Carbapenemase-producing Serratia spp. are increasingly implicated in healthcare-associated infections. This study aimed to characterize the genetic diversity, resistance mechanisms and susceptibility to last resort antimicrobials of carbapenem-resistant Serratia spp. in France. From 2016 to 2024, 193 carbapenemase-producing Serratia spp. from France were investigated. WGS enabled species identification, MLST typing, resistome characterization and phylogenetic analysis. Antimicrobial susceptibility was assessed by broth microdilution, focusing on last resort antimicrobials. Intrinsic resistance to polymyxins was explored by genomic analysis and lipid A mass spectrometry. S. sarumanii (54%) and S. nevei (41%) dominated the epidemiology while no S. marcescens was identified. The most prevalent carbapenemases were OXA-48-like (56%), NDM (25%), IMP (8%), VIM (7%). MLST identified 67 sequence types (ST) with 42% of the isolates belonging to four high-risk clones: ST-601, ST-298, ST-477, ST-600 and ST-474. β-lactams susceptibility was low, but aztreonam-avibactam remained highly active (98%). Intrinsic resistance to polymyxin did not result from lipid A modifications as reported for Proteae. In France, carbapenemase-producing Serratia spp. were dominated by S. sarumanii and S. nevei. The absence of S. marcescens, the genus leader, highlighted the need of updating MALDI-TOF database. This study highlights Serratia as an underestimated reservoir of multidrug resistance.

Carbapenemase-producing Enterobacterales represent a growing global threat due to their extensive antimicrobial resistance and rapid dissemination. This study characterized the phenotypic and genomic features of Escherichia coli and Klebsiella pneumoniae isolates collected between 2020 and 2022 from four healthcare institutions in Lima, Peru. A total of 320 non-redundant isolates (61 E. coli and 259 K. pneumoniae) were analyzed through antimicrobial susceptibility testing, polymerase chain reaction, and whole-genome sequencing. The most frequent carbapenemase gene was bla NDM (69%), followed by bla KPC (16.9%) and bla OXA-48-like (4.6%). Eleven K. pneumoniae isolates co-produced NDM and KPC, and one E. coli isolate co-harbored NDM and OXA-48-like. All isolates were multidrug resistant, and 5% were pandrug resistant. Novel β-lactam/β-lactamase inhibitor combinations such as aztreonam/avibactam and cefiderocol showed complete activity against all classes of carbapenemases. Genomic analysis revealed predominant E. coli sequence types ST167 and ST410 and K. pneumoniae lineages ST147, ST15, ST45, and ST273. The bla NDM-5 allele was detected for the first time in Peru, mostly in E. coli ST167 , carried on multireplicon IncF-type plasmids. In K. pneumoniae , ST147 was identified as a dominant clone associated with bla NDM-1 , indicating sustained local dissemination of high-risk clonal groups. The coexistence of multiple carbapenemases and plasmid backbones highlights the ongoing evolution of resistance mechanisms. These findings provide actionable evidence to guide treatment strategies in settings with high prevalence of metallo-β-lactamases and underscores the need for continuous genomic surveillance and antimicrobial stewardship to mitigate their clinical and epidemiological impact.

We assessed the in vitro activity of aztreonam-nacubactam and cefepime-nacubactam against a 2021-2023 global collection of clinical isolates of Gram-negative bacilli (12 613 Enterobacterales, 3748 Pseudomonas aeruginosa and 601 Acinetobacter baumannii). Nacubactam is a novel diazabicyclooctane β-lactamase inhibitor that also possesses intrinsic antimicrobial (PBP2 inhibition) and β-lactam enhancer (for β-lactams that bind PBP3 and other non-PBP2 PBPs) activities against Enterobacterales. Aztreonam-nacubactam and cefepime-nacubactam are in clinical development for the treatment of complicated urinary tract infections, acute uncomplicated pyelonephritis and various infections caused by carbapenem-resistant Enterobacterales (CRE).

