Multi-resistant Pathogenic Bacteria Research Articles

One Earth: The Equilibrium between the Human and the Bacterial Worlds.

Misuse and abuse of antibiotics on humans, cattle, and crops have led to the selection of multi-resistant pathogenic bacteria, the most feared 'superbugs'. Infections caused by superbugs are progressively difficult to treat, with a subsequent increase in lethality: the toll on human lives is predicted to reach 10 million by 2050. Here we review three concepts linked to the growing resistance to antibiotics, namely (i) the Resistome, which refers to the collection of bacterial genes that confer resistance to antibiotics, (ii) the Mobilome, which includes all the mobile genetic elements that participate in the spreading of antibiotic resistance among bacteria by horizontal gene transfer processes, and (iii) the Nichome, which refers to the set of genes that are expressed when bacteria try to colonize new niches. We also discuss the strategies that can be used to tackle bacterial infections and propose an entente cordiale with the bacterial world so that instead of war and destruction of the 'fierce enemy' we can achieve a peaceful coexistence (the One Earth concept) between the human and the bacterial worlds. This, in turn, will contribute to microbial biodiversity, which is crucial in a globally changing climate due to anthropogenic activities.

Study on toxicity responses and their mechanisms in Xenopus tropicalis long-term exposure to Shigella flexneri and ciprofloxacin

The abuse and overuse of antibiotics increased not only the exposure of aquatic animals to antibiotics but also the development of resistance in pathogenic bacteria. To investigate the effects and mechanisms of exposure, a long-term experiment lasting 120 days was conducted in which Xenopus tropicalis was exposed to single and combined stress factors of multiresistant pathogenic Shigella flexneri and ciprofloxacin (CIP). The intestinal oxidative stress, immune factors and flora, as well as the brain-gut axis correlation factors of X. tropicalis, were tracked to account for the response of aquatic animals to the exogenous pollutants. SOD activity and MDA content were significantly increased in stressed X. tropicalis (p < 0.001), while the levels of proinflammatory factors (IL-1β, IFN-γ) were significantly reduced (p < 0.01). The content of intestinal beneficial bacteria decreased and that of harmful bacteria increased in the intestinal flora of the stressed X. tropicalis (p < 0.001). These results suggested that S. flexneri and CIP disturbed the intestinal flora and caused oxidative damage in the host, and the body produced a series of responses, such as oxidative stress responses and regulation of the expression of immune factors, to maintain the balance of antioxidant inflammation. Significant changes in the expression of intestinal neurotransmitters (5-HT, CGRP) and brain peptides (BDNF, NCAM, NPY) (p < 0.05) also indicated that the brain-gut axis interaction was disrupted. In addition, although the coexisting CIP could reduce intestinal toxicity caused by S. flexneri, the amount of intestinal pathogenic bacteria Desulfovibrio increased significantly. Moreover, compared with the single exposure group, SOD activity, CAT activity and MDA content were significantly reduced in the dual exposure group. Therefore, the health risks of multiresistant pathogenic bacteria on the intestinal and brain-gut axis interaction should be given more attention, and the interaction of brain-gut axis is more important when antibiotics coexist.

Bacterial Profile and Antibiotic Use in Catheter-Associated Urinary Tract Infection Patients at a Tertiary Referral Hospital in Surabaya, Indonesia

