated by survival assays and whole transcriptome analysis. None of the strains survived at 46°C for more than 8 h and approximately 20% of the genes of C. coli RM2228 and C. lari RM2100 were differentially expressed. The transcriptomic profiles showed enhanced gene expression of several chaperones like dnaK, groES, groEL, and clpB in both strains, indicating a general involvement in the heat stress response within the Campylobacter species. However, the pronounced differences in the expression pattern between C. coli and C. lari suggest that stress response mechanisms described for one Campylobacter species might be not necessarily transferable to other Campylobacter species.

The gastrointestinal pathogen Campylobacter jejuni metabolizes sugars with potential help from commensal Bacteroides vulgatus

Although the gastrointestinal pathogen Campylobacter jejuni was considered asaccharolytic, >50% of sequenced isolates possess an operon for L-fucose utilization. In C. jejuni NCTC11168, this pathway confers L-fucose chemotaxis and competitive colonization advantages in the piglet diarrhea model, but the catabolic steps remain unknown. Here we solved the putative dehydrogenase structure, resembling FabG of Burkholderia multivorans. The C. jejuni enzyme, FucX, reduces L-fucose and D-arabinose in vitro and both sugars are catabolized by fuc-operon encoded enzymes. This enzyme alone confers chemotaxis to both sugars in a non-carbohydrate-utilizing C. jejuni strain. Although C. jejuni lacks fucosidases, the organism exhibits enhanced growth in vitro when co-cultured with Bacteroides vulgatus, suggesting scavenging may occur. Yet, when excess amino acids are available, C. jejuni prefers them to carbohydrates, indicating a metabolic hierarchy exists. Overall this study increases understanding of nutrient metabolism by this pathogen, and identifies interactions with other gut microbes.

The Rho-Independent Transcription Terminator for the porA Gene Enhances Expression of the Major Outer Membrane Protein and Campylobacter jejuni Virulence in Abortion Induction

Campylobacter jejuni is a leading cause of foodborne illnesses worldwide. Its porA gene encodes the major outer membrane protein (MOMP) that is abundantly expressed and has important physiological functions, including a key role in systemic infection and abortion induction in pregnant animals. Despite the importance of porA in C. jejuni pathogenesis, mechanisms modulating its expression levels remain elusive. At the 3' end of the porA transcript, there is a Rho-independent transcription terminator (named T _porA in this study). Whether T _porA affects the expression and function of MOMP remains unknown and is investigated in this study. Green fluorescent protein (GFP) fusion constructs with the porA promoter at the 5' end and an intact T _porA or no T _porA at the 3' end of the gfp coding sequence revealed that both the transcript level of gfp and its fluorescence signals were more than 2-fold higher in the construct with T _porA than in the one without T _porA Real-time quantitative PCR (qRT-PCR) analysis of the porA mRNA and immunoblot detection of MOMP in C. jejuni showed that disruption of T _porA significantly reduced the porA transcript level and the expression of MOMP. An mRNA decay assay demonstrated that disruption of T _porA resulted in a shortened transcript half-life of the upstream gfp or porA gene, indicating that T _porA enhances mRNA stability. In the guinea pig model, the C. jejuni construct with an interrupted T _porA was significantly attenuated in abortion induction. Together, these results indicate that T _porA enhances the expression level of MOMP by stabilizing its mRNA and influences the virulence of C. jejuni.

Investigating the influence of iron on Campylobacter jejuni transcriptome in response to acid stress

The capacity of C. jejuni to survive acid and capture iron is a requirement for C. jejuni to colonize host and cause infection. Herein, we aimed to characterize the influence of iron on Campylobacter acid response. The capacity of C. jejuni to survive acid stress was greatly enhanced in presence of iron. Moreover, the acid stimulon of C. jejuni under iron-enriched condition was investigated using the microarray approach. A total of 211 genes were differentially expressed in C. jejuni. Differentially expressed genes were included in 21 functional groups that control Campylobacter physiology. C. jejuni induced expression of many genes that were previously shown to be important for Campylobacter acid survival such as flagella biogenesis genes and genes involved in cell envelope biogenesis. The microarray results were validated using RT-qPCR where there was a great similarity in data obtained by both techniques. Finally, comparative analysis with previous studies showed that acid exposure induced expression of many genes in C. jejuni that were not detected in other studies such as genes encoding for the heat shock proteins GroEL and GroES. Current data could help us understand the mechanism of C. jejuni acid survival and consequently overcome infection by this enteric pathogen.

