Fluoroquinolone resistance: mechanisms, impact on bacteria, and role in evolutionary success

Metal-mediated oxidation of fluoroquinolone antibiotics in water: A review on kinetics, transformation products, and toxicity assessment

Fluoroquinolones (FQs) are among the most potent antimicrobial agents, which have seen their increasing use as human and veterinary medicines to control bacterial infections. FQs have been extensively found in surface water and municipal wastewaters, which has raised great concerns due to their negative impacts to humans and ecological health. It is of utmost importance that FQs are treated before their release into the environment. This paper reviews oxidative removal of FQs using reactive oxygen (O₃ and OH), sulfate radicals (SO₄^-), and high-valent transition metal (Mn^VII and Fe^VI) species. The role of metals in enhancing the performance of reactive oxygen and sulfur species is presented. The catalysts can significantly enhance the production of OH and/or SO₄^- radicals. At neutral pH, the second-order rate constants (k, M^-1s^-1) of the reactions between FQs and oxidants follow the order as k(OH)>k(O₃)>k(Fe^VI)>k(Mn^VII). Moieties involved to transform target FQs to oxidized products and participation of the catalysts in the reaction pathways are discussed. Generally, the piperazinyl ring of FQs was found as the preferential attack site by each oxidant. Meanwhile, evaluation of aquatic ecotoxicity of the transformation products of FQs by these treatments is summarized.

Molecular epidemiology of fluoroquinolone resistant Salmonella in Africa: A systematic review and meta-analysis

BACKGROUND

Wide-ranging evidence on the occurrence of fluoroquinolone (FQ) resistance genetic determinants in African Salmonella strains is not available. The main objectives of this study were to assess the heterogeneity, estimate pooled proportions and describe the preponderance of FQ-resistance determinants in typhoidal and non-typhoidal Salmonella (NTS) isolates of Africa.

METHODS

Genetic and phenotypic data on 6103 Salmonella isolates were considered. Meta- and frequency analyses were performed depending on the number of studies by category, number of isolates and risks of bias. A random effects model was used to assess heterogeneity and estimate pooled proportions. Relative and cumulative frequencies were calculated to describe the overall preponderance of FQ-resistance determinants in quinolone resistant isolates.

RESULTS

The pooled proportion of gyrA mutants (Salmonella enterica serovar Typhi, Salmonella enterica serovar Typhimurium, and Salmonella enterica serovar Enteritidis) was estimated at 5.7% (95% Confidence interval (CI) = 2.6, 9.8; Tau squared (T2) = 0.1105), and was higher in S. Typhi than in S. Typhimurium (odds ratio (OR) = 3.3, 95%CI = 2, 5.7). The proportions of each of gyrB and parC mutants, and strains with Plasmid Mediated Quinolone Resistance genes (qnrA, qnrB and qnrS) were low (≤ 0.3%). Overall, 23 mutant serotypes were identified, and most strains had mutations at codons encoding Ser83 and Asp87 of gyrA (82%, 95%CI = 78, 86).

CONCLUSIONS

Mutations at gyrA appear to account for ciprofloxacin non-susceptibility in most clinical Salmonella strains in Africa. The estimates could be harnessed to develop a mismatch-amplification mutation-assay for the detection of FQ-resistant strains in Africa.

Besifloxacin: A Critical Review of Its Characteristics, Properties, and Analytical Methods

Bacterial conjunctivitis has high impact on the health of the population, since it represents more than a third of ocular pathologies reported by health services worldwide. There is a high incidence of bacterial resistance to the antimicrobials most commonly used for the treatment of conjunctivitis. In this context, besifloxacin stands out, since it is a fluoroquinolone developed exclusively for topical ophthalmic use, presenting a low risk of developing resistance due to its reduced systemic exposure. Bausch & Lomb markets it as ophthalmic suspension, under the trade name Besivance™. Literature review on besifloxacin is presented, covering its pharmaceutical and clinical characteristics, and the analytical methods used to measure the drug in pharmaceutical products and biological samples. High performance liquid chromatography is the most used method for this purpose. A discussion on Green Chemistry is also presented, focusing the importance of the development of green analytical methods for the analysis of drugs.

Fitness Tradeoffs of Antibiotic Resistance in Extraintestinal Pathogenic Escherichia coli

Evolutionary trade-offs occur when selection on one trait has detrimental effects on other traits. In pathogenic microbes, it has been hypothesized that antibiotic resistance trades off with fitness in the absence of antibiotic. Although studies of single resistance mutations support this hypothesis, it is unclear whether trade-offs are maintained over time, due to compensatory evolution and broader effects of genetic background. Here, we leverage natural variation in 39 extraintestinal clinical isolates of Escherichia coli to assess trade-offs between growth rates and resistance to fluoroquinolone and cephalosporin antibiotics. Whole-genome sequencing identifies a broad range of clinically relevant resistance determinants in these strains. We find evidence for a negative correlation between growth rate and antibiotic resistance, consistent with a persistent trade-off between resistance and growth. However, this relationship is sometimes weak and depends on the environment in which growth rates are measured. Using in vitro selection experiments, we find that compensatory evolution in one environment does not guarantee compensation in other environments. Thus, even in the face of compensatory evolution and other genetic background effects, resistance may be broadly costly, supporting the use of drug restriction protocols to limit the spread of resistance. Furthermore, our study demonstrates the power of using natural variation to study evolutionary trade-offs in microbes.

Enrofloxacin Permeation Pathways across the Porin OmpC

In Gram-negative bacteria, the lack or quenching of antibiotic translocation across the outer membrane is one of the main factors for acquiring antibiotic resistance. An atomic-level comprehension of the key features governing the transport of drugs by outer-membrane protein channels would be very helpful in developing the next generation of antibiotics. In a previous study [ J. D. Prajapati et al. J. Chem. Theory Comput. 2017 , 13 , 4553 ], we characterized the diffusion pathway of a ciprofloxacin molecule through the outer membrane porin OmpC of Escherichia coli by combining metadynamics and a zero-temperature string method. Here, we evaluate the diffusion route through the OmpC porin for a similar fluoroquinolone, that is, the enrofloxacin molecule, using the previously developed protocol. As a result, it was found that the lowest-energy pathway was similar to that for ciprofloxacin; namely, a reorientation was required on the extracellular side with the carboxyl group ahead before enrofloxacin reached the constriction region. In turn, the free-energy basins for both antibiotics are located at similar positions in the space defined by selected reaction coordinates, and their affinity sites share a wide number of porin residues. However, there are some important deviations due to the chemical differences of these two drugs. On the one hand, a slower diffusion process is expected for enrofloxacin, as the permeation pathway exhibits higher overall energy barriers, mainly in the constriction region. On the other hand, enrofloxacin needs to replace some polar interactions in its affinity sites with nonpolar ones. This study demonstrates how minor chemical modifications can qualitatively affect the translocation mechanism of an antibiotic molecule.

