Isothermal microcalorimetry minimal inhibitory concentration testing in extensively drug resistant Gram-negative bacilli: a multicentre study

Harnessing biotechnology for penicillin production: Opportunities and environmental considerations

Since the discovery of antibiotics, penicillin has remained the top choice in clinical medicine. With continuous advancements in biotechnology, penicillin production has become cost-effective and efficient. Genetic engineering techniques have been employed to enhance biosynthetic pathways, leading to the production of new penicillin derivatives with improved properties and increased efficacy against antibiotic-resistant pathogens. Advances in bioreactor design, media formulation, and process optimization have contributed to higher yields, reduced production costs, and increased penicillin accessibility. While biotechnological advances have clearly benefited the global production of this life-saving drug, they have also created challenges in terms of waste management. Production fermentation broths from industries contain residual antibiotics, by-products, and other contaminants that pose direct environmental threats, while increased global consumption intensifies the risk of antimicrobial resistance in both the environment and living organisms. The current geographical and spatial distribution of antibiotic and penicillin consumption dramatically reveals a worldwide threat. These challenges are being addressed through the development of novel waste management techniques. Efforts are aimed at both upstream and downstream processing of antibiotic and penicillin production to minimize costs and improve yield efficiency while lowering the overall environmental impact. Yield optimization using artificial intelligence (AI), along with biological and chemical treatment of waste, is also being explored to reduce adverse impacts. The implementation of strict regulatory frameworks and guidelines is also essential to ensure proper management and disposal of penicillin production waste. This review is novel because it explores the key remaining challenges in antibiotic development, the scope of machine learning tools such as Quantitative Structure-Activity Relationship (QSAR) in modern biotechnology-driven production, improved waste management for antibiotics, discovering alternative path to reducing antibiotic use in agriculture through alternative meat production, addressing current practices, and offering effective recommendations.

Accessory genes define species-specific routes to antibiotic resistance

A deeper understanding of the relationship between the antimicrobial resistance (AMR) gene carriage and phenotype is necessary to develop effective response strategies against this global burden. AMR phenotype is often a result of multi-gene interactions; therefore, we need approaches that go beyond current simple AMR gene identification tools. Machine-learning (ML) methods may meet this challenge and allow the development of rapid computational approaches for AMR phenotype classification. To examine this, we applied multiple ML techniques to 16,950 bacterial genomes across 28 genera, with corresponding MICs for 23 antibiotics with the aim of training models to accurately determine the AMR phenotype from sequenced genomes. This resulted in a >1.5-fold increase in AMR phenotype prediction accuracy over AMR gene identification alone. Furthermore, we revealed 528 unique (often species-specific) genomic routes to antibiotic resistance, including genes not previously linked to the AMR phenotype. Our study demonstrates the utility of ML in predicting AMR phenotypes across diverse clinically relevant organisms and antibiotics. This research proposes a rapid computational method to support laboratory-based identification of the AMR phenotype in pathogens.

Unraveling resistance mechanisms in combination therapy: A comprehensive review of recent advances and future directions

Antimicrobial resistance is a global health threat. Misuse and overuse of antimicrobials are the main drivers in developing drug-resistant bacteria. The emergence of the rapid global spread of multi-resistant bacteria requires urgent multisectoral action to generate novel treatment alternatives. Combination therapy offers the potential to exploit synergistic effects for enhanced antibacterial efficacy of drugs. Understanding the complex dynamics and kinetics of drug interactions in combination therapy is crucial. Therefore, this review outlines the current advances in antibiotic resistance's evolutionary and genetic dynamics in combination therapies-exposed bacteria. Moreover, we also discussed four pivotal future research areas to comprehend better the development of antibiotic resistance in bacteria treated with combination strategies.

