Mariana Castanheira

Fosmanogepix (prodrug of manogepix) is a novel antifungal agent targeting the Gwt1 enzyme. This agent has activity against a diverse spectrum of fungal species, including species refractory to other antifungal classes or multidrug-resistant fungi. A total of 332 molds from a worldwide surveillance study were susceptibility tested for manogepix and comparator antifungal agents by the Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution method. Wild-type upper limit (WT-UL) values were determined for manogepix against organism groups using cumulative surveillance data. Isolates were collected from 20 countries, 41 hospitals, and 7 different infection sources. Eighteen genera were represented. Isolates included 208 non- fumigatus Aspergillus spp.; 37.3% (124 isolates) were non- Aspergillus molds. The manogepix minimum effective concentration (MEC _50/90 ) was lower than the MIC _50/90 for azole comparators or amphotericin B against all Aspergillus spp., Fusarium spp., Scedosporium spp., Lomentospora spp., Mucor spp., and Penicillium spp. Only Rhizopus spp. had higher MEC _50/90 values for manogepix than the MIC _50/90 values of the comparators. The WT-UL values reflected this, with the highest values for Rhizopus spp. at 16 mg/L and Mucor spp. at 4 mg/L, while they were ≤0.12 mg/L for all other organisms. Between 2023 and 2024, there were no organisms with MECs for manogepix above the WT-UL value. Manogepix displayed robust in vitro activity against contemporary non- Aspergillus fumigatus mold isolates. This agent was more potent than azole comparators or amphotericin B against most organism groups. Historically, less than 5% of isolates tested ( n = 19) had MECs above the WT-UL cutoff values. These data support the continued development of manogepix for the treatment of mold infections. IMPORTANCE: Fosmanogepix (prodrug of manogepix) is a novel antifungal agent with a new mechanism of action and broad-spectrum activity, including against yeasts and molds. It is currently in two Phase 3 clinical trials for the treatment of invasive candidiasis and invasive mold infections and has previously been used for the treatment of Fusarium spp. infections during an outbreak. There are three main antifungal classes (echinocandins, azoles, and polyenes), but only azoles and amphotericin B have activity against non- Aspergillus molds; therefore, novel antifungal agents are urgently needed because invasive fungal infections have high morbidity and mortality rates. Here, we look at the in vitro activity of manogepix and comparator antifungal agents against non- Aspergillus fumigatus mold isolates collected from patient infections in 2023 and 2024. Manogepix showed potent in vitro activity against these organisms, with similar to or better activity than that of the comparators against most organism groups, and represents a promising potential future treatment option.

We evaluated the presence and phenotypic impact of PBP3 insertions YRIN ( n = 44) and YRIK ( n = 18) among 124 Escherichia coli isolates belonging to high-risk lineages selected from 1,471 isolates displaying resistance to β-lactams. PBP3 insertions were detected among 62 isolates. YRIN insertions were detected among isolates belonging to ST167 ( n = 23), ST361 ( n = 7), ST410 ( n = 10), ST617 ( n = 1), and ST648 ( n = 3), while YRIK insertions were observed in ST405 ( n = 9), ST410 ( n = 5), and ST617 ( n = 4). Aztreonam-avibactam inhibited 90.3% of all isolates from high-risk clones and 80.6% of the isolates harboring PBP3 insertions when applying the EUCAST breakpoints. Aztreonam-avibactam inhibited 66.7% of the YRIK-harboring isolates (MIC _50/90 , 2/16 mg/L) and 86.4% of the ones harboring YRIN insertions (MIC _50/90 , 1/8 mg/L); however, the susceptibilities to other β-lactams were lower among YRIN isolates (25.6%–60.5%) compared to YRIK (55.6%–88.9%). Overall, ST617 was more resistant to all agents when compared to other STs, regardless of PBP3 insertions or the presence of other examined resistance mechanisms. Acquired β-lactamase genes and OmpC deleterious alterations were present in all isolates. CMY-42, CMY-141, and CMY-145 that have been associated with elevated aztreonam-avibactam MICs were detected among 13 isolates, and 4 (30.8%) were susceptible to this combination. All isolates harboring bla _NDM-5 ( n = 37) possessed PBP3 insertions. Aztreonam-avibactam inhibited 83.8% of these isolates. Resistance to aztreonam-avibactam is multifactorial, and singular resistance mechanisms are unable to elevate MIC values to resistant categories. Additionally, lineage-specific contributions to resistance play an important role in the overall development of β-lactam resistance, although these mechanisms appear to function outside the known repertoire of resistance-conferring mutations and warrant further study.

