Protein aggregation is a consequence of the dormancy-inducing membrane toxin TisB in Escherichia coli

Bacterial dormancy is a valuable strategy to survive stressful conditions. Toxins from chromosomal toxin-antitoxin systems have the potential to halt cell growth, induce dormancy, and eventually promote a stress-tolerant persister state. Due to their potential toxicity when overexpressed, sophisticated expression systems are needed when studying toxin genes. Here, we present a moderate expression system for toxin genes based on an artificial 5' untranslated region. We applied the system to induce expression of the toxin gene tisB from the chromosomal type I toxin-antitoxin system tisB/istR-1 in Escherichia coli. TisB is a small hydrophobic protein that targets the inner membrane, resulting in depolarization and ATP depletion. We analyzed TisB-producing cells by RNA-sequencing and revealed several genes with a role in recovery from TisB-induced dormancy, including the chaperone genes ibpAB and spy. The importance of chaperone genes suggested that TisB-producing cells are prone to protein aggregation, which was validated by an in vivo fluorescent reporter system. We moved on to show that TisB is an essential factor for protein aggregation upon DNA damage mediated by the fluoroquinolone antibiotic ciprofloxacin in E. coli wild-type cells. The occurrence of protein aggregates correlates with an extended dormancy duration, which underscores their importance for the life cycle of TisB-dependent persister cells.

IMPORTANCE

Protein aggregates occur in all living cells due to misfolding of proteins. In bacteria, protein aggregation is associated with cellular inactivity, which is related to dormancy and tolerance to stressful conditions, including exposure to antibiotics. In Escherichia coli, the membrane toxin TisB is an important factor for dormancy and antibiotic tolerance upon DNA damage mediated by the fluoroquinolone antibiotic ciprofloxacin. Here, we show that TisB provokes protein aggregation, which, in turn, promotes an extended state of cellular dormancy. Our study suggests that protein aggregation is a consequence of membrane toxins with the potential to affect the duration of dormancy and the outcome of antibiotic therapy.

Warmer is better for evolutionary rescue, driving a warm-to-cold bias in habitat colonization dynamics

Evolutionary rescue occurs when populations survive lethal environmental stresses through the rising and fixation of tolerant genotypes. Temperature has long been believed to determine the evolutionary speed of populations and species. Here, we suggest that warmer temperatures can facilitate evolutionary rescue. Moreover, with dispersal among habitats, the advantage in evolutionary rescue for warmer populations may cause a bias in habitat colonization dynamics towards the warm-to-cold direction. We experimentally tested these hypotheses with a model microbial system. Our first experiment showed that bacterial populations at warmer temperatures had a greater chance to evolve resistance and escape the fate of extinction under an antibiotic treatment. In the second experiment, metapopulations that consisted of warm and cold habitats were exposed to the antibiotic stress; local populations that went extinct might be recolonized, and such recolonization events were biased to the warm-to-cold direction. We also examined possible mechanisms underlying the temperature effect on the rapid evolution of resistance in our study system. Our results may help to understand the mechanisms of maintenance of biodiversity and patterns of gene flow among climatic regions, particularly in pest species subject to chemical control treatments.

Gamma-Aminobutyric Acid (GABA) Biosynthesis from Lactobacillus plantarum subsp. plantarum IBRC10817 Optimized and Modeled in Response to Heat and Ultrasonic Shock

Gamma-aminobutyric acid is one of the major inhibitory neurotransmitters in the nervous system. Although gamma-aminobutyric acid is commonly synthesized by chemical methods, its microbial biosynthesis is regarded as one of the best production methods among the conventional techniques. This study aimed to optimize and model the production of gamma-aminobutyric acid from Lactobacillus plantarum subsp. plantarum IBRC (10,817) under the influence of heat and ultrasonic shock using the response surface methodology. Heat and ultrasonic shock were applied in the lag phase of bacterial growth. Heat shock variables included heat treatment, monosodium glutamate concentration, and incubation time. Also, ultrasonic shock variables were ultrasonic intensity, ultrasonic time, incubation time, and monosodium glutamate concentration. By applying the 30.9 h of incubation, 3.082 g/L of monosodium glutamate, and thermal shock of 49.958 °C for 30 min, the production of 295.04 mg/L of gamma amino butyric acid was predicted. As for ultrasonic shock, using 3.28 (g/L) monosodium glutamate, 70 h of bacterial incubation, 7.7 min ultrasound shock, and ultrasound frequency of 26.58 kHz, the highest amount of metabolite production was anticipated to be 215.19 mg/L. Overall, it was found that the actual values were consistent with the predicted values.

Seasonal meropenem resistance in Acinetobacter baumannii and influence of temperature-driven adaptation

BACKGROUND

Recognition of seasonal trends in bacterial infection and drug resistance rates may enhance diagnosis, direct therapeutic strategies, and inform preventive measures. Limited data exist on the seasonal variability of Acinetobacter baumannii. We investigated the seasonality of A. baumannii, the correlation between temperature and meropenem resistance, and the impact of temperature on this bacterium.

RESULTS

Meropenem resistance rates increased with lower temperatures, peaking in winter/colder months. Nonresistant strain detection exhibited temperature-dependent seasonality, rising in summer/warmer months and declining in winter/colder months. In contrast, resistant strains showed no seasonality. Variations in meropenem-resistant and nonresistant bacterial resilience to temperature changes were observed. Nonresistant strains displayed growth advantages at temperatures ≥ 25 °C, whereas meropenem-resistant A. baumannii with β-lactamase OXA-23 exhibited greater resistance to low-temperature (4 °C) stress. Furthermore, at 4 °C, A. baumannii upregulated carbapenem resistance-related genes (adeJ, oxa-51, and oxa-23) and increased meropenem stress tolerance.

CONCLUSIONS

Meropenem resistance rates in A. baumannii display seasonality and are negatively correlated with local temperature, with rates peaking in winter, possibly linked to the differential adaptation of resistant and nonresistant isolates to temperature fluctuations. Furthermore, due to significant resistance rate variations between quarters, compiling monthly or quarterly reports might enhance comprehension of antibiotic resistance trends. Consequently, this could assist in formulating strategies to control and prevent resistance within healthcare facilities.

Climate warming, environmental degradation and pollution as drivers of antibiotic resistance

Antibiotic resistance is a major challenge to public health, but human-caused environmental changes have not been widely recognized as its drivers. Here, we provide a comprehensive overview of the relationships between environmental degradation and antibiotic resistance, demonstrating that the former can potentially fuel the latter with significant public health outcomes. We describe that (i) global warming favors horizontal gene transfer, bacterial infections, the spread of drug-resistant pathogens due to water scarcity, and the release of resistance genes with wastewater; (ii) pesticide and metal pollution act as co-selectors of antibiotic resistance mechanisms; (iii) microplastics create conditions promoting and spreading antibiotic resistance and resistant bacteria; (iv) changes in land use, deforestation, and environmental pollution reduce microbial diversity, a natural barrier to antibiotic resistance spread. We argue that management of antibiotic resistance must integrate environmental goals, including mitigation of further increases in the Earth's surface temperature, better qualitative and quantitative protection of water resources, strengthening of sewage infrastructure and improving wastewater treatment, counteracting the microbial diversity loss, reduction of pesticide and metal emissions, and plastic use, and improving waste recycling. These actions should be accompanied by restricting antibiotic use only to clinically justified situations, developing novel treatments, and promoting prophylaxis. It is pivotal for health authorities and the medical community to adopt the protection of environmental quality as a part of public health measures, also in the context of antibiotic resistance management.

Antibiotic resistance determinants among carbapenemase producing bacteria isolated from wastewaters of Kathmandu, Nepal

The emergence of carbapenem resistant bacteria (CRB) possesses a remarkable threat to the health of humans. CRB and carbapenem resistance genes (CRGs) have frequently been reported in clinical isolates from hospitals, however, their occurrence and distribution in wastewaters from various sources and river water have not been emphasized in Nepal. So, this study aimed to detect carbapenem resistant bacterial isolates and their resistance determinants in river water and different types of wastewaters. River water and both untreated and treated wastewater samples from hospitals, pharmaceutical industries, and municipal sewage were collected in summer and winter seasons. From 68 grab wastewater samples, CRB were detected only in 16 samples, which included eight hospital wastewater, and four each from untreated municipal sewage and river water. A total of 25 CRB isolates were detected with dominance of E. coli (44.0%) and K. pneumoniae (24.0%). The majority of the isolates harbored blaNDM-1 (76.0%), followed by blaOXA (36.0%) and blaKPC (20.0%) genes. Hospital wastewater majorly contributed to the presence of blaNDM-1, blaKPC, and blaOXA along with intI1 genes compared to river water and untreated municipal sewage, especially during the winter season. However, CRB were not detected in treated effluents of hospitals and municipal sewage, and both influents and effluents from pharmaceutical industries. The combined presence of each blaNDM-1 & blaOXA and blaKPC & blaOXA occurred in 16.0% of the bacterial isolates. The increased minimum inhibitory concentration (MIC) of meropenem was significantly associated with the presence of CRGs. The results of this study highlight the significance of carbapenem resistance in bacteria isolated from wastewater and river water, and underscore the necessity for efficient monitoring and control strategies to prevent the dispersion of carbapenem resistance in the environment and its potential consequences on human health.

