The health burden of Campylobacter infection and the impact of antimicrobial resistance: playing chicken

Identification of a key amino acid of LuxS involved in AI-2 production in Campylobacter jejuni

Autoinducer-2 (AI-2) mediated quorum sensing has been associated with the expression of virulence factors in a number of pathogenic organisms and has been demonstrated to play a role in motility and cytolethal distending toxin (cdt) production in Campylobacter jejuni. We have initiated the work to determine the molecular basis of AI-2 synthesis and the biological functions of quorum sensing in C. jejuni. In this work, two naturally occurring variants of C. jejuni 81116 were identified, one producing high-levels of AI-2 while the other is defective in AI-2 synthesis. Sequence analysis revealed a G92D mutation in the luxS gene of the defective variant. Complementation of the AI-2⁻ variant with a plasmid encoded copy of the wild-type luxS gene or reversion of the G92D mutation by site-directed mutagenesis fully restored AI-2 production by the variant. These results indicate that the G92D mutation alone is responsible for the loss of AI-2 activity in C. jejuni. Kinetic analyses showed that the G92D LuxS has a ∼100-fold reduced catalytic activity relative to the wild-type enzyme. Findings from this study identify a previously undescribed amino acid that is essential for AI-2 production by LuxS and provide a unique isogenic pair of naturally occurring variants for us to dissect the functions of AI-2 mediated quorum sensing in Campylobacter.

Adherence, invasion, toxigenic, and chemotactic properties of Mexican campylobacter strains

To determine the virulence factors of Mexican wild-type strains of Campylobacter jejuni and Campylobacter coli, 31 wild-type strains were isolated from food and from humans. The production of cytolethal distending toxin and the adherence and invasion capabilities of these strains were assayed in Vero cells. Hard agar plugs with repellents and attractants were used to examine chemotaxis. Mueller-Hinton agar with supplements was used for motility analysis and to measure hemolytic activity. Nine strains of C. jejuni and eight strains of C. coli exhibited motility, most within a diameter of 2 to 13 mm. Most of the strains reacted to the repellent compounds analyzed, and α- and β-like hemolysis and cytotoxicity in Vero cells were observed for all strains. Isolates adhered to and invaded Vero cells to various degrees. Although strains of C. jejuni exhibited stronger adherence but less invasion compared with strains of C. coli, the difference was not significant (P > 0.05). The strains of C. jejuni and C. coli isolated from food and from patients in Mexico could have major impacts on public health.

Campylobacter jejuni induces an anti-inflammatory response in human intestinal epithelial cells through activation of phosphatidylinositol 3-kinase/Akt pathway

Campylobacter jejuni (C. jejuni) is the most common cause of human acute bacterial gastroenteritis. Poultry is a major reservoir of C. jejuni and considered an important source of human infections, thus, it is important to understand the host response to C. jejuni from chicken origin. In this study, we demonstrated firstly that a chicken isolate SC11 colonized chicks faster than clinical isolate NCTC11168. Using the SC11, we further studied the host responds to C. jejuni in terms of inflammatory response and involvement of cellular signaling pathways. Infection of C. jejuni SC11 was able to activate phosphatidylinositol 3-kinase (PI3K)/Akt pathway and induce pro-inflammatory interleukin-8 (IL-8) as well as anti-inflammatory cytokine IL-10 in human intestinal epithelial cell line Colo 205. The signalling pathways PI3K/Akt and mitogen-activated protein (MAP) kinases ERK and p38 were involved in C. jejuni-induced IL-8 and IL-10 expression. Inhibition of PI3K resulted in augmentation of C. jejuni-induced IL-8 production, concomitant with down-regulation of IL-10 mRNA, indicating an anti-inflammatory response was activated and associated with the activation of P13K/Akt. Similar effect was observed for cytolethal distending toxin (CDT) deficient mutants. Moreover, we demonstrated that heat-killed bacteria were able to induce IL-8 and IL-10 expression to a lower level than live bacteria. We therefore conclude that C. jejuni activate a PI3K/Akt-dependent anti-inflammatory pathway in human intestinal epithelial cells which may benefit the intracellular survival of C. jejuni during infection.

Caught in the act: in vivo development of macrolide resistance to Campylobacter jejuni infection

We report the first instance of macrolide resistance developing in vivo following appropriate antibiotic use in a healthy volunteer as a part of a controlled human infection with Campylobacter jejuni. In vivo development of macrolide resistance may be an important contributor to antibiotic resistance in C. jejuni.

