Dataset Information

The effects of LL-37 on virulence factors related to the quorum sensing system of Pseudomonas aeruginosa.

ABSTRACT:

Background

Antimicrobial peptides (AMPs) have shown promise in the treatment of multi-resistant pathogens. It was therefore of interest to analyze the effects of the AMP LL-37 on the regulation of several virulence factors related to the quorum sensing (QS) system of Pseudomonas aeruginosa (P. aeruginosa) in vitro.

Methods

The minimum inhibitory concentration (MIC) was evaluated by the micro broth dilution method. The expression of QS-related and QS-regulated virulence factor genes was also evaluated. Exotoxin A activity was measured with the nicotinamide adenine dinucleotide (NAD) (Coenzyme I) method; Elastase activity was detected with the elastin-Congo red (ECR) method; Pyocyanin detection was performed using the chloroform extraction method. The effects of LL-37 were assessed by measuring the expression changes of the virulence protein-encoding genes of the strains with quantitative polymerase chain reaction (PCR).

Results

The MIC of LL-37 against both P. aeruginosa reference strain (ATCC 15692 PAO1) and PA-ΔlasI/rhII was therefore determined to be 256 µg/mL. LL-37 at sub-minimum inhibitory concentrations (sub-MICs) had no significant effects on P. aeruginosa bacterial growth (P>0.05), but significantly downregulated the expression of all 3 virulence factors.

Conclusions

Interestingly, this effect appeared to be dose-related. These findings suggest that LL-37 could be a potential candidate for QS inhibition against bacterial infection and may have significant clinical potential in the treatment of P. aeruginosa biofilms.

SUBMITTER: Xiao Q

PROVIDER: S-EPMC9011280 | biostudies-literature | 2022 Mar

REPOSITORIES: biostudies-literature

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Publications

The effects of LL-37 on virulence factors related to the quorum sensing system of <i>Pseudomonas aeruginosa</i>.

Xiao Qian Q Luo Yanfen Y Shi Wen W Lu Yang Y Xiong Rui R Wu Xinggui X Huang Haihao H Zhao Chanjing C Zeng Jianming J Chen Cha C

Annals of translational medicine 20220301 6

<h4>Background</h4>Antimicrobial peptides (AMPs) have shown promise in the treatment of multi-resistant pathogens. It was therefore of interest to analyze the effects of the AMP LL-37 on the regulation of several virulence factors related to the quorum sensing (QS) system of <i>Pseudomonas aeruginosa (P. aeruginosa) in vitro</i>.<h4>Methods</h4>The minimum inhibitory concentration (MIC) was evaluated by the micro broth dilution method. The expression of QS-related and QS-regulated virulence fact ...[more]

PMID: 35434009

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Project description:With the rising development of bacterial resistance the search for new medical treatments beyond conventional antimicrobials has become a key aim of public health research. Possible innovative strategies include the inhibition of bacterial virulence. However, consideration must be given to the evolutionary and environmental consequences of such new interventions. Virulence and cooperative social behaviour of the bacterium Pseudomonas aeruginosa rely on the quorum-sensing (QS) controlled production of extracellular products (public goods). Hence QS is an attractive target for anti-virulence interventions. During colonization, non-cooperating (and hence less virulent) P. aeruginosa QS-mutants, benefiting from public goods provided by wild type isolates, naturally increase in frequency providing a relative protection from invasive infection. We hypothesized that inhibition of QS-mediated gene expression removes this growth advantage and selection of less virulent QS-mutants, and maintains the predominance of more virulent QS-wild type bacteria. We addressed this possibility in a placebo-controlled trial investigating the anti-QS properties of azithromycin, a macrolide antibiotic devoid of bactericidal activity on P. aeruginosa, but interfering with QS, in intubated patients colonized by P. aeruginosa. In the absence of azithromycin, non-cooperating (and hence less virulent) lasR (QS)-mutants increased in frequency over time. Azithromycin significantly reduced QS-gene expression measured directly in tracheal aspirates. Concomitantly the advantage of lasR-mutants was lost and virulent wild-type isolates predominated during azithromycin treatment. We confirmed these results in vitro with fitness and invasion experiments. Azithromycin reduced growth rate of the wild-type, but not of the lasR-mutant. Furthermore, the lasR-mutant efficiently invaded wild-type populations in the absence, but not in the presence of azithromycin. These in vivo and in vitro results demonstrate that anti-virulence interventions based on QS-blockade diminish natural selection towards reduced virulence and therefore may increase the prevalence of more virulent genotypes in the Hospital environment. More generally, the impact of intervention on the evolution of virulence of pathogenic bacteria should be assessed.