The global rise of multidrug-resistant (MDR) Gram-negative pathogens challenges therapy, driving development of novel β-lactam/β-lactamase inhibitor (BL/BLI) combinations. Cefepime-based combinations offer mechanistically diverse options against a broad range of resistance phenotypes.

Introduction Orthopaedic infections are one of the common causes of high morbidity and are challenging complications to treat. It includes non-healing ulcers, osteomyelitis, diabetic foot, compound fractures, and SSIs (surgical site infections), such as implant-associated infections and prosthetic joint infections. The most commonly associated organisms include Staphylococcus aureus, Escherichia coli, Pseudomonas, Proteus, and Enterococcus species. However, most of the bacterial isolates exhibit resistance to commonly used antibiotics. Moreover, the spectrum of microbial flora and the antibiotic susceptibility pattern may vary across regions. Therefore, the present study was undertaken with the primary objective of identifying the bacteria isolated from pus samples received for culture in the microbiology laboratory from the Department of Orthopaedics, Tezpur Medical College and Hospital, and determining the antimicrobial susceptibility pattern among the isolated bacteria. The secondary objectives were to analyze the distribution of culture-positive cases by age and wound aetiology and to report MRSA (methicillin-resistant Staphylococcus aureus) prevalence among the isolates. Materials and methods This hospital-based retrospective study was conducted between January 2023 and December 2023. A total of 76 culture-positive pus samples obtained from orthopaedic wound infections were included in the study. The samples were subjected to culture according to standard microbiological procedures and were identified using conventional biochemical tests. Antibiotic susceptibility testing was performed using the Kirby-Bauer disk diffusion method and interpreted according to the Clinical and Laboratory Standards Institute (CLSI) 2023 guidelines. Data were retrieved from laboratory records, test requisition forms, and hospital records. Results Of the 76 culture-positive pus samples, most of the positive samples were from the 21-40 age group and from male patients. The majority of the positive cultures were from compound fractures. Although Gram-negative bacilli constitute an overall large proportion, the most common isolate in the present study was Staphylococcus aureus (32, 42.1%). MRSA accounts for 3/32 (9.4%) among the Staphylococcus aureus isolates. Overall, the Gram-positive bacteria demonstrated higher susceptibility to linezolid and levofloxacin, whereas the Gram-negative bacteria showed good susceptibility to aztreonam, carbapenems (imipenem and meropenem), and piperacillin/tazobactam. Conclusion The study highlights the diverse bacterial aetiology of orthopaedic wound infections, with Staphylococcus aureus being the most predominant organism. It provides insight into the need for periodic surveillance to determine the local bacterial profile and its antibiogram to initiate effective empirical therapy and optimize patient outcomes.