Klebsiella pneumoniae: a major worldwide source and shuttle for antibiotic resistance

Klebsiella pneumoniae is an important multidrug-resistant (MDR) pathogen affecting humans and a major source for hospital infections associated with high morbidity and mortality due to limited treatment options. We summarize the wide resistome of this pathogen, which encompasses plentiful chromosomal and plasmid-encoded antibiotic resistance genes (ARGs). Under antibiotic selective pressure, K. pneumoniae continuously accumulates ARGs, by de novo mutations, and via acquisition of plasmids and transferable genetic elements, leading to extremely drug resistant (XDR) strains harboring a 'super resistome'. In the last two decades, numerous high-risk (HiR) MDR and XDR K. pneumoniae sequence types have emerged showing superior ability to cause multicontinent outbreaks, and continuous global dissemination. The data highlight the complex evolution of MDR and XDR K. pneumoniae, involving transfer and spread of ARGs, and epidemic plasmids in highly disseminating successful clones. With the worldwide catastrophe of antibiotic resistance and the urgent need to identify the main pathogens that pose a threat on the future of infectious diseases, further studies are warranted to determine the epidemic traits and plasmid acquisition in K. pneumoniae. There is a need for future genomic and translational studies to decipher specific targets in HiR clones to design targeted prevention and treatment.

Novel Levofloxacin-Resistant Multidrug-Resistant Streptococcus pneumoniae Serotype 11A Isolates, South Korea

Of 608 Streptococcus pneumoniae clinical strains isolated at a hospital in South Korea during 2009–2014, sixteen (2.6%) were identified as levofloxacin resistant. The predominant serotype was 11A (9 isolates). Two novel sequence types of multidrug-resistant S. pneumoniae with serotype 11A were identified, indicating continuous diversification of resistant strains.

Impacts of feeding preweaned calves milk containing drug residues on the functional profile of the fecal microbiota

Feeding drug residue-containing milk to calves is common worldwide and no information is currently available on the impact on the functional profile of the fecal microbiota. Our objective was to characterize the functional profile of the fecal microbiota of preweaned dairy calves fed raw milk with residual concentrations of antimicrobials commonly found in waste milk from birth to weaning. Calves were assigned to a controlled feeding trial being fed milk with no drug residues or milk with antibiotic residues. Fecal samples collected from each calf once a week starting at birth, prior to the first feeding in the trial, until 6 weeks of age. Antibiotic residues resulted in a significant difference in relative abundance of microbial cell functions, especially with genes linked with stress response, regulation and cell signaling, and nitrogen metabolism. These changes could directly impacts selection and dissemination of virulence and antimicrobial. Our data also identified a strong association between age in weeks and abundance of Resistance to Antibiotics and Toxic Compounds. Findings from this study support the hypothesis that drug residues, even at very low concentrations, impact the gut microbiota of calves and result in changes in the functional profile of microbial populations.

DNA replication proteins as potential targets for antimicrobials in drug-resistant bacterial pathogens

With the impending crisis of antimicrobial resistance, there is an urgent need to develop novel antimicrobials to combat difficult infections and MDR pathogenic microorganisms. DNA replication is essential for cell viability and is therefore an attractive target for antimicrobials. Although several antimicrobials targeting DNA replication proteins have been developed to date, gyrase/topoisomerase inhibitors are the only class widely used in the clinic. Given the numerous essential proteins in the bacterial replisome that may serve as a potential target for inhibitors and the relative paucity of suitable compounds, it is evident that antimicrobials targeting the replisome are underdeveloped so far. In this review, we report on the diversity of antimicrobial compounds targeting DNA replication and highlight some of the challenges in developing new drugs that target this process.

DNA Topoisomerases as Targets for Antibacterial Agents

DNA topoisomerases are proven therapeutic targets of antibacterial agents. Quinolones, especially fluoroquinolones, are the most successful topoisomerase-targeting antibacterial drugs. These drugs target type IIA topoisomerases in bacteria. Recent structural and biochemical studies on fluoroquinolones have provided the molecular basis for both their mechanism of action, as well as the molecular basis of bacterial resistance. Due to the development of drug resistance, including fluoroquinolone resistance, among bacterial pathogens, there is an urgent need to discover novel antibacterial agents. Recent advances in topoisomerase inhibitors may lead to the development of novel antibacterial drugs that are effective against fluoroquinolone-resistant pathogens. They include type IIA topoisomerase inhibitors that either interact with the GyrB/ParE subunit or form nick-containing ternary complexes. In addition, several topoisomerase I inhibitors have recently been identified. Thus, DNA topoisomerases remain important targets of antibacterial agents.

Recombinant Endolysins as Potential Therapeutics against Antibiotic-Resistant Staphylococcus aureus: Current Status of Research and Novel Delivery Strategies

Staphylococcus aureus is one of the most common pathogens of humans and animals, where it frequently colonizes skin and mucosal membranes. It is of major clinical importance as a nosocomial pathogen and causative agent of a wide array of diseases. Multidrug-resistant strains have become increasingly prevalent and represent a leading cause of morbidity and mortality. For this reason, novel strategies to combat multidrug-resistant pathogens are urgently needed. Bacteriophage-derived enzymes, so-called endolysins, and other peptidoglycan hydrolases with the ability to disrupt cell walls represent possible alternatives to conventional antibiotics. These lytic enzymes confer a high degree of host specificity and could potentially replace or be utilized in combination with antibiotics, with the aim to specifically treat infections caused by Gram-positive drug-resistant bacterial pathogens such as methicillin-resistant S. aureus. LysK is one of the best-characterized endolysins with activity against multiple staphylococcal species. Various approaches to further enhance the antibacterial efficacy and applicability of endolysins have been demonstrated. These approaches include the construction of recombinant endolysin derivatives and the development of novel delivery strategies for various applications, such as the production of endolysins in lactic acid bacteria and their conjugation to nanoparticles. These novel strategies are a major focus of this review.

