Azithromycin Minimum Inhibitory Concentrations Research Articles

The Effect of Combinations of Antibiotics and Natural Products on the Antimicrobial Resistance of Staphylococcus aureus and Pseudomonas aeruginosa

Introduction/Background The steadily increasing bacterial resistance to existing antimicrobial drugs is a significant issue, hence, it is imperative to look out for new approaches to bacterial therapy Occasionally, effective inhibitory action is not produced when antibiotics are used alone. To overcome this problem, a combination of drugs is often used. One approach to treat infectious diseases is the use of a combination of antibiotics together with plant extracts or phytochemicals. For patients with serious infections caused by pathogens resistant to drugs, combination therapy is beneficial and useful. Materials and Methods Seven antibiotics were obtained from a local pharmacy (gentamicin, ceftazidime, ciprofloxacin, doxycycline, amoxicillin, ceftriaxone, and azithromycin). Minimum inhibitory concentrations (MIC) were determined by broth micro-dilution method, and different antimicrobial combinations were studied on 20 Multidrug-resistant (MDR) clinical isolates (10 S. aureus and 10 P. aeruginosa). Moreover, the antibacterial activity of some volatile oils (limonene, rosemary, salvia, thymus, and black pepper), plant extracts (moringa seed, curcumin, and capsicum), and phytochemicals (thymol, and chitosan) was detected against S. aureus and P. aeruginosa isolates using broth micro-dilution method. Results According to our findings, ceftriaxone and ciprofloxacin or gentamicin together exhibited a substantial synergistic effect against S. aureus. Moreover, the combination of amoxicillin with ceftazidime was synergistic to reduce MIC by five to six times. Regarding MDR clinical isolates of P. aeruginosa, the combination of azithromycin with doxycycline exhibited a decrease of MIC of azithromycin by about five to sixfold. The combination of gentamicin with ceftriaxone was significant. For natural compounds, thymol, rosemary oil, curcumin, capsicum, and moringa seed extract exhibited the highest synergistic activity with the tested antibiotics against S. aureus and P. aeruginosa. Conclusion In conclusion, the lack of new antibiotics necessitates the improvement of existing ones. Our study shows that antibiotic combinations and antibiotic-natural plant combinations are very promising strategies for combating complex bacterial resistance.

Antimicrobial susceptibility testing reveals reduced susceptibility to azithromycin and other antibiotics in Legionella pneumophila serogroup 1 isolates from Portugal.

Although not fully investigated, studies show that Legionella pneumophila can develop antibiotic resistance. As there is limited data available for Portugal, we determined the antibiotic susceptibility profile of Portuguese L. pneumophila serogroup 1 (LpnSg1) isolates against antibiotics used in the clinical practice in Portugal. Minimum inhibitory concentrations (MICs) were determined for LpnSg1 clinical (n = 100) and related environmental (n = 7) isolates, collected between 2006-2022 in the context of the National Legionnaire´s Disease Surveillance Programme, against azithromycin, clarithromycin, erythromycin, levofloxacin, ciprofloxacin, moxifloxacin, rifampicin, doxycycline, tigecycline, and amoxicillin/clavulanic acid, using three different assays. Isolates were also PCR-screened for the presence of the lpeAB gene. Twelve isolates had azithromycin MICs above the EUCAST tentative highest WT MIC, 9 of which were lpeAB negative; for erythromycin and clarithromycin, all isolates tested within the susceptible range. The number of isolates with MICs above the tentative highest WT MIC for the remaining antibiotics was: ciprofloxacin: 7; levofloxacin: 17; moxifloxacin: 8; rifampicin: 11; doxycycline: 82; tigecycline: 4. EUCAST breakpoints are not available for amoxicillin/clavulanic acid. We estimated the ECOFFs and one isolate had a MIC eightfold higher than the E-test ECOFF. Additionally, a clinical isolate generated three colonies growing on the E-test inhibition zone that resulted in MICs fourfold higher than for the parental isolate. We report, for the first time, elevated MICs against first-line and other antibiotics (including azithromycin, fluoroquinolones and amoxicillin/clavulanic acid commonly used to treat pneumonia patients in Portugal) in Portuguese L. pneumophila strains. Results point towards decreased susceptibility in circulating strains, justifying further investigation.

Minimum inhibitory concentrations of azithromycin in clinical isolates of Mycobacterium avium complex in Japan.