Amino-terminal residues dictate the export efficiency of the Campylobacter jejuni filament proteins via the flagellum

Bacterial flagella play an essential role in the pathogenesis of numerous enteric pathogens. The flagellum is required for motility, colonization, and in some instances, for the secretion of effector proteins. In contrast to the intensively studied flagella of Escherichia coli and Salmonella typhimurium, the flagella of Campylobacter jejuni, Helicobacter pylori and Vibrio cholerae are less well characterized and composed of multiple flagellin subunits. This study was performed to gain a better understanding of flagellin export from the flagellar type III secretion apparatus of C. jejuni. The flagellar filament of C. jejuni is comprised of two flagellins termed FlaA and FlaB. We demonstrate that the amino-termini of FlaA and FlaB determine the length of the flagellum and motility of C. jejuni. We also demonstrate that protein-specific residues in the amino-terminus of FlaA and FlaB dictate export efficiency from the flagellar type III secretion system (T3SS) of Yersinia enterocolitica. These findings demonstrate that key residues within the amino-termini of two nearly identical proteins influence protein export efficiency, and that the mechanism governing the efficiency of protein export is conserved among two pathogens belonging to distinct bacterial classes. These findings are of additional interest because C. jejuni utilizes the flagellum to export virulence proteins.

Recrudescent Campylobacter jejuni infection in an immunocompetent adult following experimental infection with a well-characterized organism

The recrudescence of infection with Campylobacter jejuni after appropriate antibiotic treatment has not been previously reported in an immunocompetent adult. We present the complete clinical, microbiologic, and immunologic evaluation of a closely monitored healthy male with recrudescent C. jejuni infection occurring in the absence of immunodeficiency following experimental infection with a well-characterized strain. After antibiotic treatment, the initial infection was clinically cleared and microbiologically undetectable. Subsequently, two episodes of recrudescence occurred, with no change in in vitro antibiotic sensitivity being detected. The immune responses of the individual were compared to those of other participants in the experimental infection study: innate immune responses, including fecal cytokines and C-reactive protein, were intact; however, measures of Campylobacter-specific adaptive immune responses were absent, including serum antibodies, antibody-secreting cells, and in vitro gamma interferon responses. No primary or secondary immunodeficiency was identified. Recrudescent Campylobacter infections after treatment may be more common than has previously been appreciated. This work adds to our understanding of the human immune response to natural Campylobacter infection and reiterates the importance of pathogen-specific adaptive immune responses to this globally important pathogen.

Characterization of a Campylobacter jejuni VirK protein homolog as a novel virulence determinant

Campylobacter jejuni is a leading cause of food-borne illness in the United States. Despite significant recent advances, its mechanisms of pathogenesis are poorly understood. A unique feature of this pathogen is that, with some exceptions, it lacks homologs of known virulence factors from other pathogens. Through a genetic screen, we have identified a C. jejuni homolog of the VirK family of virulence factors, which is essential for antimicrobial peptide resistance and mouse virulence.

Identification of an arsenic resistance and arsenic-sensing system in Campylobacter jejuni

Arsenic is commonly present in the natural environment and is also used as a feed additive for animal production. Poultry is a major reservoir for Campylobacter jejuni, a major food-borne human pathogen causing gastroenteritis. It has been shown that Campylobacter isolates from poultry are highly resistant to arsenic compounds, but the molecular mechanisms responsible for the resistance have not been determined, and it is unclear if the acquired arsenic resistance affects the susceptibility of Campylobacter spp. to other antimicrobials. In this study, we identified a four-gene operon that contributes to arsenic resistance in Campylobacter. This operon encodes a putative membrane permease (ArsP), a transcriptional repressor (ArsR), an arsenate reductase (ArsC), and an efflux protein (Acr3). PCR analysis of various clinical C. jejuni isolates indicated a significant association of this operon with elevated resistance to arsenite and arsenate. Gene-specific mutagenesis confirmed the role of the ars operon in conferring arsenic resistance. It was further shown that this operon is subject to regulation by ArsR, which directly binds to the ars promoter and inhibits the transcription of the operon. Arsenite inhibits the binding of ArsR to the ars promoter DNA and induces the expression of the ars genes. Mutation of the ars genes did not affect the susceptibility of C. jejuni to commonly used antibiotics. These results identify the ars operon as an important mechanism for arsenic resistance and sensing in Campylobacter.

Advances in Campylobacter biology and implications for biotechnological applications

Campylobacter jejuni is a major foodborne pathogen of animal origin and a leading cause of bacterial gastroenteritis in humans. During the past decade, especially since the publication of the first C. jejuni genome sequence, major advances have been made in understanding the pathobiology and physiology of this organism. It is apparent that C. jejuni utilizes sophisticated mechanisms for effective colonization of the intestinal tracts in various animal species. Although Campylobacter is fragile in the environment and requires fastidious growth conditions, it exhibits great flexibility in the adaptation to various habitats including the gastrointestinal tract. This high adaptability is attributable to its genetically, metabolically and phenotypically diverse population structure and its ability to change in response to various challenges. Unlike other enteric pathogens, such as Escherichia coli and Salmonella, Campylobacter is unable to utilize exogenous glucose and mainly depends on the catabolism of amino acids as a carbon source. Campylobacter proves highly mutable in response to antibiotic treatments and possesses eukaryote‐like dual protein glycosylation systems, which modify flagella and other surface proteins with specific sugar structures. In this review we will summarize the distinct biological traits of Campylobacter and discuss the potential biotechnological approaches that can be developed to control this enteric pathogen.

