Single or double mutational alterations of gyrA associated with fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli

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.

Identification of knowledge gaps in whole-genome sequence analysis of multi-resistant thermotolerant Campylobacter spp

BACKGROUND

Campylobacter spp. is the most frequent cause of bacterial food-borne gastroenteritis and a high priority antibiotic resistant bacterium according to the World Health Organization (WHO). European monitoring of thermotolerant Campylobacter spp. does not reflect the global burden of resistances already circulating within the bacterial population worldwide.

METHODS

We systematically compared whole genome sequencing with comprehensive phenotypic antimicrobial susceptibility, analyzing 494 thermotolerant Campylobacter poultry isolates from Vietnam and Germany. Any discrepancy was checked by repeating the wet lab and improving the dry lab part. Selected isolates were additionally analyzed via long-read Oxford Nanopore technology, leading to closed chromosomes and plasmids.

RESULTS

Overall, 22 different resistance genes and gene variants (e. g. erm(B), aph(3')-IIIa, aph(2'')-If, catA, lnu(C), blaOXA, sat4) and point mutations in three distinct genes (gyrA, 23S rRNA, rpsL) associated with AMR were present in the Campylobacter isolates. Two AMR genes were missing in the database and one falsely associated with resistance. Bioinformatic analysis based on short-read data partly failed to identify tet(O) and aadE, when the genes were present as duplicate or homologous gene variants. Intriguingly, isolates also contained different determinants, redundantly conferring resistance to chloramphenicol, gentamicin, kanamycin, lincomycin and streptomycin. We found a novel tet(W) in tetracycline sensitive strains, harboring point mutations. Furthermore, analysis based on assemblies from short-read data was impaired to identify full length phase variable aad9, due to variations of the poly-C tract within the gene. The genetic determinant responsible for gentamicin resistance of one isolate from Germany could not be identified. GyrT86I, presenting the main determinant for (fluoro-)quinolone resistance led to a rare atypical phenotype of ciprofloxacin resistance but nalidixic acid sensitivity. Long-read sequencing predicted AMR genes were mainly located on the chromosome, and rarely on plasmids. Predictions from long- and short-read sequencing, respectively, often differed. AMR genes were often organized in multidrug resistance islands (MDRI) and partially located in proximity to transposase genes, suggesting main mobilization of resistance determinants is via natural transformation and transposition in Campylobacter.

CONCLUSIONS

The results of this study suggest that there is frequent resistance gene duplication, mosaicism, and mutation leading to gene variation and truncation in Campylobacter strains that have not been reported in previous studies and are missing from databases. Furthermore, there is a need for deciphering yet unknown resistance mechanisms and resistance spread in thermotolerant Campylobacter spp. that may pose a challenge to global food safety.

Emergence of a Novel tet(L) Variant in Campylobacter spp. of Chicken Origin in China

Tetracyclines are widely used in veterinary medicine and food animal production. Campylobacter members are major foodborne pathogens, and their resistance to tetracycline has been widely reported in different countries. To date, Tet(O), a ribosomal protection protein, is the only confirmed Tet resistance determinant in Campylobacter spp. Here, we reported the detection and characterization of a novel Tet resistance element in Campylobacter spp. of chicken origin. This gene is identified to be a variant of tet(L), which encodes an efflux pump for Tet resistance. The variant was detected in 14 of the 82 tetracycline-resistant Campylobacter isolates collected from chickens in Henan, China. Cloning of the tet(L) variant into tetracycline-susceptible Campylobacter jejuni NCTC 11168 confirmed its function in conferring resistance to tetracycline and doxycycline. In addition, this tet(L) variant elevated the MIC (4-fold increase) of tigecycline in the heterologous Escherichia coli host. Sequencing analysis indicated the tet(L) variant was located within a multidrug-resistance genomic island (MDRGI) containing tet(L) variant IS1216E-ORF1-fexA-Δtnp-IS1216E-tet(O)-tnpV-repA This MDRGI is inserted into conserved gene potB on the chromosome. Multilocus sequence type (MLST) analysis revealed that both clonal expansion and horizontal transfer were involved in the dissemination of the tet(L) variant. These findings reveal the emergence of a new Tet resistance determinant in Campylobacter spp., which may facilitate their adaptation to the antimicrobial selection pressure in chickens.

Susceptibility of Campylobacter Strains to Selected Natural Products and Frontline Antibiotics

Campylobacter species have developed resistance to existing antibiotics. The development of alternative therapies is, therefore, a necessity. This study evaluates the susceptibility of Campylobacter strains to selected natural products (NPs) and frontline antibiotics. Two C. jejuni strains (ATCC^® 33560^TM and MT947450) and two C. coli strains (ATCC^® 33559^TM and MT947451) were used. The antimicrobial potential of the NPs, including plant extracts, essential oils, and pure phytochemicals, was evaluated by broth microdilution. The growth was measured by spectrophotometry and iodonitrotetrazolium chloride. Antibiotic resistance genes (tet(O) and gyrA) were characterized at the molecular level. The minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) ranged from 25 to 1600 µg/mL. Cinnamon oil, (E)-Cinnamaldehyde, clove oil, eugenol, and baicalein had the lowest MIC and MBC values (25-100 µg/mL). MT947450 and MT947451 were sensitive to erythromycin and gentamicin but resistant to quinolones and tetracycline. Mutations in gyrA and tet(O) genes from resistant strains were confirmed by sequencing. The findings show that NPs are effective against drug-sensitive and drug-resistant Campylobacter strains. The resistance to antibiotics was confirmed at phenotypic and genotypic levels. This merits further studies to decipher the action mechanisms and synergistic activities of NPs.

