Critical (P5P_5,bull)-free graphs

Given two graphs $H_1$ and $H_2$, a graph is $(H_1,H_2)$-free if it contains no induced subgraph isomorphic to $H_1$ or $H_2$. Let $P_t$ and $C_t$ be the path and the cycle on $t$ vertices, respectively. A bull is the graph obtained from a triangle with two disjoint pendant edges. In this paper, we show that there are finitely many 5-vertex-critical ($P_5$,bull)-free graphs.Comment: 21 page

A secondary metabolite drives intraspecies antagonism in a gut symbiont that is inhibited by cell-wall acetylation

The mammalian microbiome encodes numerous secondary metabolite biosynthetic gene clusters; yet, their role in microbe-microbe interactions is unclear. Here, we characterized two polyketide synthase gene clusters (fun and pks) in the gut symbiont Limosilactobacillus reuteri. The pks, but not the fun, cluster encodes antimicrobial activity. Forty-one of 51 L. reuteri strains tested are sensitive to Pks products; this finding was independent of strains’ host origin. Sensitivity to Pks was also established in intraspecies competition experiments in gnotobiotic mice. Comparative genome analyses between Pks-resistant and -sensitive strains identified an acyltransferase gene (act) unique to Pks-resistant strains. Subsequent cell-wall analysis of wild-type and act mutant strains showed that Act acetylates cell-wall components, providing resistance to Pks-mediated killing. Additionally, pks mutants lost their competitive advantage, while act mutants lost their Pks resistance in in vivo competition assays. These findings provide insight into how closely related gut symbionts can compete and co-exist in the gastrointestinal tract

Evaluation of the antibacterial and anticancer activities of some South African medicinal plants

<p>Abstract</p> <p>Background</p> <p>Several herbs are traditionally used in the treatment of a variety of ailments particularly in the rural areas of South Africa where herbal medicine is mainly the source of health care system. Many of these herbs have not been assessed for safety or toxicity to tissue or organs of the mammalian recipients.</p> <p>Methods</p> <p>This study evaluated the cytotoxicity of some medicinal plants used, inter alia, in the treatment of diarrhoea, and stomach disorders. Six selected medicinal plants were assessed for their antibacterial activities against ampicillin-resistant and kanamycin-resistant strains of <it>Escherichia coli </it>by the broth micro-dilution methods. The cytotoxicities of methanol extracts and fractions of the six selected plants were determined using a modified tetrazolium-based colorimetric assay (3-(4, 5-dimethylthiazol)-2, 5-diphenyl tetrazolium bromide (MTT) assay).</p> <p>Results</p> <p>The average minimum inhibitory concentration (MIC) values of the plants extracts ranged from 0.027 mg/mℓ to 2.5 mg/mℓ after 24 h of incubation. <it>Eucomis autumnalis </it>and <it>Cyathula uncinulata </it>had the most significant biological activity with the least MIC values. The in vitro cytotoxicity assay on human hepatocarcinoma cell line (Huh-7) revealed that the methanol extract of <it>E. autumnalis </it>had the strongest cytotoxicity with IC₅₀of 7.8 μg/mℓ. Ethyl acetate and butanol fractions of <it>C. uncinulata, Hypoxis latifolia, E. autumnalis </it>and <it>Lantana camara </it>had lower cytotoxic effects on the cancer cell lines tested with IC₅₀values ranging from 24.8 to 44.1 μg/mℓ; while all the fractions of <it>Aloe arborescens </it>and <it>A. striatula </it>had insignificant or no cytotoxic effects after 72 h of treatment.</p> <p>Conclusions</p> <p>Our results indicate that the methanol fraction of <it>E. autumnalis </it>had a profound cytotoxic effect even though it possessed very significant antibacterial activity. This puts a query on its safety and hence a call for caution in its usage, thus a product being natural is not tantamount to being entirely safe. However, the antibacterial activities and non-cytotoxic effects of <it>A. arborescens </it>and <it>A. striatula </it>validates their continuous usage in ethnomedicine.</p