The latest guidelines include azithromycin as a preferred regimen for treating Mycobacterium avium complex (MAC) pulmonary disease. However, serially collected susceptibility data on clinical MAC isolates are limited, and no breakpoints have been determined. We investigated the minimum inhibitory concentrations (MICs) of azithromycin and clarithromycin for all MAC strains isolated in 2021 from a single center in Japan, excluding duplicates. The MICs were determined using a panel based on the microbroth dilution method, according to the latest Clinical and Laboratory Standards Institute recommendations. The MICs were determined for 318 MAC strains. Although there was a significant positive correlation between the MICs of azithromycin and clarithromycin, the MICs of azithromycin tended to be higher than those of clarithromycin. Among the cases in which the strains were isolated, 18 patients initiated treatment, including azithromycin treatment, after sample collection. Some patients infected with stains with relatively high azithromycin MICs achieved a microbiological cure with azithromycin-containing regimens. This study revealed a higher MIC distribution for azithromycin than clarithromycin, raising questions about the current practice of estimating azithromycin susceptibility based on the clarithromycin susceptibility test result. However, this was a single-center study that included only a limited number of cases treated with azithromycin. Therefore, further multicenter studies that include a greater number of cases treated with azithromycin are warranted to verify the distribution of azithromycin MICs and examine the correlation between azithromycin MICs and treatment effectiveness.IMPORTANCEThe macrolides serve as key drugs in the treatment of pulmonary Mycobacterium avium complex infection, and the administration of macrolide should be guided by susceptibility test results. Azithromycin is recommended as a preferred choice among macrolides, surpassing clarithromycin; however, drug susceptibility testing is often not conducted, and clarithromycin susceptibility is used as a surrogate. This study represents the first investigation into the minimum inhibitory concentration of azithromycin on a scale of several hundred clinical isolates, revealing an overall tendency for higher minimum inhibitory concentrations compared with clarithromycin. The results raise questions about the appropriateness of using clarithromycin susceptibility test outcomes for determining the administration of azithromycin. This study highlights the need for future discussions on the clinical breakpoints of azithromycin, based on large-scale clinical research correlating azithromycin susceptibility with treatment outcomes.

Novel Knowledge of Macrolide Resistance in Mycoplasma pneumoniae by Azithromycin Exposure.

The rise of macrolide-resistant Mycoplasma pneumoniae (MRMP), marked by point mutations in the 23S rRNA gene, poses a growing global concern since its initial detection in 2001. The prominence of the A2063G mutation during this emergence remains unexplained. This study aimed to clarify the possibility of detecting MRMP from recent clinical macrolide-susceptible M. pneumoniae through exposure to azithromycin (AZM), which has a long half-life and was launched immediately before the first MRMP detection. Six strains isolated from Japanese children in 2019 and reference strain (FH), all belonging to the recent dominant P1 genotype, two, or two subtype, were cultivated in a medium containing slightly higher concentrations than the originated minimum inhibitory concentration (MIC) of AZM and underwent sequencing if they grew. Four out of the seven strains grew after exposure to AZM, and C2617G and C2617A were detected, with no mutation in two strains. After another cultivation and sequencing, two of four strains grew, one was changed from C2617G to A2063G, and the other remained C2617A. The MIC of AZM in A2063G strains was 128 mg/mL; for C2617A, it was 0.0156 mg/mL. This is the first study to detect the strains with A2063G mutation from recent macrolide-susceptible M. pneumoniae using AZM exposure.

Non-pathogenic Neisseria species of the oropharynx as a reservoir of antimicrobial resistance: a cross-sectional study.

Commensal Neisseria species of the oropharynx represent a significant reservoir of antimicrobial resistance determinants that can be transferred to Neisseria gonorrhoeae. This aspect is particularly crucial in 'men having sex with men' (MSM), a key population in which pharyngeal co-colonization by N. gonorrhoeae and non-pathogenic Neisseria species is frequent and associated with the emergence of antimicrobial resistance. Here, we explored the antimicrobial susceptibility of a large panel of non-pathogenic Neisseria species isolated from the oropharynx of two populations: a group of MSM attending a 'sexually transmitted infection' clinic in Bologna (Italy) (n=108) and a group of males representing a 'general population' (n=119). We collected 246 strains, mainly belonging to N. subflava (60%) and N. flavescens (28%) species. Their antimicrobial susceptibility was evaluated assessing the minimum inhibitory concentrations (MICs) for azithromycin, ciprofloxacin, cefotaxime, and ceftriaxone using E-test strips. Overall, commensal Neisseria spp. showed high rates of resistance to azithromycin (90%; median MICs: 4.0 mg/L), and ciprofloxacin (58%; median MICs: 0.12 mg/L), whereas resistance to cephalosporins was far less common (<15%). Neisseria strains from MSM were found to have significantly higher MICs for azithromycin (p=0.0001) and ciprofloxacin (p<0.0001) compared to those from the general population. However, there was no significant difference in cephalosporin MICs between the two groups. The surveillance of the antimicrobial resistance of non-pathogenic Neisseria spp. could be instrumental in predicting the risk of the spread of multi-drug resistant gonorrhea. This information could be an early predictor of an excessive use of antimicrobials, paving the way to innovative screening and prevention policies.

