Clinical characteristics, tolerance mechanisms, and molecular epidemiology of reduced susceptibility to chlorhexidine among Pseudomonas aeruginosa isolated from a teaching hospital in China

Still not sterile: viability-based assessment of the skin microbiome following pre-surgical application of a broad-spectrum antiseptic reveals transient pathogen enrichment and long-term recovery

Broad-spectrum antiseptics such as chlorhexidine gluconate (CHG) have widespread use as pre-surgical tools to lower skin microbial burden and reduce the risk of surgical site infection. However, the short- and long-term effects of CHG on healthy skin microbial communities remain undefined due to the confounding effects of CHG binding with persistent bacterial DNA on the skin surface. Here, we aim to accurately characterize the immediate and long-term impact of pre-surgical preparation with CHG-based antiseptics on the human skin microbiome. Twenty-eight patients undergoing elective surgeries were enrolled. Swabs of the surgical site and a control site skin microbiome were collected at multiple time points before and up to 2 weeks after surgery. A propidium monoazide (PMAxx)-based viability assay was optimized to selectively evaluate DNA from live microbes in complex skin microbial communities with viability-qPCR and viable 16S ribosomal RNA gene profiling. Pre-operative CHG induces a measurable reduction in the viable microbial bioburden at the surgical site. On the day of surgery, surgical sites displayed a significant increase in the relative abundance of several SSI-associated bacterial genera including Acinetobacter, Bacillus, Escherichia-Shigella, and Pseudomonas compared to baseline. Bacillus species isolated from subjects at baseline also demonstrate resistance to CHG with minimum inhibitory concentrations exceeding 1,000 µg/mL. Although there are major skin microbiome shifts upon exposure to CHG, we also find that these shifts are largely transient. For the majority of individuals, skin microbial bioburden and community structure recover to near baseline by post-surgical follow-up.IMPORTANCESurgical site infections continue to occur despite widespread adoption of surgical antiseptics. Before surgery, patients often wash their whole body multiple times with chlorhexidine gluconate (CHG)-based antiseptic soap and have CHG applied to the surgical site in the operating room. However, the effects of CHG antiseptics on the healthy skin microbiome are undefined due to CHG persisting and binding DNA from dead cells on the skin. We optimized a viability assay to selectively target DNA from live microbes on the skin before and after exposure to CHG. Our findings demonstrate that pre-surgical application of CHG significantly reduces the bioburden on skin; however, potentially pathogenic bacteria remain. Post-surgery, the skin microbiome eventually recovers to resemble its pre-CHG exposed state. Collectively, these findings identify tangible avenues for improving antiseptic formulations and further support that the skin microbiome is viable, stable, and resilient to chemical perturbation.

Microbiota modulation for infectious complications following allogeneic hematopoietic stem cell transplantation in pediatric hematological malignancies

The intervention of microbiota modulation in the treatment of infection complications after allogeneic hematopoietic stem cell transplantation in pediatric patients with hematological malignancies has shown potential benefits. Through the use of probiotics, prebiotics, synbiotics, and fecal microbiota transplantation (FMT), these interventions modulate the gut microbiota and enhance immune function to prevent and treat infections. They have been shown to reduce the incidence of diarrhea and intestinal infections, mitigate the issue of antibiotic resistance, and promote the recovery of gut microbiota. Future research is needed to further assess the safety and efficacy of these interventions and to establish standardized treatment protocols.

Inhibition of biofilm formation and preformed biofilm in Acinetobacter baumannii by resveratrol, chlorhexidine and benzalkonium: modulation of efflux pump activity

Introduction

The persistence of Acinetobacter baumannii in the contaminated environment is sustained by tolerance to biocides and ability to growth as biofilm. The aim of the study was to analyze the susceptibility of A. baumannii biofilms to chlorhexidine (CHX) and benzalkonium (BZK) biocides and the ability of natural monomeric stilbenoid resveratrol (RV) to modulate the phenomenon.

Methods

Biofilm formation and preformed biofilm were tested by Crystal violet and tetrazolium salt reduction assay, respectively. Analysis of efflux pump (EP) expression during biofilm growth was performed by Real-time RT-PCR assays.

