Prevalence and characterization of Staphylococcus aureus and methicillin-resistant Staphylococcus aureus isolated from retail yak butter in Tibet,China

This study aimed to investigate the prevalence, molecular characteristics and antibiotic resistance of Staphylococcus aureus isolates from yak butter in Tibet, China. A total of 218 yak butter samples were collected from retail stores in Tibet and screened for Staph. aureus. Furthermore, the virulence genes, resistance genes, antimicrobial susceptibility, and molecular typing [pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, and staphylococcal protein A (spa) typing] of Staph. aureus isolates were detected. The results showed that 12.4% of yak butter samples were contaminated with Staph. aureus, including 5 samples positive for methicillin-resistant Staph. aureus (MRSA). Among all isolates, 96.3% harbored one or more virulence genes, including classical (sea and sec), novel enterotoxin-encoding genes (seh, sek, sel, and seq), and hemolysin genes (hla and hld). All isolates were resistant to at least 2 different antibiotic classes, and the isolates were most commonly resistant to sulfonamides, β-lactams, and erythromycin. For resistance genes, blaZ (74.1%) was most frequently detected, followed by dfrG (51.9%), erm(B) (22.2%), mecA (18.5%), tet(K) (14.8%), aph(2″)-Ia, aph(3′)-III, and ant(6)-Ia (11.1% for each), and erm(C) (7.4%). We detected 8 spa types, 6 sequence types (ST), and 5 clonal complex (CC) types. In addition, 1 isolate of Staph. aureus was nontypeable. We found that CC1-ST1-t559 (55.6%) was the most predominant clone, followed by CC59-ST59-t437 (11.1%), CC5-ST5-t002 (7.4%), CC1-ST1, CC1-ST1-t114, CC1-ST573-t4938, CC1-ST573-t8915, CC30-ST30-t021, and CC25-ST25-t167 (3.7% for each). For PFGE typing, a total of 5 clusters and 15 pulsotypes were generated, and some isolates from different samples showed indistinguishable pulsotypes. Our findings suggest that yak butter produced in Tibet, China, could be contaminated by Staph. aureus strains, including MRSA strains, carrying various virulence and resistance genes, representing multiple antimicrobial resistance phenotypes. The presence of potentially virulent and antibiotic-resistant Staph. aureus strains in yak butter poses a potential threat to consumers, and appropriate measures need to be taken in the production chain to reduce the occurrence of Staph. aureus in yak butter.     

Prevalence and Characterization of Salmonella Isolated from Chicken Meat in Turkey

This study was conducted in a Turkish province to investigate the presence of Salmonella spp. in 150 chicken meat samples using 2 phenotyping techniques: classic culture technique (CCT) and immunomagnetic separation (IMS). For the confirmation of the isolates at molecular levels, invA gene was detected in these isolates. The presence of invA, class 1 (Cls1) integrons, and integrase (Int1) genes was demonstrated by PCR assay; and the resistance of the isolated Salmonella spp. strains to antibiotics was determined by disk diffusion test. All the cultural and PCR results were evaluated together; Salmonella spp. were detected in a total of 64 (42.66%) chicken meat samples. Contamination rate was higher in carcasses (53.33%, n = 75) than in meat pieces (32%, n = 75). When results of standard culture were compared with IMS technique, IMS (n = 54) showed a clear superiority over the CCT (n = 38). A very high resistance rate (≥89.28%) to vancomycin, tetracycline, streptomycin, or nalidixic acid was found. Trimethoprim‐sulfamethoxazole resistance was present in 32.14%. Relatively lower incidence of resistance (≤8.33%) to gentamicin, chloramphenicol, ampicillin, and ceftriaxone was observed. Concurrent resistance to at least 4 antibiotics was detected in 92.85% of the isolates. Cls1 integrons and Int1 were positive in 80.95% and 95.23% of the isolates, respectively. However, Int1 alone was detected in 15.47% (n = 13). In conclusion, the high prevalence of Salmonella spp. in chicken meat may pose a potential public health risk, and the presence of antibiotic‐resistant Salmonella spp. isolate together with Cls1 integron and/or integrase might play an important role in horizontal antibiotic gene transfer.     

