Abstract Background Bacteriocins are peptides that demonstrate antimicrobial activity and are produced by bacteria. Bacillus velezensis is considered a reliable producer of bacteriocins, with a strong antimicrobial spectrum and antimicrobial activity. In this study, B. velezensis G7 isolated from mangrove plant roots was used as the experimental strain. Whole-genome sequencing (WGS) analysis was performed to annotate functional genes. Results The results demonstrated that B. velezensis G7 has a genome size of 3,894,836 bp, a GC content of 46.67%, and predicts 3,715 CDSs, 10 rRNA genes, and 83 tRNA genes. Gene annotation revealed pathways related to bacteriocin synthesis and immunity. Identified 8 bacteriocin and secondary metabolite biosynthetic gene clusters in B. velezensis G7, including Sactipeptides, LCI, Amylocyclicin, ComX4, Mersacidin, Lanthipeptide, Bacilysin, and NRPS. The crude protein from B. velezensis G7 shows broad-spectrum antibacterial activity, with the strongest inhibition against Listeria monocytogenes and the weakest against Staphylococcus aureus . Conclusions The genome of B. velezensis G7 was analyzed, and bacteriocin-related genes were identified. The results suggest that B. velezensis G7 has the potential to produce bacteriocins, thereby providing a theoretical basis for future studies on bacteriocin production in B. velezensis . In addition, these findings may facilitate further advances in bacteriocin research and bioinformatics analysis.

The global rise of antimicrobial resistance has intensified the demand for novel antimicrobial agents with broad-spectrum efficacy and unique mechanisms of action. Herein, a marine-derived strain, Bacillus velezensis (B. velezensis) AM12, exhibiting clear inhibitory activity against eight major foodborne pathogens, was isolated from coastal seawater near Zhanjiang, China. Whole-genome sequencing revealed a 3,992,266 bp circular chromosome with a GC content of 46

Bacteriocins are peptides produced by bacteria that have antibacterial effects on other bacterial species. They have emerged as novel antimicrobial alternatives or feed additives in the field of veterinary medicine. Heterologous expression systems have been demonstrated to be capable of high-level expression of bacteriocins when bacteriocins are used in commercial and industrial contexts. The bacteriocin amylocyclicin was expressed in Escherichia coli BL21 (DE3), and the induction conditions were optimized by a single-factor method. The composition of the induction medium was optimized using response surface methodology (RSM). The induction conditions that yielded optimal results were an isopropylthio-β-galactopyranoside (IPTG) concentration of 0.5 mM, an induction temperature of 28 ℃, and an induction time of 6 h. The optimal sucrose, ethanol, and NaCl additions were 0.804 g/100 mL, 1.547

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) and its robust biofilm-forming capability pose severe threats to public health, livestock production, and food safety, and underscores the urgent need for novel antibacterial and anti-biofilm agents. In this study, we identified and characterized a novel bacteriocin, PFB252, derived from Bacillus velezensis through a multistep purification process involving acid precipitation, TA-GF75 gel column chromatography, Tiderose Q HP anion-exchange chromatography (TRUKING, Changsha, China), and reversed-phase HPLC. PFB252 exhibited remarkable thermal stability, pH tolerance, and resistance to enzymatic degradation, and demonstrated potent antibacterial activity against MRSA. At subinhibitory concentrations (1/32× minimum inhibitory concentration [MIC] and 1/16× MIC), PFB252 significantly disrupted biofilm formation and impaired the metabolic viability of embedded bacteria, and it drastically reduced extracellular polysaccharide, the key component of the biofilm matrix. Transcriptional analysis further revealed that PFB252 at subinhibitory concentrations downregulated critical biofilm-associated genes. PFB252 exhibited strong antimicrobial efficacy in dairy applications and could reduce MRSA counts in milk from 103 to <10 cfu/mL within 4 d at MIC and maintain suppression in cheese below 102 cfu/g over 7 d. These properties highlight PFB252's potential as a natural biopreservative for combating MRSA in food systems and offer a promising solution for food safety applications.

