Loperamide exerts a direct bactericidal effect against M. tuberculosis,M. bovis,M. terrae and M. smegmatis

Tuberculosis (TB) is caused by Mycobacterium tuberculosis. TB is highly prevalent, characterized by the constant occurrence of drug-resistant cases, and confounded by the incidence of respiratory disease caused by non-tuberculous mycobacteria (NTB). Expanding the spectrum of drugs for the treatment of TB is indispensable. Loperamide, an antidiarrhoeal drug, enhances immune-driven antimycobacterial activity, and we aimed to evaluate its bactericidal activity against M. tuberculosis, Mycobacterium bovis BCG, Mycobacterium terrae and Mycobacterium smegmatis. Loperamide exhibited an inhibitory effect against all mycobacterial species tested, with MICs of 100 and 150 μg ml⁻¹. Thus, loperamide is a mycobactericidal drug with potential as adjunctive therapy for TB and NTB infections.     

Activity of natural antimicrobial compounds against Escherichia coli and Salmonella enterica serovar Typhimurium

AIMS: The objective of this study was to evaluate the inhibitory activity of several natural organic compounds alone or in combination with nisin against Escherichia coli and Salmonella Typhimurium. METHODS AND RESULTS: The minimum inhibitory concentration (MIC) of five natural organic compounds were determined, and the effect of their combinations with nisin was evaluated by the checkerboard assay using the Bioscreen C. As expected, nisin by itself showed no inhibition against either of the Gram-negative bacteria. Thymol was found to be the most effective with the lowest MIC values of 1.0 and 1.2 mmol 1-1 against Salm. Typhimurium and E. coli, respectively. After thymol, the antimicrobial order of the natural organic compounds was carvacrol > eugenol > cinnamic acid > diacetyl. However, the combination of nisin with the natural organic compounds did not result in the enhancement of their antimicrobial activities. On the contrary, combination of nisin with diacetyl against Salm. Typhimurium resulted in an antagonism of diacetyl activity. CONCLUSIONS: While the individual natural organic compounds showed inhibitory activity against the two Gram-negatives, their combinations with nisin showed no improvement of antimicrobial activity. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows the potential of the natural organic compounds to control E. coli and Salm. Typhimurium.     

重组溶葡萄球菌酶的PEG定点修饰

为获得高抗菌活性聚乙二醇(PEG)定点修饰的溶葡萄球菌酶(Lysn),根据该酶的高级结构,在它的催化域和结合域上优选8个位点(Q9、N13、N40、T172、N174、G197、V240和T244),将其分别突变成半胱氨酸,纯化后的溶葡萄球菌酶突变体经DTT处理后与20 kDa的单甲氧基聚乙二醇马来酰亚胺(m PEG-MAL)进行定点修饰反应,RP-HPLC分析显示PEG修饰率大于70%,修饰产物经MacroCap SP阳离子交换层析纯化后,PEG化溶葡萄球菌酶的纯度大于95%。比浊法和最小抑菌浓度(MIC)实验表明20K-PEG-Lysn V240C和20K-PEG-Lysn T244C的抗菌活性维持在原来的50%左右。研究结果为溶葡萄球菌酶全身给药治疗金黄色葡萄球菌感染奠定基础。     

The LIV-I/LS system as a determinant of azaserine sensitivity of Escherichia coli K-12

The growth of Escherichia coli is inhibited by an antibiotic compound, azaserine (O-diazoacetyl-L-serine). Previous studies revealed the biochemical properties of azaserine, which involves inhibition of various enzymatic reactions as well as introduction of DNA breakage. However, genetically, nothing has been elucidated except that all the azaserine-resistant strains isolated so far carry lesions in the aroP gene as a primary determinant. Here, we demonstrate that, in addition to AroP, the LIV-I/LS system, an ATP-binding cassette type transporter, is involved in azaserine sensitivity of E. coli, by genetic analysis and transport studies, in which Ki value for azaserine was determined to be approximately 10(-3) M.     