Highlights: This study examined patients with catheter-associated urinary tract infections (CAUTI) to find the prevalent bacteria and the frequency of antibiotic use. Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli sensitive to amikacin was found to be the most common pathogen in CAUTI, while ceftriaxone was the most commonly used antibiotic. Abstract Catheter-associated urinary tract infection (CAUTI) is the most typical type of infection associated with healthcare. This infection constitutes a significant health problem due to its complications and frequent recurrence. The high annual incidence of CAUTI leads to infectious complications and a high cost of treatment. Antibiotic-resistant bacteria further complicate the problem because multiresistant pathogenic bacteria are often responsible for these infections. Moreover, the lack of a comprehensive case reporting system in Indonesia hinders the determination of CAUTI incidence. This study aimed to determine the bacterial profile and antibiotic use in CAUTI patients (n=22) at the Internal Medicine Inpatient Unit of Dr. Soetomo General Academic Hospital, Surabaya, Indonesia. This retrospective descriptive study collected data from patient medical records to describe the incidence, type of bacteria, sensitivity patterns, and antibiotic use in CAUTI patients. The data collection process included collecting medical records, recording information on data collection sheets, and recapitulating and analyzing the data. The criteria for CAUTI diagnosis were a bacterial count of ≥105 CFU/mL and a catheterization that lasted more than 48 hours. Samples were selected using non-probability sampling, also known as saturation sampling. Meanwhile, variables analyzed in this study were the type of pathogenic bacteria, antibiotics used, age, and sex. Descriptive analysis was employed to analyze the data. The findings suggested that the most common bacteria were Escherichia coli, with eight of nine bacteria showing extended-spectrum beta-lactamase (ESBL) production. Female patients aged 35–65 years were the majority of the CAUTI patients. Amikacin was the antibiotic with the highest sensitivity (90.9%), while ceftriaxone was the most common type of antibiotic administered to the patients. In addition, intravenous (IV) administration was the most common route of antibiotic administration, with an average therapy duration of seven days. In conclusion, identifying the type of pathogenic bacteria and performing antibiotic susceptibility testing can help minimize antibiotic resistance and prevent more severe complications in CAUTI patients.

Evaluating the Synergistic Potency of Essential Oils and Antibiotics Against Klebsiella pneumoniae BLSE Strains.

Klebsiella pneumoniae producing extended-spectrum β-lactamases (ESBL) continues to pose huge therapeutic challenges in the treatment of infections, primarily urinary infections, due to its multidrug resistance to antibiotics. Therefore, there is a need for research on this topic to investigate ways to reduce the spread of antibiotic resistance, identify novel therapeutic approaches to treat these infections and gain a better understanding of the mechanisms of resistance. In this context, this study aimed to analyze the chemical composition of essential oils (EOs) of Thymus algeriensis, Syzygium aromaticum, and Eucalyptus globulus and assess their activity against K. pneumoniae ESBL strains, as well as the interaction type between these EOs and antibiotics used for the treatment of K. pneumoniae ESBL infections. The composition of the EOs was determined by gas chromatography-mass spectrometry (GC-MS). The activity of EOs was tested using the disc diffusion and liquid microdilution methods. The type of interaction between EOs and antibiotics was studied using the agar disk diffusion and chessboard methods. The analysis of the EO of T. algeriensis showed that the main compounds were thymol (23.14%), linalool (18.44%), and p-cymene (16.17%). The main constituents of EO of E. globulus were eucalyptol (54.29%), α-pinene (17.32%), aromadendrene (7.02%), and pinocarveol (6.32%). As for the EO of S. aromaticum, the major constituents were eugenol (80.46%) and eugenol acetate (16.23%). Results of the activity tests showed that all three EOs were active against the tested strains, with inhibition diameters ranging from 7.39±0.44mm to 32.4±1.05mm and minimum inhibitory concentrations (MICs) varying from 2 to 441.5±5.66 mg/ml. A synergistic interaction was obtained between amoxicillin-clavulanic acid and T. algeriensis EO against two strains of K. pneumoniae ESBL. These results demonstrate the potential of our EOs to inhibit multi-resistant pathogenic ESBL strains, as well as their synergistic interaction with antibiotics used in therapy, which could be an alternative to the use of antibiotics alone in treatment to fight against these multi-resistant pathogenic bacteria.

An Efficient, Multiplexed Strategy for Instant Detection of Bacterial Biomarker by a Lanthanide-Organic Material.

Water contamination is a highly critical issue owing to its strong relationship to human health. In addition to chemical pollutants, microorganisms such as multiresistant pathogenic bacteria have received significant attention from the World Health Organization. The main problem associated with monitoring pathogenic bacteria in water is the interference from concomitant species and their low concentrations. To address this problem, we synthesized a bilanthanide-organic material as an efficient luminescence sensor for the detection of Pseudomonas aeruginosa, a representative bacterium, via its two unique biomarkers: 1-hydroxyphenazine (1-HX) and 2-aminoacetophenone (2-AA). This multiplexed sensing approach overcomes a common issue encountered by single-marker luminescence sensors that may report false positives due to coexisting species in the complex environment. High sensitivities and low limits of detection for 1-HX and 2-AA were obtained with very fast response time. The key structural factors governing the high-performance sensing function were revealed. This work provides an alternative route for the effortless and instant detection of bacterial biomarkers in water.

