Combination Susceptibility Testing of Common Antimicrobials in Vitro and the Effects of Sub-MIC of Antimicrobials on Staphylococcus aureus Biofilm Formation

Therapeutic effects of lincomycin and level of drug degradation in broiler tissues after treatment

Background and Aim

Lincomycin is an antibiotic used in broiler farming and is commonly combined with other substances to achieve synergistic and complementary effects on the antibacterial spectrum and mechanism. We developed a specific high-performance liquid chromatography (HPLC) method to measure lincomycin levels in broiler tissues. This study aimed to determine the lincomycin level in tissues and compare it with the minimum inhibitory concentration (MIC) and maximum residue limit (MRL) of certain pathogenic bacteria.

Materials and Methods

Three groups of broiler chickens were involved in the study (n = 20 in each group): A control group without lincomycin treatment and two groups (each further divided into two sub-groups) that received oral lincomycin at a dose of 1 g/10 kg of body weight daily for 7 and 14 consecutive days. Tissue samples were collected from each group 1 day and 1 week after lincomycin administration (ALA). This study validated the development of a technique for analyzing drug level degradation in tissues using HPLC. Descriptive and statistical analyses were performed for drug levels to assess their therapeutic value and safety based on lincomycin MIC of certain pathogenic bacteria and MRL.

Results

The method validation resulted in linear regression and coefficient of determination for tissues with r2 > 0.99, with a recovery rate of 90%-110%, precision as the coefficient of variation 15%, and specificity with no peak overlap for lincomycin. The limits of detection for the liver and kidney were 0.01 μg/g, 0.05 μg/g, and 0.1 μg/g for the breast muscle and all tissues. Administration of lincomycin for 7 and 14 days resulted in therapeutic value concentrations. Lincomycin levels in the liver and kidney of ALA exceeded the MRL, whereas breast muscles were below the MRL for a week of ALA treatment.

Conclusion

Administration of lincomycin for 7 and 14 consecutive days resulted in therapeutic value; however, after a week, most tissues showed high drug concentrations that exceeded the MRL. It is necessary to carefully consider the prolonged therapeutic dose of lincomycin in broilers. Antibiotic therapy must be guided in such a way as to protect the product from harmful residues.

Sub-inhibitory concentrations of ceftriaxone induce morphological alterations and PIA-independent biofilm formation in Staphylococcus aureus

The exposure of bacteria to sub-inhibitory concentrations of antibiotics is of biological significance since it can occur in vivo under many circumstances, including low-dose treatment, poor adherence to a regimen, poor drug penetration, drug-drug interactions, and antibiotic resistance of the pathogen. In this study, we investigated the effects of subinhibitory concentrations of four antibiotics: ampicillin, ceftriaxone, gentamicin, and norfloxacin, which are commonly used in clinical settings and on cell morphology and biofilm formation in Staphylococcus aureus as one of the leading causes of nosocomial and biofilm-associated infections. Nine clinical S. aureus biofilm-producing isolates and two known biofilm-producing reference strains, S. aureus ATCC 29213 and S. aureus ATCC 6538, were used in this study. Sub-MICs of beta-lactam antibiotics (ampicillin and ceftriaxone) significantly induced biofilm formation in S. aureus ATCC 29213 and S. aureus ATCC 6538 and in six clinical isolates out of the nine selected isolates when compared with the antibiotic-free control group (P < 0.05), with an approximately 2- to 2.5-fold increase. Gentamicin and norfloxacin induced biofilms in S. aureus ATCC 29213 and S. aureus ATCC 6538, while gentamicin and norfloxacin induced biofilms only in three and two of the nine tested isolates, respectively (P < 0.05). The chemical nature of the biofilm matrix produced by half the MIC of ceftriaxone in the six isolates that showed increased biofilm was all non-polysaccharide in composition (PIA-independent). Gene expression of biofilm-encoding genes atl and sarA in biofilms of the two tested strains (S. aureus ATCC 6538) and clinical strain (S. aureus 16) showed a significant upregulation after exposure to half MIC of ceftriaxone. Additionally, the bacterial cell morphological changes in planktonic cells caused by half MIC of ceftriaxone were evaluated by scanning electron microscopy, which demonstrated a significant cell enlargement when compared with the antibiotic-free control (P < 0.05), and some deformed cells were also noticed. In S. aureus clinical isolates, sub-MICs of ampicillin, ceftriaxone, gentamicin, and norfloxacin may stimulate substantial production of biofilm, which could have important clinical significance and make infection treatment challenges. Further, in vivo research is needed to fully comprehend how sub-MIC of antibiotics can affect biofilm formation in clinical settings. Additionally, more research is required to reveal the clinical implications of the morphological alterations in S. aureus brought on by exposure to ceftriaxone at concentrations below its MIC.

Strategies for combating antibiotic resistance in bacterial biofilms

Biofilms, which are complexes of microorganisms that adhere to surfaces and secrete protective extracellular matrices, wield substantial influence across diverse domains such as medicine, industry, and environmental science. Despite ongoing challenges posed by biofilms in clinical medicine, research in this field remains dynamic and indeterminate. This article provides a contemporary assessment of biofilms and their treatment, with a focus on recent advances, to chronicle the evolving landscape of biofilm research.

Intramammary preparation of enrofloxacin hydrochloride-dihydrate for bovine mastitis (biofilm-forming Staphylococcus aureus)

BACKGROUND

Chronic bovine mastitis is linked to biofilm-producing Staphylococcus aureus (bp-Sa) or Staphylococcus coagulase-negative (bp-Scn).

OBJECTIVES

Bp-Sa and bp-Scn were treated with intramammary preparations of either enrofloxacin HCl·2H2O-dimethyl-sulfoxide-chitosan (enro-C/DMSO/chitosan) or enro-C alone. Their potential to inhibit and degrade biofilm formation in vitro was also assessed.

METHODS

Milk samples were obtained from the affected quarters in a herd. Phenotypical and genotypical identifications as biofilm-producing Staphylococcus species were carried out. Enro-C/DMSO/chitosan and enro-C alone were assessed to determine their in vitro efficacy in interfering with biofilm formation and their bactericidal effects. A prolonged eight-day treatment with a twice-daily intramammary insertion of 10 mL of enro-C/DMSO/chitosan or enro-C alone was set to evaluate the clinical and bacteriological cures on day 10 in 15 cows per group and the biofilm-inhibiting ability.

RESULTS

Fifty-seven percent of the isolates were identified as Staphylococcus spp., of which 50% were bp-Sa, 46% bp-Scn, and 4% Staphylococcus pseudintermedius. One hundred percent of the S. aureus isolated and 77% of Staphylococcus coagulase-negative were biofilm producers. In both groups, the icaA and icaD biofilm-producing genes were identified. The experimental preparation could inhibit biofilm formation, degrade mature biofilms, and have well-defined microbicidal effects on planktonic and biofilm bacteria. The respective clinical and bacteriological cure rates were 100% and 80% for enro-C/DMSO/chitosan and 41.7% and 25% for enro-C alone.

