Selected Mutations by Nemonoxacin and Fluoroquinolone Exposure Among Relevant Gram-Positive Bacterial Strains in Taiwan

Comparative In vitro antibacterial activity of nemonoxacin and other fluoroquinolones in correlation with resistant mechanisms in contemporary methicillin-resistant Staphylococcus aureus blood isolates in Taiwan

BACKGROUND

Nemonoxacin is a new quinolone with an antibacterial efficacy against methicillin-resistant Staphylococcus aureus (MRSA). Certain sequence types (STs) have been emerging in Taiwan, including fluoroquinolone-resistant ST8/USA300. It's an urgent need to determine nemonoxacin susceptibility against ST8/USA300 and other emerging lineages, if any. Additionally, molecular characterization of nemonoxacin resistance among different lineages has yet to be defined.

METHODS

Non-duplicated MRSA blood isolates from five hospitals during 2019-2020 were collected and genotyped by pulsed-field gel electrophoresis, and further correlated to their STs. Antimicrobial susceptibility testing for all antibiotics was performing by using Sensititre standard panel, except nemonoxacin by using agar dilution method. Selected isolates with nemonoxacin MICs ≥ 0.5 mg/mL were sequenced for quinolone resistance-determining regions (QRDRs).

RESULTS

Overall, 915 MRSA isolates belonged to four major lineages, ST8 (34.2%), ST59 (23.5%), ST239 (13.9%), and clonal complex 45 (13.7%). Two-thirds of tested isolates were non-susceptible to moxifloxacin, especially ST8/USA300 and ST239. Of them, proportions of nemonoxacin non-susceptibility by a tentative clinical breakpoint (tCBP) of 1 µg/mL among four major lineages appeared to be different (P = 0.06) and highest in ST239 (22.2%), followed by ST8/USA300 (13.5%). Among 89 isolates sequenced, 44.1% of ST8 and all ST239 isolates had ≥ 3 amino acid substitutions (AAS) in gyrA/parC (group A) or 2 AAS in gyrA/parC with additional AAS in gyrB/parE (group B). Compared to other AAS patterns, isolates in group A had the greatest non-susceptible proportions to nemonoxacin (86.9%; overall/pair-wised comparisons, P < 0.05).

CONCLUSIONS

Our study confirmed ST8/USA300 MRSA has disseminated in Taiwan. Using a tCBP defined by a higher parenteral daily dosage, nemonoxacin retained potency against moxifloxacin non-susceptible isolates. Patterns of AAS in QRDRs among different lineages may contribute to difference of nemonoxacin susceptibility.

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

P, Molina CA, Castillejo P. Beta-Lactam Antibiotic Resistance Genes in the Microbiome of the Public Transport System of Quito, Ecuador

Multidrug-resistant bacteria present resistance mechanisms against β-lactam antibiotics, such as Extended-Spectrum Beta-lactamases (ESBL) and Metallo-β-lactamases enzymes (MBLs) which are operon encoded in Gram-negative species. Likewise, Gram-positive bacteria have evolved other mechanisms through mec genes, which encode modified penicillin-binding proteins (PBP2). This study aimed to determine the presence and spread of β-lactam antibiotic resistance genes and the microbiome circulating in Quito's Public Transport (QTP). A total of 29 station turnstiles were swabbed to extract the surface environmental DNA. PCRs were performed to detect the presence of 13 antibiotic resistance genes and to identify and to amplify 16S rDNA for barcoding, followed by clone analysis, Sanger sequencing, and BLAST search. ESBL genes bla_TEM-1 and bla_CTX-M-1 and MBL genes bla_OXA-181 and mecA were detected along QPT stations, blaTEM being the most widely spread. Two subvariants were found for bla_TEM-1, bla_CTX-M-1, and bla_OXA-181. Almost half of the circulating bacteria found at QPT stations were common human microbiota species, including those classified by the WHO as pathogens of critical and high-priority surveillance. β-lactam antibiotic resistance genes are prevalent throughout QPT. This is the first report of bla_OXA-181 in environmental samples in Ecuador. Moreover, we detected a new putative variant of this gene. Some commensal coagulase-negative bacteria may have a role as mecA resistance reservoirs.

