Effects of bacterial physiological states and bacterial species on host–microbe interactions

Abstract

This study investigated how the physiological states of Aggregatibacter actinomycetemcomitans (Aa) and Streptococcus mitis affect their intracellular invasion capabilities and the resulting host cell responses. The physiological states included two forms of planktonic states, floating or sedimented (by centrifugation) and the biofilm state (with centrifugation). Confluent epithelial Ca9-22 cells were challenged with floating or sedimented planktonic cultures, or with 24-h biofilms for 3?h. The results show that intracellular invasion efficiencies were clearly affected by the bacterial physiological states. For both bacterial species, the sedimented-cells displayed 2–10 times higher invasion efficiency than the floating-cells (p?<?0.05). The invasion efficiency of Aa biofilms was three fold lower than sedimented cells, whereas those of S. mitis biofilms were similar to sedimented cells. Unlike invasion, the metabolic activities of Ca9-22 were unaffected by different bacterial physiological states. However, Aa biofilms induced higher IL-1β expression than planktonic cultures. In conclusion, different bacterial physiological states can affect the outcomes of (in vitro) host–microbe interaction in different ways.     

葛根素调节Nrf2/HO-1信号通路对脂多糖诱导的人牙龈成纤维细胞炎症反应的影响

摘要 目的：探讨葛根素（GGS）调节核因子E2相关因子2（Nrf2）/血红素氧合酶-1（HO-1）信号通路对脂多糖（LPS）诱导的人牙龈成纤维细胞（HGFs）炎症反应的影响。方法：体外培养HGFs细胞,将HGFs细胞分为空白对照（CK）组（0.9%氯化钠）、LPS组（100 nM LPS）、LPS+GGS低剂量（LPS+GGS-L）组（100 nM LPS+50 μM GGS）、LPS+GGS高剂量（LPS+GGS-H）组（100 nM LPS+100 μM GGS）、LPS+GGS-H+ML385（Nrf2/HO-1信号通路抑制剂）组（100 nM LPS+100 μM GGS+10 μM ML385）。采用细胞计数试剂盒-8（CCK-8）检测细胞增殖能力;酶联免疫吸附法（ELISA）检测白细胞介素（IL）-6、乳酸脱氢酶（LDH）、IL-10、IL-1β水平;试剂盒检测丙二醛（MDA）、谷胱甘肽过氧化物酶（GSH-Px）、超氧化物歧化酶（SOD）水平;流式细胞术检测HGFs细胞凋亡率;碘化丙啶（PI）染色法检测细胞膜孔的形成;Western blot法检测B淋巴细胞瘤-2（Bcl-2）、B细胞淋巴瘤-2相关X蛋白（Bax）、NOD样受体蛋白3（NLRP3）、Nrf2、HO-1蛋白表达。结果：与CK组相比,LPS组HGFs细胞OD₄₅₀（24、48 h）值、IL-10水平、GSH-Px和SOD活性、Bcl-2、Nrf2和HO-1蛋白表达显著降低,IL-6、LDH、IL-1β水平、MDA含量、细胞凋亡率、细胞PI染色阳性率、Bax和NLRP3蛋白表达显著升高（P<0.05）;与LPS组相比,LPS+GGS-L组和LPS+GGS-H组HGFs细胞OD₄₅₀（24、48 h）值、IL-10水平、GSH-Px和SOD活性、Bcl-2、Nrf2和HO-1蛋白表达显著升高,IL-6、LDH、IL-1β水平、MDA含量、细胞凋亡率、细胞PI染色阳性率、Bax和NLRP3蛋白表达显著降低（P<0.05）;ML385可减轻GGS对LPS诱导的HGFs细胞炎症损伤的改善作用（P<0.05）。结论：GGS可能通过激活Nrf2/HO-1信号通路减轻LPS诱导的HGFs细胞炎症和氧化应激反应,降低细胞凋亡。     

Anti-inflammatory activity of a globular adiponectin function on RAW 264 cells stimulated by lipopolysaccharide from Aggregatibacter actinomycetemcomitans