Enhancing Commercial Antibiotics with Trans-Cinnamaldehyde in Gram-Positive and Gram-Negative Bacteria: An In Vitro Approach

One strategy to mitigate the emergence of bacterial resistance involves reducing antibiotic doses by combining them with natural products, such as trans-cinnamaldehyde (CIN). The objective of this research was to identify in vitro combinations (CIN + commercial antibiotic (ABX)) that decrease the minimum inhibitory concentration (MIC) of seven antibiotics against 14 different Gram-positive and Gram-negative pathogenic bacteria, most of them classified as ESKAPE. MIC values were measured for all compounds using the broth microdilution method. The effect of the combinations on these microorganisms was analyzed through the checkboard assay to determine the type of activity (synergy, antagonism, or addition). This analysis was complemented with a kinetic study of the synergistic combinations. Fifteen synergistic combinations were characterized for nine of the tested bacteria. CIN demonstrated effectiveness in reducing the MIC of chloramphenicol, streptomycin, amoxicillin, and erythromycin (94-98%) when tested on Serratia marcescens, Staphylococcus aureus, Pasteurella aerogenes, and Salmonella enterica, respectively. The kinetic study revealed that when the substances were tested alone at the MIC concentration observed in the synergistic combination, bacterial growth was not inhibited. However, when CIN and the ABX, for which synergy was observed, were tested simultaneously in combination at these same concentrations, the bacterial growth inhibition was complete. This demonstrates the highly potent in vitro synergistic activity of CIN when combined with commercial ABXs. This finding could be particularly beneficial in livestock farming, as this sector witnesses the highest quantities of antimicrobial usage, contributing significantly to antimicrobial resistance issues. Further research focused on this natural compound is thus warranted for this reason.

Aminoglycoside uptake, stress, and potentiation in Gram-negative bacteria: new therapies with old molecules

SUMMARYAminoglycosides (AGs) are long-known molecules successfully used against Gram-negative pathogens. While their use declined with the discovery of new antibiotics, they are now classified as critically important molecules because of their effectiveness against multidrug-resistant bacteria. While they can efficiently cross the Gram-negative envelope, the mechanism of AG entry is still incompletely understood, although this comprehension is essential for the development of new therapies in the face of the alarming increase in antibiotic resistance. Increasing antibiotic uptake in bacteria is one strategy to enhance effective treatments. This review aims, first, to consolidate old and recent knowledge about AG uptake; second, to explore the connection between AG-dependent bacterial stress and drug uptake; and finally, to present new strategies of potentiation of AG uptake for more efficient antibiotic therapies. In particular, we emphasize on the connection between sugar transport and AG potentiation.

Morphological and physiological adaptations of psychrophilic Pseudarthrobacter psychrotolerans YJ56 under temperature stress

Both culture-independent and culture-dependent analyses using Nanopore-based 16S rRNA sequencing showed that short-term exposure of Antarctic soils to low temperature increased biomass with lower bacterial diversity and maintained high numbers of the phylum Proteobacteria, Firmicute, and Actinobacteria including Pseudarthrobacter species. The psychrophilic Pseudarthrobacter psychrotolerans YJ56 had superior growth at 13 °C, but could not grow at 30 °C, compared to other bacteria isolated from the same Antarctic soil. Unlike a single rod-shaped cell at 13 °C, strain YJ56 at 25 °C was morphologically shifted into a filamentous bacterium with several branches. Comparative genomics of strain YJ56 with other genera in the phylum Actinobacteria indicate remarkable copy numbers of rimJ genes that are possibly involved in dual functions, acetylation of ribosomal proteins, and stabilization of ribosomes by direct binding. Our proteomic data suggested that Actinobacteria cells experienced physiological stresses at 25 °C, showing the upregulation of chaperone proteins, GroEL and catalase, KatE. Level of proteins involved in the assembly of 50S ribosomal proteins and L29 in 50S ribosomal proteins increased at 13 °C, which suggested distinct roles of many ribosomal proteins under different conditions. Taken together, our data highlights the cellular filamentation and protein homeostasis of a psychrophilic YJ56 strain in coping with high-temperature stress.

Cultivating antimicrobial resistance: how intensive agriculture ploughs the way for antibiotic resistance

Antimicrobial resistance (AMR) is a growing threat to public health, global food security and animal welfare. Despite efforts in antibiotic stewardship, AMR continues to rise worldwide. Anthropogenic activities, particularly intensive agriculture, play an integral role in the dissemination of AMR genes within natural microbial communities - which current antibiotic stewardship typically overlooks. In this review, we examine the impact of anthropogenically induced temperature fluctuations, increased soil salinity, soil fertility loss, and contaminants such as metals and pesticides on the de novo evolution and dissemination of AMR in the environment. These stressors can select for AMR - even in the absence of antibiotics - via mechanisms such as cross-resistance, co-resistance and co-regulation. Moreover, anthropogenic stressors can prime bacterial physiology against stress, potentially widening the window of opportunity for the de novo evolution of AMR. However, research to date is typically limited to the study of single isolated bacterial species - we lack data on how intensive agricultural practices drive AMR over evolutionary timescales in more complex microbial communities. Furthermore, a multidisciplinary approach to fighting AMR is urgently needed, as it is clear that the drivers of AMR extend far beyond the clinical environment.

Susceptibility of emetic and enterotoxigenic Bacillus cereus grown at high temperature to disinfectants

The prevalence of emetic strains in food products is rare; however, infection with these may be fatal to the vulnerable population. Bacterial control of the emetic Bacillus cereus strains is still unclear. This study aimed to assess the influence of high temperature on the disinfection of emetic and enterotoxigenic B. cereus. Emetic B. cereus strains survived up to 50 °C; the lag time and maximum growth rate were higher at 42 °C than those at 30 °C. Compared to enterotoxigenic B. cereus, all emetic food strains showed higher minimum inhibitory concentrations and minimum bactericidal concentrations for sodium hypochlorite and citric acid. The disinfectant susceptibility of the emetic B. cereus OS-05 strain incubated at a higher temperature did not increase and was maintained at the highest MBC value. In all emetic B. cereus strains, enterotoxin gene expression was upregulated at 42 °C and 45 °C. Increased ces gene expression was also found in emetic B. cereus strains GP-15 and OS-05, with upregulation of 128- and 820-fold at 42 °C. Thus, emetic B. cereus grown at high temperatures may resist common disinfectants of the food industry. The findings may help control B. cereus in food or the food processing industry.

Biofilm Homeostasis Interference Therapy via 1 O2 -Sensitized Hyperthermia and Immune Microenvironment Re-Rousing for Biofilm-Associated Infections Elimination

The recurrence of biofilm-associated infections (BAIs) remains high after implant-associated surgery. Biofilms on the implant surface reportedly shelter bacteria from antibiotics and evade innate immune defenses. Moreover, little is currently known about eliminating residual bacteria that can induce biofilm reinfection. Herein, novel "interference-regulation strategy" based on bovine serum albumin-iridium oxide nanoparticles (BIONPs) as biofilm homeostasis interrupter and immunomodulator via singlet oxygen (¹ O₂ )-sensitized mild hyperthermia for combating BAIs is reported. The catalase-like BIONPs convert abundant H₂ O₂ inside the biofilm-microenvironment (BME) to sufficient oxygen gas (O₂ ), which can efficiently enhance the generation of ¹ O₂ under near-infrared irradiation. The ¹ O₂ -induced biofilm homeostasis disturbance (e.g., sigB, groEL, agr-A, icaD, eDNA) can disrupt the sophisticated defense system of biofilm, further enhancing the sensitivity of biofilms to mild hyperthermia. Moreover, the mild hyperthermia-induced bacterial membrane disintegration results in protein leakage and ¹ O₂ penetration to kill bacteria inside the biofilm. Subsequently, BIONPs-induced immunosuppressive microenvironment re-rousing successfully re-polarizes macrophages to pro-inflammatory M1 phenotype in vivo to devour residual biofilm and prevent biofilm reconstruction. Collectively, this ¹ O₂ -sensitized mild hyperthermia can yield great refractory BAIs treatment via biofilm homeostasis interference, mild-hyperthermia, and immunotherapy, providing a novel and effective anti-biofilm strategy.