Purpureocillium lilacinum , a common environmental fungus, can cause hyalohyphomycosis with varied clinical manifestations. Mortality rates can reach 20% with invasive disease. P. lilacinum is intrinsically resistant to amphotericin B, leaving few treatment options. In the absence of clinical breakpoints, epidemiological cutoff values (ECVs) can aid clinicians in monitoring antifungal resistance trends and in guiding initial therapy. We performed antifungal susceptibility testing (AFST) on P. lilacinum isolates to establish minimum inhibitory concentration (MIC) and minimum effective concentration (MEC) distributions and ECVs. Data were collected from 13 laboratories located in seven countries. AFST was performed by broth microdilution (CLSI M38 standard) for itraconazole, voriconazole, posaconazole, isavuconazole, terbinafine, flucytosine, amphotericin B, natamycin, and manogepix. ECVs were established using the iterative statistical method with ECOFFinder (v2.1) following CLSI M57 guidelines. Results from 479 P. lilacinum isolates were analyzed. ECVs were 1 μg/mL for voriconazole, 2 μg/mL for posaconazole, 4 μg/mL for isavuconazole, and 2 μg/mL for terbinafine. Itraconazole displayed a trimodal MIC distribution, although almost all MICs were ≥0.5 µg/mL (mode, 16 μg/mL). Amphotericin B, natamycin, and flucytosine MICs were truncated at the high end of the range and consistent with intrinsic resistance. The manogepix modal MEC was 0.008 μg/mL. These proposed P. lilacinum ECVs and MIC/MEC distributions provide baseline data to monitor resistance trends. Our results confirm that P. lilacinum is intrinsically resistant (IR) to amphotericin B and likely IR to natamycin and flucytosine. Caution is needed in interpreting itraconazole results due to high interlaboratory variability. IMPORTANCE: Purpureocillium lilacinum is a hyaline mold commonly found in the environment and used as an agricultural biopesticide. Infections caused by P. lilacinum can range from fungal eye infections to life-threatening pulmonary and disseminated disease, and mortality rates can be high (up to 20%). Single-center studies examining antifungal susceptibility testing (AFST) data found reduced susceptibility to certain antifungals, but more robust global AFST studies are needed to help interpret MICs and MECs. We performed AFST according to the Clinical Laboratory and Standards Institute reference method in thirteen independent laboratories on 479 P. lilacinum isolates to establish MIC/MEC distributions and epidemiological cutoff values (ECVs) for nine antifungals, including those recommended by global treatment guidelines. The calculated ECVs were 1 μg/mL for voriconazole, 2 μg/mL for posaconazole, 4 μg/mL for isavuconazole, and 2 μg/mL for terbinafine. Our results also confirm that P. lilacinum is intrinsically resistant to amphotericin B and likely intrinsically resistant to natamycin and flucytosine. Caution is needed in interpreting itraconazole AFST results due to high interlaboratory variability. These antifungal in vitro susceptibility data suggest limited options to treat P. lilacinum infections.