CONCLUSIONS

Enro-C/DMSO/chitosan eliminates bp-Sa and bp-Scn from cases of chronic bovine mastitis.

Multi-omics reveals the increased biofilm formation of Salmonella Typhimurium M3 by the induction of tetracycline at sub-inhibitory concentrations

Exposure to sub-inhibitory concentrations (sub-MICs) of antibiotics could induce the biofilm formation of microorganisms, but its underlying mechanisms still remain elusive. In the present work, biofilm formation by Salmonella Typhimurium M3 was increased when in the presence of tetracycline at sub-MIC, and the highest induction was observed with tetracycline at 1/8 MIC. The integration of RNA-sequencing and untargeted metabolomics was applied in order to further decipher the potential mechanisms for this observation. In total, 439 genes and 144 metabolites of S. Typhimurium M3 were significantly expressed after its exposure to 1/8 MIC of tetracycline. In addition, the co-expression analysis revealed that 6 genes and 8 metabolites play a key role in response to 1/8 MIC of tetracycline. The differential genes and metabolites were represented in 12 KEGG pathways, including five pathways of amino acid metabolism (beta-alanine metabolism, tryptophan metabolism, arginine and proline metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, and glutathione metabolism), three lipid metabolism pathways (biosynthesis of unsaturated fatty acids, fatty acid degradation, and fatty acid biosynthesis), two nucleotide metabolism pathways (purine metabolism, and pyrimidine metabolism), pantothenate and CoA biosynthesis, and ABC transporters. Metabolites (anthranilate, indole, and putrescine) from amino acid metabolism may act as signaling molecules to promote the biofilm formation of S. Typhimurium M3. The results of this work highlight the importance of low antimicrobial concentrations on foodborne pathogens of environmental origin.

Automatically showing microbial growth kinetics with a high-performance microbial growth analyzer

It is difficult to show microbial growth kinetics online when they grow in complex matrices. We presented a novel strategy to address this challenge by developing a high-performance microbial growth analyzer (HPMGA), which employed a unique 32-channel capacitively coupled contactless conductivity detector as a sensing element and fixed with a CellStatz software. It was capable of online showing accurate and repeatable growth curves of well-dispersed and bad-dispersed microbes, whether they grew in homogeneous simple culture broth or heterogeneous complex matrices. Moreover, it could automatically report key growth kinetics parameters. In comparison to optical density (OD), plate counting and broth microdilution (BMD) methods, we demonstrated its practicability in five scenarios: 1) the illustration of the growth, growth rate, and acceleration curves of Escherichia coli (E. coli); 2) the antimicrobial susceptibility testing (AST) of Oxacillin against Staphylococcus aureus (S. aureus); 3) the determination of Ag nanoparticle toxicity on Providencia rettgeri (P. rettgeri); 4) the characterization of milk fermentation; and 5) the enumeration of viable pathogenic Vibrio in shrimp body. Results highlighted that the HPMGA method had the advantages of universality and effectivity. This technology would significantly facilitate the routine analysis of microbial growth in many fields (biology, medicine, clinic, life, food, environment, and ecology), paving an avenue for microbiologists to achieve research goals that have been inhibited for years due to a lack of practical analytical methods.

The Combination of β-Glucan and Astragalus Polysaccharide Effectively Resists Nocardia seriolae Infection in Largemouth Bass (Micropterus salmoides)

Effectively treating and preventing outbreaks is crucial for improving the economic benefits of aquaculture. Therefore, utilizing immunostimulants, either alone or in combination, is regarded as a promising strategy. In this study, β-glucan + APS (200 mg/kg + 200 mg/kg), β-glucan (200 mg/kg), APS (200 mg/kg), enrofloxacin (15 mg/kg), and sulfadiazine (15 mg/kg) were added to feed to assess the effects against Nocardia seriolae infection in largemouth bass (Micropterus salmoides) within 14 days. The survival rates did not differ between the enrofloxacin group and the β-glucan + APS group, but both were significantly higher than that of the control group. Additionally, the enrofloxacin group and the β-glucan + APS group exhibited the lowest bacterial loads and tissue damage. Importantly, the β-glucan + APS treatment significantly improved serum enzyme activities (total superoxide dismutase, lysozyme, total protein) and the expression of immune genes (IL-1β, TNF-α, IFN-γ, IgM) compared to the other treatment groups. The enrofloxacin group showed similar efficacy to the β-glucan + APS group in combating N. seriolae infection, but N. seriolae in the enrofloxacin group developed drug resistance. In summary, the combined use of β-glucan and APS is a promising strategy for treating bacterial diseases, thereby contributing to the promotion of sustainable aquaculture development.

Molecular and biological characterization of pyocyanin from clinical and environmental Pseudomonas aeruginosa

BACKGROUND

Pyocyanin is a secondary metabolite secreted by P. aeruginosa. It is a redox-active blue/green phenazine pigment that has various beneficial applications. The present study aims at screening the production of pyocyanin among clinical and environmental P. aeruginosa isolates in Dakahlya governorate, Egypt. Thereafter, large-scale production, purification, structure elucidation, and assessment of the biological activity of the highest pyocyanin producers were targeted.

RESULTS

Pyocyanin from the highest clinical (PsC05) and environmental (PsE02) producers were subjected to large-scale production, followed by purification using silica gel column. Pyocyanin was characterized using TLC, UV-Vis, 1 H NMR, and FTIR spectroscopy to confirm its structure and purity. Purified pyocyanin showed remarkable antimicrobial efficacy against all tested food-borne pathogens, MDR/XDR clinically isolated bacteria and C. albicans. Furthermore, it showed a substantial effect on biofilm inhibition and eradication of pre-formed biofilm against strong biofilm producing bacterial pathogens. However, it had limited antibiofilm activity against C. albicans. Pyocyanin from PsC05 had higher antioxidant and radicals scavenging activity than that from PsE02 as determined by FRAP, DPPH, and ABTS assays. Likewise, pyocyanin from PsC05 was more active against tested cancer cell lines, especially human Breast Cancer (MCF-7) and Colorectal Carcinoma (HCT-116), than that from PsE02. More importantly, it showed minimal cytotoxicity to normal cells.

CONCLUSIONS

P. aeruginosa clinical and environmental isolates produce pyocyanin pigment in varying amounts. Pyocyanin exhibits substantial anti-bacterial, and anti-fungal activity; thus, enhancing its medical applicability. It could be used to inhibit and/or eradicate biofilm from the surfaces of medical devices which is a chief source of nosocomial infections. Its antioxidant along with cytotoxic activity against cancer cell lines, make it a promising contender for use as a substitute for synthetic agents in cancer treatment.

