Selection and characterization of fluoroquinolone-resistant mutants of Campylobacter jejuni using enrofloxacin

Genomic resistant determinants of multidrug-resistant Campylobacter spp. isolates in Peru

OBJECTIVES

Antimicrobial resistant (AMR) Campylobacter is a global health threat; however, there is limited information on genomic determinants of resistance in low- and middle-income countries. We evaluated genomic determinants of AMR using a collection of whole genome sequenced Campylobacter jejuni and C. coli isolates from Iquitos, Peru.

METHODS

Campylobacter isolates from two paediatric cohort studies enriched with isolates that demonstrated resistance to ciprofloxacin and azithromycin were sequenced and mined for AMR determinants.

RESULTS

The gyrA mutation leading to the Thr86Ile amino acid change was the only gyrA mutation associated with fluoroquinolone resistance identified. The A2075G mutation in 23S rRNA was present, but three other 23S rRNA mutations previously associated with macrolide resistance were not identified. A resistant-enhancing variant of the cmeABC efflux pump genotype (RE-cmeABC) was identified in 36.1% (35/97) of C. jejuni genomes and 17.9% (12/67) of C. coli genomes. Mutations identified in the CmeR-binding site, an inverted repeat sequence in the cmeABC promoter region that increases expression of the operon, were identified in 24/97 C. jejuni and 14/67 C. coli genomes. The presence of these variants, in addition to RE-cmeABC, was noted in 18 of the 24 C. jejuni and 9 of the 14 C. coli genomes.

CONCLUSIONS

Both RE-cmeABC and mutations in the CmeR-binding site were strongly associated with the MDR phenotype in C. jejuni and C. coli. This is the first report of RE-cmeABC in Peru and suggests it is a major driver of resistance to the principal therapies used to treat human campylobacteriosis in this setting.

Droplet Digital PCR-Based Detection and Quantification of GyrA Thr-86-Ile Mutation Based Fluoroquinolone-Resistant Campylobacter jejuni

Fluoroquinolone (FQ)-resistant Campylobacter jejuni is a serious problem worldwide that limits effective treatment of infections. The traditional detection method depends on bacterial isolation and MIC testing, or traditional PCR, which is time-consuming and hard to identify the FQ-resistant C. jejuni in a high abundance wild-type background. This study aimed to develop a rapid and accurate ddPCR assay to detect FQ-resistant C. jejuni mutants based on the crucial resistance mutation C257T (Thr-86-Ile) in gyrA. Our ddPCR gyrA assay showed high specificity and accuracy. Sanger sequencing and the qPCR assay could only recognize gyrA mutant sequences when the ratios of wild-type/mutant were 1:1 or 10:1, respectively. Our ddPCR gyrA assay was able to detect gyrA mutant sequences in the mixtures with up to at least 1000:1 wild-type/mutant ratios, which suggested a significant advantage to distinguish the low mutant signal from the wild-type background. We further monitored the occurrence of gyrA mutations under ciprofloxacin pressure using our ddPCR gyrA assay, and clearly showed that the transition of a dominant C. jejuni subpopulation from wild-type to gyrA C257T mutant, resulting in FQ-resistance. We tested 52 samples from live chickens and retail chicken meat and showed that four samples contained wild-type/mutant mixtures comprising 1.7%, 28.6%, 53.3%, and 87.0% gyrA C257T mutants, respectively. These results demonstrated that the ddPCR gyrA assay was a highly sensitive alternative method to distinguish and quantify FQ-resistant C. jejuni infections that could help guide the appropriate use of FQs in clinical practice.

IMPORTANCECampylobacter jejuni is considered to be the leading cause of human bacterial gastroenteritis worldwide, and fluoroquinolones (FQs) are the main choices for the treatment of bacterial gastroenteritis in clinical practice. In theory, antimicrobial susceptibility testing should help us to choose the most appropriate drugs for the treatment. However, to test the susceptibility of C. jejuni to FQs, the standardized method is bacteria isolation and MIC measurement, which will take more than 4 days. In addition, a low abundance of FQ-resistant C. jejuni is also hardly distinguished from a high abundance of wild-type background in the mixed infection. Therefore, the development of rapid and accurate detection technology for FQ-resistant C. jejuni is very important. This study provided a ddPCR gyrA assay, which is a highly sensitive alternative method to distinguish and quantify FQ-resistant C. jejuni infections that may help guide the appropriate use of FQs both in veterinary and human clinical practice.

Prevalence and antimicrobial resistance of Campylobacter jejuni and C. coli identified in a slaughterhouse in Argentina

The aim of this study was to evaluate the percentage of Campylobacter (C. jejuni and C. coli) from samples collected at the slaughterhouse to describe the prevalence of resistance to selected antimicrobials, and to characterize the genetic determinants. In total, from 333 samples analyzed, 31% were positive for Campylobacter. More positive samples were detected before the chiller (46%) than after the chiller (16%). C. coli (59%) was more prevalent than C. jejuni (41%). Antimicrobial resistance differences between C. jejuni and C. coli were found (p < 0.001). Multidrug resistance was found in 72% of C. coli isolates and 69% of C. jejuni isolates (p < 0.001). Most C. jejuni isolates (57%) had the three genes of the cmeABC efflux pump. The tet(O) gene and resistance-associated point mutations within both the gyrA and 23S rRNA genes were detected in 100% of C. coli isolates. On the other hand, C. jejuni only had more prevalence of the bla_OXA-61 gene than C. coli (p < 0.001), and most of the C. jejuni isolates (70–80%) had the tet(O) and gyrA point mutation. These results could contribute to knowledge about the status of thermotolerant Campylobacter resistant to antimicrobials isolated from food animals in Argentina and to develop an antimicrobial resistance surveillance system.

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From samples analyzed, 31% were positive for Campylobacter.

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More positive samples were detected before the chiller (46%) than after it (16%).

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Multidrug resistance was found in 72% of C. coli isolates and 69% of C. jejuni isolates.

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The tet(O) gene was detected in 100% of the tetracycline-, resistantC. coliisolates.

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C.jejuni only had more prevalence of the bla_OXA-61 gene than C. coli (p < 0.001).