Results

CHX and BZK at ¼ and ½ MICs alone or in combination inhibited biofilm growth of A. baumannii ATCC 19606, 4190, and 3909 strains. RV at 32 mg/L and CHX and BZK at ¼ or ½ MICs showed a synergistic effect and completely inhibited biofilm formation in all A. baumannii strains. Similarly, RV at 32 mg/L and CHX and BZK at ½ MIC significantly inhibited air-liquid biofilm formation of A. baumannii ATCC 19606, 4190 and 3909 strains. The inactivation of AdeB and AdeJ RND EPs in A. baumannii ATCC19606 increased the susceptibility to CHX and BZK alone or in the presence of 32 mg/L RV. Concordantly, carbonyl cyanide m-chlorophenylhydrazine (CCCP) increased the susceptibility to CHX, BZK and RV and dose-dependently inhibited biofilm formation in A. baumannii ATCC 19606, 4190 and 3909 strains. RV at 32 mg/L inhibited basal and CHX-induced EP genes expression, while increased EP gene expression in the presence of BZK during A. baumannii ATCC19606 biofilm growth. In addition, CHX and BZK alone or in combination dose-dependently reduced preformed biofilm of all A. baumannii strains. The combination of RV with CHX and BZK additively decreased minimal biofilm eradicating concentrations in A. baumannii strains.

Conclusion

These results demonstrate that: (i) CHX and BZK alone or in the presence of RV inhibit biofilm growth and preformed biofilm in A. baumannii; (ii) tolerance to CHX and BZK during biofilm growth is dependent on the activation of AdeB and AdeJ EPs; and (iii) the inhibitory effect of RV on biofilm growth is mediated by the inhibition of EP genes expression in A. baumannii.

Heterogeneous survival upon disinfection underlies evolution of increased tolerance

Disinfection is important to limit the spread of infections, but failure of disinfection may foster the evolution of antimicrobial resistance in bacteria. Persisters are phenotypically tolerant subpopulations that survive toxic stress longer than susceptible cells, leading to failure in treatments with antimicrobials and facilitating resistance evolution. To date, little is known about persistence in the context of disinfectants. The aim of this study was to investigate the influence of persisters on disinfection and to determine the consequences of disinfectant persistence for the evolution of increased tolerance to disinfectants. Disinfection kinetics with high temporal resolution were recorded for Escherichia coli exposed to the following six disinfectants: hydrogen peroxide (H2O2), glutaraldehyde (GTA), chlorhexidine (CHX), benzalkonium chloride (BAC), didecyldimethylammonium chloride (DDAC), and isopropanol (ISO). A mathematical model was used to infer the presence of persisters from the time-kill data. Time-kill kinetics for BAC, DDAC, and ISO were indicative of persisters, whereas no or weak evidence was found for H2O2, GTA, and CHX. When subjected to comparative experimental evolution under recurring disinfection, E. coli evolved increased tolerance to substances for which persisters were predicted (BAC and ISO), whereas adaptation failed for substances in which no persisters were predicted (GTA and CHX), causing extinction of exposed populations. Our findings have implications for the risk of disinfection failure, highlighting a potential link between persistence to disinfectants and the ability to evolve disinfectant survival mechanisms.

IMPORTANCE

Disinfection is key to control the spread of infections. But the application of disinfectants bears the risk to promote the evolution of reduced susceptibility to antimicrobials if bacteria survive the treatment. The ability of individual bacteria to survive disinfection can display considerable heterogeneity within isogenic populations and may be facilitated by tolerant persister subpopulations. Using time-kill kinetics and interpreting the data within a mathematical framework, we quantify heterogeneity and persistence in Escherichia coli when exposed to six different disinfectants. We find that the level of persistence, and with this the risk for disinfection failure, depends on the disinfectant. Importantly, evolution experiments under recurrent disinfection provide evidence that links the presence of persisters to the ability to evolve reduced susceptibility to disinfectants. This study emphasizes the impact of heterogeneity within bacterial populations on disinfection outcomes and the potential consequences for the evolution of antimicrobial resistances.

Plumbagin enhances antimicrobial and anti-biofilm capacities of chlorhexidine against clinical Klebsiella pneumoniae while reducing resistance mutations