Molecular Imaging of Isolated Escherichia coli DH5α Peptidoglycan Sacculi Identifies the Mechanism of Action of Cell Wall-Inhibiting Antibiotics

Antibiotic resistance of pathogenic bacteria needs to be urgently addressed by the development of new antibacterial entities. Although the prokaryotic cell wall comprises a valuable target for this purpose, development of novel cell wall-active antibiotics is mostly missing today. This is mainly caused by hindrances in the assessment of isolated enzymes of the co-dependent murein synthesis machineries, e.g., the elongasome and divisome. We therefore present imaging methodologies to evaluate inhibitors of bacterial cell wall synthesis by high-resolution atomic force microscopy on isolated Escherichia coli murein sacculi. With the ability to elucidate the peptidoglycan ultrastructure of E. coli cells, unprecedented molecular insights into the mechanisms of antibiotics were established. The nanoscopic impairments introduced by ampicillin, amoxicillin, and fosfomycin were not only identified by AFM but readily correlated with their known mechanism of action. These valuable in vitro capabilities will facilitate the identification and evaluation of new antibiotic leads in the future.

Cationic styryl dyes for DNA labelling and selectivity toward cancer cells and Gram-negative bacteria

Fluorescence-based methods are important tools for the analysis of nucleic acids in vitro and in cells. In this study, two cationic cyanine-styryl derivatives were produced using a two-step synthesis. Their optical properties were evaluated in different solvents, and frontier molecular orbital theory was utilized to interpret the findings. The DNA binding of these molecules was investigated to show fluorescence intensification. The molecular docking of both dyes in DNA illustrated the relevance of the electrostatic interaction between the quaternary ammonium of both dyes and the phosphate of the DNA backbone. Last but not least, applications of the synthesized styryl dyes were demonstrated to be selective towards cancer cells and particular kinds of bacteria.

Antimicrobial Treatment of Staphylococcus aureus Biofilms

Staphylococcus aureus is a microorganism frequently associated with implant-related infections, owing to its ability to produce biofilms. These infections are difficult to treat because antimicrobials must cross the biofilm to effectively inhibit bacterial growth. Although some antibiotics can penetrate the biofilm and reduce the bacterial load, it is important to understand that the results of routine sensitivity tests are not always valid for interpreting the activity of different drugs. In this review, a broad discussion on the genes involved in biofilm formation, quorum sensing, and antimicrobial activity in monotherapy and combination therapy is presented that should benefit researchers engaged in optimizing the treatment of infections associated with S. aureus biofilms.

Combined Anti-Bacterial Actions of Lincomycin and Freshly Prepared Silver Nanoparticles: Overcoming the Resistance to Antibiotics and Enhancement of the Bioactivity

Bacterial drug resistance to antibiotics is growing globally at unprecedented levels, and strategies to overcome treatment deficiencies are continuously developing. In our approach, we utilized metal nanoparticles, silver nanoparticles (AgNPs), known for their wide spread and significant anti-bacterial actions, and the high-dose regimen of lincosamide antibiotic, lincomycin, to demonstrate the efficacy of the combined delivery concept in combating the bacterial resistance. The anti-bacterial actions of the AgNPs and the lincomycin as single entities and as part of the combined mixture of the AgNPs-lincomycin showed improved anti-bacterial biological activity in the Bacillus cereus and Proteus mirabilis microorganisms in comparison to the AgNPs and lincomycin alone. The comparison of the anti-biofilm formation tendency, minimum bactericidal concentration (MBC), and minimum inhibitory concentration (MIC) suggested additive effects of the AgNPs and lincomycin combination co-delivery. The AgNPs' MIC at 100 μg/mL and MBC at 100 μg/mL for both Bacillus cereus and Proteus mirabilis, respectively, together with the AgNPs-lincomycin mixture MIC at 100 + 12.5 μg/mL for Bacillus cereus and 50 + 12.5 μg/mL for Proteus mirabilis, confirmed the efficacy of the mixture. The growth curve test showed that the AgNPs required 90 min to kill both bacterial isolates. The freshly prepared and well-characterized AgNPs, important for the antioxidant activity levels of the AgNPs material, showed radical scavenging potential that increased with the increasing concentrations. The DPPH's best activity concentration, 100 μg/mL, which is also the best concentration exhibiting the highest anti-bacterial zone inhibition, was chosen for evaluating the combined effects of the antibiotic, lincomycin, and the AgNPs. Plausible genotoxic effects and the roles of AgNPs were observed through decreased Bla gene expressions in the Bacillus cereus and Bla_CTX-M-15 gene expressions in the Proteus mirabilis.

Daptomycin exerts differential immunomodulatory effects on host responses against methicillin-resistant Staphylococcus aureus biofilms

BACKGROUND

Daptomycin (DAP) is indicated for difficult-to-treat Gram-positive infections, especially those caused by methicillin-resistant S. aureus (MRSA). Exposure of S. aureus to sub-inhibitory concentrations (sub-MICs) of antibiotics have been shown to alter cell morphology or biofilm formation.

OBJECTIVES

To investigate the influence of DAP biofilm sub-MICs on the damage caused by human polymorphonuclear neutrophils (PMNs) against MRSA biofilms and the potential immunomodulatory activity of DAP on human monocytes (MNCs) exposed to MRSA biofilms.

METHODS

DAP activity against biofilms and the impact of DAP on the PMNs-induced biofilm damage were evaluated by the XTT reduction assay, whereas pathogen recognition, signal transduction and cytokine modulation of DAP on MNCs in response to MRSA biofilms were assessed by RT-PCR and ELISA methodology.

RESULTS

The MIC50 of DAP to MRSA biofilms was 16 to 32 mg/L. Pre-treatment of MRSA to 1, 2 or 4 mg/L DAP caused a synergistic effect on PMN-mediated biofilm damage, being dependent on the effector-to-target ratio. MNCs responded to MRSA biofilms and DAP through Toll like receptor 2 (TLR2) upregulation and increased NLRP3 inflammasome production. DAP caused 2.5-fold greater TLR2 mRNA levels than those caused by MRSA biofilms. A predominantly inflammatory response was induced by either component, causing the release of significantly increased IFN-γ, TNF-α, IL-8 and IL-6 levels by MNCs exposed to the combination treatment. MRSA biofilms alone or combined with DAP caused low amounts of IL-10 production, but increased IL-1β levels.

CONCLUSIONS

DAP may condition MNCs towards an inflammatory response through TLR2 engagement and NLRP3 inflammasome activation, possibly controlling biofilm-associated pathogenicity.

