23S rRNA mutation A2074C conferring high-level macrolide resistance and fitness cost in Campylobacter jejuni

Genomic islands and their role in fitness traits of two key sepsis-causing bacterial pathogens

To survive and establish a niche for themselves, bacteria constantly evolve. Toward that, they not only insert point mutations and promote illegitimate recombinations within their genomes but also insert pieces of 'foreign' deoxyribonucleic acid, which are commonly referred to as 'genomic islands' (GEIs). The GEIs come in several forms, structures and types, often providing a fitness advantage to the harboring bacterium. In pathogenic bacteria, some GEIs may enhance virulence, thus altering disease burden, morbidity and mortality. Hence, delineating (i) the GEIs framework, (ii) their encoded functions, (iii) the triggers that help them move, (iv) the mechanisms they exploit to move among bacteria and (v) identification of their natural reservoirs will aid in superior tackling of several bacterial diseases, including sepsis. Given the vast array of comparative genomics data, in this short review, we provide an overview of the GEIs, their types and the compositions therein, especially highlighting GEIs harbored by two important pathogens, viz. Acinetobacter baumannii and Klebsiella pneumoniae, which prominently trigger sepsis in low- and middle-income countries. Our efforts help shed some light on the challenges these pathogens pose when equipped with GEIs. We hope that this review will provoke intense research into understanding GEIs, the cues that drive their mobility across bacteria and the ways and means to prevent their transfer, especially across pathogenic bacteria.

Prevalence of ciprofloxacin resistance and associated genetic determinants differed among Campylobacter isolated from human and poultry meat sources in Pennsylvania

Poultry is the primary source of Campylobacter infections and severe campylobacteriosis cases are treated with macrolides and fluoroquinolones. However, these drugs are less effective against antimicrobial-resistant strains. Here, we investigated the prevalence of phenotypic antimicrobial resistance and associated resistance genetic determinants in Campylobacter isolates collected from human clinical (N = 123) and meat (N = 80) sources in Pennsylvania in 2017 and 2018. Our goal was to assess potential differences in the prevalence of antimicrobial resistance in Campylobacter isolated from human and poultry meat sources in Pennsylvania and to assess the accuracy of predicting antimicrobial resistance phenotypes based on resistance genotypes. We whole genome sequenced isolates and identified genetic resistance determinants using the National Antimicrobial Resistance Monitoring System Campylobacter AMR workflow v2.0 in GalaxyTrakr. Phenotypic antimicrobial susceptibility testing was carried out using the E-Test and Sensititre CAMPYCMV methods for human clinical and poultry meat isolates, respectively, and the results were interpreted using the EUCAST epidemiological cutoff values. The 193 isolates were represented by 85 MLST sequence types and 23 clonal complexes, suggesting high genetic diversity. Resistance to erythromycin was confirmed in 6% human and 4% meat isolates. Prevalence of ciprofloxacin resistance was significantly higher in human isolates as compared to meat isolates. A good concordance was observed between phenotypic resistance and the presence of the corresponding known resistance genetic determinants.

Growth kinetics and fitness of fluoroquinolone resistant and susceptible Campylobacter jejuni strains of cattle origin

Human enterocolitis is frequently caused by the Gram-negative microaerobic bacterium Campylobacter jejuni. Macrolides (e.g., erythromycin) and fluoroquinolones (FQs) (e.g., ciprofloxacin) are the preferred antibiotics for the treatment of human campylobacteriosis. Rapid emergence of FQ-resistant (FQ-R) Campylobacter during treatment with FQ antimicrobials is well known to occur in poultry. Cattle is also an important reservoir of Campylobacter for humans, and FQ-R Campylobacter from cattle has become highly prevalent in recent years. Even though the selection pressure may have contributed to the expansion of FQ-R Campylobacter, the actual impact of this factor appears to be rather low. In this study, we examined the hypothesis that the fitness of FQ-R Campylobacter may have also played a role in the rise seen in FQ-R Campylobacter isolates by employing a series of in vitro experiments in MH broth and bovine fecal extract. First, it was shown that FQ-R and FQ-susceptible (FQ-S) C. jejuni strains of cattle origin had comparable growth rates when individually cultured in both MH broth and the fecal extract with no antibiotic present. Interestingly, FQ-R strains had small but statistically significant increases over FQ-S strains in growth in competition experiments performed in mixed cultures with no antibiotic present. Lastly, it was observed that FQ-S C. jejuni strains developed resistance to ciprofloxacin more readily at high initial bacterial cell density (10⁷ CFU/mL) and when exposed to low levels of the antibiotic (2-4 μg/mL) compared with that at a low level of initial bacterial cell density (10⁵ CFU/mL) and exposure to a high level of ciprofloxacin (20 μg/mL) in both MH broth and the fecal extract. Altogether, these findings indicate that even though FQ-R C. jejuni of cattle origin may have a slightly higher fitness advantage over the FQ-S population, the emergence of FQ-R mutants from susceptible strains is primarily dictated by the bacterial cell density and the antibiotic concentration exposed under in vitro condition. These observation may also provide plausible explanations for the high prevalence of FQ-R C. jejuni in cattle production due to its overall fit nature in the absence of antibiotic selection pressure and for the paucity of development of FQ-R C. jejuni in the cattle intestine in response to FQ-treatment, as observed in our recent studies.