Antibiotic treatment disrupts bacterial communities in the colon and rectum of simian immunodeficiency virus-infected macaques

Antibiotic therapies are known to disrupt gastrointestinal (GI) bacterial communities. HIV and pathogenic simian immunodeficiency virus (SIV) infections have also been associated with disrupted GI bacterial communities. We administered a combination antibiotic therapy to six SIV-infected rhesus macaques and collected colon biopsies, stool samples and rectal swabs before and after antibiotics, and evaluated the bacterial communities at each sample site using high-throughput 16S rRNA gene sequencing. The colon mucosa and stool samples displayed different bacterial communities, while the rectal swabs showed a mixture of the mucosal and stool-associated bacteria. Antibiotics disrupted the native bacterial communities at each sample site. The colon mucosa showed depleted abundances of the dominant Helicobacteraceae, while we found depleted abundances of the dominant Ruminococcaceae sp. in the stool. The rectal swabs showed similar trends as the colon mucosa, but were more variable. After the antibiotic treatment, there were increased abundances of similar taxa of facultative anaerobic bacteria, including Lactobacillaceae and Enterobacteriaceae at each sample site.

What Is Old Is New Again: Delafloxacin, a Modern Fluoroquinolone

Delafloxacin is a new fluoroquinolone antimicrobial approved for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) in adults using dosage regimens of 300 mg intravenously every 12 hours, 450 mg orally every 12 hours, or switching from intravenous to oral regimens for a 5- to 14-day treatment duration. Dosage adjustments in patients with severe renal dysfunction (estimated glomerular filtration rate [eGFR] = 15-29 ml/min/1.73 m² ) are not required for oral doses but should be decreased to 200 mg intravenously every 12 hours in patients requiring parenteral therapy. Due to insufficient data, use of delafloxacin is not recommended for patients on hemodialysis or with end-stage renal disease (eGFR < 15 ml/min/1.73 m² ). Delafloxacin works through inhibition of DNA gyrase (topoisomerase II) and topoisomerase IV, which are essential enzymes for bacterial DNA transcription, replication, repair, and recombination and exhibits bactericidal activity against gram-positive and gram-negative organisms through a concentration-dependent matter. Delafloxacin has a very broad spectrum of activity against atypical, anaerobic, and resistant gram-negative and gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. During phase 3 trials, the most common side effects associated with delafloxacin were gastrointestinal (nausea, diarrhea). Unlike other fluoroquinolones, there does not seem to be a risk of QTc prolongation or phototoxicity with delafloxacin. The availability of both parenteral and oral formulations for delafloxacin distinguishes it from many of the currently available agents approved for ABSSSIs. Phase 3 studies for the treatment of respiratory infections are currently under way, and future results of these studies will further help delineate the role of delafloxacin.

Drug repurposing: An approach to tackle drug resistance in S. typhimurium

Drug resistant S. typhimurium pose important public health problem. The development of effective drugs with novel mechanism(s) of action is needed to overcome issues pertaining to drug resistance. Drug repurposing based on computational analyses is considered a viable alternative strategy to circumvent this issue. In this context, 1309 FDA-approved drugs molecules from Mantra 2.0 database were analyzed for this study, against S. typhimurium. Sixteen compounds having similar profiles of gene expression as quinolones were identified from the database, Mantra 2.0. Further, the pharmacophore characteristics of each resultant molecule were identified and compared with the features of nalidixic acid, using the PharamGist program. Subsequently, the activities of these compounds against S. typhimurium DNA gyrase were identified, using molecular docking study. Side effects analysis was also performed for the identified compounds. Molecular dynamics simulation was carried out for the compound to validate its binding efficiency. Further, characterization of screened compound revealed IC50 values in micromolar concentration range, of which flufenamic acid showed comparable in vitro activity alongside ciprofloxacin and nalidixic acid. Thus represent interesting starting points for further optimization against S. typhimurium infections. It may be noted that the results we have obtained are the first experimental evidence of flufenamic acid activity against S. typhimurium.

Detection of resistance to fluoroquinolones and injectable drugs among antituberculosis drugs by allele-specific primer extension on a microsphere-based platform

Molecular drug susceptibility testing (DST) for antituberculosis drugs is important for improving the efficacy of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB) treatment. In this study, we developed a molecular high-throughput assay system based on allele-specific primer extension (ASPE) and MagPlex-TAG microspheres, referred to here as TAG-ASPE, which can detect mutations related to resistance to injectable second-line drugs and fluoroquinolones. Target genes were amplified by multiplex PCR using DNA from H37Rv and 190 clinical Mycobacterium tuberculosis strains and extended by ASPE using 22 ASPE primers. ASPE products were then sorted on the TAG-ASPE array and detected using a Luminex 200 system. The performance of the TAG-ASPE method was compared with that of sequencing and phenotypic DST. Comparison of the TAG-ASPE method with sequencing showed that the sensitivity and specificity of the TAG-ASPE method were 100% [95% confidence interval (CI), 96.38-100%] and 100% (95% CI, 95.70-100%) for the rrs gene and 100% (95% CI, 96.90-100%) and 100% (95% CI, 95.07-100%) for the gyrA gene, respectively. Compared with phenotypic DST, the sensitivity and specificity of the TAG-ASPE method for detecting drug-resistance mutations against injectable second-line drugs were 92.52% (95% CI, 85.8-96.72%) and 98.7% (95% CI, 92.98-99.97%), respectively. Additionally, the sensitivity and specificity for fluoroquinolone-resistance detection were 85.4% (95% CI, 78.36-90.85%) and 100% (95% CI, 92.38-100%), respectively. The results of this study demonstrate that the TAG-ASPE method can effectively detect mutations conferring resistance to second-line antituberculosis drugs in numerous clinical specimens.

Patient age as a factor of antibiotic resistance in methicillin-resistant Staphylococcus aureus

PURPOSE

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the leading causes of nosocomial infections. A thorough understanding of the epidemiology and distribution of MRSA allows the development of better preventive measures and helps to control or reduce the rate of infection among the general population.

METHODOLOGY

A retrospective survey was performed on 511 cases of MRSA infections from inpatient, outpatient and nursing home populations over a 12-month period. To study the relationships between two continuous quantitative variables (patient age vs resistance percentage), a simple linear regression was calculated for each antibiotic to predict the antibiotic resistance percentage with respect to patient age.Results/Key findings. The pattern of antibiotic resistance with respect to the age of patients depended on the antibiotic mode of action. Antibiotics that target DNA synthesis (i.e. fluoroquinolones) display a direct correlation with the age of patients, with higher rates of resistance among the older population, while antibiotics that target ribosomal functions (i.e. aminoglycosides) or cell wall synthesis (i.e. cephalosporin) do not display an age-dependent pattern and have a consistent degree of resistance across all age classes.

