Activity and selectivity of histidine-containing lytic peptides to antibiotic-resistant bacteria

Lytic peptides are a group of membrane-acting peptides that are active to antibiotic-resistant bacteria but demonstrate high toxicity to tissue cells. Here, we reported the construction of new lytic peptide derivatives through the replacement of corresponding lysine/arginine residues in lytic peptide templates with histidines. Resulting lytic peptides had the same lethality to antibiotic-resistant bacteria, including methicillin-resistant Staphylococcus aureus, but showed greatly improved selectivity to bacteria. When incubated with co-cultured bacteria and tissue cells, these histidine-containing lytic peptide derivatives killed bacteria selectively but spared co-cultured human cells. Membrane insertion and peptide-quenching studies revealed that histidine protonation controlled peptide interactions with cell membranes determined the bacterial selectivity of lytic peptide derivatives. Compared with parent peptides, lytic peptide derivatives bound to bacteria strongly and inserted deeply into the bacterial cell membrane. Therefore, histidine-containing lytic peptides represent a new group of antimicrobial peptides for bacterial infections in which the antibiotic resistance has developed.     

Modeling the role of altruism of antibiotic-resistant bacteria

Based on the new findings in a recent experimental study (Lee et al., Nature 467, 82–86, 2010) that antibiotic resistant mutants of bacteria produce indoles to protect the wild strain bacteria, we propose a mathematical model to describe the evolution of the wild strain, resistant strain and indoles with limited nutrient. We distinguish two cases: (i) mutation is negligible and a resistant strain preexists; (ii) mutation is not negligible. For (i), we establish conditions for co-persistence of both strains, which indicate that the wild strain can survive with the help from the altruistic resistant strain, whereas it dies out in the absence of such a benefit. This consolidates the experimental findings in Lee et al. (Nature 467:82–86 2010). Further analysis and simulations also reveal some new phenomena not reported in Lee et al. (Nature 467:82–86 2010), that is, periodic oscillations of the populations may occur within certain range of the parameters, and there exists bistability in the sense that a stable positive periodic solution coexists with a stable positive equilibrium.     

Dodecyl sorbitan ethers as antimicrobials against Gram-positive bacteria

A range of amphiphilic sorbitan ethers has been synthesized in two steps from sorbitan following an acetalization/hydrogenolysis sequence. These sorbitan ethers and the acetal intermediates have been evaluated as antimicrobials against Gram-negative and Gram-positive bacteria. No antimicrobial activity was observed for Gram-negative bacteria. However, the compounds bearing a linear dodecyl chain exhibit antimicrobial activity (MIC as low as 8 μg/mL) against Gram-positive bacteria such as Listeria monocytogenes, Enterococcus faecalis and Staphylococcus aureus. Encouraged by these preliminary results, dodecyl sorbitan was tested against a range of resistant strains and was found to be active against vancomycin-, methicillin- and daptomycin-resistant strains (MIC = 32–64 μg/mL).     

Proline-rich antimicrobial peptides: potential therapeutics against antibiotic-resistant bacteria

The increasing resistance of pathogens to antibiotics causes a huge clinical burden that places great demands on academic researchers and the pharmaceutical industry for resolution. Antimicrobial peptides, part of native host defense, have emerged as novel potential antibiotic alternatives. Among the different classes of antimicrobial peptides, proline-rich antimicrobial peptides, predominantly sourced from insects, have been extensively investigated to study their specific modes of action. In this review, we focus on recent developments in these peptides. They show a variety of modes of actions, including mechanism shift at high concentration, non-lytic mechanisms, as well as possessing different intracellular targets and lipopolysaccharide binding activity. Furthermore, proline-rich antimicrobial peptides display the ability to not only modulate the immune system via cytokine activity or angiogenesis but also possess properties of penetrating cell membranes and crossing the blood brain barrier suggesting a role as potential novel carriers. Ongoing studies of these peptides will likely lead to the development of more potent antimicrobial peptides that may serve as important additions to the armoury of agents against bacterial infection and drug delivery.     