一种β-内酰胺类抗生素的酶热检测方法

The penicillinase thermistor biosensor（Penicillinase sensor） was developed for the rapid monitoring of blood penem antibiotics concentration and rapid identification of extraneous penicillinase in milk on site.However, the wide application of the penicillinase thermistor biosensor was limited due to its intrinsic poor activity to hydrolyze cephem and carbapenem antibiotics.The recently identified carbapenemase New Delhi metallo-beta-lactamase 1（NDM-1） is able to hydrolyze all commercially available β-lactam antibiotics in high efficacy.We coupled the NDM-1 and the enzymatic thermistor biosensor to develop a NDM-1 thermistor biosensor（NDM-1 sensor） by the installment of the enzymatic thermistor with an enzyme column loaded with NDM-1 conjugated CPG beads.The NDM-1 sensor shows high response activity to Piperacillin（PIP）,Ceftriaxone（CTRX）, and Meropenem（MEM）, and the response activity of the NDM-1 sensor to these three β-lactam antibiotics are all Zn2+ dependent.Moreover, the response activity of the NDM-1 sensor to Penicillin G（P）, PIP, Cefazolin（CZO）, CTRX, Cefepime（FEP） and MEM all linearly correlated with antibiotic concentration from 31.25 to 1 000 mg/L.Within pH from 6.0 to 8.0, the optimal response activity of the NDM-1 sensor to P,PIP, CZO, CTRX and FEP are found at pH 6.5, while the optimal response activity of the NDM-1 sensor to MEM is found at pH8.0.These data indicate that the featured activity of NDM-1 was well maintained after conjugation on CPG beads, and NDM-1 sensor is capable to quantitate three classes of β-lactam antibiotics including penem, cephem and carbapenem within a wide concentration range

氨曲南竞争性抑制NDM-1对β-内酰胺类抗生素的水解

We investigated the effect of Aztreonam on hydrolysis of β-lactam antibiotics by MBL using New Delhi Metallo-β-lactamase-1(NDM-1) as a model. The results showed that Aztreonam significantly inhibited hydrolysis of Nitrocefin and Meropenem by soluble NDM-1, but also inhibited hydrolysis of Penicillin G by CPG beads immobilized NDM-1(NDM-1 beads). Moreover, in spite of extensive washing for multiple times, the activity to hydrolyze Penicillin G by the Aztreoman pre-treated NDM-1 beads was just partially recovered. These data suggest that Aztreonam can covalently and stably bind on NDM-1, thus efficiently inhibiting hydrolysis of other kinds of β-lactam antibiotics by NDM-1 in a competitive way

Correction: FoxO3a Modulates Hypoxia Stress Induced Oxidative Stress and Apoptosis in Cardiac Microvascular Endothelial Cells.

[This corrects the article DOI: 10.1371/journal.pone.0080342.]

Multiplex, variant-tolerant, real-time RT-LAMP for SARS-CoV-2 detection using HFman probe

Viral evolution impacts diagnostic test performance through the emergence of variants with sequences affecting the efficiency of primer binding. Such variants that evade detection by nucleic acid-based tests are subject to selective pressure, enabling them to spread more efficiently. Here, we report a variant-tolerant diagnostic test for SARS-CoV-2 using a loop-mediated isothermal nucleic acid-based amplification (LAMP) assay containing high-fidelity DNA polymerase and a high-fidelity DNA polymerase-medicated probe (HFman probe). In addition to demonstrating a high tolerance to variable SARS-CoV-2 viral sequences, the mechanism also overcomes frequently observed limitations of LAMP assays arising from non-specific amplification within multiplexed reactions performed in a single “pot”. Results showed excellent clinical performance (sensitivity 94.5%, specificity 100%, n = 190) when compared directly to a commercial gold standard reverse transcription quantitative polymerase chain reaction assay for the extracted RNA from nasopharyngeal samples and the capability of detecting a wide range of sequences containing at least alpha and delta variants. To further validate the test with no sample processing, directly from nasopharyngeal swabs, we also detected SARS-CoV-2 in positive clinical samples (n = 49), opening up the possibility for the assay’s use in decentralized testing