Tailored therapeutic release from polycaprolactone-silica hybrids for the treatment of osteomyelitis: antibiotic rifampicin and osteogenic silicates

The treatment of osteomyelitis, a destructive inflammatory process caused by bacterial infections to bone tissue, is one of the most critical challenges of orthopedics and bone regenerative medicine. The standard treatment consists of intense antibiotic therapies combined with tissue surgical debridement and the application of a bone defect filler material. Unfortunately, commercially available candidates, such as gentamicin-impregnated polymethylmethacrylate cements, possess very poor pharmacokinetics (i.e., 24 hours burst release) and little to no regenerative potential. Fostered by the intrinsic limitations associated with conventional treatments, alternative osteostimulative biomaterials with local drug delivery have recently started to emerge. In this study, we propose the use of a polycaprolactone-silica sol-gel hybrid material as carrier for the delivery of rifampicin, an RNA-polymerase blocker often used to treat bone infections, and of osteostimulative silicate ions. The release of therapeutic agents from the material is dual, offering two separate and simultaneous effects, and decoupled, meaning that the kinetics of rifampicin and silicate releases are independent from each other. A series of hybrid formulations with increasing amounts of rifampicin was prepared. The antibiotic loading efficacy, as well as the release profiles of rifampicin and silicates were measured. The characterization of cell viability and differentiation of rat primary osteoblasts and antibacterial performance were also performed. Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa and Escherichia coli were selected due to their high occurrence in bone infections. Results confirmed that rifampicin can be successfully loaded within the hybrids without significant degradation and that it is possible to tailor the antibiotic release according to need. Once in a physiological environment, the rapid release of silicates was associated with optimal cell proliferation and the overexpression of osteoblastic differentiation. Simultaneously, rifampicin is delivered over the course of several weeks with significant inhibition of all tested strains. In particular, the materials caused a growth reduction of 7-10 orders of magnitude in Staphylococcus aureus, the major strain responsible for osteomyelitis worldwide. Our data strongly suggest that PCL/silica hybrids are a very promising candidate to develop bone fillers with superior biological performance compared to currently available options. Thanks to their unique synthesis route and their dual tailored release they can promote bone regeneration while reducing the risk of infection for several weeks upon implantation.

Antibiofilm Effects of Epigallocatechin Gallate Against Proteus mirabilis Wild-Type and Ampicillin-Induced Strains

Proteus mirabilis is an opportunistic pathogen associated with nosocomial infections and foodborne diseases. The resistance and biofilm formation of P. mirabilis have been a great concern. In this study a multidrug-resistant P. mirabilis strain 012 was exposed to a lethal dose of ampicillin (10 mg/mL, 2.5-fold minimal bactericidal concentration) for 24 h at 37°C. After resuscitation and isolation, five variant isolates were selected and subjected to ampicillin induction by repeatedly streaking on ampicillin-containing plates (10 mg/mL) for at least three times. In biofilm formation assays by using crystal violet staining, we found that the variant strains had enhanced biofilm-forming abilities. (-)-epigallocatechin-3-gallate (EGCG) at a minimum inhibitory concentration (MIC) (256 μg/mL) significantly reduced the biofilm formation of all variant strains and the wild-type strain (p < 0.01). Sub-MIC of EGCG (128 μg/mL) suppressed the biofilms of wild-type and two variants. However, it stimulated the biofilms of the other three variants. The antibiofilm effects of EGCG against the wild-type strain were further confirmed by confocal laser scanning microscopy. Scanning electron microscopy revealed that EGCG induced variants to form more fibrous structures. Our results revealed that a lethal dose of antibiotic exposure increased antibiotic resistance and biofilm formation of P. mirabilis. EGCG may be used as a promising antibiofilm agent to prevent the P. mirabilis biofilm formation in the food industry. However, the sub-MIC of EGCG is not effective and will not be applied.

Successful treatment of recurrent subclinical mastitis in cows caused by enrofloxacin resistant bacteria by means of the sequential intramammary infusion of enrofloxacin HCl-2H2O and ceftiofur HCl: a clinical trial

Background

Recurrent subclinical mastitis (RScM) due to resistant bacteria has low clinical and bacteriological cure rates, often requiring the culling of cows. The sequential intra-mammary administration of enrofloxacin hydrochloride-dihydrate (enro-C) followed by ceftiofur HCl may be useful for treating these cases.

Objectives

This study assessed the bacteriological and clinical cure-efficacies of the sequentially intramammary administration of enro-C, followed by ceftiofur HCl to treat RScM in Holstein/Friesian cows.

Methods

This trial was conducted in a herd with a high prevalence of RScM, and 20 Holstein/Friesian cows were included: 45% suffering subclinical mastitis and 38.9% of the mammary quarters affected. Twenty-nine bacterial isolates in vitro resistant to enro-C were obtained (coagulase-negative Staphylococcus spp, 55.2%; Staphylococcus aureus, 27.6%; Escherichia coli, 6.9%; Streptococcus uberis, 6.9%; Corynebacterium bovis, 3.4%). Polymerase chain reaction-isolated the following genes linked to enro-C resistance: chromosomal (gyrA) and plasmid (aac(6')-lb-cr). The treatments were as follows: twice-daily intramammary infusions of enro-C (300 mg/10 mL) for 5 days. Cows clinically considered treatment failures were also treated with intramammary ceftiofur (125 mg/10 mL, twice daily for 5 days. The clinical and bacteriological cure rates were carried out when completing each treatment phase and at 14 and 21 days, aided by a California mastitis test, somatic cell count, and failure to identify the initially causative bacteria.

Results

Enro-C achieved 65% clinical and bacteriological cure rates, and 100% cure rates were obtained after the rescue treatment with ceftiofur HCl.

Conclusions

Outstanding clinical and bacteriological cure rates in cows affected by RScM were achieved with the consecutive intramammary infusions of enro-C, followed by ceftiofur HCl.

Selective estrogen receptor modulators against Gram-positive and Gram-negative bacteria: an experimental study

Aim: This study was conducted to explore the antibacterial potential of selective estrogen receptor modulators (SERMs). Materials & methods: The percentage growth retardation, bacterial growth kinetics, biofilm, checkerboard and bacterial burden assays were conducted to check antibacterial potential of SERMs. Finally, docking study was also conducted to predict possible antibacterial mechanism of SERMs. Results: In vitro and in vivo studies have shown the antibacterial activity of SERMs against different tested strains of bacteria. The synergistic activity of SERMs in combination with standard antibacterial agents was also observed and tested further under in vivo conditions. In vivo results have shown decreased bacterial bioburden. Docking studies have predicted the multimodal antibacterial mechanism of SERMs. Conclusion: SERMs can be considered as promising broad-spectrum antibacterial agents.