Prediction of antimicrobial resistance in clinical Campylobacter jejuni isolates from whole-genome sequencing data

Campylobacter jejuni is recognised as the leading cause of bacterial gastroenteritis in industrialised countries. Although the majority of Campylobacter infections are self-limiting, antimicrobial treatment is necessary in severe cases. Therefore, the development of antimicrobial resistance (AMR) in Campylobacter is a growing public health challenge and surveillance of AMR is important for bacterial disease control. The aim of this study was to predict antimicrobial resistance in C. jejuni from whole-genome sequencing data. A total of 516 clinical C. jejuni isolates collected between 2014 and 2017 were subjected to WGS. Resistance phenotypes were determined by standard broth dilution, categorising isolates as either susceptible or resistant based on epidemiological cutoffs for six antimicrobials: ciprofloxacin, nalidixic acid, erythromycin, gentamicin, streptomycin, and tetracycline. Resistance genotypes were identified using an in-house database containing reference genes with known point mutations and the presence of resistance genes was determined using the ResFinder database and four bioinformatical methods (modified KMA, ABRicate, ARIBA, and ResFinder Batch Upload). We identified seven resistance genes including tet(O), tet(O/32/O), ant(6)-Ia, aph(2″)-If, blaOXA, aph(3')-III, and cat as well as mutations in three genes: gyrA, 23S rRNA, and rpsL. There was a high correlation between phenotypic resistance and the presence of known resistance genes and/or point mutations. A correlation above 98% was seen for all antimicrobials except streptomycin with a correlation of 92%. In conclusion, we found that WGS can predict antimicrobial resistance with a high degree of accuracy and have the potential to be a powerful tool for AMR surveillance.

Genomic Analysis Reveals the Genetic Determinants Associated With Antibiotic Resistance in the Zoonotic Pathogen Campylobacter spp. Distributed Globally

The genus Campylobacter groups 32 Gram-negative bacteria species, several being zoonotic pathogens and a major cause of human gastroenteritis worldwide. Antibiotic resistant Campylobacter is considered by the World Health Organization as a high priority pathogen for research and development of new antibiotics. Genetic elements related to antibiotic resistance in the classical C. coli and C. jejuni species, which infect humans and livestock, have been analyzed in numerous studies, mainly focused on local geographical areas. However, the presence of these resistance determinants in other Campylobacter species, as well as in C. jejuni and C. coli strains distributed globally, remains poorly studied. In this work, we analyzed the occurrence and distribution of antibiotic resistance factors in 237 Campylobacter closed genomes available in NCBI, obtained from isolates collected worldwide, in different dates, from distinct hosts and comprising 22 Campylobacter species. Our data revealed 18 distinct genetic determinants, genes or point mutations in housekeeping genes, associated with resistance to antibiotics from aminoglycosides, β-lactams, fluoroquinolones, lincosamides, macrolides, phenicols or tetracyclines classes, which are differentially distributed among the Campylobacter species tested, on chromosomes or plasmids. Three resistance determinants, the bla_OXA–493 and bla_OXA–576 genes, putatively related to β-lactams resistance, as well as the lnu(AN2) gene, putatively related to lincosamides resistance, had not been reported in Campylobacter; thus, they represent novel determinants for antibiotic resistance in Campylobacter spp., which expands the insight on the Campylobacter resistome. Interestingly, we found that some of the genetic determinants associated with antibiotic resistance are Campylobacter species-specific; e.g., the bla_OXA–493 gene and the T86V mutation in gyrA were found only in the C. lari group, whereas genes associated with aminoglycosides resistance were found only in C. jejuni and C. coli. Additional analyses revealed how are distributed the resistance and multidrug resistance Campylobacter genotypes assessed, with respect to hosts, geographical locations, and collection dates. Thus, our findings further expand the knowledge on the factors that can determine or favor the antibiotic resistance in Campylobacter species distributed globally, which can be useful to choose a suitable antibiotic treatment to control the zoonotic infections by these bacteria.

Multidrug-resistant Campylobacter jejuni, Campylobacter coli and Campylobacter lari isolated from asymptomatic school-going children in Kibera slum, Kenya

Background: The objective of this study was to determine the prevalence of thermophilic Campylobacter spp. in asymptomatic school-going children and establish the antibiotic resistance patterns of the isolates towards the drugs used to treat campylobacteriosis, including macrolides, quinolones and tetracycline. Campylobacter spp. are a leading cause of enteric illness and have only recently shown resistance to antibiotics. Methods: This study isolated Campylobacter spp., including Campylobacter coli, Campylobacter jejuni and Campylobacter lari, in stool samples from asymptomatic school-going children in one of the biggest urban slums in Kenya. The disc diffusion method using EUCAST breakpoints was used to identify antibiotic-resistant isolates, which were further tested for genes encoding for tetracycline resistance using primer-specific polymerase chain reaction. Results: In total, 580 stool samples were collected from 11 primary schools considering both gender and age. Subjecting 294 biochemically characterized Campylobacter spp. isolates to genus-specific PCR, 106 (18.27% of stool samples) isolates were confirmed Campylobacter spp. Out of the 106 isolates, 28 (4.83%) were Campylobacter coli, 44 (7.58%) were Campylobacter jejuni while 11 (1.89%) were Campylobacter lari. Campylobacter jejuni had the highest number of isolates that were multi-drug resistant, with 26 out of the 28 tested isolates being resistant to ciprofloxacin (5 mg), nalidixic acid (30 mg), tetracycline (30 mg) and erythromycin (15 mg). Conclusions: In conclusion, asymptomatic school going children in the study area were found to be carriers of multidrug resistant Campylobacter coli, Campylobacter jejuni and Campylobacter lari at 84%. A one-health approach, which considers overlaps in environment, animals and human ecosystems, is recommended in addressing multidrug resistane in Campylobacter, since animals are the main reservoirs and environmental contamination is evident.