Emergence and Mechanism of Resistance of Tulathromycin Against Mycoplasma hyopneumoniae in a PK/PD Model and the Fitness Costs of 23S rRNA Mutants

Macrolides are widely used in diseases caused by Mycoplasma spp. The new semi-synthetic macrolide antibiotic tulathromycin is currently in wide use for the treatment of respiratory diseases of livestock. The objective of this study was to evaluate the antibacterial effect of tulathromycin against Mycoplasma hyopneumoniae using an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model to reveal mechanisms of antibiotic resistance and to evaluate the fitness of drug-resistant strains. In this study, high performance liquid chromatography-tandem mass spectrometry was used to determine drug concentrations for the in vitro model after dosing. The peak concentrations were in the range 0.3125–20 μg/mL (1 × MIC-64 × MIC). The ratio of the area under the concentration-time curve (AUC) over 72 h divided by the MIC (AUC_72h/MIC) had the highest correlation with the antibacterial effect of tulathromycin against M. hyopneumoniae. Tulathromycin also showed concentration-dependent antimicrobial effects and promoted the emergence of drug-resistant bacteria after being cultured for 168 h and most were mutations in 23S rRNA at site A2058G (E.coli numbering) and only a single isolate was an A2058T (E.coli numbering) mutant. In the presence of reserpine, we determined the MIC of tulathromycin, tilmicosin, tiamulin and tylosin against these drug-resistant bacteria and the strains with efflux pump mechanisms were found among the strains resistant to tilmicosin. Gene expression analysis indicated that the ABC and MATE transporter efflux pump genes RS01935, RS02670, RS01115, RS01970, RS02395 and RS03540 (MATE family efflux transporter) were up-regulated in the three strains (P < 0.05 or P < 0.01). These investigations provide guidance for clinical administration of tulathromycin and elucidate the mechanism and fitness cost of drug resistance in M. hyopneumoniae.

Antimicrobial Resistance, FlaA Sequencing, and Phylogenetic Analysis of Campylobacter Isolates from Broiler Chicken Flocks in Greece

Human campylobacteriosis caused by thermophilic Campylobacter species is the most commonly reported foodborne zoonosis. Consumption of contaminated poultry meat is regarded as the main source of human infection. This study was undertaken to determine the antimicrobial susceptibility and the molecular epidemiology of 205 Campylobacter isolates derived from Greek flocks slaughtered in three different slaughterhouses over a 14-month period. A total of 98.5% of the isolates were resistant to at least one antimicrobial agent. In terms of multidrug resistance, 11.7% of isolates were resistant to three or more groups of antimicrobials. Extremely high resistance to fluoroquinolones (89%), very high resistance to tetracycline (69%), and low resistance to macrolides (7%) were detected. FlaA sequencing was performed for the subtyping of 64 C. jejuni and 58 C. coli isolates. No prevalence of a specific flaA type was observed, indicating the genetic diversity of the isolates, while some flaA types were found to share similar antimicrobial resistance patterns. Phylogenetic trees were constructed using the neighbor-joining method. Seven clusters of the C. jejuni phylogenetic tree and three clusters of the C. coli tree were considered significant with bootstrap values >75%. Some isolates clustered together were originated from the same or adjacent farms, indicating transmission via personnel or shared equipment. These results are important and help further the understanding of the molecular epidemiology and antimicrobial resistance of Campylobacter spp. derived from poultry in Greece.

Modeling the Effect of Tylosin Phosphate on Macrolide-Resistant Enterococci in Feedlots and Reducing Resistance Transmission

Tylosin phosphate (TYL) is administered to more than 50% of U.S. beef cattle to reduce the incidence of liver abscesses but may increase the risk of macrolide-lincosamide-streptogramin-resistant bacteria disseminating from the feedlot. Limited evidence has been collected to understand how TYL affects the proportion of resistant bacteria in cattle or the feedlot environment. We created a mathematical model to investigate the effects of TYL administration on Enterococcus dynamics and examined preharvest strategies to mitigate the impact of TYL administration on resistance. The model simulated the physiological pharmacokinetics of orally administered TYL and estimated the pharmacodynamic effects of TYL on populations of resistant and susceptible Enterococcus within the cattle large intestine, feedlot pen, water trough, and feed bunk. The model parameters' population distributions were based on the available literature; 1000 Monte Carlo simulations were performed to estimate the likely distribution of outcomes. At the end of the simulated treatment period, the median estimated proportion of macrolide-resistant enterococci was only 1 percentage point higher within treated cattle compared with cattle not fed TYL, in part because the TYL concentrations in the large intestine were substantially lower than the enterococci minimum inhibitory concentrations. However, 25% of the simulated cattle had a >10 percentage point increase in the proportion of resistant enterococci associated with TYL administration, termed the TYL effect. The model predicts withdrawing TYL treatment and moving cattle to an antimicrobial-free terminal pen with a low prevalence of resistant environmental enterococci for as few as 6 days could reduce the TYL effect by up to 14 percentage points. Additional investigation of the importance of this subset of cattle to the overall risk of resistance transmission from feedlots will aid in the interpretation and implementation of resistance mitigation strategies.

