Influence of membrane fatty acid composition and fluidity on airborne survival of Escherichia coli

The bactericidal and antibiofilm effects of a lysine-substituted hybrid peptide, CM-10K14K, on biofilm-forming Staphylococcus epidermidis

Staphylococci, notably biofilm-forming Staphylococcus epidermidis, have been recognized as global nosocomial pathogens in medical device-related infections. Their potential to attach to and form biofilm on indwelling catheters are significant factors impeding conventional treatment. Due to their extensive antimicrobial and antibiofilm actions, antimicrobial peptides (AMPs) have attracted interest as promising alternative compounds for curing difficult-to-treat, biofilm-forming bacterial infections. Cecropin A-melittin or CM, a well-known hybrid peptide, exhibits broad-spectrum antimicrobial activity, however it also possesses high toxicity. In the current study, a series of hybrid CM derivatives was designed using an amino acid substitution strategy to explore potential antibacterial and antibiofilm peptides with low toxicity. Among the derivatives, CM-10K14K showed the least hemolysis along with potent antibacterial activity against biofilm-forming S. epidermidis (MICs = 3.91 μg/mL) and rapid killing after 15 min exposure (MBCs = 7.81 μg/mL). It can prevent the formation of S. epidermidis biofilm and also exhibited a dose-dependent eradication activity on mature or established S. epidermidis biofilm. In addition, it decreased the development of biofilm by surviving bacteria, and formation of biofilm on the surface of CM-10K14K-impregnated catheters. Released CM-10K14K decreased planktonic bacterial growth and inhibited biofilm formation by S. epidermidis in a dose-dependent manner for 6 and 24 h post-exposure. Impregnation of CM-10K14K prevented bacterial attachment on catheters and thus decreased formation of extensive biofilms. SEM images supported the antibiofilm activity of CM-10K14K. Flow cytometry analysis and TEM images demonstrated a membrane-active mechanism of CM-10K14K, inducing depolarization and permeabilization, and subsequent membrane rupture leading to cell death. The presence of an interaction with bacterial DNA was verified by gel retardation assay. These antibacterial and antibiofilm activities of CM-10K14K suggest its potential application to urinary catheters for prevention of biofilm-forming colonization or for treatment of medical devices infected with S. epidermidis.

Warm Cells, Hot Mitochondria: Achievements and Problems of Ultralocal Thermometry

Temperature is a crucial regulator of the rate and direction of biochemical reactions and cell processes. The recent data indicating the presence of local thermal gradients associated with the sites of high-rate thermogenesis, on the one hand, demonstrate the possibility for the existence of "thermal signaling" in a cell and, on the other, are criticized on the basis of thermodynamic calculations and models. Here, we review the main thermometric techniques and sensors developed for the determination of temperature inside living cells and diverse intracellular compartments. A comparative analysis is conducted of the results obtained using these methods for the cytosol, nucleus, endo-/sarcoplasmic reticulum, and mitochondria, as well as their biological consistency. Special attention is given to the limitations, possible sources of errors and ambiguities of the sensor's responses. The issue of biological temperature limits in cells and organelles is considered. It is concluded that the elaboration of experimental protocols for ultralocal temperature measurements that take into account both the characteristics of biological systems, as well as the properties and limitations of each type of sensor is of critical importance for the generation of reliable results and further progress in this field.

Model-driven insights into the effects of temperature on metabolism

Temperature affects cellular processes at different spatiotemporal scales, and identifying the genetic and molecular mechanisms underlying temperature responses paves the way to develop approaches for mitigating the effects of future climate scenarios. A systems view of the effects of temperature on cellular physiology can be obtained by focusing on metabolism since: (i) its functions depend on transcription and translation and (ii) its outcomes support organisms' development, growth, and reproduction. Here we provide a systematic review of modelling efforts directed at investigating temperature effects on properties of single biochemical reactions, system-level traits, metabolic subsystems, and whole-cell metabolism across different prokaryotes and eukaryotes. We compare and contrast computational approaches and theories that facilitate modelling of temperature effects on key properties of enzymes and their consideration in constraint-based as well as kinetic models of metabolism. In addition, we provide a summary of insights from computational approaches, facilitating integration of omics data from temperature-modulated experiments with models of metabolic networks, and review the resulting biotechnological applications. Lastly, we provide a perspective on how different types of metabolic modelling can profit from developments in machine learning and models of different cellular layers to improve model-driven insights into the effects of temperature relevant for biotechnological applications.