Antibiotic resistance in Campylobacter: emergence, transmission and persistence

Campylobacter is a leading foodborne bacterial pathogen, which causes gastroenteritis in humans. This pathogenic organism is increasingly resistant to antibiotics, especially fluoroquinolones and macrolides, which are the most frequently used antimicrobials for the treatment of campylobacteriosis when clinical therapy is warranted. As a zoonotic pathogen, Campylobacter has a broad animal reservoir and infects humans via contaminated food, water or milk. Antibiotic usage in both animal agriculture and human medicine, can influence the development of antibiotic-resistant Campylobacter. This review will describe the trend in fluoroquinolone and macrolide resistance in Campylobacter, summarize the mechanisms underlying the resistance to various antibiotics and discuss the unique features associated with the emergence, transmission and persistence of antibiotic-resistant Campylobacter. Special attention will be given to recent findings and emphasis will be placed on Campylobacter resistance to fluoroquinolones and macrolides. A future perspective on antibiotic resistance and potential approaches for the control of antibiotic-resistant Campylobacter, will also be discussed.

Trends of norfloxacin and erythromycin resistance of Campylobacter jejuni/Campylobacter coli isolates recovered from international travelers, 1994 to 2006

BACKGROUND

Campylobacter sp. is a major cause of bacterial enterocolitis and travelers' diarrhea. Empiric treatment regimens include fluoroquinolones and macrolides.

METHODS

Over the period 1994 to 2006, 724 Campylobacter jejuni/Campylobacter coli isolates recovered from international travelers at the outpatient clinic of the Institute of Tropical Medicine, Antwerp, Belgium, were reviewed for their susceptibility to norfloxacin and erythromycin.

RESULTS

Norfloxacin resistance increased significantly over time in isolates from travelers returning from Asia, Africa, and Latin America. For the years 2001 to 2006, norfloxacin resistance rates were 67 (70.5%) of 95 for Asia, 20 (60.6%) of 33 for Latin America, and 36 (30.6%) of 114 for Africa. The sharpest increase was noted for India, with no resistance in 1994, but 41 (78.8%) of 52 resistant isolates found during 2001 to 2006. Erythromycin resistance was demonstrated in 20 (2.7%) isolates, with a mean annual resistance of 3.1% +/- 2.8%; resistance increased over time, with up to 3(7.5%) of 40 and 3 (8.6%) of 35 resistant isolates in 2004 and 2006, respectively (p < 0.05); there was no apparent geographic association. Combined resistance to norfloxacin and erythromycin was observed in five isolates.

CONCLUSIONS

The high resistance rates to fluoroquinolones warrant reconsideration of their use as drugs of choice in patients with severe gastroenteritis when Campylobacter is the presumed cause. Continued monitoring of the incidence and the spread of resistant Campylobacter isolates is warranted.

Cytokine responses in primary chicken embryo intestinal cells infected with Campylobacter jejuni strains of human and chicken origin and the expression of bacterial virulence-associated genes

Background

Campylobacter jejuni is a major cause of inflammatory diarrhoea in humans and is considered a commensal of the gastroenteric tract of the avian host. However, little is known about the interaction between C. jejuni and the avian host including the cytokine responses and the expression of the bacterial genes. We have investigated the invasiveness of primary chicken embryo intestinal cells (CEICs) by C. jejuni strains of human and chicken origins and the production of pro-inflammatory cytokines as well as the expression of the bacterial virulence-associated genes during co-cultivation.

Results

C. jejuni strains are capable of invading the CEICs and stimulate these cells in a pro-inflammatory manner and during this interaction the expression of the bacterial virulence-associated genes ciaB, dnaJ and racR is increased. Furthermore, incubation of bacteria with conditioned cell- and bacteria-free media from another co-cultivation experiment also increased the expression of the virulence-associated genes in the C. jejuni chicken isolate, indicating that the expression of bacterial genes is regulated by component(s) secreted upon co-cultivation of bacteria and CEICs.

Conclusion

We show that under in vitro culture condition C. jejuni strains of both human and chicken origins can invade avian host cells with a pro-inflammatory response and that the virulence-associated genes of C. jejuni may play a role in this process.