Commonly used antibiotics use multiple administrations for providing a continuous bactericidal effect but can increase systemic toxicity, as well as lead to bacterial drug resistance [1,2]. The use of plant-based antibacterial compounds in combination with conventional antibiotics to treat drug-resistant infections could be an alternative to overcoming the problem of bacterial resistance [3]. The combination of antibiotics with plant-based antibacterial compounds has been shown synergistic advantages due to the inhibition of drug efflux and the presence of alternative mechanisms of action [4]. Moreover, the nanoencapsulation of antibiotics is another effective technique to overcome antibiotic resistance [1]. Nano-encapsulated antimicrobials have a better performance in comparison with traditional antibiotics due to their small size which leads to better interaction with bacterial cells [5]. The different nanocarriers are effective in efficiently administering antibiotics by improving pharmacokinetics and accumulation while reducing the adverse effects [6]. Additionally, the surface engineering of nanocarriers provides benefits such as targeting and modulating various resistance mechanisms [7]. Furthermore, most nanocarriers are suitable platforms for co-loading of plant-based antibacterial compounds and traditional antibiotics to provide synergistic effects [8]. This study outlines recent attempts to combat infectious diseases, with a focus on the use of plant-based nanoantibiotics as novel tools to address today's issues in infectious disease treatment.

Multiple drug-resistant bacterial strains are showing new different mechanisms to overcome the antimicrobial action which reduces the efficacy of conventional antibiotics [1]. Therefore, drug discovery research has focused on developing fast, effective and safe alternatives to prevent this multiresistance. Phlorotannins are a diverse class of polyphenols, secondary metabolites described in brown algae, that are mainly constituted of polymers of phloroglucinol and depending on their linkage and structure can be classified mainly as fucols, fucophlorethols, eckols and phloroethols [2]. These polyphenols have been described in both macro- and microalgae, suggesting that they can be recovered from a great variety of sources [2]. Phlorotannins have been extensively described to possess several biological properties, foremost as antioxidant and antimicrobial compounds. Several in vitro reports have described that phlorotannins showed growth inhibition and bactericidal effects against Gram + (e.g. Bacillus cereus, Streptococcus pneumoniae, Staphylococcus aureus) and Gram ‒ bacteria (e.g. Salmonella sp., Campylobacter jejuni, Pseudomonas aeruginosa), also including antibiotic-resistant strains like MRSA [3]. Although the mechanisms of action of this group of compounds has not been fully elucidated, tannins are described to interact with membrane proteins and key metabolic enzymes, impeding bacterial growth and resulting in membrane lysis [3,4]. Moreover, different phlorotannins were able to inhibit bacterial biofilm formation, production of quorum-sensing molecules, and also viral replication (e.g. influenza) [5,6]. Few in vivo studies support their effectiveness as antibiotics, whereas clinical trials studying other properties, consistently report high bioavailability and null toxicity of phlorotannins [6,7]. Considering current evidence, phlorotannins could be considered as interesting candidates for antibiotic therapy clinical trials. The diversity of these natural compounds provides a promising gateway for researchers and the pharmaceutical industry to develop novel nontoxic, cost-effective and highly efficient antibacterial formulations with a broad scope of applications. This review focuses on potential use of phlorotannins as natural antimicrobial compounds, supported by scientific evidence.

In the last 30 years, a significant increase in resistance of pathogenic microorganisms (to humans and animals) to conventional therapeutic strategies has been observed, in an alarming manner, which constitutes, per se, a drive force and need for the search of new products or bioactive molecular systems of low toxicity, high specificity of action and bioavailability, for the treatment of diseases (dermatological, respiratory, gastrointestinal, etc.) generated by microbial pathogens. In this molecule- antimicrobial bioactivity race, should be emphasized the ethnobotanical and traditional use of plants and microorganisms and their secondary metabolites (botanical extracts, peptides, monoterpenes and triterpenoids, alkaloids) modified or not biotechnologically. In this context, it should be noted that the search for agents with antimicrobial activity from natural sources such as terrestrial invertebrates associated with mega edapho-fauna has not been considered as a source of poly-component systems or molecular entities with potential antimicrobial action. The defensive secretions of Diplopods (millipedes, Spirobolida), given the presence of benzenoids and volatile monoterpenes, possess recognized antimicrobial activity. In the present communication we report the isolation of repugnatorial secretions from millipedes gen. Rhinocricus inhabiting in Cuban neotropical island conditions and the analysis, by GC/Ms, of their composition pattern, highlighting the existence of hydroxylated quinonoids (methylhydroxylated benzoquinones, phenolic derivatives, amines, aldehydes) that show, under in vitro conditions, a significative antimicrobial activity against pathogenic microorganisms (Candida albicans, Epidermophyton sp, Mycosporum sp, etc.). These natural derivatives can be used, as bioactive components, in formulations for topical treatment of epidermal infections of microbial origin.