Resistance to Antibiotics in Thermophilic Campylobacters

Campylobacter jejuni (C. jejuni) is one of the most frequent causes of bacterial enterocolitis globally. The disease in human is usually self-limiting, but when complications arise antibiotic therapy is required at a time when resistance to antibiotics is increasing worldwide. Mechanisms of antibiotic resistance in bacteria are diverse depending on antibiotic type and usage and include: enzymatic destruction or drug inactivation; alteration of the target enzyme; alteration of cell membrane permeability; alteration of ribosome structure and alteration of the metabolic pathway(s). Resistance of Campylobacter spp. to antibiotics, especially fluoroquinolones is now a major public health problem in developed and developing countries. In this review the mechanisms of resistance to fluoroquinolones, macrolides, tetracycline, aminoglycoside and the role of integrons in resistance of Campylobacter (especially at the molecular level) are discussed, as well as the mechanisms of resistance to β-lactam antibiotics, sulphonamides and trimethoprim. Multiple drug resistance is an increasing problem for treatment of campylobacter infections and emergence of resistant strains and resistance are important One Health issues.

Distribution of CRISPR Types in Fluoroquinolone-Resistant Campylobacter jejuni Isolates

To aid development of phage therapy against Campylobacter, we investigated the distribution of the clustered regularly interspaced short palindromic repeats (CRISPR) systems in fluoroquinolone (FQ)-resistant Campylobacter jejuni. A total of 100 FQ-resistant C. jejuni strains from different sources were analyzed by PCR and DNA sequencing to determine resistance-conferring mutation in the gyrA gene and the presence of various CRISPR systems. All but one isolate harbored 1-5 point mutations in gyrA, and the most common mutation was the Thr86Ile change. Ninety-five isolates were positive with the CRISPR PCR, and spacer sequences were found in 86 of them. Among the 292 spacer sequences identified in this study, 204 shared 93-100% nucleotide homology to Campylobacter phage D10, 44 showed 100% homology to Campylobacter phage CP39, and 3 had 100% homology with Campylobacter phage CJIE4-5. The remaining 41 spacer sequences did not match with any phages in the database. Based on the results, it was inferred that the FQ-resistant C. jejuni isolates analyzed in this study were potentially resistant to Campylobacter phages D10, CP39, and CJIE4-5 as well as some unidentified phages. These phages should be excluded from cocktails of phages that may be utilized to treat FQ-resistant Campylobacter.

Microevolution of Campylobacter jejuni during long-term infection in an immunocompromised host

Campylobacteriosis typically manifests as a short-lived, self-limiting gastrointestinal infection in humans, however prolonged infection can be seen in cases with underlying immunodeficiency. Public Health England received 25 isolates of Campylobacter jejuni from an individual with combined variable immunodeficiency over a period of 15 years. All isolates were typed and archived at the time of receipt. Whole genome sequencing (WGS) and antimicrobial susceptibility testing were performed to examine the relatedness of the isolates and to investigate the changes in the genome that had taken place over the course of the infection. Genomic typing methods were compared to conventional phenotypic methods, and revealed that the infection was caused by a single, persistent strain of C. jejuni belonging to clonal complex ST-45, with evidence of adaptation and selection in the genome over the course of the infection. Genomic analysis of sequence variants associated with antimicrobial resistance identified the genetic background behind rRNA gene mutations causing variable levels of resistance to erythromycin. This application of WGS to examine a persistent case of campylobacteriosis provides insight into the mutations and selective pressures occurring over the course of an infection, some of which have important clinical relevance.

Comparison of relative expressions of genes involved in iron acquisition and regulation in fluoroquinolone-resistant and wild-type Campylobacter jejuni

Campylobacteriosis caused by C. jejuni is a serious yet common foodborne disease in the U.S. The prevalence of fluoroquinolone-resistant C. jejuni from poultry has continued to increase despite the withdrawal of fluoroquinolone use in the U.S. poultry industry in 2005. To date, no clear selective pressures that explain this effect have been documented. In this study, we investigated limited bioavailability of iron in poultry and enhanced iron uptake and regulation as potential indirect selective pressures conferring fitness advantages in fluoroquinolone-resistant C. jejuni compared to its susceptible wild-type counterpart. Five fluoroquinolone-susceptible C. jejuni isolates were selected from litter collected from commercial broiler farms. Using antibiotic selection, five fluoroquinolone-resistant strains were created. Relative expressions of six genes involved in iron acquisition and regulation were compared between the resistant and susceptible strains using RT-qPCR under normal and iron-limiting conditions. High variability in the relative gene expressions was observed among the strains, with only one resistant strain showing the consistent upregulation of the measured genes compared to the matching susceptible wild-type. Our results suggest that the hypothesis tested in the study may not be an adequate explanation of the molecular mechanism behind the enhanced fitness of fluoroquinolone-resistant C. jejuni compared to susceptible C. jejuni. This study highlights the need for a better understanding of the complex ecology and dynamics of fluoroquinolone resistance in C. jejuni in poultry environment and warrants an examination of fluoroquinolone-resistant C. jejuni strains recovered from the natural broiler chicken environment.

Antimicrobial Resistance in Campylobacter spp

Campylobacter is a major foodborne pathogen and has become increasingly resistant to clinically important antimicrobials. To cope with the selection pressure from antimicrobial use in both veterinary and human medicine, Campylobacter has developed multiple mechanisms for antibiotic resistance, including modification or mutation of antimicrobial targets, modification or inactivation of antibiotics, and reduced drug accumulation by drug efflux pumps. Some of these mechanisms confer resistance to a specific class of antimicrobials, while others give rise to multidrug resistance. Notably, new antibiotic resistance mechanisms continuously emerge in Campylobacter, and some examples include the recently discovered multidrug resistance genomic islands harboring multiple genes involved in the resistance to aminoglycosides and macrolides, a novel Cfr(C) conferring resistance to phenicols and other drugs, and a potent multidrug efflux pump CmeABC variant (RE-CmeABC) that shows a significantly enhanced function in multidrug resistance and is associated with exceedingly high-level resistance to fluoroquinolones. These newly emerged resistance mechanisms are horizontally transferable and greatly facilitate the adaptation of Campylobacter in the food-producing environments where antibiotics are frequently used. In this article, we will discuss how Campylobacter resists the action of various classes of antimicrobials, with an emphasis on newly discovered mechanisms.