Antibiotics against Pseudomonas aeruginosa on Human Skin Cell Lines: Determination of the Highest Non-Cytotoxic Concentrations with Antibiofilm Capacity for Wound Healing Strategies

Pseudomonas aeruginosa is one of the most common microorganisms causing infections of severe skin wounds. Antibiotic or antiseptic treatments are crucial to prevent and curb these infections. Antiseptics have been reported to be cytotoxic to skin cells and few studies evaluate the impact of commonly used antibiotics. This study evaluates how clinical antibiotics affect skin cells' viability, proliferation, migration, and cytokine secretion and defines the highest non-cytotoxic concentrations that maintain antibacterial activity. Cell proliferation, viability, and migration were evaluated on cell monolayers. Cytokines related to the wound healing process were determined. The minimum inhibitory concentrations and the impact on bacterial biofilm were assessed. Results showed that 0.02 mg/mL ciprofloxacin and 1 mg/mL meropenem are the highest non-cytotoxic concentrations for fibroblasts and keratinocytes while 1.25 mg/mL amikacin and 0.034 mg/mL colistin do not affect fibroblasts' viability and cytokine secretion but have an impact on keratinocytes. These concentrations are above the minimum inhibitory concentration but only amikacin could eradicate the biofilm. For the other antibiotics, cytotoxic concentrations are needed to eradicate the biofilm. Combinations with colistin at non-cytotoxic concentrations effectively eliminate the biofilm. These results provide information about the concentrations required when administering topical antibiotic treatments on skin lesions, and how these antibiotics affect wound management therapies. This study set the basis for the development of novel antibacterial wound healing strategies such as antibiotic artificial skin substitutes.

Biofilm antimicrobial susceptibility testing: where are we and where could we be going?

Our knowledge about the fundamental aspects of biofilm biology, including the mechanisms behind the reduced antimicrobial susceptibility of biofilms, has increased drastically over the last decades. However, this knowledge has so far not been translated into major changes in clinical practice. While the biofilm concept is increasingly on the radar of clinical microbiologists, physicians, and healthcare professionals in general, the standardized tools to study biofilms in the clinical microbiology laboratory are still lacking; one area in which this is particularly obvious is that of antimicrobial susceptibility testing (AST). It is generally accepted that the biofilm lifestyle has a tremendous impact on antibiotic susceptibility, yet AST is typically still carried out with planktonic cells. On top of that, the microenvironment at the site of infection is an important driver for microbial physiology and hence susceptibility; but this is poorly reflected in current AST methods. The goal of this review is to provide an overview of the state of the art concerning biofilm AST and highlight the knowledge gaps in this area. Subsequently, potential ways to improve biofilm-based AST will be discussed. Finally, bottlenecks currently preventing the use of biofilm AST in clinical practice, as well as the steps needed to get past these bottlenecks, will be discussed.

Isothermal microcalorimetry improves accuracy and time to bacterial detection of periprosthetic joint infection after total joint arthroplasty

Isothermal microcalorimetry (IMC) was evaluated compared to conventional cultures to determine the clinical performance for diagnosing periprosthetic joint infection (PJI) of hip/knee replacements. We prospectively collected three to five deep tissue samples per patient from 152 patients undergoing conversion or revision hip/knee arthroplasty from July 2020 to November 2022. Cultures and IMC for each sample were compared for concordance, median time to detection (TTD), and diagnostic performance based on 2013 Musculoskeletal Infection Society criteria. Secondary analyses involved patients on antibiotics at sampling. The 152 total patients had 592 tissue samples (mean 3.9 ± 0.3) with sample concordance between cultures and IMC of 90%. IMC demonstrated a sensitivity of 83%, specificity of 100%, negative predictive value (NPV) of 89%, and positive predictive value (PPV) of 100% for PJI. Cultures resulted in 69% sensitivity, 100% specificity, 81% NPV, and 100% PPV. The accuracy of IMC was 93% compared to 87% for cultures (P < 0.001). The median TTD of PJI by cultures was 51 (21-410) hours compared to 10 (0.5-148) hours for IMC (P < 0.001). For 39 patients on chronic antibiotics, sensitivity in PJI detection was 93%, specificity 100%, NPV 85%, and PPV 100% by IMC compared to 79% sensitivity, 100% specificity, 65% NPV, and 100% PPV for cultures. The accuracy was 95% for IMC compared to 85% for cultures (P < 0.001) with median TTD of 12 (0.5-127) hours compared to 52 (21-174) hours (P < 0.001). Utilizing IMC for PJI detection improves TTD by nearly 2 days while improving diagnostic accuracy compared to cultures, particularly in patients on chronic antibiotics.