Alteration of Proteomes in First-Generation Cultures of Bacillus pumilus Spores Exposed to Outer Space

Bacillus pumilus SAFR-032 was originally isolated from the Jet Propulsion Lab Spacecraft Assembly Facility and thoroughly characterized for its enhanced resistance to UV irradiation and oxidative stress. This unusual resistance of SAFR-032 is of particular concern in the context of planetary protection and calls for development of novel disinfection techniques to prevent extraterrestrial contamination. Previously, spores of SAFR-032 were exposed for 18 months to a variety of space conditions on board the International Space Station to investigate their resistance to Mars-like conditions and space travel. Here, proteomic characterization of vegetative SAFR-032 cells from space-surviving spores is presented in comparison to a ground control. Vegetative cells of the first passage were processed and subjected to quantitative proteomics using tandem mass tags. Approximately 60% of all proteins encoded by SAFR-032 were identified, and 301 proteins were differentially expressed among the strains. We found that proteins predicted to be involved in carbohydrate transport/metabolism and energy production/conversion had lower abundance than those of the ground control. For three proteins, we showed that the expected metabolic activities were decreased, as expected with direct enzymatic assays. This was consistent with a decrease of ATP production in the space-surviving strains. The same space-surviving strains showed increased abundance of proteins related to survival, growth advantage, and stress response. Such alterations in the proteomes provide insights into possible molecular mechanisms of B. pumilus SAFR-032 to adapt to and resist extreme extraterrestrial environments.IMPORTANCE Spore-forming bacteria are well known for their resistance to harsh environments and are of concern for spreading contamination to extraterrestrial bodies during future life detection missions. Bacillus pumilus has been regularly isolated from spacecraft-associated surfaces and exhibited unusual resistance to ultraviolet light and other sterilization techniques. A better understanding of the mechanisms of microbial survival and enhanced resistance is essential for developing novel disinfection protocols for the purpose of planetary protection. While genomic analyses did not reveal the unique characteristics that explain elevated UV resistance of space-exposed B. pumilus, the proteomics study presented here provided intriguing insight on key metabolic changes. The observed proteomics aberrations reveal a complex biological phenomenon that plays a role in bacterial survival and adaptation under long-term exposure to outer space. This adaptive ability of microorganisms needs to be considered by those tasked with eliminating forward contamination.

In-Package Air Cold Plasma Treatment of Chicken Breast Meat: Treatment Time Effect

The objective of this study was to investigate the effects of in-package dielectric barrier discharge (DBD) atmospheric cold plasma (CP) on meat color, microbiological quality and safety of chicken breast meat (pectoralis major). Raw broiler breast meat was collected from a local commercial plant. Noninoculated meat samples and meat samples inoculated with Campylobacter and Salmonella were packed in polymeric trays with air. The packaged samples were CP-treated at 70 kV for different times (0, 60, 180, or 300 sec) and stored at 4°C for 5 days. Microbial counts (psychrophiles, Campylobacter, Salmonella) and meat color (International Commission on Illumination (CIE) L∗a∗b∗) were measured before CP treatments and after 5 days of posttreatment storage. Psychrophile growth was inhibited (P<0.05), and both food-borne pathogens were reduced (P<0.05) by more than 90% with CP treatments regardless of treatment time. No differences in pathogenic bacterial counts were observed between the three treatment times; however, increasing treatment time beyond 60 sec resulted in additional inhibition of psychrophilic growth. There were no differences (P>0.05) in a∗ and b∗ values between pretreatment and posttreatment plus storage; however, all CP treatments resulted in increased L∗ value (P<0.05). Results indicate that in-package CP treatments can be used to reduce both microbial spoilage and food-borne pathogen risks, which could increase microbial food safety, although it may result in an overall paler breast meat, and the reduction (about 1 log) in pathogenic and spoilage microbes are limited.