The Molecular Mechanisms of Ciprofloxacin Resistance in Clinical Campylobacter jejuni and Their Genotyping Characteristics in Beijing, China

We assessed the susceptibility of 182 Campylobacter jejuni isolates from patients with diarrhea to eight antibiotics and analyzed the molecular mechanisms of ciprofloxacin resistance as well as the genetic characteristics based on multilocus sequence typing (MLST). The C257T mutation was found on the quinolone resistance-determining region (QRDR) of the gyrA gene in all ciprofloxacin-resistant strains. Mutations on the QRDR of the gyrB gene were silent. A total of 74 strains had 7 inverted repeat (IR) (a 16-bp IR on the intergenic region between cmeR and cmeABC) mutation polymorphisms. Compared with strains without the IR mutations, strains with the IR mutations had higher resistance rates to ciprofloxacin (94.6% vs. 83.3%), nalidixic acid (94.6% vs. 83.3%), tetracycline (98.6% vs. 85.2%), doxycycline (91.9% vs. 71.3%), florfenicol (59.5% vs. 17.6%), chloramphenicol (25.7% vs. 4.6%), gentamicin (16.2% vs. 3.7%), and multidrug resistance than those without IR mutations (all p < 0.05). With C257T mutation alone, 89.9% strains with minimum inhibitory concentration (MIC) values focused on 16, 32, and 64 μg/mL, whereas strains with C257T mutation in combination with the IR mutations had a higher ciprofloxacin resistance level with 88.6% MIC values focused on 64, 128, and 512 μg/mL (p < 0.0001). The strains in this study showed a high genetic variability based on MLST with 117 sequence types (STs), 37 of which were novel. CC-21 was the most common clonal complex (CC) followed by CC-353 and CC-45. No association was found between STs and ciprofloxacin resistance. In conclusion, the C257T mutation on gyrA was the major mechanism for ciprofloxacin resistance, and the C257T mutation in combination with the IR mutations might result in more severe ciprofloxacin resistance to C. jejuni.

Differential Distribution of Salmonella Serovars and Campylobacter spp. Isolates in Free-Living Crows and Broiler Chickens in Aomori, Japan

Salmonella and Campylobacter cause foodborne enteritis mainly via the consumption of raw/undercooked contaminated poultry meat and products. Broiler flocks are primarily colonized with these bacteria; however, the underlying etiology remains unclear. The present study was conducted in order to obtain further information on the prevalence and genotypic distribution of Salmonella and Campylobacter in free-living crows and broiler flocks in a region for 2 years, thereby facilitating estimations of the potential risk of transmission of C. jejuni from crows to broiler flocks. Salmonella serovars Bredeney and Derby were isolated from 8 and 3 out of 123 captured crows, respectively, both of which are not common in broiler chickens. Campylobacter were isolated from all 89 crows tested and C. jejuni was prevalent (85 crows). Pulsed field gel electrophoresis showed broad diversity in the crow isolates of C. jejuni. However, 3 crow isolates and 2 broiler isolates showing similar banding patterns were assigned to different sequence types in multi-locus sequence typing. These results indicate that crows do not share Salmonella serovars with broilers, and harbor various genotypes of C. jejuni that differ from those of broiler flocks. Thus, our results indicate that crows are not a potential vector of these bacteria to broiler flocks in this region.

Methods to Study Antimicrobial Resistance in Campylobacter jejuni

Campylobacter jejuni is a leading bacterial cause of foodborne gastroenteritis worldwide and is increasingly resistant to clinically important antibiotics. Detection of antibiotic resistance in C. jejuni can be performed with both phenotypic and genotypic methods. In this chapter, we describe the most commonly used molecular biology methods for detection of resistance to clinically important antibiotics. These methods can be employed in both clinical and research settings to facilitate clinical therapy and to monitor the emergence and dissemination of antibiotic-resistant C. jejuni.

Antibiotic resistance trends and mechanisms in the foodborne pathogen,Campylobacter

Campylobacteris a major foodborne pathogen and is commonly present in food producing animals. This pathogenic organism is highly adaptable and has become increasingly resistant to various antibiotics. Recently, both the Centers for Disease Control and Prevention and the World Health Organization have designated antibiotic-resistantCampylobacteras a serious threat to public health. For the past decade, multiple mechanisms conferring resistance to clinically important antibiotics have been described inCampylobacter, and new resistance mechanisms constantly emerge in the pathogen. Some of the recent examples include theerm(B)gene conferring macrolide resistance, thecfr(C)genes mediating resistance to florfenicol and other antimicrobials, and a functionally enhanced variant of the multidrug resistance efflux pump, CmeABC. The continued emergence of new resistance mechanisms illustrates the extraordinary adaptability ofCampylobacterto antibiotic selection pressure and demonstrate the need for innovative strategies to control antibiotic-resistantCampylobacter. In this review, we will briefly summarize the trends of antibiotic resistance inCampylobacterand discuss the mechanisms of resistance to antibiotics used for animal production and important for clinical therapy in humans. A special emphasis will be given to the newly discovered antibiotic resistance.

Seabirds (Laridae) as a source of Campylobacter spp., Salmonella spp. and antimicrobial resistance in South Africa

Zoonotic thermophilic Campylobacter and nontyphoidal Salmonella enterica are a major cause of foodborne human gastroenteritis worldwide. There is little information about reservoirs of these zoonotic agents in Africa. Thus, chicks of kelp gulls (Larus dominicanus, n = 129) and greater crested terns (Thalasseus bergii, n = 100) were studied at five colonies on the Western Cape coast (South Africa) during summer 2013/2014. Campylobacter spp. occurrence was 14.0% (CI_95% : 9.9-19.3), with C. jejuni the most frequently isolated species, whilst that of Salmonella was 27.5% (CI_95% : 21.9-33.9) overall, with a higher prevalence in gulls (43.0%, CI_95% : 34.8-52.4) than terns (7.0%, CI_95% : 3.1-14.4). Among the 16 different S. enterica serovars found, Anatum, Enteritidis and Hadar were the most frequent. The same or highly similar pulsed-field gel electrophoresis genotype was found in some Salmonella isolates from seabirds and humans presenting with salmonellosis in Cape Town hospitals. Both Campylobacter and Salmonella isolates exhibited antimicrobial resistance to several agents, including critically important antimicrobials (quinolones, tetracyclines and β-lactams) and multidrug resistance in Salmonella serovars from kelp gulls. Our results highlight the importance of seabirds as reservoirs of Campylobacter and Salmonella resistant strains and their role in the maintenance and transmission of these bacteria in the environment, with implications for public health.

