The origin of sequence type 72 community-associated methicillin-resistant Staphylococcus aureus (MRSA) and fusidic acid (FA) resistant sequence type 5 MRSA: Analysis of FA resistance and spa type in a single center in South Korea

INTRODUCTION

We investigated the prevalence of fusidic acid (FA) resistance in MSSA and MRSA stratified by sequence (ST) and spa types, and determined the prevalence of FA resistance mechanisms.

METHODS

From August 2014 to April 2020, S. aureus blood isolates were collected in Asan Medical Center, Seoul, South Korea. Antimicrobial susceptibility tests were performed using broth microdilution and interpreted according to EUCAST's FA criteria. We performed spa typing for fusA mutation presence and acquired FA resistance determinants (fusB, fusC, and fusD) by PCR.

RESULTS

Of the 590 MRSA isolates, 372 were FA resistant, and among 425 MSSA isolates, 136 were resistant. Of the 380 ST5-MRSA isolates, 350 were FA resistant, whereas only 1 of 14 ST5-MSSA isolates was FA resistant. Conversely, of the 163 ST72-MRSA isolates, only 8 were resistant, whereas 37 of 42 ST72-MSSA were resistant. The fusA mutation (80%) was the most common determinant. The one FA resistant ST5-MSSA isolate belonged to the t2460 spa type, the most common spa type (24 of 35 isolates) of FA resistant ST5-MRSA. In addition, t324 and t148, which are minor spa types of ST72-MSSA, were susceptible to FA, in contrast to other ST72-MSSA spa types, and the major spa type of ST72-MRSA (110 of 163 isolates).

CONCLUSIONS

FA resistance was common in ST5-MRSA and ST72-MSSA, and rare in ST5-MSSA and ST72-MRSA. Our findings suggest that minor clones of ST5-MSSA isolates, with the fusA mutation and minor clones of ST72-MSSA susceptible to FA, may have evolved to harbor the mecA gene.

A Nanocomposite Dynamic Covalent Cross-Linked Hydrogel Loaded with Fusidic Acid for Treating Antibiotic-Resistant Infected Wounds

Methicillin-resistant Staphylococcus aureus (MRSA) is associated with high levels of morbidity and is considered a difficult-to-treat infection, often requiring nonstandard treatment regimens and antibiotics. Since over 40% of the emerging antibiotic compounds have insufficient solubility that limits their bioavailability and thus efficacy through oral or intravenous administration, it is crucial that alternative drug delivery products be developed for wound care applications. Existing effective treatments for soft tissue MRSA infections, such as fusidic acid (FA), which is typically administered orally, could also benefit from alternative routes of administration to improve local efficacy and bioavailability while reducing the required therapeutic dose. Herein, we report an antimicrobial poly(oligoethylene glycol methacrylate) (POEGMA)-based composite hydrogel loaded with fusidic acid-encapsulating self-assembled polylactic acid-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (PLA-POEGMA) nanoparticles for the treatment of MRSA-infected skin wounds. The inclusion of the self-assembled nanoparticles (380 nm diameter when loaded with fusidic acid) does not alter the favorable mechanical properties and stability of the hydrogel in the context of its use as a wound dressing, while fusidic acid (FA) can be released from the hydrogel over ∼10 h via a diffusion-controlled mechanism. The antimicrobial studies demonstrate a clear zone of inhibition in vitro and a 1-2 order of magnitude inhibition of bacterial growth in vivo in an MRSA-infected full-thickness excisional murine wound model even at very low antibiotic doses. Our approach thus can both circumvent challenges in the local delivery of hydrophobic antimicrobial compounds and directly deliver antimicrobials into the wound to effectively combat methicillin-resistant infections using a fraction of the drug dose required using other clinically relevant strategies.

Novel Microemulsion Containing Benzocaine and Fusidic Acid Simultaneously: Formulation, Characterization, and In Vitro Evaluation for Wound Healing

Modern drug carrier technologies, such as microemulsions with small droplet sizes and high surface areas, improve the ability of low water solubility active ingredients to permeate and localize. The goal of this study was to create microemulsion formulations for wound healing that contained both fusidic acid (FA), an antibacterial agent, and benzocaine (BNZ), a local anesthetic. Studies on characterization were carried out, including viscosity, droplet size, and zeta potential. The drug-loaded microemulsion had a stable structure with -3.014 ± 1.265 mV of zeta potential and 19.388 ± 0.480 nm of droplet size. In both in vitro release and ex vivo permeability studies, the microemulsion was compared with Fucidin cream and oily BNZ solution. According to the drug release studies, BNZ release from the microemulsion and the BNZ solution showed a similar profile (p > 0.05), while FA release from the microemulsion had a higher drug release compared to Fucidin cream (p < 0.001). The microemulsion presented lower drug permeation (p > 0.05) for both active ingredients, on the other hand, provided higher drug accumulation compared to the control preparations. Moreover, according to the results of in vitro wound healing activity, the microemulsion indicated a dose-dependent wound healing potential with the highest wound healing activity at the highest concentrations. To the best of our knowledge, this developed BNZ- and FA-loaded microemulsion would be a promising candidate to create new opportunities for wound healing thanks to present the active ingredients, which have low water solubility, in a single formulation and achieved higher accumulation than control preparations.

The anti-staphylococcal fusidic acid as an efflux pump inhibitor combined with fluconazole against vaginal candidiasis in mouse model

BACKGROUND

Candida albicans is the most common fungus that causes vaginal candidiasis in immunocompetent women and catastrophic infections in immunocompromised patients. The treatment of such infections is hindered due to the increasing emergence of resistance to azoles in C. albicans. New treatment approaches are needed to combat candidiasis especially in the dwindled supply of new effective and safe antifungals. The resistance to azoles is mainly attributed to export of azoles outside the cells by means of the efflux pump that confers cross resistance to all azoles including fluconazole (FLC).

OBJECTIVES

This study aimed to investigate the possible efflux pump inhibiting activity of fusidic acid (FA) in C. albicans resistant isolates and the potential use of Fusidic acid in combination with fluconazole to potentiate the antifungal activity of fluconazole to restore its activity in the resistant C. albicans isolates.

METHODS

The resistance of C. albicans isolates was assessed by determination of minimum inhibitory concentration. The effect of Fusidic acid at sub-inhibitory concentration on efflux activity was assayed by rhodamine 6G efflux assay and intracellular accumulation. Mice model studies were conducted to evaluate the anti-efflux activity of Fusidic acid and its synergistic effects in combination with fluconazole. Impact of Fusidic acid on ergosterol biosynthesis was quantified. The synergy of fluconazole when combined with Fusidic acid was investigated by determination of minimum inhibitory concentration. The cytotoxicity of Fusidic acid was tested against erythrocytes. The effect of Fusidic acid on efflux pumps was tested at the molecular level by real-time PCR and in silico study. In vivo vulvovaginitis mice model was used to confirm the activity of the combination in treating vulvovaginal candidiasis.

RESULTS

Fusidic acid showed efflux inhibiting activity as it increased the accumulation of rhodamine 6G, a substrate for ABC-efflux transporter, and decreased its efflux in C. albicans cells. The antifungal activity of fluconazole was synergized when combined with Fusidic acid. Fusidic acid exerted only minimal cytotoxicity on human erythrocytes indicating its safety. The FA efflux inhibitory activity could be owed to its ability to interfere with efflux protein transporters as revealed by docking studies and downregulation of the efflux-encoding genes of both ABC transporters and MFS superfamily. Moreover, in vivo mice model showed that using fluconazole-fusidic acid combination by vaginal route enhanced fluconazole antifungal activity as shown by lowered fungal burden and a negligible histopathological change in vaginal tissue.