Experimental infection of Asian house geckos with Enterococcus lacertideformus demonstrates multiple disease transmission routes and the in-vivo efficacy of antibiotics

The disease caused by Enterococcus lacertideformus is multisystemic and ultimately fatal. Since its emergence, the bacterium has significantly impacted the captive breeding programs of the extinct in the wild Christmas Island Lister's gecko (Lepidodactylus listeri) and blue-tailed skink (Cryptoblepharus egeriae). The bacterium's pathogenicity, inability to grow in-vitro, and occurrence beyond the confines of Christmas Island necessitated the development of an experimental infection and treatment model. Asian house geckos (Hemidactylus frenatus) were challenged with a single dose of E. lacertideformus inoculum either by mouth, application to mucosal abrasion or skin laceration, subcutaneous injection, coelomic injection, or via co-housing with an infected gecko. Five healthy geckos acted as controls. Each transmission route resulted in disease in at least 40% (n = 2) geckos, expanding to 100% (n = 5) when E. lacertideformus was applied to skin laceration and mucosal abrasion groups. Incubation periods post-infection ranged between 54 and 102 days. To determine the efficacy of antibiotic treatment, infected geckos were divided into six groups (enrofloxacin 10 mg/kg, per os (PO), every 24 h (q24), amoxicillin-clavulanic acid 10 mg/kg, PO, q24, enrofloxacin 10 mg/kg combined with amoxicillin-clavulanic acid 10 mg/kg, PO, q24, rifampicin 15 mg/kg, PO, q24, clarithromycin 15 mg/kg, PO, q24, and untreated controls) for 21 days. Response to treatment was assessed by the change in lesion size, bacterial dissemination, and histological evidence of a host immune response. Irrespective of the antibiotic given, histology revealed that geckos inoculated by skin laceration were observed to have more extensive disease spread throughout the animal's body compared to other inoculation routes. The reduction in the average surface area of gross lesions was 83.6% for geckos treated with enrofloxacin, followed by the combination therapy amoxicillin-clavulanic acid and enrofloxacin (62.4%), amoxicillin-clavulanic acid (58.2%), rifampicin (45.5%), and clarithromycin (26.5%). Lesions in geckos untreated with antibiotics increased in size between 100 and 300%. In summary, enrofloxacin and amoxicillin-clavulanic acid show promising properties for the treatment of E. lacertideformus infection in geckos. The Asian house gecko E. lacertideformus infection model therefore provides foundational findings for the development of effective therapeutic treatment protocols aimed at conserving the health of infected and at-risk reptiles.

Evaluation of the impact of adaptation of Klebsiella pneumoniae clinical isolates to benzalkonium chloride on biofilm formation

Background

The percentage of the multidrug resistant Klebsiella pneumoniae clinical isolates is increasing worldwide. The excessive exposure of K. pneumoniae isolates to sublethal concentrations of biocides like benzalkonium chloride (BAC) in health care settings and communities could be one of the causes contributing in the global spread of antibiotic resistance.

Results

We collected 50 K. pneumoniae isolates and these isolates were daily exposed to gradually increasing sublethal concentrations of BAC. The consequence of adaptation to BAC on the cell surface hydrophobicity (CSH) and biofilm formation of K. pneumoniae isolates was explored. Remarkably, 16% of the tested isolates showed an increase in the cell surface hydrophobicity and 26% displayed an enhanced biofilm formation. To evaluate whether the influence of BAC adaptation on the biofilm formation was demonstrated at the transcriptional level, the RT-PCR was employed. Noteworthy, we found that 60% of the tested isolates exhibited an overexpression of the biofilm gene (bssS). After sequencing of this gene in K. pneumoniae isolates before and after BAC adaptation and performing pairwise alignment, 100% identity was detected; a finding that means the absence of mutation after adaptation to BAC.

Conclusion

This study suggests that the widespread and increased use of biocides like BAC at sublethal concentrations has led to an increase biofilm formation by K. pneumoniae isolates. Enhanced biofilm formation could result in treatment failure of the infections generated by this pathogen.

Regulatory mechanisms of sub-inhibitory levels antibiotics agent in bacterial virulence

Antibiotics play a key role in the prevention and treatment of bacterial diseases for human and animals. The widespread use of antibiotics results in bacterial exposure to the concentrations that are lower than the MIC (that is, sub-inhibitory concentration (sub-MIC)) in the environment, humans, and livestock, which can lead to antibiotic resistance. In this review, we focus on the impact of sub-MIC antibiotics in bacterial virulence. This paper summarized the known relationships between sub-MIC antibiotics in the environment and bacterial virulence. Together, considering the impact of sub-MIC antibiotics and their alternative products in the virulence of bacteria, it is helpful to the rational use of antibiotics and the development of antibiotic alternative products to provide new insights.Key points• Sub-MIC level antibiotics exist in the environment, humans, and livestock.• The review includes mechanisms of sub-MIC antibiotics in bacterial virulence.• New antibacterial strategies and agents are being a new way to weaken virulence. Graphical Abstract.

Coagulase negative staphylococci from ovine bulk-tank milk: Effects of the exposure to sub-inhibitory concentrations of disinfectants for teat-dipping

Teat-dipping is one of the most effective methods to prevent mammary infections in ruminants, including sub-clinical mastitis caused by coagulase-negative staphylococci (CoNS). Improper disinfectant application could expose microorganisms to sub-inhibitory concentrations leading to phenotypic variations. In this study, 12 chlorhexidine-digluconate (CHDG)-tolerant (of which 4 qac positive) and 12 benzalkonium chloride (BC)-tolerant (of which 7 qac-positive) CoNS isolates from ovine milk were exposed to sub-inhibitory concentrations of CHDG and BC, respectively. Changes in disinfectant susceptibility against BC and CHDG, antibiotic resistance against 12 antibiotics and biofilm production were then assessed for both groups. After CHDG stress, 67 % and 83 % of the CHDG-stressed isolates doubled their MICs for BC and CHDG, respectively and 2 qac-negative isolates showed a four-fold increase of their MBCs for CHDG. After BC stress, MICs for BC and CHDG doubled in 58 % and 83 % of the BC-stressed isolates, respectively, while one qac-positive isolate increased four-fold the MIC for BC. Cross-resistance to antibiotics was assessed by disc diffusion method. Some qac-positive isolates varied their resistance profile, while a blaZ-positive isolate showed a resistant phenotype against ampicillin only after the exposure to the disinfectant. As for qac-positive isolates, one CHDG-stressed and 2 BC-stressed increased their resistance to kanamycin and cefoxitin, respectively. The Congo Red Agar test was carried out to assess the in vitro slime production: all isolates were negative after stress. In conclusion, sub-inhibitory exposure to disinfectants may affect disinfectant and antibiotic susceptibility, the latter in particular for qac-positive isolates and those hosting unexpressed antibiotic resistance genes.