Core Genome Multilocus Sequence Typing for Food Animal Source Attribution of Human Campylobacter jejuni Infections

Campylobacter jejuni is a major foodborne pathogen and common cause of bacterial enteritis worldwide. A total of 622 C. jejuni isolates recovered from food animals and retail meats in the United States through the National Antimicrobial Resistance Monitoring System between 2013 and 2017 were sequenced using an Illumina MiSeq. Sequences were combined with WGS data of 222 human isolates downloaded from NCBI and analyzed by core genome multilocus sequence typing (cgMLST) and traditional MLST. cgMLST allelic difference (AD) thresholds of 0, 5, 10, 25, 50, 100 and 200 identified 828, 734, 652, 543, 422, 298 and 197 cgMLST types among the 844 isolates, respectively, and traditional MLST identified 174 ST. The cgMLST scheme allowing an AD of 200 (cgMLST₂₀₀) revealed strong correlation with MLST. cgMLST₂₀₀ showed 40.5% retail chicken isolates, 56.5% swine, 77.4% dairy cattle and 78.9% beef cattle isolates shared cgMLST sequence type with human isolates. All ST-8 had the same cgMLST₂₀₀ type (cgMLST₂₀₀-12) and 74.3% of ST-8 and 75% cgMLST₂₀₀-12 were confirmed as sheep abortion virulence clones by PorA analysis. Twenty-nine acquired resistance genes, including 21 alleles of bla_OXA, tetO, aph(3′)-IIIa, ant(6)-Ia, aadE, aad9, aph(2′)-Ig, aph(2′)-Ih, sat4 plus mutations in gyrA, 23SrRNA and L22 were identified. Resistance genotypes were strongly linked with cgMLST₂₀₀ type for certain groups including 12/12 cgMLST₂₀₀-510 with the A103V substitution in L22 and 10/11 cgMLST₂₀₀-608 with the T86I GyrA substitution associated with macrolide and quinolone resistance, respectively. In summary, the cgMLST₂₀₀ threshold scheme combined with resistance genotype information could provide an excellent subtyping scheme for source attribution of human C. jejuni infections.

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.

Antimicrobial resistance of Campylobacter isolates recovered from broilers in the Republic of Ireland in 2017 and 2018: an update

1. Campylobacteriosis is the leading cause of human bacterial gastroenteritis. Broilers are considered the most important source of human Campylobacter infection. In the 2008 European baseline survey Ireland had a 98% prevalence of campylobacter-contaminated broiler carcases. 2. Randomly-selected Campylobacter isolates (296 C. jejuni, 54 C. coli) recovered in 2017 and 2018, from Irish broiler neck skin and caeca were tested for their resistance to tetracycline, erythromycin, gentamicin, ciprofloxacin, nalidixic acid and streptomycin. 3. Overall, 45% of the Campylobacter spp. isolates tested were resistant to at least one antimicrobial. Tetracycline resistance (38%) was most prevalent in C. jejuni, followed by ciprofloxacin and nalidixic acid resistance (29%). In C. coli, resistance to ciprofloxacin and nalidixic acid (26%) was most prevalent followed by resistance to tetracycline (13%). Gentamicin resistance was undetected and resistance to streptomycin was low for C. jejuni (1%) and C. coli (4%). All C. jejuni isolates examined were erythromycin-sensitive, while 9% of C. coli isolates were erythromycin-resistant. Three multidrug-resistant C. coli isolates were recovered. 4. While antibiotic resistance rates were somewhat similar to figures reported nationally over the past 20 years, the prevalence of tetracycline resistance in C. jejuni has increased. The persistence of substantial ciprofloxacin resistance in the Irish broiler population was noteworthy, despite fluoroquinolones having been banned for growth promotion in Europe since 2006.

Neisseria gonorrhoeae 23S rRNA A2059G mutation is the only determinant necessary for high-level azithromycin resistance and improves in vivo biological fitness

Objectives

The global emergence of Neisseria gonorrhoeae isolates displaying high-level azithromycin resistance is a major concern for the currently recommended azithromycin/ceftriaxone dual therapy. N. gonorrhoeae high-level azithromycin resistance has been associated with an A2059G mutation in 23S rRNA. Here we investigated the specific contribution of this 23S rRNA A2059G mutation to high-level azithromycin resistance and its impact on biological fitness.

Methods

A2059G/G2059A alleles were specifically cloned into all four genomic copies of 23S rDNA of an azithromycin-susceptible isolate and a high-level azithromycin-resistant isolate. WT and mutant strains were subsequently investigated for azithromycin susceptibility using the agar dilution method. In addition, their biological fitness was studied by comparative liquid growth in the presence of hydrophobic and amphipathic compounds, by competition assays in a mouse vaginal tract infection model and by competition assays for invasion and intracellular survival.

Results

Azithromycin susceptibility analyses showed that the 23S rRNA A2059G mutation is the only genetic determinant required for N. gonorrhoeae to display the high-level azithromycin resistance phenotype. Further analysis of biological fitness showed that strains containing 2059G outcompeted isogenic strains containing 2059A for colonization in the mouse vaginal tract infection model and for invasion of HeLa cervical epithelial cells. Furthermore, the A2059G mutation enhanced growth in the presence of lithocholic acid or Triton X-100.

Conclusions

Our findings that the 23S rRNA A2059G mutation is sufficient for high-level azithromycin resistance and that this mutation generally enhanced the biological fitness of N. gonorrhoeae have important implications for the currently recommended treatment policies and antimicrobial stewardship programmes.