Antimicrobial Resistance Determinants Circulating among Thermophilic Campylobacter Isolates Recovered from Broilers in Ireland Over a One-Year Period

Campylobacteriosis is the leading cause of human bacterial gastroenteritis, very often associated with poultry consumption. Thermophilic Campylobacter (Campylobacter jejuni and Campylobacter coli) isolates (n = 158) recovered from broiler neck skin and caecal contents in Ireland over a one-year period, resistant to at least one of three clinically relevant antimicrobial classes, were screened for resistance determinants. All ciprofloxacin-resistant isolates (n = 99) harboured the C257T nucleotide mutation (conferring the Thr-86-Ile substitution) in conjunction with other synonymous and nonsynonymous mutations, which may have epidemiological value. The A2075G nucleotide mutation and amino acid substitutions in L4 and L22 were detected in all erythromycin-resistant isolates (n = 5). The tetO gene was detected in 100% (n = 119) of tetracycline-resistant isolates and three of which were found to harbour the mosaic tetracycline resistance gene tetO/32/O. Two streptomycin-resistant C. jejuni isolates (isolated from the same flock) harboured ant(6)-Ib, located in a multidrug resistance genomic island, containing aminoglycoside, streptothricin (satA) and tetracycline resistance genes (truncated tetO and mosaic tetO/32/O). The ant(6)-Ie gene was identified in two streptomycin-resistant C. coli isolates. This study highlights the widespread acquisition of antimicrobial resistance determinants among chicken-associated Campylobacter isolates, through horizontal gene transfer or clonal expansion of resistant lineages. The stability of such resistance determinants is compounded by the fluidity of mobile genetic element.

Transferable Mechanisms of Quinolone Resistance from 1998 Onward

While the description of resistance to quinolones is almost as old as these antimicrobial agents themselves, transferable mechanisms of quinolone resistance (TMQR) remained absent from the scenario for more than 36 years, appearing first as sporadic events and afterward as epidemics. In 1998, the first TMQR was soundly described, that is, QnrA. The presence of QnrA was almost anecdotal for years, but in the middle of the first decade of the 21st century, there was an explosion of TMQR descriptions, which definitively changed the epidemiology of quinolone resistance. Currently, 3 different clinically relevant mechanisms of quinolone resistance are encoded within mobile elements: (i) target protection, which is mediated by 7 different families of Qnr (QnrA, QnrB, QnrC, QnrD, QnrE, QnrS, and QnrVC), which overall account for more than 100 recognized alleles; (ii) antibiotic efflux, which is mediated by 2 main transferable efflux pumps (QepA and OqxAB), which together account for more than 30 alleles, and a series of other efflux pumps (e.g., QacBIII), which at present have been sporadically described; and (iii) antibiotic modification, which is mediated by the enzymes AAC(6')Ib-cr, from which different alleles have been claimed, as well as CrpP, a newly described phosphorylase.

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.

Host cellular unfolded protein response signaling regulates Campylobacter jejuni invasion

Campylobacter jejuni is a major cause of bacterial foodborne illness in humans worldwide. Bacterial entry into a host eukaryotic cell involves the initial steps of adherence and invasion, which generally activate several cell-signaling pathways that induce the activation of innate defense systems, which leads to the release of proinflammatory cytokines and induction of apoptosis. Recent studies have reported that the unfolded protein response (UPR), a system to clear unfolded proteins from the endoplasmic reticulum (ER), also participates in the activation of cellular defense mechanisms in response to bacterial infection. However, no study has yet investigated the role of UPR in C. jejuni infection. Hence, the aim of this study was to deduce the role of UPR signaling via induction of ER stress in the process of C. jejuni infection. The results suggest that C. jejuni infection suppresses global protein translation. Also, 12 h of C. jejuni infection induced activation of the eIF2α pathway and expression of the transcription factor CHOP. Interestingly, bacterial invasion was facilitated by knockdown of UPR-associated signaling factors and treatment with the ER stress inducers, thapsigargin and tunicamycin, decreased the invasive ability of C. jejuni. An investigation into the mechanism of UPR-mediated inhibition of C. jejuni invasion showed that UPR signaling did not affect bacterial adhesion to or survival in the host cells. Further, Salmonella Enteritidis or FITC-dextran intake were not regulated by UPR signaling. These results indicated that the effect of UPR on intracellular intake was specifically found in C. jejuni infection. These findings are the first to describe the role of UPR in C. jejuni infection and revealed the participation of a new signaling pathway in C. jejuni invasion. UPR signaling is involved in defense against the early step of C. jejuni invasion and thus presents a potential therapeutic target for the treatment of C. jejuni infection.

Fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli from poultry and human samples assessed by PCR-restriction fragment length polymorphism assay

The objective of this study was to determine fluoroquinolone resistance in Campylobacter spp from poultry and human isolates. Forty-one Campylobacter jejuni isolates (30 of poultry origin and 11 of human origin) and 11 Campylobacter coli isolates (10 of human origin and 1 of poultry origin) were examined for ciprofloxacin, norfloxacin, and nalidixic acid resistance using the minimal inhibitory concentration (MIC) method. Thereafter, the isolates were analyzed by PCR-Restriction Fragment Length Polymorphism (RFLP) assay for detection of Thr-86 mutation. Finally, DNA sequencing was performed for confirmation of gyrA gene mutation. A complete correlation was observed between MICs, PCR-RFLP assay, and sequencing. The results revealed high quinolone resistance rates for C. jejuni (100%) and C. coli (100%) isolates obtained from poultry and moderate resistance for C. jejuni (9.1%) and C. coli (40%) samples of human origin. A mutation in codon 86 of the gyrA gene with a Thr-to-Ile substitution is reported to be the main cause of high resistance to quinolones. This mutation can be analyzed by PCR-RFLP assay, which has been proven to be a simple and fast method for the detection of fluoroquinolone resistance in Campylobacter spp.

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.

