The rise of antibiotic resistance and the dwindling antimicrobial pipeline have emerged as significant threats to public health. The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a global threat, with limited options available for targeted therapy. The CRKP has experienced various changes and discoveries in recent years regarding its frequency, transmission traits, and mechanisms of resistance. In this comprehensive review, we present an in-depth analysis of the global epidemiology of K. pneumoniae, elucidate resistance mechanisms underlying its spread, explore evolutionary dynamics concerning carbapenem-resistant hypervirulent strains as well as KL64 strains of K. pneumoniae, and discuss recent therapeutic advancements and effective control strategies while providing insights into future directions. By going through up-to-date reports, we found that the ST11 KL64 CRKP subclone with high risk demonstrated significant potential for expansion and survival benefits, likely due to genetic influences. In addition, it should be noted that phage and nanoparticle treatments still pose significant risks for resistance development; hence, innovative infection prevention and control initiatives rooted in One Health principles are advocated as effective measures against K. pneumoniae transmission. In the future, further imperative research is warranted to comprehend bacterial resistance mechanisms by focusing particularly on microbiome studies’ application and implementation of the One Health strategy.

Extra-intestinal PathogenicEscherichia coli(ExPEC) is defined as an extra-intestinal foodborne pathogen, and several dominant sequence types (STs) ExPEC isolates are highly virulent, with zoonotic potential. Bacteria extracellular vesicles (EVs) carry specific subsets of molecular cargo, which affect various biological processes in bacteria and host. The mechanisms of EVs formation in ExPEC remains to be elucidated. Here, the purified EVs of ExPEC strains of different STs were isolated with ultracentrifugation processes. A comparative analysis of the strain proteomes showed that cytoplasmic proteins accounted for a relatively high proportion of the proteins among ExPEC EVs. The proportion of cytoplasm-carrying vesicles in ExPEC EVs was calculated with a simple green fluorescent protein (GFP) expression method. The RecA/LexA-dependent SOS response is a critical mediator of generation of cytoplasm-carrying EVs. The SOS response activates the expression of prophage-associated endolysins, Epel1, Epel2.1, and Epel2.2, which triggered cell lysis, increasing the production of ExPEC cytoplasm-carrying EVs. The repressor LexA controlled directly the expression of these endolysins by binding to the SOS boxes in the endolysin promoter regions. Reducing bacterial viability stimulated the production of ExPEC EVs, especially cytoplasm-carrying EVs. The imbalance in cell division caused by exposure to H₂O₂, the deletion offtsKgenes, or t⁶A synthesis defects activated the RecA/LexA-dependent SOS response, inducing the expression of endolysins, and thus increasing the proportion of cytoplasm-carrying EVs in the total ExPEC EVs. Antibiotics, which decreased bacterial viability, also increase the production of ExPEC cytoplasm-carrying EVs through the SOS response. Changes in the proportion of cytoplasm-carrying EVs affected the total DNA content of ExPEC EVs. When macrophages are exposed to a higher proportion of cytoplasm-carrying vesicles, ExPEC EVs were more cytotoxic to macrophages, accompanied with more-severe mitochondrial disruption and a higher level of induced intrinsic apoptosis. In summary, we offered comprehensive insight into the proteome analysis of ExPEC EVs. This study demonstrated the novel formation mechanisms ofE.colicytoplasm-carrying EVs.

The extended-spectrum cephalosporin resistant E. coli from food animals transferring to community settings of humans causes a serious threat to public health. Unlike phylogroup B2 E. coli strains, the clinical significance of isolates in phylogroup F is not well revealed. Here, we report on a collection (n = 563) of phylogroup F E. coli isolates recovered from chicken colibacillosis tissues and retail raw chicken meat samples in Eastern China. There was an overlapped distribution of MLST types between chicken colibacillosis-origin and meat-source phylogroup F E. coli, including dominant STs (ST648, ST405, ST457, ST393, ST1158, etc). This study further investigated the presence of extended-spectrum beta-lactamase (ESBL/pAmpC) producers in these chicken-source phylogroup F E. coli strains. The prevalence of extended-spectrum cephalosporin resistant strains in phylogroup F E. coli from chicken colibacillosis and raw meat separately accounted for 66.1 and 71.2%. The resistance genotypes and plasmid replicon types of chicken-source phylogroup F E. coli isolates were characterized by multiplex PCR. Our results revealed beta-lactamase CTX-M, OXA, CMY and TEM genes were widespread in chicken-source phylogroup F E. coli, and blaCTX-M was the most predominant ESBL gene. Moreover, there was a high prevalence of non-lactamase resistance genes in these beta-lactam-resistant isolates. The replicons IncB/O/K/Z, IncI1, IncN, IncFIC, IncQ1, IncX4, IncY, and p0111, associated with antibiotic-resistant large plasmids, were widespread in chicken-source phylogroup F E. coli. There was no obvious difference for the populations, resistance spectrums, and resistance genotypes between phylogroup F E. coli from chicken colibacillosis tissues and retail meats. This detail assessment of the population and resistance genotype showed chicken-source phylogroup F E. coli might hold zoonotic risk and contribute the spread of multidrug-resistant E. coli to humans.