Raman-activated sorting of antibiotic-resistant bacteria in human gut microbiota

The antibiotic-resistant bacteria (ARB) and antibiotic-resistant genes (ARGs) in human gut microbiota have significant impact on human health. While high throughput metagenomic sequencing reveals genotypes of microbial communities, the functionality, phenotype and heterogeneity of human gut microbiota are still elusive. In this study, we applied Raman microscopy and deuterium isotope probing (Raman–DIP) to detect metabolic active ARB (MA-ARB) in situ at the single-cell level in human gut microbiota from two healthy adults. We analysed the relative abundances of MA-ARB under different concentrations of amoxicillin, cephalexin, tetracycline, florfenicol and vancomycin. To establish the link between phenotypes and genotypes of the MA-ARB, Raman-activated cell sorting (RACS) was used to sort MA-ARB from human gut microbiota, and mini-metagenomic DNA of the sorted bacteria was amplified, sequenced and analysed. The sorted MA-ARB and their associated ARGs were identified. Our results suggest a strong relation between ARB in human gut microbiota and personal medical history. This study demonstrates that the toolkit of Raman–DIP, RACS and DNA sequencing can be useful to unravel both phenotypes and genotypes of ARB in human gut microbiota at the single-cell level.     

临床常见病原性细菌对抗生素的耐药性分析

目的了解长春地区部分医院临床分离的致病菌对抗菌药物的耐药情况。方法收集吉林大学中日联谊医院和长春中医药大学附属医院临床分离的致病菌,采用K—B法进行抗生素敏感性试验,参照CLSI2009年版的标准判断结果。结果从这两家医院共分离细菌447株,其中革兰阴性菌353株,占78．9％,革兰阳性菌94株,占21．1％。肠杆菌科细菌对氨苄西林的耐药率在70％以上,对庆大霉素的耐药率超过了50％,但对亚胺培南保持较高的敏感性（耐药率〈5％）。金黄色葡萄球菌和表皮葡萄球菌对红霉素耐药率分别为65．2％和82．1％,对万古霉素的耐药率较低,分别为4．5％和3．6％。非发酵革兰阴性杆菌对头孢他啶的耐药率超过50％,铜绿假单胞菌对氨曲南的耐药率达到了62．9％,对他唑巴坦复合制剂、亚胺培南、美罗培南和阿米卡星较为敏感,而鲍曼不动杆菌对各类抗生素的耐药率都较高。结论细菌对抗生素的耐药性仍表现出增长趋势,加强细菌耐药性的检测,对于指导临床正确、合理使用抗生素,减少耐药菌的产生和传播具有重要意义。     

羧基荧光素脂质体的制备及其与病原菌的响应行为

【背景】由于目前临床上检测细菌感染的方法既耗时又昂贵,所以开发快速简便的鉴别方法势在必行。【目的】通过在脂质体膜材料中添加不同的稳定剂,研究它们对于脂质体稳定性的影响,并探究荧光素脂质体与病原菌之间的响应情况。【方法】以磷脂酰胆碱和胆固醇为主要原料,1,2-棕榈酰磷脂酰甘油[1,2-Dipalmitoyl-sn-glycero-3-phospho-(1?-rac-glycerol),DPPG]、十八胺和10,12-二十三二炔酸(10,12-Tricosadiyonic acid,TCDA)为稳定剂,采用薄膜分散-超声法制备羧基荧光素脂质体。利用病原菌能够分泌毒力因子造成脂质体渗漏的原理,将病原菌菌液和上清液分别与荧光素脂质体孵育,检测从脂质体渗漏的羧基荧光素的荧光强度,反映病原菌的毒性程度。【结果】DPPG和TCDA都能增加脂质体的稳定性,而十八胺的添加则导致脂质体稳定性的降低。与金黄色葡萄球菌ATCC25923和铜绿假单胞菌PAO1菌液和上清液共同孵育的脂质体荧光强度大量增加,与大肠杆菌DH5α和PBS缓冲液共同孵育的脂质体荧光强度几乎不变。【结论】能够分泌外毒素的金黄色葡萄球菌和铜绿假单胞菌都能对脂质体产生响应,而不分泌外毒素的大肠杆菌则不会对脂质体产生响应。     

