Resistance studies with Streptococcus pneumoniae using an in vitro dynamic model: amoxicillin versus azithromycin at clinical exposures

Inhibitory Mechanisms of Lekethromycin in Dog Liver Cytochrome P450 Enzymes Based on UPLC-MS/MS Cocktail Method

Lekethromycin (LKMS) is a synthetic macrolide compound derivative intended for use as a veterinary medicine. Since there have been no in vitro studies evaluating its potential for drug-drug interactions related to cytochrome P450 (CYP450) enzymes, the effect of the inhibitory mechanisms of LKMS on CYP450 enzymes is still unclear. Thus, this study aimed to evaluate the inhibitory effects of LKMS on dog CYP450 enzymes. A cocktail approach using ultra-performance liquid chromatography-tandem mass spectrometry was conducted to investigate the inhibitory effect of LKMS on canine CYP450 enzymes. Typical probe substrates of phenacetin, coumarin, bupropion, tolbutamide, dextromethorphan, chlorzoxazone, and testosterone were used for CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, CYP2E1, and CYP3A4, respectively. This study showed that LKMS might not be a time-dependent inhibitor. LKMS inhibited CYP2A6, CYP2B6, and CYP2D6 via mixed inhibition. LKMS exhibited mixed-type inhibition against the activity of CYP2A6 with an inhibition constant (Ki) value of 135.6 μΜ. LKMS inhibited CYP2B6 in a mixed way, with Ki values of 59.44 μM. A phenotyping study based on an inhibition assay indicated that CYP2D6 contributes to the biotransformation of LKMS. A mixed inhibition of CYP2D6 with Ki values of 64.87 μM was also observed. Given that this study was performed in vitro, further in vivo studies should be conducted to identify the interaction between LKMS and canine CYP450 enzymes to provide data support for the clinical application of LKMS and the avoidance of adverse interactions between other drugs.

Gaps in the wall: understanding cell wall biology to tackle amoxicillin resistance in Streptococcus pneumoniae

Streptococcus pneumoniae is the most common cause of community-acquired pneumonia, and one of the main pathogens responsible for otitis media infections in children. Amoxicillin (AMX) is a broad-spectrum β-lactam antibiotic, used frequently for the treatment of bacterial respiratory tract infections. Here, we discuss the pneumococcal response to AMX, including the mode of action of AMX, the effects on autolysin regulation, and the evolution of resistance through natural transformation. We discuss current knowledge gaps in the synthesis and translocation of peptidoglycan and teichoic acids, major constituents of the pneumococcal cell wall and critical to AMX activity. Furthermore, an outlook of AMX resistance research is presented, including the development of natural competence inhibitors to block evolution via horizontal gene transfer, and the use of high-throughput essentiality screens for the discovery of novel cotherapeutics.

Trial-of-antibiotics to assist tuberculosis diagnosis in symptomatic adults in Malawi (ACT-TB study): a randomised controlled trial

BACKGROUND

Clinical practice and diagnostic algorithms often assume that tuberculosis can be ruled out in mycobacteriology-negative individuals whose symptoms improve with a trial-of-antibiotics. We aimed to investigate diagnostic performance, clinical benefit, and antimicrobial resistance using a randomised controlled trial.

METHODS

In this three-arm, individually randomised, open-label, controlled trial, we enrolled Malawian adults (aged ≥18 years) attending primary care who reported being unwell for at least 14 days (including cough) with no immediate indication for hospitalisation at Limbe and Ndirande Health Centres in Blantyre. Participants were randomly allocated (1:1:1) to azithromycin (500 mg taken once per day for 3 days), amoxicillin (1 g taken three times per day for 5 days), or standard of care with no immediate antibiotics, stratified by study site. Sputum at enrolment and day 8 was tested for tuberculosis (microscopy, Xpert MTB/RIF, and culture). The primary efficacy outcome was day 8 specificity (percentage with symptom improvement among mycobacteriology-negative participants), and day 29 clinical outcome (death, hospitalisation, or missed tuberculosis diagnosis) among all randomised participants. This study is registered with ClinicalTrials.gov, NCT03545373.

FINDINGS

Between Feb 25, 2019, and March 14, 2020, 5825 adults were screened and 1583 (mean age 36 years; 236 [14·9%] HIV positive) were randomly assigned to standard of care (530 participants), azithromycin (527 participants), or amoxicillin (526 participants) groups. Overall, 6·3% (100 of 1583 participants) had positive baseline sputum mycobacteriology. 310 (79·1%) of 392 patients receiving standard of care reported symptom improvement at day 8, compared with 340 (88·7%) of 383 patients receiving azithromycin (adjusted difference 8·6%, 95% CI 3·9-13·3%; p<0·0004) and 346 (89·4%) of 387 receiving amoxicillin (adjusted difference 8·8%, 4·0-13·6%; p=0·0003). The proportion of participants with day 29 composite clinical outcomes was similar between groups (standard of care 1% [7 of 530 participants], azithromycin 1% [6 of 527 participants], amoxicillin 2% [12 of 526 participants]).