CONCLUSION

Antibiotics that target DNA synthesis result in a progressively higher number of resistant isolates among the older population. The results emphasize the importance of patient age on antibiotic selection as a preventive measure to reduce the rate of resistant infections in each susceptible population. This pattern suggests that physicians should take into consideration patient age as another factor in determining the best antibiotic regiment with the aim of curtailing the emergence of newer resistant phenotypes in the future.

Ubiquitous Nature of Fluoroquinolones: The Oscillation between Antibacterial and Anticancer Activities

Fluoroquinolones are synthetic antibacterial agents that stabilize the ternary complex of prokaryotic topoisomerase II enzymes (gyrase and Topo IV), leading to extensive DNA fragmentation and bacteria death. Despite the similar structural folds within the critical regions of prokaryotic and eukaryotic topoisomerases, clinically relevant fluoroquinolones display a remarkable selectivity for prokaryotic topoisomerase II, with excellent safety records in humans. Typical agents that target human topoisomerases (such as etoposide, doxorubicin and mitoxantrone) are associated with significant toxicities and secondary malignancies, whereas clinically relevant fluoroquinolones are not known to exhibit such propensities. Although many fluoroquinolones have been shown to display topoisomerase-independent antiproliferative effects against various human cancer cells, those that are significantly active against eukaryotic topoisomerase show the same DNA damaging properties as other topoisomerase poisons. Empirical models also show that fluoroquinolones mediate some unique immunomodulatory activities of suppressing pro-inflammatory cytokines and super-inducing interleukin-2. This article reviews the extended roles of fluoroquinolones and their prospects as lead for the unmet needs of "small and safe" multimodal-targeting drug scaffolds.

Association of the exoU genotype with a multidrug non-susceptible phenotype and mRNA expressions of resistance genes in Pseudomonas aeruginosa

The increased prevalence of the virulence factor exoU + genotype among multidrug-resistant Pseudomonas aeruginosa has been previously reported. However, the genes that are related to the multidrug resistance of the exoU + genotype strain have not been analyzed and remain to be elucidated. The objective of this study was to analyze the correlations between virulence factors and resistance genes. The exoU + genotype was frequently found in carbapenem and fluoroquinolone non-susceptible strains. The imp carbapenemase genotype, the quinolone-resistance-determining region mutation in GyrA and ParC and the defective mutation in OprD were not frequently found in the exoU + genotype and carbapenem and fluoroquinolone non-susceptible strains. On the other hand, mexY and ampC mRNA overexpressing strains were more frequently found in the exoU + genotype and carbapenem and fluoroquinolone non-susceptible strains. Moreover, sequence type 235, a high risk clone of multidrug-resistant P. aeruginosa, was prevalent among the exoU + genotype and carbapenem and fluoroquinolone non-susceptible strains. ExoU is highly virulent protein, and the overexpression of efflux pumps and AmpC β-lactamase induce a multidrug-resistant phenotype. Therefore, the increased prevalence of P. aeruginosa strains with an exoU + genotype and the overexpression of efflux pumps and AmpC β-lactamase are likely to make P. aeruginosa infections difficult to treat. An understanding of the prevalence of both the exoU + genotype and the mRNA overexpression of resistance genes may help to select empirical therapy for the treatment of nosocomial infections caused by P. aeruginosa.

Enhancing the Potency of Nalidixic Acid toward a Bacterial DNA Gyrase with Conjugated Peptides

Quinolones and fluoroquinolones are widely used antibacterial agents. Nalidixic acid (NA) is a first-generation quinolone-based antibiotic that has a narrow spectrum and poor pharmacokinetics. Here, we describe a family of peptide-nalidixic acid conjugates featuring different levels of hydrophobicity and molecular charge prepared by solid-phase peptide synthesis that exhibit intriguing improvements in potency. In comparison to NA, which has a low level of potency in S. aureus, the NA peptide conjugates with optimized hydrophobicities and molecular charges exhibited significantly improved antibacterial activity. The most potent NA conjugate-featuring a peptide containing cyclohexylalanine and arginine-exhibited efficient bacterial uptake and, notably, specific inhibition of S. aureus DNA gyrase. A systematic study of peptide-NA conjugates revealed that a fine balance of cationic charge and hydrophobicity in an appendage anchored to the core of the drug is required to overcome the intrinsic resistance of S. aureus DNA gyrase toward this quinolone-based drug.

Highly Diversified Pandoraea pulmonicola Population during Chronic Colonization in Cystic Fibrosis

Several environmental bacteria are considered as opportunistic pathogens in cystic fibrosis (CF) and are able to persistently colonize the CF respiratory tract (CFRT). Beside Pseudomonas aeruginosa and Burkholderia cepacia complex, Pandoraea spp. are defined as pathogenic. During chronic colonization, adaptive evolution and diversified population have been demonstrated, notably for P. aeruginosa. However, the persistence of Pandoraea in the CFRT remains largely unexplored. We studied genomic and phenotypic traits of Pandoraea pulmonicola isolates successively recovered from the airways of a single CF patient and relate the results to qualitative and quantitative evolution of other cultivable pathogens and to patient clinical status. A total of 31 isolates recovered from 18 sputum samples over a 7-year period in a single CF patient were studied. Genome dynamics was assessed by pulsed-field gel electrophoresis, ERIC-PCR fingerprinting and 16S rRNA gene PCR-temporal temperature gel electrophoresis. Phenotypic features included antimicrobial susceptibility, motility, biofilm production, and virulence in Caenorhabditis elegans model. Variability was observed for all the characteristics studied leading to highly diversified patterns (24 patterns) for the 31 clonally related isolates. Some of these modifications, mainly genomic events were concomitantly observed with CFRT microbiota composition shifts and with severe exacerbations. The diversity of P. pulmonicola population studied, observed for isolates recovered from successive samples but also within a sample suggested that existence of a diversified population may represent a patho-adaptive strategy for host persistence in the heterogeneous and fluctuating CFRT environment.