Isolation of nonlysogenic bacteria from lambda-lysogenized strains using antibiotic-resistant phage

A simple and efficient method for obtaining nonlysogenic bacteria from lambda-lysogenized strains using phage with an inserted antibiotic-resistant plasmid is described. When the lysogenic culture is infected with antibiotic-resistant phage, single non-lysogenic cells are lysogenized, isolated on selective medium, and cured of phage during incubation at 37 degrees C.     

Carriage of antibiotic-resistant bacteria in urban versus rural wild boars

The Western European population of wild boar (Sus scrofa) has increased its distribution over the past several decades, and some populations have colonized areas strongly influenced by human activity. Wild boars are known carriers of antibiotic-resistant bacteria acquired from the environment, and urban populations of wild boars may be more exposed than their rural counterparts. In this work, we compared the frequency of antibiotic resistance in indicator bacteria (Escherichia coli, Enterococcus faecalis, Enterococcus faecium) isolated from urban wild boars with that from rural wild boars in NE Spain. We further assessed whether bacterial isolates from the urban wild boars had a higher probability of showing antibiotic resistance when their host was highly associated to urban features. Seventy-two and 100 bacterial isolates from urban and rural habitat, respectively, were screened for antibiotic resistance against a set of antibiotics (13 per bacterial species). We found a significantly higher frequency of E. faecium showing resistance to tetracycline (70.0% vs 36.4%) and high-level resistance to streptomycin (30.0% vs 4.5%) in urban wild boars compared to rural wild boars (p?<?0.05). E. faecalis was more frequently resistant to trimethoprim in urban than rural wild boars (33.3% vs 0.0%, p?<?0.05). In isolates from urban origin, 55.6% of the likelihood of detecting antibiotic resistance depended only on the bacterial species, being more likely in the enterococci than in E. coli. These results suggest that urban wild boars may be more exposed to certain antibiotic-resistant bacteria or antibiotic resistance genes that they may acquire from the urban environment, although implications are uncertain.     

Use of Lactobacillus to prevent infection by pathogenic bacteria

This review focuses on the use and potential of Lactobacillus to prevent infections of the urogenital and intestinal tracts. The presence and dominance of Lactobacillus in the vagina is associated with a reduced risk of bacterial vaginosis and urinary tract infections. The mechanisms appear to involve anti-adhesion factors, by-products such as hydrogen peroxide and bacteriocins lethal to pathogens, and perhaps immune modulation or signaling effects. The instillation of Lactobacillus GR-1 and B-54 or RC-14 strains into the vagina has been shown to reduce the risk of urinary tract infections, and improve the maintenance of a normal flora. Ingestion of these strains into the gut has also been shown to modify the vaginal flora to a more healthy state. In addition, these strains inhibit the growth of intestinal, as well as urogenital pathogens, colonize the gut and protect against infections as shown in mice. Other probiotic strains, such as Lactobacillus GG, have been shown to prevent and treat gastroenteritis caused by rotavirus and bacteria. Given that lactobacilli are not the dominant commensals in a gut which comprises around 10(10) organisms, much work is still needed to define the mechanisms whereby GR-1, RC-14, GG and other strains contribute to health restoration and maintenance. Such critically important studies will require the medical science community to show a willingness to turn away from pharmaceutical remedies as the only solution to health and disease.     

Genetic variation in pathogenic bacteria

In contrast to textbook ideas of pure cultures and defined strains, genetic variation is a fact of life in the microbial world. It not only allows pathogens to establish themselves in their chosen host, but also allows them to resist that host's subsequent attempts to evict them. Here we review some of the mechanisms that bring about this variation, and some of the functional consequences that result from it.