Broth microdilution (BMD) susceptibility testing with Acinetobacter spp. can be challenging with skipped wells and trailing observed for some agents. This also applies to cefiderocol, where isolates can display different growth patterns, such as trailing, regrowth, or hazy growth. To better understand the growth patterns observed with cefiderocol BMD testing, the content of wells was evaluated microscopically. Analysis of the trailing, hazy, and regrowth wells above the MIC endpoints showed disturbed growth with long filamentous and spherical cells characteristic of cell envelope instability observed with other β-lactams. When a cell metabolic activity reagent was used to evaluate the viability of the cells in wells above the MIC, inconclusive results were obtained, but when plated, substantial growth was noted for most wells, demonstrating that those cells were able to escape cefiderocol’s bactericidal activity. Replicate testing ( n = 5) showed that aberrant growth patterns were reproducible, with some MIC variability observed with isolates showing regrowth or trailing, and did not correlate with growth patterns that can be noted in cefiderocol disk diffusion testing (inner colonies, ghost zones, or fuzzy edges). When the prevalence of the different BMD growth patterns was evaluated with 455 isolates from Europe and the United States tested as part of a surveillance program for cefiderocol, about 60% of the isolates exhibited unclear endpoints, and these were noted in most countries, Acinetobacter species, and different genetic backgrounds. Unclear endpoints are not uncommon when testing Acinetobacter spp. against cefiderocol, and tolerability of cells in the presence of cefiderocol seems to be the cause of this. IMPORTANCE: Cefiderocol susceptibility testing for Acinetobacter spp. is challenging due to the aberrant growth patterns that occur in the broth microdilution method, including trailing, regrowth, and haziness. We initiated this study to better understand these phenomena and assess if these growth patterns were reproducible. We concluded that cefiderocol is not bactericidal against certain isolates and that, despite the cell membrane biosynthesis process being impaired, the cells do not undergo lysis as expected with β-lactam agents. We also evaluated the prevalence of these aberrant growth patterns and evaluated the genetic traits of the isolates producing them, showing that these patterns are common and not related to geographic origin or specific genetic traits.

Gepotidacin is a novel, first-in-class triazaacenaphthylene antibiotic that inhibits bacterial DNA replication through a distinct binding site and unique mechanism of action that provides well-balanced inhibition of two different type II topoisomerase enzymes (DNA gyrase and topoisomerase IV) for most pathogens. Gepotidacin was recently approved by the US Food and Drug Administration (FDA) and the Medicines and Healthcare Products Regulatory Agency (MHRA) for the treatment of uncomplicated urinary tract infections (uUTI) and by the FDA for uncomplicated urogenital gonorrhea. This study investigated the in vitro time-kill kinetics, post-antibiotic effect (PAE), and sub-inhibitory MIC effect (PAE-SME) of gepotidacin, as well as interactions between gepotidacin and select marketed antibacterial agents for species where the published activity of gepotidacin was limited. Species included are those known to be associated with uUTI: Citrobacter freundii species complex, Enterobacter cloacae species complex, Klebsiella aerogenes , Klebsiella pneumoniae , Proteus mirabilis , Providencia rettgeri , Enterococcus faecalis , and Staphylococcus saprophyticus . Isolates were selected to represent various phenotypes, including wild type, extended-spectrum beta-lactamase positive (ESBL), and fluoroquinolone-resistant. Gepotidacin displayed concentration-dependent activity in time-kill, PAE, and PAE-SME experiments. Gepotidacin displayed bactericidal activity, often by 8 h, against 83% of isolates when tested at 4× and 10× MIC. In general, modest PAEs (>1–4 h) and extended PAE-SMEs (>4 h) were observed for gepotidacin. No antagonism was observed in broth microdilution checkerboard studies with marketed antibiotics, and the only consistent synergy observed was with gepotidacin and vancomycin against S. saprophyticus . These data add to the understanding of pharmacodynamics at play when treating with gepotidacin relevant uUTI species other than Escherichia coli . IMPORTANCE: Antibiotic resistance continues to limit treatment options for common infections such as urinary tract infections (UTIs). Gepotidacin is a recently approved antibiotic that works in a new way compared with existing drugs, allowing it to remain active against bacteria that are resistant to many commonly used treatments. In this study, we examined how effectively gepotidacin kills several bacterial species that cause UTIs, including organisms that are resistant to fluoroquinolones or produce extended-spectrum β-lactamases. Gepotidacin was shown to rapidly reduce bacterial populations at clinically relevant concentrations and continued to suppress bacterial growth even after short exposures. Importantly, gepotidacin did not interfere with the activity of other commonly used antibiotics, suggesting it can potentially be used alongside existing therapies if needed. These findings provide additional evidence supporting the effectiveness of gepotidacin against a broad range of UTI pathogens and help improve our understanding of how this new antibiotic may perform in clinical treatment.