Biochanin A partially restores the activity of ofloxacin and ciprofloxacin against topoisomerase IV mutation-associated fluoroquinolone-resistant Ureaplasma species

PURPOSE

This study aims to investigate the synergistic antimicrobial activity of four phytoalexins in combination with fluoroquinolones against Ureaplasma spp., a genus of cell wall-free bacteria that are intrinsically resistant to many available antibiotics, making treatment inherently difficult.

METHODOLOGY

A total of 22 958 urogenital tract specimens were assessed for Ureaplasma spp. identification and antimicrobial susceptibility. From these, 31 epidemiologically unrelated strains were randomly selected for antimicrobial susceptibility testing to determine the minimum inhibitory concentration (MIC) of four fluoroquinolones and the corresponding quinolone resistance-determining regions (QRDRs). Synergistic effects between fluoroquinolones and four phytoalexins (reserpine, piperine, carvacrol and biochanin A) were evaluated by fractional inhibitory concentration indices (FICIs).

RESULTS

Analysis of the QRDRs suggested a vital role for the mutation of Ser-83→Leu in ParC in fluoroquinolone-resistant strains, and the occurrence of mutations in QRDRs showed significant associations with the breakpoint of levofloxacin. Moreover, diverse synergistic effects of the four phytoalexins with ofloxacin or ciprofloxacin were observed and biochanin A was able to enhance the antimicrobial activity of fluoroquinolones significantly.

CONCLUSION

This is the first report of the antimicrobial activity of biochanin A in combination with fluoroquinolones against a pathogenic mycoplasma, and opens up the possibility of using components of biochanin A as a promising therapeutic option for treating antibiotic-resistant Ureaplasma spp. infections.

Emergence of Salmonella enterica serovar Indiana and California isolates with concurrent resistance to cefotaxime, amikacin and ciprofloxacin from chickens in China

The aim of this study was to investigate the prevalence and characterization of Salmonella concerning the poultry industry in China. A total of 170 non-duplicate Salmonella isolates were recovered from the 1540 chicken samples. Among the Salmonella isolates from chickens, the predominant serovars were S. enterica serovar Enteritidis (S. Enteritidis) (49/170, 28.8%), S. enterica serovar Indiana (S. Indiana) (37/170, 21.8%) and S. enterica serovar California (S. California) (34/170, 20.0%). High antimicrobial resistance was observed for ciprofloxacin (68.2%), amikacin (48.2%) and cefotaxime (44.7%). Of particular concerns were the 18 S. Indiana and 17 S. California isolates, which were concurrently resistant to cefotaxime, amikacin and ciprofloxacin. The bla_CTX-M genes, 16S rRNA methylase genes (armA, rmtD or rmtC) and five plasmid-mediated quinolone resistance (PMQR) determinants (aac(6')-Ib-cr, oqxAB, qnrB, qepA and qnrD) were identified in 18 S. Indiana and 17 S. California isolates. To clarify their genetic correlation, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were further conducted. PFGE profiles showed that the majority of S. Indiana and S. California isolates were clonally unrelated with a standard cut-off of 85%. The results of MLST demonstrated that ST17 and ST40 were the most common ST types in S. Indiana and S. California isolates, respectively. Our findings indicated that the multiple antibiotic resistant S. Indiana and S. California isolates were widespread in chicken in China and might pose a potential threat to public health.

The role of ATP pools in persister cell formation in (fluoro)quinolone-susceptible and -resistant strains of Salmonella enterica ser. Typhimurium

In this study, we investigated the reported dependence on the ATP pools for persister cell formation in fluoroquinolone-resistant variants of the facultative intracellular pathogen Salmonella enterica serovar Typhimurium. We compared the generation of persister cell populations after ciprofloxacin challenge of wildtype and a nalidixic acid-resistant variant of S. Typhimurium with reduced ciprofloxacin-susceptibility, as well as strains containing a deletion of the atp operon or harbouring the cloned atp genes. A gyrA mutation (D87Y) was found to contribute to increased stationary phase formation of persister cells in S. Typhimurium. However, in contrast to expectations from prior studies, while treatment with the ATP synthase poison arsenate showed the expected increase in persister cells surviving ciprofloxacin treatment, a more direct approach using a strain of Salmonella deleted for the atp operon showed severe reductions in persister cell formation. Persister cell formation was recovered after introduction of the cloned atp operon which restored the reduced ATP levels. These results suggest either an alternative explanation for previous studies, or that persister cell formation in Salmonella is differently regulated.

Subproteomic signature comparison of in vitro selected fluoroquinolone resistance and ciprofloxacin stress in Salmonella Typhimurium DT104B

BACKGROUND

Fluoroquinolone resistance in nontyphoidal Salmonella is a situation of serious and international concern, particularly in S. Typhimurium DT104B multiresistant strains. Although known to be multifactorial, fluoroquinolone resistance is still far from a complete understanding.

METHODS

Subproteome changes between an experimentally selected fluoroquinolone-resistant strain (Se6-M) and its parent strain (Se6), and also in Se6-M under ciprofloxacin (CIP) stress, were evaluated in order to give new insights into the mechanisms involved. Proteomes were compared at the intracellular and membrane levels by a 2-DE~LC-MS/MS and a shotgun LC-MS/MS approach, respectively.

RESULTS

In total, 35 differentially abundant proteins were identified when comparing Se6 with Se6-M (25 more abundant in Se6 and 10 more abundant in Se6-M) and 82 were identified between Se6-M and Se6-M+CIP (51 more abundant in Se6-M and 31 more abundant under ciprofloxacin stress).

CONCLUSION

Several proteins with known and possible roles in quinolone resistance were identified which provide important information about mechanism-related differential protein expression, supporting the current knowledge and also leading to new testable hypotheses on the mechanism of action of fluoroquinolone drugs.

