Source: International Respiratory Journal, Issue 11, 2020
Author: Dong Ying, Cheng Sijun, Jin Liyuan, Fu Fangjie, Liu Junxiu, Chen Yu
Department of Respiratory and Critical Care Medicine, Shengjing Hospital, China Medical University, Shenyang 110004
Corresponding author: Chen Yu Email:[email protected]
summary
Pseudomonas aeruginosa is a common pathogenic bacteria accompanied by lung infections in patients with structural lung disease, which often causes bacteria to be difficult to remove, infection to become chronic, and repeated acute infections induce increased bacterial resistance, making clinical treatment difficult. This paper focuses on the mechanism of pseudomonas aeruginosa group sensing effect, introduces the role of macrolides in inhibiting pseudomonas aeruginosa from the perspective of basic research, and reviews the research progress of macrolides on the treatment of structural lung disease from the perspective of clinical research.
The famous ancient Greek thinker Aristotle observed the phenomenon of ants lining up to carry food and bonito gathering when they encounter danger, and for the first time proposed animal social behavior in his book "Animal History", that is, animals can transmit information between individuals, and when forming groups, they can play roles and functions that individuals cannot achieve. The sociality of microorganisms only began to emerge in the 1960s and 1970s. Tomasz[1] found that a gene of Streptococcus pneumoniae can be expressed and is expressed only when bacteria proliferate in a certain number, and a peak occurs rapidly, and this gene expression can be transmitted between the same bacteria through a small hormone-like molecule secreted by the bacteria. The study was the cornerstone of the theory of the group sense effect, which has since been established by scientists through luminescent bacteria and explored in depth. Pseudomonas aeruginosa is the most in-depth bacterium on the effect of group sensibility, and this paper briefly introduces the research progress in this area and the clinical treatment of macrolides.
1 Group sensing effect of microorganisms
1.1 Concept of group sense effect
Hawaiian short-tailed squid has the biological property of luminescence, which comes from the fluorescein produced by Vibrio fischerii, which is symbiotic with it. Nealson et al. [2] In 1970, through the study of the luminescence mechanism of the marine luminous bacterium Vibrio ferri, it was proposed that bacteria exchange information with each other with the help of small molecular substances secreted by themselves. Whether the bacteria emit light and the intensity of luminescence are related to the expression of luciferin synthase gene, the study found that the gene is not expressed when the number of bacteria is small, and the gene is activated after the bacterial proliferation reaches a certain amount during the exponential growth period, and the rapid synthesis of luciferase follows the luminescence, and the control of luciferase synthesis is at the transcriptional level. Since this phenomenon has no external intervention and is caused by cell growth itself, the concept of "self-induction" was first proposed[2], and the signaling molecules that transmit information are called self-inducers. In 1981, the inducer was first isolated from the ultra-bright strain of Vibrio fischeri (MJ-1) by high performance liquid chromatography, the chemical composition of which was N-3-oxyhexanoyl-L-high serine lactone (3OC6-HSL), and the synthetic compound was added to the very low bright strain (B-61) to induce its luminescence [3].
Based on the study of luminescent bacteria, it is extended to other bacteria. Scientists have found that when bacteria produce signaling molecules that reach a certain number and reach thresholds, bacteria can adjust the overall behavior of the bacterial population by regulating the expression of relevant genes after feeling the signals produced by themselves and other bacteria[4], such as bacterial agency, virulence, and antibiotic production[5], a phenomenon known as the group sense effect, which is a cell information exchange phenomenon that relies on cell density. In recent years, with advances in scientific research, studies have shown that the group sensing effect is also present in fungi and viruses [6,7,8]. In plant and animal pathogens, the virulence of group effect gene mutants is significantly reduced [9,10,11].
1.2 Group sense effect regulates pathways
Studies of the luminescence mechanism of Vibrio fischeri revealed the classical pathway luxI-luxR system of the group sense effect [12]. In the absence of activation of the group-sensing effect system, signaling molecule synthases in cells can generate a small number of signaling molecules (auto-inducers) that can freely pass through cell membranes because of their low concentrations and do not bind to transcriptional regulatory proteins [13,14]. Along with the proliferation of bacteria, when the number of signaling molecules in the environment reaches a threshold, it will return to the cell and form a transcriptional regulatory protein signaling molecule polymer with the transcriptional regulator protein, which further activates the signaling molecule synthase gene (luxI) and the transcriptional regulatory protein gene (luxR), thereby synthesizing more signaling molecules, forming a positive feedback loop, while activating the expression of downstream operons and luminescent genes. Most Gram-negative bacillus group sensing effects are regulated by the luxI-luxR system. Other signaling systems include the peptide signaling system, which involves most gram-positive cocci; some gram-negative and positive bacteria are regulated by the AI-2 system for germline-to-line communication. Auto-inducers are species-specific, and to date, eight auto-inducers with different chemical structures have been discovered [12].