CONCLUSION

The current findings highlight FA's potential as a potential adjuvant to FLC in the treatment of vulvovaginal candidiasis.

New fusidane-type nortriterpenoids from the Arctic marine-derived fungus Simplicillium lamellicola culture medium with their inhibitory effect on benign prostatic hyperplasia

Three new fusidane-type nortriterpenoids, simplifusinolide A, 24-epi simplifusinolide A, and simplifusidic acid L (1-3), were isolated from the EtOAc extract of the Arctic marine-derived fungus Simplicillium lamellicola culture medium, together with fusidic acid (4) and 16-O-deacetylfusicid acid (5). The structures of the isolated compounds were elucidated by NMR and MS analyses. The absolute configurations of compounds 1-3 were established by the quantum mechanical calculations of electronic circular dichroism and gauge-including atomic orbital NMR chemical shifts, followed by DP4 + analysis. Benign prostatic hyperplasia (BPH) is a major urological disorder in men worldwide. The anti-BPH potentials of the isolated compounds were evaluated using BPH-1 and WPMY-1 cells. Treatment with simplifusidic acid L (3) and fusidic acid (4) significantly downregulated the mRNA levels of the androgen receptor (AR) and its downstream effectors, inhibiting the proliferation of BPH-1 cells. Specifically, treatment with 24-epi simplifusinolide A (2) significantly suppressed the cell proliferation of both BPH-1 and DHT-stimulated WPMY-1 cells by inhibiting AR signaling. These results suggest the potential of 24-epi simplifusinolide A (2), simplifusidic acid L (3) and fusidic acid (4) as alternative agents for BPH treatment by targeting AR signaling.

Neutrophil-targeted combinatorial nanosystems for suppressing bacteremia-associated hyperinflammation and MRSA infection to improve survival rates

There is currently no specific and effective treatment for bacteremia-mediated sepsis. Hence, this study engineered a combinatorial nanosystem containing neutrophil-targeted roflumilast-loaded nanocarriers and non-targeted fusidic acid-loaded nanoparticles to enable the dual mitigation of bacteremia-associated inflammation and methicillin-resistant Staphylococcus aureus (MRSA) infection. The targeted nanoparticles were developed by conjugating anti-lymphocyte antigen 6 complex locus G6D (Ly6G) antibody fragment on the nanoparticulate surface. The particle size and zeta potential of the as-prepared nanosystem were about 200 nm and -25 mV, respectively. The antibody-conjugated nanoparticles showed a three-fold increase in neutrophil internalization compared to the unfunctionalized nanoparticles. As a selective phosphodiesterase (PDE) 4 inhibitor, the roflumilast in the nanocarriers largely inhibited cytokine/chemokine release from the activated neutrophils. The fusidic acid-loaded nanocarriers were vital to eliminate biofilm MRSA colony by 3 log units. The nanoparticles drastically decreased the intracellular bacterial count compared to the free antibiotic. The in vivo mouse bioimaging demonstrated prolonged retention of the nanosystem in the circulation with limited organ distribution and liver metabolism. In the mouse bacteremia model, the multifunctional nanosystem produced a 1‒2 log reduction of MRSA burden in peripheral organs and blood. The functionalized nanosystem arrested the cytokine/chemokine overexpression greater than the unfunctionalized nanocarriers and free drugs. The combinatory nanosystem also extended the median survival time from 50 to 103 h. No toxicity from the nanoformulation was found based on histology and serum biochemistry. Furthermore, our data proved that the active neutrophil targeting by the versatile nanosystem efficiently alleviated MRSA infection and organ dysfunction caused by bacteremia. STATEMENT OF SIGNIFICANCE: Bacteremia-mediated sepsis poses a significant challenge in clinical practice, as there is currently no specific and effective treatment available. In our study, we have developed a novel combinatorial nanosystem to address this issue. Our nanosystem consists of neutrophil-targeted roflumilast-loaded nanocarriers and non-targeted fusidic acid-loaded nanoparticles, enabling the simultaneous mitigation of bacteremia-associated inflammation and MRSA infection. Our nanosystem demonstrated the decreased neutrophil activation, effective inhibition of cytokine release, elimination of MRSA biofilm colonies, and reduced intracellular bacterial counts. In vivo experiments showed prolonged circulation, limited organ distribution, and increased survival rates in a mouse bacteremia model. Importantly, our nanosystem exhibited no toxicity based on comprehensive assessments.

Synthesis and structure-activity relationship studies of fusidic acid derivatives as anti-inflammatory agents for acute lung injury

Acute lung injury (ALI) are severe forms of diffuse lung disease that impose a substantial health burden all over the world. In the United States, approximately 190,000 cases per year of ALI each year, with an associated 74,500 deaths per year. Anti-inflammatory therapy has become a reasonable approach for the treatment of patients with ALI. In this study, fusidic acid derivatives were used to design new anti-inflammatory compounds with high pharmacological activity and low toxicity. A total of 30 new fusidic acid derivatives were discovered, synthesized, and screened for their anti-inflammatory activity against lipopolysaccharide (LPS)-treated RAW264.7 cells. Of them, b2 was found to be the most active, with a higher efficiency compared with fusidic acid and celecoxib in 10 μM. In vitro, we further measured b2 inhibited inflammatory factor NO (IC50 = 5.382 ± 0.655 μM), IL-6 (IC50 = 7.767 ± 0.871 μM), and TNF-α (IC50 = 7.089 ± 0.775 μM) and b2 inhibited inflammatory cytokines COX-2 and iNOS, ROS production, NF-κB/MAPK and Bax/Bcl-2 signaling pathway pathway. In vivo,b2 attenuated ALI pathological changes and inhibited inflammatory cytokines COX-2 and iNOS in lung tissue and NF-κB/MAPK and Bax/Bcl-2 signaling pathway. In conclusion, b2 may be a promising anti-inflammatory lead compound.

An unusual outbreak in the Netherlands: community-onset impetigo caused by a meticillin-resistant Staphylococcus aureus with additional resistance to fusidic acid, June 2018 to January 2020

In this retrospective observational study, we analysed a community outbreak of impetigo with meticillin-resistant Staphylococcus aureus (MRSA), with additional resistance to fusidic acid (first-line treatment). The outbreak occurred between June 2018 and January 2020 in the eastern part of the Netherlands with an epidemiological link to three cases from the north-western part. Forty nine impetigo cases and eight carrier cases were identified, including 47 children. All but one impetigo case had community-onset of symptoms. Pharmacy prescription data for topical mupirocin and fusidic acid and GP questionnaires suggested an underestimated outbreak size. The 57 outbreak isolates were identified by the Dutch MRSA surveillance as MLVA-type MT4627 and sequence type 121, previously reported only once in 2014. Next-generation sequencing revealed they contained a fusidic acid resistance gene, exfoliative toxin genes and an epidermal cell differentiation inhibitor gene. Whole-genome multilocus sequence typing revealed genetic clustering of all 19 sequenced isolates from the outbreak region and isolates from the three north-western cases. The allelic distances between these Dutch isolates and international isolates were high. This outbreak shows the appearance of community-onset MRSA strains with additional drug resistance and virulence factors in a country with a low prevalence of antimicrobial resistance.