Microbial Shifts in the Intestinal Microbiota of Salmonella Infected Chickens in Response to Enrofloxacin

Fluoroquinolones (FQs) are important antibiotics used for treatment of Salmonella infection in poultry in many countries. However, oral administration of fluoroquinolones may affect the composition and abundance of a number of bacterial taxa in the chicken intestine. Using 16S rRNA gene sequencing, the microbial shifts in the gut of Salmonella infected chickens in response to enrofloxacin treatments at different dosages (0, 0.1, 4, and 100 mg/kg b.w.) were quantitatively evaluated. The results showed that the shedding levels of Salmonella were significantly reduced in the high dosage group as demonstrated by both the culturing method and 16S rRNA sequencing method. The average values of diversity indices were higher in the control group than in the three medicated groups. Non-metric multidimensional scaling (NMDS) analysis results showed that the microbial community of high dosage group was clearly separated from the other three groups. In total, 25 genera were significantly enriched (including 6 abundant genera: Lactococcus, Bacillus, Burkholderia, Pseudomonas, Rhizobium, and Acinetobacter) and 23 genera were significantly reduced in the medicated groups than in the control group for the treatment period, but these bacterial taxa recovered to normal levels after therapy withdrawal. Additionally, 5 genera were significantly reduced in both treatment and withdrawal periods (e.g., Blautia and Anaerotruncus) and 23 genera (e.g., Enterobacter and Clostridium) were significantly decreased only in the withdrawal period, indicating that these genera might be the potential targets for the fluoroquinolones antimicrobial effects. Specially, Enterococcus was significantly reduced under high dosage of enrofloxacin treatment, while significantly enriched in the withdrawal period, which was presumably due to the resistance selection. Predicted microbial functions associated with genetic information processing were significantly decreased in the high dosage group. Overall, enrofloxacin at a dosage of 100 mg/kg b.w. significantly altered the microbial community membership and structure, and microbial functions in the chicken intestine during the medication. This study fully investigates the chicken intestinal microbiota in response to enrofloxacin treatment and identifies potential targets against which the fluoroquinolones may have potent antimicrobial effects. These results provide insights into the effects of the usage of enrofloxacin on chicken and will aid in the prudent and rational use of antibiotics in poultry industry.

Computational discovery and functional validation of novel fluoroquinolone resistance genes in public metagenomic data sets

BACKGROUND

Fluoroquinolones are broad-spectrum antibiotics used to prevent and treat a wide range of bacterial infections. Plasmid-mediated qnr genes provide resistance to fluoroquinolones in many bacterial species and are increasingly encountered in clinical settings. Over the last decade, several families of qnr genes have been discovered and characterized, but their true prevalence and diversity still remain unclear. In particular, environmental and host-associated bacterial communities have been hypothesized to maintain a large and unknown collection of qnr genes that could be mobilized into pathogens.

RESULTS

In this study we used computational methods to screen genomes and metagenomes for novel qnr genes. In contrast to previous studies, we analyzed an almost 20-fold larger dataset comprising almost 13 terabases of sequence data. In total, 362,843 potential qnr gene fragments were identified, from which 611 putative qnr genes were reconstructed. These gene sequences included all previously described plasmid-mediated qnr gene families. Fifty-two of the 611 identified qnr genes were reconstructed from metagenomes, and 20 of these were previously undescribed. All of the novel qnr genes were assembled from metagenomes associated with aquatic environments. Nine of the novel genes were selected for validation, and six of the tested genes conferred consistently decreased susceptibility to ciprofloxacin when expressed in Escherichia coli.

CONCLUSIONS

The results presented in this study provide additional evidence for the ubiquitous presence of qnr genes in environmental microbial communities, expand the number of known qnr gene variants and further elucidate the diversity of this class of resistance genes. This study also strengthens the hypothesis that environmental bacterial communities act as sources of previously uncharacterized qnr genes.

Interplay of the Quality of Ciprofloxacin and Antibiotic Resistance in Developing Countries

Ciprofloxacin, a second generation broad spectrum fluoroquinolone, is active against both Gram-positive and Gram-negative bacteria. Ciprofloxacin has a high oral bioavailability and a large volume of distribution. It is used for the treatment of a wide range of infections including urinary tract infections caused by susceptible bacteria. However, the availability and use of substandard and spurious quality of oral ciprofloxacin formulations in the developing countries has been thought to have contributed toward increased risk of treatment failure and bacterial resistance. Therefore, quality control and bioequivalence studies of the commercially available oral ciprofloxacin formulations should be monitored. Appropriate actions should be taken against offending manufacturers in order to prevent the sale of substandard and spurious quality of ciprofloxacin formulations.

Drug-resistant gram-negative uropathogens: A review

Urinary tract infection(UTI) caused by Gram-negative bacteria is the second most common infectious presentation in community medical practice. Approximately 150 million people are diagnosed with UTI each year worldwide. Drug resistance in Gram-negative uropathogens is a major global concern which can lead to poor clinical outcomes including treatment failure, development of bacteremia, requirement for intravenous therapy, hospitalization, and extended length of hospital stay. The mechanisms of drug resistance in these bacteria are important due to they are often not identified by routine susceptibility tests and have an exceptional potential for outbreaks. Treatment of UTIs depends on the access to effective drugs, which is now threatened by antibiotic resistant Gram-negative uropathogens. Although several effective antibiotics with activity against highly resistant Gram-negatives are available, there is not a unique antibiotic with activity against the high variety of resistance. Therefore, antimicrobial susceptibility tests, correlation between clinicians and laboratories, development of more rapid diagnostic methods, and continuous monitoring of drug resistance are urgent priorities. In this review, we will discuss about the current global status of drug-resistant Gram-negative uropathogens and their mechanisms of drug resistance to provide new insights into their treatment options.

Recreational sandboxes for children and dogs can be a source of epidemic ribotypes of Clostridium difficile

Different studies have suggested that the sand of public playgrounds could have a role in the transmission of infections, particularly in children. Furthermore, free access of pets and other animals to the playgrounds might increase such a risk. We studied the presence of Clostridium difficile in 20 pairs of sandboxes for children and dogs located in different playgrounds within the Madrid region (Spain). Clostridium difficile isolation was performed by enrichment and selective culture procedures. The genetic (ribotype and amplified fragment length polymorphism [AFLP]) diversity and antibiotic susceptibility of isolates was also studied. Overall, 52.5% (21/40) of samples were positive for the presence of C. difficile. Eight of the 20 available isolates belonged to the toxigenic ribotypes 014 (n = 5) and 106 (n = 2), both regarded as epidemic, and CD047 (n = 1). The other 12 isolates were non-toxigenic, and belonged to ribotypes 009 (n = 5), 039 (n = 4), and 067, 151 and CD048 (one isolate each). Nevertheless, all isolates (even those of a same ribotype) were classified into different AFLP genotypes indicating non-relatedness. In conclusion, our results revealed the presence of epidemic ribotypes of C. difficile in children's and dog's sandboxes located nearby, which constitutes a major health risk.

