Infection following orthopedic surgery is a major complication that can have serious implications on patient health. The present study aimed to investigate the antibacterial effects of bacteriocins obtained from Lactobacillus rhamnosus on a rabbit model of Staphylococcus aureus infection following knee replacement surgery. Blood samples were collected 1, 2, 3, 4 and 5 days after bacteriocin injection, and C‑reactive protein (CRP) and interleukin (IL)‑6 levels were measured using commercial ELISA kits. In addition, biofilm formation was evaluated by fluorescence microscopy. Bacteriocins were identified to exhibit significant inhibitory effects on Staphylococcus aureus biofilm formation, and on CRP and IL‑6 levels in the serum, following surgery and infection (all P<0.05 vs. the control group). The results of the present study indicate that bacteriocins are a potential agent for the prevention of orthopedic postoperative infections.

Aeromonas schubertii is the etiological pathogen of internal organ nodules in snakehead fish. Infections with A. schubertii produce a significant economic loss in aquaculture. Therefore, it is important to examine the immune mechanisms by which snakeheads defend against A. schubertii infection. In this study, we established a hybrid snakehead infection model by intraperitoneal injection of A. schubertii that produced internal organ nodules. The splenic immune response of infected fish was examined at the transcriptome level by Illumina-seq analysis. Results showed 14,796 differentially expressed genes (DEGs) following A. schubertii infection, including 4441 up-regulated unigenes and 10,355 down-regulated unigenes. KEGG analysis showed 2084 DEGs to be involved in 192 pathways, 14 of which were immune-related. Twelve DEGs were used to validate quantitative real-time PCR results with RNA-seq data. Time-course expression analysis of six genes demonstrated modulation of the snakehead immune response by A. schubertii. Furthermore, transcriptome analysis identified a substantial number of DEGs that were involved in the apoptosis signaling pathway. TUNEL analysis of infected spleens confirmed the presence of apoptotic cells. This study provided new information for a further understanding of the pathogenesis of A. schubertii in snakeheads, which can be used to prevent and possibly treat A. schubertii infections.

Recently, the outbreak of a serious infectious disease of unknown etiology was noted in Percocypris pingi (Tchang, 1930) farms in Yunnan province. Due to currently limited information, we aimed to identify the pathogen isolates, determine the susceptibility of the isolates, evaluate the pathogenicity and analyze the genome of the representative strain. Ten strains of Gram-negative rods were isolated from diseased P. pingi and the isolates were identified as Plesiomonas shigelloides based on biochemical characteristics, 16S rRNA gene sequencing and species-specific PCR detection. The results of susceptibility analysis showed that two selected strains LS1 and LL2 were resistant to ampicillin, penicillin G, trimethoprim/sulfamethoxazole, tetracycline, enrofloxacin, nalidixic acid and enoxacin. A virulence assay indicated that the pathogen was virulent to zebrafish. Genomic analysis revealed that the LS1 isolate was closely related to strain GN7, which was isolated from animal farms. To the best of our knowledge, this is the first report of P. shigelloides as a pathogen of P. pingi. This study will provide a rational framework for exploration of epidemiological analysis of P. shigelloides in fish diseases and would further benefit conservation of the species.

Aeromonas septicemia and columnaris disease are major bacterial diseases in grass carp; however, the drugs currently used to control these diseases pose environmental and health risks. This study aimed to screen for a probiotic Bacillus strain with antagonistic activity to prevent and control bacterial diseases in grass carp and to evaluate the antimicrobial activities, biosafety, and biocontrol effects of this strain. A Bacillus strain with antagonistic activity against Aeromonas hydrophila, obtained from grass carp intestines, was screened, and the isolate CYS06 was identified by analyzing the 16S rRNA and gyrA gene sequences. The antimicrobial spectrum of the strain CYS06 was determined, and the activities of amylase, cellulase, protease, and lipase of the strain CYS06 were determined. The whole genome of the strain CYS06 was sequenced using the nanopore sequencing technology platform, followed by the analysis of the antagonistic substance synthesis gene clusters and CAZy enzyme gene families. The biosafety of the strain CYS06 was evaluated via intraperitoneal injection into healthy grass carp. After the strain CYS06 was fed to the grass carp, its biological control effect on this fish was evaluated through artificial infection experiments. The strain CYS06 was identified as Bacillus velezensis, based on molecular identification, which shows broad antimicrobial activity against various fish pathogens. The strain CYS06 secretes amylase, cellulase, protease, and lipase. The genome size of the strain CYS06 is 3,914,159 bp, and it contains eight antagonistic substance synthesis gene clusters and many CAZy enzymes. The strain CYS06 exhibits high biological safety for grass carp, based on the challenge test. Feeding grass carp with the strain CYS06 for 4 weeks significantly enhanced the resistance of the fish to A. hydrophila. Strain CYS06 could inhibit the growth of Flavobacterium columnare under co-culture and reduce the amount of F. columnare adherence on the gills of grass carp, indicating that CYS06 has good potential for the prevention and control of columnaris disease. In conclusion, we isolated an antagonistic probiotic strain, CYS06, which exhibits a biological control effect on septicemia and columnaris disease caused by Aeromonas spp. and F. columnare in grass carp, respectively. This strain contains many antagonistic substance synthesis-related gene clusters and holds the potential to degrade various types of carbohydrates. As a biological control agent, the strain CYS06 exhibits significant potential for the prevention and control of bacterial diseases in grass carp.