Point Deletion or Insertion in CmeR-Box, A2075G Substitution in 23S rRNA, and Presence of erm(B) Are Key Factors of Erythromycin Resistance in Campylobacter jejuni and Campylobacter coli Isolated From Central China

Campylobacter jejuni and Campylobacter coli are major food-borne pathogens that cause bacterial gastroenteritis in humans, and poultry is considered as their most important reservoir. Macrolides, such as erythromycin, are the first-line choice for treatment of campylobacteriosis. In this study, of the 143 Campylobacter isolates recovered from poultry in central China during 2015–2017, 25.2% were erythromycin resistant. A2075G substitution in 23S ribosomal RNA (rRNA) and ribosomal methylase encoded by erm(B) were found in 4.2 and 4.9% isolates, respectively, and correlated with erythromycin resistance. The polymorphisms of CmeR-Box were also analyzed in our isolates. Among them, 9.1% isolates harbored a point deletion or insertion within the CmeR-Box, and we first showed that point deletion or insertion, but not substitution, in CmeR-Box led to high expression of cmeABC, which was significantly associated with erythromycin resistance (p < 0.05). These results suggest that point deletion or insertion in CmeR-Box, A2075G substitution in 23S rRNA, and presence of erm(B) are three main factors to erythromycin resistance in C. jejuni and C. coli.

Genotypic diversity, antimicrobial resistance and biofilm-forming abilities of Campylobacter isolated from chicken in Central China

Background

Campylobacter is considered to be the leading cause of human bacterial gastroenteritis, of which poultry is the main reservoir. Campylobacter contaminated chicken products are a major cause of human Campylobacter infection. In this study, the prevalence of Campylobacter in chicken in central China was investigated, and the genotypic diversity, antimicrobial resistance and biofilm of these isolates were characterized.

Results

A total of 206 Campylobacter isolates, including 166 C. jejuni and 40 C. coli, were isolated from chicken farms and live poultry markets in central China. Multilocus sequence typing and phylogenetic analysis showed that the Campylobacter isolates had diverse genetic backgrounds, which covered most of the dominant clone complexes (CCs) reported throughout China. The most prevalent CCs were CC-464, CC-1150, CC-353, and CC-828. All the isolates showed resistance to norfloxacin, ciprofloxacin and Cefazolin, and a prevalent resistance to fluoroquinolones, β-lactams and tetracyclines was also observed. Among all the isolates, 133 strains showed the ability to form biofilm, thereinto, the isolates in two genetic branches, mainly including CC-21, CC-48, CC-677 and CC-45, showed a significantly lower ability to form biofilm than other genetic branches (p < 0.05). However, in general, the ability to form biofilm varied among different genetic branches, suggesting a complex genetic background to biofilm formation, but not only the genetic lineages. Compared with the strains unable to form biofilm, biofilm-producing strains possessed a significantly higher resistance to ampicillin, neomycin, sulfamethoxazole, amikacin, clindamycin and erythromycin (p < 0.05).

Conclusions

To the best of our knowledge, this is the first report on the relationship of the genotypic diversity, antimicrobial resistance and biofilm-forming abilities of Campylobacter isolated from chicken in Central China, which showed the potential importance of biofilm in antimicrobial resistance. This study will help us better understand the epidemiology and antimicrobial resistance of Campylobacter.

The Current State of Macrolide Resistance in Campylobacter spp.: Trends and Impacts of Resistance Mechanisms

Campylobacter spp., especially Campylobacter jejuni and C. coli, are leading bacterial foodborne pathogens worldwide. In the United States, an estimated 0.8 million cases of campylobacteriosis occur annually, mostly involving C. jejuni Campylobacteriosis is generally self-limiting, but in severe cases, treatment with antibiotics may be mandated. The increasing incidence of fluoroquinolone resistance in Campylobacter has rendered macrolides such as erythromycin and azithromycin the drugs of choice for human campylobacteriosis. The prevalence of macrolide resistance in C. jejuni remains low, but macrolide resistance can be common in C. coli Substitutions in the 23S rRNA gene, specifically A2075G, and less frequently A2074C/G, remain the most common mechanism for high-level resistance to macrolides. In C. jejuni, resistance mediated by such substitutions is accompanied by a reduced ability to colonize chickens and other fitness costs, potentially contributing to the low incidence of macrolide resistance. Interestingly, similar fitness impacts have not been noted in C. coli Also noteworthy is a novel mechanism first reported in 2014 for a C. coli isolate from China and mediated by erm(B) harbored on multidrug resistance genomic islands. The incidence of erm(B) appears to reflect clonal expansion of certain strains, and whole-genome sequencing has been critical to the elucidation of erm(B)-associated macrolide resistance in Campylobacter spp. With the exception of one report from Spain, erm(B)-mediated macrolide resistance has been restricted to Campylobacter spp., mostly C. coli, of animal and human origin from China. If erm(B)-mediated macrolide resistance does not confer fitness costs in C. jejuni, the range of this gene may expand in C. jejuni, threatening to compromise treatment effectiveness for severe campylobacteriosis cases.

Prevalence and antimicrobial resistance of Campylobacter jejuni and Campylobacter coli isolated from children and environmental sources in urban and suburban areas

BACKGROUND

Campylobacteriosis is a dominant bacterial cause of foodborne infection and is considered the main public health problem in Europe and many other countries worldwide. In the study lasting from 2011 to 2013 we compared the prevalence and antimicrobial resistance of Campylobacter jejuni and Campylobacter coli isolated from children, domestic animals, poultry meat and surface water in Northern Poland.