Guangdong Province is an important area of poultry breeding in China. Zhanjiang city is located in the western part of Guangdong Province, where there are many broiler farms. To investigate antimicrobial resistance (AMR) and the presence of resistance genes in Escherichia coli from broiler farms, a total of 220 samples were collected from soil and feces at eight broiler farms. Subsequently, 220 strains of E. coli were isolated for drug resistance analysis and detection of AMR genes. The results revealed that the isolated E. coli strains exhibited high prevalence of multidrug resistance to 12 antimicrobial drugs including amoxicillin, tetracycline, cotrimoxazole and sulfisoxazole. Among the isolated strains, 95% of the isolates were resistant to more than three antimicrobial agents; notably, thirty-nine strains showed multidrug resistance to ten tested drugs, while four strain exhibits multidrug resistance to as many as fifteen antibacterial drugs. Additionally, seven AMR genes such as blaTEM and sul2 were detected in over half (≥50%) of the isolated E. coli samples; thirteen AMR genes had relatively low detection prevalence (≤30%). Correlation analysis indicated a strong association between certain AMR genes (blaTEM, pexA, aadA1, blaAIM, ant(3")-I, sul2, sul3, tet(D)) and AMR (≥50%). In conclusion, E.coli strains obtained from soil and fecal samples in broiler farms exhibited multidrug resistant phenotypes along with carrying various AMR genes. This provides a reference for the scientific control of E. coli multidrug resistance in this area.

Listeria monocytogenes is a significant zoonotic pathogen capable of forming biofilms on food and other materials, representing a considerable risk to human health and animal husbandry. The use of bacteriocins as potential new antibacterial and antibiofilm reagents has attracted considerable interest. This study aimed to determine the inhibitory effects of bacteriocin PCM7−4 on L. monocytogenes biofilm formation. In this study, bacteriocin PCM7−4 of SICs (1/16 × MIC, 1/8 × MIC) significantly inhibited the formation of L. monocytogenes biofilm. Bacteriocin PCM7−4 of SICs significantly reduced the production of bacterial extracellular polysaccharides, and could decrease the bacterial motility, meanwhile, PCM7−4 significantly reduced the number and viability of bacteria within the biofilm. RT-qPCR results showed that bacteriocin PCM7−4 significantly reduced the expression of flagella, community sensing and virulence factor genes associated with biofilm formation. The results demonstrated the considerable potential of bacteriocin PCM7−4 as a therapeutic agent for the prevention and treatment of L. monocytogenes biofilms.

Bacteriocins are defined as proteins that are produced by bacteria and that have antibacterial effects on various pathogenic bacteria. This study explored the effects of the crude extract of bacteriocin produced by Bacillus velezensis G02 (PRJNA1303554) on the intestinal microbiota of normal mice. Observation through liver and kidney tissue sections showed that the bacteriocin crude extract had no obvious adverse reactions on the internal organs of mice, and no mice died. A 16 S rDNA amplicon sequencing analysis revealed that the crude extract of the bacteriocin significantly changed the α-diversity (Shannon (P = 0.51), Simpson (P = 0.51), and Chao1 (P = 0.28)) and β-diversity (PCoA, (P = 0.1) NMDS, (P = 0.0132)) of the intestinal microbiota in normal mice, reducing the species abundance and increasing the evenness of their intestinal microbiota. In addition, the bacteriocin PG02 crude extract exhibited broad-spectrum antibacterial activity against both gram-positive and gram-negative bacteria. The purified bacteriocin was identified by LC-MS/MS in combination with sequence coverage analysis; its molecular weight was found to be 20.1 31 kDa, and it was speculated to be a putative novel bacteriocin named bacteriocin PG02. This study provides a reference for the microbiology field research and development of feed additive.

