Quorum sensing regulates heteroresistance in Pseudomonas aeruginosa

Antibacterial activity and mechanism of Sodium houttuyfonate against heteroresistant Pseudomonas aeruginosa

Background

Pseudomonas aeruginosa is a common gram-negative opportunistic pathogen that is now commonly treated with carbapenems, such as Meropenem. However, the increasing rate of emergence of heteroresistant strains poses a therapeutic challenge. Therefore, we examined the antibacterial activity of Sodium houttuyfonate (SH, a compound derived from Houttuynia cordata) in combination with Meropenem (MEM) against heteroresistant Pseudomonas aeruginosa and investigated the mechanism of Sodium houttuyfonate.

Methods

Heteroresistant Pseudomonas aeruginosa was used as the experimental strain for the study and the combined action activity of the two drugs was inves-tigated by determining the Minimum Inhibitory Concentration (MIC), Fractional Inhibitory Concentration Index (FICI), and time killing curves. Also the effect of Sodium houttuyfonate on biofilm as well as bacterial swimming motility assay was investigated by crystal violet staining of bacterial biofilm, microanalysis of biofilm, bacterial swimming motility assay, quantitative real-time PCR (qRT-PCR) and population sensing related virulence factors.

Results

For the screened experimental strains, the MIC of SH was 4,000 μg/ml; the FICI of both drugs on the four experimental strains was ≤0.5, which showed a synergistic effect. When SH ≥ 250 μg/ml, it was able to effectively inhibit bacterial biofilm formation as well as swimming ability compared with the blank control group. In the qRT-PCR experiment, the expression of biofilm formation-related genes (pslA, pelA, aglD, lasI, lasR, and rhlA) and swimming ability-related genes (fliC, pilZ, and pilA) were decreased in the SH-treated group, compared with the blank control group.

Conclusion

Our study demonstrated that Sodium houttuyfonate and Meropenem exhibited synergistic inhibition against heteroresistant Pseudomonas aeruginosa, and that Sodium houttuyfonate may achieve its inhibitory effect by inhibiting bacterial biofilm formation, inhibiting motility, and down-regulating related genes.

Evaluation of ampicillin plus ceftobiprole combination therapy in treating Enterococcus faecalis infective endocarditis and bloodstream infection

Enterococcus faecalis is responsible for numerous serious infections, and treatment options often include ampicillin combined with an aminoglycoside or dual beta-lactam therapy with ampicillin and a third-generation cephalosporin. The mechanism of dual beta-lactam therapy relies on the saturation of penicillin-binding proteins (PBPs). Ceftobiprole exhibits high affinity binding to nearly all E. faecalis PBPs, thus suggesting its potential utility in the treatment of severe E. faecalis infections. The availability of therapeutic drug monitoring (TDM) for ampicillin and ceftobiprole has prompted the use of this drug combination in our hospital. Due to the time-dependent antimicrobial properties of these antibiotics, an infusion administration longer than indicated was chosen. From January to December 2020, twenty-one patients were admitted to our hospital for severe E. faecalis infections and were treated with this approach. We retrospectively analyzed their clinical characteristics and pharmacological data. Most patients achieved an aggressive PK/PD target (T > 4-8 minimum inhibitory concentration, MIC) when this alternative drug combination regimen was used. Our analysis included the study of E. faecalis biofilm production, as well as the kinetics of bacterial killing of ceftobiprole alone or in combination with ampicillin. Time-kill experiments revealed strong bactericidal activity of ceftobiprole alone at concentrations four times higher than the MIC for some enterococcal strains. In cases where a bactericidal effect of ceftobiprole alone was not evident, synergism with ampicillin and bactericidal activity were demonstrated instead. The prolonged infusion of ceftobiprole, either alone or with ampicillin, emerges as a valuable option for the treatment of severe invasive E. faecalis infections.