Antimicrobial susceptibilities of Neisseria gonorrhoeae in Canada, 2021.

In Canada, gonorrhea is the second most prevalent bacterial sexually transmitted infection. The Gonococcal Antimicrobial Surveillance Programme (GASP - Canada), a passive surveillance system monitoring antimicrobial resistance in Neisseria gonorrhoeae in Canada since 1985, is the source for this summary of demographics, antimicrobial resistance and N. gonorrhoeae multi-antigen sequence typing (NG-MAST) of gonococcal isolates collected in Canada in 2021. Provincial and territorial public health laboratories submitted N. gonorrhoeae cultures and data to the National Microbiology Laboratory in Winnipeg as part of the surveillance system. The antimicrobial resistance and molecular type of each isolate received were determined. In total, 3,439 N. gonorrhoeae cultures were received from laboratories across Canada in 2021, a 9.9% increase since 2020 (n=3,130). Decreased susceptibility to cefixime increased significantly (p<0.001) in 2021 (1.5%) compared to 2017 (0.6%). No significant change in decreased susceptibility to ceftriaxone was detected between 2017 and 2021 (0.6%) (p>0.001); however, one ceftriaxone-resistant isolate was identified. Azithromycin resistance decreased significantly (p<0.001) in 2021 (7.6%) compared to 2017 (11.7%); however, there was a significant increase (p<0.001) in the proportion of cultures with an azithromycin minimum inhibitory concentration of at least 1 mg/L (2017=22.2% to 2021=28.1%). In 2021, NG-MAST-19875 (15.3%) was the most prevalent sequence type in Canada; 20.3% of isolates with this sequence type were resistant to azithromycin. The spread of antimicrobial-resistant gonorrhea is a significant public health concern. The continued regional and national surveillance of antimicrobial resistance in N. gonorrhoeae is essential in ensuring effective treatment therapies are recommended.

Phenotypic and Genotypic Antimicrobial Susceptibility Testing of Chlamydia trachomatis Isolates from Patients with Persistent or Clinical Treatment Failure in Spain

The aim of this multicentre project (seven hospitals across the Spanish National Health Service) was to study the phenotypic and genotypic susceptibility of C. trachomatis to the main antimicrobials used (macrolides, doxycycline, and quinolones) in isolates from patients with clinical treatment failure in whom reinfection had been ruled out. During 2018–2019, 73 clinical isolates were selected. Sixty-nine clinical specimens were inoculated onto confluent McCoy cell monolayers for phenotypic susceptibility testing. The minimum inhibitory concentration for azithromycin and doxycycline was defined as the lowest concentration associated with an at least 95% reduction in inclusion-forming units after one passage in the presence of the antibiotic compared to the initial inoculum for each strain (control). Sequencing analysis was performed for the genotypic detection of resistance to macrolides, analysing mutations in the 23S rRNA gene (at positions 2057, 2058, 2059, and 2611), and quinolones, analysing a fragment of the gyrA gene, and searching for the G248T mutation (Ser83-&gt;Ile). For tetracyclines, in-house RT-PCR was used to test for the tet(C) gene. The phenotypic susceptibility testing was successful for 10 isolates. All the isolates had minimum inhibitory concentrations for azithromycin ≤ 0.125 mg/L and for doxycycline ≤ 0.064 mg/L and were considered sensitive. Of the 73 strains studied, no mutations were found at positions T2611C or G248T of the gyrA gene. We successfully sequenced 66 isolates. No macrolide resistance-associated mutations were found at positions 2057, 2058, 2059, or T2611C. None of the isolates carried the tet(C) gene. We found no evidence for genomic resistance in this large, clinically relevant dataset.

Reporting of Azithromycin Activity against Clinical Isolates of Extensively Drug-Resistant Salmonella enterica Serovar Typhi.