CoFe2O4/NiFe2O4 S-scheme composite for photocatalytic decomposition of antibiotic contaminants

Keeping in view of the hazardous application of tetracycline hydrochloride antibiotic, an efficient CoFe₂O₄/NiFe₂O₄ heterojunction photocatalyst has been prepared hydrothermally by combining CoFe₂O₄ and NiFe₂O₄ nanoplates. The CoFe₂O₄/NiFe₂O₄ composite with the improved photocatalytic activity can be employed for removal of tetracycline hydrochloride antibiotic, comparing to the bare CoFe₂O₄ and NiFe₂O₄. The optimized sample 5%-CoFe₂O₄/NiFe₂O₄ shows the high photocatalytic degrading tetracycline with 76.1% removal efficiency in 60 min. These improved photocatalytic activities are attributed to the extended visible light absorption and enhanced charge separation following S-scheme route as confirmed from photoluminescence and electrochemical studies. From the charge trapping experiments, it is confirmed that superoxide radical and holes in the valence band of NiFe₂O₄ with high thermodynamic energies are responsible for the photodegradation of the target pollutant. This work provides sufficient attention towards the preparation of low cost materials for the removal of highly hazardous pollutants being present in water.     

新型“超级细菌”及抗菌新药的筛选

新型"超级细菌"爆发后,各国科学家和医药工作者对感染此病菌可能引发的结果表示"担忧"。本文综合有关信息及文献介绍了新型"超级细菌"及其传播途径和防控措施,探讨了其抗生素耐药性,提出了抗菌新药的筛选思路和研究方向,为新抗生素和抗菌新药的进一步研究开发提供有益的参考。     

纸片法筛选抗生素敏感菌株及其敏感性研究

目的 建立一种快速检测微生物的纸片法, 实现抗生素残留的快速检测。方法 利用纸片法对4株菌株(分别为枯草芽孢杆菌CMCC-63501、枯草芽孢杆菌DSM 17299、地衣芽孢杆菌DSM 5749和康地恩枯草芽孢杆菌)进行筛选敏感菌株实验。选取16种抗生素, 在抗生素浓度为0.05~30 μg/mL的范围下, 利用该法进行枯草芽孢杆菌CMCC-63501的敏感性实验。结果 筛选敏感菌株实验结果显示枯草芽孢杆菌CMCC-63501为最敏感菌株; 通过绘制盐酸多西环素、恩诺沙星、硫酸庆大霉素、替米考星、土霉素、头孢噻呋钠、乳酸环丙沙星和硫酸新霉素的标准曲线发现: 在一定的浓度范围下, 抑菌圈的大小与抗生素浓度的变化成线性关系。结论 该法操作快捷简便, 能对抗生素残留进行初步定量分析, 在动物性食品安全检测中起到重要作用, 使之更有效的保障我国动物性食品安全。     

鸡源细菌中5种四环素耐药基因多重PCR检测方法的建立

为建立一种同步检测鸡源细菌中5种四环素耐药基因tetA、tetD、tetG、tetS和tetX的多重聚合酶链式反应(PCR)方法,优化了多重PCR体系的引物和Taq DNA聚合酶浓度及退火温度等参数,并考察了方法的灵敏度、特异性和适用性。建立的多重PCR反应技术的最佳反应体系为:混合DNA模板5μL,Taq酶1μL,tetA和tetX的正反向引物各0.5μL,tetG、tetD和tetS的正反向引物各1.0μL,dNTP4μL,MgCl24μL,10×PCR反应缓冲液5μL,最终用dd H2O补齐至50μL;反应程序为:95℃预变性5min;95℃变性30s,55℃退火30s,72℃延伸1min,35个循环;72℃延伸10min。该方法的灵敏度为102 CFU/mL,且能广谱地检测多种鸡源细菌中的5种四环素耐药基因。与传统的单重PCR方法相比,该多重PCR技术快速高效、适用性广。     

超声提取野菊花总黄酮及其抑菌活性的研究

以野菊花中总黄酮含量作为考察指标,用正交实验法优化野菊花总黄酮超声提取工艺,并考察超声波法对总黄酮抑菌活性的影响.结果表明,野菊花总黄酮的最佳提取工艺为:在超声功率200 W条件下,用12倍量45%的乙醇提取15 min.此时野菊花总黄酮的得率达到2.86%.该工艺简单可行、重现性好,且超声波对总黄酮抑菌活性没有影响,适用于工业化生产.     