RESULTS

During a 3-years study 1973 samples were analysed. The results proved the presence of Campylobacter spp. in 306 (15.5%) samples. The percentage of Campylobacter-positive samples differed among the sample types, from 0% (freshwater beaches) to 38.6% (poultry meat in 2011). Prevalence of Campylobacter spp. in children isolates was 9.6%. It decreased from 13.2% in 2011 to 8.0% in 2013. It should be highlighted with a particular concern that Campylobacter jejuni was detected in 20.0% of fountains. All children and poultry meat isolates were susceptible to azithromycin. Two C. coli (3.7%) and four C. jejuni (3.3%) isolated from poultry meat were resistant to erythromycin. The highest percentage of C. jejuni isolates with resistance to ciprofloxacin were found in samples from 80% dogs and 85% ponds. Among isolates resistant to two antimicrobials 74.7% C. jejuni and 59.2% C. coli isolates were resistant to ciprofloxacin as well as to tetracycline. Only one cat C. coli isolate was resistant to both azithromycin and erythromycin. One C. jejuni isolate from a fountain was resistant to four antimicrobial agents (erythromycin, azithromycin, tetracycline and ciprofloxacin).

CONCLUSIONS

The study proved that surface water, poultry meat and pets constituted potential sources of Campylobacter to children. Fountains can be a direct source of children campylobacteriosis but can also pollute other environments with multidrug-resistant Campylobacter. The high resistance to some antimicrobials among the isolates may lead to increasing numbers of difficult-to-treat campylobacteriosis cases among children.

Pathogens of Food Animals: Sources, Characteristics, Human Risk, and Methods of Detection

Pathogens associated with food production (livestock) animals come in many forms causing a multitude of disease for humans. For the purpose of this review, these infectious agents can be divided into three broad categories: those that are associated with bacterial disease, those that are associated with viruses, and those that are parasitic in nature. The goal of this chapter is to provide the reader with an overview of the most common pathogens that cause disease in humans through exposure via the food chain and the consequence of this exposure as well as risk and detection methods. We have also included a collection of unusual pathogens that although rare have still caused disease, and their recognition is warranted in light of emerging and reemerging diseases. These provide the reader an understanding of where the next big outbreak could occur. The influence of the global economy, the movement of people, and food makes understanding production animal-associated disease paramount to being able to address new diseases as they arise.

Molecular epidemiological analysis of human- and chicken-derived isolates of Campylobacter jejuni in Japan using next-generation sequencing

In this research, we analyzed the main sequence types (ST) and ST complexes of human- and chicken-derived isolates of Campylobacter jejuni in Japan by using multilocus sequence typing (MLST). We also analyzed lipooligosaccharide biosynthesis locus classes (LOS locus classes) and the numbers of isolates carrying genes coding resistance factors against various antibiotics, and observed their relationships. ST-21 complex was the main ST complex in isolates from humans (n = 38) and chickens (n = 25). None of the isolates showed resistance to imipenem, chloramphenicol, or erythromycin. Few isolates were resistant to ampicillin and streptomycin (1.3%-15%), whereas many showed resistance to tetracycline, ciprofloxacin, and nalidixic acid (38%-48%). Among the ST-21 complex isolates, ST4526 was detected at a very high rate. Those isolates showed resistance to tetracycline and ciprofloxacin, and were susceptible to ampicillin. Among the chicken-derived isolates, 37 of the 38 isolates that showed resistance to ciprofloxacin and nalidixic acid had threonine to isoleucine amino acid substitution in GyrA at codon 86 (T86I). Among the human-derived isolates, 17 of the 47 isolates that showed resistance to ciprofloxacin and 16 of the 48 isolates that showed resistance to nalidixic acid did not have T86I amino acid mutations in GyrA. The human-derived ST-21 complex isolates were classified into LOS locus classes A, B, C, D, and E. The chicken-derived ST-21 complex isolates, with the exception of one isolate, were all classified into LOS locus classes C and D. Among chicken-derived isolates, the most prevalent was ST51 (ST-443 complex) (10 isolates) and all of those were LOS locus class E.

The Risk of Some Veterinary Antimicrobial Agents on Public Health Associated with Antimicrobial Resistance and their Molecular Basis

The risk of antimicrobial agents used in food-producing animals on public health associated with antimicrobial resistance continues to be a current topic of discussion as related to animal and human public health. In the present review, resistance monitoring data, and risk assessment results of some important antimicrobial agents were cited to elucidate the possible association of antimicrobial use in food animals and antimicrobial resistance in humans. From the selected examples, it was apparent from reviewing the published scientific literature that the ban on use of some antimicrobial agents (e.g., avoparcin, fluoroquinolone, tetracyclines) did not change drug resistance patterns and did not mitigate the intended goal of minimizing antimicrobial resistance. The use of some antimicrobial agents (e.g., virginiamycin, macrolides, and cephalosporins) in food animals may have an impact on the antimicrobial resistance in humans, but it was largely depended on the pattern of drug usage in different geographical regions. The epidemiological characteristics of resistant bacteria were closely related to molecular mechanisms involved in the development, fitness, and transmission of antimicrobial resistance.

Virulence and Genomic Feature of Multidrug Resistant Campylobacter jejuni Isolated from Broiler Chicken

The aim of this study was to reveal the molecular mechanism involved in multidrug resistance and virulence of Campylobacter jejuni isolated from broiler chickens. The virulence of six multidrug resistant C. jejuni was determined by in vitro and in vivo methods. The de novo whole genome sequencing technology and molecular biology methods were used to analyze the genomic features associated with the multidrug resistance and virulence of a selected isolate (C. jejuni 1655). The comparative genomic analyses revealed a large number of single nucleotide polymorphisms, deletions, rearrangements, and inversions in C. jejuni 1655 compared to reference C. jejuni genomes. The co-emergence of Thr-86-Ile mutation in gyrA gene, A2075G mutation in 23S rRNA gene, tetO, aphA and aadE genes and pTet plasmid in C. jejuni 1655 contributed its multidrug resistance to fluoroquinolones, macrolides, tetracycline, and aminoglycosides. The combination of multiple virulence genes may work together to confer the relative higher virulence in C. jejuni 1655. The co-existence of mobile gene elements (e.g., pTet) and CRISPR-Cas system in C. jejuni 1655 may play an important role in the gene transfer and immune defense. The present study provides basic information of phenotypic and genomic features of C. jejuni 1655, a strain recently isolated from a chicken displaying multidrug resistance and relatively high level of virulence.