Background: Avian pathogenic Escherichia coli (APEC) is the major pathogen causing important avian diseases in poultry. As an important subtype of extraintestinal pathogenic E. coli, APEC has zoonotic potential and is considered a foodborne pathogen. APEC extracellular vesicles (EVs) may play vital roles in the interaction of the pathogen with its host cells. However, the precise roles played by APEC EVs are still not completely clear, especially in immune cells. Results: In this study, we investigated the relationships between APEC EVs and immune cells. The production and characteristics of the EVs of APEC isolate CT265 were identified. Toll like receptor 4 (TLR4) triggered the cellular immune responses when it interacted with APEC EVs. APEC EVs induced a significant release of proinflammatory cytokines in THP-1 macrophages. APEC EVs induced the macrophage inflammatory response via the TLR4/MYD88/NF-κB signaling pathway, which participated in the activation of the APEC-EV-induced NLRP3 inflammasome. However, the loss of lipopolysaccharide (LPS) from APEC EVs reduced the activation of the NLRP3 inflammasome mediated by TLR4/MYD88/NF-κB signaling. Because APEC EVs activated the macrophage inflammatory response and cytokines release, we speculated that the interaction between APEC EVs and macrophages activated and promoted neutrophil migration during APEC extraintestinal infection. This study is the first to report that APEC EVs induce the formation of neutrophil extracellular traps (NETs) and chicken heterophil extracellular traps. Treatment with APEC EVs induced SAPK/JNK activation in neutrophils. The inhibition of TLR4 signaling suppressed APEC-EV-induced NET formation. However, although APEC EVs activated the immune response of macrophages and initiated NET formation, they also damaged macrophages, causing their apoptosis. The loss of LPS from APEC EVs did not prevent this process. Conclusion: APEC-derived EVs induced inflammatory responses in macrophages and NETs in neutrophils, and that TLR4 was involved in the APEC-EV-activated inflammatory response. These findings provided a basis for the further study of APEC pathogenesis.

As the leading cause of bovine respiratory disease (BRD), bacterial pneumonia can result in tremendous losses in the herd farming industry worldwide. N-acetylcysteine (NAC), an acetylated precursor of the amino acid L-cysteine, has been reported to have anti-inflammatory and antioxidant properties. To explore the protective effect and underlying mechanisms of NAC in ALI, we investigated its role in lipopolysaccharide (LPS)-induced bovine embryo tracheal cells (EBTr) and mouse lung injury models. We found that NAC pretreatment attenuated LPS-induced inflammation in EBTr and mouse models. Moreover, LPS suppressed the expression of oxidative-related factors in EBTr and promoted gene expression and the secretion of inflammatory cytokines. Conversely, the pretreatment of NAC alleviated the secretion of inflammatory cytokines and decreased their mRNA levels, maintaining stable levels of antioxidative gene expression. In vivo, NAC helped LPS-induced inflammatory responses and lung injury in ALI mice. The relative protein concentration, total cells, and percentage of neutrophils in BALF; the level of secretion of IL-6, IL-8, TNF-α, and IL-1β; MPO activity; lung injury score; and the expression level of inflammatory-related genes were decreased significantly in the NAC group compared with the LPS group. NAC also ameliorated LPS-induced mRNA level changes in antioxidative genes. In conclusion, our findings suggest that NAC affects the inflammatory and oxidative response, alleviating LPS-induced EBTr inflammation and mouse lung injury, which offers a natural therapeutic strategy for BRD.