Nanopore Sequencing for De Novo Bacterial Genome Assembly and Search for Single-Nucleotide Polymorphism

Nanopore sequencing (ONT) is a new and rapidly developing method for determining nucleotide sequences in DNA and RNA. It serves the ability to obtain long reads of thousands of nucleotides without assembly and amplification during sequencing compared to next-generation sequencing. Nanopore sequencing can help for determination of genetic changes leading to antibiotics resistance. This study presents the application of ONT technology in the assembly of an E. coli genome characterized by a deletion of the tolC gene and known single-nucleotide variations leading to antibiotic resistance, in the absence of a reference genome. We performed benchmark studies to determine minimum coverage depth to obtain a complete genome, depending on the quality of the ONT data. A comparison of existing programs was carried out. It was shown that the Flye program demonstrates plausible assembly results relative to others (Shasta, Canu, and Necat). The required coverage depth for successful assembly strongly depends on the size of reads. When using high-quality samples with an average read length of 8 Kbp or more, the coverage depth of 30× is sufficient to assemble the complete genome de novo and reliably determine single-nucleotide variations in it. For samples with shorter reads with mean lengths of 2 Kbp, a higher coverage depth of 50× is required. Avoiding of mechanical mixing is obligatory for samples preparation. Nanopore sequencing can be used alone to determine antibiotics-resistant genetic features of bacterial strains.     

Design and Synthesis of Menthol and Thymol Derived Ciprofloxacin: Influence of Structural Modifications on the Antibacterial Activity and Anticancer Properties

Sixteen new Ciprofloxacin derivatives were designed and successfully synthesized. In an in silico experiment, lipophilicity was established for obtained compounds. All compounds were screened for antimicrobial activity using standard and clinical strains. As for Gram-positive hospital microorganisms, all tested derivatives were active. Measured MICs were in the range 1–16 µg/mL, confirming high antimicrobial potency. Derivative 12 demonstrated activity against all standard Gram-positive Staphylococci, within the range of 0.8–1.6 µg/mL and was confirmed as the leading structure with MICs 1 µg/mL for S. pasteuri KR 4358 and S. aureus T 5591 (clinical strains). All compounds were screened for their in vitro cytotoxic properties via the MTT method. Three of the examined compounds (3, 11 and 16) showed good activity against cancer cells, and in parallel were found not to be cytotoxic toward normal cells. Doxorubicin SI ranged 0.14–1.11 while the mentioned three ranged 1.9–3.4. Selected Ciprofloxacin derivatives were docked into the crystal structure of topoisomerase II (DNA gyrase) in complex with DNA (PDB ID: 5BTC). In summary, leading structures were established (3, 11, 12 and 16). We have observed poor results in preformed studies for disubstituted derivatives, suggesting that 3-oxo-4-carboxylic acid core is the active DNA-gyrase binding site, and when structural changes were made in this fragment, there was an observed decrease in antibacterial potency.     

基于全基因组测序技术的食品分离致泻大肠埃希菌的分子特征及耐药性研究

目的 了解上海市肉品和水产品中分离致泻大肠埃希菌（DEC）的生物学特征及耐药性,为防控由该菌引起的食源性疾病提供科学依据。方法对食品分离DEC菌株进行全基因组测序及药物敏感性试验,利用BioNumerics软件对全基因组测序数据进行拼接,利用拼接序列开展多位点序列分型、毒力基因和耐药基因分析。结果本研究中56株DEC菌株中肠道聚集性大肠埃希菌（EAEC）占比最高,达73.2%,且以astA基因为主（90.2%）。56株DEC分为37个ST型,显示高度多样性。DEC菌株对喹诺酮类抗生素耐药性较高（64.3%）,其次是对氨基糖苷类、β-内酰胺类抗生素和四环素类抗生素耐药,且多重耐药性菌株占48.2%,耐药基因相应的以喹诺酮类、氨基糖苷类、β-内酰胺类抗生素耐药基因为主,且大多数对抗生素耐药的菌株均携带其相应的耐药基因。结论 EAEC是上海市食品中分离DEC菌株的主要型别,对喹诺酮类、β-内酰胺类、氨基糖苷类抗生素的耐药率较高,且携带相应的耐药基因,全基因组测序技术可应用于DEC的分子生物学监测中,为疾病预防控制提供科学依据。