Polymyxin B stabilized DNA micelles for sustained antibacterial and antibiofilm activity against P. aeruginosa

Nucleic acid-based materials showcase an increasing potential for antimicrobial drug delivery. Although numerous reports on drug-loaded DNA nanoparticles outline their pivotal antibacterial activities, their potential as drug delivery systems against bacterial biofilms awaits further studies. Among different oligonucleotide structures, micellar nanocarriers derived from amphiphilic DNA strands are of particular interest due to their spontaneous self-assembly and high biocompatibility. However, their clinical use is hampered by structural instability upon cation depletion. In this work, we used a cationic amphiphilic antibiotic (polymyxin B) to stabilize DNA micelles destined to penetrate P. aeruginosa biofilms and exhibit antibacterial/antibiofilm properties. Our study highlights how the strong affinity of this antibiotic enhances the stability of the micelles and confirms that antibacterial activity of the novel micelles remains intact. Additionally, we show that PMB micelles can penetrate P. aeruginosa biofilms and impact their metabolic activity. Finally, PMB micelles were highly safe and biocompatible, highlighting their possible application against P. aeruginosa biofilm-colonized skin wounds.

Protocol to assess metabolic activity of Pseudomonas aeruginosa by measuring heat flow using isothermal calorimetry

Here, we present a protocol for assessing metabolic activity of bacterial populations by measuring heat flow using isothermal calorimetry. We outline the steps for preparing the different growth models of Pseudomonas aeruginosa and performing continuous metabolic activity measurements in the calScreener. We detail simple principal component analysis to differentiate between metabolic states of different populations and probabilistic logistic classification to assess resemblance to wild-type bacteria. This protocol for fine-scale metabolic measurement can aid in understanding microbial physiology. For complete details on the use and execution of this protocol, please refer to Lichtenberg et al. (2022).¹.

Conventional methods and future trends in antimicrobial susceptibility testing

Antimicrobial susceptibility testing is an essential task for selecting appropriate antimicrobial agents to treat infectious diseases. Constant evolution has been observed in methods used in the diagnostic microbiology laboratories. Disc diffusion or broth microdilution are classical and conventional phenotypic methods with long turnaround time and labour-intensive but still widely practiced as gold-standard. Scientists are striving to develop innovative, novel and faster methods of antimicrobial susceptibility testing to be applicable for routine microbiological laboratory practice and research. To meet the requirements, there is an increasing trend towards automation, genotypic and micro/nano technology-based innovations. Automation in detection systems and integration of computers for online data analysis and data sharing are giant leaps towards versatile nature of automated methods currently in use. Genotypic methods detect a specific genetic marker associated with resistant phenotypes using molecular amplification techniques and genome sequencing. Microfluidics and microdroplets are recent addition in the continuous advancement of methods that show great promises with regards to safety and speed and have the prospect to identify and monitor resistance mechanisms. Although genotypic and microfluidics methods have many exciting features, however, their applications into routine clinical laboratory practice warrant extensive validation. The main impetus behind the evolution of methods in antimicrobial susceptibility testing is to shorten the overall turnaround time in obtaining the results and to enhance the ease of sample processing. This comprehensive narrative review summarises major conventional phenotypic methods and automated systems currently in use, and highlights principles of some of the emerging genotypic and micro/nanotechnology-based methods in antimicrobial susceptibility testing.

Isothermal microcalorimetry versus checkerboard assay to evaluate in vitro synergism of meropenem-amikacin and meropenem-colistin combinations against multidrug-resistant Gram-negative pathogens

OBJECTIVES

To evaluate the activity of meropenem-amikacin and meropenem-colistin combinations with checkerboard broth microdilution (CKBM) compared to isothermal microcalorimetry (ITMC) assays against a multicentric collection of multidrug-resistant Gram-negative (MDR-GN) clinical isolates, to compare the Fractional inhibitory concentration index (FICI) and time to results of CKBM and ITMC assays.

METHODS

A collection of 333 MDR-GNs showing reduced susceptibility to meropenem (121 Klebsiella pneumoniae, 14 Escherichia coli, 130 Pseudomonas aeruginosa and 68 Acinetobacter baumannii) isolated from different centres (Florence, Madrid, Rotterdam, and Stockholm) was included in the study. The antimicrobial activity of selected combinations was evaluated with CKBM and ITMC. FICI results were interpreted as synergistic/additive and indifferent for values ≤0.5/0.5<x≤1 and >1, respectively. WGS data in a subset of strains was used to evaluate their clonality.