This study aimed to evaluate the minimum inhibitory concentration (MIC) of azithromycin (AZM) in clinical isolates of extensively drug-resistant (XDR) Salmonella Typhi (i.e., resistant to chloramphenicol, ampicillin, trimethoprim-sulfamethoxazole, fluoroquinolones, and third-generation cephalosporin) using the E-test versus the broth microdilution method (BMD). From January to June 2021, a retrospective cross-sectional study was carried out in Lahore, Pakistan. Antimicrobial susceptibility was performed initially by the Kirby-Bauer disk diffusion method for 150 XDR Salmonella enterica serovar Typhi isolates, and MICs of all the recommended antibiotics were determined by the VITEK 2 (BioMérieux) fully automated system using Clinical Laboratory Standard Institute (CLSI) 2021 guidelines. The E-test method was used to determine AZM MICs. These MICs were compared with the BMD, which is the method recommended by the CLSI but not adopted in routine laboratory reporting. Of 150 isolates, 10 (6.6%) were resistant by disk diffusion. Eight (5.3%) of these had high MICs against AZM by the E-test. Only three isolates (2%) were resistant by E-test, having an MIC of 32 μg/mL. All eight isolates had a high MIC by BMD with different MIC distributions, but only one was resistant, having an MIC of 32 μg/mL by BMD. The sensitivity, specificity, negative predictive value, positive predictive value, and diagnostic accuracy of the E-test method versus BMD were 98.65%,100%, 99.3%, 33.3%, and 98.6%, respectively. Similarly, the concordance rate was 98.6%, negative percent agreement was 100%, and positive percent agreement was 33%. The BMD is the most reliable approach for reporting AZM sensitivity in XDR S. Typhi compared with the E-test and disk diffusion methods. Potentially, AZM resistance in XDR S. Typhi is around the corner. Sensitivity patterns should be reported with MIC values, and if possible, higher values should be screened for the presence of any potential resistance genes. Antibiotic stewardship should be strictly implemented.

Travel-associated lineages and unique endemic antimicrobial-susceptible lineages of Neisseria gonorrhoeae predominate in Western Australia.

In Australia, gonococcal isolates are monitored for antimicrobial susceptibilities. In Western Australia (WA), gonorrhoea notification rates increased by 63 % between 2013 and 2016, with the steepest increase occurring between 2015 and 2016, before stabilizing at this higher baseline between 2017 and 2020. This increased prevalence was associated with antimicrobial-susceptible (AMS) lineages. To understand the provenance of these isolates causing gonorrhoea in WA, whether they were introduced or expanded from endogenous lineages, 741 isolates were collected in 2017 and characterized by both iPLEX typing and whole genome sequencing (WGS). Antibiograms and genocoding of the isolates revealed that AMS isolates were most prevalent in the remote regions, while the urban/rural regions were characterized by antimicrobial-resistant (AMR) isolates. iPLEX typing identified 78 iPLEX genotypes (WA-1 to WA-78) of which 20 accounted for over 88 % of isolates. WA-10 was the most frequently identified genotype in the urban/rural regions whilst WA-29 was the most frequently identified genotype in the remote regions. Genotypes WA-38, WA-52 and WA-13 accounted for 81 % (n=36/44) of the azithromycin-resistant N. gonorrhoeae (AziR) isolates. A representative isolate of each iPLEX genotype and AMR biotype was whole genome sequenced and analysed using MLST, NG-MAST and NG-STAR, and the novel core genome clustering Ng_cgc_400 typing scheme. Five predominant Bayesian population groups (termed BPG-1 to 5) were identified in the study collection. BPG-1 and BPG-2 were associated with AMS isolates from the remote regions. BPG-1 and BPG-2 were shown to be unique to the remote regions based on a minimum spanning tree against 4000 international isolates. AMS isolates in urban/rural regions were dominated by international lineages. AziR and Cef DS (decreased susceptibility to ceftriaxone) was concentrated in three urban/rural genomic groups (BPG-3, 4 and 5). Azithromycin minimum inhibitory concentrations (0.5-16 mg l-1) correlated with the accumulation of mtrR mutations or/and the fraction of 23S rRNA C2611T mutated copies. The majority of isolates in BPG-3, 4 and 5 could be correlated with known AMR lineages circulating globally and nationally. In conclusion, the surge in AMS isolates in WA in 2017 was due to importation of international AMS lineages into urban/rural regions, whilst the local AMS lineages persisted largely in the remote regions. Bridging between the urban/rural and remote regions was relatively rare, but continued surveillance is required to prevent ingress of AMR strains/lineages into the remote regions of WA.

Evaluation of Neisseria gonorrhoeae Isolates Susceptibility to Antibiotics in Zhejiang Province Since 2007.

This study aimed to assess the drug susceptibility of clinical isolates of Neisseria gonorrhoeae to spectinomycin, ceftriaxone and azithromycin. Moreover, the temporal trends in the minimum inhibitory concentration (MIC) of five antibiotics from Zhejiang, China, are also in the scope of this study. A total of 1710 gonococcal clinical strains were collected between 2007 and 2021 from health-care institutions in Zhejiang. The MICs of ceftriaxone, azithromycin, spectinomycin, penicillin and ciprofloxacin were assessed by agar dilution method on 1710 Neisseria gonorrhoeae isolates. Count data were expressed as strains and rates, and MICs distribution was elucidated using descriptive statistics. The total resistance rates of gonococci to azithromycin, spectinomycin, penicillin and ciprofloxacin in this study were 19.3%, 0.3%, 75.4% and 99.7%, respectively. The in vitro results showed a high prevalence of resistance to ciprofloxacin and penicillin. Azithromycin resistance rate has exceeded 5%, suggested a high prevalence of resistance. Ceftriaxone and spectinomycin are suggested based on this study for the treatment of Neisseria gonorrhoeae in Zhejiang.