First Report on the Versatile Secretome of an Environmental Isolate Acinetobacter pittii S-30

Acinetobacter species is currently ranked as high-priority pathogen for their extraordinary ability to become resistant to almost all existing antibiotics. The diverse range of effectors secreted by Acinetobacter spp. constitutes a significant proportion of the virulence arsenal. Therefore, our study aims to characterize the secretome of Acinetobacter pittii S-30. Analysis of extracellular secreted proteins of A. pittii S-30 revealed the presence of transporter proteins, outer membrane proteins, molecular chaperones, porins, and several proteins of unknown function. Additionally, proteins related to metabolism, as well as those involved in gene expression and protein translation, type VI secretion system (T6SS) proteins, and stress response-related proteins were also identified in the secretome. The comprehensive analysis of secretome revealed putative protein antigens which could elicit substantial immune response. The limited availability of effective antibiotics and the worldwide growth of secretome data make this approach appealing in the development of effective vaccines against Acinetobacter and other bacterial pathogens.

Estimating the effect of increasing ambient temperature on antimicrobial resistance in China: A nationwide ecological study with the difference-in-differences approach

Antimicrobial resistance (AMR) and the possible consequences of rising ambient temperatures brought on by global warming have been extensively discussed. However, the epidemiological evidence on the effects of temperature on AMR is rare and little is known about the role of socioeconomic inequities. This ecological study obtained 31 provinces AMR data of Escherichia Coli (E. coli) from the China Antimicrobial Resistance Surveillance System (CARSS) over the period from 2014 to 2020, which were linked to the meteorological and socioeconomic data published in the China Statistical Yearbook. Modified difference-in-differences (DID) analyses were performed to estimate the effect of ambient temperature on AMR of E. coli to third-generation cephalosporins (ceftriaxone and cefotaxime), carbapenems, and quinolones, adjusting for variations in meteorological and socioeconomic factors. We estimated that every 1 °C increase in average ambient temperature was associated with 2.71 % (95 % confidence interval [CI]: 1.20-4.24), 32.92 % (95 % CI: 15.62-52.81), and 1.81 % (95 % CI: 0.47-3.16) increase in the prevalence of E. coli resistance to third-generation cephalosporins (ceftriaxone and cefotaxime), carbapenems and quinolones, respectively. The link was more profound in the regions with lower temperature and a median level of average humidity, and the regions with lower income, lower expenditure (in economics), lower health resources, and lower hospital admissions. Neither the replacement of the temperature variable nor the alternative approaches for confounding adjustment changed the positive association between ambient temperature and AMR. In general, there exists a positive association between ambient temperature and AMR, although the strength of such an association varies by socioeconomic and health services factors. The association is possibly nonlinear, especially for E. coli resistance to third-generation cephalosporins. The findings suggest that AMR control programs should explicitly incorporate weather patterns to increase their effectiveness.

Pyrogallol downregulates the expression of virulence-associated proteins in Acinetobacter baumannii and showing anti-infection activity by improving non-specific immune response in zebrafish model

Acinetobacter baumannii, a virulent uropathogen with widespread antibiotic resistance, has arisen as a critical scientific challenge, necessitating the development of innovative therapeutic agents. This is the first study reveal the proteomic changes in A. baumannii upon pyrogallol treatment for understanding the mechanisms using nano-LC-MS/MS-based quantitative proteomics and qPCR analysis. The obtained results found that pyrogallol treatment dramatically downregulated the expression level of several key proteins such as GroEL, DnaK, ClpB, SodB, KatE, Bap, CsuA/B, PgaA, PgaC, BfmR, OmpA, and SecA in A. baumannii, which are involved in chaperone-mediated oxidative stress responses, antioxidant defence system, biofilm formation, virulence enzyme production, bacterial adhesion, capsule formation, and antibiotic resistance. Accordingly, the pyrogallol dramatically enhanced the lifespan of A. baumannii-infected zebrafish by inhibiting bacterial colonization, demonstrating the anti-infective potential of pyrogallol against A. baumannii. Further, the histopathological results also demonstrated the disease protection efficacy of pyrogallol against the pathognomonic sign of A. baumannii infection. In addition, the pyrogallol treatment effectively improved the immune parameters such as serum myeloperoxidase activity, leukocyte respiratory burst activity, and serum lysozyme activity in zebrafish against A. baumannii infection. Based on the results, the present study strongly proposes pyrogallol as a promising therapeutic agent for treating A. baumannii infection.

Association between antibiotic resistance and increasing ambient temperature in China: An ecological study with nationwide panel data

Background

Antibiotic resistance leads to longer hospital stays, higher medical costs, and increased mortality. However, research into the relationship between climate change and antibiotic resistance remains inconclusive. This study aims to address the gap in the literature by exploring the association of antibiotic resistance with regional ambient temperature and its changes over time.

Methods

Data were obtained from the China Antimicrobial Surveillance Network (CHINET), monitoring the prevalence of carbapenem-resistant Acinetobacter baumannii (CRAB), Klebsiella pneumoniae (CRKP) and Pseudomonas aeruginosa (CRPA) in 28 provinces/regions over the period from 2005 to 2019. Log-linear regression models were established to determine the association between ambient temperature and antibiotic resistance after adjustment for variations in socioeconomic, health service, and environmental factors.

Findings

A 1 °C increase in average ambient temperature was associated with 1.14-fold increase (95%-CI [1.07–1.23]) in CRKP prevalence and 1.06-fold increase (95%-CI [1.03–1.08]) in CRPA prevalence. There was an accumulative effect of year-by-year changes in ambient temperature, with the four-year sum showing the greatest effect on antibiotic resistance. Higher prevalence of antibiotic resistance was also associated with higher antibiotic consumption, lower density of health facilities, higher density of hospital beds and higher level of corruption.

Interpretation

Higher prevalence of antibiotic resistance is associated with increased regional ambient temperature. The development of antibiotic resistance under rising ambient temperature differs across various strains of bacteria.

Funding

The 10.13039/501100012166National Key R&D Program of China (grant number: 2018YFA0606200), 10.13039/501100001809National Natural Science Foundation of China (grant number: 72074234), 10.13039/501100012476Fundamental Scientific Research Funds for Central Universities, P.R. China (grant number: 22qntd4201), 10.13039/100001547China Medical Board (grant number: CMB-OC-19-337).

Transcriptome Analysis of Acinetobacter baumannii in Rapid Response to Subinhibitory Concentration of Minocycline

The increasing emergence of multidrug-resistant Acinetobacter baumannii brings great threats to public health. Minocycline is a kind of semisynthetic derivative of the antibacterial drug tetracycline and is often used to treat infections caused by multidrug-resistant A. baumannii with other antibiotics. However, minocycline-resistant A. baumannii appears constantly. To rapidly explore the response of A. baumannii to minocycline stress, RNA-seq was carried out to compare the difference in the transcriptome of A. baumannii ATCC19606 in the presence or absence of minocycline. The results showed that 25 genes were differentially expressed, including 10 downregulated genes and 15 upregulated genes, and 24 sRNA were upregulated and 24 were downregulated based on the filter criteria (Log2FC > 1 or <−1 and FDR < 0.05). RtcB family protein and ABC transporter ATP-binding protein were upregulated by 2.6- and 11.3-fold, and molecular chaperone GroES, chaperonin GroL, class C beta-lactamase ADC-158, amino acid ABC transporter permease, and APC family permease were downregulated by at least two-fold in the presence of half-MIC minocycline. The differentially expressed genes are mainly involved in the stress response, the GroES/GroEL chaperonin system, and transport metabolic pathways. sRNA 1248 was significantly upregulated, and sRNA 1767, 5182, and 6984 were downregulated in a rapid response to minocycline. These results provide insights into the adaptive mechanism of A. baumannii to minocycline.