High Prevalence of Resistance to Fluoroquinolones and Tetracycline Campylobacter Spp. Isolated from Poultry in Poland

Campylobacter spp. is a major cause of foodborne diseases in humans, particularly when transmitted by the handling or consumption of undercooked poultry meat. Most Campylobacter infections are self-limiting, but antimicrobial treatment (e.g., fluoroquinolones and macrolides) is necessary in severe or prolonged cases. The indiscriminate use of these drugs, both in clinical medicine and animal production, has a major impact on public health. The aim of the present study was to identify Campylobacter strains, isolated from turkey and broilers, using both PCR and the matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF) methods to reveal the accuracy of identification, as well to evaluate the antimicrobial and genetic resistance of the investigated strains. MALDI-TOF and PCR methods were used to show differences, if any, in the specificity of that test. In this study, MALDI-TOF mass spectrometry gave the same results as multiplex PCR, in all cases. The highest rate of resistance (i.e., 100% of turkey and broiler strains) was detected against ciprofloxacin, whereas 58.1% of turkey and 78.6% of broiler strains were resistant to tetracycline. Multidrug-resistant isolates were not found in the study. All ciprofloxacin-resistant strains had a mutation in the gyrA gene, at the Thr-86 position. The presence of the tetO gene was found in 71% of turkey and in 100% of broiler strains. All resistant to tetracycline strains included tetO gene. Additionally, in five turkey and three broiler strains, susceptible to tetracycline, tetO gene was present. These results indicate the high prevalence of Campylobacter strains, which are phenotypically and genetically resistant to fluoroquinolones and tetracycline.

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.

High Prevalence and Predominance of the aph(2″)-If Gene Conferring Aminoglycoside Resistance in Campylobacter

Campylobacter is a major foodborne pathogen, and previous studies revealed that Campylobacter isolates from food-producing animals are increasingly resistant to gentamicin in China. The molecular epidemiology and genetic mechanisms responsible for gentamicin resistance in China have not been well understood. In this study, 607 Campylobacter isolates of chicken and swine origins collected in 2014 were analyzed, revealing that 15.6% (25/160) of the Campylobacter jejuni isolates and 79.9% (357/447) of the Campylobacter coli isolates were resistant to gentamicin. PCR detection of the gentamicin resistance genes indicated that aph(2″)-If was more prevalent than the previously identified aacA/aphD gene and has become the dominant gentamicin resistance determinant in Campylobacter Transformation and whole-genome sequencing as well as long-range PCR discovered that aph(2″)-If was located on a chromosomal segment inserted between two conserved genes, Cj0299 and panB Cloning of aph(2″)-If into gentamicin-susceptible C. jejuni NCTC 11168 confirmed its function in conferring high-level resistance to gentamicin and kanamycin. Molecular typing by pulsed-field gel electrophoresis suggested that both regional expansion of a particular clone and horizontal transmission were involved in the dissemination of the aph(2″)-If gene in Campylobacter To our knowledge, this is the first report describing the high prevalence of a chromosomally encoded aph(2″)-If gene in Campylobacter The high prevalence and predominance of this gene might be driven by the use of aminoglycoside antibiotics in food animal production in China and potentially compromise the usefulness of gentamicin as a therapeutic agent for Campylobacter-associated systemic infection.

Impact of mutations in DNA gyrase genes on quinolone resistance in Campylobacter jejuni

Amino acid substitutions providing quinolone resistance to Campyloabcter jejuni have been found in the quinolone resistance-determining region of protein DNA gyrase subunit A (GyrA), with the highest frequency at position 86 followed by position 90. In this study, wild-type and mutant recombinant DNA gyrase subunits were expressed in Escherichia coli and purified using Ni-NTA agarose column chromatography. Soluble 97 kDa GyrA and 87 kDa DNA gyrase subunit B were shown to reconstitute ATP-dependent DNA supercoiling activity. A quinolone-inhibited supercoiling assay demonstrated the roles of Thr86Ile, Thr86Ala, Thr86Lys, Asp90Asn, and Asp90Tyr amino acid substitutions in reducing sensitivity to quinolones. The marked effect of Thr86Ile on all examined quinolones suggested the advantage of this substitution in concordance with recurring isolation of quinolone-resistant C. jejuni. An analysis of the structure-activity relationship showed the importance of the substituent at position 8 in quinolones to overcome the effect of Thr86Ile. Sitafloxacin (SIT), which has a fluorinate cyclopropyl ring at R-1 and a chloride substituent at R-8, a characteristic not found in other quinolones, showed the highest inhibitory activity against all mutant C. jejuni gyrases including ciprofloxacin-resistant mutants. The results suggest SIT as a promising drug for the treatment of campylobacteriosis caused by CIP-resistant C. jejuni. Copyright © 2016 John Wiley & Sons, Ltd.

Antibiotic resistance and polymorphism in the quinolone resistance-determining region of Campylobacter spp. isolated from 1-day-old ducklings

Thirty-three isolates of Campylobacter coli and three isolates of Campylobacter jejuni were recovered from 150 1-day-old ducklings. All isolates were sensitive to chloramphenicol and amikacin, but resistant to sulfamethoxazole-trimethoprim (SXT) by the disc diffusion method. Most isolates were susceptible to tetracycline and erythromycin, but resistant to ofloxacin and ciprofloxacin. Of the 33 C. coli isolates, nine were positive for the tetracycline resistance gene tet(O), although only two of these were resistant to tetracycline in the disc diffusion test. None of the isolates possessed mutations in the quinolone resistance-determining region (QRDR) of the gyrA gene infrequently linked to FQ-resistance. The finding indicated that ducklings may be a source of antibiotic resistant Campylobacter spp. with potential poultry and public health hazard.