Identification of Campylobacter jejuni and determination of point mutations associated with macrolide resistance using a multiplex TaqMan MGB real-time PCR

AIMS

The aim of the study was to develop a multiplex real-time PCR method to identify Campylobacter jejuni containing mutations commonly associated with macrolide resistance.

METHODS AND RESULTS

A multiplex fluorescence real-time PCR assay was developed based on TaqMan minor groove binder (MGB) probes. The VS1-MGB probe was designed based on the VS1 gene and was used to identify Camp. jejuni. The 23S rDNA-MGB probe was designed to distinguish macrolide resistance mutations in 23S rDNA, while 57D-MGB and 74D-MGB were designed to detect resistance mutations in ribosomal protein L4. The specificity and accuracy of our method were identical to the conventional biochemical tests, mapA PCR, minimum inhibitory concentration (MIC) determination and DNA sequencing. The linear detection limit of the method was 0·03 ng genomic DNA and three colony formation unit (CFU) per reaction. In 6 of 18 cases, the nature of Erythromycin resistance could be correctly determined from natural isolates; absence of the tested mutations was demonstrated in the remaining four resistant isolates.

CONCLUSIONS

A multiplex TaqMan MGB real-time PCR assay with high specificity and accuracy was developed to simultaneously identify Camp. jejuni and detect the gene mutations associated with macrolide resistance.

SIGNIFICANCE AND IMPACT OF THE STUDY

This multiplex method can potentially simplify the identification of Camp. jejuni and determine macrolide resistance due to mutations in 23S rDNA or ribosomal protein L4. This method has a potential for application in different research areas and molecular surveillance.

The challenge of efflux-mediated antibiotic resistance in Gram-negative bacteria

The global emergence of multidrug-resistant Gram-negative bacteria is a growing threat to antibiotic therapy. The chromosomally encoded drug efflux mechanisms that are ubiquitous in these bacteria greatly contribute to antibiotic resistance and present a major challenge for antibiotic development. Multidrug pumps, particularly those represented by the clinically relevant AcrAB-TolC and Mex pumps of the resistance-nodulation-division (RND) superfamily, not only mediate intrinsic and acquired multidrug resistance (MDR) but also are involved in other functions, including the bacterial stress response and pathogenicity. Additionally, efflux pumps interact synergistically with other resistance mechanisms (e.g., with the outer membrane permeability barrier) to increase resistance levels. Since the discovery of RND pumps in the early 1990s, remarkable scientific and technological advances have allowed for an in-depth understanding of the structural and biochemical basis, substrate profiles, molecular regulation, and inhibition of MDR pumps. However, the development of clinically useful efflux pump inhibitors and/or new antibiotics that can bypass pump effects continues to be a challenge. Plasmid-borne efflux pump genes (including those for RND pumps) have increasingly been identified. This article highlights the recent progress obtained for organisms of clinical significance, together with methodological considerations for the characterization of MDR pumps.

Analysis of Neisseria gonorrhoeae azithromycin susceptibility in the United States by the Gonococcal Isolate Surveillance Project, 2005 to 2013

Azithromycin, administered with ceftriaxone, is recommended by the CDC for the treatment of gonorrhea. Many experts have expressed concern about the ease with which Neisseria gonorrhoeae can acquire macrolide resistance. We sought to describe gonococcal azithromycin susceptibility in the United States and to determine whether azithromycin susceptibility has changed over time. We analyzed data from 2005 to 2013 from the Gonococcal Isolate Surveillance Project, a CDC-supported sentinel surveillance network that monitors gonococcal antimicrobial susceptibility. A total of 44,144 N. gonorrhoeae isolates were tested for azithromycin susceptibility by agar dilution methods. The overall azithromycin MIC50 was 0.25 μg/ml, and the MIC90 was 0.5 μg/ml. There were no overall temporal trends in geometric means. Isolates from men who had sex with men had significantly higher geometric mean MICs than isolates from men who had sex exclusively with women. The overall prevalence of reduced azithromycin susceptibility (MIC, ≥2 μg/ml) was 0.4% and varied by year from 0.3% (2006 and 2009) to 0.6% (2013). We did not find a clear temporal trend in gonococcal azithromycin MICs in the United States, and the prevalence of reduced azithromycin susceptibility remains low. These findings support the continued use of azithromycin in a combination therapy regimen for gonorrhea.

The fitness costs of antibiotic resistance mutations

Antibiotic resistance is increasing in pathogenic microbial populations and is thus a major threat to public health. The fate of a resistance mutation in pathogen populations is determined in part by its fitness. Mutations that suffer little or no fitness cost are more likely to persist in the absence of antibiotic treatment. In this review, we performed a meta-analysis to investigate the fitness costs associated with single mutational events that confer resistance. Generally, these mutations were costly, although several drug classes and species of bacteria on average did not show a cost. Further investigations into the rate and fitness values of compensatory mutations that alleviate the costs of resistance will help us to better understand both the emergence and management of antibiotic resistance in clinical settings.