Escherichia coli is naturally transformable in a novel transformation system

A novel transformation system, in which neither a nonphysiological concentration of Ca2+ and temperature shifts nor electronic shocks were required, was developed to determine whether Escherichia coli is naturally transformable. In the new protocol, E. coli was cultured normally to the stationary phase and then cultured statically at 37 degrees C in Luria-Bertani broth. After static culture, transformation occurred in bacteria spread on Luria-Bertani plates. The protein synthesis inhibitor chloramphenicol inhibited this transformation process. The need for protein synthesis in plated bacteria suggests that the transformation of E. coli in this new system is regulated physiologically.     

Compensatory evolution reveals functional interactions between ribosomal proteins S12, L14 and L19

Certain mutations in S12, a ribosomal protein involved in translation elongation rate and translation accuracy, confer resistance to the aminoglycoside streptomycin. Previously we showed in Salmonella typhimurium that the fitness cost, i.e. reduced growth rate, due to the amino acid substitution K42N in S12 could be compensated by at least 35 different mutations located in the ribosomal proteins S4, S5 and L19. Here, we have characterized in vivo the fitness, translation speed and translation accuracy of four different L19 mutants. When separated from the resistance mutation located in S12, the three different compensatory amino acid substitutions in L19 at position 40 (Q40H, Q40L and Q40R) caused a decrease in fitness while the G104A change had no effect on bacterial growth. The rate of protein synthesis was unaffected or increased by the mutations at position 40 and the level of read-through of a UGA nonsense codon was increased in vivo, indicating a loss of translational accuracy. The mutations in L19 increased sensitivity to aminoglycosides active at the A-site, further indicating a perturbation of the decoding step. These phenotypes are similar to those of the classical S4 and S5 ram (ribosomal ambiguity) mutants. By evolving low-fitness L19 mutants by serial passage, we showed that the fitness cost conferred by the L19 mutations could be compensated by additional mutations in the ribosomal protein L19 itself, in S12 and in L14, a protein located close to L19. Our results reveal a novel functional role for the 50 S ribosomal protein L19 during protein synthesis, supporting published structural data suggesting that the interaction of L14 and L19 with 16 S rRNA could influence function of the 30 S subunit. Moreover, our study demonstrates how compensatory fitness-evolution can be used to discover new molecular functions of ribosomal proteins.     

乳源耐甲氧西林金黄色葡萄球菌icaA/D基因缺失株的构建及其生物被膜形成能力与耐药性分析

[背景]耐甲氧西林金黄色葡萄球菌(Methicillin Resistant Staphylococcus aureus,MRSA)是一种具有多重耐药性的人畜共患病原菌,常引起奶牛乳房炎等疾病.形成生物被膜是MRSA重要的耐药机制之一.研究发现ica操纵子调控的胞间多糖黏附素(Polysaccharide Interc...     

Peptide-mediated delivery of green fluorescent protein into yeasts and bacteria

Stringent microbial cell barriers limit the application of many substances in research and therapeutics. Carrier peptides that penetrate or translocate across cell membranes may help overcome this problem. To assess peptide-mediated delivery into two yeast and three bacterial species, a range of cell penetrating and signal peptide sequences were fused to green fluorescent protein (GFP), expressed in Escherichia coli, partially purified and incubated with growing cells. Fluorescence microscopy indicated several peptides that mediated delivery. In particular, VLTNENPFSDP efficiently delivered GFP into Candida albicans and Staphylococcus aureus, while YKKSNNPFSD was most efficient for Bacillus subtilis and CFFKDEL for Escherichia coli. Carrier peptides may improve delivery of certain large molecular mass molecules into microorganisms for research and therapeutic applications.     

A novel fluorescent probe based on naphthalimide for imaging nitroreductase (NTR) in bacteria and cells

A nitroreductase (NTR) responsive fluorescent probe, Na-NO₂, comprising p-nitrobenzyl as the unique recognition group and 1,8-naphthalimide as fluorophore, was synthesized. Na-NO₂ showed remarkable fluorescence “turn-on” signal in the presence of NTR under DMSO/H₂O (1:19, v/v) buffered with PBS (pH = 7) solution in the presence of NADH (300 µM). Furthermore, the probe has a low detection limit down to 3.4 ng/mL and it is very sensitive towards the NTR in Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), normal and tumor cells such as HL-7702, HepG-2 and MCF-7.     