Presence of genes associated with adhesion, invasion, and toxin production in Campylobacter jejuni isolates and effect of temperature on their expression

The aims of this study were to evaluate the presence of genes associated with adhesion (cadF), invasion (ciaB), and cytotoxin production (cdtA, cdtB, and cdtC) among Campylobacter jejuni isolates from a poultry slaughterhouse and to investigate the effect of different temperatures on the expression of these virulence-associated genes. A total of 88 C. jejuni isolates from cecum, liver, chicken carcasses, chilled water, and scalding water were submitted to PCR assay for detection of virulence genes. Representative isolates were selected for gene expression evaluation at 37 and 42 °C, according to their virulence gene profile and genotypic typing. All C. jejuni isolates carried the five virulence-associated genes, which play an important role in the infectious process. Differential gene expression by RT-qPCR was observed among C. jejuni isolates at 37 and 42 °C. The expression levels at 37 °C showed upregulation of the ciaB, cdtA, cdtB, and cdtC genes in five isolates, with the exception of ciaB for isolate 4. At 42 °C, upregulation was observed for ciaB and cdtC, cdtA and cdtB, and cadF in four, three, and two isolates, respectively. The C. jejuni isolates expressed the virulence genes evaluated, and the expression is gene- and isolate-dependent and varied according the temperature.

Transcriptome analysis reveals a stress response of Shewanella oneidensis deprived of background levels of ionizing radiation

Natural ionizing background radiation has exerted a constant pressure on organisms since the first forms of life appeared on Earth, so that cells have developed molecular mechanisms to avoid or repair damages caused directly by radiation or indirectly by radiation-induced reactive oxygen species (ROS). In the present study, we investigated the transcriptional effect of depriving Shewanella oneidensis cultures of background levels of radiation by growing the cells in a mine 655 m underground, thus reducing the dose rate from 72.1 to 0.9 nGy h^-1 from control to treatment, respectively. RNASeq transcriptome analysis showed the differential expression of 4.6 and 7.6% of the S. oneidensis genome during early- and late-exponential phases of growth, respectively. The greatest change observed in the treatment was the downregulation of ribosomal proteins (21% of all annotated ribosomal protein genes during early- and 14% during late-exponential) and tRNA genes (14% of all annotated tRNA genes in early-exponential), indicating a marked decrease in protein translation. Other significant changes were the upregulation of membrane transporters, implying an increase in the traffic of substrates across the cell membrane, as well as the up and downregulation of genes related to respiration, which could be interpreted as a response to insufficient oxidants in the cells. In other reports, there is evidence in multiple species that some ROS not just lead to oxidative stress, but act as signaling molecules to control cellular metabolism at the transcriptional level. Consistent with these reports, several genes involved in the metabolism of carbon and biosynthesis of amino acids were also regulated, lending support to the idea of a wide metabolic response. Our results indicate that S. oneidensis is sensitive to the withdrawal of background levels of ionizing radiation and suggest that a transcriptional response is required to maintain homeostasis and retain normal growth.

Impact of human Campylobacter infections in Southeast Asia: The contribution of the poultry sector

Campylobacter is globally recognized as a major cause of foodborne infection in humans, whilst the development of antimicrobial resistance and the possibility of repelling therapy increase the threat to public health. Poultry is the most frequent source of Campylobacter infection in humans, and southeast Asia is a global leader in poultry production, consumption, and exports. Though three of the world's top 20 most populated countries are located in southeast Asia, the true burden of Campylobacter infection in the region has not been fully elucidated. Based on published data, Campylobacter has been reported in humans, animals, and food commodities in the region. To our knowledge, this study is the first to review the status of human Campylobacter infection in southeast Asia and to discuss future perspectives. Gaining insight into the true burden of the infection and prevalence levels of Campylobacter spp. in the southeast Asian region is essential to ensuring global and regional food safety through facilitating improvements in surveillance systems, food safety regulations, and mitigation strategies.

Physiology of the Inactivation of Vegetative Bacteria by Thermal Treatments: Mode of Action, Influence of Environmental Factors and Inactivation Kinetics

Heat has been used extensively in the food industry as a preservation method, especially due to its ability to inactivate microorganisms present in foods. However, many aspects regarding the mechanisms of bacterial inactivation by heat and the factors affecting this process are still not fully understood. The purpose of this review is to offer a general overview of the most important aspects of the physiology of the inactivation or survival of microorganisms, particularly vegetative bacteria, submitted to heat treatments. This could help improve the design of current heat processes methods in order to apply milder and/or more effective treatments that could fulfill consumer requirements for fresh-like foods while maintaining the advantages of traditional heat treatments.