Seven Years of Culture Collection of Neisseria gonorrhoeae: Antimicrobial Resistance and Molecular Epidemiology.

The emergence of Neisseria gonorrhoeae isolates displaying resistance to antimicrobials, in particular to ceftriaxone monotherapy or ceftriaxone plus azithromycin, represents a global public health concern. This study aimed to analyze the trend of antimicrobial resistance in a 7-year isolate collection retrospective analysis in Italy. Molecular typing on a subsample of gonococci was also included. A total of 1,810 culture-positive gonorrhea cases, collected from 2013 to 2019, were investigated by antimicrobial susceptibility, using gradient diffusion method, and by the N. gonorrhoeae multiantigen sequence typing (NG-MAST). The majority of infections occurred among men with urogenital infections and 57.9% of male patients were men who have sex with men. Overall, the cefixime resistance remained stable during the time. An increase of azithromycin resistance was observed until 2018 (26.5%) with a slight decrease in the last year. In 2019, gonococci showing azithromycin minimum inhibitory concentration above the EUCAST epidemiological cutoff value (ECOFF) accounted for 9.9%. Ciprofloxacin resistance and penicillinase-producing N. gonorrhoeae (PPNG) percentages increased reaching 79.1% and 18.7% in 2019, respectively. The most common sequence types identified were 5,441, 1,407, 6,360, and 5,624. The predominant genogroup (G) was the 1,407; moreover, a new genogroup G13070 was also detected. A variation in the antimicrobial resistance rates and high genetic variability were observed in this study. The main phenotypic and genotypic characteristics of N. gonorrhoeae isolates were described to monitor the spread of drug-resistant gonorrhea.

Emergence of high-level azithromycin-resistant Neisseria gonorrhoeae causing male urethritis in Johannesburg, South Africa, 2021.

In South Africa, Neisseria gonorrhoeae , which is the predominant cause of male urethritis, is treated syndromically using dual ceftriaxone and azithromycin therapy. We determined antimicrobial susceptibilities of N. gonorrhoeae isolates from urethral discharge specimens, and genetically characterised those with elevated minimum inhibitory concentrations (MICs) for first-line antimicrobials. Routine antimicrobial susceptibility testing (AST) of N. gonorrhoeae isolates included E-test for ceftriaxone, cefixime and gentamicin and agar dilution for azithromycin and spectinomycin. Neisseria gonorrhoeae Sequence Typing for Antimicrobial Resistance (NG-STAR) was performed for isolates with elevated MICs to identify antimicrobial resistance (AMR) determinants, and Neisseria gonorrhoeae Multi-Antigen Sequence Typing (NG-MAST) was used to determine strain relatedness. N. gonorrhoeae was cultured from urethral discharge swab specimens obtained from 196 of 238 (82.4%) men presenting to a primary healthcare facility in Johannesburg in 2021. All viable isolates were susceptible to extended-spectrum cephalosporins. Four isolates had high azithromycin MICs ranging from 32mg/L to >256mg/L and grouped into two novel NG-MAST and NG-STAR groups. Two isolates from Group 1 (NG-MAST ST20366, NG-STAR ST4322) contained mutated mtrR (G45D) and 23S rRNA (A2059G) alleles, while the two isolates from Group 2 (NG-MAST ST20367, NG-STAR ST4323) had different mutations in mtrR (A39T) and 23S rRNA (C2611T). We report the first cases of high-level azithromycin resistance in N. gonorrhoeae from South Africa. Continued AMR surveillance is critical to detect increasing azithromycin resistance prevalence in N. gonorrhoeae , which may justify future modifications to the STI syndromic management guidelines.

Antimicrobial susceptibilities of Neisseria gonorrhoeae in Canada, 2020.