Trimethylamine N-Oxide Reduces the Susceptibility of Escherichia coli to Multiple Antibiotics

Trimethylamine N-oxide (TMAO), an important intestinal flora-derived metabolite, plays a role in the development of cardiovascular disease and tumor immunity. Here, we determined the minimum inhibitory concentration (MIC) of antibiotics against Escherichia coli under gradient concentrations of TMAO and performed a bacterial killing analysis. Overall, TMAO (in the range of 10 ~ 100 mM) increased the MIC of quinolones, aminoglycosides, and β-lactams in a concentration-dependent manner, and increased the lethal dose of antibiotics against E. coli. It implies that TMAO is a potential risk for failure of anti-infective therapy, and presents a case for the relationship between intestinal flora-derived metabolites and antibiotic resistance. Further data demonstrated that the inhibition of antibiotic efficacy by TMAO is independent of the downstream metabolic processes of TMAO and the typical bacterial resistance mechanisms (mar motif and efflux pump). Interestingly, TMAO protects E. coli from high-protein denaturant (urea) stress and improves the viability of bacteria following treatment with two disinfectants (ethanol and hydrogen peroxide) that mediate protein denaturation by chemical action or oxidation. Since antibiotics can induce protein inactivation directly or indirectly, our work suggests that disruption of protein homeostasis may be a common pathway for different stress-mediated bacterial growth inhibition/cell death. In addition, we further discuss this possibility, which provides a different perspective to address the global public health problem of antibiotic resistance.

Loss of thermotolerance in antibiotic-resistant Acinetobacter baumannii

Bacterium Acinetobacter baumannii is a leading cause of nosocomial infections. The occurrence of antibiotic-resistant A. baumannii isolates outside hospitals suggests that monitoring of this pathogen in environmental samples is needed. Survival of pandrug-resistant A. baumannii was followed on selective plates with and without carbapenems in water and soil. After a few days of starvation, A. baumannii lost the ability to be cultivated at 44°C on plates supplemented with carbapenems. Once cultivated on plates without carbapenems and/or at 36°C, A. baumannii could grow again at 44°C in the presence of carbapenems. Comparative proteomic analysis revealed that impaired membrane integrity and reduced function of efflux pumps due to elevated temperature combined with antibiotic exposure were the main reasons for this phenomenon. Loss of thermotolerance in the presence of antibiotics points to the need for temperature adjustment in long-term monitoring of A. baumannii in environmental samples, to avoid the underestimation of viable bacteria.

Proton motive force underpins respiration-mediated potentiation of aminoglycoside lethality in pathogenic Escherichia coli

It is well known that loss of aerobic respiration in Gram-negative bacteria can diminish the efficacy of a variety of bactericidal antibiotics, which has lead to subsequent demonstrations that the formation of reactive oxygen species (ROS) and the proton motive force (PMF) can both play a role in antibiotic toxicity. The susceptibility of Gram-negative bacteria to aminoglycoside antibiotics, particularly gentamicin, has previously been linked to both the production of ROS and the rate of antibiotic uptake that is mediated by the PMF, although the relative contributions of ROS and PMF to aminoglycoside toxicity has remained poorly understood. Herein, gentamicin was shown to elicit a very modest increase in ROS levels in an aerobically grown Escherichia coli clinical isolate. The well-characterised uncoupler 2,4-dinitrophenol (DNP) was used to disrupt the PMF, which resulted in a significant decrease in gentamicin lethality towards E. coli. DNP did not significantly alter respiratory oxygen consumption, supporting the hypothesis that this uncoupler does not increase ROS production via elevated respiratory oxidase activity. These observations support the hypothesis that maintenance of PMF rather than induction of ROS production underpins the mechanism for how the respiratory chain potentiates the toxicity of aminoglycosides. This was further supported by the demonstration that the uncoupler DNP elicits a dramatic decrease in gentamicin lethality under anaerobic conditions. Together, these data strongly suggest that maintenance of the PMF is the dominant mechanism for the respiratory chain in potentiating the toxic effects of aminoglycosides.

The DegU Orphan Response Regulator Contributes to Heat Stress Resistance in Listeria monocytogenes

Listeria monocytogenes is more heat-resistant than most other non-spore-forming foodborne pathogens, posing a severe threat to food safety and human health, particularly during chilled food processing. The DegU orphan response regulator is known to control heat resistance in L. monocytogenes; however, the underlying regulatory mechanism is poorly understood. Here, we show that DegU contributes to L. monocytogenes exponential growth under mild heat-shock stress. We further demonstrate that DegU directly senses heat stress through autoregulation and upregulates the hrcA-grpE-dnaK-dnaJ operon, leading to increased production of heat-shock proteins. We also show that DegU can directly regulate the expression of the hrcA-grpE-dnaK-dnaJ operon. In conclusion, our results shed light on the regulatory mechanisms underlying how DegU directly activates the hrcA-grpE-dnaK-dnaJ operon, thereby regulating heat resistance in L. monocytogenes.

Evaluation of antimicrobial effects of photo-sonodynamic antimicrobial chemotherapy based on nano-micelle curcumin on virulence gene expression patterns in Acinetobacter baumannii

BACKGROUND

Abaumannii baumannii rapidly resistance to a wide range of antimicrobial agents. The combination of antimicrobial photodynamic therapy (aPDT) and sonodynamic antimicrobial chemotherapy (SACT) known as photo-sonodynamic antimicrobial chemotherapy (PSACT) has received considerable attention as one of the emerging and promising strategies against microbial infections.

OBJECTIVE

This study aimed to investigate the antimicrobial effects of PSACT based on nano-micelle curcumin (N-MCur) on the virulence gene expression patterns in A. baumannii.

MATERIALS AND METHODS

N-MCur as a photo-sonosensitizer was synthesized and confirmed. To determine sub-significant reduction dose of PSACT, sub-significant reduction dose of N-MCur and blue laser light during aPDT, and ultrasound power output during SACT were assessed. Finally, changes in the expression of genes involved in treated A. baumannii by minimum sub-significant reduction dose of PSACT were determined using quantitative real-time-PCR (qRT-PCR).

RESULTS

PSACT using 12.5 mM N-MCur at the ultrasound power outputs of 28.7, 36.9, and 45.2 mW/cm2 with 4 min irradiation time of blue laser, as well as, 6.2 mM N-MCur at an ultrasound power output of 45.2 mW/cm2 plus 3 min blue laser irradiation time exhibited the significant dose-dependent reduction against A. baumannii cell viability compared to the control group (P<0.05). After treatment of A. baumannii using 3.1 mM N-MCur + 2 min blue laser irradiation time + 28.7 mW/cm2 ultrasound as the minimum sub-significant reduction doses of PSACT, mRNA expression was significantly upregulated to 6.0-, 11.2-, and 13.7-folds in recA, blsA, and dnaK and downregulated to 8.6-, 10.1-, and 14.5-folds in csuE, espA, and abaI, respectively.

CONCLUSIONS

N-MCur-mediated PSACT could regulate the expression of genes involved in A. baumannii pathogenesis. Therefore, PSACT can be proposed as a promising application to treat infections caused by A. baumannii.

Effects of ethanol stress on epsilon-poly-l-lysine (ε-PL) biosynthesis in Streptomyces albulus X-18

The aim of the study was to reveal the effects of ethanol stress on the production of epsilon-poly-l-lysine (ε-PL) in Streptomyces albulus X-18. The results showed that biomass and the utilization of glucose were respectively increased by ethanol stress. The ε-PL yield was increased by 41.42 % in the shake flask and 37.02 % in 10 L fermenter with 1% (v/v) ethanol. The morphology of colonies and mycelia showed significant differences. The intracellular reactive oxygen species level was increased by about 100 %. The ratio of unsaturated fatty acids to saturated fatty acids in the cell membrane was increased by ethanol stress. Isobaric Tags for Relative and Absolute Quantitation (iTRAQ) proteomic profile showed that 265 identified proteins were differentially expressed. The differentially expressed proteins (DEPs) were mainly involved in biological processes. The up-regulated DEPs were mainly involved in the redox reaction and stress response. The metabolic flux of l-Asp was shifted to l-Lys biosynthesis, and the DAP pathway was strengthened. Protein-protein interaction analysis showed that 30 DEPs interacted with l-Lys biosynthesis. The changes of ten proteins by Parallel Reaction Monitoring (PRM) were consistent with those by iTRAQ. The study provided valuable clues to better understand the mechanism of ε-PL biosynthesis improvement by ethanol stress.