Listeria monocytogenes, a pathogenic bacterium causing zoonotic diseases, necessitates the urgent search for novel anti-Listeria monocytogenes drugs due to the continuous emergence of drug-resistant bacteria. In this study, we isolated and identified a bacteriocin-producing strain CM7-4 from seawater as Bacillus velezensis through 16S rRNA sequence analysis. Moreover, we successfully purified a novel bacteriocin named PCM7-4 from Bacillus velezensis CM7-4. The molecular weight of PCM7-4 was determined to be 40,228.99 Da. Notably, PCM7-4 exhibited broad-spectrum antibacterial activity against both Gram-positive and Gram-negative bacteria with a minimum inhibitory concentration (MIC) of 5.625 mu g/mL against Listeria monocytogenes specifically. It demonstrated heat resistance and high stability within the pH range of 2-12 while being sensitive to proteinase K degradation without any observed hemolytic activity. Furthermore, SEM analysis revealed that PCM7-4 effectively inhibited biofilm formation and disrupted cell membranes in Listeria monocytogenes cells. Transcriptome analysis revealed that PCM7-4 exerts an impact on genes associated with crucial metabolic pathways, encompassing the biosynthesis of secondary metabolites, phosphotransferase systems (PTS), and starch/sucrose metabolism. These findings highlight the significant potential of bacteriocin PCM7-4 for the development of effective antimicrobial interventions targeting food-borne pathogenic bacteria.

To investigate the impact of florfenicol on soil microbial community structure and diversity, an indoor florfenicol exposure model was established. Soil samples were collected at different concentrations of florfenicol (0, 0.05, 0.5, 5, and 50 mg/kg) on days 0, 7, 30, and 60. High-throughput sequencing was employed to examine the changes in soil microbial community structure, diversity, and abundance. The analysis revealed a total of 31874 operational taxonomic units ( OTUs ) in the soil samples, averaging 9524 OTUs per sample. The number of soil microbial community OTUs declined with increasing florfenicol concentration. The microbial species richness and diversity showed a decreasing trend at day 7, while the treatment group with 50 mg/kg florfenicol at 60 days exhibited the lowest richness index. Examination of the soil microbial community structure identified 50 phyla and 1303 genera. At the phylum level, the abundance of Actinobacteria and Bacteroides decreased with increasing florfenicol concentration. Similarly, at the genus level, some of the dominant genera displayed a decline in abundance with the rise of florfenicol concentration. Cluster analysis demonstrated significant temporal and concentration variability. The results indicate differences in the composition, diversity, dominance, abundance, and evenness of soil bacterial communities among different groups. Florfenicol has a significant negative impact on the structure and diversity of soil microbial communities. The findings of this study provide a scientific basis for the rational use of florfenicol in livestock farming to maintain a healthy and stable soil microecological environment.

Introduction: The antibacterial protein PAG14 was extracted from a metabolite of Bacillus G14 isolated from mangrove plants.Methods: In this study, Pseudomonas aeruginosa, Pasteurell multocide, Enterobacter aerogenes, and Enterococcus faecalis were used as indicator bacteria to screen endophytes that exhibited antibacterial activity. The endophyte culture conditions were optimized to enhance productivity. Subsequently, the culture supernatant was salted using ammonium sulfate, followed by purification using dextran gel chromatography and ion exchange column techniques. Finally, the structures of antibacterial proteins were identified using mass spectrometry.Results and Discussion: The optimal culture conditions for Bacillus G14 were 2% mannitol, 0.5% fish peptone, 0.05% KH2PO4 + 0.05% K2HPO4 + 0.025% MnSO4·H2O. The antibacterial substances exhibited stability within the temperature range of 30–40°C and pH range of 5.0–7.0, while displaying sensitivity toward enzymes. The antibacterial activity decreased as the duration of UV irradiation increased. The antibacterial protein PAG14, isolated from the culture broth of Bacillus G14 through purification using dextran gel and ion-exchange columns, was identified as a class III bacteriocin using LC-MS/MS, similar to Lysozyme C. These findings serve as a theoretical foundation for the investigation and application of bacteriocins in food products.