With the widespread misuse of disinfectants, the clinical susceptibility of Klebsiella pneumoniae (K. pneumoniae) to chlorhexidine (CHX) has gradually diminished, posing significant challenges to clinical disinfection and infection control. K. pneumoniae employs overexpression of efflux pumps and the formation of thick biofilms to evade the lethal effects of CHX. Plumbagin (PLU) is a natural plant extract that enhances membrane permeability and reduces proton motive force. In this study, we elucidated the synergistic antimicrobial activity of PLU in combination with CHX, effectively reducing the MIC of CHX against K. pneumoniae to 1 µg/mL and below. Crucially, through crystal violet staining and confocal laser scanning microscopy live/dead staining, we discovered that PLU significantly enhances the anti-biofilm capability of CHX. Mechanistically, experiments involving membrane permeability, alkaline phosphatase leakage, reactive oxygen species, and RT-qPCR suggest that the combination of PLU and CHX improves the permeability of bacterial inner and outer membranes, promotes bacterial oxidative stress, and inhibits oqxA/B efflux pump expression. Furthermore, we conducted surface disinfection experiments on medical instruments to simulate clinical environments, demonstrating that the combination effectively reduces bacterial loads by more than 3 log10 CFU/mL. Additionally, results from resistance mutation frequency experiments indicate that combined treatment reduces the generation of resistant mutants within the bacterial population. In summary, PLU can serve as an adjuvant, enhancing the anti-biofilm capability of CHX and reducing the occurrence of resistance mutations, thereby extending the lifespan of CHX.IMPORTANCEAs disinfectants are extensively and excessively utilized worldwide, clinical pathogens are progressively acquiring resistance against these substances. However, high concentrations of disinfectants can lead to cross-resistance to antibiotics, and concurrent use of different disinfectants can promote bacterial resistance mutations and facilitate the horizontal transfer of resistance genes, which poses significant challenges for clinical treatment. Compared with the lengthy process of developing new disinfectants, enhancing the effectiveness of existing disinfectants with natural plant extracts is important and meaningful. CHX is particularly common and widely used compared with other disinfectants. Meanwhile, Klebsiella pneumoniae, as a clinically significant pathogen, exhibits high rates of resistance and pathogenicity. Previous studies and our data indicate a significant decrease in the sensitivity of clinical K. pneumoniae to CHX, highlighting the urgent need for novel strategies to address this issue. In light of this, our research is meaningful.

Molecular Characterization of Pseudomonas aeruginosa Clinical Isolates Through Whole-Genome Sequencing: A Comprehensive Analysis of Biotypes, Sequence Types, and Antimicrobial and Virulence Genes

Introduction Pseudomonas aeruginosa (PA) is a bacterial species commonly isolated from human clinical specimens. Despite being present in the environment as a saprophyte, PA possesses the ability to cause human infections, especially among debilitated patients. It is therefore essential to understand the genomic imprints of antimicrobial resistance (AMR) and virulence genes associated with PA isolated from patient samples. Methods The study carried out next-generation sequencing (NGS) or whole-genome sequencing (WGS) of nine PA strains isolated from various human clinical specimens from patients at Prathima Institute of Medical Sciences, Karimnagar, India. All the isolates were identified by conventional microbiological methods and confirmed by automated systems. Antimicrobial susceptibility patterns of the isolates were carried out using the Kirby-Bauer disc diffusion method. Additionally, NGS/WGS was done to evaluate the carriage of AMR and virulence genes associated with each PA strain. Sequence type was identified through multi-locus sequence typing (MLST). Results The genotype and phenotypic antimicrobial susceptibility patterns revealed the same (11.11% resistance) results with carbapenems and fluoroquinolone antibiotics. However, discordant antimicrobial susceptibility patterns were noticed with trimethoprim-sulfamethoxazole (66.66% resistance phenotype vs. 100% sensitive genotype), aminoglycosides (100% sensitive phenotype vs. 100% resistant genotype), and beta-lactamase/extended-spectrum beta-lactamase (ESBL) (44.44% sensitive phenotype vs. 100% resistant genotype) antibiotics. All (100%, 9/9) the PA isolates included in the study demonstrated the presence of multiple antibiotic resistance and virulence genes. The antibiotic resistance genes identified included aph, aad, aac, bla PDC, bla OXA, bla VIM, catB7, fosA, qnrVC1, and crpP. All (100%, 9/9) isolates demonstrated the presence of class C beta-lactamase bla PDC and class B metallo-beta-lactamase bla OXA. Only one (11.11%, 1/9) isolate showed the presence of subclass B1 metallo-beta-lactamase bla VIM. Among the virulence genes identified were toxA, fih, xcp, wzz, pvc, pvd, and many others. This study showed the presence of ST244, a high-risk PA strain with global significance. Conclusions PA is an opportunistic pathogen, and its isolation among hospitalized patients should be carefully evaluated. Tracking PA for the presence of high-risk sequence types and the prevalence of resistance and virulence genes could improve the understanding of the organism. Molecular data obtained from this study demonstrated that the PA isolates carried multiple antibiotic-resistant and virulence genes that could potentially enable them to cause invasive infections and treatment failures. The data obtained from this study could be applied to devise treatment and management strategies favorable to the hospital or healthcare institution.