RESULTS

A total of 254 and 286 strains were tested with meropenem-colistin and meropenem-amikacin combinations with ITMC and CKBM, respectively. Synergism/additive effects were observed with 46 strains (20 K. pneumoniae, 4 E. coli, 22 P. aeruginosa) and 20 strains (3 K. pneumoniae, 11 P. aeruginosa and 6 A. baumannii) with meropenem-amikacin and meropenem-colistin combination, respectively, with CKBM. ITMC showed a good concordance with CKBM with 89.5% and 92.2% of cases interpreted within the same FICI category for meropenem-amikacin and meropenem-colistin combinations, respectively. Most of the synergism/additivity effects were detected within 6 hours by ITMC.

CONCLUSIONS

ITMC showed a very good concordance with CKBM against a large collection of MDR-GN and could be implemented for the rapid evaluation of in vitro activity of antimicrobial combinations.

Low-dose intravenous plus inhaled versus intravenous polymyxin B for the treatment of extensive drug-resistant Gram-negative ventilator-associated pneumonia in the critical illnesses: a multi-center matched case-control study

Background

The mortality of extensively drug-resistant Gram-negative (XDR GN) bacilli-induced ventilator-associated pneumonia (VAP) is extremely high. The purpose of this study was to compare the efficacy and safety of inhaled (IH) plus intravenous (IV) polymyxin B versus IV polymyxin B in XDR GN bacilli VAP patients.

Methods

A retrospective multi-center observational cohort study was performed at eight ICUs between January 1^st 2018, and January 1^st 2020 in China. Data from all patients treated with polymyxin B for a microbiologically confirmed VAP were analyzed. The primary endpoint was the clinical cure of VAP. The favorable clinical outcome, microbiological outcome, VAP-related mortality and all-cause mortality during hospitalization, and side effects related with polymyxin B were secondary endpoints. Favorable clinical outcome included clinical cure or clinical improvement.

Results

151 patients and 46 patients were treated with IV polymyxin B and IH plus IV polymyxin B, respectively. XDR Klebsiella pneumoniae was the main isolated pathogen (n = 83, 42.1%). After matching on age (± 5 years), gender, septic shock, and Apache II score (± 4 points) when polymyxin B was started, 132 patients were included. 44 patients received simultaneous IH plus IV polymyxin B and 88 patients received IV polymyxin B. The rates of clinical cure (43.2% vs 27.3%, p = 0.066), bacterial eradication (36.4% vs 23.9%, p = 0.132) as well as VAP-related mortality (27.3% vs 34.1%, p = 0.428), all-cause mortality (34.1% vs 42.0%, p = 0.378) did not show any significant difference between the two groups. However, IH plus IV polymyxin B therapy was associated with improved favorable clinical outcome (77.3% vs 58.0%, p = 0.029). Patients in the different subgroups (admitted with medical etiology, infected with XDR K. pneumoniae, without bacteremia, with immunosuppressive status) were with odd ratios (ORs) in favor of the combined therapy. No patient required polymyxin B discontinuation due to adverse events. Additional use of IH polymyxin B (aOR 2.63, 95% CI 1.06, 6.66, p = 0.037) was an independent factor associated with favorable clinical outcome.

Conclusions

The addition of low-dose IH polymyxin B to low-dose IV polymyxin B did not provide efficient clinical cure and bacterial eradication in VAP caused by XDR GN bacilli.

Keypoints

Additional use of IH polymyxin B was the sole independent risk factor of favorable clinical outcome. Patients in the different subgroups were with HRs substantially favoring additional use of IH polymyxin B. No patients required polymyxin B discontinuation due to adverse events.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01033-5.

Isothermal Microcalorimetry Improves the Time to Diagnosis of Fracture-related Infection Compared With Conventional Tissue Cultures

BACKGROUND

A consensus definition recently was formulated for fracture-related infection, which centered on confirmatory criteria including conventional cultures that take time to finalize and have a 10% to 20% false-negative rate. During this time, patients are often on broad-spectrum antibiotics and may remain hospitalized until cultures are finalized to adjust antibiotic regimens.