Resistance to β-lactam and tetracycline in Campylobacter spp.isolated from broiler slaughterhouses in southern Brazil

Abstract The study was carried out to screen and analyze the genetic characteristics of antimicrobial resistance in Campylobacter spp. from poultry sources. A total of 141 strains of Campylobacter isolated from samples of broilers of slaughterhouses in southern Brazil was identified by phenotypic and genotypic methods. Campylobacter isolates were evaluated for its antimicrobial susceptibility and the presence of resistance genes. The strains were investigated for antimicrobial susceptibility against two agents (ampicillin and tetracycline) by disk diffusion method. PCR assay was used to confirm the specie and the presence of ampicillin (blaOXA-61), tetracycline tet(O), and the energy-dependent multi-drug efflux pump (cmeB) genes. Campylobacter jejuni was the most ubiquitous; its presence was determined in 140 samples out of 141 (99.3%), whereas Campylobacter coli was found only in one of the contaminated samples (0.70%). The results obtained showed 65% and 35.5% of Campylobacter isolates resistant to β-lactams and tetracyclines, respectively. The cmeB gene responsible for multidrug resistance was detected in 26 isolates out 141 strains (18.5%). Moreover, 36 out of 141 Campylobacter strains (25.6%) were found to be resistant to at least two different antimicrobia resistance markers (β-lactams and tetracyclines).

Resistance mechanisms in Campylobacter jejuni

Campylobacter jejuni is a major cause of food-borne gastroenteritis worldwide. While mortality is low, morbidity imparted by post-infectious sequelae such as Guillain-Barré syndrome, Reiter syndrome/reactive arthritis and irritable bowel syndrome is significant. In addition, the economic cost is high due to lost productivity. Food animals, particularly poultry, are the main reservoirs of C. jejuni. The over-use of antibiotics in the human population and in animal husbandry has led to an increase in antibiotic-resistant infections, particularly with fluoroquinolones. This is problematic because C. jejuni gastroenteritis is clinically indistinguishable from that caused by other bacterial pathogens, and such illnesses are usually treated empirically with fluoroquinolones. Since C. jejuni is naturally transformable, acquisition of additional genes imparting antibiotic resistance is likely. Therefore, an understanding of the antibiotic resistance mechanisms in C. jejuni is needed to provide proper therapy both to the veterinary and human populations.

A fluoroquinolone resistance associated mutation in gyrA Affects DNA supercoiling in Campylobacter jejuni

The prevalence of fluoroquinolone (FQ)-resistant Campylobacter has become a concern for public health. To facilitate the control of FQ-resistant (FQ^R) Campylobacter, it is necessary to understand the impact of FQ^R on the fitness of Campylobacter in its natural hosts as understanding fitness will help to determine and predict the persistence of FQ^RCampylobacter. Previously it was shown that acquisition of resistance to FQ antimicrobials enhanced the in vivo fitness of FQ^RCampylobacter. In this study, we confirmed the role of the Thr-86-Ile mutation in GyrA in modulating Campylobacter fitness by reverting the mutation to the wild-type (WT) allele, which resulted in the loss of the fitness advantage. Additionally, we determined if the resistance-conferring GyrA mutations alter the enzymatic function of the DNA gyrase. Recombinant WT gyrase and mutant gyrases with three different types of mutations (Thr-86-Ile, Thr-86-Lys, and Asp-90-Asn), which are associated with FQ^R in Campylobacter, were generated in E. coli and compared for their supercoiling activities using an in vitro assay. The mutant gyrase with the Thr-86-Ile change showed a greatly reduced supercoiling activity compared with the WT gyrase, while other mutant gyrases did not show an altered supercoiling. Furthermore, we measured DNA supercoiling within Campylobacter cells using a reporter plasmid. Consistent with the results from the in vitro supercoiling assay, the FQ^R mutant carrying the Thr-86-Ile change in GyrA showed much less DNA supercoiling than the WT strain and the mutant strains carrying other mutations. Together, these results indicate that the Thr-86-Ile mutation, which is predominant in clinical FQ^RCampylobacter, modulates DNA supercoiling homeostasis in FQ^RCampylobacter.

Lack of correlation between the 257C-to-T mutation in the gyrA gene and clinical severity of Campylobacter jejuni infection in a region of high incidence of ciprofloxacin resistance

BACKGROUND

Fluoroquinolone resistance is increasingly detected in Campylobacter jejuni worldwide. Despite the fact that a point mutation in the gyrA gene has been linked with increased fitness in animals, the association of resistant organisms with more severe infections in man remains controversial.

METHODS

Erythromycin and quinolone susceptibility of 147 C. jejuni strains isolated from individual patients with diarrhoea in southwest Hungary were investigated and the molecular background of fluoroquinolone resistance was determined. Hospitalization and the presence of macroscopic blood in the stool were correlated with the presence of 257C-to-T mutation of the gyrA gene causing resistance to fluoroquinolones.

RESULTS

Isolates showed an extensive genetic heterogeneity by macrorestriction analysis of the chromosome. While all strains retained susceptibility to erythromycin, 68% were non-susceptible to ciprofloxacin. The mutation causing a Thr-86-to-Ile replacement in the gyrA gene was present in 98% of non-susceptible isolates. Infection caused by isolates containing this mutation did not show any significant association with either hospitalization or with the development of bloody diarrhoea.

CONCLUSIONS

Our findings indicate that in a region with high-level ciprofloxacin resistance in C. jejuni, non-susceptibility to this antibiotic did not correlate with the severity of infection.

Selecting for development of fluoroquinolone resistance in a Campylobacter jejuni strain 81116 in chickens using various enrofloxacin treatment protocols

AIMS

To determine the effect of various enrofloxacin dose regimes on the colonization and selection of resistance in Campylobacter jejuni strain 81116P in experimentally colonized chickens.