2 Group sensing effect of Pseudomonas aeruginosa
2.1 Regulatory pathways for pseudomonas aeruginosa group sensing effect
Pseudomonas aeruginosa is currently the most well-studied pathogen in terms of group sensing effects, and its group sensing effect system can regulate gene expression of more than 300 toxic factors when activated [15,16]. The group-sensing effect core pathways of Pseudomonas aeruginosa are lasI-lasR and rhalI-rhlR systems, which have regulatory mechanisms similar to those of luminescent bacteria, in addition to the recently discovered quinolone signaling molecular system. The lasI and RHLI genes are signaling molecular synthetase genes, and the LASR and RHL genes are transcriptional regulatory protein genes. When the bacterial sensing signaling molecular density reaches a threshold, the transcriptional regulator protein binds to the signaling molecule to form a polymer, which further activates the I gene and R gene and the downstream operon gene, forming a positive feedback of gene expression and the expression of a variety of toxic factors. The signaling molecule chemistry and regulatory genes of the Las system and the Rhel system are different, and the signaling molecule of the Las system is 3OC12-HSL, which mainly regulates the gene expression of toxic factors such as alkaline protease, exotoxin A, and elastase. The signaling molecule of the Rhl system is C4-HSL, which regulates the production of secondary metabolites such as rhamnolysin, chitinase, cyanide, and chloropusin [17,18,19]. The Rhl system is regulated by the Las system.
2.2 Pseudomonas aeruginosa group sensing effects and biofilm
At present, the study has found that there are at least 2 kinds of social behaviors of microorganisms, one is the group sense effect, and the other is the formation of biofilm. Biofilm means that when a certain number of bacteria are gathered together, the polysaccharide polymer secreted by bacteria can form a membrane to envelop the bacteria, which protects the internal bacteria, so as to resist the invasion of foreign substances, making it difficult for antibacterial drugs to play a role, resulting in chronic infection. Pseudomonas aeruginosa infection often forms a biofilm in the body, making it difficult for bacteria to remove. Davies et al. [20] Compared the formation of biofilm of each group of pseudomonas aeruginosa by wild strain (WT), group effect signaling gene mutant strain (lasI/rhlI, rhlI, lasI), lasI mutant strain, and autoorder. The study found that the biofilm of the WT strain is loosely structured mushroom-shaped, and the internal colonies form water channels that can transport oxygen, metabolites and nutrients. The lasI mutant strain forms a thin plate-like biofilm with dense cell-to-cell connections, and restores the WT strain morphology after the addition of self-inducers (3OC12-HSL). Adhesion to the solid surface is an important part of the formation of a biofilm. The study found that after the addition of the detergent sodium lauryl sulfate, the biofilm of the lasI mutant strain was detached from the glass surface for 5 minutes, while the biological cover membrane of the WT strain and the lasI mutant strain was still adhered to the biofilm after adding the inducer for 19 hours. The above results show that the group sensing effect system affects the formation of biotextrane[20], which is one of the upstream regulatory systems of biotextrane.
3 Effect of macrolides on pseudomonas aeruginosa and clinical treatment
3.1 Macrolides inhibit the pseudomonas aeruginosa group sensing effect
Tatea et al. [21] found that azithromycin can inhibit the transcription of lasR/rhlR genes in pseudomonas aeruginosa group sensing system, partially recovered after the addition of self-inducers, and inhibited the expression of lasI/rhlI genes, resulting in reduced production of autoorgeners 3OC12-HSL and C4-HSL; resulting in a decrease in the toxicity factor elastase, which can also be partially restored after the addition of self-inducers. Macrolides block the group sensing effect by inhibiting the production of Pseudomonas aeruginosa autoorogene, thereby inhibiting the formation of biofilm and the release of toxicity factors [22]. Macrolides have a basic lactone ring structure, which can be divided into 14, 15 and 16 yuan cyclic macrolides according to the amount of carbon contained on the lactone structure parent nucleus. 14-membered cyclic macrolides (erythromycin, roxithromycin) and 15-membered cyclic macrolides (azithromycin) have been found to inhibit the growth of Pseudomonas aeruginosa, while 16-membered cyclic macrolides (crosalicin, astoriamycin) have no inhibitory effect [23].