QUESTIONS/PURPOSES

(1) What is the diagnostic accuracy of isothermal microcalorimetry, and how does its accuracy compare with that of conventional cultures? (2) Does isothermal microcalorimetry decrease time to detection (or diagnosis) of fracture-related infection compared with conventional cultures? (3) Does isothermal microcalorimetry have a diagnostic accuracy or time advantage over conventional cultures in patients on chronic suppressive antibiotics?

METHODS

Between July 2020 and August 2021, we treated 310 patients with concerns for infection after prior fracture repair surgery. Of those, we considered all patients older than 18 years of age with fixation hardware in place at the time of presentation as potentially eligible. All included patients returned to the operating room with cultures obtained and assessed by both isothermal microcalorimetry and conventional cultures, and all were diagnosed using the consensus criteria for fracture-related infection. Based on that, 81% (250 of 310) of patients were eligible; a further 51% (157 of 310) were excluded because of the following reasons: the capacity of the isothermal microcalorimetry instrument limited the throughput on that day (34% [106 of 310]), they had only swab cultures obtained in surgery (15% [46 of 310]), or they had less than 3 months follow-up after surgery for infectious concerns (2% [5 of 310]), leaving 30% (93 of 310) of the originally identified patients for analysis. We obtained two to five cultures from each patient during surgery, which were sent to our clinical microbiology laboratory for standard processing (conventional cultures). This included homogenization of each tissue sample individually and culturing for aerobic, anaerobic, acid-fast bacilli, and fungal culturing. The remaining homogenate from each sample was then taken to our orthopaedic research laboratory, resuspended in growth media, and analyzed by isothermal microcalorimetry for a minimum of 24 hours. Aerobic and anaerobic cultures were maintained for 5 days and 14 days, respectively. Overall, there were 93 patients (59 males), with a mean age of 43 ± 14 years and a mean BMI of 28 ± 8 kg/m 2 , and 305 tissue samples (mean 3 ± 1 samples per patient) were obtained and assessed by conventional culturing and isothermal microcalorimetry. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of isothermal microcalorimetry to diagnose fracture-related infection were compared with conventional cultures using a McNemar test based on the consensus definition of fracture-related infection. This consensus criteria is comprised of two levels of certainty for the diagnostic variables. The first is confirmatory criteria, where infection is considered definitely present and includes the presence of fistula/sinus tract/wound breakdown, purulent drainage or the presence of pus, presence of microorganisms in deep tissue specimens on histopathologic examination, presence of more than five neutrophils/high-powered field by histopathologic examination (only for chronic/late onset cases), and identification of phenotypically indistinguishable pathogens by conventional culture from at least two separate deep tissue/implant specimens. The second is suggestive criteria in which further investigation is required to achieve confirmatory status. Fracture-related infection was diagnosed for this study to minimize subjectivity based on the presence of at least one of the confirmatory criteria as documented by the managing surgeon. When suggestive criteria were present without confirmatory criteria, patients were considered negative for fracture-related infection and followed further in clinic after surgical exploration (n = 25 patients). All 25 patients deemed not to have fracture-related infection were considered infection-free at latest follow-up (range 3 to 12 months). The time to detection or diagnosis was recorded and compared via the Mann-Whitney U test.

RESULTS

Using the consensus criteria for fracture-related infection, there were no differences with the numbers available between isothermal microcalorimetry and conventional cultures in terms of sensitivity (87% [95% confidence interval 77% to 94%] versus 81% [95% CI 69% to 89%]), specificity (100% [95% CI 87% to 100%] versus 96% [95% CI 79% to 99%]), PPV (100% [95% CI 90% to 100%] versus 98% [95% CI 89% to 99%]), NPV (74% [95% CI 60% to 84%] versus 65% [95% CI 52% to 75%]), or accuracy (90% [95% CI 83% to 96%] versus 85% [95% CI 76% to 91%]; p = 0.13). The concordance by sample between conventional cultures and isothermal microcalorimetry was 85%. Isothermal microcalorimetry had a shorter median (range) time to detection or diagnosis compared with conventional cultures (2 hours [0.5 to 66] versus 51 hours [18 to 147], difference of medians 49 hours; p < 0.001). Additionally, 32 patients used antibiotics for a median (range) duration of 28 days (7 to 1095) before presentation. In these unique patients, there were no differences with the numbers available between isothermal microcalorimetry and conventional cultures in terms of sensitivity (89% [95% CI 71% to 98%] versus 74% [95% CI 53% to 88%]), specificity (100% [95% CI 48% to 100%] versus 83% [95% CI 36% to 99%]), PPV (100% [95% CI 85% to 100%] versus 95% [95% CI 77% to 99%]), NPV (63% [95% CI 37% to 83%] versus 42% [95% CI 26% to 60%]), or accuracy (91% [95% CI 75% to 98%] versus 78% [95% CI 57% to 89%]; p = 0.17). Isothermal microcalorimetry again had a shorter median (range) time to detection or diagnosis compared with conventional cultures (1.5 hours [0.5 to 48] versus 51.5 hours [18 to 125], difference of medians 50 hours; p < 0.001).