The dissemination of KPC carbapenemase-producing Pseudomonas aeruginosa is currently considered a public health problem. Although these enzymes are responsible of being part of the resistance to carbapenem, the genetic mechanisms that have favored the spread of KPC in this species are still unclear. Therefore, the objective of this research was to identify the mobile genetic elements (MGE) associated with the mobilization of bla_KPC in P. aeruginosa, through a systematic review, to provide valuable information for the epidemiological knowledge of circulating strains worldwide.

The medical literature analysis and retrieval system online, were searched without language restrictions via PubMed and EMBASE on September 31, 2021. We select studies that included isolates of P. aeruginosa resistant to carbapenems and a description of the KPC mobilization platforms. Of the 132 potential articles, 42 were included after a screening based on inclusion/exclusion criteria. A descriptive analysis of the MGE was conducted to observe the dissemination factors of resistance to carbapenems.

The collected articles were reported on 12 countries located on America (n=42:62%), Asia (n=42:24%) and Europe (n=42:2%); from this information we identified 494 isolates of P. aeruginosa harboring bla_KPC related with the different ST, such as: ST463 (n=494:22%), ST654 (n=494:13%), ST664 (n=494:4%) and ST235 (n=494:3%). Additionally, most isolates were associated with bla_KPC-2, a largely reported variant.

We also analyzed the general location of this resistance gene (Plasmids (n=494:46%), chromosome (n=494:1%), non-specified (n=494:52,8%)) and its surroundings, revealing that the most common genetic environment is the Tn4401 (n=494:17%), followed by a diversity of non-Tn4401 elements (n=494:11%).

This constitutes the first review about the genetic panorama of KPC dissemination in P. aeruginosa strains by MGE, and suggest that the plasmids and some transposable elements, are responsible for the epidemiological success worldwide; also, the different reported STs reveal alarming dynamic of the increase in carbapenem resistant P. aeruginosa clones.

Surgical site infections (SSI) are one of the main healthcare-related infections in developing nations. Regardless of upgrades in surgical strategy and the utilization of best disease avoidance techniques, SSI stayed the significant reason for medical clinic obtained infections. Subsequently, the target of this paper was to describe risk factors for SSI and the utilization of antibiotics to decrease the risk involved for the SSI. SSI is a possibly morbid and expensive intricacy of medical procedure. In this way, an underlying pursuit recognized various titles distributed in 2012-2022. Extracted data including design of study and procedure, revealed combined occurrence and time taken as post-surgery until the beginning of SSI, and probabilities proportions and associated inconstancy for all variables considered in univariate and additionally multivariable investigations. In a wide survey of available works, risk factors for SSI were portrayed as depicting decreased wellness, patient fragility, medical procedure length, and intricacy. The occurrence of SSI was high in the review set. There were critical quantities of contributing variables to the event of surgical site infections. Recognition of risk factors habitually connected with SSI considers the identification of such patients with the best requirement for ideal protective actions to be recognized and pre-treatment before medical procedure.

Spiramycin is a 16-membered macrolide used in human medicine as an antibacterial and antiparasitic agent (active against Toxoplasma spp.). Spiramycin is effective against various bacterial pathogens including Gram-positive (Staphylococcus aureus, streptococci of groups A, B, C and D, and pneumococcus), Gram-negative (Neisseria, Legionella) and more (Mycoplasma, Chlamydia). In contrast, Pseudomonas aeruginosa is considered intrinsically resistant to macrolides including azithromycin and spiramycin. Despite the results of in vitro susceptibility tests, interest in macrolides in the treatment of some pseudomonal infections arose from both clinical and preclinical studies. For example, in a mouse model of P. aeruginosa bacteraemia, treatment with erythromycin led to a survival rate of 80% compared with 20% in controls. For this reason, macrolides have drawn attention as adjunct therapy against chronic and/or biofilm-mediated P. aeruginosa infections. While most of the studies on the antivirulence activity of macrolides focus on erythromycin and on its derivative azithromycin, there is almost no information on spiramycin, which differs from erythromycin for a larger macrolactone ring and a different sugar decoration. In this study, we test spiramycin as an antivirulence factor using different assays to characterize the phenotype changes in P. aeruginosa.

Our results show as spiramycin inhibits the production of pyocyanin, pyoverdine and rhamnolipids in P. aeruginosa. Moreover, the treatment of the bacterium with this antibiotic inhibits biofilm formation in an artificial biomimetic system and blocks the motility on the agar surface. Finally, to test the effect of spiramycin against P. aeruginosa in an in-vivo system we used the insect Galleria mellonella and the preliminary data obtained by this colonization model show a marked reduction in mortality. Finally, using computational modeling and docking simulation we explored the probable mechanisms of action of spiramycin against P. aeruginosa.