Florfenicol has a significant therapeutic effect on animal bacterial diseases, most of metabolites enter the soil in the form of metabolites in feces or urine and pollute environment. Soil ecological model was established by experiment to investigate the effects of florfenicol residues in soil on 16S rDNA sequence diversity of phosphorus-solubilizing bacteria. Five different concentrations of florfenicol (0 mg center dot kg-1, 0.1 mg center dot kg-1, 1 mg center dot kg-1, 10 mg center dot kg-1 and 100 mg center dot kg-1) were used to collect soil samples on the 7 d, 21 d and 49 d after dosing. The effects of florfenicol on 16S rDNA sequence diversity of soil phosphorus-solubilizing bacteria were determined by amplifed ribosomal DNA restriction analysis (ARDRA) and enterobacterial repetitive intergenic consensus-polymerase chain reaction (ERIC-PCR) method. The results showed that the number of Operational Taxonomic Units (OTUs) types decreased with the increase of florfenicol concentration, and the percentage of OTUs number to bacteria were the lowest at 100 mg center dot kg-1 florfenicol concentration after 21d treating, which was 8.33%. The phosphorus-solubilizing bacteria were amplified by ERIC-PCR after 21d treating, the fingerprint type of ERIC-PCR decreased with the increase of drug concentration, and the diversity index of the drug group was significantly lower than that of the blank control group. This indicated that florfenicol had an effect on the dominance, richness and evenness of soil phosphorus-solubilizing bacteria community.

为探究犬血液中头孢唑啉的有效抗菌浓度及维持时间,以便为临床给药途径、剂量及给药时间间隔等提供理论依据,本试验以金黄色葡萄球菌(金葡菌)为供试菌株,用纸片扩散法(K-B法)从30种抗菌药中筛选出金葡菌敏感的抗菌药物——头孢唑啉;采用试管二倍稀释法测定所选药物的最小抑菌浓度(MIC)及最小杀菌浓度(MBC);选用3只中华田园犬肌肉注射头孢唑啉,用微生物法检测犬血浆中头孢唑啉的有效抗菌浓度及维持时间.结果显示:头孢唑啉对金葡菌的MIC为0.25μg/mL,MBC为0.50μg/mL;肌肉注射头孢唑啉1 h后犬血药浓度达到峰值418.67μg/mL,给药后9 h血药浓度降至0.17μg/mL,小于MIC(0.25μg/mL).这表明中华田园犬肌肉注射头孢唑啉抑制金葡菌有效浓度维持时间在8h以上.

Introduction:The widespread use of antibiotics in animal agriculture has increased the resistance of Escherichia coli, and pathogenic E. coli often harbor complex virulence factors. Antimicrobial resistance in pathogenic bacteria can cause public health problems. Correlation analyses of the resistance, virulence, and serotype data from the pathogenic bacteria found on farms and in the surrounding environment can thus provide extremely valuable data to help improve public health management.Methods:In this investigation, we have assessed the drug resistance and virulence genes as well as the molecular typing characteristics of 30 E. coli strains isolated from duck farms in the Zhanjiang area of China. Polymerase chain reaction was used to detect the drug resistance and virulence genes as well as serotypes, and whole-genome sequencing was used to analyze the multilocus sequence typing.Results:The detection rates for the oqxA resistance gene and fimC virulence gene were highest (93.3%, respectively). There were no correlations between the drug resistance and virulence gene numbers in the same strain. The epidemic serotype was O81 (5/24), ST3856 was an epidemic sequence type, and strains I-9 and III-6 carried 11 virulence genes. The E. coli strains from the duck farms in the Zhanjiang area were thus found to have a broad drug resistance spectrum, various virulence genes, complex serotypes, and certain pathogenicity and genetic relationship.Discussion:Monitoring the spread of pathogenic bacteria and the provision of guidance regarding the use of antibiotics in the livestock and poultry industries will be required in the future in the Zhanjiang area.

Bovine Streptococcus are one of the main pathogens causing bacterial disease such as mastitis and endometritis in dairy farming. The virulence factors produced by Streptococcus are related to the occurrence of inflammation. To investigate the correlation between antimicrobial resistance and virulence traits of bovine Streptococcal isolates. Induced resistance was conducted for Streptococcus pneumonia ATCC49619 and erythromycin-sensitive strains by gradually increasing the antimicrobial concentration. Plasmid conjugation test was carried out by membrane filtration method. The correlation between antimicrobial resistance and virulence traits was analyzed by LD50 and related genes. Sensitive Streptococcus isolates to erythromycin and S. pneumoniae ATCC49619 were induced to resistance in vitro, MIC value was from <= 0.5 mu g/mL up to >= 64 mu g/mL, and ermB or mefA resistant gene were carried. Transfer rate of resistance was 100% by plasmid conjugant, conjugants had obtained the resistance phenotype and the related resistance genes from the donor bacteria. The LD50 of conjugants and induced resistance strains compared with parental strain, the virulence was lower than sensitive strains. The present study demonstrated that the virulence of resistant Streptococcus strains obtained by different drug resistance transfer methods was lower than that of their parents.