[Susceptibility of drug-resistant staphylococci isolated from different parts of the ocular anterior segment to common ophthalmic antibiotics]

Objectie To investigate the susceptibility of drug-resistant staphylococci isolated from different parts of the anterior segment to levofloxacin, tobramycin, cefazolin sodium, fusidic acid and clindamycin. Methods: Experimental Study. A total of 67 patients with anterior segment infection (33 cases of conjunctivitis, 6 cases of bacterial keratitis, 7 cases of blepharitis, 9 cases of neonatal dacryocystitis, 9 cases of neonatal dacryocystitis, 1 case of adult dacryocystitis and 11 cases of other infectious eye diseases) were collected from the conjunctival sac, cornea, eyelid margin and lacrimal sac. Minimum inhibitory concentration (MIC) determination of methicillin-resistant Staphylococcus (MRS) strains and β-lactamase-producing (β-Lac) strains by a micro-liquid-based method, according to the M100 standard of the American Institute for Clinical and Laboratory Standardization Susceptibility and resistance determinations were made. Data were statistically analyzed using Chi-square or Fisher's exact test. Results: Thirty-five MRS, 30 β-Lac and 2 β-Lac MRS isolates were identified from 67 multidrug-resistant Staphylococcus . There were 3, 9, 4, and 19 MRS isolates isolated from the lacrimal sac, cornea, eyelid margin and conjunctival sac, accounting for 3/4, 9/12, 4/8, 19/43 (44.2%) of the isolated sites respectively. There were 1, 3, 3, and 23 β-Lac isolates, accounting for 1/4, 3/12, 3/8 and 23/43 (53.5%) of the isolated sites, respectively. The highest proportion of β-Lac isolates isolated from patients with a diagnosis of conjunctivitis was 17 (25.3%) from the conjunctival sac. Among the MRS strains isolated from the cornea and lacrimal sac, 5 (7.5%) and 3 (4.5%) were from patients diagnosed with bacterial keratitis and neonatal tear, respectively. The number of MRS strains and β-Lac isolates isolated from patients with a diagnosis of blepharitis were both 3 (4.5%) from the lid margin.Among the strains isolated from the eyelid margin and the conjunctival sac, drug-resistant Staphylococcus epidermidis was the main strain, the drug-resistant Staphylococcus aureus was the major isolates in lacrimal sac and cornea. Among the 35 MRS isoaltes, 25, 24, 12, 12, and 11 were sensitive to cefazolin sodium, fusidic acid, levofloxacin, clindamycin and tobramycin, and the sensitivity rates were 71.4%, 68.6%, 34.3%, 34.3% and 31.4%, the difference was statistically significant (χ²=22.756, P<0.001), The sensitivity rates of levofloxacin, tobramycin, cefazolin sodium, fusidic acid and clindamycin against MRS isolates from the anterior segment were both statistically significant differences (χ²=18.493, 11.594, 8.906, 9.841, 16.059; all P<0.05). The susceptibility rates of MRS isolates against five antibiotics was statistically significant differences (χ²=33.080, P<0.001). Among the 30 β-Lac isolates, 27, 22, 19, 16, and 8 were sensitive to cefazolin sodium, fusidic acid, levofloxacin, tobramycin and clindamycin, and the sensitivity rates were 90.0 % , 73.3%, 63.3%, 53.3% and 26.7%, the difference was statistically significant (χ²=28.280, P<0.001). The sensitivity rates of five antibiotics against β-Lac isolates from the anterior segment were both statistically significant differences (χ²=50.971, 24.543, 48.147, 44.899, 18.676; all P<0.001). The susceptibility rates of β-Lac isolates against five antibiotics was statistically significant differences (χ²=23.383, P<0.001). The sensitivity of cefazolin sodium and fusidic acid against β-Lac isolates were higher than MRS isolates. Conclusions: Cefazolin sodium and fusidic acid may be the best choice for the treatment of drug-resistant Staphylococcus isolated from anterior conjunctival sac, cornea, eyelid margin and lacrimal sac, especially for β-Lac-producing drug-resistant Staphylococcus infection.

A fusidic acid-resistant (PVL+) clone is associated with the increase in methicillin-resistant Staphylococcus aureus in New Caledonia

OBJECTIVES

Since 2014, Staphylococcus aureus methicillin resistance is rapidly increasing in New Caledonia and is associated with potential serious clinical repercussions. In the present study, we investigated the epidemiology of Methicillin-Resistant S. aureus (MRSA) in New Caledonia and the possible emergence of a particular clonal strain.

METHODS

An overview of the distribution of MRSA in New Caledonia in 2019 is presented. We collected and analysed 171 clinical MRSA isolates from New Caledonia medical laboratories during August and September 2019. Among this collection, 49 representative isolates were analyzed by the French National Reference Center for Staphylococci using StaphyType DNA microarray allowing genetic characterization of the isolates.

RESULTS

Among the 1144 S. aureus isolated over the year 2019, 442 isolates (39%) were resistant to methicillin and 62% of these isolates were resistant to fusidic acid (FA). During the inclusion period, FA resistance rate was similar (60%). Genetic characterization evidenced CC6 as the predominant clonal complex (70%) with 26 isolates (53%) identified as CC6-MRSA-[IV+fus] (PVL+).

CONCLUSIONS

These findings demonstrated a low diversity of MRSA in New Caledonia with the dominance of a clonal complex not reported previously. The frequent fusidic acid (FA) resistance in MRSA was associated with a high prevalence of fusC, suggesting that FA misuse contributed to driving the selection of this clone. Our findings suggest the recommendation to stop the topical use of FA to control the emergence of this severe MRSA clone and decrease the rate of MRSA in New Caledonia.

Fusidic acid in a tertiary hospital: an observational study focusing on prescriptions, tolerance and susceptibility of Staphylococcus and Cutibacterium spp. strains from bone samples

Adverse drug reactions of broad-spectrum fluoroquinolones or rifampicin are not uncommon during osteomyelitis and orthopaedic implant infections (OOII). Thus, we made an overview (i) of the prescription of fusidic acid (FA) and (ii) of FA susceptibility of Staphylococcus sp. and Cutibacterium sp. strains isolated from bone samples. All prescriptions of FA and all bone samples with positive culture for Staphylococcus sp. or Cutibacterium sp. (Reims University Hospital June 2017-May 2021) were included. All Staphylococcus aureus strains were considered as significant, whereas Coagulase-negative Staphylococcus and Cutibacterium spp. strains were not if these strains grew only on one sole sample. The antibiotic susceptibility of Staphylococcus sp. strains and the susceptibility to FA of Cutibacterium sp. strains had been determined using disk diffusion methods, as described for Staphylococcus sp. in the CASFM/EUCAST guidelines. The mean FA consumption was 0.6 daily defined doses/1000 patient days. FA was prescribed for OOII due to Staphylococcus sp. and Cutibacterium sp. in 24 and 2 cases, respectively. Among 401 Staphylococcus sp. strains, there were 254 S. aureus (63.3%), 84 methicillin-resistant (20.9%) and 333 FA-susceptible (83.0%) strains. S. aureus and methicillin-sensitive strains were more likely to be susceptible to FA (p < 0.001). Among 39 Cutibacterium sp. strains, the FA inhibition zone diameter geometric mean was 28.6 mm (24-35 mm), suggesting that all these strains could be considered as susceptible to FA. These data suggested that FA could be more frequently used in OOII due to Staphylococcus sp. and Cutibacterium sp., subject to the absence of other resistant bacteria.