Antibiotics Shift the Temperature Response Curve of Escherichia coli Growth

Temperature variation-through time and across climatic gradients-affects individuals, populations, and communities. Yet how the thermal response of biological systems is altered by environmental stressors is poorly understood. Here, we quantify two key features-optimal temperature and temperature breadth-to investigate how temperature responses vary in the presence of antibiotics. We use high-throughput screening to measure growth of Escherichia coli under single and pairwise combinations of 12 antibiotics across seven temperatures that range from 22°C to 46°C. We find that antibiotic stress often results in considerable changes in the optimal temperature for growth and a narrower temperature breadth. The direction of the optimal temperature shifts can be explained by the similarities between antibiotic-induced and temperature-induced damage to the physiology of the bacterium. We also find that the effects of pairs of stressors in the temperature response can often be explained by just one antibiotic out of the pair. Our study has implications for a general understanding of how ecological systems adapt and evolve to environmental changes. IMPORTANCE The growth of living organisms varies with temperature. This dependence is described by a temperature response curve that is described by an optimal temperature where growth is maximized and a temperature range (termed breadth) across which the organism can grow. Because an organism's temperature response evolves or acclimates to its environment, it is often assumed to change over only evolutionary or developmental timescales. Counter to this, we show here that antibiotics can quickly (over hours) change the optimal growth temperature and temperature breadth for the bacterium Escherichia coli. Moreover, our results suggest a shared-damage hypothesis: when an antibiotic damages similar cellular components as hot (or cold) temperatures do, this shared damage will combine and compound to more greatly reduce growth when that antibiotic is administered at hot (or cold) temperatures. This hypothesis could potentially also explain how temperature responses are modified by stressors other than antibiotics.

Quantitative mapping of mRNA 3' ends in Pseudomonas aeruginosa reveals a pervasive role for premature 3' end formation in response to azithromycin

Pseudomonas aeruginosa produces serious chronic infections in hospitalized patients and immunocompromised individuals, including patients with cystic fibrosis. The molecular mechanisms by which P. aeruginosa responds to antibiotics and other stresses to promote persistent infections may provide new avenues for therapeutic intervention. Azithromycin (AZM), an antibiotic frequently used in cystic fibrosis treatment, is thought to improve clinical outcomes through a number of mechanisms including impaired biofilm growth and quorum sensing (QS). The mechanisms underlying the transcriptional response to AZM remain unclear. Here, we interrogated the P. aeruginosa transcriptional response to AZM using a fast, cost-effective genome-wide approach to quantitate RNA 3’ ends (3pMap). We also identified hundreds of P. aeruginosa genes with high incidence of premature 3’ end formation indicative of riboregulation in their transcript leaders using 3pMap. AZM treatment of planktonic and biofilm cultures alters the expression of hundreds of genes, including those involved in QS, biofilm formation, and virulence. Strikingly, most genes downregulated by AZM in biofilms had increased levels of intragenic 3’ ends indicating premature transcription termination, transcriptional pausing, or accumulation of stable intermediates resulting from the action of nucleases. Reciprocally, AZM reduced premature intragenic 3’ end termini in many upregulated genes. Most notably, reduced termination accompanied robust induction of obgE, a GTPase involved in persister formation in P. aeruginosa. Our results support a model in which AZM-induced changes in 3’ end formation alter the expression of central regulators which in turn impairs the expression of QS, biofilm formation and stress response genes, while upregulating genes associated with persistence.

Pseudomonas aeruginosa is a common source of hospital-acquired infections and causes prolonged illness in patients with cystic fibrosis. P. aeruginosa infections are often treated with the macrolide antibiotic azithromycin, which changes the expression of many genes involved in infection. By examining such expression changes at nucleotide resolution, we found azithromycin treatment alters the locations of mRNA 3’ ends suggesting most downregulated genes are subject to premature 3’ end formation. We further identified candidate RNA regulatory elements that P. aeruginosa may use to control gene expression. Our work provides new insights in P. aeruginosa gene regulation and its response to antibiotics.

Understanding tolerance to cell wall-active antibiotics

Antibiotic tolerance-the ability of bacteria to survive for an extended time in the presence of bactericidal antibiotics-is an understudied contributor to antibiotic treatment failure. Herein, I review the manifestations, mechanisms, and clinical relevance of tolerance to cell wall-active (CWA) antibiotics, one of the most important groups of antibiotics at the forefront of clinical use. I discuss definitions of tolerance and assays for tolerance detection, comprehensively discuss the mechanism of action of β-lactams and other CWA antibiotics, and then provide an overview of how cells mitigate the potentially lethal effects of CWA antibiotic-induced cell damage to become tolerant. Lastly, I discuss evidence for a role of CWA antibiotic tolerance in clinical antibiotic treatment failure.

Antibiotic-Resistant Bacteria in Aquaculture and Climate Change: A Challenge for Health in the Mediterranean Area

Aquaculture is the productive activity that will play a crucial role in the challenges of the millennium, such as the need for proteins that support humans and the respect for the environment. Aquaculture is an important economic activity in the Mediterranean basin. A great impact is presented, however, by aquaculture practices as they involve the use of antibiotics for treatment and prophylaxis. As a consequence of the use of antibiotics in aquaculture, antibiotic resistance is induced in the surrounding bacteria in the column water, sediment, and fish-associated bacterial strains. Through horizontal gene transfer, bacteria can diffuse antibiotic-resistance genes and mobile resistance genes further spreading genetic determinants. Once triggered, antibiotic resistance easily spreads among aquatic microbial communities and, from there, can reach human pathogenic bacteria, making vain the use of antibiotics for human health. Climate change claims a significant role in this context, as rising temperatures can affect cell physiology in bacteria in the same way as antibiotics, causing antibiotic resistance to begin with. The Mediterranean Sea represents a 'hot spot' in terms of climate change and aspects of antibiotic resistance in aquaculture in this area can be significantly amplified, thus increasing threats to human health. Practices must be adopted to counteract negative impacts on human health, with a reduction in the use of antibiotics as a pivotal point. In the meantime, it is necessary to act against climate change by reducing anthropogenic impacts, for example by reducing CO2 emissions into the atmosphere. The One Health type approach, which involves the intervention of different skills, such as veterinary, ecology, and medicine in compliance with the principles of sustainability, is necessary and strongly recommended to face these important challenges for human and animal health, and for environmental safety in the Mediterranean area.

Bioinformatic and Functional Characterization of Hsp70s in Myxococcus xanthus

Hsp70 proteins are among the most ubiquitous chaperones and play important roles in maintaining proteostasis and resisting environmental stress. Multiple copies of Hsp70s are widely present in eukaryotic cells with redundant and divergent functions, but they have been less well investigated in prokaryotes. Myxococcus xanthus DK1622 is annotated as having many hsp70 genes. In this study, we performed a bioinformatic analysis of Hsp70 proteins and investigated the functions of six hsp70 genes in DK1622, including two genes that encode proteins with the conserved PRK00290 domain (MXAN_3192 and MXAN_6671) and four genes that encode proteins with the cl35085 or cd10170 domain. We found that only MXAN_3192 is essential for cell survival and heat shock induction. MXAN_3192, compared with the other hsp70 genes, has a high transcriptional level, far exceeding that of any other hsp70 gene, which, however, is not the reason for its essentiality. Deletion of MXAN_6671 (sglK) led to multiple deficiencies in development, social motility, and oxidative resistance, while deletion of each of the other four hsp70 genes decreased sporulation and oxidative resistance. MXAN_3192 or sglK, but not the other genes, restored the growth deficiency of the E. colidnaK mutant. Our results demonstrated that the PRK00290 proteins play a central role in the complex cellular functions of M. xanthus, while the other diverse Hsp70 superfamily homologues probably evolved as helpers with some unknown specific functions.

IMPORTANCE Hsp70 proteins are highly conserved chaperones that occur in all kingdoms of life. Multiple copies of Hsp70s are often present in genome-sequenced prokaryotes, especially taxa with complex life cycles, such as myxobacteria. We investigated the functions of six hsp70 genes in Myxococcus xanthus DK1622 and demonstrated that the two Hsp70 proteins with the PRK00290 domain play a central role in complex cellular functions in M. xanthus, while other Hsp70 proteins probably evolved as helpers with some unknown specific functions.

Protein Aggregation as a Bacterial Strategy to Survive Antibiotic Treatment

While protein aggregation is predominantly associated with loss of function and toxicity, it is also known to increase survival of bacteria under stressful conditions. Indeed, protein aggregation not only helps bacteria to cope with proteotoxic stresses like heat shocks or oxidative stress, but a growing number of studies suggest that it also improves survival during antibiotic treatment by inducing dormancy. A well-known example of dormant cells are persisters, which are transiently refractory to the action of antibiotics. These persister cells can switch back to the susceptible state and resume growth in the absence of antibiotics, and are therefore considered an important cause of recurrence of infections. Mounting evidence now suggests that this antibiotic-tolerant persister state is tightly linked to-or perhaps even driven by-protein aggregation. Moreover, another dormant bacterial phenotype, the viable but non-culturable (VBNC) state, was also shown to be associated with aggregation. These results indicate that persisters and VBNC cells may constitute different stages of the same dormancy program induced by progressive protein aggregation. In this mini review, we discuss the relation between aggregation and bacterial dormancy, focusing on both persisters and VBNC cells. Understanding the link between protein aggregation and dormancy will not only provide insight into the fundamentals of bacterial survival, but could prove highly valuable in our future battle to fight them.