Revealing quorum-sensing networks in Pseudomonas aeruginosa infections through internal and external signals to prevent new resistance trends

In the context of growing antibiotic resistance in bacteria, the quorum-sensing (QS) system of Pseudomonas aeruginosa (P. aeruginosa) has become a target for new therapeutic strategies. QS is a crucial communication process and an essential pathogenic mechanism. This comprehensive review explores the critical role of QS in the pathogenesis of P. aeruginosa infections, including lung, burn, bloodstream, gastrointestinal, corneal, and urinary tract infections. In addition, this review delves into the complexity of the bacterial QS communication network and highlights the intricate mechanisms underlying these pathological processes. Notably, in addition to the four main QS systems, bacterial QS can interact with various external and internal signaling networks, such as host environments and nutrients in the external microbiome, as well as internal virulence regulation systems within bacteria. These elements can significantly influence the behavior and virulence of microbial communities. Therefore, this review reveals that inhibitors targeting singular QS pathways may inadvertently promote virulence in other pathways, leading to new trends in drug resistance. In response to evolving resistance challenges, this study proposes more cautious treatment strategies, including multitarget interventions and combination therapies, aimed at combating the escalating issue of resistance.

Cephalosporin resistance, tolerance, and approaches to improve their activities

Cephalosporins comprise a β-lactam antibiotic class whose first members were discovered in 1945 from the fungus Cephalosporium acremonium. Their clinical use for Gram-negative bacterial infections is widespread due to their ability to traverse outer membranes through porins to gain access to the periplasm and disrupt peptidoglycan synthesis. More recent members of the cephalosporin class are administered as last resort treatments for complicated urinary tract infections, MRSA, and other multi-drug resistant pathogens, such as Neisseria gonorrhoeae. Unfortunately, there has been a global increase in cephalosporin-resistant strains, heteroresistance to this drug class has been a topic of increasing concern, and tolerance and persistence are recognized as potential causes of cephalosporin treatment failure. In this review, we summarize the cephalosporin antibiotic class from discovery to their mechanisms of action, and discuss the causes of cephalosporin treatment failure, which include resistance, tolerance, and phenomena when those qualities are exhibited by only small subpopulations of bacterial cultures (heteroresistance and persistence). Further, we discuss how recent efforts with cephalosporin conjugates and combination treatments aim to reinvigorate this antibiotic class.

Comparative evaluation of colistin broth disc elution (CBDE) and broth microdilution (BMD) in clinical isolates of Pseudomonas aeruginosa with special reference to heteroresistance

PURPOSE

Antimicrobial resistance (AMR) in Pseudomonas aeruginosa has been ever-increasing. Among other reasons, colistin resistance might be attributed to limited routine testing by approved methods. Both broth microdilution (BMD) and colistin broth disc elution (CBDE) methods have been advocated, with limited data on the performance of these methods in the Indian settings. This prospective study was conducted to determine colistin resistance in P. aeruginosa, compare the BMD and CBDE methods with special reference to heteroresistance.

MATERIALS AND METHODS

A total of 100 isolates of P. aeruginosa from admitted patients were included. Antimicrobial susceptibility testing was done against standard antibiotics by disc diffusion test. Minimum inhibitory concentration (MIC) against polymyxins was studied by BMD and CBDE (for colistin only). Heteroresistance to colistin was studied by population analysis profile (PAP). CBDE and BMD were compared by performance calculations. Discrepancy in results were analyzed based on heteroresistance.

RESULTS

Majority of the P. aeruginosa isolates were from pus samples (62, 62 ​%). Disc diffusion method revealed maximum susceptibility towards aztreonam (74, 74 ​%) followed by meropenem (68, 68 ​%) and piperacillin-tazobactam (65, 65 ​%). Polymyxin B resistance was seen in 6 ​% (6) while colistin resistance was seen in 9 ​% (9) isolates by BMD. CBDE revealed 8 ​% (8) resistance to colistin, having 97 ​% essential agreement and 95 ​% categorical agreement with BMD. Further, by PAP analysis, 9 isolates were resistant to colistin which included 9 resistant isolates by BMD. On discrepancy analysis, 1 isolate was found to be heteroresistant to colistin. No heteroresistance was seen in the isolates that were susceptible by all the methods.