Adiponectin is an adipokine with potent anti-inflammatory properties. We previously reported that a globular adiponectin (gAd) suppresses Aggregatibacter actinomycetemcomitans lipopolysaccharide-induced nuclear factor-κB activity, suggesting an anti-inflammatory effect of gAd. In this study, we investigated whether gAd is able to modulate the effect of A. actinomycetemcomitans lipopolysaccharide on cytokine induction in a murine macrophage cell line (RAW 264). The phosphorylation of p38 mitogen-activated protein kinase, c-Jun N-terminal kinase, extracellular signal-regulated kinase, and IκB kinase α/β and the degradation of IκB, which were induced by A. actinomycetemcomitans lipopolysaccharide intoxication, were clearly reduced in gAd-pretreated RAW 264 cells compared with the untreated cells. Expression levels of tumor necrosis factor (TNF)-α and interleukin-10 (IL-10) mRNA were assessed by real-time PCR. Cell-free supernatants were collected after 12 h of stimulation and analyzed by enzyme-linked immunosorbent assay for TNF-α and IL-10. Pretreatment with gAd significantly inhibited the A. actinomycetemcomitans lipopolysaccharide-induced TNF-α mRNA expression and protein secretion. In contrast, pretreatment with gAd significantly enhanced the A. actinomycetemcomitans lipopolysaccharide-induced IL-10 mRNA expression and protein secretion. These data suggest a mechanism for the anti-inflammatory activity of gAd in local inflammatory lesions, such as periodontitis.     

Actinomycetemcomitin: a new bacteriocin produced by <Emphasis Type="Italic">Aggregatibacter</Emphasis> (<Emphasis Type="Italic">Actinobacillus</Emphasis>) <Emphasis Type="Italic">actinomycetemcomitans</Emphasis>

Aggregatibacter (Actinobacillus) actinomycetemcomitans P_7–20 strain isolated from a periodontally diseased patient has produced a bacteriocin (named as actinomycetemcomitin) that is active against Peptostreptococcus anaerobius ATCC 27337. Actinomycetemcomitin was produced during exponential and stationary growth phases, and its amount decreased until it disappeared during the decline growth phase. It was purified by ammonium sulphate precipitation (30–60% saturation), and further by FPLC (mono-Q ionic exchange and Phenyl Superose hydrophobic interaction) and HPLC (C-18 reversed-phase). This bacteriocin loses its activity after incubation at a pH below 7.0 or above 8.0, following heating for 30 min at 45°C, and after treatment with proteolytic enzymes such as trypsin, α-chymotrypsin, and papain. Actinomycetemcomitin has a molecular mass of 20.3 KDa and it represents a new bacteriocin from A. actinomycetemcomitans.     

Serotype‐dependent expression patterns of stabilized lipopolysaccharide aggregates in Aggregatibacter actinomycetemcomitans strains

Above a critical concentration, amphiphilic lipopolysaccharide (LPS) molecules in an aqueous environment form aggregate structures, probably because of interactions involving hydrophobic bonds. Ionic bonds involving divalent cations stabilize these aggregate structures, making them resistant to breakdown by detergents. The aim of this study was to examine expression patterns of stabilized LPS aggregates in Aggregatibacter actinomycetemcomitans, a microorganism that causes periodontitis. A. actinomycetemcomitans strains of various serotypes and truncated LPS mutants were prepared for this study. Following treatment with a two‐phase separation system using the detergent Triton X‐114, crude LPS extracts of the study strains were separated into detergent‐phase LPS (DP‐LPS) and aqueous‐phase LPS (AP‐LPS). Repeated treatment of the aqueous phase with the two‐phase separation system produced only a slight decrease in AP‐LPS, suggesting that AP‐LPS was resistant to the detergent and thus distinguishable from DP‐LPS. The presence of divalent cations increased the yield of AP‐LPS. AP‐LPS expression patterns were serotype‐dependent; serotypes b and f showing early expression, and serotypes a and c late expression. In addition, highly truncated LPS from a waaD (rfaD) mutant were unable to generate AP‐LPS, suggesting involvement of the LPS structure in the generation of AP‐LPS. The two‐phase separation was able to distinguish two types of LPS with different physical states at the supramolecular structure level. Hence, AP‐LPS likely represents stabilized LPS aggregates, whereas DP‐LPS might be derived from non‐stabilized aggregates. Furthermore, time‐dependent expression of stabilized LPS aggregates was found to be serotype‐dependent in A. actinomycetemcomitans.     

