- Volume 7, Issue 12, 2025

The rise of multidrug-resistant Enterobacterales and Pseudomonas aeruginosa has diminished the reliability of conventional antibiotics for treating Multidrug Resistant (MDR) infections. The combination of ceftazidime–avibactam with aztreonam has demonstrated in vitro synergism against multidrug-resistant organisms, notably metallo-beta-lactamase-producing strains. Treatment with the ceftazidime–avibactam/aztreonam combination may provide clinical benefits for patients with multidrug-resistant bacterial infections. The present study aimed to detect genes encoding carbapenem resistance in clinical strains and to determine the efficacy of ceftazidime–avibactam/aztreonam against carbapenemase co-producers. A cross-sectional research study was conducted on 62 carbapenem-resistant clinical isolates collected from November 2022 to February 2024. Ceftazidime–avibactam/aztreonam synergy against 55 carbapenemase producers [New Delhi metallo-beta-lactamase (NDM), imipenem-hydrolysing metallo-beta-lactamase (IMP), Verona Integron-encoded metallo-beta-lactamase (VIM) and oxacillinase-48 (OXA-48)] was determined using the disc diffusion method. Data analysis was performed by chi-square test. Ceftazidime–avibactam/aztreonam synergy was identified against 25 (64.1%) out of 39 isolates exhibiting the NDM gene, seven (77.8%) out of nine isolates that were co-producers of NDM and OXA-48 genes, two (50%) out of four isolates co-producing NDM and VIM carbapenemase genes and a single isolate (33.3%) out of three isolates with NDM, VIM and OXA-48 genes. A wide zone of 3–23 mm diameter was observed for Enterobacterales and 6–7 mm for P. aeruginosa with ceftazidime–avibactam/aztreonam in relative to ceftazidime–avibactam and aztreonam discs when tested alone. More than 30% of isolates showed a statistically significant difference in zone diameter for the ceftazidime–avibactam/aztreonam combination (P<0.05), when compared with the zone size for ceftazidime–avibactam and aztreonam discs when tested alone. The present study showed the in vitro effectiveness of the ceftazidime–avibactam/aztreonam combination against 63.6% of carbapenem-resistant isolates studied. The disc diffusion method requires less technical expertise, and the test result aids in identifying true clinical synergy by observing the widening of the zone diameter that exceeds the aztreonam susceptibility breakpoint.

Proteins facilitating bacterial cell wall (CW) biosynthesis are crucial for survival and broadly remain the target of numerous antimicrobial agents. Herein, we focused on characterizing the physiological roles of low-molecular-weight penicillin-binding proteins (LMW PBPs), with dd-carboxypeptidase (dd-CPase) activity, in Mycobacterium smegmatis. Following various combinatorial gene deletions, cell viability, colony structure and the ability to produce biofilms remained unperturbed. Whilst small changes in cellular morphology and permeability were evident, hierarchical roles could not be ascribed to specific dd-CPase homologues. Strains exposed to lysozyme exhibited low levels of compensatory expression for the remaining homologues, but this was not evident for exposure to the CW-targeting Augmentin. When tested against a broader concentration range of various antibiotics, using MIC and spotting assays, only marginal changes in drug susceptibility were evident. Strains cultured under conditions of excess NaCl or enhanced pH levels grew normally. Given the established role of remodelling in dd-CPase enzymes of other bacteria, we further assessed whether the ability to repair lysozyme-induced CW damage was compromised. With the incorporation of the fluorescent d-amino acid peptidoglycan probe, TAMRA-d-alanine, as a proxy for remodelling, no changes in staining patterns were evident. However, the frequency of cells containing unresolved septa increased in all mutant strains, suggesting a potential role for dd-CPases in the mycobacterial cell process. In conclusion, we have demonstrated that the combinatorial deletion of non-essential mycobacterial dd-CPase homologues largely has no significant impact on mycobacterial physiology or involvement in the response to the various environmental stressors tested herein.

Background. Nitrate-dependent iron (Fe2+) oxidation (NDFO) is an important biogeochemical process, but whether NDFO provides a direct metabolic benefit to facultative anaerobes with diverse lifestyles, such as Salmonella enterica, and what role the respiratory nitrate reductases play in this process is unknown.

Methods. This study investigated NDFO in S. enterica serovar Typhimurium strain SL1344. We compared the WT strain with a ∆narGHIJ ∆narZYW mutant (∆nar), which lacks the primary respiratory nitrate reductase (Nar). Cultures were grown anaerobically in lysogeny broth medium amended with 4 mM nitrate and 10 mM FeSO₄ as defined nitrate and iron sources. Growth, nitrate depletion, nitrite accumulation, and Fe2+ oxidation were monitored over 14 days. Abiotic controls amended with either nitrate or nitrite were included to control for abiotic iron oxidation.

