新疆家蚕抗菌肽抗菌作用的超微结构观察及抗菌机理初探

为探讨基因工程表达的新疆家蚕(Bombyx mori)抗菌肽(cecropin-XJ)的抗菌机制,通过紫外分光光度法研究抗菌肽的抑菌动力学,并采用透射电镜观察抗菌肽作用于金黄色葡萄球菌(Staphylococcus aureus)后的超微结构,对抗菌肽抗菌机理进行初步探讨。结果表明,抗菌肽抑菌作用比较明显,抗菌肽的活性与作用时间有关。抗菌肽可能是通过"桶-板"模式渗透细胞膜,从而影响细胞膜的结构和功能,使细胞膜形成许多孔道,增强了金黄色葡萄球菌细胞的通透性,造成细胞内的原生质扩散,并从孔道向胞外渗漏,影响了细菌的代谢系统,从而起到抑菌、杀菌作用。抗菌肽使金黄色葡萄球菌细胞内容物大量渗漏而死亡,死亡细胞的细胞壁保持完整,表明细胞膜是抗菌肽作用的主要靶位点。     

Antimicrobial agents

The adaptation of dermatophytes to antimycotics leads to the development of two independent processes—the induction of degrading enzyme systems detoxicating the antimycotic to less active or completely inactive derivatives, and temporary resistance, accompanied by increasing loss of sensitivity of the dermatophytes to the given antimycotics. These processes can both be regarded as part of the defences of the microbial cell.     

Antimicrobial agents

In the microbial transformation of 2-chloro-4-nitrophenol and its 2-aminotridecane compound salt, 2-chloro-4-nitrophenol was found to be degraded to four metabolites only on using strains resistant to 2-chloro-4-nitrophenol. Sensitive strains lacked this property. In the case of the 2-amino-tridecane compound salt, the first reaction produced by strains resistant to 2-chloro-4-nitrophenol was dissociation of the compound salt into the two initial components, followed by degradation of 2-chloro-4-nitrophenol. Microbial degradation resulted in diminished antifungal activity. The other antimicrobi-ally active component of the compound salt, i.e. 2-aminotridecane, was not affected by biotransformation and kept its original activity.     

Antimicrobial agents

The development of acquired, temporary resistance induced by an adaptation mechanism as a result of direct contact of the cell with an antimycotic, was demonstrated in pathogenic species of the genusCandida. Acquired resistance induced by one substance was manifested in multiresistance to other, structurally quite different, antimycotics. Cultivation of the strain on antimycotic-free medium led to relatively rapid deadaptation and the strain regained its initial sensitivity. The sensitivity of adapted and deadapted strains was studied by the dilution method (determining MIC values) and by the “direct” Warburg method (evaluating metabolic quotients).     

Antimicrobial agents

In a study of the effect of progesterone, its hydroxy derivatives and various sterols on the growth of dermatophytes, it was demonstrated that all the steroid compounds employed inhibited growth of the 51 strains of dermatophytes tested. No significant differences were found in sensitivity to the given steroids, either in dermatophyte strains of the same species, but of different origin, ior in different species of the four genera used (Trichophyton, Microsporum, Epidermophyton andKeratinomyces). Hydroxylation of the progesterone molecule in any except the C-21 position lowered the inhibitory effect. The course of the transformation reaction on the progesterone or cholesterol molecule was likewise of a uniform character from the aspect of species specificity. Progesterone was simultaneously hydroxylated in positions 15α and 15β by all the strains, giving rise to monohydroxy-derivatives as the main metabolites, and cholesterol was oxidized to cholestenone.     

Antimicrobial betalains

Betalains are nitrogen-containing plant pigments that can be red-violet (betacyanins) or yellow-orange (betaxanthins), currently employed as natural colourants in the food and cosmetic sectors. Betalains exhibit antimicrobial activity against a broad spectrum of microbes including multidrug-resistant bacteria, as well as single-species and dual-species biofilm-producing bacteria, which is highly significant given the current antimicrobial resistance issue reported by The World Health Organization. Research demonstrating antiviral activity against dengue virus, in silico studies including SARS-CoV-2, and anti-fungal effects of betalains highlight the diversity of their antimicrobial properties. Though limited in vivo studies have been conducted, antimalarial and anti-infective activities of betacyanin have been observed in living infection models. Cellular mechanisms of antimicrobial activity of betalains are yet unknown; however existing research has laid the framework for a potentially novel antimicrobial agent. This review covers an overview of betalains as antimicrobial agents and discussions to fully exploit their potential as therapeutic agents to treat infectious diseases.     

Antimicrobial agents

Among 15 antimycotic agents tested, maximum activity was displayed by 5,7-dichloro-8-oxyquinoline, both as regards the microorganism spectrum and the minimum inhibitory concentration. The antimycotic effect of 2-aminotridecane-undecylenate and 2-aminotridecane-2-chloro-4-nitrophenolate was greater than that of 2-aminotridecane, undecylenic acid and 2-chloro-4-nitrophenol alone. Biochemical resistance develops relatively rapidly in aTrichophyton mentagrophytes strain on contact with fungicidin, 2-chloro-4-nitrophenol and 5,7-dichloro-8-oxyquinoline. ATrichophyton mentagrophytes strain resistant to one of these three agents is also several times less sensitive to all the other test substances except septonex.     

Antimicrobial agents

In the microbial degradation of Fungicidin by lower pathogenic fungi, no significant differences were found in the rate of its degradation by the various species of dermatophytes employed (Trichophyton mentagrophytes, Trichophyton rubrum andMicrosporum gypseum), but there was a marked difference in the rate of enzymatic degradation by microorganisms adapted and not adapted to Fungicidin or Amphotericin B. After four hours' degradation of Fungicidin by non-adapted strains, about 70% of the Fungicidin in the medium was still intact, whereas it was completely degraded by adapted strains during the same interval. The addition of protein biosynthesis inhibitors (chloramphenicol and tetracycline) and of the antifungally active substance 2-aminotridecane did not influence the microbial degradation of Fungicidin by dermatophytes.