Acinetobacter baumannii: An Ancient Commensal with Weapons of a Pathogen

Acinetobacter baumannii is regarded as a life-threatening pathogen associated with community-acquired and nosocomial infections, mainly pneumonia. The rise in the number of A. baumannii antibiotic-resistant strains reduces effective therapies and increases mortality. Bacterial comparative genomic studies have unraveled the innate and acquired virulence factors of A. baumannii. These virulence factors are involved in antibiotic resistance, environmental persistence, host-pathogen interactions, and immune evasion. Studies on host–pathogen interactions revealed that A. baumannii evolved different mechanisms to adhere to in order to invade host respiratory cells as well as evade the host immune system. In this review, we discuss current data on A. baumannii genetic features and virulence factors. An emphasis is given to the players in host–pathogen interaction in the respiratory tract. In addition, we report recent investigations into host defense systems using in vitro and in vivo models, providing new insights into the innate immune response to A. baumannii infections. Increasing our knowledge of A. baumannii pathogenesis may help the development of novel therapeutic strategies based on anti-adhesive, anti-virulence, and anti-cell to cell signaling pathways drugs.

Proteomic Analyses of Acinetobacter baumannii Clinical Isolates to Identify Drug Resistant Mechanism

Acinetobacter baumannii is one of the main causes of nosocomial infections. Increasing numbers of multidrug-resistant Acinetobacter baumannii cases have been reported in recent years, but its antibiotic resistance mechanism remains unclear. We studied 9 multidrug-resistant (MDR) and 10 drug-susceptible Acinetobacter baumannii clinical isolates using Label free, TMT labeling approach and glycoproteomics analysis to identify proteins related to drug resistance. Our results showed that 164 proteins exhibited different expressions between MDR and drug-susceptible isolates. These differential proteins can be classified into six groups: a. proteins related to antibiotic resistance, b. membrane proteins, membrane transporters and proteins related to membrane formation, c. Stress response-related proteins, d. proteins related to gene expression and protein translation, e. metabolism-related proteins, f. proteins with unknown function or other functions containing biofilm formation and virulence. In addition, we verified seven proteins at the transcription level in eight clinical isolates by using quantitative RT-PCR. Results showed that four of the selected proteins have positive correlations with the protein level. This study provided an insight into the mechanism of antibiotic resistance of multidrug-resistant Acinetobacter baumannii.

Review on Stress Tolerance in Campylobacter jejuni

Campylobacter spp. are the leading global cause of bacterial colon infections in humans. Enteropathogens are subjected to several stress conditions in the host colon, food complexes, and the environment. Species of the genus Campylobacter, in collective interactions with certain enteropathogens, can manage and survive such stress conditions. The stress-adaptation mechanisms of Campylobacter spp. diverge from other enteropathogenic bacteria, such as Escherichia coli, Salmonella enterica serovar Typhi, S. enterica ser. Paratyphi, S. enterica ser. Typhimurium, and species of the genera Klebsiella and Shigella. This review summarizes the different mechanisms of various stress-adaptive factors on the basis of species diversity in Campylobacter, including their response to various stress conditions that enhance their ability to survive on different types of food and in adverse environmental conditions. Understanding how these stress adaptation mechanisms in Campylobacter, and other enteric bacteria, are used to overcome various challenging environments facilitates the fight against resistance mechanisms in Campylobacter spp., and aids the development of novel therapeutics to control Campylobacter in both veterinary and human populations.

Non-walled spherical Acinetobacter baumannii is an important type of persister upon β-lactam antibiotic treatment

Bacterial persistence is one of the major causes of antibiotic treatment failure and the step stone for antibiotic resistance. However, the mechanism by which persisters arise has not been well understood. Maintaining a dormant state to prevent antibiotics from taking effect is believed to be the fundamental mechanistic basis, and persisters normally maintain an intact cellular structure. Here we examined the morphologies of persisters in Acinetobacter baumannii survived from the treatment by three major classes of antibiotics (i.e. β-lactam, aminoglycoside, and fluoroquinolone) with microcopy and found that a fraction of enlarged spherical bacteria constitutes a major sub-population of bacterial survivors from β-lactam antibiotic treatment, whereas survivors from the treatment of aminoglycoside and fluoroquinolone were less changed morphologically. Further studies showed that these spherical bacteria had completely lost their cell wall structures but could survive without any osmoprotective reagent. The spherical bacteria were not the viable-but-non-culturable cells and they could revive upon the removal of β-lactam antibiotics. Importantly, these non-walled spherical bacteria also persisted during antibiotic therapy in vivo using Galleria mellonella as the infection model. Additionally, the combinational treatment on A. baumannii by β-lactam and membrane-targeting antibiotic significantly enhanced the killing efficacy. Our results indicate that in addition to the dormant, structure intact persisters, the non-wall spherical bacterium is another important type of persister in A. baumannii. The finding suggests that targeting the bacterial cell membrane during β-lactam chemotherapy could enhance therapeutic efficacy on A. baumannii infection, which might also help to reduce the resistance development of A. baumannii.

Proteomic and Systematic Functional Profiling Unveils Citral Targeting Antibiotic Resistance, Antioxidant Defense, and Biofilm-Associated Two-Component Systems of Acinetobacter baumannii To Encumber Biofilm and Virulence Traits

Acinetobacter baumannii is a nosocomial-infection-causing bacterium and also possesses multidrug resistance to a wide range of conventional antibiotics. The biofilm-forming ability of A. baumannii plays a major role in its resistance and persistence. There is an alarming need for novel treatment strategies to control A. baumannii biofilm-associated issues. The present study demonstrated the strong antibiofilm and antivirulence efficacy of citral against A. baumannii. In addition, proteomic analysis revealed the multitarget potential of citral against A. baumannii. Furthermore, citral treatment enhances the susceptibility of A. baumannii to the host innate immune system and reactive oxygen species (ROS). Cytotoxicity analysis revealed the nonfatal effect of citral on human PBMCs. Therefore, citral could be the safest therapeutic compound and can be taken for further clinical evaluation for the treatment of biofilm-associated infections by A. baumannii.

Acinetobacter baumannii has been reported as a multidrug-resistant bacterium due to biofilms and antimicrobial resistance mechanisms. Hence, novel therapeutic strategies are necessary to overcome A. baumannii infections. This study revealed that citral at 200 μg/ml attenuated A. baumannii biofilms by up to 90% without affecting viability. Furthermore, microscopic analyses and in vitro assays confirmed the antibiofilm efficacy of citral. The global effect of citral on A. baumannii was evaluated by proteomic, transcriptional, and in silico approaches. Two-dimensional (2D) gel electrophoresis and matrix-assisted laser desorption ionization–time of flight/time of flight (MALDI-TOF/TOF) analyses were used to assess the effect of citral on the A. baumannii cellular proteome. Quantitative real-time PCR (qPCR) analysis was done to validate the proteomic data and identify the differentially expressed A. baumannii genes. Protein-protein interactions, gene enrichment, and comparative gene network analyses were performed to explore the interactions and functional attributes of differentially expressed proteins of A. baumannii. Global omics-based analyses revealed that citral targeted various mechanisms such as biofilm formation, antibiotic resistance, antioxidant defense, iron acquisition, and type II and type IV secretion systems. The results of antioxidant analyses and antibiotic sensitivity, blood survival, lipase, and hemolysis assays validated the proteomic results. Cytotoxicity analysis showed a nontoxic effect of citral on peripheral blood mononuclear cells (PBMCs). Overall, the current study unveiled that citral has multitarget efficacy to inhibit the biofilm formation and virulence of A. baumannii.

IMPORTANCEAcinetobacter baumannii is a nosocomial-infection-causing bacterium and also possesses multidrug resistance to a wide range of conventional antibiotics. The biofilm-forming ability of A. baumannii plays a major role in its resistance and persistence. There is an alarming need for novel treatment strategies to control A. baumannii biofilm-associated issues. The present study demonstrated the strong antibiofilm and antivirulence efficacy of citral against A. baumannii. In addition, proteomic analysis revealed the multitarget potential of citral against A. baumannii. Furthermore, citral treatment enhances the susceptibility of A. baumannii to the host innate immune system and reactive oxygen species (ROS). Cytotoxicity analysis revealed the nonfatal effect of citral on human PBMCs. Therefore, citral could be the safest therapeutic compound and can be taken for further clinical evaluation for the treatment of biofilm-associated infections by A. baumannii.