The protein family YjgF/YER057c/UK114 (Rid) is widespread in all domains of life. The only member of this superfamily biochemically well-characterized is the archetypal RidA that is involved in detoxification. Besides RidA, seven families named Rid1 to Rid7 are identified in prokaryotes. A conserved arginine residue is shared by all Rid members with the detoxifying activity. Conversely, other members lack the arginine residue, and their role is mysterious.

A step toward understanding the role of these proteins has been achieved by studying a protein, called Rid7C, in Nonomuraea gerenzanensis, a rare actinomycete used to produce the A40926, which is the precursor of dalbavancin, an FDA approved antibiotic effective against Staphylococcus aureus MRSA. This actinomycete is characterized by the presence of duplicated genes encoding β-subunit of RNA polymerase: rpoB(S) (wild-type gene) and rpoB(R) (specialist rpoB gene). RpoB(R) isoform controls the morphological differentiation and the activation of secondary metabolism (including the production of A40926). Translation of the RpoB(R) mRNA is negatively modulated by a self-complementary hairpin loop in its 5’-UTR which hides the Shine & Dalgarno sequence. Rid7C is the endoribonuclease involved in resolving the hairpin loop by removing a ~80 nt segment from the rpoB(R) mRNA end. In addition, Rid7C may be associated with ribonuclease P M1 RNA, although M1 RNA is not required for rpoB(R) mRNA processing in vitro. Computational, in vitro and in vivo evidence suggest that Rid7C endoribonuclease activity is inhibited by A40926 suggesting the existence of a negative feedback loop on A40926 production, and a role of the A40926 in the modulation of differentiation in this microorganism. This new molecular tool, namely the co-overexpression of RpoB (R) and Rid7C, can be used to increase antibiotic production in actinomycetes. Computational modelling suggests that Rid7 proteins may be involved in the molecular mechanisms of infections in pathogens, so these proteins could be a new target for innovative anti-infective agents.

Biofilm-production facilitates the survival of Staphylococcus spp. both in harsh environmental conditions, and provides protection against in vivo and in protecting against various environmental noxa. The possible relationship between the antibiotic-resistant phenotype and biofilm-forming capacity has raised considerable interest in various bacterial species. In the present study, the interdependence between biofilm-forming capacity and the antibiotic-resistant phenotype in 299 environmental Staphylococcus spp. (S. aureus n=143, non-aureus staphylococci [NAS] n=156) was determined. Antimicrobial susceptibility testing and detection of methicillin-resistance (MR) was performed. Biofilm-forming capacity was assessed using Congo Red agar (CRA) plates and a crystal violet micro-titer-plate-based (CV-MTP) method. MR was identified in 46.9% of S. aureus and 53.8% of NAS isolates (p>0.05). Among the commonly-used antimicrobials, resistance was highest for clindamycin (57.9%), erythromycin (52.2%) and trimethoprim-sulfamethoxazole (51.1%). Based on the CRA plates, biofilm was produced by 30.8% of S. aureus and 44.9% of NAS, while based on the CV-MTP method, 51.7% of S. aureus and 62.8% of NAS were identified as strong biofilm-biofilm producers. (mean OD₅₇₀ values: S. aureus: 0.779±0.471 vs. NAS: 1.053±0.551; p<0.001). No significant differences in biofilm-formation were shown observed on the basis of MR (susceptible: 0.824 ± 0.325 vs. resistant: 0.896 ± 0.367; p=0.101). On the other hand, significant differences in biofilm-formation were identified based on rifampicin susceptibility (S: 0.784 ± 0.281 vs. R: 1.239 ± 0.286; p=0.011). The association of the antibiotic-resistant phenotype and biofilm-formation is still inconclusive, due to the heterogeneity of the results in the presently available studies, however, the understanding of these mechanisms in Staphylococcus spp. is crucial to appropriately address the therapy and eradication of these pathogens.

Background: Over the past years, Acinetobacter baumanni has emerged as a serious nosocomial pathogen especially due to its extensively resistant antimicrobial profile. Colistin is currently used as one of the last resort agents to treat the related infections but resistance because of monotherapy has increasingly been reported. We evaluated the in vitro susceptibility of colistin-based antimicrobial combinations against extensively drug-resistant (XDR) A. baumannii isolates from a tertiary hospital in Northern Greece.