Tagetes lucida Cav. essential oil and the mixture of its main compounds are antibacterial and modulate antibiotic resistance in multi-resistant pathogenic bacteria.

We evaluated an essential oil (EO) of Tagetes lucida Cav. and the mixture of its main compounds against multi-drug resistant bacteria. We found that EO and the partially reconstituted blend of its main components have antibacterial activity and inhibit antibiotic resistance (ampicillin, chloramphenicol, nalidixic acid, vancomycin and imipenem) in strains of Staphylococcus aureus ATCC 29213 and Pseudomonas aeruginosa HIM-MR01. The T. lucida EO alone or added to the antibiotics showed antimicrobial activity against S. aureus and P. aeruginosa. The EO main bioactive compounds were methyl eugenol (relative abundance in EO: 46·15%), estragole (32·93%), linalool (2·48%) and geraniol (0·33%). The mixture (PREO) of those compounds at those proportions inhibited the growth of P. aeruginosa in 45% at 683·62 µg ml-1 and that of S. aureus in 51·7% at 39·04 µg ml-1 . The PREO had higher antibacterial and modulatory activities than the original EO. In conclusion, we overcame the unpredictability of EO activity (due to their natural variability) by determining which EO components inhibited bacteria and then producing a PREO to generate a reproducible mixture with predictable antibacterial and modulation of resistance activities. Thus, the PREO, and its components, show potential as alternatives to manage multidrug-resistant pathogens.

Phytochemical characterization, antioxidant potential and antimicrobial activity of Averrhoa carambola L. (Oxalidaceae) against multiresistant pathogens

The objective of this work was to perform the phytochemical characterization, to determine total phenols, antioxidant (AAO%) and antimicrobial potential of the ethanolic extracts of carambola. The phytochemical study was carried out through a qualitative analysis of the chemical constituents and quantitative determination of the phenol content By the Folin-Ciocalteu test. Qualitative and quantitative antioxidant tests were performed using the DPPH method (2,2 diphenyl-1-picryl-hydrazila) and iron reduction (FRAP). The minimum inhibitory concentration (MIC) was determined by microdilution in 96-well plates. The presence of pyrogallic tannins, steroids and saponins has been identified. The highest total phenol content, quantified in the samples, was found in the stem bark (0.0866 mgEAG/g) and in the fruit (0.0734 mgEAG/g). In the antioxidant evaluation, the extracts of the green fruit bagasse (AAO% 71.9%,) and stem bark at 50 μg/mL (AAO% 94%) with CE50 23.7 μg/mL. Leaf extracts, stem bark, ripe fruit bagasse and green fruit bagasse presented MICs of 100 μg/mL against multiresistant pathogenic bacteria and fungi.

Evaluation of the Bacteriological risk of solid Medical and Pharmaceutical waste from a Moroccan Hospital Center

Medical and pharmaceutical waste (MPW) pose a big problem in society and at the healthcare centers because they cause a bacteriological risk in the living being and the environment. Morocco, since 1991, has developed a legal arsenal on medical and pharmaceutical waste. In order to identify pathogens at the level of hospital waste, and to assess their treatment system, this study was carried out at a Moroccan hospital center. The analysis of the samples was performed at the medical biology laboratory of the same hospital. Eleven samples were done at four care units, including two at the internal storage room before treating waste with an ECODAX T300 type mill, and two after treatment from the ground material and leachate. Before crushing 63.6% (7/11) of the samples gave positive cultures. The presence of pathogenic microorganisms such as (Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Pseudomonas stuzerie and Pseudomonas fluorescens) have been identified and their sensitivity to antibiotics has also been determined. After the grinding cycle, the microbiological characterization of the samples on ground material and leachate revealed 100% of bacterial presence, the microorganisms (Escherichia coli and Klebsiella pneumoniae) were identified. The results show that hospital waste encloses multi-resistant pathogenic bacteria before and after their treatment, which raises a big question mark on the quality and effectiveness of the treatment of MPW.

