P. aeruginosa is a common nosocomial pathogen that causes diverse opportunistic infections in humans. The virulence crucial for infection is mainly regulated by QS.

The acid tolerance mechanism is important for Escherichia coli to resist acidic conditions encountered in mammalian host digestive tract environment. Here, we explored how the LuxR protein SdiA influenced E. coli acid tolerance ability in the context of the glutamate- and glutamine-dependent acid resistance system (AR2). First, using a growth and acid shock assay under different acid stresses, we demonstrated that the deletion of sdiA in SM10λpir or BW25113 led to impaired growth under the acidic environment of pH 3–6, which was restored by complementary expression of SdiA. Next, transcriptome sequencing and qPCR disclosed that the expression of glutamate decarboxylase W (GadW) and GadY, the key members of the AR2 system, were regulated by SdiA. Further, β-galactosidase reporter assays showed that the promoter activity of gadW and gadY was positively regulated by SdiA. Moreover, qPCR and β-galactosidase reporter assays confirmed that the regulation of SdiA on GadW, but not GadY, could be enhanced by quorum sensing (QS) signal molecules AHLs. Collectively, these data suggest that SdiA plays a crucial role in acid tolerance regulation of E. coli. Our findings provide new insights into the important contribution of quorum sensing system AHLs–SdiA to the networks that regulate acid tolerance.

Intratumoral bacteria have been identified as prevalent in various solid tumors, playing a significant role in tumor progression. Lymph node metastasis is a major clinical feature and the primary cause of mortality in cervical cancer (CC). However, the effect of intratumoral bacteria on lymphatic node metastasis in CC remains unclear. This study employed 16S rDNA sequencing and targeted bacterial culture to investigate the distribution of intratumoral bacteria in human CC tissues. The identified Gram-negative bacteria, including Escherichia coli (E. coli), Prevotella bivia (P. bivia), and Fusobacterium nucleatum (F. nucleatum), were isolated, and their roles in metastasis were examined using in vitro transwell and capillary tube formation assays on human lymphatic endothelial cells (HLEC). The signaling pathways involved in metastasis were assessed by examining TLR4/MAPK activation and the expression of prometastatic factors EFNA1 and EDN2. In vivo studies using a mouse footpad tumorigenesis model were also conducted to observe the effect of LPS, which was extracted from these three gram-negative intratumoral bacteria and E. coli on lymph node metastasis. A higher abundance of Gram-negative bacteria, especially in metastatic CC tissues, was observed. E. coli, P. bivia, and F. nucleatum enhanced capillary tube formation in lymphatic endothelial cells and facilitated metastasis of uninfected tumor cells through paracrine signaling. These bacteria activated the TLR4/MAPK signaling pathway via lipopolysaccharide (LPS), leading to the upregulation of prometastatic factors EFNA1 and EDN2. Knockdown of EFNA1 and EDN2 attenuated the bacteria-induced metastasis, whereas overexpression of these factors mimicked the effects of bacterial infection. In vivo, LPS, which was extracted from E. coli, P. bivia, and F. nucleatum and live E. coli promoted lymph node metastasis, with elevated LPS levels and MAPK-EFNA1/EDN2 expression observed in infected mice compared to controls. The study suggests that Gram-negative bacteria, particularly E. coli, P. bivia, and F. nucleatum, play a causal role in exacerbating lymph node metastasis in CC. These findings highlight the potential of targeting these bacteria and their associated signaling pathways as therapeutic strategies to improve clinical outcomes in CC patients.

Indole works as an interspecies signal molecule to regulate multiple physiological activities, like antibiotic resistance, acid resistance, and virulence. However, the effect of indole on conjugation is unknown. Here, with Escherichia coli SM10λπ as a donor strain that carries a chromosomally integrated conjugative RP4 plasmid, we explored the effect of indole on conjugation of a mobilizable pUCP24T plasmid imparting gentamycin resistance. The results showed that exogenous indole treatment inhibited conjugative transfer of pUCP24T from SM10λπ to recipient strains, Pseudomonas aeruginosa PAO1 and E. coli EC600. Furthermore, raising endogenous indole production through overexpression of TnaA, a tryptophanase, in SM10λπ significantly inhibited both SM10λπ-PAO1 and SM10λπ-EC600 conjugation, whereas deficiency of tnaA reversed the phenotype. Subsequent mechanistic studies revealed that exogenous indole significantly inhibited the expression of mating pair formation gene (trbB) and the DNA transfer and replication gene (trfA), mainly due to the promotion of regulatory genes (korA and korB), and the result was confirmed in tnaA knockout and overexpression strains. Additionally, we found that both extracellular indole production and tnaA expression of SM10λπ were downregulated by ciprofloxacin (CIP). Intriguingly, one-eighth minimum inhibitory concentration of CIP treatment clearly facilitated both SM10λπ-PAO1 and SM10λπ-EC600 conjugation, and indole inhibited CIP-induced conjugation frequency. These data suggest that indole may play a negative role in the process of CIP-induced conjugation. This is the first study to reveal the biological function of indole-inhibiting conjugation and its role in CIP-induced conjugation, which may be developed into a new way of controlling the spread of antibiotic resistance.

Eravacycline (ERV) has emerged as a therapeutic option for the treatment of carbapenem-resistant pathogens. However, the advent of heteroresistance (HR) to ERV poses a challenge to these therapeutic strategies. This study aimed to investigate ERV HR prevalence among common clinical isolates and further characterize ERV HR in carbapenem-resistant Klebsiella pneumoniae (CRKP). A total of 280 clinical pathogens from two centers were selected for HR and analyzed using population analysis profiling (PAP) and modified E-tests. The PAP assay revealed an overall ERV HR prevalence of 0.7% (2/280), with intermediate heterogeneity observed in 24.3% (68/280) of strains. The proportion of heteroresistant strains was 18.3% according to modified E-test results. A time-killing assay demonstrated that CRKP CFU increased significantly after 10 h of ERV treatment, contributing to the reduced bactericidal effect of ERV in vitro. Interestingly, dual treatment with ERV and polymyxin B effectively inhibited the total CFU, simultaneously reducing the required polymyxin B concentration. Furthermore, fitness cost measurements revealed a growth trade-off in CRKP upon acquiring drug resistance, highlighting fitness costs as crucial factors in the emergence of ERV HR in CRKP. Overall, the findings of the current study suggest that ERV HR in clinical strains presents a potential obstacle in its clinical application.