Potentiation of the Activity of Antibiotics against ATCC and MDR Bacterial Strains with (+)-α-Pinene and (-)-Borneol

The increasing rates of antimicrobial resistance have demanded the development of new drugs as conventional antibiotics have become significantly less effective. Evidence has identified a variety of phytocompounds with the potential to be used in the combat of infections caused by multidrug-resistant (MDR) bacteria. Considering the verification that terpenes are promising antibacterial compounds, the present research aimed to evaluate the antibacterial and antibiotic-modulating activity of (+)-α-pinene and (-)-borneol against MDR bacterial strains. The broth microdilution method was used to determine the minimum inhibitory concentration (MIC) of the compounds and antibiotics and further evaluate the intrinsic and associated antibiotic activity. These analyses revealed that (+)-α-pinene showed significant antibacterial activity only against E. coli (MIC = 512 μg.mL⁻¹), while no significant inhibition of S. aureus and P. aeruginosa growth was observed (MIC ≥ 1024 μg mL⁻¹). However, when combined with antibiotics, this compound induced a significant improvement in the activity of conventional antibiotics, as observed for ciprofloxacin, amikacin, and gentamicin against Staphylococcus aureus, as well as for amikacin and gentamicin against Escherichia coli, and amikacin against Pseudomonas aeruginosa. On the other hand, (-)-borneol was found to inhibit the growth of E. coli and enhance the antibiotic activity of ciprofloxacin and gentamicin against S. aureus. The present findings indicate that (+)-α-pinene and (-)-borneol are phytocompounds with the potential to be used in the combat of antibacterial resistance.

Nemonoxacin enhances antibacterial activity and anti-resistant mutation ability of vancomycin against methicillin-resistant Staphylococcus aureus in an in vitro dynamic pharmacokinetic/pharmacodynamic model

Reduced susceptibility and emergence of resistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) have led to the development of various vancomycin based combinations. Nemonoxacin is a novel nonfluorinated quinolone with antibacterial activity against MRSA. The present study aimed to investigate the effects of nemonoxacin on antibacterial activity and the anti-resistant mutation ability of vancomycin for MRSA and explore whether quinolone resistance genes are associated with a reduction in the vancomycin minimal inhibitory concentration (MIC) and mutant prevention concentration (MPC) when combined with nemonoxacin. Four isolates, all with a vancomycin MIC of 2 μg/mL, were used in a modified in vitro dynamic pharmacokinetic/pharmacodynamic model to investigate the effects of nemonoxacin on antibacterial activity (M04, M23 and M24) and anti-resistant mutation ability (M04, M23 and M25, all with MPC ≥19.2 μg/mL) of vancomycin. The mutation sites of gyrA, gyrB, parC, and parE of 55 clinical MRSA isolates were sequenced. We observed that in M04 and M23, the combination of vancomycin (1g q12h) and nemonoxacin (0.5g qd) showed a synergistic bactericidal activity and resistance enrichment suppression. All clinical isolates resistant to nemonoxacin harbored gyrA (S84→L) mutation; gyrA (S84→L) and parC (E84→K) mutations were the two independent risk factors for the unchanged vancomycin MPC in combination. Nemonoxacin enhances the bactericidal activity and suppresses resistance enrichment ability of vancomycin against MRSA with a MIC of 2 μg/mL. Our in vitro data support the combination of nemonoxacin and vancomycin for the treatment of MRSA infection with a high MIC.

Tentative clinical breakpoints and epidemiological cut-off values of nemonoxacin for Streptococcus pneumoniae and Staphylococcus aureus isolates associated with community-acquired pneumonia

OBJECTIVES

To determine the minimum inhibitory concentration (MIC) distribution, epidemiological cut-off (ECOFF) values and clinical breakpoints (CBPs) of nemonoxacin, a non-fluorinated quinolone, for community-acquired pneumonia (CAP)-related Streptococcus pneumoniae and Staphylococcus aureus.