Nanoparticles as therapeutic options for treating multidrug-resistant bacteria: research progress, challenges, and prospects.

Resistance to antimicrobial agents has been alarming in recent years and poses a huge public health threat globally according to the WHO. The increase in morbidity and mortality resulting from microbial infections has been attributed to the emergence of multidrug-resistant microbes. Associated with the increase in multidrug resistance is the lack of new and effective antimicrobials. This has led to global initiatives to identify novel and more effective antimicrobial agents in addition to discovering novel and effective drug delivery and targeting methods. The use of nanoparticles as novel biomaterials to fully achieve this feat is currently gaining global attention. Nanoparticles could become an indispensable viable therapeutic option for treating drug-resistant infections. Of all the nanoparticles, the metals and metal oxide nanoparticles appear to offer the most promise and have attracted tremendous interest from many researchers. Moreover, the use of nanomaterials in photothermal therapy has received considerable attention over the years. This review provides current insight on antimicrobial resistance as well as the mechanisms of nanoparticle antibacterial activity. It offers an in-depth review of all the recent findings in the use of nanomaterials as agents against multi-resistant pathogenic bacteria. Also, nanomaterials that can respond to light stimuli (photothermal therapy) to kill microbes and facilitate enhanced drug delivery and release are discussed. Moreover, the synergistic interactions of nanoparticles with antibiotics and other nanomaterials, microbial adaptation strategies to nanoparticles, current challenges, and future prospects were extensively discussed.Graphic abstract

Using an Ensemble to Identify and Classify Macroalgae Antimicrobial Peptides.

The rapid spread of multi-drug resistant microbes has lead researchers to discover natural alternative remedies such as antimicrobial peptides (AMPs). In the first line of defense, AMPs display a broad spectrum of potent activity against multi-resistant pathogenic bacteria, viruses, fungi, and even cancer. AMPs can be further characterised into families according to amino acid composition, secondary structure, and function. However, despite recent advancements in rapid computational methods for AMP prediction from various mammalian, aquatic, and terrestrial species, there is limited information regarding their presence, functional roles, and family type from marine macroalgae. In this paper, we present a promising two-tier ensemble of heterogeneous machine learning models that integrates seven well-known machine learning classifiers to predict AMPs from macroalgae. The first tier of the ensemble consists of a suite of binary classifiers that identify AMPs from protein sequence data which are then forwarded to a second-tier multi-class ensemble to characterise their functional family type. The two-tier ensemble was successfully used to identify 39 putative AMP sequences in 12 macroalgae species from three different phyla groups. The approach we describe is not limited to AMPs and can also be applied to search sequence data for other types of proteins.

Assessment of the microbiological quality of beverages sold in collective cafes on the campuses of the University of Abomey-Calavi, Benin Republic

Fresh juices are highly nutritious foods for human beings, but the inability to observe requirements for their preparation, packaging and storage subjects them to microbial contamination which poses a potential health risk to consumers. The purpose of this study was to evaluate the microbiological quality of beverages sold within the cafes of the campuses of Abomey-Calavi University (Benin). A survey carried out among beverage vendors showed that the sources of contamination were uncontrolled and the raw materials used were of questionable quality as the operators lacked good hygienic practices. Thus, the microbial quality of forty-five samples of four types of beverages sold in these cafes was investigated for mesophilic aerobic flora, Coliforms, Escherichia coli, Staphylococcus aureus, sulfate-reducing anaerobic spores, fungal flora and Salmonella spp. using standardized methods. Then, molecular studies identified the pathogenic strains isolated from the beverages. An antibiotic susceptibility test was performed on the strains identified for the detection of multi-resistant bacteria. These analyses revealed a non-compliance rate of 100% in the analyzed samples. The indicators that caused this non-compliance in the samples were mesophilic aerobic flora, coliforms and fungi. In addition, 85.7% of the samples contained other Enterobacteriaceae including Klebsiella pneumoniae, Morganella morganii, Kluyvera georgiana, Citrobacter murliniae, Yersinia intermedia. While the non-compliance rates of the samples for Salmonella spp and E.coli were 4.4% each, the non-compliance rate for S. aureus was 2.2% with the presence of sometimes multi-resistant pathogenic bacteria. Sellers' awareness of good hygiene practices is important for improving the quality of food sold.