Acetophenones with selective antimycobacterial activity

AIMS: Mycobacteria are a serious cause of infections in humans, with limited treatment options, as no new antibiotics have been developed against mycobacteria since the 1960s. In this study, the antimycobacterial activity of a small library of acetophenone (AP) compounds was analysed. METHODS AND RESULTS: Twenty-three AP derivatives were examined for activity against mycobacteria using a microbroth assay. The compounds were bacteriostatic, with the most effective (cyclohexylacetophenone and piperidinoacetophenone) having minimal inhibitory concentrations of 246 microM. Active compounds tended to be more hydrophobic, and may work by alkylation of as yet undetermined intracellular target protein(s). Cytotoxicity against eukaryotic cells was also determined and appears to be unrelated to the bacteriostatic activity. SIGNIFICANCE AND IMPACT OF THE STUDY: AP may serve as a novel group of useful therapeutics against the mycobacteria.     

Susceptibility of food-borne bacteria to binary combinations of antimicrobials at selected a(w) and pH

AIM: To evaluate the antibacterial susceptibilities of food-borne bacteria to individual and binary mixtures of a synthetic antimicrobial agent with a natural phenolic compound. METHODS AND RESULTS: Antibacterial susceptibilities of Escherichia coli, Listeria innocua, Salmonella Typhimurium and Staphylococcus aureus to individual and binary mixtures of potassium sorbate with a phenolic compound (thymol, carvacrol, or eugenol) were evaluated, at selected water activity (a(w); 0.99 or 0.97) and pH (5.5 or 4.5). The bacteria studied were susceptible to the action of the antimicrobials individually with minimal inhibitory concentrations that varied from 800-ppm potassium sorbate for Staph. aureus at a(w) 0.99, and pH 5.5 to 100-ppm thymol or carvacrol for the four studied bacteria at a(w) 0.97 and pH 4.5. Several binary mixtures of potassium sorbate with thymol, carvacrol or eugenol inhibited bacterial growth. Antimicrobial agent inhibitory concentrations in the mixture varied among bacteria, additionally depending on the a(w) and the pH tested. CONCLUSIONS: Synergistic binary mixtures with fractional inhibitory concentration index <0.6 include 100- or 200-ppm potassium sorbate with 50- or 100-ppm thymol, carvacrol or eugenol. SIGNIFICANCE AND IMPACT OF THE STUDY: The synergistic combinations could be useful in reducing the amounts of antimicrobials needed to inhibit growth, thus diminishing consumer concerns regarding chemical preservatives.     

Bioactive stilbenes from a Bacillus sp. N strain associated with a novel rhabditid entomopathogenic nematode

Aims: The aim of the present study was to purify and characterize a natural antimicrobial compound from Bacillus sp. strain N associated with a novel rhabditid entomopathogenic nematode. Methods and Results: The cell‐free culture filtrate of a bacterium associated with a novel entomopathogenic nematode (EPN), Rhabditis (Oscheius) sp. exhibited strong antimicrobial activity. The ethyl acetate extract of the bacterial culture filtrate was purified by column chromatography, and two bioactive compounds were isolated and their chemical structures were established based on spectral analysis. The compounds were identified as 3,4′,5‐trihydroxystilbene (1) and 3,5‐dihydroxy‐4‐isopropylstilbene (2). The presence of 3,4′,5‐trihydroxystilbene (resveratrol) is reported for the first time in bacteria. Compound 1 showed antibacterial activity against all the four test bacteria, whereas compound 2 was effective against the Gram‐positive bacteria only. Compounds 1 and 2 were active against all the five fungi tested and are more effective than bavistin, the standard fungicide. The antifungal activity of the compounds against the plant pathogenic fungi, Rhizoctonia solani is reported for the first time. Conclusions: Cell‐free extract of the bacterium and isolated stilbenes demonstrated high antibacterial activity against bacteria and fungi especially against plant pathogenic fungi. We conclude that the bacterium‐associated EPN are promising sources of natural bioactive secondary metabolites. Significance and Impact of the Study: Stilbene compounds can be used for the control of fungi and bacteria.     