The cyclic octapeptide antibiotic argyrin B inhibits translation by trapping EF-G on the ribosome during translocation

Argyrins are a family of naturally produced octapeptides that display promising antimicrobial activity against Pseudomonas aeruginosa. Argyrin B (ArgB) has been shown to interact with an elongated form of the translation elongation factor G (EF-G), leading to the suggestion that argyrins inhibit protein synthesis by interfering with EF-G binding to the ribosome. Here, using a combination of cryo-electron microscopy (cryo-EM) and single-molecule fluorescence resonance energy transfer (smFRET), we demonstrate that rather than interfering with ribosome binding, ArgB rapidly and specifically binds EF-G on the ribosome to inhibit intermediate steps of the translocation mechanism. Our data support that ArgB inhibits conformational changes within EF-G after GTP hydrolysis required for translocation and factor dissociation, analogous to the mechanism of fusidic acid, a chemically distinct antibiotic that binds a different region of EF-G. These findings shed light on the mechanism of action of the argyrin-class antibiotics on protein synthesis as well as the nature and importance of rate-limiting, intramolecular conformational events within the EF-G-bound ribosome during late-steps of translocation.

Fusidic acid derivatives from the endophytic fungus Acremonium pilosum F47

Fusidic acid, a representative member of fungal fusidane triterpenoids, has been clinically used as an antibiotic. In the present study, fusidic acid (1), and its known analogs 16-desacetylfusidic acid (2) and 3β,20-dihydroxy-protosta-16,24-dien-29-oic acid (4), together with one new derivative acremonidiol A (3), were isolated from the endophytic fungus, Acremonium pilosum F47. Their structures were determined by MS and NMR. The spectroscopic data of 2 are firstly reported here. The antibacterial efficacies of 1-4 were evaluated against four selected Gram-positive or Gram-negative bacteria. As expected, only compound 1 showed strong inhibitory effect on Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis.

The global prevalence of fusidic acid resistance in clinical isolates of Staphylococcus aureus: a systematic review and meta-analysis

BACKGROUND AND AIM

Staphylococcus aureus (S. aureus) is one of the most common pathogens causing nosocomial and community-acquired infections with high morbidity and mortality rates. Fusidic acid has been increasingly used for the treatment of infections due to methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). The present study aimed to determine the precise prevalence of fusidic acid resistant MRSA (FRMRSA), fusidic acid resistant MSSA (FRMSSA), and total fusidic acid resistant S. aureus (FRSA) on a global scale.

METHODS

Several international databases including Medline, Embase, and the Web of Sciences were searched (2000-2020) to discern studies addressing the prevalence of FRSA, FRMRSA, and FRMSSA. STATA (version14) software was used to interpret the data.

RESULTS

Of the 1446 records identified from the databases, 215 studies fulfilled the eligibility criteria for the detection of FRSA (208 studies), FRMRSA (143 studies), and FRMSSA (71 studies). The analyses manifested that the global prevalence of FRSA, FRMRSA, and FRMSSA was 0.5%, 2.6% and 6.7%, respectively.

CONCLUSION

This meta-analysis describes an increasing incidence of FRSA, FRMSSA, and FRMRSA. These results indicate the need for prudent prescription of fusidic acid to stop or diminish the incidence of fusidic acid resistance as well as the development of strategies for monitoring the efficacy of fusidic acid use.

New Helvolic Acid Derivatives with Antibacterial Activities from Sarocladium oryzae DX-THL3, an Endophytic Fungus from Dongxiang Wild Rice (Oryza rufipogon Griff.)

Three new helvolic acid derivatives (named sarocladilactone A (1), sarocladilactone B (2) and sarocladic acid A (3a)), together with five known compounds (6,16-diacetoxy-25-hy- droxy-3,7-dioxy-29-nordammara-1,17(20)-dien-21-oic acid (3b), helvolic acid (4), helvolinic acid (5), 6-desacetoxy-helvolic acid (6) and 1,2-dihydrohelvolic acid (7)), were isolated from the endophytic fungus DX-THL3, obtained from the leaf of Dongxiang wild rice (Oryza rufipogon Griff.). The structures of the new compounds were elucidated via HR-MS, extensive 1D and 2D NMR analysis and comparison with reported data. Compounds 1, 2, 4, 5, 6 and 7 exhibited potent antibacterial activities. In particular, sarocladilactone B (2), helvolinic acid (5) and 6-desacetoxy-helvolic acid (6) exhibited strongly Staphylococcus aureus inhibitory activity with minimum inhibitory concentration (MIC) values of 4, 1 and 4 μg/mL, respectively. The structure–activity relationship (SAR) of these compounds was primarily summarized.

Do Antimicrobial Resistance Patterns Matter? An Algorithm for the Treatment of Patients With Impetigo

BACKGROUND

Impetigo, a highly contagious bacterial skin infection commonly occurring in young children, but adults may also be affected. The superficial skin infection is mainly caused by Staphylococcus aureus (S. aureus) and less frequently by Streptococcus pyogenes (S. pyogenes). Antimicrobial resistance has become a worldwide concern and needs to be addressed when selecting treatment for impetigo patients. An evidence-based impetigo treatment algorithm was developed to address the treatment of impetigo for pediatric and adult populations.

METHODS

An international panel of pediatric dermatologists, dermatologists, pediatricians, and pediatric infectious disease specialists employed a modified Delphi technique to develop the impetigo treatment algorithm. Treatment recommendations were evidence-based, taking into account antimicrobial stewardship and the increasing resistance to oral and topical antibiotics.

RESULTS

The algorithm includes education and prevention of impetigo, diagnosis and classification, treatment measures, and follow-up and distinguishes between localized and widespread or epidemic outbreaks of impetigo. The panel adopted the definition of localized impetigo of fewer than ten lesions and smaller than 36 cm2 area affected in patients of two months and up with no compromised immune status. Resistance to oral and topical antibiotics prescribed for the treatment of impetigo such as mupirocin, retapamulin, fusidic acid, have been widely reported.

CONCLUSIONS

When prescribing antibiotics, it is essential to know the local trends in antibiotic resistance. Ozenoxacin cream 1% is highly effective against S. pyogenes and S. aureus, including methycyllin-susceptible and resistant strains (MRSA), and may be a suitable option for localized impetigo.J Drugs Dermatol. 2021;20(2):134-142. doi:10.36849/JDD.5475 THIS ARTICLE HAD BEEN MADE AVAILABLE FREE OF CHARGE. PLEASE SCROLL DOWN TO ACCESS THE FULL TEXT OF THIS ARTICLE WITHOUT LOGGING IN. NO PURCHASE NECESSARY. PLEASE CONTACT THE PUBLISHER WITH ANY QUESTIONS.