Identification of a novel G2073A mutation in 23S rRNA in amphenicol-selected mutants of Campylobacter jejuni

OBJECTIVES

This study was conducted to examine the development and molecular mechanisms of amphenicol resistance in Campylobacter jejuni by using in vitro selection with chloramphenicol and florfenicol. The impact of the resistance development on growth rates was also determined using in vitro culture.

METHODS

Chloramphenicol and florfenicol were used as selection agents to perform in vitro stepwise selection. Mutants resistant to the selective agents were obtained from the selection process. The mutant strains were compared with the parent strain for changes in MICs and growth rates. The 23S rRNA gene and the L4 and L22 ribosomal protein genes in the mutant strains and the parent strain were amplified and sequenced to identify potential resistance-associated mutations.

RESULTS

C. jejuni strains that were highly resistant to chloramphenicol and florfenicol were obtained from in vitro selection. A novel G2073A mutation in all three copies of the 23S rRNA gene was identified in all the resistant mutants examined, which showed resistance to both chloramphenicol and florfenicol. In addition, all the mutants selected by chloramphenicol also exhibited the G74D modification in ribosomal protein L4, which was previously shown to confer a low-level erythromycin resistance in Campylobacter species. The mutants selected by florfenicol did not have the G74D mutation in L4. Notably, the amphenicol-resistant mutants also exhibited reduced susceptibility to erythromycin, suggesting that the selection resulted in cross resistance to macrolides.

CONCLUSIONS

This study identifies a novel point mutation (G2073A) in 23S rRNA in amphenicol-selected mutants of C. jejuni. Development of amphenicol resistance in Campylobacter likely incurs a fitness cost as the mutant strains showed slower growth rates in antibiotic-free media.

Adaptive mechanisms of Campylobacter jejuni to erythromycin treatment

Background

Macrolide is the drug of choice to treat human campylobacteriosis, but Campylobacter resistance to this antibiotic is rising. The mechanisms employed by Campylobacter jejuni to adapt to erythromycin treatment remain unknown and are examined in this study. The transcriptomic response of C. jejuni NCTC 11168 to erythromycin (Ery) treatment was determined by competitive microarray hybridizations. Representative genes identified to be differentially expressed were further characterized by constructing mutants and assessing their involvement in antimicrobial susceptibility, oxidative stress tolerance, and chicken colonization.

Results

Following the treatment with an inhibitory dose of Ery, 139 genes were up-regulated and 119 were down-regulated. Many genes associated with flagellar biosynthesis and motility was up-regulated, while many genes involved in tricarboxylic acid cycle, electron transport, and ribonucleotide biosynthesis were down-regulated. Exposure to a sub-inhibitory dose of Ery resulted in differential expression of much fewer genes. Interestingly, two putative drug efflux operons (cj0309c-cj0310c and cj1173-cj1174) were up-regulated. Although mutation of the two operons did not alter the susceptibility of C. jejuni to antimicrobials, it reduced Campylobacter growth under high-level oxygen. Another notable finding is the consistent up-regulation of cj1169c-cj1170c, of which cj1170c encodes a known phosphokinase, an important regulatory protein in C. jejuni. Mutation of the cj1169c-cj1170c rendered C. jejuni less tolerant to atmospheric oxygen and reduced Campylobacter colonization and transmission in chickens.

Conclusions

These findings indicate that Ery treatment elicits a range of changes in C. jejuni transcriptome and affects the expression of genes important for in vitro and in vivo adaptation. Up-regulation of motility and down-regulation of energy metabolism likely facilitate Campylobacter to survive during Ery treatment. These findings provide new insight into Campylobacter adaptive response to antibiotic treatment and may help to understand the mechanisms underlying antibiotic resistance development.

Antimicrobial resistance and virulence: a successful or deleterious association in the bacterial world?

Hosts and bacteria have coevolved over millions of years, during which pathogenic bacteria have modified their virulence mechanisms to adapt to host defense systems. Although the spread of pathogens has been hindered by the discovery and widespread use of antimicrobial agents, antimicrobial resistance has increased globally. The emergence of resistant bacteria has accelerated in recent years, mainly as a result of increased selective pressure. However, although antimicrobial resistance and bacterial virulence have developed on different timescales, they share some common characteristics. This review considers how bacterial virulence and fitness are affected by antibiotic resistance and also how the relationship between virulence and resistance is affected by different genetic mechanisms (e.g., coselection and compensatory mutations) and by the most prevalent global responses. The interplay between these factors and the associated biological costs depend on four main factors: the bacterial species involved, virulence and resistance mechanisms, the ecological niche, and the host. The development of new strategies involving new antimicrobials or nonantimicrobial compounds and of novel diagnostic methods that focus on high-risk clones and rapid tests to detect virulence markers may help to resolve the increasing problem of the association between virulence and resistance, which is becoming more beneficial for pathogenic bacteria.

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.