INTERPRETATION

Routine outpatient trial-of-antibiotics during tuberculosis investigations modestly improved diagnostic specificity for mycobacteriologically confirmed tuberculosis but had no appreciable effect on death, hospitalisation, and missed tuberculosis diagnosis. These results confirm the limited benefit of trial-of-antibiotics, presenting an opportunity for discontinuation of trial-of-antibiotics and improved antimicrobial stewardship during tuberculosis screening, without affecting clinical outcomes.

FUNDING

Northern Norway Regional Health Authority (Helse Nord RHF), Commonwealth Scholarship Commission in the UK, Wellcome Trust, UK Medical Research Council, and the UK Department for International Development.

In vitro evaluation of antimicrobial resistance selection in Neisseria gonorrhoeae

Gonococcal infections represent an urgent public-health threat as >50% of cases caused by Neisseria gonorrhoeae strains display reduced susceptibility to at least one antimicrobial agent. We evaluated the pharmacodynamics of a number of antimicrobials against N. gonorrhoeae in order to assess the likelihood of mutant selection by these agents. The mutant prevention concentration (MPC) and mutant selection window (MSW) were determined for azithromycin, ceftriaxone, doxycycline, ertapenem, gentamicin, ciprofloxacin, levofloxacin and moxifloxacin against a wild-type strain of N. gonorrhoeae (ATCC 49226) and a gyrA mutant of ATCC 49226. Pharmacokinetic parameters, including peak concentration (C_max), half-life (t_1/2) and area under the plasma concentration-time curve over 24 h (AUC), associated with each agent were used to calculate the time within the MSW (T_MSW, percentage of the dosing interval that antimicrobial concentrations fall within the MSW), C_max/MPC ratio and AUC/MPC ratio for each antimicrobial agent. Concentrations of ceftriaxone (500 mg), ertapenem, ciprofloxacin, levofloxacin and moxifloxacin surpass the MPC for both strains. Results of pharmacodynamic analyses suggest that ertapenem, ciprofloxacin, levofloxacin and moxifloxacin may be most likely to prevent mutant selection in N. gonorrhoeae. Use of ceftriaxone, azithromycin, doxycycline or gentamicin for gonorrhoea is expected to lead to the ongoing emergence of resistance to these agents. There is a clear need to develop novel treatment regimens for gonococcal infections in order to limit the dissemination of resistance in N. gonorrhoeae.

A Review: Effects of Macrolides on CYP450 Enzymes

As a kind of haemoglobin, cytochrome P450 enzymes (CYP450) participate in the metabolism of many substances, including endogenous substances, exogenous substances and drugs. It is estimated that 60% of common prescription drugs require bioconversion through CYP450. The influence of macrolides on CYP450 contributes to the metabolism and drug-drug interactions (DDIs) of macrolides. At present, most studies on the effects of macrolides on CYP450 are focused on CYP3A, but a few exist on other enzymes and drug combinations, such as telithromycin, which can decrease the activity of hepatic CYP1A2 and CYP3A2. This article summarizes some published applications of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. And the article may subsequently guide the rational use of drugs in clinical trials. To a certain extent, poisoning caused by adverse drug interactions can be avoided. Unreasonable use of macrolide antibiotics may enable the presence of residue of macrolide antibiotics in animal-origin food. It is unhealthy for people to eat food with macrolide antibiotic residues. So it is of great significance to guarantee food safety and protect the health of consumers by the rational use of macrolides. This review gives a detailed description of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. Moreover, it offers a perspective for researchers to further explore in this area.

In Vitro and In Vivo Comparison of Changes in Antibiotics Susceptibility of E. coli and Chicken's Intestinal Flora after Exposure to Amoxicillin or Thymol

This study aims at verifying, in vitro, the extent to which the use of amoxicillin or thymol induces the selection of resistant bacteria and at evaluating in vivo their effects on the development of antimicrobial resistance in the intestinal flora of poultry. E. coli strain was subcultured on agar plates containing increasing concentrations of either amoxicillin or thymol. Thereafter, minimal inhibitory concentrations (MICs) of thymol, amoxicillin, and two other antibiotics, tylosin and colistin, were determined using the microdilution method. Groups of chicks were subjected to a 2-week regime of either amoxicillin or thymol added to their drinking water. During the treatment with either thymol or amoxicillin, the total aerobic mesophilic flora (TAMF) was counted on thymol-gradient plates or amoxicillin-gradient plates and the MICs of antibiotics and thymol for E. coli isolates were determined. The in vitro test showed that for E. coli, which had been serially subcultured on increasing concentrations of amoxicillin, a 32-fold increase in MIC values for amoxicillin and a 4-fold increase for colistin and tylosin were noted. However, the MIC of thymol for this strain remained constant. For the E. coli, which had been serially subcultured on increasing concentrations of thymol, no change in the MIC values for antibiotics and thymol was observed. The in vivo test confirmed the in vitro one. It demonstrated that exposure to amoxicillin induced a selection of antimicrobial resistance in TAMF and intestinal E. coli, whereas exposure to thymol did not. The results showed that the group receiving thymol had a lower consumption index compared to the other groups. This study demonstrates the feasibility of this natural product as an alternative solution to the current use of antibiotics in poultry farming.