Cheminformatics-Based Identification of Potential Novel Anti-SARS-CoV-2 Natural Compounds of African Origin

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome virus 2 (SARS-CoV-2) has impacted negatively on public health and socioeconomic status, globally. Although, there are currently no specific drugs approved, several existing drugs are being repurposed, but their successful outcomes are not guaranteed. Therefore, the search for novel therapeutics remains a priority. We screened for inhibitors of the SARS-CoV-2 main protease and the receptor-binding domain of the spike protein from an integrated library of African natural products, compounds generated from machine learning studies and antiviral drugs using AutoDock Vina. The binding mechanisms between the compounds and the proteins were characterized using LigPlot+ and molecular dynamics simulations techniques. The biological activities of the hit compounds were also predicted using a Bayesian-based approach. Six potential bioactive molecules NANPDB2245, NANPDB2403, fusidic acid, ZINC000095486008, ZINC0000556656943 and ZINC001645993538 were identified, all of which had plausible binding mechanisms with both viral receptors. Molecular dynamics simulations, including molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) computations revealed stable protein-ligand complexes with all the compounds having acceptable free binding energies <-15 kJ/mol with each receptor. NANPDB2245, NANPDB2403 and ZINC000095486008 were predicted as antivirals; ZINC000095486008 as a membrane permeability inhibitor; NANPDB2403 as a cell adhesion inhibitor and RNA-directed RNA polymerase inhibitor; and NANPDB2245 as a membrane integrity antagonist. Therefore, they have the potential to inhibit viral entry and replication. These drug-like molecules were predicted to possess attractive pharmacological profiles with negligible toxicity. Novel critical residues identified for both targets could aid in a better understanding of the binding mechanisms and design of fragment-based de novo inhibitors. The compounds are proposed as worthy of further in vitro assaying and as scaffolds for the development of novel SARS-CoV-2 therapeutic molecules.

Fusidic Acid Resistance Determinants in Methicillin-Resistant Staphylococcus aureus Isolated in Kuwait Hospitals

OBJECTIVE

The aim of this study was to investigate the genetic determinants of fusidic acid (FA) resistance in MRSA isolated from patients in Kuwait hospitals.

METHODS

The minimum inhibitory concentration (MIC) of FA was tested with E-test strips. Genetic determinants of FA were determined by PCR and DNA microarray. Staphylococcal protein A gene (spa) typing and DNA microarray analysis were used to study their genetic backgrounds.

RESULTS

The FA MIC ranged from 2 mg/L to >256 mg/L. Of the 97 isolates, 79 (81.4%) harbored fusC, 14 isolates harbored fusA mutations (fusA), and 4 isolates harbored fusB. Isolates with fusA mutations expressed high FA MIC (MIC >256 mg/L), whereas those with fusC and fusB expressed low FA MIC (MIC 2-16 mg/L). The isolates belonged to 23 spa types and 12 clonal complexes (CCs). The major spa types were t688 (n = 25), t311 (n = 14), t860 (n = 8), and t127 (n = 6) which constituted 54.6% of the isolates. The 12 CCs were CC1, CC5, CC8, CC15, CC22, CC80, CC88, and CC97 with CC5 (45.6%) and CC97 (13.2%) as the dominant CCs.

CONCLUSIONS

The MRSA isolates belonged to diverse genetic backgrounds with the majority carrying the fusC resistance determinants. The high prevalence of FA resistance belonging to diverse genetic backgrounds warrants a review of FA usage in the country to preserve its therapeutic benefits.

Fusidic acid resistance through changes in the dynamics of the drug target

Antibiotic resistance in clinically important bacteria can be mediated by target protection mechanisms, whereby a protein binds to the drug target and protects it from the inhibitory effects of the antibiotic. The most prevalent source of clinical resistance to the antibiotic fusidic acid (FA) is expression of the FusB family of proteins that bind to the drug target (Elongation factor G [EF-G]) and promote dissociation of EF-G from FA-stalled ribosome complexes. FusB binding causes changes in both the structure and conformational flexibility of EF-G, but which of these changes drives FA resistance was not understood. We present here detailed characterization of changes in the conformational flexibility of EF-G in response to FusB binding and show that these changes are responsible for conferring FA resistance. Binding of FusB to EF-G causes a significant change in the dynamics of domain III of EF-GC3 that leads to an increase in a minor, more disordered state of EF-G domain III. This is sufficient to overcome the steric block of transmission of conformational changes within EF-G by which FA prevents release of EF-G from the ribosome. This study has identified an antibiotic resistance mechanism mediated by allosteric effects on the dynamics of the drug target.

Antimicrobial activity of fusidic acid inclusion complexes

OBJECTIVES

To synthesize and characterize the inclusion complexes of fusidic acid with β - cyclodextrin, followed by the evaluation of their antimicrobial activity against pure strain (Staphylococcus aureus ATCC 25,923) and isolated Staphylococcus from clinical cases.

METHODS

The desired compounds were synthesized using molar ratio of fusidic acid: β-cyclodextrin of 1:1. Synthesized compounds were analyzed by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Thermal Analysis, and the results confirmed the formation of inclusion compounds by fusidic acid with β-cyclodextrin.

RESULTS

Physical-chemical characterization confirmed the preparation of desired inclusion compounds, and the antimicrobial test confirmed that all compounds obtained have antimicrobial activity. Antimicrobial activity of freeze-drying complex againstS. aureus is similar with pure fusidic acid activity, being better than the cefoxitin one. Similar behavior was observed against methicillin-resistant S. aureus and S. epidermidis.

CONCLUSIONS

In the present work, three different inclusion complexes of fusidic acid were prepared using three different preparation methods. All inclusion complexes obtained presented good antimicrobial activity against differentS. aureus strains. Antimicrobial activity of these new prepared compounds was observed to be better than that of cefoxitin.

NF-κB Inhibitory and Antibacterial Helvolic and Fumagillin Derivatives from Aspergillus terreus

Two new helvolic acid analogues (1 and 2) and one new fumagillin derivative containing an octahydroisobenzofuran moiety (3), together with four known compounds (4-7), were isolated from an Aspergillus terreus, isolated from soil collected from Mauna Kea, the highest mountain in Hawaii. Compound 4 was recorded in SciFinder with a CAS Registry Number of 1379525-35-5, but it was not documented in the cited reference (ACS Chem. Biol. 2012, 7, 137). The structures of compounds 1-4 were elucidated by NMR spectroscopy and HRMS and ECD analysis. Compounds 5 and 6 showed significant inhibitory activity against NF-κB with IC₅₀ values of 2.7 ± 2.6 and 6.5 ± 0.8 μM, respectively. Compounds 1 and 2 were active against S. aureus with MICs of 6.25 and 6.25 μg/mL, respectively, while compound 5 inhibited E. coli with an MIC of 3.12 μg/mL.

Disruption of transcription-translation coordination in Escherichia coli leads to premature transcriptional termination

Tight coordination between transcription and translation is crucial to maintaining the integrity of gene expression in bacteria, yet how bacteria manage to coordinate these two processes remains unclear. Possible direct physical coupling between the RNA polymerase and ribosome has been thoroughly investigated in recent years. Here, we quantitatively characterize the transcriptional kinetics of Escherichia coli under different growth conditions. Transcriptional and translational elongation remain coordinated under various nutrient conditions, as previously reported. However, transcriptional elongation was not affected under antibiotics that slowed down translational elongation. This result was also found by introducing nonsense mutation that completely dissociated transcription from translation. Our data thus provide direct evidence that translation is not required to maintain the speed of transcriptional elongation. In cases where transcription and translation are dissociated, our study provides quantitative characterization of the resulting process of premature transcriptional termination (PTT). PTT-mediated polarity caused by translation-targeting antibiotics substantially affected the coordinated expression of genes in several long operons, contributing to the key physiological effects of these antibiotics. Our results also suggest a model in which the coordination between transcriptional and translational elongation under normal growth conditions is implemented by guanosine tetraphosphate.