Mechanisms Protecting Acinetobacter baumannii against Multiple Stresses Triggered by the Host Immune Response, Antibiotics and Outside-Host Environment

Acinetobacter baumannii is considered one of the most persistent pathogens responsible for nosocomial infections. Due to the emergence of multidrug resistant strains, as well as high morbidity and mortality caused by this pathogen, A. baumannii was placed on the World Health Organization (WHO) drug-resistant bacteria and antimicrobial resistance research priority list. This review summarizes current studies on mechanisms that protect A. baumannii against multiple stresses caused by the host immune response, outside host environment, and antibiotic treatment. We particularly focus on the ability of A. baumannii to survive long-term desiccation on abiotic surfaces and the population heterogeneity in A. baumannii biofilms. Insight into these protective mechanisms may provide clues for the development of new strategies to fight multidrug resistant strains of A. baumannii.

Intracellular Staphylococcus aureus persisters upon antibiotic exposure

Bacterial persister cells are phenotypic variants that exhibit a transient non-growing state and antibiotic tolerance. Here, we provide in vitro evidence of Staphylococcus aureus persisters within infected host cells. We show that the bacteria surviving antibiotic treatment within host cells are persisters, displaying biphasic killing and reaching a uniformly non-responsive, non-dividing state when followed at the single-cell level. This phenotype is stable but reversible upon antibiotic removal. Intracellular S. aureus persisters remain metabolically active but display an altered transcriptomic profile consistent with activation of stress responses, including the stringent response as well as cell wall stress, SOS and heat shock responses. These changes are associated with multidrug tolerance after exposure to a single antibiotic. We hypothesize that intracellular S. aureus persisters may constitute a reservoir for relapsing infection and could contribute to therapeutic failures.

Bacterial persister cells exhibit a transient non-growing state and antibiotic tolerance. Here, Peyrusson et al. provide evidence of metabolically active Staphylococcus aureus persisters within infected host cells exposed to antibiotics and analyse transcriptomic alterations associated with persistence.

Compounding Effects of Climate Warming and Antibiotic Resistance

Bacteria have evolved diverse mechanisms to survive environments with antibiotics. Temperature is both a key factor that affects the survival of bacteria in the presence of antibiotics and an environmental trait that is drastically increasing due to climate change. Therefore, it is timely and important to understand links between temperature changes and selection of antibiotic resistance. This review examines these links by synthesizing results from laboratories, hospitals, and environmental studies. First, we describe the transient physiological responses to temperature that alter cellular behavior and lead to antibiotic tolerance and persistence. Second, we focus on the link between thermal stress and the evolution and maintenance of antibiotic resistance mutations. Finally, we explore how local and global changes in temperature are associated with increases in antibiotic resistance and its spread. We suggest that a multidisciplinary, multiscale approach is critical to fully understand how temperature changes are contributing to the antibiotic crisis.

Aerobic composting as an effective cow manure management strategy for reducing the dissemination of antibiotic resistance genes: An integrated meta-omics study

Livestock manure is considered as an important source for spreading antibiotic resistance genes (ARGs) into the environment, and therefore poses a direct threat to public health. Whereas the effects of reused manure on soil microbial communities and ARGs have been studied extensively, comprehensive characterizations of microbial communities and ARGs of manure produced by different management methods are not well understood. Here, we analyzed the fate of microbial communities and ARGs of cow manure treated by three conventional management strategies: aerobic composting, mechanical drying and precipitation, applying an integrated-omics approach combining metagenomics and metaproteomics. Integrated-omics demonstrated that composted manure contained the lowest diversity of microbial community and ARGs compared with manure treated by other two strategies. Quantitative PCR methods revealed that the abundances of ARGs were reduced by over 83 % after composting for 14 days, regardless of the season. Besides, the potential ARG hosts Acinetobacter and Pseudomonas dominating mechanical drying process were sharply decreased in abundances after composting. The significant co-occurrence networks among bacteria, ARGs and transposase gene tnpA-01 in composting samples indicated the important role of these bacteria in the dissemination of ARGs. These findings offer insight into potential strategies to control the spread of ARGs during livestock manure reuse.

Role of antibiotic stress in phenotypic switching to persister cells of antibiotic-resistant Staphylococcus aureus

Purpose

This study was designed to evaluate phenotypic and genotypic properties of persister cells formed by Staphylococcus aureus ATCC 15564 (SAWT), oxacillin-induced S. aureus (SAOXA), ciprofloxacin-induced S. aureus (SACIP), and clinically isolated multidrug-resistant S. aureus CCARM 3080 (SAMDR).

Methods

The dose-dependent biphasic killing patterns were observed for SAWT, SAOXA, SACIP, and SAMDR in response to twofold minimum inhibitory concentrate (MIC) of ciprofloxacin. The surviving cells of SAWT, SAOXA, SACIP, and SAMDR after twofold MIC of ciprofloxacin treatment were analyzed using a metabolic-based assay to estimate the fractions of persister cells.

Results

The least persister formation was induced in SACIP after twofold MIC of ciprofloxacin treatment, showing 58% of persistence. The lowest fitness cost of resistance was observed for the recovered persister cells of SACIP (relative fitness = 0.95), followed by SAMDR (relative fitness = 0.70), while the highest fitness cost was observed for SAWT (relative fitness = 0.26). The mRNA transcripts were analyzed by RT-PCR assay in recovered persister cells pre-incubated with ciprofloxacin. The highest expression levels of stress-related genes (dnaK and groEL) and efflux pump-related genes (mepR, norA, and norB) were observed in the recovered persister cells of SAOXA and SAMDR.

Conclusion

This study provides valuable information for understanding crosstalk between antibiotic resistance, tolerance, and persistence in different antibiotic-resistant S. aureus strains.

Antimicrobial Activity of, and Cellular Pathways Targeted by, p-Anisaldehyde and Epigallocatechin Gallate in the Opportunistic Human Pathogen Pseudomonas aeruginosa

Plant-derived aldehydes are constituents of essential oils that possess broad-spectrum antimicrobial activity and kill microorganisms without promoting resistance. In our previous study, we incorporated p-anisaldehyde from star anise into a polymer network called proantimicrobial networks via degradable acetals (PANDAs) and used it as a novel drug delivery platform. PANDAs released p-anisaldehyde upon a change in pH and humidity and controlled the growth of the multidrug-resistant pathogen Pseudomonas aeruginosa PAO1. In this study, we identified the cellular pathways targeted by p-anisaldehyde by generating 10,000 transposon mutants of PAO1 and screened them for hypersensitivity to p-anisaldehyde. To improve the antimicrobial efficacy of p-anisaldehyde, we combined it with epigallocatechin gallate (EGCG), a polyphenol from green tea, and demonstrated that it acts synergistically with p-anisaldehyde in killing P. aeruginosa We then used transcriptome sequencing to profile the responses of P. aeruginosa to p-anisaldehyde, EGCG, and their combination. The exposure to p-anisaldehyde altered the expression of genes involved in modification of the cell envelope, membrane transport, drug efflux, energy metabolism, molybdenum cofactor biosynthesis, and the stress response. We also demonstrate that the addition of EGCG reversed many p-anisaldehyde-coping effects and induced oxidative stress. Our results provide insight into the antimicrobial activity of p-anisaldehyde and its interactions with EGCG and may aid in the rational identification of new synergistically acting combinations of plant metabolites. Our study also confirms the utility of the thiol-ene polymer platform for the sustained and effective delivery of hydrophobic and volatile antimicrobial compounds.IMPORTANCE Essential oils (EOs) are plant-derived products that have long been exploited for their antimicrobial activities in medicine, agriculture, and food preservation. EOs represent a promising alternative to conventional antibiotics due to their broad-range antimicrobial activity, low toxicity to human commensal bacteria, and capacity to kill microorganisms without promoting resistance. Despite the progress in the understanding of the biological activity of EOs, our understanding of many aspects of their mode of action remains inconclusive. The overarching aim of this work was to address these gaps by studying the molecular interactions between an antimicrobial plant aldehyde and the opportunistic human pathogen Pseudomonas aeruginosa The results of this study identify the microbial genes and associated pathways involved in the response to antimicrobial phytoaldehydes and provide insights into the molecular mechanisms governing the synergistic effects of individual constituents within essential oils.