METHODS AND RESULTS

Two experiments were undertaken, in which 14-day-old chickens were colonized with 1 × 10(7) -1 × 10(9 ) CFU g(-1) Camp. jejuni strain 81116P and then treated with enrofloxacin at 12-500 ppm in drinking water for various times. Caecal colonization levels were determined at various time-points after start-of-treatment, and the susceptibility of recovered isolates to ciprofloxacin was monitored. Resistance was indicated by growth on agar containing 4 μg ml(-1) ciprofloxacin, MICs of 16 μg ml(-1) and the Thr86Ile mutation in gyrA. Enrofloxacin at doses of 12-250 ppm reduced Camp. jejuni colonization over the first 48-72 h after start-of-treatment. The degree of reduction in colonization was dose, but not treatment time, dependent. In all cases, maximal colonization was re-established within 4-6 days. Fluoroquinolone-resistant organisms were recoverable within 48 h of start-of-treatment; after a further 24 h all recovered isolates were resistant. In contrast, a dose of 500 ppm enrofloxacin reduced colonization to undetectable levels within 48 h, and the treated birds remained Campylobacter negative throughout the remaining experimental period. By high pressure liquid chromatography, for all doses, the maximum concentrations of enrofloxacin and ciprofloxacin in the caecal contents were detected at the point of treatment completion. Thereafter, levels declined to undetectable by 7 days post-treatment withdrawal.

CONCLUSIONS

In a model using chickens maximally colonized with Camp. jejuni 81116P, treatment with enrofloxacin, at doses of 12-250 ppm in drinking water, enables the selection, and clonal expansion, of fluoroquinolone-resistant organisms. However, this is preventable by treatment with 500 ppm of enrofloxacin.

SIGNIFICANCE AND IMPACT OF THE STUDY

Treatment of chickens with enrofloxacin selects for resistance in Camp. jejuni in highly pre-colonized birds. However, a dose of 500 ppm enrofloxacin prevented the selection of resistant campylobacters.

Prevalence and Biomolecular Characterization of Campylobacter spp. Isolated from Retail Meat

We estimated the prevalence of Campylobacter spp. in retail meat (n = 352 samples; 104 chicken, 106 pork, and 142 beef) collected in Campobasso, Italy, comparing two microbiological methods. All the isolates were characterized by biomolecular techniques for epidemiological purposes. Campylobacter isolation was performed by selective culture and membrane filtration methods. Phenotypic and genotypic methods for genus and species identification were evaluated together with antimicrobial resistance and plasmid profiling. Sixty-nine (86.2%) samples were positive by selective culture, 49 (61.2%) by membrane filtration, and 38 (47.5%) by both methods. Only 74 of 80 strains were confirmed as Campylobacter spp. by PCR, and two Campylobacter coli were identified as Campylobacter jejuni . Chicken meat was more frequently contaminated than other meats. Selective culture was more sensitive than membrane filtration (85 versus 66%), and specificity of the methods was 98 and 100%, respectively. Among Campylobacter isolates from chicken meat, 86.5% were multidrug resistant. Resistance to ciprofloxacin (51.3%) and enrofloxacin (52.7%) was lower than to nalidixic acid (71.6%). C. coli strains showed the highest cross-resistance for quinolones (82.6%) and fluoroquinolones (60.9%) as well as a high resistance to tetracycline. Plasmids were isolated from six C. coli and two C. jejuni isolates, but no association was detected between antimicrobial resistance and plasmid DNA carriage. Selective culture is considered as the optimal method for Campylobacter isolation, although it was unable to detect all contaminated samples. Membrane filtration provided more specific results but with low sensitivity. A combination of both techniques may offer better results.

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.

Role of Cj1211 in natural transformation and transfer of antibiotic resistance determinants in Campylobacter jejuni

Campylobacter jejuni, an important food-borne human pathogen, is increasingly resistant to antimicrobials. Natural transformation is considered to be a main mechanism for mediating the transfer of genetic materials encoding antibiotic resistance determinants in C. jejuni, but direct evidence for this notion is still lacking. In this study, we determined the role of Cj1211 in natural transformation and in the development of antibiotic resistance in C. jejuni. Insertional mutagenesis of Cj1211, a Helicobacter pylori ComH3 homolog, abolished natural transformation in C. jejuni. In vitro coculture of C. jejuni strains carrying either kanamycin or tetracycline resistance markers demonstrated the development of progenies that were resistant to both antibiotics, indicating that the horizontal transfer of antibiotic resistance determinants actively occurs in mixed Campylobacter populations. A mutation of Cj1211 or the addition of DNase I in culture media completely inhibited the formation of progenies that were resistant to both antibiotics, indicating that the horizontal transfer of the resistance determinants is mediated by natural transformation. Interestingly, the mutation of Cj1211 also reduced the frequency of emergence of spontaneous mutants that were resistant to fluoroquinolone (FQ) and streptomycin but did not affect the outcome of FQ resistance development under FQ treatment, suggesting that natural transformation does not play a major role in the emergence of FQ-resistant Campylobacter strains during treatment with FQ antimicrobials. These results define Cj1211 as a competence factor in Campylobacter, prove the role of natural transformation in the horizontal transfer of antibiotic resistance determinants in Campylobacter, and provide new insights into the mechanism underlying the development of FQ-resistant Campylobacter strains.

Phylogenetic relationships of Campylobacter jejuni based on porA sequences

Campylobacter porins are the dominant major outer membrane protein (MOMP) of these bacteria. They are composed of hypervariable, surface-exposed, peptide loops and membrane-embedded, conserved peptide regions. Porins are functionally important and may also be useful for molecular subtyping methods but have not yet been well characterized. We therefore sequenced the porA gene from 39 Campylobacter isolates, including multilocus sequence type (MLST) reference strains, isolates from patients with the Guillain-Barré syndrome, other clinical isolates, and serotyping reference strains. These were compared with additional sequences available from GenBank. Three distinct porA lineages were observed after phylogenetic analysis. Both Campylobacter coli and Campylobacter jejuni were found with group 3 porA sequences, and this was the only group showing any evidence of recombination among porA genes. There was no recombination between porA genes from C. jejuni groups 1 and 2, suggesting there may be functional constraints on changes at this locus. Most of the amino acid differences among the three groups were present in surface-exposed loops, and dissimilar substitutions were found when groups 1 and 2 MOMP were compared. Different MOMP sequence groups may have different biological or antigenic properties, which in turn may be associated with survival in different environments, host adaptation, or virulence.