Antimicrobial susceptibilities of Shiga toxin-producing Escherichia coli isolates from pigs with edema disease in Japan

Fifty-seven Shiga toxin-producing Escherichia coli (STEC) strains isolated from pigs with edema disease (ED) from 1997 to 2001 in Japan were examined for antimicrobial susceptibilities. The susceptibilities were compared with those of E. coli ATCC 23546 isolated from pig with ED in the 1950's. Consequently, the isolated STECs showed high susceptibility to peptides and bicozamycin in a way similar to the reference strain. On the other hand, the STECs showed low susceptibility to beta-lactams, tetracyclines, novobiocin, fosfomycin, trimethoprim, and old quinolones. It became clear that the susceptibilities of the isolated STECs had diminished in regard to antimicrobials.     

The effect of levofloxacin concentration on the development and maintenance of antibiotic-resistant clones of Escherichia coli in chemostat culture

A levofloxacin-sensitive strain of Escherichia coli (broth MIC: 0.0625 mg l⁻¹) was grown in carbon-limited chemostat culture for 316 h (D=0.294 h⁻¹). Hyperresistant strains isolated after 58 and 91 generations of culture retained a 16- to 47-fold increase in tolerance to levofloxacin during antibiotic-free serial batch and continuous culture (20 generations, glucose-limited, D=0.2 h⁻¹). Isolates differed from the original strain in their maximum growth rates in the presence and absence of subinhibitory levels of levofloxacin, protein-banding profiles, and resistance to a range of antibiotics. Competition between resistant isolates and the original sensitive strain was studied in glucose-limited chemostat cultures (D=0.2 h⁻¹). At levofloxacin concentrations less than 0.03 mg l⁻¹, the sensitive strain outcompeted resistant isolates and displaced them from the culture, whereas the reverse was true at higher concentrations. These results have clinical and environmental implications for those administering levofloxacin. Journal of Industrial Microbiology & Biotechnology (2002) 29, 155–162 doi:10.1038/sj.jim.7000295 Received 26 September 2001/ Accepted in revised form 13 June 2002     

棘白菌素对氟康唑耐药的念珠菌体外药物敏感性的研究

目的评价3种棘白菌素类药物（卡泊芬净、米卡芬净、阿尼多芬净）体外对氟康唑耐药念珠菌的药物敏感性。方法采用微量液体稀释法和琼脂稀释法测定最小抑制浓度（MIC）。结果微量液体稀释法：59株耐药白念珠菌3种药物MIC50均为0.06μg/mL,米卡芬净、阿尼多芬净的MIC范围均为0.015～0.125μg/mL,卡泊芬净为0.015～0.25μg/mL;8株耐药光滑念珠菌MIC值均为0.063μg/mL。琼脂稀释法：59株耐药白念珠菌和8株耐药光滑念珠菌3种药物MIC值均为0.063μg/mL。结论3种棘白菌素类药物可能具有治疗氟康唑耐药的念珠菌感染的临床价值。     

乳酸杆菌细胞裂解物对金黄色葡萄球菌、大肠埃希菌的抑制作用

目的探讨乳杆菌DM8909裂解物在体内外对金黄色葡萄球菌、大肠埃希菌的抑制作用。方法通过对乳杆菌超声波破碎制成裂解物,分别用乳杆菌裂解物原液、裂解物稀释液、发酵上清液、乳杆菌活菌制剂进行体内、体外实验,观察乳杆菌各成分对金黄色葡萄球菌、大肠埃希菌的抑制作用。结果德氏乳酸杆菌裂解物对金黄色葡萄球菌、大肠埃希菌的抑制作用与乳杆菌活菌制剂的抑制作用相近。结论德氏乳酸杆菌裂解物在体内外对金黄色葡萄球菌、大肠埃希菌均有较强的抑制作用。