Upregulation of the clpB gene in response to heat shock and beta-lactam antibiotics in Acinetobacter baumannii

The role of the clpB gene encoding HSP/chaperone ClpB was evaluated in the multiresistant antibiotic cells of Acinetobacter baumannii (RS4 strain) under stress-induced heat shock and different beta-lactams. The expression of the clpB gene was assessed by qPCR during heat shock at 45 °C and subinhibitory concentrations of ampicillin (30 μg mL^-1), amoxicillin + sulbactam (8/12 μg mL^-1), cefepime (30 μg mL^-1), sulfamethoxazole + trimethoprim (120/8 μg mL^-1) and meropenem (18 μg mL^-1). The results indicated a transient increase in clpB transcription in all treatments except cefepime. Both in the presence of ampicillin and amoxicillin/sulbactam for 20 min, the mRNA-clpB synthesis was 1.4 times higher than that of the control at time zero. Surprisingly, the mRNA-clpB levels were more than 30-fold higher after 10 min of incubation with meropenem and more than eightfold higher in the presence of trimethoprim/sulfamethoxazole. In addition, western blot assays showed that the RS4 strain treated with meropenem showed a marked increase in ClpB protein expression. Our data indicate that during exposure to beta-lactams, A. baumannii adjusts the transcription levels of the clpB mRNA and protein to respond to stress, suggesting that the chaperone may act as a key cellular component in the presence of antibiotics in this bacterium.

Label-Free Quantitative Proteomics Reveals the Multitargeted Antibacterial Mechanisms of Lactobionic Acid against Methicillin-Resistant Staphylococcus aureus (MRSA) using SWATH-MS Technology

The objective of the present study was to reveal the antibacterial mechanism of lactobionic acid (LBA) against methicillin-resistant Staphylococcus aureus (MRSA) using quantitative proteomics by sequential window acquisition of all theoretical mass spectra (SWATH-MS) to analyze 100 differentially expressed proteins after LBA treatment. Furthermore, multiple experiments were conducted to validate the results of the proteomic analysis including reactive oxygen species (ROS), virulence-associated gene expression, and the relative quantification of target proteins and genes by parallel reaction monitoring and quantitative real-time PCR. Combining the ultrastructure observations, proteomic analysis, and our previous research, the mode of LBA action against MRSA was speculated as cell wall damage and loss of membrane integrity; inhibition of DNA repair and protein synthesis; inhibition of virulence factors and biofilm production; induction of oxidative stress; and inhibition of metabolic pathways. These results suggest potential applications for LBA in food safety and pharmaceuticals, considering its multitarget effects against MRSA.

Actinobacillus seminis GroEL-homologous protein agglutinates sheep erythrocytes

Actinobacillus seminis, a commensal of ovine and caprine reproductive organs, is able to induce epididymitis in the small ruminants that it infects. In this work, we characterised two protein bands of approximately 150 kDa and 65 kDa. These proteins cross-reacted with a polyclonal serum against Gallibacterium anatis hemagglutinin and with a polyclonal serum from sheep with epididymitis, indicating that the proteins are expressed in vivo; the two proteins also interacted with biotin-labeled sheep fibrinogen and fibronectin, suggesting that they may function as adhesins. The participation of these proteins as adhesins was confirmed by a cultured human bladder cell-A. seminis adhesion assay and adherence inhibition by preincubation of A. seminis with polyclonal antiserum to the 150 kDa protein. Both proteins presented sequence identity with an A. seminis GroEL protein by mass spectrometry analysis and agglutinated glutaraldehyde-fixed sheep red blood cells. Immunogold labeling was observed by transmission electron microscopy on bacterial cells that were negatively stained, and a peroxidase reaction was detected in A. seminis biofilms, when an anti-A. seminis 150 kDa protein serum was used, indicating the presence of this protein on the surface of A. seminis and in biofilms. The A. seminis GroEL-homologue is a multifunctional protein that likely acts as a hemagglutinin.

Stressor interaction networks suggest antibiotic resistance co-opted from stress responses to temperature

Environmental factors like temperature, pressure, and pH partly shaped the evolution of life. As life progressed, new stressors (e.g., poisons and antibiotics) arose as part of an arms race among organisms. Here we ask if cells co-opted existing mechanisms to respond to new stressors, or whether new responses evolved de novo. We use a network-clustering approach based purely on phenotypic growth measurements and interactions among the effects of stressors on population growth. We apply this method to two types of stressors-temperature and antibiotics-to discover the extent to which their cellular responses overlap in Escherichia coli. Our clustering reveals that responses to low and high temperatures are clearly separated, and each is grouped with responses to antibiotics that have similar effects to cold or heat, respectively. As further support, we use a library of transcriptional fluorescent reporters to confirm heat-shock and cold-shock genes are induced by antibiotics. We also show strains evolved at high temperatures are more sensitive to antibiotics that mimic the effects of cold. Taken together, our results strongly suggest that temperature stress responses have been co-opted to deal with antibiotic stress.

Beyond proteostasis: Roles of type I chaperonins in bacterial pathogenesis

Nearly all bacterial species express two or more chaperonin genes. Recent data indicate that type I chaperonins may be key players in bacterial infections. This is partly due to the well-known contribution of chaperonins in cellular proteostasis, the latter being compromised during bacterial host infection. In addition to their protein-folding activity, it has been revealed that certain chaperonins also exhibit moonlighting functions that can contribute in different ways to bacterial pathogenicity. Examples range from inducing adhesion molecules in Chlamydophila pneumoniae to supporting intracellular survival in Mycobacterium tuberculosis and Leishmania donovani, to inducing cytokines in Helicobacter pylori to promoting antimicrobial resistance in Escherichia coli, amongst others. This article provides a thorough reviews of our current understanding of the different mechanisms involving type I chaperonins during bacteria-host interactions, and suggests new areas to be explored and the potential of finding new targets for fighting bacterial infections.

ClpA and HtpX Proteases Are Involved in Intrinsic Aminoglycoside Resistance of Stenotrophomonas maltophilia and Are Potential Aminoglycoside Adjuvant Targets

The linkage of the protease-chaperon system, SmeYZ pump, and aminoglycoside resistance was assessed in Stenotrophomonas maltophilia The clpA, clpS, clpP, and htpX genes were upregulated in response to kanamycin exposure. Of these, clpA and htpX were the primary determinants responsible for intrinsic aminoglycoside (AG) resistance. Inactivation of clpA and htpX compromised protease-mediated intrinsic aminoglycoside resistance and weakened SmeYZ pump-mediated aminoglycoside resistance, signifying HtpX and ClpA as potential AG adjuvant targets for treatment of S. maltophilia infections.

The higBA Toxin-Antitoxin Module From the Opportunistic Pathogen Acinetobacter baumannii - Regulation, Activity, and Evolution

Acinetobacter baumannii is one of the major causes of hard to treat multidrug-resistant hospital infections. A. baumannii features contributing to its spread and persistence in clinical environment are only beginning to be explored. Bacterial toxin-antitoxin (TA) systems are genetic loci shown to be involved in plasmid maintenance and proposed to function as components of stress response networks. Here we present a thorough characterization of type II system of A. baumannii, which is the most ubiquitous TA module present in A. baumannii plasmids. higBA of A. baumannii is a reverse TA (the toxin gene is the first in the operon) and shows little homology to other TA systems of RelE superfamily. It is represented by two variants, which both are functional albeit exhibit strong difference in sequence conservation. The higBA2 operon is found on ubiquitous 11 Kb pAB120 plasmid, conferring carbapenem resistance to clinical A. baumannii isolates and represents a higBA variant that can be found with multiple sequence variations. We show here that higBA2 is capable to confer maintenance of unstable plasmid in Acinetobacter species. HigB2 toxin functions as a ribonuclease and its activity is neutralized by HigA2 antitoxin through formation of an unusually large heterooligomeric complex. Based on the in vivo expression analysis of gfp reporter gene we propose that HigA2 antitoxin and HigBA2 protein complex bind the higBA2 promoter region to downregulate its transcription. We also demonstrate that higBA2 is a stress responsive locus, whose transcription changes in conditions encountered by A. baumannii in clinical environment and within the host. We show elevated expression of higBA2 during stationary phase, under iron deficiency and downregulated expression after antibiotic (rifampicin) treatment.

Heterologous Expression of Chaperones from Hyperthermophilic Archaea Inhibits Aminoglycoside-Induced Protein Misfolding in Escherichia coli

Aminoglycoside antibiotics affect protein translation fidelity and lead to protein aggregation and an increase in intracellular oxidative stress level as well. The overexpression of the chaperonin GroEL/GroES system promotes short-term tolerance to aminoglycosides in Escherichia coli. Here, we demonstrated that the coexpression of prefoldin or Hsp60 originating from the hyperthermophilic archaeon Pyrococcus furiosus in E. coli cells can rescue cell growth and inhibit protein aggregation induced by streptomycin exposure. The results of our study show that hyperthermophilic chaperones endow E. coli with a higher tolerance to streptomycin than the GroEL/GroES system, and that they exert better effects on the reduction of intracellular protein misfolding, indicating that these chaperones have unique features and functions.