[目的]了解常见致病菌产生耐药性后耐药基因和毒力基因的变化.[方法]采用微量肉汤二倍稀释法测定21种临床常见抗生素对大肠杆菌、金黄色葡萄球菌等5种标准菌株的最小抑菌浓度,选取敏感药物进行体外诱导耐药试验,采用PCR法检测耐药基因和毒力基因.[结果]5个标准菌株均对氨基糖苷类药物敏感;大肠杆菌对四环素类药物敏感;鼠伤寒沙门氏菌、多杀性巴氏杆菌和肺炎链球菌对喹诺酮类药物敏感;金黄色葡萄球菌对克林霉素敏感.与标准菌株相比,氨基糖苷类和四环素类耐药菌株中均检测出新出现的相关耐药基因;喹诺酮类耐药基因parE在多杀性巴氏杆菌的标准菌株和耐诺氟沙星菌株中检测出,gyrB基因仅在肺炎链球菌的标准菌株和耐氧氟沙星菌株中检测出.在大肠杆菌中均检测出CS31A毒力基因,此外标准菌株中检测出fimH基因,耐多西环素菌株中检测出afa基因;多杀性巴氏杆菌标准菌株未检测出毒力基因,耐药菌株中均检测出oma87和tbpA基因;而鼠伤寒沙门氏菌、金黄色葡萄球菌和肺炎链球菌仅在标准菌株中检测出毒力基因.[结论]说明氨基糖苷类抗生素更容易诱导菌株产生耐药基因,而毒力基因与耐药基因无明显的相关性.细菌获得耐药性后,其毒力基因变化因菌株不同存在差异.

Florfenicol is used worldwide for its low side effects and strong bactericidal effect. Florfenicol is physicochemically stable and can persist in natural water bodies and affect water denitrification. Indoor aquatic microcosm models were constructed and water samples were collected at different florfenicol concentrations (0.1, 1, 10, and 100 mg/L) on days 0, 7, 30, and 60 to extract the microbial genome DNA and determine the water properties. qPCR and amplicon sequencing were used to study the dynamic changes of nirS gene and nirS-type denitrifying communities structure, diversity and abundance, respectively. The results showed that higher florfenicol concentrations caused accumulation of nitrate and ammonium nitrogen in water. Florfenicol stress caused orders of magnitude changes in nirS gene abundance, showing a trend of increasing first and then decreasing. 100 mg/L florfenicol addition led to a sustained increase of nirS gene abundance in water bodies. The florfenicol addition altered denitrifying community structure and suppressed the richness and diversity index of denitrifying bacteria in water body. Over time, the richness and diversity index gradually recovered. Proteobacteria was always the dominant denitrifying phylum in water. The relative abundance of Pseudomonas and beta proteobacterium showed obvious positive correlation with nirS gene abundance and were the dominant genera under florfenicol stress. Our study provided a scientific basis for the rational use of florfenicol in aquaculture to maintain a healthy and stable microecological environment, and also provided a preliminary understanding of the response characteristics of water denitrifying microorganisms to florfenicol exposure.

Florfenicol is one of the most widely used antibiotics in aquaculture and veterinary clinics because of its low side effects and strong bactericidal effect. A total of 45~60% of florfenicol is not absorbed by the animal body and accumulates in the aquatic environment through a variety of pathways, which affects denitrification. Indoor aquatic microcosm models were constructed and sediment samples were collected at different florfenicol concentrations (0.1, 1, 10, and 100 mg/L) on days 0, 7, 30, and 60 to extract the microbial genome DNA and determine the water properties. qPCR and amplicon sequencing were used to study the dynamic changes in the nirS gene and nirS-type denitrification community structure, diversity, and abundance, respectively. The results showed that high florfenicol stress influenced the sediment's physicochemical properties, reducing conductivity, alkaline dissolved nitrogen, and organic matter content. In addition, the abundance of nirS, a functional denitrification gene, increased obviously with increased florfenicol concentrations but decreased the diversity of nirS-type denitrification microorganisms. Proteobacteria was the dominant denitrifying phylum in the sediment. Our study provides a scientific basis for the rational use of florfenicol in aquaculture to maintain a healthy and stable microecological environment and also provides a preliminary understanding of the response characteristics of water denitrifying microorganisms to florfenicol exposure.