CONCLUSIONS

Heteroresistance to colistin in P. aeruginosa accounted for the discrepancy in results where CBDE method failed to detect heteroresistant isolate. As heteroresistance is a least studied phenotype, it's exact prevalence should be studied so that challenges in susceptibility testing could be addressed.

T2SS-peptidase XcpA associated with LasR evolutional phenotypic variations provides a fitness advantage to Pseudomonas aeruginosa PAO1

The Gram-negative opportunistic pathogen Pseudomonas aeruginosa possesses hierarchical quorum sensing (QS) systems. The intricate QS network of P. aeruginosa synchronizes a suite of virulence factors, contributing to the mortality and morbidity linked to the pathogenicity of this bacterium. Previous studies have revealed that variations in the lasR gene are frequently observed in chronic isolates of cystic fibrosis (CF). Specifically, LasRQ45stop was identified as a common variant among CF, lasR mutants during statistical analysis of the clinical lasR mutants in the database. In this study, we introduced LasRQ45stop into the chromosome of P. aeruginosa PAO1 through allelic replacement. The social traits of PAO1 LasRQ45stop were found to be equivalent to those of PAO1 LasR-null isolates. By co-evolving with the wild-type in caseinate broth, elastase-phenotypic-variability variants were derived from the LasRQ45stop subpopulation. Upon further examination of four LasRQ45stop sublines, we determined that the variation of T2SS-peptidase xcpA and mexT genes plays a pivotal role in the divergence of various phenotypes, including public goods elastase secretion and other pathogenicity traits. Furthermore, XcpA mutants demonstrated a fitness advantage compared to parent strains during co-evolution. Numerous phenotypic variations were associated with subline-specific genetic alterations. Collectively, these findings suggest that even within the same parental subline, there is ongoing microevolution of individual mutational trajectory diversity during adaptation.

Aspergillus fumigatus Can Display Persistence to the Fungicidal Drug Voriconazole

Aspergillus fumigatus is a filamentous fungus that can infect the lungs of patients with immunosuppression and/or underlying lung diseases. The mortality associated with chronic and invasive aspergillosis infections remain very high, despite availability of antifungal treatments. In the last decade, there has been a worrisome emergence and spread of resistance to the first-line antifungals, the azoles. The mortality caused by resistant isolates is even higher, and patient management is complicated as the therapeutic options are reduced. Nevertheless, treatment failure is also common in patients infected with azole-susceptible isolates, which can be due to several non-mutually exclusive reasons, such as poor drug absorption. In addition, the phenomena of tolerance or persistence, where susceptible pathogens can survive the action of an antimicrobial for extended periods, have been associated with treatment failure in bacterial infections, and their occurrence in fungal infections already proposed. Here, we demonstrate that some isolates of A. fumigatus display persistence to voriconazole. A subpopulation of the persister isolates can survive for extended periods and even grow at low rates in the presence of supra-MIC of voriconazole and seemingly other azoles. Persistence cannot be eradicated with adjuvant drugs or antifungal combinations and seemed to reduce the efficacy of treatment for certain individuals in a Galleria mellonella model of infection. Furthermore, persistence implies a distinct transcriptional profile, demonstrating that it is an active response. We propose that azole persistence might be a relevant and underestimated factor that could influence the outcome of infection in human aspergillosis. IMPORTANCE The phenomena of antibacterial tolerance and persistence, where pathogenic microbes can survive for extended periods in the presence of cidal drug concentrations, have received significant attention in the last decade. Several mechanisms of action have been elucidated, and their relevance for treatment failure in bacterial infections demonstrated. In contrast, our knowledge of antifungal tolerance and, in particular, persistence is still very limited. In this study, we have characterized the response of the prominent fungal pathogen Aspergillus fumigatus to the first-line therapy antifungal voriconazole. We comprehensively show that some isolates display persistence to this fungicidal antifungal and propose various potential mechanisms of action. In addition, using an alternative model of infection, we provide initial evidence to suggest that persistence may cause treatment failure in some individuals. Therefore, we propose that azole persistence is an important factor to consider and further investigate in A. fumigatus.