Prevalence and Antimicrobial Resistance of Campylobacter Isolated from Dressed Beef Carcasses and Raw Milk in Tanzania

Campylobacter species are commonly transmitted to humans through consumption of contaminated foods such as milk and meat. The aim of this study was to investigate the prevalence, antimicrobial resistance, and genetic determinants of resistance of Campylobacter isolated from raw milk and beef carcasses in Tanzania. The antimicrobial resistance genes tested included blaOXA-61 (ampicillin), aph-3-1 (aminoglycoside), tet(O) (tetracycline), and cmeB (multi-drug efflux pump). The prevalence of Campylobacter was 9.5% in beef carcasses and 13.4% in raw milk, respectively. Using multiplex-polymerase chain reaction (PCR), we identified 58.1% of the isolates as Campylobacter jejuni, 30.7% as Campylobacter coli, and 9.7% as other Campylobacter spp. One isolate (1.6%) was positive for both C. jejuni and C. coli specific PCR. Antimicrobial susceptibility testing using the disk diffusion assay and the broth microdilution method showed resistance to: ampicillin (63% and 94.1%), ciprofloxacin (9.3% and 11.8%), erythromycin (53.7% and 70.6%), gentamicin (0% and 15.7%), streptomycin (35.2% and 84.3%), and tetracycline (18.5% and 17.7%), respectively. Resistance to azithromycin (42.6%), nalidixic acid (64.8%), and chloramphenicol (13%) was determined using the disk diffusion assay only, while resistance to tylosin (90.2%) was quantified using the broth microdilution method. The blaOXA-61 (52.6% and 28.1%), cmeB (26.3% and 31.3%), tet(O) (26.3% and 31.3%), and aph-3-1 (5.3% and 3.0%) were detected in C. coli and C. jejuni. These findings highlight the extent of antimicrobial resistance in Campylobacter occurring in important foods in Tanzania. The potential risks to consumers emphasize the need for adequate control approaches, including the prudent use of antimicrobials to minimize the spread of antimicrobial-resistant Campylobacter.

Detecção de resistência às fluoroquinolonas em Campylobacter isolados de frangos de criação orgânica

Resumo Estudos têm revelado que a resistência às quinolonas em cepas de Campylobacter está relacionada à presença da mutação Treonina-86 para Isoleucina. Com o objetivo de investigar a presença dessa mutação em cepas de Campylobacter sensíveis e resistentes à ciprofloxacina e enrofloxacina, o conteúdo cecal de 80 frangos de corte de criação orgânica, abatidos sob Serviço de Inspeção Estadual (S.I.E.) do Estado do Rio de Janeiro, foram coletados e investigados para a presença de Campylobacter. A determinação da resistência à ciprofloxacina e enrofloxacina foi feita pela técnica de difusão em disco e de diluição em ágar para determinação da Concentração Inibitória Mínima (CIM). A detecção da mutação na Região Determinante de Resistencia às Quinolonas (RDRQ) no gene gyrA foi realizada através de sequenciamento. Campylobacter foi isolado a partir de 100% das amostras avaliadas, sendo 68,75% correspondente à C. jejuni e 31,25% à C. coli. No teste de difusão em disco, 100% das cepas foram resistentes à ciprofloxacina e 56,25% das cepas foram resistentes à enrofloxacina. No teste de diluição em ágar, todas as cepas foram resistentes à ciprofloxacina apresentando CIM variando de ≥ 16-64μg/mL, e resistência ou resistência intermediaria à enrofloxacina foi detectada em 42,50% (CIM ≥ 4-32μg/mL) e 38,75% (CIM = 2μg/mL) das cepas, respectivamente. A mutação Tre-86-Ile, foi observada em 100% das cepas analisadas. Além dessa mutação, foram observadas outras mutações não silenciosas (Val-73-Glu, Ser-114-Leu, Val-88-Asp, Ala-75-Asp, Ser-119-Gli, Arg-79-Lis) e mutações silenciosas (His-81-His, Ser-119-Ser, Ala-120-Ala, Fen-99-Fen, Ala-122-Ala, Gli-74-Gli, Ile-77-Ile, Ala-91-Ala, Leu-92-Leu, Val-93-Val, Ile-106-Ile, Tre-107-Tre, Gli-113-Gli, Ile-115-Ile, Gli-110-Gli). A observação de que cepas sensíveis à enrofloxacina pelos testes fenotípicos apresentavam a substituição Tre-86 para Ile sugere que outros mecanismos podem contribuir para a resistência à enrofloxacina em Campylobacter.

Characterization of Campylobacter jejuni DNA gyrase as the target of quinolones

Quinolones have long been used as the first-line treatment for Campylobacter infections. However, an increased resistance to quinolones has raised public health concerns. The development of new quinolone-based antibiotics with high activity is critical for effective, as DNA gyrase, the target of quinolones, is an essential enzyme for bacterial growth in several mechanisms. The evaluation of antibiotic activity against Campylobacter jejuni largely relies on drug susceptibility tests, which require at least 2 days to produce results. Thus, an in vitro method for studying the activity of quinolones against the C. jejuni DNA gyrase is preferred. To identify potent quinolones, we investigated the interaction of C. jejuni DNA gyrase with a number of quinolones using recombinant subunits. The combination of purified subunits exhibited DNA supercoiling activity in an ATP dependent manner. Drug concentrations that inhibit DNA supercoiling by 50% (IC50s) of 10 different quinolones were estimated to range from 0.4 (sitafloxacin) to >100 μg/mL (nalidixic acid). Sitafloxacin showed the highest inhibitory activity, and the analysis of the quinolone structure-activity relationship demonstrated that a fluorine atom at R-6 might play the important role in the inhibitory activity against C. jejuni gyrase. Measured quinolone IC50s correlated well with minimum inhibitory concentrations (R = 0.9943). These suggest that the in vitro supercoiling inhibition assay on purified recombinant C. jejuni DNA gyrase is a useful and predictive technique to monitor the antibacterial potency of quinolones. And furthermore, these data suggested that sitafloxacin might be a good candidate for clinical trials on campylobacteriosis.