Aggregatibacter actinomycetemcomitans biofilm killing by a targeted ciprofloxacin prodrug

A pH-sensitive ciprofloxacin prodrug was synthesized and targeted against biofilms of the periodontal pathogen Aggregatibacter actinomycetemcomitans (Aa). The dose required to reduce the viability of a mature biofilm of Aa by ～80% was in the range of ng?cm^?2 of colonized area (mean biofilm density 2.33?×?10⁹?cells?cm^?2). A mathematical model was formulated that predicts the temporal change in the concentration of ciprofloxacin in the Aa biofilm as the drug is released and diffuses into the bulk medium. The predictions of the model were consistent with the extent of killing obtained. The results demonstrate the feasibility of the strategy to induce mortality, and together with the mathematical model, provide the basis for design of targeted antimicrobial prodrugs for the topical treatment of oral infections such as periodontitis. The targeted prodrug approach offers the possibility of optimizing the dose of available antimicrobials in order to kill a chosen pathogen while leaving the commensal microbiota relatively undisturbed.     

Recombinant expression and redox properties of triheme c membrane-bound quinol peroxidase

The qpo gene of Aggregatibacter actinomycetemcomitans encodes a triheme c -containing membrane-bound enzyme, quinol peroxidase (QPO) that catalyzes peroxidation reaction in the respiratory chain and uses quinol as the physiological electron donor. The QPO of A. actinomycetemcomitans is the only characterized QPO, but homologues of the qpo gene are widely distributed among many gram-negative bacteria, including Haemophils ducreii, Bacteroides fragilis , and Escherichia coli . One-third of the amino acid sequence of QPO from the N-terminal end is unique, whereas two-thirds of the sequence from the C-terminal end exhibits high homology with the sequence of the diheme bacterial cytochrome c peroxidase. In order to obtain sufficient protein for biophysical studies, the present study aimed to overproduce recombinant QPO (rQPO) from A. actinomycetemcomitans in E. coli . Coexpression of qpo with E. coli cytochrome c maturation ( ccm ) genes resulted in the expression of an active QPO with a high yield. Using purified rQPO, we determined the midpoint reduction potentials of the three heme molecules.     

2型糖尿病人口腔高温G蛋白(HTPG)生物信息学分析

利用一系列生物信息学软件分析了2型糖尿病患者口腔微生物(放线共生放线杆菌)中的高温G蛋白的氨基酸组成、等电点、结构域、特征位点、二级结构等蛋白质性质。结果表明:高温G蛋白分子式为:C3167H4975N849O975S14,属于稳定蛋白;二级结构主要是以α-螺旋为主。初步预测了高温G蛋白的理化性质并初步确定了其二级结构。     

Differential effects of anticytoskeletal compounds on the localization and chemical patterns of actin in germinating conidia of Neurospora crassa

Abstract Anti-actin drugs, cytochalasins A and B, inhibited both normal single, and benomyl-induced multiple, germ tube outgrowth from conidia of Neurospora crassa . Actin was cytochemically found to be concentrated in each of the benomyl-induced germ tube tips. No significant quantitative changes either in total actin or its isoforms were measured in the inhibitor-treated germlings. While intact microtubules are required for normal, monopolar axiation of the germ tube, they appear not to be necessary for benomyl-induced multipolar outgrowth which, in contrast, still requires intact actin microfilaments. Microfilaments and microtubules thus play complementary roles in the normal germination of conidia.