Antimicrobial Peptides Impair Bacteria Cell Structures within Seconds

Novel antibiotics based on membrane-active antimicrobial peptides (AMPs) are promising candidates for defending the spread of diseases caused by multi-resistant pathogenic bacteria. Notwithstanding the number of works that explore the relationship between AMP activity and membrane architecture, the dynamics and full mechanism that lead to cell death are currently not clear. This prompted us to investigate the cinematographic effects of human lactoferricin derivatives on live E. coli using high-resolution small-angle X-ray and neutron scattering (USAXS/SAXS - VSANS/SANS) measurements and complementary techniques.

Phytochemical Screening, Antibacterial and Synergistic activity of Dittrichia Viscosa Extracts against Multi-Resistant Pathogenic Bacteria

Study contextual: Faced with the global problem of antimicrobial resistance, and the use of traditional medicine for the research of antibacterial biomolecules. Aim: our work focused on the valorization of a medicinal plant Dittrichia viscosa which has many therapeutic and culinary virtues worldwide. Methods: To do this, a phytochemical screening of the leafy stems of the plant is carried out according to a set of physicochemical reactions, as well as an in vitro evaluation of the antibacterial activity, of the aqueous and ethanolic extracts against multi-resistant bacterial strains, by microdilution technique on microplates. An evaluation of the synergistic interaction between extracts and weakened antibiotics against pathogenic bacteria was also highlighted in this study. Results: The tests revealed the richness of Dittrichia viscosa species by tannins, flavonoids, saponosides, sterols and triterpenes. As for the antibacterial effect, the MICs range from 0.858±0.29 to 66.66 ± 0.00 mg / ml and the MBCs from 4.300 ± 1.01 to 11.610 ± 2.31 mg / ml is an interesting antibacterial activity. Regarding the combination of extracts with antibiotics tested, it revealed a synergistic action inducing an amplification of the antibacterial power of Penicillin, Imipenem and Erythromycin with a rate that reaches 471%. Conclusion: The results of this study show that the aqueous and ethanolic extracts of Dittrichia viscosa have interesting and promising antibacterial activity in the pharmaceutical, food and cosmetic industries.

Deciphering how Cpl-7 cell wall-binding repeats recognize the bacterial peptidoglycan

Endolysins, the cell wall lytic enzymes encoded by bacteriophages to release the phage progeny, are among the top alternatives to fight against multiresistant pathogenic bacteria; one of the current biggest challenges to global health. Their narrow range of susceptible bacteria relies, primarily, on targeting specific cell-wall receptors through specialized modules. The cell wall-binding domain of Cpl-7 endolysin, made of three CW_7 repeats, accounts for its extended-range of substrates. Using as model system the cell wall-binding domain of Cpl-7, here we describe the molecular basis for the bacterial cell wall recognition by the CW_7 motif, which is widely represented in sequences of cell wall hydrolases. We report the crystal and solution structure of the full-length domain, identify N-acetyl-D-glucosaminyl-(β1,4)-N-acetylmuramyl-L-alanyl-D-isoglutamine (GMDP) as the peptidoglycan (PG) target recognized by the CW_7 motifs, and characterize feasible GMDP-CW_7 contacts. Our data suggest that Cpl-7 cell wall-binding domain might simultaneously bind to three PG chains, and also highlight the potential use of CW_7-containing lysins as novel anti-infectives.