Molecular mechanisms of quinolone, macrolide, and tetracycline resistance among Campylobacter isolates from initial stages of broiler production

The aim of this study was to investigate the resistance mechanisms of quinolones, macrolides and tetracycline in campylobacter isolates from grandparent and parent broiler breeders in Spain. Twenty-six isolates were investigated for quinolone resistance, three isolates for macrolide resistance and 39 for tetracycline resistance. All of the quinolone-resistant isolates possessed the mutation Thr86Ile in the quinolone resistance-determining region of gyrA and one isolate possessed the mutation Pro104Ser. Only one Campylobacter coli population (defined by restriction fragment length polymorphism-polymerase chain reaction of flaA and pulsed field gel electrophoresis) was resistant to erythromycin, and the mutation A2075G (23S rDNA) was responsible for macrolide resistance. The tetO gene was found in all of the tetracycline-resistant isolates. Twenty-two out of the 39 isolates investigated by Southern blot possessed chromosomic location of tetO and 17 were located on plasmids. Most of the plasmids with tetO were of around 60 kb and conjugation was demonstrated in a selection of them. In conclusion, we showed that Thr86Ile is highly prevalent in quinolone-resistant isolates as well as mutation A2075G in macrolide-resistant isolates of poultry origin. More variability was found for tetO. The possibility of horizontal transmission of tetO among campylobacter isolates is also an issue of concern in public health.

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.

Fitness cost of fluoroquinolone resistance in Campylobacter coli and Campylobacter jejuni

In this study, the fitness cost of fluoroquinolone resistance was evaluated in vitro, on food matrices, and in vivo, using Campylobacter coli and Campylobacter jejuni in vitro selected mutants. In vitro, the growth rate of the susceptible (wild type) and resistant (mutant) strains did not differ when cultured separately. However, by conducting sequential passages of mixed cultures, the ratio of the resistant mutant to the susceptible strain decreased for C. coli but not for C. jejuni. When the wild type and the mutant were co-inoculated on food matrices, mutants were no longer detectable 3 to 5 days after artificial contamination, but the wild-type strains remained detectable for over 13 days. In mono-inoculated animals, no difference was observed between wild-type and mutant fecal titers. When co-inoculated into chickens, the susceptible strain outcompeted the resistant mutant for C. coli and for C. jejuni. However, for C. coli, if the resistant strain was already present in animals, it could persist at high titers in the digestive tract even in the presence of the wild-type strain. Together, these findings suggest that, depending on strain and study conditions, fluoroquinolone resistance can impose a fitness cost on Campylobacter.

Prevalence and antimicrobial resistance of Campylobacter isolates in broilers from China

The prevalence and antimicrobial resistance of Campylobacter spp. in broiler chickens were determined in Shandong Province, China. In total, 275 Campylobacter isolates were obtained from 767 broiler cecal samples, including 208 Campylobacter jejuni, 53 Campylobacter coli, and 14 unidentified Campylobacter isolates. Minimal inhibitory concentrations of 11 antimicrobial agents were determined using the agar dilution method recommended by CLSI. More than 98% of the tested Campylobacter isolates were resistant to quinolones (nalidixic acid, ciprofloxacin and enrofloxacin) and tetracyclines (tetracycline and doxycycline). The C. jejuni isolates also exhibited a high rate of resistance to phenicol antibiotics and a moderate rate of resistance to macrolides and gentamicin. On the contrary, the C. coli isolates showed a high-level resistance to macrolides and gentamicin and little resistance to phenicol antibiotics. The vast majority of the Campylobacter isolates were classified as multidrug resistant. These findings reveal a broad extent of antimicrobial resistance in Campylobacter isolates from poultry in China and underline the need for prudent use of antibiotics in poultry production to minimize the spread of antibiotic resistant Campylobacter.

Fitness cost of macrolide resistance in Campylobacter jejuni

Whether the acquisition of macrolide resistance imposes a biological burden on Campylobacter jejuni is unknown. In this study, C. jejuni macrolide-resistant mutants and the susceptible parent were compared by non-competitive growth, pair-wise competitive growth, and the ability to tolerate a chilling process commonly used in poultry processing plants. Overall, mutants demonstrated slower growth rates (average doubling time of 136 min vs. 112 min for the parent strain) and a lower survival ratio in the competitive growth experiment. However, mutants were equally competent in tolerating the chilling treatment. Our findings indicate that macrolide resistance incurs an obvious fitness cost in C. jejuni. However, the ability of macrolide-resistant C. jejuni mutants to tolerate the chilling process may render them equally capable of persisting in poultry products.

Multiplex strategy for multilocus sequence typing, fla typing, and genetic determination of antimicrobial resistance of Campylobacter jejuni and Campylobacter coli isolates collected in Switzerland

We present an optimized multilocus sequence typing (MLST) scheme with universal primer sets for amplifying and sequencing the seven target genes of Campylobacter jejuni and Campylobacter coli. Typing was expanded by sequence determination of the genes flaA and flaB using optimized primer sets. This approach is compatible with the MLST and flaA schemes used in the PubMLST database and results in an additional typing method using the flaB gene sequence. An identification module based on the 16S rRNA and rpoB genes was included, as well as the genetic determination of macrolide and quinolone resistances based on mutations in the 23S rRNA and gyrA genes. Experimental procedures were simplified by multiplex PCR of the 13 target genes. This comprehensive approach was evaluated with C. jejuni and C. coli isolates collected in Switzerland. MLST of 329 strains resulted in 72 sequence types (STs) among the 186 C. jejuni strains and 39 STs for the 143 C. coli isolates. Fourteen (19%) of the C. jejuni and 20 (51%) of the C. coli STs had not been found previously. In total, 35% of the C. coli strains collected in Switzerland contained mutations conferring antibiotic resistance only to quinolone, 15% contained mutations conferring resistance only to macrolides, and 6% contained mutations conferring resistance to both classes of antibiotics. In C. jejuni, these values were 31% and 0% for quinolone and macrolide resistance, respectively. The rpoB sequence allowed phylogenetic differentiation between C. coli and C. jejuni, which was not possible by 16S rRNA gene analysis. An online Integrated Database Network System (SmartGene, Zug, Switzerland)-based platform for MLST data analysis specific to Campylobacter was implemented. This Web-based platform allowed automated allele and ST designation, as well as epidemiological analysis of data, thus streamlining and facilitating the analysis workflow. Data networking facilitates the exchange of information between collaborating centers. The described approach simplifies and improves the genotyping of Campylobacter, allowing cost- and time-efficient routine monitoring.