[目的]建立水体模型,探究氟苯尼考对水生细菌耐药性的影响.[方法]将水体样品分成Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ组,每组3个重复,各组添加不同浓度的氟苯尼考.分离培养建模前以及建模后第14、28、56天水生细菌,利用微量肉汤二倍稀释法和KB药敏纸片法对分离的水生细菌分别进行氟苯尼考和17种抗菌药物的敏感性试验.[结果]第56天收集的Ⅴ组水生细菌对氟苯尼考的耐药率最高,达到25.00％;分离的氟苯尼考敏感菌和耐药菌对阿莫西林、链霉素和多西环素等8种药物的敏感性差异极显著(P<0.01).[结论]氟苯尼考在一定程度上增加了水生细菌的耐药性.

This study evaluates the effects of a broad-spectrum antibiotic (florfenicol) on antibiotic resistance genes (ARGs) and bacterial community structure in aquatic environments. We constructed an indoor aquatic microcosm model, adding different concentrations of florfenicol (0.1, 1, 10, 100 mg L−1), and water and sediment samples were collected after 0, 7, 30, and 60 days. qPCR and 16S rDNA amplicon sequencing were used to study the changes in the ARGs and bacterial community structure of the collected samples. The results show that the inclusion of florfenicol resulted in an increased abundance of the floR and optrA genes. Adding 100 mg L−1 florfenicol to the water increased the abundance of optrA gene copies with the maximum on the Day 7, and increased the abundance of floR gene copies with the maximum on Day 30. Adding 100 mg L−1 florfenicol to the sediment increased the abundance of floR and optrA genes by one order of magnitude on Day 60. Meanwhile, the average number of operational taxonomic units (OTUs) in the water samples was 257, and the average number of OTUs in sediment samples was 823. The bacterial community diversity and richness in sediments were higher than those in water. The difference between the maximal and minimal values of the Shannon diversity index in the water and sediment samples was 4.36 and 1.95, respectively. The effect of florfenicol on the bacterial community structure in water was much higher than that in sediment. At 30 days, the diversity index and richness index of the florfenicol treatment groups with 1 and 10 mg L−1 concentrations began to increase; at 60 days, the diversity and richness indices of the 100 mg L−1 florfenicol treatment group began to increase. The samples at the same sampling time in the sediments clustered closer together. The results of this study provide a scientific basis for guiding the rational use of florfenicol in aquaculture, maintaining a healthy and stable microecological environment in aquaculture, and provide theoretical data for environmental ecological risk assessment and safety management caused by microbial resistance under the abuse of florfenicol.

[目的]研究盐浓度对水稻土壤固氮微生物nifH基因多样性的影响.[方法]在不同盐浓度的土壤区域采集样品,提取土壤总DNA,采用末端限制性片段长度多样性分析技术(T-RFLP)对土壤固氮微生物nifH基因进行多样性分析.[结果]随着水稻土壤盐度上升,土壤有机质、全氮和碱解氮含量也呈现一定程度的上升趋势;水稻土壤nifH基因的分类操作单元(OTU)总数在土壤盐度最高时达最大值,各组优势细菌数量在2.5种左右,样本丰度主要集中在4个片段内,各组相对丰度差异不显著(P>0.05);水稻组土壤与富贵竹土壤相比,多样性和均匀度均差异显著(P<0.05),水稻各组间微生物多样性呈现盐度依赖效应,但差异不显著(P>0.05).[结论]土壤盐度影响土壤性质及固氮微生物,微生物多样性呈现一定盐度依赖效应.