Effect of prolonged exposure to disinfectants in the antimicrobial resistance profile of relevant micro-organisms: a systematic review

BACKGROUND

Antimicrobial resistance (AMR) constitutes a major global health threat, to a very large extent due to the inadequate use of antibiotics. Additionally, the misuse of disinfectants can also trigger the selection of resistant clones, where micro-organisms develop an adaptative response and progress to resistance mechanisms. Cross-resistance may occur when a biocide's selective pressure induces antimicrobial resistance.

AIM

To acknowledge the potential relationship between repeated and/or prolonged exposure to disinfectants and antimicrobial resistance profile adjustment.

METHODS

This systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies published until December 2023 that were related to the interaction between disinfectants and antimicrobials were included. Further selection was based on the methodology of exposure.

FINDINGS

Selected studies included testing about 'exposure to sublethal concentrations' for seventeen disinfectants. The mechanism of action for the majority of the disinfectants involved interactions with the cell membrane. Chlorhexidine was the most studied disinfectant.

CONCLUSION

Adaptation phenomena related to disinfectant exposure were documented and development of cross-resistance to antimicrobials was verified for several species, including Streptococcus spp., Klebsiella pneumoniae, Acinetobacter baumannii, Staphylococcus aureus, Pseudomonas aeruginosa, and Candida spp. Changes associated with disinfectant exposure also influenced biofilm formation, colony morphology, and efflux pump activity - three relevant determinants of loss of antibiotic efficacy.

Biocides in the Hospital Environment: Application and Tolerance Development

Hospital-acquired infections are a rising problem with consequences for patients, hospitals, and health care workers. Biocides can be employed to prevent these infections, contributing to eliminate or reduce microorganisms' concentrations at the hospital environment. These antimicrobials belong to several groups, each with distinct characteristics that need to be taken into account in their selection for specific applications. Moreover, their activity is influenced by many factors, such as compound concentration and the presence of organic matter. This article aims to review some of the chemical biocides available for hospital infection control, as well as the main factors that influence their efficacy and promote susceptibility decreases, with the purpose to contribute for reducing misusage and consequently for preventing the development of resistance to these antimicrobials.

Study of Combined Effect of Bacteriophage vB3530 and Chlorhexidine on the Inactivation of Pseudomonas aeruginosa

BACKGROUND

Chlorhexidine (CHG) is a disinfectant commonly used in hospitals. However, it has been reported that the excessive use of CHG can cause resistance in bacteria to this agent and even to other clinical antibiotics. Therefore, new methods are needed to alleviate the development of CHG tolerance and reduce its dosage. This study aimed to explore the synergistic effects of CHG in combination with bacteriophage against CHG-tolerant Pseudomonas aeruginosa (P. aeruginosa) and provide ideas for optimizing disinfection strategies in clinical environments as well as for the efficient use of disinfectants.

METHODS

The CHG-tolerant P. aeruginosa strains were isolated from the First Affiliated Hospital of Wenzhou Medical University in China. The bacteriophage vB3530 was isolated from the sewage inlet of the hospital, and its genome was sequenced. Time-killing curve was used to determine the antibacterial effects of vB3530 and chlorohexidine gluconate (CHG). The phage sensitivity to 16 CHG-tolerant P. aeruginosa strains and PAO1 strain was detected using plaque assay. The emergence rate of resistant bacterial strains was detected to determine the development of phage-resistant and CHG-tolerant strains. Finally, the disinfection effects of the disinfectant and phage combination on the surface of the medical devices were preliminarily evaluated.

RESULTS

The results showed that (1) CHG combined with bacteriophage vB3530 significantly inhibited the growth of CHG-resistant P. aeruginosa and reduced the bacterial colony forming units (CFUs) after 24 h. (2) The combination of CHG and bacteriophage inhibited the emergence of phage-resistant and CHG-tolerant strains. (3) The combination of CHG and bacteriophage significantly reduced the bacterial load on the surface of medical devices.

CONCLUSIONS

In this study, the combination of bacteriophage vB3530 and CHG presented a combined inactivation effect to CHG-tolerant P. aeruginosa and reduced the emergence of strains resistant to CHG and phage. This study demonstrated the potential of bacteriophage as adjuvants to traditional disinfectants. The use of bacteriophage in combination with commercial disinfectants might be a promising method for controlling the spread of bacteria in hospitals.