Regulation of the expression of the CmeABC efflux pump in Campylobacter jejuni: identification of a point mutation abolishing the binding of the CmeR repressor in an in vitro-selected multidrug-resistant mutant

A multidrug-resistant mutant of Campylobacter jejuni was selected in vitro using increasing concentrations of enrofloxacin. This mutant accumulated less ethidium bromide than the parental strain, suggesting the participation of active efflux as a resistance mechanism. Inactivation of the cmeB gene confirmed active efflux and indicated the involvement of the CmeABC efflux pump in the multidrug resistance of the mutant. Sequencing of the cmeR-cmeA intergenic region revealed a point mutation in the binding site of the CmeR repressor. Transcriptional lacZ fusions showed an increase of transcription of the cmeABC operon in the multidrug-resistant mutant. Gel mobility shift assays and Surface Plasmon Resonance experiments further indicated a decrease in the affinity of the CmeR for the promoting region of the cmeABC operon consecutive to this mutation. Thus, these results showed that the point mutation was responsible, via a lack of binding of the CmeR repressor, for increased expression of the CmeABC efflux pump and consecutive multidrug resistance.

Antibiotic-resistant Campylobacter: could efflux pump inhibitors control infection?

Campylobacter is the most common cause of bacterial gastroenteritis in the world. Poultry is the main reservoir of human infections. The widespread use of antibiotics in agriculture and veterinary medicine has resulted in the emergence of an increasing number of antibiotic-resistant Campylobacter strains that can be transmitted to humans through the food chain. Of particular concern to public health is the prevalence of resistance to macrolides and fluoroquinolones that are used in the treatment of life-threatening campylobacteriosis. The CmeABC efflux system has been shown to contribute to the intrinsic and acquired resistance to these antibiotics. In addition, by mediating resistance to bile, it is essential for colonization of the chicken gut in vivo. Inhibition of CmeABC may provide an effective means of reversing antibiotic resistance and decreasing the transmission of Campylobacter via the food chain. This would positively impact on public health by decreasing the morbidity, mortality and increased healthcare costs associated with the treatment of antibiotic-resistant Campylobacter.

Synergy between efflux pump CmeABC and modifications in ribosomal proteins L4 and L22 in conferring macrolide resistance in Campylobacter jejuni and Campylobacter coli

Macrolide-resistant mutants of Campylobacter jejuni and Campylobacter coli were selected in vitro using erythromycin and tylosin. These mutants exhibited modifications in the ribosomal proteins L4 (G74D) and L22 (insertions at position 86 or 98). A synergy between the CmeABC efflux pump and these modifications in conferring macrolide resistance was observed.

Mechanisms of fluoroquinolone and macrolide resistance in Campylobacter spp

The incidence of human Campylobacter infections is increasing worldwide, as well as the proportion of isolates resistant to fluoroquinolones and/or macrolides, the drugs of choice to treat campylobacteriosis. In this review, we report recent developments in the understanding of the resistance mechanisms to fluoroquinolones and macrolides. In addition, we will discuss the recent findings on multidrug resistance in Campylobacter spp.

Practical applications and feasibility of efflux pump inhibitors in the clinic--a vision for applied use

The world of antibiotic drug discovery and development is driven by the necessity to overcome antibiotic resistance in common Gram-positive and Gram-negative pathogens. However, the lack of Gram-negative activity among both recently approved antibiotics and compounds in the developmental pipeline is a general trend despite the fact that the plethora of covered drug targets are well-conserved across the bacterial kingdom. Such intrinsic resistance in Gram-negative bacteria is largely attributed to the activity of multidrug resistance (MDR) efflux pumps. Moreover, these pumps also play a significant role in acquired clinical resistance. Together, these considerations make efflux pumps attractive targets for inhibition in that the resultant efflux pump inhibitor (EPI)/antibiotic combination drug should exhibit increased potency, enhanced spectrum of activity and reduced propensity for acquired resistance. To date, at least one class of broad-spectrum EPI has been extensively characterized. While these efforts indicated a significant potential for developing small molecule inhibitors against efflux pumps, they did not result in a clinically useful compound. Stemming from the continued clinical pressure for novel approaches to combat drug resistant bacterial infections, second-generation programs have been initiated and show early promise to significantly improve the clinical usefulness of currently available and future antibiotics against otherwise recalcitrant Gram-negative infections. It is also apparent that some changes in regulatory decision-making regarding resistance would be very helpful in order to facilitate approval of agents aiming to reverse resistance and prevent its further development.

Comparison of Campylobacter isolated from humans and food-producing animals in Japan

AIMS

To compare the antimicrobial resistance, serotypes and flagellin gene types of Campylobacter isolated from humans and food-producing animals and thereby facilitate elucidation of the origin of Campylobacter causing human infection in Japan.

METHODS AND RESULTS

The MIC values of ampicillin, dihydrostreptomycin, gentamicin, erythromycin, oxytetracycline, nalidixic acid and enrofloxacin for Campylobacter isolated from humans (134 isolates), cattle (38 isolates), pigs (69 isolates), layers (84 isolates) and broilers (51 isolates) were compared. The MIC(90) values of ampicillin for Campylobacter jejuni isolates from poultry were higher than those from humans and cattle. Campylobacter coli that was resistant to dihydrostreptomycin and erythromycin was observed at a higher frequency in humans and pigs than in poultry. The restriction fragment profiles of flaA of human, bovine and broiler isolates were analysed by clustering, and the isolates were classified into five clusters. Cluster I contained only human and bovine isolates. Clusters III, IV and V contained human, bovine and broiler isolates.

CONCLUSIONS

Campylobacter isolates from humans included isolates that exhibited characteristics identical to those of the bovine, porcine and poultry isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

In addition to poultry, cattle and pigs are believed to be sources of campylobacteriosis in Japan.

A double mutation in the gyrA gene is necessary to produce high levels of resistance to moxifloxacin in Campylobacter spp. clinical isolates

The aim of this study was to compare different fluoroquinolones against Campylobacter spp., analysing the molecular mechanisms of resistance. Moxifloxacin exhibited the greatest activity of the quinolones tested, being active against isolates carrying a single mutation in the gyrA gene. High resistance levels to moxifloxacin were related to the presence of a double gyrA mutation.