Genomic Insights Into the Pathogenicity of a Novel Biofilm-Forming Enterococcus sp. Bacteria (Enterococcus lacertideformus) Identified in Reptiles

Whole genome analysis of a novel species of enterococci, Enterococcus lacertideformus, causing multi-systemic and invariably fatal disease in critically endangered Christmas Island reptiles was undertaken to determine the genetic elements and potential mechanisms conferring its pathogenic nature, biofilm-forming capabilities, immune recognition avoidance, and inability to grow in vitro. Comparative genomic analyses with related and clinically significant enterococci were further undertaken to infer the evolutionary history of the bacterium and identify genes both novel and absent. The genome had a G + C content of 35.1%, consisted of a circular chromosome, no plasmids, and was 2,419,934 bp in length (2,321 genes, 47 tRNAs, and 13 rRNAs). Multi-locus sequence typing (MLST), and single nucleotide polymorphism (SNP) analysis of multiple E. lacertideformus samples revealed they were effectively indistinguishable from one another and highly clonal. E. lacertideformus was found to be located within the Enterococcus faecium species clade and was closely related to Enterococcus villorum F1129D based on 16S rDNA and MLST house-keeping gene analysis. Antimicrobial resistance (DfreE, EfrB, tetM, bcrRABD, and sat4) and virulence genes (Fss3 and ClpP), and genes conferring tolerance to metals and biocides (n = 9) were identified. The detection of relatively few genes encoding antimicrobial resistance and virulence indicates that this bacterium may have had no exposure to recently developed and clinically significant antibiotics. Genes potentially imparting beneficial functional properties were identified, including prophages, insertion elements, integrative conjugative elements, and genomic islands. Functional CRISPR-Cas arrays, and a defective prophage region were identified in the genome. The study also revealed many genomic loci unique to E. lacertideformus which contained genes enriched in cell wall/membrane/envelop biogenesis, and carbohydrate metabolism and transport functionality. This finding and the detection of putative enterococcal biofilm determinants (EfaAfs, srtC, and scm) may underpin the novel biofilm phenotype observed for this bacterium. Comparative analysis of E. lacertideformus with phylogenetically related and clinically significant enterococci (E. villorum F1129D, Enterococcus hirae R17, E. faecium AUS0085, and Enterococcus faecalis OG1RF) revealed an absence of genes (n = 54) in E. lacertideformus, that encode metabolic functionality, which potentially hinders nutrient acquisition and/or utilization by the bacterium and precludes growth in vitro. These data provide genetic insights into the previously determined phenotype and pathogenic nature of the bacterium.

Coatable and Resistance-Proof Ionic Liquid for Pathogen Eradication

Antibiotic-resistant bacteria infect close to 3 million people, and kill 35,000, each year in the United States. Ionic liquid (IL)-based antimicrobial agents have the potential to diversify our ever-diminishing antibiotic arsenal. Here, we describe an IL with potent submicromolar antimicrobial activity in vitro against clinically relevant Gram-negative and Gram-positive bacterial pathogens as well as anti-infective activity in a mouse model. The IL kills pathogenic bacteria such as Acinetobacter baumannii, Salmonella enterica, and Escherichia coli by disrupting their outer membrane and does not select for bacterial resistance. We show incorporation of our IL into surface coatings to generate a type of antibiofilm material. The IL-loaded ionogel surfaces demonstrate high-antimicrobial and antifouling activity by killing bacteria in both static and dynamic tests. Our IL-based antibiofilm surfaces are low-cost and easy to manufacture, can be formed on glass, latex, plastic, and metal surfaces, such as catheters and other medical devices where high local concentrations of antimicrobials are needed, and may have applications in other clinical and industrial settings.

Virulence alterations in staphylococcus aureus upon treatment with the sub-inhibitory concentrations of antibiotics

Background

The treatment of patients with Staphylococcus aureus infections mainly relies on antistaphylococcal regimens that are established with effective antibiotics. In antibiotic therapy or while living in nature, pathogens often face the sub-inhibitory concentrations (sub-MICs) of antibiotics due to drug pharmacokinetics, diffusion barriers, waste emission, resistant organism formation, and farming application. Different categories of antibiotics at sub-MICs have diverse effects on the physiological and chemical properties of microorganisms. These effects can result in virulence alterations. However, the mechanisms underlying the actions of antibiotics at sub-MICs on S. aureus virulence are obscure.

Aim of review

In this review, we focus on the effects of sub-MICs of antibiotics on S. aureus virulence from the aspects of cell morphological change, virulence factor expression, bacterial adherence and invasion, staphylococcal biofilm formation, and small-colony variant (SCV) production. The possible mechanisms of antibiotic-induced S. aureus virulence alterations are also addressed.

Key scientific concepts of review

Five main aspects of bacterial virulence can be changed in S. aureus exposure to the sub-MIC levels of antibiotics, resulting in deformed bacterial cells to stimulate abnormal host immune responses, abnormally expressed virulence factors to alter disease development, changed bacterial adhesion and invasion abilities to affect colonization and diffusion, altered biofilm formation to potentate material-related infections, and increased SCV formation to achieve persistent infection and recurrence. These advanced findings expand our knowledge to rethink the molecular signaling roles of antibiotics beyond their actions as antimicrobial agents.

Antimicrobial properties of diethylamine NONOate, a nitric oxide donor, against Escherichia coli: a pilot study

The emergence of SARS-CoV-2, the causative agent of COVID-19, highlights the increasing need for new and effective antiviral and antimicrobial agents. The FDA has recently banned several active ingredients used in hand sanitizers, including triclosan and benzethonium chloride. Nitric oxide (NO) is involved in the innate immune response and is a major component of macrophage-mediated attack on foreign viruses and bacteria. The specific aim of this study was to assess the antibacterial effects of 2-(N,N-diethylamino)-diazenolate-2-oxide (DEA-NONOate) against Escherichia coli (E. coli). A bacterial growth assay was compared to an adenosine triphosphate (ATP) activity assay at various time points to assess effects of DEA-NONOate on E. coli growth. A UV/Vis spectrophotometer was used to determine concentration of E. coli by measuring optical density (OD) at 630 nm. A luminescent assay was used to measure ATP activity correlating to viable cells. DEA-NONOate at a concentration of 65 mM was able to inhibit the growth of E. coli with the same efficacy as 1 μg ml^-1 concentration of ciprofloxacin. Both the OD and ATP assays demonstrated a 99.9% reduction in E. coli. Both a 1 μg ml^-1 concentration of ciprofloxacin and a 65 mM concentration of DEA-NONOate achieved 99.9% inhibition of E. coli, verified using both optical density measurement of bacterial cultures in 96 well plates and a luminescent ATP activity assay. The bactericidal effects of DEA-NONOate against E. coli is proof-of-concept to pursue evaluation of nitric oxide-based formulations as antimicrobial and antiviral agents as hand sanitizers.