Currently, the increasing isolation rates of New Delhi metallo-beta-lactamase (NDM) positive Klebsiella pneumoniae and the lack of a standard algorithm for the treatment of infections caused by these isolates necessitate the search for effective treatment options. This study aimed to investigate the efficacy of the combination of ceftazidime-avibactam (CZA), frequently used in the treatment of carbapenem-resistant Enterobacterales (CRE) infections in recent years with aztreonam (AZT), which is expected to become available in our country soon and the combination of meropenem (MEM) with colistin (COL), which is frequently preferred in our hospital against NDM-positive K.pneumoniae isolates using in vitro synergy tests and to determine the susceptibility of these isolates to cefiderocol (FDC), which is recommended as an alternative treatment option in CRE infections. A total of 63 K.pneumoniae isolates, isolated from clinical samples in the Bacteriology Laboratory of the Department of Medical Microbiology at Süleyman Demirel University Faculty of Medicine and identified as NDM positive by real-time polymerase chain reaction, were included in the study. The susceptibility of the isolates to CZA, AZT, MEM and COL was tested by broth microdilution method and FDC susceptibility was tested by Kirby-Bauer disk diffusion method according to the European Committee on Antimicrobial Susceptibility Testing criteria. The efficacy of CZA-AZT and MEM-COL combinations against NDM positive K.pneumoniae isolates was tested using the checkerboard method. Time-kill assays were performed to investigate the bactericidal activity of CZA-AZT and MEM-COL combinations at different concentrations and time points in five isolates harboring different carbapenemase genes (two NDM+OXA-48, one NDM, one NDM+OXA-48+KPC, and one NDM+OXA-48/VIM/IMP). All isolates included in our study were found as resistant to CZA, AZT and MEM, while 77.8% were resistant to FDC and 54% were resistant to COL. According to the checkerboard test results, the CZA-AZT combination showed synergistic interaction against all isolates, while the MEM-COL combination exhibited synergistic interaction against 57.1% of the isolates, additive interaction against 25.4% and undefined interaction against 17.5%. In time-kill assays, synergistic activity was observed at various time points in all isolates with the CZA-AZT combination and in four isolates with the MEM-COL combination, while bactericidal activity was detected at certain time points. Although an undefined interaction was determined in the checkerboard test against one isolate (NDM+OXA-48 positive) with the MEM-COL combination, synergistic activity and bactericidal effect were observed at the 12th and 24th hours with the 1xMIC MEM + 1xMIC COL combination in the time-kill assay against the same isolate. In conclusion, the combination of CZA-AZT seems to be a promising treatment option in infections caused by NDM positive K.pneumoniae isolates. In cases where CZA-AZT combination therapy cannot be applied, MEM-COL combination therapy may be considered as an alternative treatment option. In situations where both treatment options cannot be used, cefiderocol monotherapy may be considered as an alternative in selected cases, given the low and heterogeneous susceptibility rates among NDM-positive isolates, provided that close clinical and microbiological monitoring is ensured. However, careful monitoring is required during cefiderocol therapy and treatment modification should be considered in cases of clinical non-response.

Background/Objectives: The impact of antimicrobial susceptibility testing methodology on the categorization and positioning of cefiderocol and aztreonam-avibactam against metallo-β-lactamase (MBL)-producing Gram-negative bacilli remains unclear. This study aimed to evaluate the in vitro activity of cefiderocol and aztreonam-avibactam against clinical MBL-producing isolates and to assess the agreement between different cefiderocol susceptibility testing methods. Methods: A total of 299 non-duplicate clinical MBL-producing Gram-negative isolates were collected from clinical samples between 2022 and 2025. Antimicrobial susceptibility testing was performed using broth microdilution, disc diffusion, and gradient strip diffusion according to European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. Carbapenemase genes were identified by immunochromatography and multiplex PCR. Categorical agreement and error rates between cefiderocol testing methods were analyzed. Results:Klebsiella pneumoniae was the predominant species, mainly producing NDM alone or in combination with OXA-48-like carbapenemases. Aztreonam-avibactam demonstrated complete activity against all Enterobacterales isolates (262/262, 100%) and high activity against Pseudomonas spp. (33/37, 89%). Cefiderocol susceptibility among Enterobacterales varied markedly depending on the testing method. Disc diffusion yielded 14% susceptibility (37/262), which increased to 52% (136/262) after ATU resolution, whereas broth microdilution showed 85% susceptibility (224/262). This resulted in low categorical agreement (42%) and a high rate of major errors (58%), with no very major errors detected. Cefiderocol activity did not differ substantially across carbapenemase types and was highest against VIM-producing Pseudomonas spp. Conclusions: Aztreonam-avibactam showed consistent in vitro activity against MBL-producing Enterobacterales, whereas cefiderocol activity was strongly influenced by the susceptibility testing methodology. Disc diffusion substantially underestimated cefiderocol susceptibility compared with broth microdilution. These findings highlight the critical impact of testing methodology on cefiderocol categorization and support the therapeutic role of last-line agents in the management of MBL-producing Gram-negative infections, with direct implications for clinical microbiology laboratories and antimicrobial stewardship programs.