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.

Effects of low-level ciprofloxacin challenge in the in vitro development of ciprofloxacin resistance in Campylobacter jejuni

The effects on MIC values and the selection of different base substitutions in the quinolone resistance determining region (QRDR) of gyrA were studied on initially ciprofloxacin-susceptible Campylobacter jejuni strains by challenging them to 0.125 mg/L of ciprofloxacin. This ciprofloxacin challenge selected variants with ciprofloxacin MIC levels up to 32 mg/L. Repeated experiments under identical conditions resulted in different responses in MIC levels and alterations in the QRDR of gyrA. A characteristic outcome to ciprofloxacin challenges was the appearance of double peaks in the sequencing chromatograms of QRDR. This finding suggested the coexistence of subpopulations possessing Thr86 --> Ile and/or Asp90 --> Asn mutations alongside the unmutated parent population. In some cases, bacterial variants expressing ciprofloxacin-resistant phenotypes possessed no mutations in their QRDR. These variants were prone to regain susceptibility to ciprofloxacin rapidly after the removal of the selection pressure, whereas the QRDR-mutated variants persisted over several subcultivations in a medium without ciprofloxacin. In conclusion, a low ciprofloxacin concentration of 0.125 mg/L selects a variety of QRDR mutations and also a QRDR-independent resistance mechanism, which may coexist with each other in a C. jejuni population. Persistent ciprofloxacin challenge selects Thr86 --> Ile and/or Asp90 --> Asn mutants.

Key role of Mfd in the development of fluoroquinolone resistance in Campylobacter jejuni

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.

Quinolone resistance in the food chain

Antimicrobials are used in pet animals and in animal husbandry for prophylactic and therapeutic reasons and also as growth promoters, causing selective pressure on bacteria of animal origin. The impact of quinolones or quinolone-resistant bacteria on the management of human infections may be associated with three different scenarios. (i) Quinolone-resistant zoonotic bacterial pathogens are selected and food is contaminated during slaughter and/or preparation. (ii) Quinolone-resistant bacteria non-pathogenic to humans are selected in the animal. When the contaminated food is ingested, the bacteria may transfer resistance determinants to other bacteria in the human gut (commensal and potential pathogens). And (iii) quinolones remain in residues of food products, which may allow the selection of antibiotic-resistant bacteria after the food is consumed. In this review, we analyse the abovementioned aspects, emphasising the molecular basis of quinolone resistance in Escherichia coli, Salmonella spp. and Campylobacter spp.

Comparison of antimicrobial resistance of Campylobacter jejuni and Campylobacter coli isolated from humans and chicken carcasses in Poland

Campylobacter-associated gastroenteritis remains an important cause of morbidity worldwide, and some evidence suggests that poultry is an important source of this foodborne infection in humans. This study was conducted to analyze the prevalence and genetic background of resistance of 149 Campylobacter jejuni and 54 Campylobacter coli strains isolated from broiler chicken carcasses and from stool samples of infected children in Poland from 2003 through 2005. Nearly all isolates were susceptible to macrolides and aminoglycosides. The highest resistance in both human and chicken strains was observed for ciprofloxacin (more than 40%), followed by ampicillin (13 to 21%), and tetracycline (8 to 29%). Resistance to ampicillin and tetracycline rose significantly between 2003 and 2005. Slight differences in resistance between human and chicken isolates indicate that although chicken meat is not the only source of Campylobacter infection in our population, it can be involved in the transmission of drug-resistant Campylobacter strains to humans.

Prevalence and antimicrobial resistance of Campylobacter in US dairy cattle

AIMS

To obtain an overview of the prevalence and antimicrobial resistance of Campylobacter in faeces of US dairy cows in 2002.

METHODS AND RESULTS

Faeces from 1435 cows, representing 96 dairy operations in 21 US states, were collected for the culture of Campylobacter. A total of 735 Campylobacter strains were isolated (51.2% positive samples) with 94 operations positive (97.9%) for Campylobacter. From this collection, 532 isolates (473 Campylobacter jejuni and 59 Campylobacter coli) were randomly selected for susceptibility testing to eight antimicrobials: azithromycin, chloramphenicol, ciprofloxacin, clindamycin, erythromycin, gentamicin, nalidixic acid and tetracycline. The C. jejuni isolates exhibited resistance to tetracycline (47.4%), nalidixic acid (4.0%) and ciprofloxacin (2.5%), while the C. coli strains exhibited some resistance to all antimicrobials except chloramphenicol and ciprofloxacin. Only 3.6% of the C. jejuni isolates were resistant to two or more antimicrobials but 20.3% of the C. coli strains were multiresistant.

CONCLUSIONS

On most operations, at least one cow was positive for Campylobacter and more than half of the cows sampled were shedding Campylobacter. The C. coli isolates had significantly higher levels of resistance to macrolides and to tetracycline compared with the C. jejuni strains, but were susceptible to ciprofloxacin.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated a high prevalence of Campylobacter on US dairy operations; however, US dairy cattle have not been recognized as a major source of human infection compared with poultry. Campylobacter coli appears to develop antimicrobial resistance more readily than C. jejuni from the same environment.

Analysis of topoisomerase mutations in fluoroquinolone-resistant and -susceptible Campylobacter jejuni strains isolated in Senegal

In this study, topoisomerase mutations in ciprofloxacin-resistant and -susceptible Campylobacter jejuni were analysed by DNA sequencing. In certain ciprofloxacin-resistant C. jejuni, the mechanism of resistance was complex. The Thr86-Ala substitution in the GyrA protein appears to play a role in increasing the minimum inhibitory concentration of nalidixic acid only. In addition, isolates with this amino acid change and those resistant to quinolones but lacking a mutation in the GyrA quinolone resistance-determining region could be derived from two different clones. Based on gyrA and gyrB polymorphisms, C. jejuni isolates from the Dakar region of Senegal appeared to be less diverse than those from other countries. Moreover, C. jejuni isolates in Senegal appeared to differ from European isolates by lack of a silent mutation at codon 120 of the gyrA gene.