Background: Catheter-related bloodstream infections are common in patients receiving hemodialysis through a central venous catheter. Taurolidine, a novel broad-spectrum antimicrobial catheter lock solution, is FDA-approved in combination with heparin for reducing the incidence of such infections. Methods: In vitro activity of taurolidine was assessed against 442 bacterial and 50 yeast clinical bloodstream infection isolates selected from the SENTRY Antimicrobial Surveillance Program and tested according to the Clinical and Laboratory Standards Institute methodology. Multidrug-resistant species and phenotypes were included. Results: Taurolidine was highly active against all isolates, with MIC₅₀/MIC₉₀ values of ≤1024/1024 μg/mL for most species. The highest MICs observed were among isolates of Mycobacterium avium complex and Burkholderia cepacia complex (MIC₉₀, 2048 μg/mL) and Candida albicans (MIC₉₀, 4096 μg/mL). All isolates were inhibited by 13,500 μg/mL of taurolidine, the concentration of the commercially available product. Conclusions: Taurolidine activity was very similar among Gram-positive, Gram-negative, and yeast clinical isolates, with the activity of taurolidine being unaffected by phenotypic resistance to other antimicrobials. Taken together with clinical efficacy data from clinical trials, this provides a theoretical basis for the idea that taurolidine-based lock solutions may be able to reduce the risk of catheter-related bloodstream infections from a wide variety of pathogens and resistance phenotypes.

We evaluated 14 304 Pseudomonas aeruginosa isolates from 56 US medical centers (2015–2024). Ceftazidime-avibactam, ceftolozane-tazobactam, and imipenem-relebactam were active against 97.0%–97.9% of isolates overall. Piperacillin-tazobactam and ceftazidime activities decreased slightly during the study period, whereas the activities of meropenem, levofloxacin, and tobramycin improved since 2017.

Background: We analysed 10 years of data from the INFORM programme, which surveys β-lactamases and the activity of ceftazidime-avibactam in US hospitals. Methods: A total of 33 701 Enterobacterales isolates consecutively collected in 22 US hospitals during 2013–22 were susceptibility tested. Escherichia coli and Klebsiella pneumoniae displaying MICs ≥ 2 mg/L for two of ceftriaxone, ceftazidime, cefepime or aztreonam; or carbapenem-resistant Enterobacterales (CRE) were evaluated for the presence of β-lactamase genes using microarray/PCR (2013–15) or whole genome sequencing (2016–22). Results: ESBLs were detected among 2325/2681 (15.5% of 14 923 overall non-CRE isolates) E. coli and 874/954 (13.3% of 6572) K. pneumoniae. The most common ESBL in both groups was CTX-M-15–like (10.4% of E. coli and 10.7% of K. pneumoniae isolates). A decline in E. coli producing CTX-M-15–like was noted in 2022 (12.6% in 2021 and 8.3% in 2022), and SHV ESBLs had a steady decline among K. pneumoniae since 2015. CRE isolates declined steadily from 1.6% in 2013 to 0.8% in 2022. Carbapenemase-positive isolates also declined from 1.3% to 0.5%, with a decline in KPC producers but an increase in isolates producing NDM; NDM producers were initially detected in 2015 and ranged from 1 to 7 isolates collected in the last 5 study years. Ceftazidime-avibactam and the carbapenems are the most active agents against β-lactamase–producing isolates. Conclusions: Changes in β-lactamase–producing isolates and their susceptibility profiles should be closely monitored at a local and global level since these shifts impact patient treatment, but longitudinal data such as this information is scarce.