Microbial Risks Caused by Livestock Excrement: Current Research Status and Prospects

Livestock excrement is a major pollutant yielded from husbandry and it has been constantly imported into various related environments. Livestock excrement comprises a variety of microorganisms including certain units with health risks and these microorganisms are transferred synchronically during the management and utilization processes of livestock excrement. The livestock excrement microbiome is extensively affecting the microbiome of humans and the relevant environments and it could be altered by related environmental factors as well. The zoonotic microorganisms, extremely zoonotic pathogens, and antibiotic-resistant microorganisms are posing threats to human health and environmental safety. In this review, we highlight the main feature of the microbiome of livestock excrement and elucidate the composition and structure of the repertoire of microbes, how these microbes transfer from different spots, and they then affect the microbiomes of related habitants as a whole. Overall, the environmental problems caused by the microbiome of livestock excrement and the potential risks it may cause are summarized from the microbial perspective and the strategies for prediction, prevention, and management are discussed so as to provide a reference for further studies regarding potential microbial risks of livestock excrement microbes.

Evaluation of the antibacterial, antibiofilm, and anti-virulence effects of acetic acid and the related mechanisms on colistin-resistant Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa (P. aeruginosa) has been majorly implicated in the infection of burns, wounds, skin, and respiratory tract. Colistin is considered the last line of defense against P. aeruginosa infections. However, colistin is becoming increasingly invalid in treating patients infected with colistin-resistant (COL-R) P. aeruginosa. As one of the disinfectants used for wound infections, acetic acid (AA) offers good antibacterial and antibiofilm activities against P. aeruginosa. This study investigated the effects of AA on COL-R P. aeruginosa in terms of its antibacterial, antibiofilm, and anti-virulence properties and the corresponding underlying mechanisms.

RESULTS

The antimicrobial susceptibility and growth curve data revealed that 0.078% (v/v) AA exhibited good antibacterial activity against COL-R P. aeruginosa. Subinhibitory concentrations of AA were ineffective in inhibiting biofilm formation, but 4 × and 8 × of the minimum inhibitory concentration (MIC) was effective in removing the preformed biofilms in biofilm-eradication assays. The virulence results illustrated that AA inhibited COL-R P. aeruginosa swimming, swarming, twitching, and pyocyanin and elastase production. The analysis of the potential antibacterial mechanisms of AA on COL-R P. aeruginosa revealed that AA acted by increasing the outer and inner membrane permeability, polarizing the membrane potential, and decreasing the reduction potential in a concentration-dependent manner. The qRT-PCR results revealed that AA may inhibit the virulence of COL-R P. aeruginosa by inhibiting the expression of T3SS-related and QS-related genes.

CONCLUSIONS

AA possesses antibacterial, antibiofilm, and anti-virulence properties that ultimately lead to the alteration of the bacterial membrane permeability, membrane potential, and reduction potential. Our findings indicated that AA is presently one of the effective treatment options for infections. A high concentration of AA (> 0.156% v/v) can be used to sterilize biofilm-prone surgical instruments, for hospital disinfection, and for treating the external wound, whereas a low concentration of AA (0.00975-0.039% v/v) may be used as an anti-virulence agent for adjuvant treatment of COL-R P. aeruginosa, thereby further improving the application value of AA in the treatment of infections.

Resveratrol Reverts Tolerance and Restores Susceptibility to Chlorhexidine and Benzalkonium in Gram-Negative Bacteria, Gram-Positive Bacteria and Yeasts

The spread of microorganisms causing health-care associated infection (HAI) is contributed to by their intrinsic tolerance to a variety of biocides, used as antiseptics or disinfectants. The natural monomeric stilbenoid resveratrol (RV) is able to modulate the susceptibility to the chlorhexidine digluconate (CHX) biocide in Acinetobacter baumannii. In this study, a panel of reference strains and clinical isolates of Gram-negative bacteria, Gram-positive bacteria and yeasts were analyzed for susceptibility to CHX and benzalkonium chloride (BZK) and found to be tolerant to one or both biocides. The carbonyl cyanide m-chlorophenylhydrazine protonophore (CCCP) efflux pump inhibitor reduced the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CHX and BZK in the majority of strains. RV reduced dose-dependently MIC and MBC of CHX and BZK biocides when used as single agents or in combination in all analyzed strains, but not CHX MIC and MBC in Pseudomonas aeruginosa, Candida albicans, Klebsiella pneumoniae, Stenotrophomonas maltophilia and Burkholderia spp. strains. In conclusion, RV reverts tolerance and restores susceptibility to CHX and BZK in the majority of microorganisms responsible for HAI. These results indicates that the combination of RV, CHX and BZK may represent a useful strategy to maintain susceptibility to biocides in several nosocomial pathogens.