New Delhi metallo-β-lactamase (NDM)-carrying IncX3 plasmids is important in the transmission of carbapenem resistance in Escherichia coli. Fitness costs related to plasmid carriage are expected to limit gene exchange; however, the causes of these fitness costs are poorly understood. Compensatory mutations are believed to ameliorate plasmid fitness costs and enable the plasmid’s wide spread, suggesting that such costs are caused by specific plasmid–host genetic conflicts. By combining conjugation tests and experimental evolution with comparative genetic analysis, we showed here that the fitness costs related to ndm/IncX3 plasmids in E. coli C600 are caused by co-mutations of multiple host chromosomal genes related to sugar metabolism and cell membrane function. Adaptive evolution revealed that mutations in genes associated with oxidative stress, nucleotide and short-chain fatty acid metabolism, and cell membranes ameliorated the costs associated with plasmid carriage. Specific genetic conflicts associated with the ndm/IncX3 plasmid in E. coli C600 involve metabolism and cell-membrane-related genes, which could be ameliorated by compensatory mutations. Collectively, our findings could explain the wide spread of IncX3 plasmids in bacterial genomes, despite their potential cost.

Overuse and inappropriate use of antibiotics are important contributors to bacterial antimicrobial resistance (AMR), especially in ambulatory primary healthcare (PHC) settings in low- and middle-income countries. This study aimed to investigate antibiotic prescription patterns among patients with acute respiratory infections (ARIs) in rural PHC facilities in the Guangdong Province, China. A total of 444,979 outpatient prescriptions were extracted from the electronic medical record system of 35 township health centers (THCs) and 2 community health centers (CHCs) between November 2017 and October 2018. We used the chi-square test to analyze the antibiotic prescription patterns and binary logistic regression to explore patient-related factors associated with antibiotic prescriptions. Of the 162,742 ARI prescriptions, 85.57% (n = 139,259) included at least one antibiotic. Among the 139,259 prescriptions with antibiotics, 37.82% (n = 52,666) included two or more antibiotics, 55.29% (n = 76,993) included parenteral antibiotics, and 56.62% (n = 78,852) included Watch group antibiotics. The binary logistic regression indicated that (1) female patients were slightly less likely to be prescribed antibiotics than males (adjusted odds ratio (OR) = 0.954, 95% confidence interval [CI] [0.928–0.981]; p = 0.001); and (2) compared to patients aged ≤5 years, those who were 6–15 years old (adjusted OR = 1.907, 95% CI [1.840–1.978]; p < 0.001), 16–60 years old (adjusted OR = 1.849, 95% CI [1.785–1.916]; p < 0.001), and >60 years old (adjusted OR = 1.915, 95% CI [1.810–2.026]; p < 0.001) were more likely to be prescribed antibiotics. The overuse and irrational use of antibiotics in PHC settings remain major healthcare challenges in rural Guangdong. Thus, it is imperative to implement targeted antimicrobial stewardship (AMS) policies to address this problem.

Hypervirulent carbapenem-resistant Acinetobacter baumannii (hv-CRAB) has emerged in bloodstream infections (BSI). Cases of BSI caused by hv-CRAB (hv-CRAB-BSI) had posed a significant threat to hospitalized patients. In this study, 31 CRAB strains isolated from Chinese BSI patients were analyzed, of which 24 were identified as hv-CRAB-BSI and 7 as non-hv-CRAB-BSI, using the Galleria mellonella infection model. Patients with hv-CRAB-BSI had higher rates of septic shock (79.2% vs. 14.3%, p = 0.004) and mortality (66.7% vs. 14.3%, p = 0.028). All strains were resistant to most antibiotics but sensitive to colistin. Hv-CRAB-BSI showed lower resistance to minocycline than non-hv-CRAB-BSI (54.2% vs. 100%, p = 0.03). Whole-genome sequencing revealed that the detection rates of immune modulation genes ptk and epsA in hv-CRAB-BSI were significantly higher than in non-hv-CRAB-BSI (91.7% vs. 28.6%, p = 0.002). Additionally, all ST457 hv-CRAB-BSI lacked abaR, and all ST1486 non-hv-CRAB-BSI lacked adeG. The checkerboard dilution method assessed the efficacies of various antibiotic combinations, revealing that although synergism was rarely observed, the combination of colistin and minocycline showed the best efficacy for treating CRAB-BSI, regardless of whether the infections were hv-CRAB-BSI or non-hv-CRAB-BSI. These findings highlight the importance of analyzing molecular characteristics and exploring effective treatment strategies for hv-CRAB-BSI.