Identification of temperature regulated factors of Campylobacter jejuni and their potential roles in virulence

Campylobacter jejuni is the major cause of bacterial gastroenteritis in man, while it is generally regarded as a commensal of the avian gut. Consumption and handling of contaminated poultry meat products are major risk factors for human infection. The body temperature in man (37 °C) and chickens (42 °C) differ markedly, and differential gene regulation and protein expression at different temperatures may in part explain the behaviour in the two hosts. We performed proteomics analyses with C. jejuni cells grown at 37 °C and 42 °C. Time-of-flight mass spectrometry (Q-Tof) analysis was carried out after samples were digested with the Filter-Aided Sample Preparation (FASP) method and peptides were fractionated by strong anion exchanges. Differentially regulated proteins were identified by Mascot and Scaffold analyses. Triple quadrupole (QQQ) mass spectrometer analysis confirmed that a total of 33 proteins were differentially regulated between 37 °C and 42 °C. Several upregulated proteins were selected for their corresponding gene knock-out mutants to be tested for their virulence in the Galleria mellonella model. To correlate with other tissue/animal models, the GADH mutant was selected for its reduced ability to colonize chickens. At 37 °C, the mutants of outer membrane protein Omp50 and Chaperone GroEL significantly increased virulence; while at 42 °C, the mutants of YceI, Omp50, and GADH reduced virulence against Galleria mellonella compared with the wild type strains. The results of current and previous studies indicate that GADH is a virulent factor in G. mellonella and a colonization factor in chickens. The workflow of this study may prove a new way to identify stress related virulent factors. The implications of these findings are discussed for pathogenesis in the model and other hosts.

CmeABC Multidrug Efflux Pump Contributes to Antibiotic Resistance and Promotes Campylobacter jejuni Survival and Multiplication in Acanthamoeba polyphaga

Campylobacter jejuni is a foodborne pathogen that is recognized as the leading cause of human bacterial gastroenteritis. The widespread use of antibiotics in medicine and in animal husbandry has led to an increased incidence of antibiotic resistance in Campylobacter In addition to a role in multidrug resistance (MDR), the Campylobacter CmeABC resistance-nodulation-division (RND)-type efflux pump may be involved in virulence. As a vehicle for pathogenic microorganisms, the protozoan Acanthamoeba is a good model for investigations of bacterial survival in the environment and the molecular mechanisms of pathogenicity. The interaction between C. jejuni 81-176 and Acanthamoeba polyphaga was investigated in this study by using a modified gentamicin protection assay. In addition, a possible role for the CmeABC MDR pump in this interaction was explored. Here we report that this MDR pump is beneficial for the intracellular survival and multiplication of C. jejuni in A. polyphaga but is dispensable for biofilm formation and motility.IMPORTANCE The endosymbiotic relationship between amoebae and microbial pathogens may contribute to persistence and spreading of the latter in the environment, which has significant implications for human health. In this study, we found that Campylobacter jejuni was able to survive and to multiply inside Acanthamoeba polyphaga; since these microorganisms can coexist in the same environment (e.g., on poultry farms), the latter may increase the risk of infection with Campylobacter Our data suggest that, in addition to its role in antibiotic resistance, the CmeABC MDR efflux pump plays a role in bacterial survival within amoebae. Furthermore, we demonstrated synergistic effects of the CmeABC MDR efflux pump and TetO on bacterial resistance to tetracycline. Due to its role in both the antibiotic resistance and the virulence of C. jejuni, the CmeABC MDR efflux pump could be considered a good target for the development of antibacterial drugs against this pathogen.

Genome-wide fitness analyses of the foodborne pathogen Campylobacter jejuni in in vitro and in vivo models

Campylobacter is the most common cause of foodborne bacterial illness worldwide. Faecal contamination of meat, especially chicken, during processing represents a key route of transmission to humans. There is a lack of insight into the mechanisms driving C. jejuni growth and survival within hosts and the environment. Here, we report a detailed analysis of C. jejuni fitness across models reflecting stages in its life cycle. Transposon (Tn) gene-inactivation libraries were generated in three C. jejuni strains and the impact on fitness during chicken colonisation, survival in houseflies and under nutrient-rich and -poor conditions at 4 °C and infection of human gut epithelial cells was assessed by Tn-insertion site sequencing (Tn-seq). A total of 331 homologous gene clusters were essential for fitness during in vitro growth in three C. jejuni strains, revealing that a large part of its genome is dedicated to growth. We report novel C. jejuni factors essential throughout its life cycle. Importantly, we identified genes that fulfil important roles across multiple conditions. Our comprehensive screens showed which flagella elements are essential for growth and which are vital to the interaction with host organisms. Future efforts should focus on how to exploit this knowledge to effectively control infections caused by C. jejuni.

