CmeABC, a multidrug efflux pump, is involved in the resistance of Campylobacter jejuni to a broad spectrum of antimicrobial agents and is essential for Campylobacter colonization in animal intestine by mediating bile resistance. Previously, we have shown that expression of this efflux pump is under the control of a transcriptional repressor named CmeR. Inactivation of CmeR or mutation in the cmeABC promoter (P cmeABC ) region derepresses cmeABC, leading to overexpression of this efflux pump. However, it is unknown if the expression of cmeABC can be conditionally induced by the substrates it extrudes. In this study, we examined the expression of cmeABC in the presence of various antimicrobial compounds. Although the majority of the antimicrobials tested did not affect the expression of cmeABC, bile salts drastically elevated the expression of this efflux operon. The induction was observed with both conjugated and unconjugated bile salts and was in a dose-and time-dependent manner. Experiments using surface plasmon resonance demonstrated that bile salts inhibited the binding of CmeR to P cmeABC , suggesting that bile compounds are inducing ligands of CmeR. The interaction between bile salts and CmeR likely triggers conformational changes in CmeR, resulting in reduced binding affinity of CmeR to P cmeABC . Bile did not affect the transcription of cmeR, indicating that altered expression of cmeR is not a factor in bile-induced overexpression of cmeABC. In addition to the CmeR-dependent induction, some bile salts (e.g., taurocholate) also activated the expression of cmeABC by a CmeR-independent pathway. Consistent with the elevated production of CmeABC, the presence of bile salts in culture media resulted in increased resistance of Campylobacter to multiple antimicrobials. These findings reveal a new mechanism that modulates the expression of cmeABC and further support the notion that bile resistance is a natural function of CmeABC.

CmeDEF interacts with CmeABC in conferring antimicrobial resistance and maintaining cell viability in C. jejuni. CmeABC is the predominant efflux pump in C. jejuni, whereas CmeDEF plays a secondary role in conferring intrinsic resistance to antimicrobials.

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Campylobacter jejuni is a major food-borne pathogen and a common causative agent of human enterocolitis. Fluoroquinolones are a key class of antibiotics prescribed for clinical treatment of enteric infections including campylobacteriosis, but fluoroquinolone-resistant Campylobacter readily emerges under the antibiotic selection pressure. To understand the mechanisms involved in the development of fluoroquinolone-resistant Campylobacter, we compared the gene expression profiles of C. jejuni in the presence and absence of ciprofloxacin using DNA microarray. Our analysis revealed that multiple genes showed significant changes in expression in the presence of a suprainhibitory concentration of ciprofloxacin. Most importantly, ciprofloxacin induced the expression of mfd, which encodes a transcription-repair coupling factor involved in strand-specific DNA repair. Mutation of the mfd gene resulted in an approximately 100-fold reduction in the rate of spontaneous mutation to ciprofloxacin resistance, while overexpression of mfd elevated the mutation frequency. In addition, loss of mfd in C. jejuni significantly reduced the development of fluoroquinolone-resistant Campylobacter in culture media or chickens treated with fluoroquinolones. These findings indicate that Mfd is important for the development of fluoroquinolone resistance in Campylobacter, reveal a previously unrecognized function of Mfd in promoting mutation frequencies, and identify a potential molecular target for reducing the emergence of fluoroquinolone-resistant Campylobacter.

The blood flukes Schistosoma mansoni and Schistosoma japonicum inflict immense suffering as agents of human schistosomiasis. Previous investigations have found the nervous systems of these worms contain abundant immunoreactivity to antisera targeting invertebrate neuropeptide Fs (NPFs) as well as structurally similar neuropeptides of the mammalian neuropeptide Y (NPY) family. Here, cDNAs encoding NPF in these worms were identified, and the mature neuropeptides from the two species differed by only a single amino acid. Both neuropeptides feature the characteristics common among NPFs; they are 36 amino acids long with a carboxyl-terminal Gly-Arg-X-Arg-Phe-amide and Tyr residues at positions 10 and 17 from the carboxyl terminus. Synthetic S. mansoni NPF potently inhibits the forskolin-stimulated accumulation of cAMP in worm homogenates, with significant effects at 10 ؊11 M. This is the first demonstration of an endogenous inhibition of cAMP by an NPF, and because this is the predominant pathway associated with vertebrate NPY family peptides, it demonstrates a conservation of downstream signaling pathways used by NPFs and NPY peptides.Blood fluke parasites of the genus Schistosoma are the most important metazoan parasites of humans and are the etiological agents of schistosomiasis (bilharzia), which afflicts over 200 million people. Schistosomiasis ranks second, behind only malaria, in terms of its overall negative socio-economic and public health impact on the tropical and subtropical world, and it remains among the top five disease priorities of the World Health Organization (WHO) 1 (1). Control of the disease rests almost solely on chemotherapy using the anthelmintic praziquantel (2-4). Most disturbingly, the long term utility of praziquantel has been brought into question because of growing reports of infections not responding to the recommended dosage (5-8) and worms with decreased sensitivity (9, 10). WHO has accordingly identified research into the basic biology of schistosomes as a priority, with the hope of identifying targets for the next generation of antischistosomal drugs (1).Schistosomes belong to the class Trematoda of the phylum Platyhelminthes (flatworms) and, as such, are among the simplest extant animals to display brain development with the concomitant distinction between central and peripheral neuronal elements. One distinct feature of platyhelminths and other early diverging phyla is a prominent peptidergic component within their nervous systems. One family of neuropeptides abundant among these early animals is the neuropeptide F (NPF) family (11-14). NPFs are 36 -40-amino acid peptides featuring a carboxyl-terminal Gly-Arg-X-Arg-Phe-amide (GRXRF-NH 2 ) motif and tyrosine residues at positions 10 and 17 relative to the carboxyl terminus.These characteristics are common to those of vertebrate NPY family peptides, 36 amino acid neuropeptides with RXR(F/Y)-NH 2 carboxyl termini, Tyr residues at positions 10 and 17 relative to the carboxyl termini, and prolines in a PXXPXXP motif near the amino ter...