Diane E. Taylor

We investigated the involvement of the CmeABC efflux pump in acquired resistance of Campylobacter jejuni to macrolides and tetracycline. Inactivation of the cmeB gene had no effect on macrolide resistance when all copies of the target gene carried an A2074C mutation. In contrast, the CmeABC pump significantly contributed to macrolide resistance when two or three copies of the 23S rRNA had an A2075G transition. Inactivation of the cmeB gene led to restoration of tetracycline susceptibility in the isolates examined. Complete susceptibility to tetracycline or macrolides, however, was not restored when phenylalanine-arginine β-naphthylamide was used. These data confirm contribution of the CmeABC efflux pump to acquired resistance of Campylobacter jejuni to tetracycline and macrolides.

Infection with Campylobacter jejuni is now considered to be the most common cause of acute bacterial gastroenteritis in humans worldwide. It occurs more frequently than infections caused by Salmonella species, Shigella species, or Escherichia coli O157:H7. Although C. jejuni is also recognized for its association with serious post-infection neurological complications, most patients with C. jejuni infections have a self-limited illness. Nevertheless, a substantial proportion of these infections are treated with antibiotics. These include severe and prolonged cases of enteritis, infections in immune-suppressed patients, septicaemia and other extra-intestinal infections. Under these circumstances, erythromycin is often recommended as the drug of first choice. However, erythromycin-resistant Campylobacter have emerged during therapy with macrolides. Moreover, the widespread use of macrolides, including erythromycin, in veterinary medicine has accelerated this resistance trend. Several countries including Canada, Japan and Finland have reported C. jejuni isolates with low and stable rates of macrolide resistance. In contrast, the increasing level of macrolide resistance in C. jejuni is becoming a major public health concern in other parts of the world such as the United States, Europe and Taiwan. Macrolide resistance in Campylobacter is mainly associated with point mutation(s) occurring in the peptidyl-encoding region in domain V of the 23S rRNA gene, the target of macrolides. Several rapid and practical techniques have recently been developed for the identification of macrolide-resistant isolates of C. jejuni. The aim of this mini-review is to give an overview of the worldwide distribution of macrolide resistance in C. jejuni and Campylobacter coli as well as its possible association with the massive use of these agents in food animals. Mechanisms implicated in macrolide resistance in C. jejuni and also techniques that have been developed for the efficient detection of macrolide-associated mutation(s) will be discussed in detail.

Campylobacter curvus was isolated from blood cultures of a patient with liver abscesses. Bacterial identification involved Gram staining, biochemical analysis, gas-liquid chromatography, and 16S rRNA sequencing. The difficulty in isolation, identification, and growth of the species confirms previous work that these organisms may be overlooked by conventional detection methods.

One hundred four isolates of Campylobacter jejuni from poultry in Alberta, Canada, collected during 2001 were tested for resistance to 10 antimicrobial agents using agar dilution. This study provides a baseline of resistance profiles and the mechanisms of resistance observed in C. jejuni in poultry from Alberta, Canada.

One of the characteristic features of IncHI1 plasmids is a thermosensitive process of conjugation, which is optimal between 22 °C and 30 °C but inhibited at 37 °C. R27, the prototypical IncHI1 plasmid, contains transfer genes clustered in two regions of the plasmid, Tra1 and Tra2. In the present study, transcriptional analyses of thetragenes were undertaken at both 30 °C and 37 °C. Screening of 38tragenes showed thattragenes are transcriptionally linked in six operons, three in each Tra region. RT-PCR analysis showed that gene expression was reduced at 37 °C relative to that observed at 30 °C. The transcription start sites of the six transcripts were identified, promoters and upstream regions were cloned, and transcription was tested at both temperatures. In cells grown at 37 °C, in the presence of R27, the promoters were inhibited, except for promoters of the H operon and AN operon. Conditions that influenced DNA topology, such as osmolarity, anaerobiosis, quorum sensing and acidity, showed no significant influence on transfer frequency. These results should facilitate future understanding of the basis of temperature-sensitive transfer in this large conjugative plasmid.

Bacterial conjugation is a horizontal gene transfer event mediated by the type IV secretion system (T4SS) encoded by bacterial plasmids. Within the T4SS, the coupling protein plays an essential role in linking the membrane-associated pore-forming proteins to the cytoplasmic, DNA-processing proteins. TraG is the coupling protein encoded by the incompatibility group HI plasmids. A hallmark feature of the IncHI plasmids is optimal conjugative transfer at 30 °C and an inability to transfer at 37 °C. Transcriptional analysis of the transfer region 1 (Tra1) of R27 has revealed thattraGis transcribed in a temperature-dependent manner, with significantly reduced levels of expression at 37 °C as compared to expression at 30 °C. The R27 coupling protein contains nucleoside triphosphate (NTP)-binding domains, the Walker A and Walker B boxes, which are well conserved among this family of proteins. Site-specific mutagenesis within these motifs abrogated the conjugative transfer of R27 into recipient cells. Mutational analysis of the TraG periplasmic-spanning residues, in conjunction with bacterial two-hybrid and immunoprecipitation analysis, determined that this region is essential for a successful interaction with the T4SS protein TrhB. Further characterization of TraG by immunofluorescence studies revealed that the R27 coupling protein forms membrane-associated fluorescent foci independent of R27 conjugative proteins. These foci were found at discrete positions within the cell periphery. These results allow the definition of domains within TraG that are involved in conjugative transfer, and determination of the cellular location of the R27 coupling protein.