Role of the LuxR family transcriptional regulator Lpg2524 in the survival of Legionella pneumophila in water

The water-borne Gram-negative bacterium Legionella pneumophila (Lp) is the causative agent of Legionnaires' disease. Lp is typically transmitted to humans from water systems, where it grows inside amoebae. Survival of Lp in water is central to its transmission to humans. A transcriptomic study previously identified many genes induced by Lp in water. One such gene, lpg2524, encodes a putative LuxR family transcriptional regulator. It was hypothesized that this gene could be involved in the survival of Lp in water. Deletion of lpg2524 does not affect the growth of Lp in rich medium, in the amoeba Acanthamoeba castellanii, or in human macrophage-like THP-1 cells, showing that Lpg2524 is not required for growth in vitro and in vivo. Nevertheless, deletion of lpg2524 results in a faster colony-forming unit (CFU) reduction in an artificial freshwater medium, Fraquil, indicating that Lpg2524 is important for Lp to survive in water. Overexpression of Lpg2524 also results in a survival defect, suggesting that a precise level of this transcriptional regulator is essential for its function. However, our result shows that Lpg2524 is dispensable for survival in water when Lp is at a high cell density (10⁹ CFU/mL), suggesting that its regulon is regulated by another regulator activated at high cell density.

Insights into the fluoride-resistant regulation mechanism of Acidithiobacillus ferrooxidans ATCC 23270 based on whole genome microarrays

Acidophilic microorganisms involved in uranium bioleaching are usually suppressed by dissolved fluoride ions, eventually leading to reduced leaching efficiency. However, little is known about the regulation mechanisms of microbial resistance to fluoride. In this study, the resistance of Acidithiobacillus ferrooxidans ATCC 23270 to fluoride was investigated by detecting bacterial growth fluctuations and ferrous or sulfur oxidation. To explore the regulation mechanism, a whole genome microarray was used to profile the genome-wide expression. The fluoride tolerance of A. ferrooxidans cultured in the presence of FeSO4 was better than that cultured with the S(0) substrate. The differentially expressed gene categories closely related to fluoride tolerance included those involved in energy metabolism, cellular processes, protein synthesis, transport, the cell envelope, and binding proteins. This study highlights that the cellular ferrous oxidation ability was enhanced at the lower fluoride concentrations. An overview of the cellular regulation mechanisms of extremophiles to fluoride resistance is discussed.

Prevalence of Virulence/Stress Genes in Campylobacter jejuni from Chicken Meat Sold in Qatari Retail Outlets

Chicken meat from the shelves of supermarkets in Qatar was tested for the presence of Campylobacter spp. and the presence of five virulence genes (htrB, cdtB, clpP, cadF and ciaB) was assessed in isolates. Forty eight percent of the chickens provided for supermarkets by Saudi (53%) and Qatari (45.9%) producers were found to be contaminated and the most important factor affecting the overall prevalence of contaminated chickens was the store from which chicken samples originated. Variation in prevalence of Campylobacter in chicken meat from different stores was evident even when the same producer supplied the three stores in our survey. Differences in the prevalence and in the combinations of virulence genes in isolates that can and cannot grow in a classic maintenance medium (Karmali) were identified, providing a starting point for linking presence/absence of particular virulence genes with actual in vivo virulence and pathogenicity. Because of the relatively low infective doses of Campylobacter that are required to initiate infection in humans, it will be important to explore further the relationships we identified between certain Campylobacter virulence genes and their capacity for survival in poultry meat, and hence their contribution to the incidence of campylobacteriosis.