In vitro and in vivo evaluation of fluoroquinolone resistance associated with DNA gyrase mutations in Francisella tularensis, including in tularaemia patients with treatment failure

Fluoroquinolones (FQs) are highly effective for treating tularaemia, a zoonosis caused by Francisella tularensis, but failures and relapses remain common in patients with treatment delay or immunocompromised status. FQ-resistant strains of F. tularensis harboring mutations in the quinolone-resistance determining region (QRDR) of gyrA and gyrB, the genes encoding subunits A and B of DNA gyrase, have been selected in vitro. Such mutants have never been isolated from humans as this microorganism is difficult to culture. In this study, the presence of FQ-resistant mutants of F. tularensis was assessed in tularaemia patients using combined culture- and PCR-based approaches. We analyzed 42 F. tularensis strains and 82 tissue samples collected from 104 tularaemia cases, including 32 (30.7%) with FQ treatment failure or relapse. Forty F. tularensis strains and 55 clinical samples were obtained before any FQ treatment, while 2 strains and 15 tissue samples were collected after treatment. FQ resistance was evaluated by the minimum inhibitory concentration (MIC) for the bacterial strains, and by newly developed PCR-based methods targeting the gyrA and gyrB QRDRs for both the bacterial strains and the clinical samples. None of the F. tularensis strains displayed an increased MIC compared with FQ-susceptible controls. Neither gyrA nor gyrB QRDR mutation was found in bacterial strains and tissue samples tested, including those from patients with FQ treatment failure or relapse. Further phenotypic and genetic resistance traits should be explored to explain the poor clinical response to FQ treatment in such tularaemia patients.

Antibiotic use and microbiome function

Our microbiome should be understood as one of the most complex components of the human body. The use of β-lactam antibiotics is one of the microbiome covariates that influence its composition. The extent to which our microbiota changes after an antibiotic intervention depends not only on the chemical nature of the antibiotic or cocktail of antibiotics used to treat specific infections, but also on the type of administration, duration and dose, as well as the level of resistance that each microbiota develops. We have begun to appreciate that not all bacteria within our microbiota are vulnerable or reactive to different antibiotic interventions, and that their influence on both microbial composition and metabolism may differ. Antibiotics are being used worldwide on a huge scale and the prescription of antibiotics is continuing to rise; however, their effects on our microbiota have been reported for only a limited number of them. This article presents a critical review of the antibiotics or antibiotic cocktails whose use in humans has been linked to changes in the composition of our microbial communities, with a particular focus on the gut, oral, respiratory, skin and vaginal microbiota, and on their molecular agents (genes, proteins and metabolites). We review the state of the art as of June 2016, and cover a total of circa 68 different antibiotics. The data herein are the first to compile information about the bacteria, fungi, archaea and viruses most influenced by the main antibiotic treatments prescribed nowadays.

Mounting resistance of uropathogens to antimicrobial agents: A retrospective study in patients with chronic bacterial prostatitis relapse

Purpose

Despite recent progress in the management of chronic bacterial prostatitis (CBP), many cases relapse. Increased drug resistance patterns of responsible bacteria have been proposed as the most probable causative factor. Driven by the limited number of previous studies addressing this topic, we aimed to study whether antibiotic resistance increases in patients with CBP when relapse occurs. A secondary aim of this study was to determine the resistance patterns of responsible bacteria from patients with CBP.

Materials and Methods

The study material consisted of bacterial isolates from urine and/or prostatic secretions obtained from patients with CBP. Bacterial identification was performed by using the Vitek 2 Compact system and susceptibility testing was performed by disc diffusion and/or the Vitek 2 system. Interpretation of susceptibility results was based on Clinical and Laboratory Standards Institute guidelines.

Results

A total of 253 samples from patients diagnosed with CBP for the first time (group A) and 137 samples from relapsing patients with a history of CBP and previous antibiotic treatment (group B) were analyzed. A significant reduction in bacterial resistance to the less used antibiotics (TMP-SMX, tetracyclines, aminoglycosides, penicillins, and macrolides) was noted. An increase in resistance to quinolones of many bacteria that cause CBP was also noted with the increase in resistance of enterococcus strains being alarming.

Conclusions

Comparison of the resistance profile of CBP-responsible bacteria between samples from first-time-diagnosed patients and samples from relapsing patients revealed notable differences that could be attributed to previous antibiotic treatment.

Exposure to sub-inhibitory concentrations of gentamicin, ciprofloxacin and cefotaxime induces multidrug resistance and reactive oxygen species generation in meticillin-sensitive Staphylococcus aureus

PURPOSE

The role of antibiotics below their MIC in the development of bacterial drug resistance is becoming increasingly important. We investigated the effect of sub-MICs of bactericidal antibiotics on the susceptibility pattern of Staphylococcus aureus and evaluated the role of free radicals.

METHODOLOGY

A total of 12 S. aureus strains were recovered from pus samples and their antibiograms determined. The test isolates were treated with sub-MIC levels of tetracycline, gentamicin, ciprofloxacin and cefotaxime. Alterations in their respective breakpoints were observed along with measurements of free radical generation by nitro blue tetrazolium test.Results/Key findings. Gentamicin, ciprofloxacin and cefotaxime exposure significantly altered the breakpoints of exposed isolates against several tested antibiotics and higher levels of free radicals were generated after antibiotic exposure.

CONCLUSIONS

Our study demonstrates that sub-MIC levels of antimicrobials can lead to resistance and cross-resistance across several classes of antibiotics in wild strains of S. aureus, possibly by free radical production. The molecular mechanisms behind the acquisition of drug resistance at low antibiotic concentrations and the specific target genes of reactive oxygen speciesneed to be explored further.

In vitro emergence of fluoroquinolone resistance in Cutibacterium (formerly Propionibacterium) acnes and molecular characterization of mutations in the gyrA gene

In vitro occurrence of levofloxacin (LVX) resistance in C. acnes and characterization of its molecular background were investigated. The mutation frequency was determined by inoculation of 10⁸ cfu of C. acnes ATCC 11827 (LVX MIC = 0.25 mg/L) on LVX-containing agar plates. The progressive emergence of resistance was studied by a second exposure to increasing LVX concentrations. For mutants, the QRDR regions including the gyrA and parC genes were sequenced and compared to both C. acnes ATCC 11827 and C. acnes KPA171202 reference sequences (NC006085). The importance of the efflux pump system in resistance was investigated by using inhibitors on selected resistant mutants with no mutation in the QRDR. C. acnes growth was observed on LVX-containing plates with mutation frequencies of 3. 8 cfu × 10^-8 (8 × MIC) and 1.6 cfu × 10^-7 (4 × MIC). LVX resistance emerged progressively after one-step or two-step assays. In LVX-resistant isolates, the MIC ranged from 0.75 to >32 mg/L. Mutations were detected exclusively in the gyrA gene. Ten genotypes were identified: G99 C, G99 D, D100N, D100 H, D100 G, S101L, S101W, A102 P, D105 H and A105 G. Mutants S101L and S101W were always associated with a high level of resistance. Mutants with no mutation in the QRDR were more susceptible when incubated with an efflux pump inhibitor (phenyl-arginine β-naphthylamide) only, suggesting, for the first time, the expression of such a system in C. acnes LVX-resistant mutants.