CONCLUSION

Given that isothermal microcalorimetry considerably decreases the time to the diagnosis of a fracture-related infection without compromising the accuracy of the diagnosis, managing teams may eventually use isothermal microcalorimetry-pending developmental improvements and regulatory approval-to rapidly detect infection and begin antibiotic management while awaiting speciation and susceptibility testing to modify the antibiotic regimen. Given the unique thermograms generated, further studies are already underway focusing on speciation based on heat curves alone. Additionally, increased study sizes are necessary for both overall fracture-related infection diagnostic accuracy and test performance on patients using long-term antibiotics given the promising results with regard to time to detection for this groups as well.

LEVEL OF EVIDENCE

Level II, diagnostic study.

Efficacy of Experimental Mouth Rinses on Caries-Related Biofilms in vitro

This study assessed the efficacy of tin and Polyethylenglycol (PEG-3) tallow aminopropylamine in different concentrations on Streptococcus mutans (S. mutans) biofilms to establish a new screening process for different antimicrobial agents and to gain more information on the antibacterial effects of these agents on cariogenic biofilms. Isothermal microcalorimetry (IMC) was used to determine differences in two growth parameters: lag time and growth rate; additionally, reduction in active biofilms was calculated. Experimental mouth rinses with 400 and 800 ppm tin derived from stannous fluoride (SnF₂) revealed results (43.4 and 49.9% active biofilm reduction, respectively) similar to meridol mouth rinse (400 ppm tin combined with 1,567 ppm PEG-3 tallow aminopropylamine; 55.3% active biofilm reduction) (p > 0.05), while no growth of S. mutans biofilms was detected during 72 h for samples treated with an experimental rinse containing 1,600 ppm tin (100% active biofilm reduction). Only the highest concentration (12,536 ppm) of rinses containing PEG-3 tallow aminopropylamine derived from amine fluoride (AmF) revealed comparable results to meridol (57.5% reduction in active biofilm). Lower concentrations of PEG-3 tallow aminopropylamine showed reductions of 16.9% for 3,134 ppm and 33.5% for 6,268 ppm. Maximum growth rate was significantly lower for all the samples containing SnF₂ than for the samples containing control biofilms (p < 0.05); no differences were found between the control and all the PEG-3 tallow aminopropylamine (p > 0.05). The growth parameters showed high reproducibility rates within the treated groups of biofilms and for the controls; thus, the screening method provided reliable results.

Effective antimicrobial combination in vivo treatment predicted with microcalorimetry screening

Objectives

The worldwide emergence of antibiotic resistance calls for effective exploitation of existing antibiotics. Antibiotic combinations with different modes of action can synergize for successful treatment. In the present study, we used microcalorimetry screening to identify synergistic combination treatments against clinical MDR isolates. The synergistic effects were validated in a murine infection model.

Methods

The synergy of meropenem combined with colistin, rifampicin or amikacin was tested on 12 isolates (1 Escherichia coli, 5 Klebsiella pneumoniae, 3 Pseudomonas aeruginosa and 3 Acinetobacter baumannii) in an isothermal microcalorimeter measuring metabolic activity. One A. baumannii strain was tested with two individual pairings of antibiotic combinations. The microcalorimetric data were used to predict in vivo efficacy in a murine peritonitis/sepsis model. NMRI mice were inoculated intraperitoneally and after 1 h treated with saline, drug X, drug Y or X+Y. Bacterial load was determined by cfu in peritoneal fluid and blood after 4 h.