Mutational and transcriptomic changes involved in the development of macrolide resistance in Campylobacter jejuni

Macrolide antibiotics are important for clinical treatment of infections caused by Campylobacter jejuni. Development of resistance to this class of antibiotics in Campylobacter is a complex process, and the dynamic molecular changes involved in this process remain poorly defined. Multiple lineages of macrolide-resistant mutants were selected by stepwise exposure of C. jejuni to escalating doses of erythromycin or tylosin. Mutations in target genes were determined by DNA sequencing, and the dynamic changes in the expression of antibiotic efflux transporters and the transcriptome of C. jejuni were examined by real-time reverse transcription-PCR, immunoblotting, and DNA microarray analysis. Multiple types of mutations in ribosomal proteins L4 and L22 occurred early during stepwise selection. On the contrary, the mutations in the 23S rRNA gene, mediating high resistance to macrolides, were observed only in the late-stage mutants. Upregulation of antibiotic efflux genes was observed in the intermediately resistant mutants, and the magnitude of upregulation declined with the occurrence of mutations in the 23S rRNA gene. DNA microarray analysis revealed the differential expression of 265 genes, most of which occurred in the intermediate mutant, including the upregulation of genes encoding ribosomal proteins and the downregulation of genes involved in energy metabolism and motility. These results indicate (i) that mutations in L4 and L22 along with temporal overexpression of antibiotic efflux genes precede and may facilitate the development of high-level macrolide resistance and (ii) that the development of macrolide resistance affects the pathways important for physiology and metabolism in C. jejuni, providing an explanation for the reduced fitness of macrolide-resistant Campylobacter.

Impaired fitness and transmission of macrolide-resistant Campylobacter jejuni in its natural host

Campylobacter jejuni is a major zoonotic pathogen transmitted to humans via the food chain and is prevalent in chickens, a natural reservoir for this pathogenic organism. Due to the importance of macrolide antibiotics in clinical therapy of human campylobacteriosis, development of macrolide resistance in Campylobacter has become a concern for public health. To facilitate the control of macrolide-resistant Campylobacter, it is necessary to understand if macrolide resistance affects the fitness and transmission of Campylobacter in its natural host. In this study we conducted pairwise competitions and comingling experiments in chickens using clonally related and isogenic C. jejuni strains, which are either susceptible or resistant to erythromycin (Ery). In every competition pair, Ery-resistant (Ery(r)) Campylobacter was consistently outcompeted by the Ery-susceptible (Ery(s)) strain. In the comingling experiments, Ery(r) Campylobacter failed to transmit to chickens precolonized by Ery(s) Campylobacter, while isogenic Ery(s) Campylobacter was able to transmit to and establish dominance in chickens precolonized by Ery(r) Campylobacter. The fitness disadvantage was linked to the resistance-conferring mutations in the 23S rRNA. These findings clearly indicate that acquisition of macrolide resistance impairs the fitness and transmission of Campylobacter in chickens, suggesting that the prevalence of macrolide-resistant C. jejuni will likely decrease in the absence of antibiotic selection pressure.

Impact of erythromycin resistance on the virulence properties and fitness of Campylobacter jejuni

Epidemiological studies of macrolide resistance in Campylobacter jejuni demonstrated that infections with macrolide-resistant C. jejuni could be associated with an increased risk of adverse events, development of invasive illness or death compared to macrolide-susceptible isolates. In this study, an in vitro induction experiment was conducted using susceptible C. jejuni strain and erythromycin as a selecting agent to obtain Ery-resistant mutant with 23S rRNA gene mutation (A2074C). Changes in the virulence characteristics and fitness between the susceptible parent strain and Ery-resistant mutant were examined. Ery-resistant mutant demonstrated slightly more resistance to bile in the bile tolerance assay compared to the susceptible strain but with no statistical significant difference. However Ery-resistant mutant apparently demonstrated reduced adhesion and invasion characteristics to intestinal epithelial cells, murine macrophage and short time intracellular survivability within macrophage compared to the susceptible strain. Co-inoculation of the two strains in the mice resulted in low colonization level of the resistant strain compared to the susceptible strain. Competition experiments resulted in mutant that grew significantly slower than the susceptible parent strain and the mutation imposed a fitness cost in Ery-resistant mutant. Taken together these findings demonstrated the increment of the virulence characteristics of Ery-susceptible strain rather than Ery-resistant strain. The adverse events previously observed in the epidemiological studies for macrolide-resistant strains infection, we suggested this maybe attributed to the resistivity of the resistant strains to the treatment and consequently prolonged the symptoms and compromised the disease in patients.

Repeated therapeutic dosing selects macrolide-resistant Campylobacter spp. in a turkey facility

AIMS

This study assessed the effects of the therapeutic use of Tylan® in a large-scale turkey production facility on the selection of macrolide-resistant Campylobacter.

METHODS AND RESULTS

A flock of production turkeys (c. 30,000 birds) was followed from brooding to slaughter, and the effects of macrolide application was assessed in one half of the flock from finishing stage to final product and compared against the control barn where no macrolide was used. Overall, Campylobacter prevalence in turkeys was almost 100% by 4 weeks of age. When Campylobacter prevalence was assessed in relation to treatment, high levels of macrolide resistance were evident in this group following treatment, with Campylobacter coli becoming the dominant strain type. Over time, and in the absence of a selection agent, the population of resistant strains decreased suggesting that there was a fitness cost associated with macrolide resistance carriage and persistence. Macrolide resistance was detected in the control barn at a very low level (four isolates recovered during the study), suggesting that the creation or selection of macrolide-resistant Campylobacter was correlated with the treatment regime used. Molecular analysis of a selection of macrolide-resistant Campylobacter recovered was assessed using PCR, RFLP and sequence analysis of the 23S rRNA. The majority of isolates displaying high-level macrolide resistance (>256 μg ml(-1)) possessed an A2075G transition mutation in the 23S rRNA and the CmeABC efflux pump.

CONCLUSIONS

These studies suggest that macrolide resistance can be promoted through the application of treatment during the grow-out phase and once established in a production facility has the potential to persist and be transferred to final product.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study highlights the prudent use of antimicrobials in treatment of disease in poultry. Of significance is the presence of macrolide-resistant Campylobacter in poultry production and finished product as a consequence of macrolide usage.

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

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