Characterization of acmeABCOperon in a Quinolone- ResistantCampylobacter coliIsolate of Irish Origin

In this study, a tripartite-operon-encoding efflux system together with its regulatory gene was characterized in an Irish Campylobacter coli isolate CIT-382 showing high-level resistance to nalidixic acid and ciprofloxacin. Sequence comparisons revealed significant homology between C. coli and the cmeABC operon of Campylobacter jejuni. Conservation of functional sequence domains and motifs were noted among C. coli and similar operons in unrelated organisms. A transcriptional regulatory gene cmeR located proximal to cmeABC was also identified. C. coli CIT-382 harbored the Thr-86-Ile amino acid substitution in the gyrA gene. Accumulation studies with ethidium bromide in the presence of known efflux pump inhibitors confirmed the presence of efflux pump activity in C. coli CIT-382. The efflux pump inhibitor PAbetaN had no effect on the MICs to quinolones. Our data suggest that the gyrA gene mutation is the main contributor to the high-level nalidixic acid and ciprofloxacin resistance observed in this Irish C. coli CIT-382 isolate.

Emergence of Fluoroquinolone Resistance in Campylobacter jejuni in Chickens Exposed to Enrofloxacin Treatment at the Inherent Dosage Licensed in Japan

The objective of the present study was to determine whether selection of fluoroquinolone resistance could be easily induced in Campylobacter jejuni-colonized chickens by treatment with enrofloxacin of representative fluoroquinolones at the inherent dosage licensed in Japan (50 ppm in drinking water for 3 days). In the case of isolates from chickens of study 1, an increase in the population of susceptible isolates appeared after the cessation of treatment and maintained throughout the experiments. On the contrary, our results of study 2 demonstrated that administration of enrofloxacin generated a rapid increase of fluoroquinolone resistance in C. jejuni showing the mutation of Asp-90-Asn in the gyrA gene. Present results indicate that the enrofloxacin treatment for broilers at the inherent dosage is able to select fluoroquinolone resistance in C. jejuni. We conclude that whatever enrofloxacin dosage is used, an emergence of fluoroquinolone resistant of C. jejuni occurs.

Bile salts modulate expression of the CmeABC multidrug efflux pump in Campylobacter jejuni

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 (PcmeABC) 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 PcmeABC, 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 PcmeABC. 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.

Interaction of CmeABC and CmeDEF in conferring antimicrobial resistance and maintaining cell viability in Campylobacter jejuni

OBJECTIVES

To determine the role of CmeDEF in conferring antimicrobial resistance in Campylobacter jejuni and examine the interaction of CmeABC and CmeDEF in mediating antimicrobial resistance and maintaining cell viability.

METHODS

Single and double mutants of cmeF and cmeB were generated in multiple strains using insertional mutagenesis. The mutants were compared with their wild-type strains for antimicrobial susceptibility and growth characteristics. Transcription fusion was used to quantify the expression of cmeDEF and cmeABC. Ethidium bromide (EB) accumulation assay was used to measure the efflux function.

RESULTS

Insertional mutagenesis of the cmeF gene in C. jejuni NCTC 11168 resulted in a 2-fold decrease in the resistance to ampicillin, polymyxin B and EB, whereas the same mutation in C. jejuni 81-176 and 21190 led to a 2-4-fold increase in the resistance to multiple antimicrobials and toxic compounds. The increased resistance in the cmeF mutants of 81-176 and 21190 was associated with the elevated efflux in the mutants. Compared with the cmeB mutant, the cmeF/cmeB double mutants of 81-176 and 21190 showed further decrease in the resistance to various antimicrobials and toxic compounds. Transcription fusion assay indicated that the expression level of cmeF was substantially lower than that of cmeB. Notably, the cmeB/cmeF double mutation, not the single mutations, impaired cell viability in Campylobacter.

CONCLUSIONS

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.

Relative contribution of target gene mutation and efflux to varying quinolone resistance in Irish Campylobacter isolates

The contribution of target gene mutations and active efflux to varying levels of quinolone resistance in Irish Campylobacter isolates was studied. The Thr-86-Ile modification of GyrA did not correlate with the level of quinolone resistance. The efflux pump inhibitor Phe-Arg-beta-Naphthylamide (PAbetaN) had no effect on the MICs to ciprofloxacin. In contrast, a PAbetaN sensitive efflux system contributed to the low-level nalixidic acid resistance phenotype. The lack of effect of PAbetaN in high-level resistant nalidixic isolates may be attributable to mutations identified in the CmeB efflux pump of these isolates. PAbetaN may have limited diagnostic value in the assessment of the contribution of efflux pump activity to ciprofloxacin resistance in Campylobacter.

Role of efflux pumps and topoisomerase mutations in fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli

Point mutations in the topoisomerase (DNA gyrase A) gene are known to be associated with fluoroquinolone resistance in Campylobacter. Recent studies have shown that an efflux pump encoded by cmeABC is also involved in decreased susceptibilities to fluoroquinolones, as well as other antimicrobials. Genome analysis suggests that Campylobacter jejuni contains at least nine other putative efflux pumps. Using insertional inactivation and site-directed mutagenesis, we investigated the potential contributions of these pumps to susceptibilities to chloramphenicol, ciprofloxacin, erythromycin, and tetracycline in C. jejuni and Campylobacter coli. Insertional inactivation of cmeB resulted in 4- to 256-fold decreases in the MICs of chloramphenicol, ciprofloxacin, erythromycin, and tetracycline, with erythromycin being the most significantly affected. In contrast, inactivation of all other putative efflux pumps had no effect on susceptibility to any of the four antimicrobials tested. Mutation of gyrA at codon 86 (Thr-Ile) caused 128- and 64-fold increases in the MICs of ciprofloxacin and nalidixic acid, respectively. The replacement of the mutated gyrA with a wild-type gyrA allele resulted in a 32-fold decrease in the ciprofloxacin MIC and no change in the nalidixic acid MIC. Our findings indicate that CmeABC is the only efflux pump among those tested that influences antimicrobial resistance in Campylobacter and that a point mutation (Thr-86-Ile) in gyrA directly causes fluoroquinolone resistance in Campylobacter. These two mechanisms work synergistically in acquiring and maintaining fluoroquinolone resistance in Campylobacter species.

Involvement of the CmeABC efflux pump in the macrolide resistance of Campylobacter coli

OBJECTIVES

This study was conducted to examine the role of the CmeABC efflux pump in decreasing the susceptibility of Campylobacter coli to macrolides and ketolides in the context of absence or presence of mutations in the 23S rRNA genes.