The susceptibility to fosfomycin of Gram-negative bacteria isolates from urinary tract infection in the Czech Republic: data from a unicentric study

BackgroundAgainst a background of rapid increase of β-lactamase-producing or multi-resistant pathogenic bacteria and the resulting lack of effective antibiotic treatment, some older antibiotics have been tested for new therapeutic uses. One of these is fosfomycin, to which according to studies these resistant bacteria are very sensitive. Our study was designed because there is no data on the fosfomycin susceptibility rate in the Czech Republic.MethodIn this study from January 2013 to June 2014 3295 unique isolates of Gram-negative bacteria which had caused urinary tract infections were examined. The antibiotic susceptibility was measured by disk diffusion test. Both EUCAST and CLSI guidelines criteria (for fosfomycin only) were used for the antibiotic susceptibility evaluation.ResultsThe most frequently tested bacterial isolates were Escherichia coli (51.3%, n = 1703), Klebsiella pneumoniae (19.4%, n = 643) and Proteus spp. (11.8%, n = 392). Among all isolates 29.0% (n = 963) were resistant to fluoroquinolones, 11.3% (n = 374) produced extended spectrum β-lactamase and 4.2% (n = 141) produced AmpC β-lactamase. The overall in vitro susceptibility was significantly higher for fosfomycin compared to the other tested per-oral antibiotics (nitrofurantoin, ampicillin, co-trimoxazole, ciprofloxacin and cefuroxime) against all tested Gram-negative rod isolates (excluding Morganella morgani and Acinetobacter spp. isolates). Fosfomycin also remained highly active against those isolates with extended spectrum β-lactamase (ESBL) production (95.8% in Escherichia coli isolates and 85.3% in Klebsiella pneumoniae isolates), unlike other tested per-oral antibiotics, which showed significant (p < 0.0001) susceptibility decrease.ConclusionWe have confirmed in the Czech Republic the very high susceptibility to fosfomycin trometamol of urinary tract infection pathogens, particularly Gram-negative rods including those producing β-lactamase.

Mobilizable genomic islands, different strategies for the dissemination of multidrug resistance and other adaptive traits.

ABSTRACTMobile genetic elements are near ubiquitous DNA segments that revealed a surprising variety of strategies for their propagation among prokaryotes and between eukaryotes. In bacteria, conjugative elements were shown to be key drivers of evolution and adaptation by efficiently disseminating genes involved in pathogenicity, symbiosis, metabolic pathways, and antibiotic resistance. Conjugative plasmids of the incompatibility groups A and C (A/C) are important vehicles for the dissemination of antibiotic resistance and the consequent global emergence and spread of multi-resistant pathogenic bacteria. Beyond their own mobility, A/C plasmids were also shown to drive the mobility of unrelated non-autonomous mobilizable genomic islands, which may also confer further advantageous traits. In this commentary, we summarize the current knowledge on different classes of A/C-dependent mobilizable genomic islands and we discuss other DNA hitchhikers and their implication in bacterial evolution. Furthermore, we glimpse at the complex genetic network linking autonomous and non-autonomous mobile genetic elements, and at the associated flow of genetic information between bacteria.

Antibacterial synergism of extracts from climbers belonging to Bignoniaceae family and commercial antibiotics against multi-resistant bacteria

The objective of this work was to study the effect of interactions between four extracts of climbers belonging to the Bignoniaceae family and commercial antibiotics against multi-resistant pathogenic bacteria and to identify the main antibacterial compounds in the most active extract. The plant species tested were Adenocalymma marginatum, Amphilophium vauthieri, Cuspidaria convoluta and Fridericia caudigera. Synergy between the plant extracts with ampicillin, gentamicin and oxacillin was studied by the checkerboard assay method against multi-resistant Staphylococcus strains and Gram negative bacteria. A synergistic effect was observed in all extracts. The F. caudigera leaf extracts were most active. The main antibacterial compounds present in these extracts were isolated and identified by UV–VIS spectra and HPLC/MS/MS. Three main active compounds were identified, apigenin, chrysin and luteolin. Our results indicated that the combinations of species extracts of Bignoniaceae family and commercial antibiotics could be useful in the treatment of many infectious diseases caused by multi-resistant bacteria. In addition, the results highlighted the potential phyto-therapeutic of a total set of phytochemical compounds within a single plant.