The Gonococcal Antimicrobial Surveillance Programme is a passive surveillance system that has monitored antimicrobial resistance in Neisseria gonorrhoeae in Canada since the 1980s. This article summarizes the demographics, antimicrobial resistances and NG-MAST (N. gonorrhoeae multiantigen sequence typing) for cultures collected in 2020. The National Microbiology Laboratory (NML) in Winnipeg received resistant N. gonorrhoeae cultures from provincial and territorial public health laboratories. Agar dilution was used to determine the minimum inhibitory concentrations to ten antimicrobials for all cultures received at NML, according to Clinical and Laboratory Standards Institute guidelines. The NG-MAST typing was also determined for each culture. A total of 3,130 N. gonorrhoeae cases were cultured across Canada in 2020; a 36% decrease from 2019 (n=4,859). The level of decreased susceptibility to cefixime increased significantly between 2016 and 2020 to 2.8% (p=0.0054). Decreased susceptibility to ceftriaxone declined significantly between 2016 (1.8%) and 2020 to 0.9% (p=0.001), and there was no significant change with azithromycin between 2016 (7.2%) and 2020 (6.1%). The proportion of cultures with an azithromycin minimum inhibitory concentrations of ≥1 mg/L increased significantly from 11.6% in 2016 to 15.3% in 2020 (p=0.0017). The most common NG-MAST type in Canada for 2020 was sequence type (ST)-11461, while ST-12302 was most commonly associated with azithromycin resistance and ST-16639 with cephalosporin decreased susceptibility. Antimicrobial resistance in N. gonorrhoeae remains an important public health concern and continued surveillance is imperative to monitor trends to ensure the recommended therapies will be the most effective.

Analysis of treatment protocols using azithromycin eye drops for bacterial blepharitis: second report-bacteriological investigation.

To gain new insights into the etiology of blepharitis, we investigated the causative bacteria in patients with blepharitis and the effects of 1% azithromycin ophthalmic solution. A multicenter, prospective observational study. After the subjects were diagnosed as having blepharitis they were administered 1% azithromycin ophthalmic solution for up to 14 days. Bacterial cultures and smear microscopic examinations of the eyelid margin were conducted at the initial visit, after administering eye drops, and 1 month after the end of eye drop administration. The minimum inhibitory concentrations (MICs) of azithromycin were measured. At the initial visit, the bacterial morphology determined by smear microscopic examinations coincided with that of strains isolated by culture taken from 22 of 45 patients. All detected bacteria were gram-positive, and Corynebacterium spp., Cutibacterium acnes, Staphylococcus epidermidis, Streptococcus spp., and Enterococcus faecalis were isolated most commonly. Compared with the initial visit the number of isolated strains per eye decreased significantly at 7 days after the start of eye drop administration and 1 month after the end of eye drop administration. The azithromycin MICs were temporarily increased after the start of eye drops but then decreased. Our study suggests that in blepharitis pathogenicity is characterized by increased strain numbers and amounts of indigenous bacteria. Administering a 1% azithromycin ophthalmic solution suppresses the number of bacterial strains within 1 month after the end of eye drop administration without increasing drug resistance.

In Vitro Study of the Interaction of Gentamicin with Ceftriaxone and Azithromycin against Neisseria gonorrhoeae Using Agar Dilution Method.

The susceptibility to gentamicin of N. gonorrhoeae isolates collected in three Chinese provinces and the correlation among the MICs of gentamicin, azithromycin, and ceftriaxone were investigated in this study. The effects of combinations from those three antibiotics were also in the scope of this study to determine the efficacy of gentamicin as a combination therapeutic drug. The agar dilution method was used to measure the minimum inhibitory concentrations (MICs) of ceftriaxone, azithromycin and gentamicin on N. gonorrhoeae isolates. The synergy between these three antimicrobials were determined using the agar dilution checkerboard method. Subgroup studies were conducted to explore differences between azithromycin- and ceftriaxone-sensitive and resistant isolates. A total of 139 (36.60%) and 233 (61.30%) isolates demonstrated full susceptibility and intermediate susceptibility to gentamicin, respectively. The correlation analysis showed that the MICs of ceftriaxone and azithromycin weakly correlated with the value of gentamicin. The overall results of the three antibiotic combinations revealed indifferent effects. Combination therapy established a significant reduction on the MIC value. Most of the N. gonorrhoeae isolates tested in this study demonstrated a certain degree of susceptibility to gentamicin. Overall, antimicrobial combinations of gentamicin with ceftriaxone or azithromycin demonstrate indifferent effects.

Whole-genome sequence analysis of high-level penicillin-resistant strains and antimicrobial susceptibility of Neisseria gonorrhoeae clinical isolates from Thailand.