The Campylobacter jejuni Ferric Uptake Regulator Promotes Acid Survival and Cross-Protection against Oxidative Stress

Campylobacter jejuni is a prevalent cause of bacterial gastroenteritis in humans worldwide. The mechanisms by which C. jejuni survives stomach acidity remain undefined. In the present study, we demonstrated that the C. jejuni ferric uptake regulator (Fur) plays an important role in C. jejuni acid survival and acid-induced cross-protection against oxidative stress. A C. jejuni Δfur mutant was more sensitive to acid than the wild-type strain. Profiling of the acid stimulon of the C. jejuni Δfur mutant allowed us to uncover Fur-regulated genes under acidic conditions. In particular, Fur was found to upregulate genes involved in flagellar and cell envelope biogenesis upon acid stress, and mutants with deletions of these genes were found to be defective in surviving acid stress. Interestingly, prior acid exposure of C. jejuni cross-protected against oxidative stress in a catalase (KatA)- and Fur-dependent manner. Western blotting and reverse transcription-quantitative PCR revealed increased expression of KatA upon acid stress. Electrophoretic mobility shift assays (EMSAs) demonstrated that the binding affinity between Fur and the katA promoter is reduced in vitro under conditions of low pH, rationalizing the higher levels of expression of katA under acidic conditions. Strikingly, the Δfur mutant exhibited reduced virulence in both human epithelial cells and the Galleria mellonella infection model. Altogether, this is the first study showing that, in addition to its role in iron metabolism, Fur is an important regulator of C. jejuni acid responses and this function cross-protects against oxidative stress. Moreover, our results clearly demonstrate Fur's important role in C. jejuni pathogenesis.

The response of foodborne pathogens to osmotic and desiccation stresses in the food chain

In combination with other strategies, hyperosmolarity and desiccation are frequently used by the food processing industry as a means to prevent bacterial proliferation, and particularly that of foodborne pathogens, in food products. However, it is increasingly observed that bacteria, including human pathogens, encode mechanisms to survive and withstand these stresses. This review provides an overview of the mechanisms employed by Salmonella spp., Shiga toxin producing E. coli, Cronobacter spp., Listeria monocytogenes and Campylobacter spp. to tolerate osmotic and desiccation stresses and identifies gaps in knowledge which need to be addressed to ensure the safety of low water activity and desiccated food products.

Assessing Bacterial Interactions Using Carbohydrate-Based Microarrays

Carbohydrates play a crucial role in host-microorganism interactions and many host glycoconjugates are receptors or co-receptors for microbial binding. Host glycosylation varies with species and location in the body, and this contributes to species specificity and tropism of commensal and pathogenic bacteria. Additionally, bacterial glycosylation is often the first bacterial molecular species encountered and responded to by the host system. Accordingly, characterising and identifying the exact structures involved in these critical interactions is an important priority in deciphering microbial pathogenesis. Carbohydrate-based microarray platforms have been an underused tool for screening bacterial interactions with specific carbohydrate structures, but they are growing in popularity in recent years. In this review, we discuss carbohydrate-based microarrays that have been profiled with whole bacteria, recombinantly expressed adhesins or serum antibodies. Three main types of carbohydrate-based microarray platform are considered; (i) conventional carbohydrate or glycan microarrays; (ii) whole mucin microarrays; and (iii) microarrays constructed from bacterial polysaccharides or their components. Determining the nature of the interactions between bacteria and host can help clarify the molecular mechanisms of carbohydrate-mediated interactions in microbial pathogenesis, infectious disease and host immune response and may lead to new strategies to boost therapeutic treatments.

Profiling of Brevibacillus borstelensis transcriptome exposed to high temperature shock

To understand the molecular mechanisms underlying the ability of the bacteria to survive at high temperature, gene expression profile of Brevibacillusborstelensis at 55°C during 5 and 10min heat shock period was carried out by high-throughput sequencing technology. A total of 2555 non-redundant transcripts were annotated. A total of 575 genes at 5min and 400 genes at 10min exhibited significant differential expression in response to temperature upshift from 50 to 55°C. Genes up-regulated under heat shock were associated with metabolism (mtnE), membrane transport, signal transduction, transcriptional regulation (ycxD, codY) and folding and sorting (hsp90). A larger number of genes encoding hypothetical proteins were identified. RT-PCR experimental results carried out on genes expressed under heat shock were found to be consistent with transcriptome data. The results enhance our understanding of adaptation strategy of thermophilic bacteria thereby providing a strong background for in depth research in thermophiles.

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.