Materials: One hundred A. baumannii single clinical isolates with resistance to carbapenems and colistin between March and October 2021 were included in the study; 46 were isolated from blood, 41 from bronchoalveolar secretions, 6 from urine, 3 from central lines, 3 from skin and soft tissues and 1 from cerebrospinal fluid. Antimicrobial susceptibility testing was performed by Vitek2 (bioMérieux, France) whereas tigecycline, rifampicin, daptomycin were tested with MIC test strip (Liofilchem, Italy) and colistin with broth microdilution method (Liofilchem, Italy). MIC range, MIC50, MIC90 and resistance rates were calculated according to EUCAST breakpoints. The MIC test strip fixed ratio method was used for the synergistic activity for three antimicrobial combinations of colistin with either meropenem or rifampicin or daptomycin. The results were interpreted using fractional inhibitory concentration index (FICI). 'Synergy', 'additivity', 'indifference' and 'antagonism' were interpreted when the FICI was ≤0.5, >0.5 - ≤1, >1 - ≤4 and >4, respectively.

Results: All the studied strains displayed high rates of resistance to major classes of antimicrobials (>97%) including carbapenems (imipenem, meropenem), aminoglycosides (amikacin, gentamicin) and with 100% resistance to colistin. MIC50/MIC90 (mg/L) for tigecycline were 3/6, for ampicillin/sulbactam 32/32, for rifampicin 6/32 and for daptomycin 256/256. All 100 isolates were tested for colistin-meropenem combination exhibiting 87% synergy (FICI range=0.00078-0.5) while 13% additivity (FICI range=0.56-0.84). Although rifampicin and daptomycin are typically inactive against Gram-negative bacteria, higher rates of synergy were observed using colistin-rifampicin combination with 93.75% (75/80) synergy (FICI range=0.002-0.47), 3.75% (3/80) additivity (FICI range=0.56-0.62) and 2.5% (2/80) indifference (FICI range=1-1.42). Colistin-daptomycin combination was tested in 30 isolates resulting in 90% (27/30) synergy (FICI range=0.017-0.42), and 10% (3/30) additivity (FICI range=0.51-0.76).

Conclusions: In vitro colistin-based combinations with either rifampicin or daptomycin or meropenem resulted in high synergy rates rendering them a valuable option for the treatment of colistin-resistant A. baumannii infections.

INTRODUCTION

Dalbavancin is a long-acting lipoglycopeptide antibiotic (half-life 14.40 days) that inhibits cell wall synthesis. It is commonly used off-label, as it has potent activity against gram-positive pathogens that cause bone and joint infections.

The objective is to describe the cases in which dalbavancin has been used as an off-label use for the treatment of infections by gram-positive microorganisms in a tertiary hospital.

METHODS

Case report series study of all patients treated with dalbavancin as off-label use from January 2017 to March 2022.

Demographic, clinical and pharmacotherapeutic variables were considered: age, sex, justification for the request as off-label, diagnosis, microorganism, location, previous antibiotic treatment, posology, duration, concomitant antibiotic treatment and follow-up at 3 months.

RESULTS AND DISCUSSION

Nineteen patients were included, one of whom died, and the other received another antibiotic treatment.

Dalbavancin was administered to seventeen patients (median age 76(33-99) years, 64.70% men). The justification for off-label use was in all patients due to early discharge and impossibility of treatment with other oral antibiotics due to interactions, adverse effects and/or severity.

The main diagnosis were: bacteremia (29.40%), osteoarticular infection (52.94%) and endocarditis (11.76%). The isolated microorganism was Staphylococcus epidermidis (47.00%), methicillin-resistant Staphylococcus aureus (17.65%), methicillin-sensitive Staphylococcus aureus (23.53%), Staphylococcus haemolyticus (5.89%) and Staphylococcus warneri (5.89%). The location of the microorganism was: 33% blood culture, 25% joint fluid, 16.67% abscess, 16.67% osteosynthesis and 8.33% ulcer.

Previous antibiotic treatment: 13 patients daptomycin (76.47%) (9 of them also received other antibiotics), 3 patients linezolid (17.65%) (2 of them also received other antibiotics) and 2 patients received others (11.76%).

The posology was: 2 doses of 1500mg biweekly (17.65%), 1 dose of 1000mg+500mg at two weeks (17.65%), 1 dose of 1500mg+1000mg biweekly (23.53%), single dose of 1500 mg (11.76%), 1 dose of 750mg+375mg weekly (11.76%) and 1 dose of 1500mg+500mg weekly (17.65%).

The median number of days of treatment was 14(1-56). 29.41% patients received concomitant antibiotic treatment: rifampicin(5) and levofloxacin(2). At 3 months of treatment only 2 patient died and no patient had reinfection.

CONCLUSIONS

Dalbavancin is an antibiotic with a novel dosage in infectious diseases, whose main contribution in our setting has been to allow earlier hospital discharge in patients who did not have oral alternatives and the only reason for hospitalization was the need for intravenous antibiotic treatment. It has proven to be highly effective because no patient manifested symptoms of reinfection., which is why we have recently drawn up a protocol for its off-label use in patients who meet specific criteria.