The increasing rate of antimicrobial-resistant Neisseria gonorrhoeae poses a considerable public health threat due to the difficulty in treating gonococcal infections. This study examined antimicrobial resistance (AMR) to drugs recommended for gonorrhea treatment between 2015 and 2017, and the AMR determinants and genetic compositions of plasmids in 3 gonococcal strains with high-level penicillin resistance. We collected 117 N. gonorrhoeae isolates from patients with gonococcal infections who attended Siriraj Hospital, Bangkok, Thailand, between 2015 and 2017. Minimum inhibitory concentrations (MICs) of penicillin, tetracycline, ciprofloxacin, azithromycin, spectinomycin, cefixime, and ceftriaxone were determined by the agar dilution method. PCR amplification and sequencing of 23S rRNA and mtrR (a negative regulator of MtrCDE efflux pump) were performed. Whole genomes of 3 PPNG strains with high-level penicillin resistance (MIC ≥ 128 μg/ml) were sequenced using Illumina and Nanopore sequencing platforms. The proportions of N. gonorrhoeae isolates with resistance were 84.6% for penicillin, 91.5% for tetracycline, and 96.6% for ciprofloxacin. All isolates were susceptible to spectinomycin, azithromycin, cefixime, and ceftriaxone. An adenine deletion within a 13 bp inverted repeat sequence in the mtrR promoter and an H105Y mutation in the mtrR coding region were found in the N. gonorrhoeae isolate with the highest azithromycin MIC value (1 μg/ml). Three high-level penicillin-resistant isolates contained nonmosaic type II penA and had mutations in penB and the mtrR coding region. All isolates with high-level penicillin resistance carried the conjugative plasmids with or without the Dutch type tetM determinant, the beta-lactamase plasmid (Rio/Toronto), and the cryptic plasmid. The gonococcal population in Thailand showed high susceptibility to ceftriaxone and azithromycin, current dual therapy recommended for gonorrhea treatment. As elevated MIC of azithromycin has been observed in 1 strain of N. gonorrhoeae, expanded and enhanced surveillance of antimicrobial susceptibility and study of genetic resistance determinants are essential to improve treatment guidelines.

New antimicrobial peptide-antibiotic combination strategy for Pseudomonas aeruginosa inactivation.

Novel antimicrobials or new treatment strategies are urgently needed to treat Pseudomonas aeruginosa (P. aeruginosa) related infections and especially to address the problem of antibiotic resistance. We propose a novel strategy that combines the human antimicrobial peptide (AMP) LL37 with different antibiotics to find synergistic AMP-antibiotic combinations against P. aeruginosa strains in vitro. Our results showed that LL37 exhibited synergistic inhibitory and bactericidal effects against P. aeruginosa strains PAO1 and PA103 when combined with the antibiotics vancomycin, azithromycin, polymyxin B, and colistin. In addition, LL37 caused strong outer membrane permeabilization, as demonstrated through measurement of an increased uptake of the fluorescent probe N-phenyl-1-naphthylamine. The membrane permeabilization effects appear to explain why it was easier to rescue the effectiveness of the antibiotic toward the bacteria because the outer membrane of P. aeruginosa exhibits barrier function for antibiotics. Furthermore, the change in the zeta potential was measured for P. aeruginosa strains with the addition of LL37. Zeta potentials for P. aeruginosa strains PAO1 and PA103 were -40.9 and -10.9 mV, respectively. With the addition of LL37, negative zeta potentials were gradually neutralized. We found that positively charged LL37 can interact with and neutralize the negatively charged bacterial outer membrane through electrostatic interactions, and the process of neutralization is believed to have contributed to the increase in outer membrane permeability. Finally, to further illustrate the relationship between outer membrane permeabilization and the uptake of antibiotics, we used LL37 to make the outer membrane of P. aeruginosa strains more permeable, and minimum inhibitory concentrations (MICs) for several antibiotics (colistin, gentamicin, polymyxin B, vancomycin, and azithromycin) were measured. The MICs decreased were twofold to fourfold, in general. For example, the MICs of azithromycin and vancomycin decreased more than fourfold when against P. aeruginosa strain PAO1, which were the greatest decrease of any of the antibiotics tested in this experiment. As for PA103, the MIC of polymyxin B2 decreased fourfold, which was the strongest decrease seen for any of the antibiotics tested in this experiment. The increased uptake of antibiotics not only demonstrates the barrier role of the outer membrane but also validates the mechanism of synergistic effects that we have proposed. These results indicate the great potential of an LL37-antibiotic combination strategy and provide possible explanations for the mechanisms behind this synergy.

Significant increase in azithromycin “resistance” and susceptibility to ceftriaxone and cefixime in Neisseria gonorrhoeae isolates in 26 European countries, 2019