Hyponatremia is a common electrolyte abnormality encountered in hospitalized patients and may arise from a variety of etiologies, including infection, medications, endocrine disorders, and inappropriate fluid management. Severe hyponatremia can lead to significant neurological morbidity and requires careful evaluation and management. We report the case of a 72-year-old woman with a background of chronic obstructive pulmonary disease (COPD) and type 2 respiratory failure who developed persistent severe hyponatremia during treatment for sepsis secondary to bronchopneumonia. Despite treatment with broad-spectrum antibiotics and fluid restriction, the patient's sodium remained low at approximately 116 mmol/L. Extensive investigations, including serum osmolality and serum cortisol, were within normal limits. Following the escalation of antibiotic therapy from aztreonam to meropenem and the removal of the fluid restriction, the patient's sodium levels gradually improved over several days. This case highlights the importance of reassessing fluid management and ongoing sepsis as contributing factors in persistent hyponatremia.

Aztreonam-avibactam (AZA) is a new monobactam/beta-lactamase inhibitor combination that recently received regulatory approval in the United States (U.S.) and Europe. In this study, we evaluated the performance of ETEST AZA, a gradient diffusion method, compared to reference broth microdilution for 650 challenge (n = 77) and clinical (n = 573) Enterobacterales isolates across four study sites. Using the U.S. Food and Drug Administration (FDA) interpretive breakpoints for ETEST AZA, challenge isolates demonstrated a 97.3% (72/74) essential agreement (EA), 93.2% (69/74) categorical agreement (CA), 0% very major errors (VME) and major errors (ME), and 6.8% (5/74) minor errors (mE). Clinical isolates demonstrated a 95.5% (504/528) EA, 98.7% (521/528) CA, 0% VME, 0.2% (1/516) ME, and 1.1% (6/528) mE. Overall, the combined set achieved a 95.7% (576/602) EA and 98.0% (590/602) CA, with 0% VME, 0.2% (1/577) ME, and 1.8% (11/602) mE. Using the European Committee on Antimicrobial Susceptibility Testing (EUCAST) interpretive breakpoints, challenge isolates demonstrated a 96.1% (74/77) EA, 93.5% (72/77) CA, and 31.3% (5/16) VMEs, while clinical isolates demonstrated a 94.1% (539/573) EA and 99.7% (571/573) CA including 7.7% (1/13) VME and 0.2% (1/560) ME. The combined set demonstrated a 94.3% (613/650) EA, 98.9% (643/650) CA, 0.2% (1/573) MEs, but 20.7% (6/21) VMEs due to the lack of an intermediate breakpoint that is addressed as a limitation in the European package insert. Both bias and trending were in alignment with regulatory requirements. In reproducibility testing of 10 on-scale strains, 100% (270/270) of the results were within ±1 doubling dilution of the modal minimal inhibitory concentration. In conclusion, ETEST AZA provides accurate, reproducible susceptibility results that meet regulatory requirements for many Enterobacterales species when interpreted using FDA or EUCAST criteria.