Results. There was no significant difference in the growth rate and biomass production between the WT and ∆nar strains. However, there was significant variation in nitrite reduction and iron oxidation. 56.9% of the nitrate was depleted from the growth medium (initially 4 mM) with the WT cultures compared to 19.7% with the ∆nar strain. Fe2+ oxidation in the WT cultures reached a Fe²+/Fe total ratio of ~0.52–0.61 during exponential growth and was consistent during the stationary phase, whereas for the mutant, the maximum Fe²+/Fe total ratio was ~0.78, which returned to a more reduced state in stationary phase (Fe²+/Fe total ~0.95). Abiotic controls amended with nitrite showed rapid Fe2+ oxidation, highlighting the role of nitrite as an oxidant.

Conclusion. The respiratory nitrate reductases are the primary drivers of NDFO in S. enterica SL1344 and are required for the generation of nitrite, which then abiotically oxidizes Fe2+ to Fe3+. This did not confer a growth advantage, suggesting NDFO is an indirect consequence of nitrate respiration rather than a direct energy-conserving pathway in this organism.

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disorder in preterm infants with a high mortality rate. The aetiology of NEC appears to be multifaceted; however, gut microbiota dysbiosis likely plays a significant role. This systematic review aimed to describe how the gut microbiota of preterm infants with NEC differs from infants without NEC (PROSPERO: CRD42022344126). Databases were searched from inception to 22 June 2022 to identify eligible studies that examined the gut microbiota composition of preterm infants with and without NEC using sequencing methods. Results were described narratively. We identified 28 eligible studies. Overall, findings were heterogeneous and no single gut microbiota signature was associated with NEC in all studies. Importantly, 3 studies reported no difference in the gut microbiota composition between NEC and healthy infants, while studies reported a difference using one or more analytical method (i.e. alpha diversity, beta diversity or differential abundance analysis). Of note, NEC (or development of NEC) was positively associated with increased detection and/or abundance of Enterobacteriaceae (n=11 studies), Clostridium (n=8) and Proteobacteria (n=2). The taxa most frequently associated with NEC (Enterobacteriaceae, Clostridium, and Proteobacteria) may play an important role in the pathogenesis of NEC and should be further explored.

Antimicrobial-resistant (AMR) bacteria are an increasing concern for human and animal medicine. As a result, biosecurity measures such as cleaning and disinfection are becoming heavily relied upon to eradicate and control AMR pathogens. However, evidence of co- and cross-resistance between antimicrobials and disinfectants is rising. The influence of AMR on disinfectant tolerance is poorly understood for pathogens of veterinary and public health importance. Therefore, this study aimed to compare disinfectant tolerance of fluoroquinolone-resistant Campylobacter jejuni, livestock-associated methicillin-resistant Staphylococcus aureus, multi-drug-resistant Escherichia coli and vancomycin-resistant Enterococcus faecium, with their antibiotic-susceptible counterparts. In vitro disinfectant efficacy was assessed, in the presence of organic matter, against a panel of eight disinfectants from six classes. The disinfectant efficacy varied widely depending on bacterial species and disinfectant class. Furthermore, approved disinfectant concentrations were not always deemed effective. All four bacterial species were typically most susceptible to aldehyde and/or quaternary ammonium compound-based products. Mixed evidence was found to suggest a role of AMR in disinfectant tolerance; no role of AMR was identified in E. coli, C. jejuni or E. faecium, whereas a potential role was identified in S. aureus.

Background. Carbapenem-resistant Gram-negative bacteria (CR-GNB), particularly metallo-β-lactamase (MBL) producers, are WHO critical-priority pathogens. In Libya, laboratory-based data are scarce, and no study has assessed endemic medicinal plants as adjunctive options.

Objectives. To generate baseline data on carbapenem resistance and MBL production among clinical Gram-negative pathogens in Misurata, Libya, and to preliminarily evaluate the antibacterial activity and phytochemical composition of Arbutus pavarii extracts.

Methods. We conducted a cross-sectional study of 244 non-duplicate clinical isolates. Carbapenem susceptibility was determined by Kirby–Bauer disc diffusion; MBL production was confirmed by double-disc synergy and combined-disc tests. Ethanolic and aqueous extracts from A. pavarii leaves, stems and fruits were tested against resistant isolates by disc diffusion. Phytochemicals were profiled by HPLC.

Results. The predominant carbapenem-resistant species were Acinetobacter baumannii (29.5%), Klebsiella pneumoniae (26.2%) and Pseudomonas aeruginosa (19.7%). Resistance to both imipenem and meropenem exceeded 60% across these isolates, and MBL activity was detected in 54.5% of carbapenem-resistant K. pneumoniae. Among plant extracts, the aqueous leaf extract showed the highest antibacterial activity against MBL-producing isolates (mean inhibition zone 9.46±7.61 mm at 100%), slightly exceeding the corresponding ethanolic extract (9.31±7.30 mm). Both extracts demonstrated concentration-dependent effects (P<0.05; ANOVA/Kruskal–Wallis). HPLC analysis identified catechin and quercetin as major components, which may underlie the observed activity.

Conclusions. This first laboratory-based report from Libya documents high rates of CR-GNB and MBL production and introduces A. pavarii as a promising endemic plant with adjunctive antibacterial potential. Findings support enhanced AMR surveillance and the exploration of resource-sensitive alternatives in African healthcare settings.