Results

In vitro, of the 13 combinations tested on the 12 strains, 3 of them exhibited a synergistic reduction in MIC (23% n = 3/13), 5 showed an additive effect (38.5% n = 5/13) and 5 had indifferent or antagonistic effects (38.5% n = 5/13). There was a significant correlation (P = 0.024) between microcalorimetry-screening FIC index values and the log reduction in peritoneal fluid from mice that underwent combination treatment compared with the most effective mono treatment. No such correlation could be found between chequerboard and in vivo results (P = 0.16).

Conclusions

These data support microcalorimetic metabolic readout to predict additive or synergistic effects of combination treatment of MDR infections within hours.

The Quorum-Sensing Inhibitor Furanone C-30 Rapidly Loses Its Tobramycin-Potentiating Activity against Pseudomonas aeruginosa Biofilms during Experimental Evolution

The use of quorum-sensing inhibitors (QSI) has been proposed as an alternative strategy to combat antibiotic resistance. QSI reduce the virulence of a pathogen without killing it and it is claimed that resistance to such compounds is less likely to develop, although there is a lack of experimental data supporting this hypothesis. Additionally, such studies are often carried out in conditions that do not mimic the in vivo situation. In the present study, we evaluated whether a combination of the QSI furanone C-30 and the aminoglycoside antibiotic tobramycin would be "evolution-proof" when used to eradicate Pseudomonas aeruginosa biofilms grown in a synthetic cystic fibrosis sputum medium. We found that the biofilm-eradicating activity of the tobramycin/furanone C-30 combination already decreased after 5 treatment cycles. The antimicrobial susceptibility of P. aeruginosa to tobramycin decreased 8-fold after 16 cycles of treatment with the tobramycin/furanone C-30 combination. Furthermore, microcalorimetry revealed changes in the metabolic activity of P. aeruginosa exposed to furanone C-30, tobramycin, and the combination. Whole-genome sequencing analysis of the evolved strains exposed to the combination identified mutations in mexT, fusA1, and parS, genes known to be involved in antibiotic resistance. In P. aeruginosa treated with furanone C-30 alone, a deletion in mexT was also observed. Our data indicate that furanone C-30 is not "evolution-proof" and quickly becomes ineffective as a tobramycin potentiator.

Adjunctive Use of Phage Sb-1 in Antibiotics Enhances Inhibitory Biofilm Growth Activity versus Rifampin-Resistant Staphylococcus aureus Strains

Effective antimicrobials are crucial for managing Staphylococcus aureus implant-associated bone infections (IABIs), particularly for infections due to rifampin-resistant S. aureus (RRSA). Failure to remove the implant results in persistent infection; thus, prolonged suppressive antibiotic therapy may be a reasonable alternative. However, a high incidence of adverse events can necessitate the discontinuation of therapy. In this scenario, commercial Staphylococcal bacteriophage Sb-1 combined with antibiotics is an option, showing a promising synergistic activity to facilitate the treatment of biofilm infections. Therefore, we evaluated the efficacy of the inhibitory activity of five antibiotics (doxycycline, levofloxacin, clindamycin, linezolid, and rifampin) alone or combined with phage Sb-1 (10⁶ PFU/mL) in a simultaneous and staggered manner, to combat five clinical RRSA strains and the laboratory strain MRSA ATCC 43300 in 72 h by isothermal microcalorimetry. The synergistic effects were observed when phage Sb-1 (10⁶ PFU/mL) combined with antibiotics had at least 2 log-reduction lower concentrations, represented by a fractional biofilm inhibitory concentration (FBIC) of <0.25. Among the antibiotics that we tested, the synergistic effect of all six strains was achieved in phage/doxycycline and phage/linezolid combinations in a staggered manner, whereas a distinctly noticeable improvement in inhibitory activity was observed in the phage/doxycycline combination with a low concentration of doxycycline. Moreover, phage/levofloxacin and phage/clindamycin combinations also showed a synergistic inhibitory effect against five strains and four strains, respectively. Interestingly, the synergistic inhibitory activity was also observed in the doxycycline-resistant and levofloxacin-resistant profile strains. However, no inhibitory activity was observed for all of the combinations in a simultaneous manner, as well as for the phage/rifampin combination in a staggered manner. These results have implications for alternative, combined, and prolonged suppressive antimicrobial treatment approaches.