Effect of temperature and humidity on dynamics and transmission of Pseudomonas amygdali pv. lachrymans aerosols

Cucumber angular leaf spot (ALS) disease, caused by Pseudomonas amygdali pv. lachrymans (Pal), is an emerging disease with a high incidence that causes severe damage to cucumber worldwide. Bacterial aerosols play a crucial role in the epidemiology of greenhouse ALS disease. However, little is known about the influence of temperature and relative humidity (RH) on the dynamics of Pal in aerosols. A study was conducted to investigate the relationships between the concentration of Pal aerosols and their dependence on temperature and RH in aerosol chambers and greenhouses. The results demonstrated that temperature and RH are both significant factors influencing the release amount, survival time and infectivity of Pal in aerosols, while RH has a greater influence on particle size than temperature across the range of conditions tested. The release amount and survival time of Pal in aerosols under high RH (95%) and low temperature (≤ 25°C) conditions were significantly higher than those under low RH (35%) and high temperature (35°C) conditions. The highest release amount of Pal aerosol (96 CFU/m³) and highest survival rate (98.41%) were found at 18°C and 95% RH, while the highest disease index (DI = 60.9) caused by Pal aerosol was found at 25°C and 95% RH. In addition, Pal aerosols presented a larger diameter (4.7->7.0 μm) under high RH (95% RH) than under dry conditions (≤ 65% RH). These findings will play a crucial role in elucidating the influence of environmental parameters on the dynamics and transmission of Pal in aerosols. Based on our findings, preliminary recommendations for controlling airborne Pal spread involve controlling air temperature and RH, which will contribute to the effective alleviation and control of cucumber ALS disease.

Felodipine enhances aminoglycosides efficacy against implant infections caused by methicillin-resistant Staphylococcus aureus, persisters and biofilms

Methicillin-resistant Staphylococcus aureus (MRSA), biofilms, and persisters are three major factors leading to recurrent and recalcitrant implant infections. Although antibiotics are still the primary treatment for chronic implant infections in clinical, only few drugs are effective in clearing persisters and formed biofilms. Here, felodipine, a dihydropyridine calcium channel blocker, was reported for the first time to have antibacterial effects against MRSA, biofilm, and persisters. Even after continuous exposure to sub-lethal concentrations of felodipine, bacteria are less likely to develop resistance. Besides, low doses of felodipine enhances the antibacterial activity of gentamicin by inhibiting the expression of protein associated with aminoglycoside resistance (aacA-aphD). Next, biofilm eradication test and persisters killing assay suggested felodipine has an excellent bactericidal effect against formed biofilms and persisters. Furthermore, the result of protein profiling, and quantitative metabonomics analysis indicated felodipine reduce MRSA virulence (agrABC), biofilm formation and TCA cycle. Then, molecular docking showed felodipine inhibit the growth of persisters by binding to the H pocket of ClpP protease, which could lead to substantial protein degradation. Furthermore, murine infection models suggested felodipine in combination with gentamicin alleviate bacterial burden and inflammatory response. In conclusion, low dose of felodipine might be a promising agent for biomaterial delivery to enhance aminoglycosides efficacy against implant infections caused by MRSA, biofilm, and persisters.

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Felodipine inhibits MRSA gene expression associated with aminoglycoside resistance and biofilm formation.

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Felodipine eradicates formed biofilm and persisters on the surface of implants.

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Felodipine induces proteolysis of MRSA and decreases energy metabolism.

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Felodipine in combination with gentamicin alleviates murine periprosthetic joint infection.

Mechanisms regulating the airborne survival of Klebsiella pneumoniae under different relative humidity and temperature levels

In this study, Klebsiella pneumoniae was suspended in synthetic saliva in a nebulizer (N₀ ) and nebulized for 5 min (N₅ ) into an aerosol chamber and further prolonged in the aerosolization phase for 15 min (A₁₅ ) under four different conditions: 20°C, 50% relative humidity (RH); 20°C, 80% RH; 30°C, 50% RH; and 30°C, 80% RH. Samples were collected at N₀ , N₅ , and A₁₅ , then subjected to survival analysis and comparative transcriptomic analysis in order to help elucidate the underlying mechanisms of airborne survival. Survival analysis shows that a higher humidity and lower temperature were favorable for the airborne survival of K. pneumoniae, and the effect of RH was more remarkable at 20°C than that at 30°C. The RNA-seq results show that during the nebulization phase (N₀ vs. N₅ ), a total number of 201 differentially expressed genes (DEGs) were identified (103 downregulated and 98 upregulated). Comparison between nebulization and aerosolization phases (N₅ vs. A₁₅ ) indicates up to 132 DEGs, with 46 downregulated and 86 upregulated. The most notable groups of genes are those involved in cellular remodeling, metabolism and energy processes. Alarmingly, the mbl gene, which encodes antibiotic resistance in K. pneumoniae, was upregulated during the suspension phase under all the tested conditions. This study provides insights into the control of airborne transmitted diseases.