3.2 Clinical study of macrolides for the treatment of structural lung disease
Structural lung disease refers to lung diseases that cause irreversible changes in lung structure, such as bronchiectasis, cystic fibrosis (CF), COPD, chronic lung abscesses, tuberculosis that cause changes in lung structure, etc. Pseudomonas aeruginosa is a common pathogenic bacteria accompanied by lung infections in patients with structural lung disease, which often causes bacteria to be difficult to remove, infection to become chronic, and repeated acute infections induce increased bacterial resistance, making clinical treatment difficult. The formation of pseudomonas aeruginosa biofilm and the release of toxicity factors are related to the drug resistance of bacteria and the severity of infection, when Pseudomonas aeruginosa develops into multi-drug resistant bacteria, pan-resistant bacteria or fully resistant bacteria, the clinical choice of antibacterial drugs is limited or even no choice. Several clinical studies have evaluated the clinical efficacy of low-dose macroscopic lipids for structural lung disease. The EMBRACE Study in New Zealand is a randomized, double-blind, placebo-controlled study evaluating azithromycin for the prevention of acute exacerbations in patients with non-CF bronchiectasis, with a list of patients with bronchiectasis requiring antimicrobial therapy at least once in the previous year, with azithromycin 500 mg (3 doses/week) orally for 6 months. Results showed that the number of exacerbations of acute exacerbations was 0.59 per person in the azithromycin group and 1.57 per person per person in the placebo group (P<0.000 1), and the authors proposed that azithromycin was a new option for preventing acute exacerbations of bronchiectasis [24]. Randomized controlled studies of CF Pseudomonas aeruginosa infection in 23 centers in the United States showed a significant improvement in the volume of forced expiratory volume at 168 days with azithromycin treatment, and a significant increase in the azithromycin group without acute exacerbations [25]. In the BLESS study, Burr et al. [26] further studied the clinically isolated Pseudomonas aeruginosa through rigorous screening, and the selected cases were patients with sputum at the end of observation, Positive Pseudomonas aeruginosa cultures, and adequate expression of the strain steward gene mRNA. There were 15 cases in the placebo group and 11 cases in the erythromycin group. The results showed that compared with the placebo group, the expression levels of the Pseudomonas aeruginosa group sensing genes LasR and PqsA isolated from the treatment group were reduced, and the macrolides could inhibit the group sensing effect from a clinical perspective. In a forward parallel placebo-controlled study in 17 medical centers in the United States, the effect of oral azithromycin 250 mg for 1 year in preventing acute exacerbations of COPD was 266 d in the azithromycin group and 174 d in the placebo group (P<0.001), and the frequency of acute exacerbations in the azithromycin group was reduced (P=0.01) and the quality of life score was improved (P=0.004) compared with the placebo group [27]. Fan et al. [28] Conducted a meta-analysis of the efficacy of long-term use of macrolides in non-CF patients, and the results showed that the number of acute exacerbations, lung function improvement, and quality of life in the macrolide group were reduced, but the symptoms of diarrhea increased, and the macrolide-resistant Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pneumoniae increased compared with the placebo group (P<0.001).
3.3 Clinical treatment guidelines or consensus
In the 2017 European guidelines for the treatment of bronchiectasis in adults, it is recommended that patients with acute exacerbations ≥ 3 times a year can be treated with long-term antibacterial drugs (≥3 months), and those with chronic Pseudomonas aerugin infection recommend inhaled antibacterial treatment such as polymyxin, etc., while those who have contraindications, intolerances, and non-feasible inhalation drugs are recommended for macrolides (azithromycin, erythromycin), and if inhaled antibacterial drugs are still frequently aggravated, it is recommended to add macrolides or replace the original inhaled drugs. Adverse effects such as diarrhea and drug resistance should also be of concern [29]. The 2019 edition of the COPD Global Initiative proposes that long-term treatment with azithromycin or erythromycin for more than one year reduces acute exacerbations of COPD, but treatment of azithromycin has been associated with bacterial resistance and hearing impairment [30].
In summary, the pseudomonas aeruginosa group sensing mechanism affects the virulence and drug resistance in its infection process, macrolides can inhibit the group sensing effect system, and its non-antibacterial effect plays a certain role in the structural lung disease treatment of chronic infection of Pseudomonas aeruginosa. Indications for macrolides should be mastered when applying macrolides, and adverse drug reactions should be concerned.
Conflicts of Interest All authors declare that there is no conflict of interest
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