Campylobacter coli isolates derived from chickens in Senegal: Diversity, genetic exchange with Campylobacter jejuni and quinolone resistance

We used the multilocus sequence typing (MLST) method to study the genetic diversity of Campylobacter coli isolated from chickens in Senegal, and to check the presence of genetic exchange with Campylobacter jejuni. In addition, we assessed the resistance of the isolates to ciprofloxacin and nalidixic acid, and their gyrA sequences. MLST revealed a low level of diversity and the absence of lineages among C. coli isolates. In addition, an exchange of alleles with C. jejuni was found. Twenty percent of the ciprofloxacin-resistant isolates lacked mutations within the quinolone resistance-determining region (QRDR) of GyrA. There was no link between quinolone resistance and sequence type (ST).

Genetic characterization and antibiotic resistance of Campylobacter spp. isolated from poultry and humans in Senegal

AIMS

The main objectives of this study were to investigate the diversity of Campylobacter genotypes circulating in Senegal and to determine the frequency of antibiotic resistance.

METHODS AND RESULTS

Strains of Campylobacter jejuni isolated from poultry (n = 99) and from patients (n = 10) and Campylobacter coli isolated from poultry (n = 72) were subtyped by pulsed-field gel electrophoresis (PFGE). The pulsotypes obtained after digestion by SmaI and KpnI revealed a significant genetic diversity in both species, but without any predominant pulsotypes. However, farm-specific clones were identified in the majority of poultry houses (76.5%). Human and poultry isolates of C. jejuni had common PFGE patterns. High quinolone-resistance rates were observed for C. jejuni (43.4%) and C. coli (48.6%) isolates obtained from poultry.

CONCLUSIONS

The results showed a genetic diversity of Campylobacter between farms indicating multiple sources of infection; but specific clones had the ability to colonize the broiler farms. The antimicrobial resistance patterns were not related to any specific PFGE pattern suggesting that resistance was due to the selective pressure of antibiotic usage. Campylobacter with similar genotypes were circulating in both human and poultry.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is important for the understanding of the epidemiology of Campylobacter in broiler farms in Senegal. It also emphasizes the need for a more stringent policy in the use of antimicrobial agents in food animals.

Two distinct mutations in gyrA lead to ciprofloxacin and nalidixic acid resistance in Campylobacter coli and Campylobacter jejuni isolated from chickens and beef cattle

AIMS

The aim of this study was to identify point mutations in the gyrA quinolone resistance determining region (QRDR) of Campylobacter coli (n = 27) and Campylobacter jejuni (n = 26) that confer nalidixic acid (NAL) resistance without conferring resistance to ciprofloxacin (CIP).

METHODS AND RESULTS

Point mutations in the QRDR of gyrA from C. coli and C. jejuni isolates were identified by direct sequencing. All isolates (n = 14) with minimum inhibitory concentrations (MICs) >or=4 microg ml(-1) for CIP and >or=32 microg ml(-1) for NAL possessed a missense mutation leading to substitution of Ile for Thr at codon 86. Three isolates with a missense mutation leading to a Thr86Ala substitution had MICs <4 mug ml(-1) for CIP and >or=32 microg ml(-1) for NAL.

CONCLUSIONS

These data confirm previous findings that Thr86Ile mutations confer resistance to both CIP and NAL. However, resistance to NAL alone was conferred by a single Thr86Ala mutation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Resistance to NAL alone arises independently from CIP resistance. In addition, the role of other previously described point mutations in quinolone resistance is discussed.

Genetic diversity and quinolone resistance in Campylobacter jejuni isolates from poultry in Senegal

We used the multilocus sequence typing (MLST) method to evaluate the genetic diversity of 46 Campylobacter jejuni isolates from chickens and to determine the link between quinolone resistance and sequence type (ST). There were a total of 16 ST genotypes, and the majority of them belonged to seven clonal complexes previously identified by using isolates from human disease. The ST-353 complex was the most common complex, whereas the ST-21, ST-42, ST-52, and ST-257 complexes were less well represented. The resistance phenotype varied for each ST, and the Thr-86-Ile substitution in the GyrA protein was the predominant mechanism of resistance to quinolone. Nine of the 14 isolates having the Thr-86-Ile substitution belonged to the ST-353 complex. MLST showed that the emergence of quinolone resistance is not related to the diffusion of a unique clone and that there is no link between ST genotype and quinolone resistance. Based on silent mutations, different variants of the gyrA gene were shown to exist for the same ST. These data provide useful information for understanding the epidemiology of C. jejuni in Senegal.

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.

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.

Genetic diversity in fluoroquinolone and macrolide-resistant Campylobacter coli from pigs

The genetic diversity of 115 Campylobacter coli strains, isolated from pigs of 59 geographical distant farms in Switzerland, were characterized on the basis of their DNA fingerprints and resistance to macrolides and fluoroquinolones. Sequence analysis showed that the macrolide-resistant isolates had a point mutation in the 23S ribosomal RNA (rRNA) genes (A2075G) and that the fluoroquinolone-resistant isolates had a point mutation in the gyrase gene gyrA (C257T). One fluoroquinolone-resistant strain had an additional transition mutation in the gyrB gene (A1471C). The flaA restriction fragment length polymorphism (RFLP) genotyping revealed that 57% of the isolates were genetically different. Point mutations in the 23S rRNA and gyrA genes could be found in both genetically distant and genetically related isolates. Additionally, isolates with and without point mutations were found within individual farms and on different farms. This study showed that the ciprofloxacin and erythromycin-resistant C. coli population present on the pig farms is not issued from a common ancestral clone, but individual Campylobacter strains have most likely mutated independently to acquire resistances under the selective pressure of an antibiotic.

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.