Characterisation of a novel SCCmec VI element harbouring fusC in an emerging Staphylococcus aureus strain from the Arabian Gulf region

Fusidic acid is a steroid antibiotic known since the 1960s. It is frequently used in topical preparations, i.e., ointments, for the treatment of skin and soft tissue infections caused by Staphylococcus aureus. There is an increasing number of methicillin-resistant S. aureus (MRSA) strains that harbour plasmid-borne fusB/far1 or fusC that is localised on SCC elements. In this study we examined a series of related CC30-MRSA isolates from the Arabian Gulf countries that presented with SCCmec elements and fusC, including a variant that-to the best of our knowledge-has not yet formally been described. It consisted of a class B mec complex and ccrA/B-4 genes. The fusidic acid resistance gene fusC was present, but contrary to the previously sequenced element of HDE288, it was not accompanied by tirS. This element was identified in CC30 MRSA from Kuwait, Saudi Arabia and the United Arab Emirates that usually also harbour the Panton-Valentin leukocidin (PVL) genes. It was also identified in CC8 and ST834 isolates. In addition, further CC30 MRSA strains with other SCCmec VI elements harbouring fusC were found to circulate in the Arabian Gulf region. It can be assumed that MRSA strains with SCCmec elements that include fusC have a selective advantage in both hospital and community settings warranting a review of the use of topical antibiotics and indicating the necessity of reducing over-the-counter sale of antibiotics, including fusidic acid, without prescription.

Evaluating the influence of common antibiotics on the efficacy of a recombinant immunotoxin in tissue culture

OBJECTIVE

Recombinant immunotoxins (RITs) are antibody-toxin fusion proteins that can selectively eliminate populations of cells expressing specific surface receptors. They are in evaluation as therapeutic agents for cancer. RITs based on Pseudomonas exotoxin A (PE) are in use clinically for the treatment of hairy cell leukemia, and under trial for the treatment of other cancers. In an effort to improve the efficacy of PE-based RITs, we evaluated the potential of combination therapy with several common antibiotics (tetracycline, chloramphenicol, streptomycin, linezolid, fusidic acid, and kanamycin) on human cell lines HEK293, OVCAR8, and CA46. Antibiotics were selected based on their potential to inhibit mitochondrial protein synthesis and disrupt energy metabolism in cancer cells.

RESULTS

Tetracycline, chloramphenicol, linezolid, and fusidic acid alone killed cultured human cells at high concentrations. At high but nontoxic concentrations of each antibiotic, only chloramphenicol treatment of the Burkitt's lymphoma cell line CA46 showed enhanced cytotoxicity when paired with an anti-transferrin receptor/PE RIT. This result, however, could not be replicated in additional Burkitt's lymphoma cell lines Ramos and Raji. Although the six antibiotics we tested are not promising candidates for RIT combination therapy, we suggest that fusidic acid could be considered independently as a potential cancer therapeutic.

Efficacy of Silver-based Gel Compared With Fusidic Acid Cream in Topical Treatment Following Trichloroacetic Acid Facial Skin Peeling: A Pilot Study

BACKGROUND

Trichloroacetic acid (TCA) is a nontoxic chemical that has been used for more than 20 years in skin rejuvenation treatments for various skin conditions. Currently, there is no single accepted protocol for local burn care following TCA peeling.

OBJECTIVE

This pilot study assesses the efficacy and tolerability of a silver-based gel compared with fusidic acid cream as a complementary topical treatment for burns following TCA peeling.

MATERIALS AND METHODS

The authors conducted a comparative study on healthy female patients in the Department of Plastic and Reconstructive Surgery at Assaf Harofe Medical Center (Zerifin, Israel). Patients were treated with TCA 15% for superficial facial skin peeling, followed by applications of both the silver-based gel and fusidic acid cream on opposite sides of their face. Patient evaluation included high-resolution photographic evaluation pre- and post-peeling; physician assessment for the presence of complications such as infection, edema, and allergic reactions; and a self-completed questionnaire in reference to the outcomes and side effects (eg, burning, itching) experienced.

RESULTS

Seventeen women were included in the study. None of the patients experienced an infection or allergic reaction. Photographic analysis found no significant differences in the outcomes between topical treatments, with a trend for better results with the silver-based gel. Pain, edema, and burning sensations were not significantly different between the topical treatments. Itching was less prevalent in the silver-based gel group (P = .046).

CONCLUSIONS

Comparing between the groups treated with silver-based gel and fusidic acid cream, the authors found no inferiority in the outcomes or the prevalence of any complaints, and a superior effect on the prevention of wound itch using a silver-based gel.

Discovery, synthesis of novel fusidic acid derivatives possessed amino-terminal groups at the 3-hydroxyl position with anticancer activity

A series of novel fusidic acid (FA) derivatives were synthesized and screened for their in vitro cytotoxicity against the Hela, U87, KBV and MKN45 cancer cell lines. Selected FA derivatives with anti-tumor activity were firstly identified including compound 4, which exhibited good anti-proliferative activity with IC₅₀ values in the range of 1.26-3.57 μM. Further research revealed that compound 4 induced Hela cells to undergo apoptosis by increasing the ratio of the cells in the Sub-G₀/G₁ phase via decreasing the neo-synthesized proteins in a dose-dependent manner from 1 to 10 μM. Compound 4 also showed good in vivo anti-tumor activity against the xenograft tumor of Hela cells and had no apparent toxicity. This study highlights the advantage of introducing the medium-length amino-terminal groups at the 3-OH position of FA to enhance its anti-tumor activity and suggests that compound 4 provides a starting point for designing more potent derivatives in the future.

Helvolic Acid Derivatives with Antibacterial Activities against Streptococcus agalactiae from the Marine-Derived Fungus Aspergillus fumigatus HNMF0047

Streptococcus agalactiae is a hazardous pathogen that can cause great harm to humans and fish. In the present study, the known fungal metabolite helvolic acid (10), seven new helvolic acid derivatives named 16- O-deacetylhelvolic acid 21,16-lactone (2), 6- O-propionyl-6,16- O-dideacetylhelvolic acid 21,16-lactone (3), 1,2-dihydro-6,16- O-dideacetylhelvolic acid 21,16-lactone (4), 1,2-dihydro-16- O-deacetylhelvolic acid 21,16-lactone (5), 16- O-propionyl-16- O-deacetylhelvolic acid (6), 6- O-propionyl-6- O-deacetylhelvolic acid (7), and 24- epi-6β,16β-diacetoxy-25-hydroxy-3,7-dioxo-29-nordammara-1,17(20)-diene-21,24-lactone (9), and two known ones (1 and 8) were isolated from the marine-derived fungus Aspergillus fumigatus HNMF0047 obtained from an unidentified sponge from Wenchang Beach, Hainan Province, China. The structures and the absolute configurations of the new compounds were unambiguously elucidated by spectroscopic data and electronic circular dichroism (ECD) spectroscopic analyses along with quantum ECD calculations. In addition, the spectroscopic data of compound 1 are reported here for the first time, the configuration of C-24 of known compound 8 was revised based on comparison of its ROESY data with its C-24 epimer 9, and the absolute configuration of 8 was also determined for the first time. Compounds 6, 7, and 10 showed stronger antibacterial activity than a tobramycin control against S. agalactiae with MIC values of 16, 2, and 8 μg/mL, respectively.