Background: Ceftobiprole is an advanced-generation cephalosporin approved in Europe in 2013 for various indications, and in the United States (US) in 2024 for community-acquired bacterial pneumonia (CABP), acute bacterial skin and skin structure infections, and Staphylococcus aureus bacteremia, including right-sided endocarditis. Methods: The in vitro activity of ceftobiprole and comparators was evaluated against 2793 Streptococcus pneumoniae causing lower respiratory tract infections in 32 US sites (2016–2020), including against subsets from various geographic regions, resistance phenotypes and prevalent serotypes. Results: Ceftobiprole inhibited 99.5% of all S. pneumoniae at the MIC of ≤0.5 mg/L (MIC_50/90, 0.015/0.25 mg/L). Susceptibilities of 98.2% to 100% were observed for ceftobiprole against isolates originating from each surveyed year or each US Census Division. Ceftobiprole retained activity against isolates resistant to macrolides (98.8%), tetracycline (98.2%), oral penicillin (95.4%), against multidrug-resistant isolates (97.0%), and various serotypes (93.8–100%). Ceftriaxone (97.4%) and amoxicillin–clavulanate (95.1%) also showed elevated susceptibilities overall, but inconsistent results and lower than those observed for ceftobiprole were noted against isolates with elevated penicillin MIC or specific serotypes (i.e., 19A). Conclusions: These in vitro results, coupled with documented clinical efficacy, indicate that ceftobiprole is a valuable option to treat CABP caused by S. pneumoniae in the US.

Objectives: The primary objective was to evaluate the antimicrobial susceptibility of Pseudomonas aeruginosa causing infection in elderly (≥65 years old) patients hospitalized in intensive care units (ICUs) of United States medical centers. Susceptibility results from isolates of elderly patients in ICUs were compared to isolates from elderly patients not in ICUs (elderly non-ICU) and adult ICU patients (18 to 64 years old; adult ICU). Methods: P. aeruginosa isolates were consecutively collected from 74 US medical centers in 2021–2025 and susceptibility tested by reference broth microdilution in the monitoring laboratory (Element Iowa City [JMI Laboratories]). The organism collection included 999 isolates from elderly ICU, 2027 isolates from elderly non-ICU, and 1022 isolates from adult ICU patients. Results: The most active agents against P. aeruginosa from all three patient groups were ceftazidime-avibactam (95.8% to 97.3% susceptible), ceftolozane-tazobactam (96.0% to 98.3% susceptible), imipenem-relebactam (97.6% to 98.7% susceptible), and tobramycin (91.4% to 94.7% susceptible). Susceptibility to piperacillin-tazobactam, ceftazidime, cefepime, meropenem, and imipenem were markedly lower among isolates from elderly and adult ICU patients compared to elderly non-ICU patients. Susceptibility to levofloxacin and tobramycin were lower among isolates from adult ICU patients compared to elderly ICU and non-ICU patients. Moreover, the frequency of multidrug-resistant (MDR) isolates was markedly higher among elderly (18.4%) and adult (22.4%) ICU patients compared to elderly non-ICU (11.0%) patients. An annual analysis of susceptibility to selected β-lactams showed a slight variation in susceptibility rates without a clear trend. Conclusions: Ceftazidime-avibactam, ceftolozane-tazobactam, and imipenem-relebactam were highly active and exhibited similar coverage against a large contemporary collection of P. aeruginosa isolates from ICU elderly, non-ICU elderly, and ICU adult patients. Cross-resistance among these β-lactamase inhibitor combinations (BLICs) varied markedly, indicating that all three should be tested in the clinical laboratory and available for clinical use.