METHODS

We pooled the susceptibility and clinical data of CAP patients enrolled in five clinical trials conducted in three countries from 2006 to 2017. Published pharmacokinetic (PK) profiles of oral (500 mg) and intravenous (IV) (500, 650 and 750 mg) nemonoxacin formulations and pharmacodynamic (PD) parameters of the two aforementioned CAP-related Gram-positive cocci (GPC) were used to determine plausible CBPs. Moreover, nemonoxacin MIC distributions of CAP-relatedS. pneumoniae (n = 1800) and S. aureus (n = 2000) isolates were obtained to evaluate ECOFF values using a visual estimation approach and ECOFFinder.

RESULTS

More than 92% of patients with CAP caused byS. pneumoniae or S. aureus with nemonoxacin MICs ≤ 0.25 mg/L presented positive clinical and microbiological outcomes. The ECOFF, MIC₉₀ and MIC₉₉ values of nemonoxacin were, respectively, 0.06, 0.125 and 1 mg/L for S. pneumoniae and 0.125, 1 and 8 mg/L for S. aureus. Based on differences in the PK profiles of oral and IV formulations, PD parameters of nemonoxacin for these CAP-GPC and clinical in vivo efficacy data, tentative CBPs of 0.5, 0.5 and 1 mg/L, respectively, were established for the 500 mg oral and 500 mg and 750 mg IV nemonoxacin formulations for S. pneumoniae, and 0.25, 0.5 and 1 mg/L for S. aureus.

CONCLUSION

This study provides plausible nemonoxacin CBPs for two important CAP-GPC.

Prevalence and Therapies of Antibiotic-Resistance in Staphylococcus aureus

Infectious diseases are the second most important cause of human death worldwide; Staphylococcus aureus (S. aureus) is a very common human pathogenic microorganism that can trigger a variety of infectious diseases, such as skin and soft tissue infections, endocarditis, osteomyelitis, bacteremia, and lethal pneumonia. Moreover, according to the sensitivity to antibiotic drugs, S. aureus can be divided into methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA). In recent decades, due to the evolution of bacteria and the abuse of antibiotics, the drug resistance of S. aureus has gradually increased, the infection rate of MRSA has increased worldwide, and the clinical anti-infective treatment for MRSA has become more difficult. Accumulating evidence has demonstrated that the resistance mechanisms of S. aureus are very complex, especially for MRSA, which is resistant to many kinds of antibiotics. Therefore, understanding the drug resistance of MRSA in a timely manner and elucidating its drug resistance mechanism at the molecular level are of great significance for the treatment of S. aureus infection. A large number of researchers believe that analyzing the molecular characteristics of S. aureus can help provide a basis for designing effective prevention and treatment measures against hospital infections caused by S. aureus and further monitor the evolution of S. aureus. This paper reviews the research status of MSSA and MRSA, the detailed mechanisms of the intrinsic antibiotic resistance and the acquired antibiotic resistance, the advanced research on anti-MRSA antibiotics and novel therapeutic strategies for MRSA treatment.

Prevalence and Therapies of Antibiotic-Resistance in Staphylococcus aureus

Infectious diseases are the second most important cause of human death worldwide; Staphylococcus aureus (S. aureus) is a very common human pathogenic microorganism that can trigger a variety of infectious diseases, such as skin and soft tissue infections, endocarditis, osteomyelitis, bacteremia, and lethal pneumonia. Moreover, according to the sensitivity to antibiotic drugs, S. aureus can be divided into methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA). In recent decades, due to the evolution of bacteria and the abuse of antibiotics, the drug resistance of S. aureus has gradually increased, the infection rate of MRSA has increased worldwide, and the clinical anti-infective treatment for MRSA has become more difficult. Accumulating evidence has demonstrated that the resistance mechanisms of S. aureus are very complex, especially for MRSA, which is resistant to many kinds of antibiotics. Therefore, understanding the drug resistance of MRSA in a timely manner and elucidating its drug resistance mechanism at the molecular level are of great significance for the treatment of S. aureus infection. A large number of researchers believe that analyzing the molecular characteristics of S. aureus can help provide a basis for designing effective prevention and treatment measures against hospital infections caused by S. aureus and further monitor the evolution of S. aureus. This paper reviews the research status of MSSA and MRSA, the detailed mechanisms of the intrinsic antibiotic resistance and the acquired antibiotic resistance, the advanced research on anti-MRSA antibiotics and novel therapeutic strategies for MRSA treatment.