Microbial Oxidation of the Fusidic Acid Side Chain by Cunninghamella echinulata

Biotransformation of fusidic acid (1) was accomplished using a battery of microorganisms including Cunninghamella echinulata NRRL 1382, which converted fusidic acid (1) into three new metabolites 2⁻4 and the known metabolite 5. These metabolites were identified using 1D and 2D NMR and HRESI-FTMS data. Structural assignment of the compounds was supported via computation of ¹H- and ¹³C-NMR chemical shifts. Compounds 2 and 3 were assigned as the 27-hydroxy and 26-hydroxy derivatives of fusidic acid, respectively. Subsequent oxidation of 3 afforded aldehyde 4 and the dicarboxylic acid 5. Compounds 2, 4 and 5 were screened for antimicrobial activity against different Gram positive and negative bacteria, Mycobacterium smegmatis, M. intercellulare and Candida albicans. The compounds showed lower activity compared to fusidic acid against the tested strains. Molecular docking studies were carried out to assist the structural assignments and predict the binding modes of the metabolites.

Effect of Fusidic Acid on Pancreatic Islet Allograft Rejection

We examined in fully mismatched rats, the survival of pancreatic islet allografts in recipients treated with either fusidic acid (FA), an antistaphyllococcal antibiotic that has been shown to possess an immunosuppressive effect in vitro and in vivo, or cyclosporin-A (CsA). Islets were isolated by collagenase digestion, separated from acinar tissue by handpicking under a dissecting microscope and transplanted into the liver by portal vein injection of streptozotocin(STZ)-induced diabetic rats. The results indicated that while a temporary immunosuppression with CsA achieved an indefinite islet allograft survival, FA administered to recipients daily was not able to prevent islet allograft rejection across a major histocompatibility barrier. We conclude that despite the fact that fusidic acid has been claimed to act as an immunosuppressant drug in vitro with effects similar to those of CsA, unlike CsA, FA given either orally or by s.c. injection was not effective to prolong islet allograft survival in vivo. Copyright © 1997 Elsevier Science Inc.

Molecular characterization and antimicrobial susceptibility of the CA-MRSA isolated from healthcare workers, Tehran, Iran

INTRODUCTION

Methicillin resistant Staphylococcus aureus (MRSA) has become as a nosocomial pathogen worldwide. Considering the importance of MRSA typing for understanding the evolution and dissemination of these strains, we studied the molecular characteristics of MRSA colonized healthcare workers (HCWs).

METHODOLOGY

All MRSA isolated from HCWs, were genotyped using staphylococcal cassette chromosome mec (SCCmec) with multiplex PCR assay, multilocus sequence typing (MLST) and spa typing. Then antibiotic susceptibility pattern and presence of pvl genes were evaluated in MRSA isolates.

RESULTS

Cluster analysis by eBURSTv3 showed that MRSA isolates belonged to two major clonal complexes (CC); CC88 (ST88, ST825, ST859) and CC30 (ST39, ST2, ST24) and five singletons. The most prevalent SCCmec type was type IV (70.59%) followed by type V (29.41%). Totally 11 different spa types were discriminated among which type t186 was predominant. All of the MRSA tested (100%) were susceptible to teicoplanin, linezolid and fusidic acid. Totally 52.94% of isolates were positive for pvl genes.

CONCLUSIONS

The ST88-MRSA-IV accounted for most colonized MRSA isolates. We documented a different molecular epidemiology of MRSA nasal colonization in hospitals under studied, due to the introduction of epidemic clones (ST88, ST39, ST2235, ST80, ST813, ST398, ST825, ST24, ST22, ST859 and ST2).

Real time determination of bacterial in vivo ribosome translation elongation speed based on LacZα complementation system

Bacterial growth significantly depends on protein synthesis catalyzed by ribosome. Ribosome translation elongation speed is a key factor determining the bacterial protein synthesis rate. However, existing methods for determining translation elongation speed have limited applications. Here we developed a simple and convenient method for measuring bacterial translation elongation speed based on LacZα complementation system. It enables the measurement of in vivo translation elongation speed of different individual genes. Tests related to ribosome translation elongation speed under various growth perturbations including different nutrient conditions, low temperature, a low-speed ribosome mutant, and fusidic acid treatment, were performed to quantitatively validate this method. Using this approach, we further found that nutrient starvation caused a remarkable slow-down of ribosome translation of Escherichia coli (E. coli). We also studied the dynamic change of translation elongation speed during the process of nutrient up-shift. This method will boost the quantitative understanding of bacterial ribosome translation capacity and growth.

New Cyclotetrapeptides and a New Diketopiperzine Derivative from the Marine Sponge-Associated Fungus Neosartorya glabra KUFA 0702

Two new cyclotetrapeptides, sartoryglabramides A (5) and B (6), and a new analog of fellutanine A (8) were isolated, together with six known compounds including ergosta-4, 6, 8 (14), 22-tetraen-3-one, ergosterol 5, 8-endoperoxide, helvolic acid, aszonalenin (1), (3R)-3-(1H-indol-3-ylmethyl)-3,4-dihydro-1H-1,4-benzodiazepine-2,5-dione (2), takakiamide (3), (11aR)-2,3-dihydro-1H-pyrrolo[2,1-c][1,4]benzodiazepine-5,11(10H,11aH)-dione (4), and fellutanine A (7), from the ethyl acetate extract of the culture of the marine sponge-associated fungus Neosartorya glabra KUFA 0702. The structures of the new compounds were established based on extensive 1D and 2D spectral analysis. X-ray analysis was also used to confirm the relative configuration of the amino acid constituents of sartoryglabramide A (5), and the absolute stereochemistry of the amino acid constituents of sartoryglabramide A (5) and sartoryglabramides B (6) was determined by chiral HPLC analysis of their hydrolysates by co-injection with the d- and l- amino acids standards. Compounds 1-8 were tested for their antibacterial activity against Gram-positive (Escherichia coli ATCC 25922) and Gram-negative (Staphyllococus aureus ATCC 25923) bacteria, as well as for their antifungal activity against filamentous (Aspergillus fumigatus ATCC 46645), dermatophyte (Trichophyton rubrum ATCC FF5) and yeast (Candida albicans ATCC 10231). None of the tested compounds exhibited either antibacterial (MIC > 256 μg/mL) or antifungal activities (MIC > 512 μg/mL).

Activity of Colistin in Combination with Meropenem, Tigecycline, Fosfomycin, Fusidic Acid, Rifampin or Sulbactam against Extensively Drug-Resistant Acinetobacter baumannii in a Murine Thigh-Infection Model

Few effective therapeutic options are available for treating severe infections caused by extensively drug-resistant Acinetobacter baumannii (XDR-AB). Using a murine thigh-infection model, we examined the in vivo efficacy of colistin in combination with meropenem, tigecycline, fosfomycin, fusidic acid, rifampin, or sulbactam against 12 XDR-AB strains. Colistin, tigecycline, rifampin, and sulbactam monotherapy significantly decreased bacterial counts in murine thigh infections compared with those observed in control mice receiving no treatment. Colistin was the most effective agent tested, displaying bactericidal activity against 91.7% of strains at 48 h post-treatment. With strains showing a relatively low minimum inhibitory concentration (MIC) for meropenem (MIC ≤ 32 mg/L), combination therapy with colistin plus meropenem caused synergistic inhibition at both 24 h and 48 h post-treatment. However, when the meropenem MIC was ≥64 mg/L, meropenem did not significantly alter the efficacy of colistin. The addition of rifampin and fusidic acid significantly improved the efficacy of colistin, showing a synergistic effect in 100% and 58.3% of strains after 24 h of treatment, respectively, while the addition of tigecycline, fosfomycin, or sulbactam did not show obvious synergistic activity. No clear differences in activities were observed between colistin-rifampin and colistin-fusidic acid combination therapy with most strains. Overall, our in vivo study showed that administering colistin in combination with rifampin or fusidic acid is more efficacious in treating XDR-AB infections than other combinations. The colistin-meropenem combination may be another appropriate option if the MIC is ≤32 mg/L. Further clinical studies are urgently needed to confirm the relevance of these findings.