Members of the genus Psychrobacillus are widely distributed across diverse environments, and novel representatives continue to be identified. Here, we describe the strain nc5.1[T], isolated from soil near Lake Syltran-Kel in the Kabardino-Balkarian Republic, Russia. Phylogenomic analysis indicated that P. glaciei PB01[T] was its closest relative, placing the isolate within the genus Psychrobacillus. The average nucleotide identity (84.3%) and digital DNA-DNA hybridization (31%) values compared with PB01[T] suggested that the isolate represents a novel species. The strain nc5.1[T] was a Gram-negative, motile, rod-shaped bacterium forming circular, smooth, beige-brown colonies. No morphologically detectable endospores were observed under sporulation-inducing conditions. Optimal growth conditions were pH 6.5, 0.5% NaCl, and 30°C; however, a minor but reproducible viable fraction persisted after exposure to 80°C. Biochemical profiling revealed that the strain assimilated 46 carbon sources spanning carbohydrates, amino acids, and organic acids and exhibited growth in the presence of aztreonam, nalidixic acid, and potassium tellurite. The dominant cellular fatty acids were C14:1 (52.8%), C14:0 (16.0%), and C16:0 (7.7%), which distinguished the isolate from P. glaciei. Genomic analysis identified biosynthetic gene clusters associated with the synthesis of iturin and a streptozotocin-like moiety, suggesting the capacity for biosynthesis of secondary metabolites with beneficial properties. MTT assays showed that culture supernatants did not reduce mammalian cell viability but, conversely, moderately stimulated the proliferation of PANC-1 cells. Together, the phenotypic, chemotaxonomic, and genomic data indicate that strain nc5.1[T] represents a novel species with the proposed name Psychrobacillus syltrankelensis sp. nov. The type strain is nc5.1[T] (=RCAM 07221).IMPORTANCEThe discovery of the P. syltrankelensis species extends our understanding of diversity within Bacillaceae and reveals traits that challenge the established views of the family. Based on genomic thresholds, nc5.1ᵀ clearly represents a novel species while also displaying atypical morphological features, such as Gram-negative staining and absence of sporulation. Despite the lack of morphologically detectable endospores, the strain retained viability after exposure to elevated temperatures, further emphasizing its unusual physiological profile. These characteristics underscore the limitations of morphology-based taxonomy and the necessity of genome-guided classification. Genome analysis revealed two adaptive groups within Psychrobacillus, distinguished by mutually exclusive biosynthetic clusters responsible for the synthesis of either iturin or bacillomycin D, with nc5.1ᵀ belonging to the iturin-producing lineage. The nc5.1ᵀ isolate also harbored a highly divergent streptozotocin-like locus, indicating unexplored secondary metabolism with potential biotechnological relevance. At the same time, culture supernatants unexpectedly stimulated the growth of human pancreatic carcinoma cells, underlining the complexity of functional predictions based solely on genomic data. Together, these findings highlight the importance of combining phenotypic, ecological, and genomic approaches for accurate species delineation and provide new insights into the hidden metabolic potential of Psychrobacillus.

The burden of antimicrobial resistant bacteria and resistance genes exists in diverse niches, where they can be disseminated to other ecosystems, including the food chain. This study was conducted to investigate the distribution of antibiotic resistant and extended spectrum beta-lactamase (ESBL) producing Enterobacteriaceae in pit latrines in urban and suburban communities in Lagos State, Nigeria. Using standard microbiological methods, bacteria strains were isolated from twenty sludge samples obtained from three sites. Isolates were molecularly identified by 16S rRNA gene amplicon sequencing and bioinformatics analysis. Antibiotic susceptibility testing and screening for ESBL production was done by the disc diffusion and double-disc synergy test. Genetic determinants that encode ESBL were detected by PCR. Forty-five bacterial strains belonging to Aeromonadaceae (5), Enterobacteriaceae (35), Erwiniaceae (1), and Vibrionaceae (4) were isolated from the sludge samples. Escherichia fergusonii, Klebsiella pneumoniae, and Shigella spp. comprised Enterobacteriaceae that were isolated. All (100%) the isolates were sensitive to cefixime and ceftriaxone, while 23% and 46% were resistant to aztreonam and ampicillin respectively. Multidrug resistance was prevalent among E. fergusonii compared to the other two bacterial species. Twenty six percent of the isolates phenotypically displayed ESBL production. blaTEM gene was detected across all three bacterial species and blaSHV was the dominant (49%) among ESBL encoding genes detected. Six percent of E. fergusonii isolates harboured all four ESBL encoding genes. Pit latrines are potential reservoir of antibiotic resistance bacteria and resistance genes that mediate ESBL production. Improved hygiene and sanitation should be implemented to forestall the spread of these pathogens.