METHODS

The cmeB gene was inactivated in strains of C. coli showing two different patterns of erythromycin resistance (low or high level of resistance) associated with the absence or presence of a A2075G mutation in the 23S rRNA genes. MICs of erythromycin, azithromycin, tylosin, telithromycin and ciprofloxacin were compared for wild-type (with or without efflux pump inhibitor) and mutant strains.

RESULTS

The cmeB gene inactivation (or addition of efflux pump inhibitor) led to the restoration of susceptibility of the low-level-resistant strains (no A2075G mutation in the 23S rRNA genes). In the highly resistant strains (A2075G mutation in the 23S rRNA genes), the MICs of erythromycin decreased 128- to 512-fold upon inactivation of the cmeB gene. MICs of azithromycin, tylosin and telithromycin were also affected by both addition of efflux pump inhibitor and cmeB gene inactivation, revealing these molecules as substrates of the CmeABC efflux pump. Compared with azithromycin, MICs of telithromycin drastically decreased upon cmeB gene inactivation even in the presence of a A2075G mutation in 23S rRNA genes.

CONCLUSIONS

The CmeABC efflux pump acts synergically with 23S rRNA mutations to drastically increase the MICs of erythromycin and tylosin in C. coli. In contrast, azithromycin was less affected by efflux and telithromycin, although being a good substrate for the CmeABC efflux pump, was less affected by an A2075G mutation in 23S rRNA genes.

Molecular typing of Campylobacter strains using the cmp gene encoding the major outer membrane protein

Thermophilic Campylobacter, particularly Campylobacter jejuni, is one of the major foodborne human pathogens of animal origin. Reliable and sensitive typing tools are required for understanding the epidemiology and ecology of this zoonotic bacteria agent. Currently, several molecular typing methods are available for differentiating Campylobacter strains, but each of them has limitations. Our previous study revealed that considerable sequence polymorphism exists in the cmp gene encoding the major outer membrane protein of Campylobacter and suggested that sequence variation of cmp may be utilized for discrimination of Campylobacter strains. In this study, we evaluated the feasibility of the cmp-based typing tool, using pulsed-field gel electrophoresis (PFGE) as the "gold" standard for comparison. The cmp alleles were sequenced from multiple Campylobacter strains, grouped, and compared with the PFGE profiles of these strains using Bionumerics. Results showed that 43 cmp sequence types and 43 PFGE types existed among the 60 Campylobacter isolates. Typeability of these strains is 100% using either the cmp-based method or PFGE. The discrimination indices are 0.973 for the cmp-based method and 0.969 for PFGE, respectively. The cmp sequence types are 77.6% congruent with the PFGE types. These results indicate that the cmp-based typing is a simple, yet highly discriminatory approach for molecular differentiation of C. jejuni strains.

Relationship between mutations in the gyrA gene and quinolone resistance in clinical isolates of Corynebacterium striatum and Corynebacterium amycolatum

Quinolone susceptibility was analyzed in 17 clinical isolates of Corynebacterium striatum and 9 strains of Corynebacterium amycolatum by the E-test method in Mueller-Hinton agar plates. The C. striatum ATCC 6940 strain was used as a control strain. The amplified quinolone resistance determining regions of the gyrA genes of C. amycolatum and C. striatum were characterized. Four in vitro quinolone-resistant mutants of C. amycolatum were selected and analyzed. Both in vivo and in vitro quinolone-resistant strains of C. amycolatum showed high levels of fluoroquinolone resistance in strains with a double mutation leading to an amino acid change in positions 87 and 91 or positions 87 and 88 (unusual mutation) of GyrA, whereas the same concomitant mutations at amino acid positions 87 and 91 in GyrA of C. striatum produced high levels of resistance to ciprofloxacin and levofloxacin but only showed a moderate increase in the MIC of moxifloxacin, suggesting that other mechanism(s) of quinolone resistance could be involved in moxifloxacin resistance in C. amycolatum. Moreover, a PCR-RFLP-NcoI of the gyrA gene was developed to distinguish between C. amycolatum and C. striatum species.

Antimicrobial resistance profiles of Campylobacter jejuni isolates from wild birds in Sweden

In order to determine the occurrence and frequency of resistant strains of the bacterium Campylobacter jejuni and to establish baseline MICs in isolates from an environmental reservoir, the resistance profiles of 10 antimicrobial substances were determined for 137 C. jejuni isolates from wild birds in Sweden. Observed MICs were generally low, with only low to moderate incidence of resistance to the tested compounds. One isolate, however, was resistant to nalidixic acid and ciprofloxacin, indicating that quinolone-resistant genotypes of C. jejuni have the potential to spread to wild bird hosts.

Evidence for multiple-antibiotic resistance in Campylobacter jejuni not mediated by CmeB or CmeF

An efflux system, CmeABC, in Campylobacter jejuni was previously described, and a second efflux system, CmeDEF, has now been identified. The substrates of CmeDEF include ampicillin, ethidium bromide, acridine, sodium dodecyl sulfate (SDS), deoxycholate, triclosan, and cetrimide, but not ciprofloxacin or erythromycin. C. jejuni NCTC11168 and two efflux pump knockout strains, cmeB::Kan(r) and cmeF::Kan(r), were exposed to 0.5 to 1 microg of ciprofloxacin/ml in agar plates. All mutants arising from NCTC11168 were resistant to ciprofloxacin but not to other agents and contained a mutation resulting in the replacement of threonine 86 with isoleucine in the quinolone resistance-determining region of GyrA. Mutants with two distinct phenotypes were selected from the efflux pump knockout strains. Mutants with the first phenotype were resistant to ciprofloxacin only and had the same substitution within GyrA as the NCTC11168-derived mutants. Irrespective of the parent strain, mutants with the second phenotype were resistant to ciprofloxacin, chloramphenicol, tetracycline, ethidium bromide, acridine orange, and SDS and had no mutation in gyrA. These mutants expressed levels of the efflux pump genes cmeB and cmeF and the major outer membrane protein gene porA similar to those expressed by the respective parent strains. No mutations were detected in cmeF or cmeB. Accumulation assays revealed that the mutants accumulated lower concentrations of drug. These data suggest the involvement of a non-CmeB or -CmeF efflux pump or reduced uptake conferring multiple-antibiotic resistance, which can be selected after exposure to a fluoroquinolone.