BackgroundThe European Gonococcal Antimicrobial Surveillance Programme (Euro-GASP) performs annual sentinel surveillance of Neisseria gonorrhoeae susceptibility to therapeutically relevant antimicrobials across the European Union/European Economic Area (EU/EEA). We present the Euro-GASP results from 2019 (26 countries), linked to patient epidemiological data, and compared with data from previous years.MethodsAgar dilution and minimum inhibitory concentration (MIC) gradient strip methodologies were used to determine the antimicrobial susceptibility (using EUCAST clinical breakpoints, where available) of 3239 N. gonorrhoeae isolates from 26 countries across the EU/EEA. Significance of differences compared with Euro-GASP results in previous years was analysed using Z-test and the Pearson's χ2 test was used to assess significance of odds ratios for associations between patient epidemiological data and antimicrobial resistance.ResultsEuropean N. gonorrhoeae isolates collected between 2016 and 2019 displayed shifting MIC distributions for; ceftriaxone, with highly susceptible isolates increasing over time and occasional resistant isolates each year; cefixime, with highly-susceptible isolates becoming increasingly common; azithromycin, with a shift away from lower MICs towards higher MICs above the EUCAST epidemiological cut-off (ECOFF); and ciprofloxacin which is displaying a similar shift in MICs as observed for azithromycin. In 2019, two isolates displayed ceftriaxone resistance, but both isolates had MICs below the azithromycin ECOFF. Cefixime resistance (0.8%) was associated with patient sex, with resistance higher in females compared with male heterosexuals and men-who-have-sex-with-men (MSM). The number of countries reporting isolates with azithromycin MICs above the ECOFF increased from 76.9% (20/26) in 2016 to 92.3% (24/26) in 2019. Isolates with azithromycin MICs above the ECOFF (9.0%) were associated with pharyngeal infection sites. Following multivariable analysis, ciprofloxacin resistance remained associated with isolates from MSM and heterosexual males compared with females, the absence of a concurrent chlamydial infection, pharyngeal infection sites and patients ≥ 25 years of age.ConclusionsResistance to ceftriaxone and cefixime remained uncommon in EU/EEA countries in 2019 with a significant decrease in cefixime resistance observed between 2016 and 2019. The significant increase in azithromycin “resistance” (azithromycin MICs above the ECOFF) threatens the effectiveness of the dual therapy (ceftriaxone + azithromycin), i.e., for ceftriaxone-resistant cases, currently recommended in many countries internationally and requires close monitoring.

Role of Efflux in Antibiotic Resistance of Achromobacter xylosoxidans and Achromobacter insuavis Isolates From Patients With Cystic Fibrosis.

Achromobacter genus (including Achromobacter xylosoxidans, the most prevalent Achromobacter species in patients with cystic fibrosis) is poorly susceptible to most conventional antibiotics. Contribution of efflux by AxyABM, AxyXY-OprZ, and AxyEF-OprN and of target mutations were studied in clinical isolates of A. xylosoxidans and Achromobacter insuavis. Forty-one isolates longitudinally collected from 21 patients with CF were studied by whole-genome sequencing (WGS)-typing, determination of minimum inhibitory concentrations (MICs) of β-lactams, aminoglycosides, colistin, azithromycin, ciprofloxacin, chloramphenicol, and doxycycline, and expression (quantitative RT-PCR) and function (measure of the uptake of a fluorescent substrate) of efflux pumps. WGS-based typing resulted in 10 clusters comprising 2 or 3 isolates and 20 singletons. The efflux activity was high in strains with elevated MICs for amikacin or azithromycin. This work sheds a new light on the impact of efflux and target mutations in resistance of Achromobacter to several drugs.

Evaluation of Neisseria gonorrhoeae Isolates Susceptibility to Tetracycline Antibiotics from 9 Provinces in China Since 2020.

PurposeThe increasing drug resistance of Neisseria gonorrhoeae has become a serious public health concern. This study investigated N. gonorrhoeae isolates susceptibility to tetracycline antibiotics and the correlation between minimum inhibitory concentrations (MICs) of different antibiotics. The presence of resistance determinants in N. gonorrhoeae strains displaying different levels of tigecycline resistance was also compared.MethodsThe minimum inhibitory concentrations (MICs) of tetracycline, minocycline, tigecycline, eravacycline, omadacycline on 412 N. gonorrhoeae isolates were measured by the agar dilution method. The MICs of ceftriaxone and azithromycin were also measured to determine the correlations between antibiotics by the value of the correlation coefficient R. The presence of resistance determinants was identified through polymerase chain reaction (PCR) and sequencing.ResultsThe MIC90 was 64mg/L for tetracycline, 64mg/L for minocycline, 0.5mg/L for tigecycline, 0.5mg/L for eravacycline, 4mg/L for omadacycline, 0.25 mg/L for ceftriaxone, and 1mg/L for azithromycin. The MIC90 and mode of tigecycline and eravacycline were much lower than those of tetracycline and minocycline. A poor correlation between omadacycline, eravacycline and tetracycline susceptibility was observed. Minocycline has a strong correlation with tetracycline. PorB1 typing, TetM-encoding plasmid, and mtrR promoter adenine deletion were significantly correlated with tigecycline MIC > 0.25mg/L.ConclusionThis study suggested that tigecycline and eravacycline had better in vitro activity and might be alternative antibiotics against resistant N. gonorrhoeae infections. Nevertheless, further in vitro experiments and clinical studies are needed for verification.