Next generation sequencing study on RNA viruses of Vespa velutina and Apis mellifera sharing the same foraging area

The predator Asian hornet (Vespa velutina) represents one of the major threats to honeybee survival. Viral spillover from bee to wasp has been supposed in several studies, and this work aims to identify and study the virome of both insect species living simultaneously in the same foraging area. Transcriptomic analysis was performed on V. velutina and Apis mellifera samples, and replicative form of detected viruses was carried out by strand-specific RT-PCR. Overall, 6 and 9 different viral types were reported in V. velutina and A. mellifera, respectively, and five of these viruses were recorded in both hosts. Varroa destructor virus-1 and Cripavirus NB-1/2011/HUN (now classified as Triato-like virus) were the most represented viruses detected in both hosts, also in replicative form. In this investigation, Triato-like virus, as well as Aphis gossypii virus and Nora virus, was detected for the first time in honeybees. Concerning V. velutina, we report for the first time the recently detected honeybee La Jolla virus. A general high homology rate between genomes of shared viruses between V. velutina and A. mellifera suggests the efficient transmission of the virus from bee to wasp. In conclusion, our findings highlight the presence of several known and newly reported RNA viruses infecting A. mellifera and V. velutina. This confirms the environment role as an important source of infection and indicates the possibility of spillover from prey to predator.

Synergistic Effect of Tazobactam on Amikacin MIC in Acinetobacter baumannii Isolated from Burn Patients in Tehran, Iran

BACKGROUND

Burn is still an important global public health challenge. Wound colonization of antibiotic resistant bacteria such as Acinetobacter baumannii can lead to high morbidity and mortality in burn patients. The aim of this study was to evaluate the inhibitory effect of tazobactam on efflux pump, which can cause aminoglycoside resistant in A. baumannii isolated from burn patients.

METHODS

In this study, 47 aminoglycoside resistant A. baumannii spp. were obtained from burn patients, admitted to the Shahid Motahari Burns Hospital in Tehran, Iran, during June-August 2018. The inhibitory effect of tazobactam against adeB such as efflux pump was evaluated by Minimum Inhibitory Concentration (MIC) determination of amikacin alone and in combination with tazobactam. Fractional Inhibitory Concentration index (FIC) was used to determine the efficacy of tazobactam/ amikacin combination. Further, semi-quantitative Real- Time PCR was performed to quantify the expression rates of the adeB gene before and after addition of tazobactam/amikacin.

RESULTS

The MIC values were significantly reduced when a combined amikacin and tazobactam was utilized. The most common interaction observed was synergistic (78.2%), followed by.additive effects (21.8%), as per FIC results. The adeB mRNA expression levels were found to be downregulated in 60.7% of isolates treated with tazobactam.

CONCLUSION

Tazobactam can have impact on resistance to aminoglycoside by inhibiting efflux pump. Thus, the combination of tazobactam with amikacin can be used as an alternative treatment approach in multidrug resistant A. baumannii infections.

Immunomodulatory effects of colistin on host responses against carbapenem-resistant Klebsiella pneumoniae biofilms

Colistin (CST) is a last-resort therapeutic option for carbapenem-resistant Klebsiella pneumoniae (CR-Kp) infections in critically ill patients. The effect of subinhibitory CST concentrations (sub-MICs) on biofilm formation is organism-dependent. We investigated the interactions between CST and innate immune cells against CR-Kp biofilms (CR-KpBF) by studying the effect of biofilm sub-MICs of CST on (i) damage induced by human polymorphonuclear neutrophils (PMNs) on CR-KpBF and (ii) the immunomodulatory potential on human mononuclear cells (MNCs) exposed to CR-KpBF. The impact of CST on PMN-induced biofilm damage was assessed by XTT reduction assay. Signal transduction and gene expression profiles in response to CST sub-MICs of MNCs exposed to CR-KpBF were studied by RT-PCR and multiplex ELISA. Pre-exposure of CR-Kp to 0.06 mg/L CST led to subsequent increased PMN-mediated biofilm damage against CR-KpBF in the presence of CST biofilm sub-MICs: there was an additive effect at 2, 4, 8 and 16 mg/L. However, the overall biofilm damage was not >52%. MNCs responded to CR-KpBF through Toll-like receptor 2 (TLR2) by 2.5-fold upregulation and NLRP3 inflammasome activation. CR-KpBF stimulated increased production of interleukin 1-beta (IL-1β), tumour necrosis factor-alpha (TNFα), IL-8 and IL-6. In the combination treatment, 0.5 mg/L CST reduced IL-1β, TNFα and IL-8 levels, whereas at 2 mg/L and 8 mg/L it increased the anti-inflammatory cytokine IL-10 (P < 0.05). Biofilm sub-MICs of CST enhance PMN killing capacity and attenuate production of inflammatory cytokines by MNCs exposed to CR-KpBF, playing a potentially important immunotherapeutic role especially for patients with cytokine deregulation.

Detection of Heavy Metal Tolerance among different MLSB Resistance Phenotypes of Methicillin-Resistant S. aureus (MRSA)

Methicillin-resistant Staphylococcus aureus (MRSA) strains are widespread globally. Besides their virulence factors, the co-occurrence of antimicrobial and metal resistance has been reported. This study was designed to evaluate the antibiotic resistance and resistance phenotypes, investigate the occurrence of virulence factors, and detect heavy metal tolerance among MRSA strains. Antibiogram profiling was done as recommended by CLSI instructions. Resistance phenotypes were detected by D test, followed by characterization of enzymatic activities and biofilm formation assay. Antibacterial activity of different heavy metals was tested, and predictable synergistic assay was performed. Among MRSA strains collected, high resistance to ampicillin and amoxicillin/clavulanate (100%) and high susceptibility to clindamycin (70%) were obtained. Resistance phenotypes were detected as S, constitutive MLSB, inducible MLSB, and MS by percentages of 10%, 30%, 30% and 30% respectively. Virulence factors like lipolytic (50%) and hemolytic (70%) activity, and biofilm formation ability (100%) were detected. High resistance towards potassium and magnesium was observed. MTC of 500 ppm was detected for all isolates in case of cobalt and iron. In case of zinc and copper, MTC was detected as 500 ppm except for one isolate which was highly resistant, and 500 ppm for all isolates except for two isolates which were highly sensitive respectively. Magnesium in different concentrations (500 and 2000 ppm) showed synergistic activity with erythromycin and clindamycin. Results reveal high heavy metal tolerance among antibiotic resistant MRSA strains, in addition to the presence of virulence factors. Upcoming studies must be focused on the combination of sub-inhibitory concentration of different heavy metals with the available antibiotics.