A Thermostable, Modified Cathelicidin-Derived Peptide With Enhanced Membrane-Active Activity Against Salmonella enterica serovar Typhimurium

Foodborne illness caused by consumption of food contaminated with Salmonella is one of the most common causes of diarrheal disease and affects millions of people worldwide. The rising emergence and spread of antimicrobial resistance, especially in some serotypes of Salmonella, has raised a great awareness of public health issues worldwide. To ensure safety of the food processing chain, the development of new food preservatives must be expedited. Recently, thermal- and pH-stable antimicrobial peptides have received much attention for use in food production, and represent safe alternatives to chemical preservatives. A 12-mer cathelicidin-derived, α-helical cationic peptide, P7, displayed rapid killing activity, against strains of drug-resistant foodborne Salmonella enterica serovar Typhimurium and its monophasic variant (S. enterica serovar 4,5,12:i:-) and had minimal toxicity against mouse fibroblast cells. P7 tended to form helical structure in the membrane-mimic environments as evaluated by circular dichroism (CD) spectroscopy. The action mode of P7 at the membrane-level was affirmed by the results of flow cytometry, and confocal, scanning and transmission electron microscopy. P7 killed bacteria through binding to bacterial membranes, penetration and the subsequent accumulation in S. enterica serovar Typhimurium cytoplasm. This induced membrane depolarization, permeabilization, and sequential leakage of intracellular substances and cell death. Except for sensitivity to proteolytic digestive enzymes, P7 maintained its inhibitory activity against S. enterica serovar Typhimurium in the presence of different conditions [various salts, extreme pHs and heat (even at 100°C)]. Moreover, the peptide is unlikely to induce bacterial resistance in vitro. Taken together, this study demonstrated that the membrane-permeabilizing P7 peptide has much potential as a new antimicrobial agent for use in food processing and preservation.

Airborne Survival of Escherichia coli under Different Culture Conditions in Synthetic Wastewater

Bioaerosol generated in wastewater treatment plants has potential to harm human health. Survival of bacteria in bioaerosol during suspension is one of the major factors that affect its biological risk. It is hypothesized that bacteria grown in different wastewater have different physiology and lead to variation in airborne survival. This study investigated the relationship between the cultured conditions and the bioaerosol survival. Synthetic wastewater was used as the culture medium to simulate the water quality of wastewater. Escherichia coli BW25113 were cultured in different conditions, including growth salinity, growth temperature, growth pH, and presence of pesticide. The fatty acid composition and the reduction in airborne survival of the E. coli cultured under these conditions were determined and compared. Results showed that increasing growth salinity and temperature led to a lower reduction in airborne survival of E. coli.E. coli cultured at pH 6 had a higher reduction in airborne survival than those cultured at pH 7 and 8. Moreover, a correlation was observed between the membrane fluidity (fluidity index) and the reduction airborne survival for both aerosolization and airborne suspension. A link between culture conditions, bacterial membrane fluidity, and airborne survival was established. Culture conditions (wastewater quality) that lead to a low membrane fluidity of bacteria increase the airborne survival of bioaerosol, and vice versa. This provides a new aspect to evaluate bioaerosol survival and improve assessment on biological risk of bioaerosols.

Impact of Deficiencies in Branched-Chain Fatty Acids and Staphyloxanthin in Staphylococcus aureus

Staphylococcus aureus is a well-known human pathogen with the ability to cause mild superficial skin infections to serious deep-tissue infections, such as osteomyelitis, pneumonia, and infective endocarditis. A key to S. aureus infections and its pathogenicity is its ability to survive in adverse environments, especially at lower temperatures, by regulation of its cell membrane. Branched-chain fatty acids (BCFAs) and staphyloxanthin have been shown to regulate membrane fluidity and staphylococcal virulence. This study was conducted with the hypothesis that the simultaneous lack of BCFAs and staphyloxanthin will have a far greater implication on environmental survival and virulence of S. aureus. Lack of a functional branched-chain α-keto acid dehydrogenase (BKD) enzyme because of a mutation in the lpdA gene led to a decrease in the production of BCFAs, membrane fluidity, slower growth, and poor in vivo survival of S. aureus. A mutation in the crtM gene eliminated the production of staphyloxanthin but it did not affect membrane BCFA levels, fluidity, growth, or in vivo survival. A crtM:lpdA double mutant showed much slower growth and attenuation compared to individual mutants. The results of this study suggest that simultaneous targeting of the BCFA and staphyloxanthin biosynthetic pathways can be a strategy to control S. aureus infections.