Assessment of factors influencing the outcome of new-onset infiltrative pulmonary tuberculosis

To identify predictors for the poor outcome of infiltrative pulmonary tuberculosis (IPTB). The social, epidemiological, and medical risk factors and clinical features of IPTB were assessed in 130 first detected patients. The findings were classified using a cluster analysis and then a variance analysis, followed by the ranking of its results. The primarily diagnosed disseminated destructive process with respiratory and cardiopulmonary failure, excretion of both resistant and multi-resistant pathogenic bacteria had a strong impact on the poor outcome of tuberculosis (TB) in the first detected patients. Its outcome was also influenced by a set of social factors, such as poor material living conditions, stay in corrective labor facilities, and a lack of education. The unfavorable outcome of TB was significantly due to organizational factors, such as bad habits; refusal to undergo fluorography during a few years; and a medical factor as comorbidities. Based on the identified factors, the authors formulated recommendations for working with the first detected IPTB patients at risk for a poor disease outcome.

Bioactive volatile organic compounds from Antarctic (sponges) bacteria

Antarctic bacteria represent a reservoir of unexplored biodiversity, which, in turn, might be correlated to the synthesis of still undescribed bioactive molecules, such as antibiotics. In this work we have further characterized a panel of four marine Antarctic bacteria able to inhibit the growth of human opportunistic multiresistant pathogenic bacteria belonging to the Burkholderia cepacia complex (responsible for the 'cepacia' syndrome in Cystic Fibrosis patients) through the production of a set of microbial Volatile Organic Compounds (mVOCs). A list of 30 different mVOCs synthesized under aerobic conditions by Antarctic bacteria was identified by GC-SPME analysis. Cross-streaking experiments suggested that Antarctic bacteria might also synthesize non-volatile molecules able to enhance the anti-Burkholderia activity. The biosynthesis of such a mixture of mVOCs was very probably influenced by both the presence/absence of oxygen and the composition of media used to grow the Antarctic strains. The antimicrobial activity exhibited by Antarctic strains also appeared to be more related to their taxonomical position rather than to the sampling site. Different Bcc bacteria were differently sensitive to the 'Antarctic' mVOCs and this was apparently related neither to the taxonomical position of the different strains nor to their source. The genome sequence of three new Antarctic strains was determined revealing that only P. atlantica TB41 possesses some genes belonging to the nrps-pks cluster. The comparative genomic analysis performed on the genome of the four strains also revealed the presence of a few genes belonging to the core genome and involved in the secondary metabolites biosynthesis. Data obtained suggest that the antimicrobial activity exhibited by Antarctic bacteria might rely on a (complex) mixture of mVOCs whose relative concentration may vary depending on the growth conditions. Besides, it is also possible that the biosynthesis of these compounds might occur through still unknown metabolic pathways.

Influence of different pre-treatment methods on isolation of extracts with strong antibacterial activity from lichen Usnea barbata using carbon dioxide as a solvent

Multiplication and spreading of multiresistant pathogenic bacteria that cause fatal infections in humans and animals have boosted research on implementation of newer technologies for producing natural substances with strong antibacterial activities. In this study, SFE from lichen Usnea barbata was investigated for different pre-treatment methods with respect to extracts’ yield, usnic acid recovery and antibacterial activity against more than thirty methicillin resistant staphylococci strains. Extraction of U. barbata with subcritical carbon dioxide was studied as well. Extraction yield, usnic acid content and antibacterial activity of the extracts were strongly affected by the pre-treatment method. Intensive pre-treatment methods such as flaking and cutting+grinding caused a considerable comminution of the lichen thallus and enabled high extraction yields. On the other hand, mild pre-treatment of the lichen such as impact+shearing enabled isolation of extracts with lower MIC values. Experimental results indicated that extraction with liquid carbon dioxide at 30MPa and 25°C was the most favorable condition at which a satisfactory high extraction yield was obtained (2.08%). Extract isolated with liquid carbon dioxide had a high usnic acid content in the extract (632g/kg) and a very strong antibacterial activity (average MIC of 19.11μg/mL). Antibacterial activity of all the extracts against tested strains was comparable to the pure usnic acid or even stronger. This study indicated a potential use of the supercritical extracts of U. barbata in pharmaceutical formulations for treatment of infections caused by staphylococci.