Potentiating the activity of berberine for Staphylococcus aureus in a combinatorial treatment with thymol

A plethora of natural products emerges as attractive molecules in the struggle against antibiotic resistance. These molecules impose their bioactivities not only alone but also in combinations as well, which further enhances their effects. Berberine is a well-known isoquinoline alkaloid with antibacterial activity. Unfortunately, it is readily extruded, which significantly reduces its efficacy and restricts its potential. Thymol is a monoterpenic phenol that exhibits different biological activities but its major effect is observed only at relatively high concentrations, which raises concern on cytotoxicity. The aim of the study was to potentiate the antibacterial activity of berberine, in a combination treatment with thymol in the opportunistic pathogen Staphylococcus aureus and understand the antibacterial mechanism of the combination treatment. The synergism of berberine and thymol was first established by the checkerboard assay. Then the antibacterial mechanism of the synergistic combination was explored by growth curves, biofilm formation assay, SEM observation, and RNA-Seq based transcriptomic profiling. Checkerboard assay showed that 32 μg mL^-1 berberine and 64 μg mL^-1 thymol was a synergistic combination, both concentrations below their cytotoxicity limits for many cells. 32 μg mL^-1 berberine and 32 μg mL^-1 thymol was sufficient to inhibit biofilm formation. SEM images confirmed the morphological changes on the structure of combination treated cells. The major finding of the combination treatment from the transcriptomic analysis was the repression in the expression of virulence factors or genes related to virulence factors. Apart from the particular changes related to the cell envelope, the majority of expressional changes seemed to be similar to berberine-treated cells or to be resulting from general stress conditions. The findings of this work showed that when thymol was used in combination with berberine, it enhanced the antibacterial activity of berberine in a synergistic manner. Furthermore, thymol could be considered as an antivirulence agent, disarming S. aureus cells.

Pharmacokinetic profile of enrofloxacin and its metabolite ciprofloxacin in Asian house geckos (Hemidactylus frenatus) after single-dose oral administration of enrofloxacin

The pharmacokinetics of enrofloxacin and its active metabolite ciprofloxacin were determined following oral administration in 21 Asian house geckos (Hemidactylus frenatus) at a dose of 10 mg/kg. Changes in enrofloxacin and ciprofloxacin plasma concentrations were quantified at regular intervals over 72 h (1, 2, 6, 12, 24, 48, and 72 h). Samples were analysed by high-pressure liquid chromatography (HPLC) and the enrofloxacin pharmacokinetic data underwent a two-compartment analysis. Due to the limited ciprofloxacin plasma concentrations above the lower limit of quantification (LLOQ), the ciprofloxacin data underwent non-compartment analysis and the half-life was determined by the Lineweaver-Burke plot and analysis. The enrofloxacin and ciprofloxacin mean half-lives (t _½) were 0.95 h (α) / 24.36 h (β), and 11.06 h respectively, area under the curve (AUC_0-24h) were 60.56 and 3.14 µg/mL*h, respectively, maximum concentrations (C _max) were 12.31 and 0.24 µg/mL, respectively, and time required to reach the C _max (T _max) were 1 and 2 h respectively. Enrofloxacin was minimally converted to the active metabolite ciprofloxacin, with ciprofloxacin concentrations contributing only 4.91% of the total fluoroquinolone concentrations (AUC_0-24h). Based on the pharmacokinetic indices when using susceptibility breakpoints when determined at mammalian body temperature it is predicted that single oral administration of enrofloxacin (10 mg/kg) would result in plasma concentrations effective against susceptible bacterial species inhibited by an enrofloxacin MIC ≤ 0.5 µg/mL in vitro, but additional studies will be required to determine its efficacy in vivo.

Potential efficacy of garlic lock therapy in combating biofilm and catheter-associated infections; experimental studies on an animal model with focus on toxicological aspects

Background

Life-threatening central venous catheter-related infections are primarily initiated by biofilm formation on the catheter surface. Antibiotic lock therapy is recommended for eradicating intraluminal biofilm. In the era of antibiotic resistance, antibiotics of natural origins provide an effective and cheap option for combating resistant strains. Garlic especially stole the spotlight because of its impressive antimicrobial effectiveness against such superbugs.

Aim

Is to estimate the potential use of fresh garlic extract (FGE) as a lock agent against multi-drug resistant (MDR) bacteria.

Methods

The agar well diffusion and broth microdilution techniques were employed to test the antimicrobial activities of FGE against five MDR strains; E. coli, Pseudomonas aeruginosa (P. aeruginosa), Klebsiella pneumoniae (K. pneumoniae), Serratia marscens (S. marscens) and Methicillin-resistant Staphylococcus aureus (MRSA). Then the protective and therapeutic efficiencies of FGE against bacterial biofilms were in-vitro evaluated; at concentrations of 100, 75, 50 and 25%; in tissue culture plate (TCP) and on the polyurethane (PU) sheets using the crystal violet (CV) assay and colony-forming unit (CFU), respectively. Scanning electron microscopy (SEM) was also used to confirm eradication of biofilms on PU sheets. Finally, systemic and deep tissue infections by P. aeruginosa and MRSA were induced in mice that were then treated by FGE at either 100 or 200 mg/kg for seven days. Where the antibacterial activity was assessed by tissue and blood culturing at the end of the treatment period. Biochemical, hematological and histological parameters were also investigated.

Results

FGE exhibited potent in-vitro and in-vivo antibacterial and antibiofilm activities against MDR strains. It not only didn’t exhibit toxicological effects at the hematological and the histological levels but also provided protective effects as demonstrated by the significant drop in the biochemical parameters.

Conclusion

FGE has the potential to be used as a prophylactic and/or therapeutic lock agent against biofilm-associated infections caused by MDR bacteria.

Adaptation of Pseudomonas aeruginosa clinical isolates to benzalkonium chloride retards its growth and enhances biofilm production

The increasing percentage of Pseudomonas aeruginosa strains that are resistant to multiple antibiotics is a global problem. The exposure of P. aeruginosa isolates to repeated sub lethal concentrations of biocides in hospitals and communities may be one of the causes leading to increased antibiotic resistance. Benzalkonium chloride (BAC) is widely used as disinfectant and preservative. This study investigated the effect of exposure of P. aeruginosa clinical isolates to sub lethal concentrations of BAC on their antibiotic resistance, growth process and biofilm formation. The collected 43 P. aeruginosa clinical isolates were daily subjected to increasing sub lethal concentrations of BAC. The effect of adaptation on antibiotic resistance, growth process, cell surface hydrophobicity and biofilm formation of P. aeruginosa isolates were examined. Interestingly, Most P. aeruginosa isolates adapted to BAC showed an increase in antibiotic resistance and 66% of the isolates showed retardation of growth, 63% showed increased cell surface hydrophobicity and 23.5% exhibited enhanced biofilm formation by crystal violet assay. To define whether the effect of BAC adaptation on biofilm production was manifested at the transcriptional level, quantitative RT-PCR was used. We found that 60% of the tested isolates showed overexpression of ndvB biofilm gene. More efforts are required to diminish the increasing use of BAC to avoid bacterial adaptation to this biocide with subsequent retardation of growth and enhanced biofilm formation which could lead to antibiotic resistance and treatment failure of infections caused by this opportunistic pathogen.