Novel 3-fluoro-6-methoxyquinoline derivatives as inhibitors of bacterial DNA gyrase and topoisomerase IV

Novel (non-fluoroquinolone) inhibitors of bacterial type II topoisomerases (NBTIs) are an emerging class of antibacterial agents. We report an optimized series of cyclobutylaryl-substituted NBTIs. Compound 14 demonstrated excellent activity both in vitro (S. aureus MIC₉₀=0.125μg/mL) and in vivo (systemic and tissue infections). Enhanced inhibition of Topoisomerase IV correlated with improved activity in S. aureus strains with mutations conferring resistance to NBTIs. Compound 14 also displayed an improved hERG IC₅₀ of 85.9μM and a favorable profile in the anesthetized guinea pig model.

Comparative subproteomic analysis of clinically acquired fluoroquinolone resistance and ciprofloxacin stress in Salmonella Typhimurium DT104B

PURPOSE

Antimicrobial resistance is a worldwide public health threat and Salmonella enterica subsp. enterica serotype Typhimurium phage type DT104B multiresistant strains with additional quinolone resistance have been responsible for global outbreaks and high mortality. Quinolone resistance is known to be multifactorial but is still far from a complete understanding. To give new insights about the resistance mechanisms involved, this work aimed to evaluate subproteome changes between an S. Typhimurium DT104B clinical strain that acquired fluoroquinolone resistance after treatment (Se20) and its pretreatment parental strain (Se6), and also subproteome variations in Se20 under ciprofloxacin (CIP) stress (Se20+CIP).

EXPERIMENTAL DESIGN

The proteomes were compared at the intracellular and membrane levels by a 2-DE∼LC-MS/MS and a shotgun LC-MS/MS approach, respectively.

RESULTS

In total, 14 differentially abundant proteins were identified when comparing Se6 with Se20 and 91 were identified between Se20 and Se20+CIP. Several proteins with known and possible roles in quinolone resistance (AAC(6')-Ib-cr4, OmpD, OmpX, GlmS, GlmU, H-NS, etc.) were identified and discussed.

CONCLUSIONS AND CLINICAL RELEVANCE

The great number of proteins identified in this study provides important information about mechanism-related differential protein expression which supports the current knowledge and might lead to new testable hypotheses on the mechanism of action of fluoroquinolone drugs.

Mechanisms of resistance to quinolones in Salmonella Typhimurium from patients with infectious diarrhea

This study investigated the mechanisms of resistance of 36 quinolone-resistant Salmonella Typhimurium strains isolated from outpatients with infectious diarrhea in Beijing Tian Tan Hospital between 2013 and 2015. The resistance spectrum of the 36 strains was measured using a broth dilution method. Class 1 integrons harboring the β-lactamase gene and mutations in quinolone resistance determining regions were also investigated. All 36 quinolone-resistant Salmonella Typhimurium strains were found to be multidrug-resistant and the majority of these strains harbored Class 1 integrons. These findings study suggests that strategies for determining resistance spectrums should be implemented with greater urgency.

Pharmacophore generation, atom-based 3D-QSAR and molecular dynamics simulation analyses of pyridine-3-carboxamide-6-yl-urea analogues as potential gyrase B inhibitors

DNA gyrase subunit B (GyrB) is an attractive drug target for the development of antibacterial agents with therapeutic potential. In the present study, computational studies based on pharmacophore modelling, atom-based QSAR, molecular docking, free binding energy calculation and dynamics simulation were performed on a series of pyridine-3-carboxamide-6-yl-urea derivatives. A pharmacophore model using 49 molecules revealed structural and chemical features necessary for these molecules to inhibit GyrB. The best fitted model AADDR.13 was generated with a coefficient of determination (r²) of 0.918. This model was validated using test set molecules and had a good r² of 0.78. 3D contour maps generated by the 3D atom-based QSAR revealed the key structural features responsible for the GyrB inhibitory activity. Extra precision molecular docking showed hydrogen bond interactions with key amino acid residues of ATP-binding pocket, important for inhibitor binding. Further, binding free energy was calculated by the MM-GBSA rescoring approach to validate the binding affinity. A 10 ns MD simulation of inhibitor #47 showed the stability of the predicted binding conformations. We identified 10 virtual hits by in silico high-throughput screening. A few new molecules were also designed as potent GyrB inhibitors. The information obtained from these methodologies may be helpful to design novel inhibitors of GyrB.

Ecotoxicity of veterinary enrofloxacin and ciprofloxacin antibiotics on anuran amphibian larvae

The ecological risks posed by two β-diketone antibiotics (DKAs, enrofloxacin, ENR and ciprofloxacin, CPX), characterized by their long persistence in aqueous environments and known deleterious effect on model organisms such as zebrafish were analysed using Rhinella arenarum larvae. Sublethal tests were conducted using environmentally relevant concentrations of both ENR and CPX (1-1000μgL^-1) under standard laboratory conditions for 96h. Biological endpoints and biomarkers evaluated were body size, shape, development and growth rates, and antioxidant enzymes (glutathione-S-transferase, GST; Catalase, CAT). Risk assessment was analysed based on ration quotients (RQ). The size and shape measurements of the larvae exposed to concentrations greater than 10μgL^-1 of CPX were lower compared to controls (Dunnett post hoc p<0.05) and presented signs of emaciation. Concentrations of 1000μgL^-1of CPX induced GST activity, in contrast with inhibited GST and CAT of larvae exposed to ENR. Risk assessments indicated that concentrations greater than or equal to10μgL^-1 of CPX and ENR are ecotoxic for development, growth, detoxifying, and oxidative stress enzymes. It is suggested that additional risk assessments may provide evidence of bioaccumulation of CPX and ENR in tissues or organs of amphibian larvae by mesocosm sediment test conditions. Finally, intestinal microbiome studies should be considered to establish the mechanisms of action of both antibiotics.