Contribution of the serine protease HtrA in Escherichia coli to infection in foxes

Drug resistance and pathogenicity characteristics of Escherichia coli causing pneumonia in farmed foxes

Bacterial pneumonia is a leading cause of mortality in fur-bearing animals, posing significant threat to fur production. To clarify the pathogenic agent of bacterial pneumonia in farmed foxes from eastern Hebei province, China, we performed bacterial isolation and identification from samples between 2020 and 2023. A total of 142 bacterial strains were isolated, of which 101 were identified as Escherichia coli (E. coli), indicating that E. coli is the major cause responsible for bacterial pneumonia in farmed foxes. Serotyping identification showed that a total of 8 serotypes were prevalent in the E. coli isolates, with O1, O8, O78 and O12 being the dominant ones. Five E. coli isolates were randomly picked for pathogenicity testing, and all of them were able to cause pneumonia symptoms in 6-week-old Kunming mice, accompanied by organ damage in lung. Eleven virulence genes were demonstrated present among the E. coli isolates. Antibiotic susceptibility tests showed that 78 of 101 E. coli strains exhibited multi-drug resistance (MDR), with the highest resistance rates against tetracyclines, and some strains showed resistance to carbapenems. Notably, no single antibiotic was effective against all strains. Twenty antibiotic resistance genes (ARGs) were detected among the isolates. Multilocus sequence typing (MLST) revealed 11 sequence types (STs) among 19 E. coli isolates, with ST-101 predominating (4/19). These findings enhance our understanding of the epidemiology, resistance traits, and pathogenicity of fox-derived pathogenic E. coli in Hebei.

HtrA is involved in stress response and adhesion in Glaesserella parasuis serovar 5 strain Nagasaki

Glaesserella parasuis is an important pathogen that causes fibrinous polyserositis, peritonitis and meningitis in pigs, leading to considerable economic losses to the swine industry worldwide. It is well established that the serine protease HtrA is closely associated with bacterial virulence, but the role of HtrA in G. parasuis pathogenesis remains largely unknown. To characterize the function of the htrA gene in G. parasuis, a ΔhtrA mutant was constructed. We found that the ΔhtrA mutant showed significant growth inhibition under heat shock and alkaline stress conditions, indicating HtrA is involved in stress tolerance and survival of G. parasuis. In addition, deletion of htrA gene resulted in decreased adherence to PIEC and PK-15 cells and increased phagocytic resistance to 3D4/2 macrophages, suggesting that htrA is essential for adherence of G. parasuis. Scanning electron microscopy revealed morphological surface changes of the ΔhtrA mutant, and transcription analysis confirmed that a number of adhesion-associated genes are downregulated, which corroborated the aforementioned phenomenon. Furthermore, G. parasuis HtrA induced a potent antibody response in piglets with Glässer's disease. These observations confirmed that the htrA gene is related to the survival and pathogenicity of G. parasuis.

A Regulatory SRNA Rli43 Is Involved in the Modulation of Biofilm Formation and Virulence in Listeria monocytogenes

Small RNAs (sRNAs) are a kind of regulatory molecule that can modulate gene expression at the post-transcriptional level, thereby involving alteration of the physiological characteristics of bacteria. However, the regulatory roles and mechanisms of most sRNAs remain unknown in Listeria monocytogenes(L. monocytogenes). To explore the regulatory roles of sRNA Rli43 in L. monocytogenes, the rli43 gene deletion strain LM-Δrli43 and complementation strain LM-Δrli43-rli43 were constructed to investigate the effects of Rli43 on responses to environmental stress, biofilm formation, and virulence, respectively. Additionally, Rli43-regulated target genes were identified using bioinformatic analysis tools and a bacterial dual plasmid reporter system based on E. coli. The results showed that the intracellular expression level of the rli43 gene was significantly upregulated compared with those under extracellular conditions. Compared with the parental and complementation strains, the environmental adaptation, motility, biofilm formation, adhesion, invasion, and intracellular survival of LM-Δrli43 were significantly reduced, respectively, whereas the LD₅₀ of LM-Δrli43 was significantly elevated in BALB/c mice. Furthermore, the bacterial loads and pathological damages were alleviated, suggesting that sRNA Rli43 was involved in the modulation of the virulence of L. monocytogenes. It was confirmed that Rli43 may complementarily pair with the 5'-UTR (-47--55) of HtrA mRNA, thereby regulating the expression level of HtrA protein at the post-transcriptional level. These findings suggest that Rli43-mediated control was involved in the modulation of environmental adaptation, biofilm formation, and virulence in L. monocytogenes.