High-throughput screening of antibiotic-resistant bacteria in picodroplets

The prevalence of clinically-relevant bacterial strains resistant to current antibiotic therapies is increasing and has been recognized as a major health threat. For example, multidrug-resistant tuberculosis and methicillin-resistant Staphylococcus aureus are of global concern. Novel methodologies are needed to identify new targets or novel compounds unaffected by pre-existing resistance mechanisms. Recently, water-in-oil picodroplets have been used as an alternative to conventional high-throughput methods, especially for phenotypic screening. Here we demonstrate a novel microfluidic-based picodroplet platform which enables high-throughput assessment and isolation of antibiotic-resistant bacteria in a label-free manner. As a proof-of-concept, the system was used to isolate fusidic acid-resistant mutants and estimate the frequency of resistance among a population of Escherichia coli (strain HS151). This approach can be used for rapid screening of rare antibiotic-resistant mutants to help identify novel compound/target pairs.

Emergent and evolving antimicrobial resistance cassettes in community-associated fusidic acid and meticillin-resistant Staphylococcus aureus

Fusidic acid is a topical and systemic antimicrobial used for the treatment of staphylococcal infections in hospitals and the community. Sales of fusidic acid and resistance rates among meticillin-resistant Staphylococcus aureus (MRSA) doubled between 1990 and 2001. For the following decade, fusidic acid resistance rates among isolates from Addenbrooke's Hospital (Cambridge, UK) were compared with national resistance rates from MRSA bacteraemia surveillance data and with antimicrobial sales data. Sales of fusidic acid remained relatively constant between 2002 and 2012, whilst fusidic acid resistance increased two- and four-fold in MRSA bacteraemias nationally and in MRSA isolates from Cambridge, respectively. A subgroup of MRSA resistant only to fusidic acid increased after 2006 by 5-fold amongst bacteraemias nationally and 17-fold (to 7.7% in 2012) amongst Cambridge MRSA isolates. All of the available local isolates from 2011 to 2012 (n=23) were acquired in the community, were not related epidemiologically and belonged to multilocus sequence typing (MLST) groups ST1, 5, 8, 45 or 149 as revealed from analysis of whole-genome sequence data. All harboured the fusC gene on one of six distinct staphylococcal cassette chromosome (SCC) elements, four of which were dual-resistance chimeras that encoded β-lactam and fusidic acid resistance. In summary, fusidic acid-resistant MRSA increased in prevalence during the 2000s with notable rises after 2006. The development of chimeric cassettes that confer dual resistance to β-lactams and fusidic acid demonstrates that the genetics underpinning resistance in community-associated MRSA are evolving.

Fusidic acid is an effective treatment against Toxoplasma gondii and Listeria monocytogenes in vitro, but not in mice

Fusidic acid is a bacteriostatic antibiotic that inhibits the growth of bacteria by preventing the release of translation elongation factor G (EF-G) from the ribosome. The apicomplexan parasite Toxoplasma gondii has an orthologue of bacterial EF-G that can complement bacteria and is necessary for parasite virulence. Fusidic acid has been shown to be effective in tissue culture against the related pathogen Plasmodium falciparum, and current drug treatments against T. gondii are limited. We therefore investigated the therapeutic value of fusidic acid for T. gondii and found that the drug was effective in tissue culture, but not in a mouse model of infection. To determine whether this trend would occur in another intracellular pathogen that elicits a T helper 1-type immune response, we tested the efficacy of fusidic acid for the bacterium Listeria monocytogenes. Similar to its effects on T. gondii, fusidic acid inhibits the growth of L. monocytogenes in vitro, but not in mice. These findings highlight the necessity of in vivo follow-up studies to validate in vitro drug investigations.

Antibiotics that affect the ribosome

The ribosome is a major bacterial target for antibiotics. Drugs inhibit ribosome function either by interfering in messenger RNA translation or by blocking the formation of peptide bonds at the peptidyl transferase centre. These effects are the consequence of the binding of drugs to the ribosomal subunits. Various mechanisms, including enzymatic detoxification, target alteration (ribosomal [r]RNAs and ribosomal proteins) and reduced accumulation (impermeability and efflux) are involved in bacterial resistance to protein synthesis inhibitors. The fact that some positions in rRNA participate in the binding of antibiotics belonging to distinct families explains why bacteria have developed mechanisms that can lead to cross-resistance.

Response of methicillin-resistant Staphylococcus aureus to amicoumacin A

Amicoumacin A exhibits strong antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), hence we sought to uncover its mechanism of action. Genome-wide transcriptome analysis of S. aureus COL in response to amicoumacin A showed alteration in transcription of genes specifying several cellular processes including cell envelope turnover, cross-membrane transport, virulence, metabolism, and general stress response. The most highly induced gene was lrgA, encoding an antiholin-like product, which is induced in cells undergoing a collapse of Δψ. Consistent with the notion that LrgA modulates murein hydrolase activity, COL grown in the presence of amicoumacin A showed reduced autolysis, which was primarily caused by lower hydrolase activity. To gain further insight into the mechanism of action of amicoumacin A, a whole genome comparison of wild-type COL and amicoumacin A-resistant mutants isolated by a serial passage method was carried out. Single point mutations generating codon substitutions were uncovered in ksgA (encoding RNA dimethyltransferase), fusA (elongation factor G), dnaG (primase), lacD (tagatose 1,6-bisphosphate aldolase), and SACOL0611 (a putative glycosyl transferase). The codon substitutions in EF-G that cause amicoumacin A resistance and fusidic acid resistance reside in separate domains and do not bring about cross resistance. Taken together, these results suggest that amicoumacin A might cause perturbation of the cell membrane and lead to energy dissipation. Decreased rates of cellular metabolism including protein synthesis and DNA replication in resistant strains might allow cells to compensate for membrane dysfunction and thus increase cell survivability.

ppGpp inhibits peptide elongation cycle of chloroplast translation system in vitro

Chloroplasts possess common biosynthetic pathways for generating guanosine 3',5'-(bis)pyrophosphate (ppGpp) from GDP and ATP by RelA-SpoT homolog enzymes. To date, several hypothetical targets of ppGpp in chloroplasts have been suggested, but they remain largely unverified. In this study, we have investigated effects of ppGpp on translation apparatus in chloroplasts by developing in vitro protein synthesis system based on an extract of chloroplasts isolated from pea (Pisum sativum). The chloroplast extracts showed stable protein synthesis activity in vitro, and the activity was sensitive to various types of antibiotics. We have demonstrated that ppGpp inhibits the activity of chloroplast translation in dose-effective manner, as does the toxic nonhydrolyzable GTP analog guanosine 5'-(β,γ-imido)triphosphate (GDPNP). We further examined polyuridylic acid-directed polyphenylalanine synthesis as a measure of peptide elongation activity in the pea chloroplast extract. Both ppGpp and GDPNP as well as antibiotics, fusidic acid and thiostrepton, inhibited the peptide elongation cycle of the translation system, but GDP in the similar range of the tested ppGpp concentration did not affect the activity. Our results thus show that ppGpp directly affect the translation system of chloroplasts, as they do that of bacteria. We suggest that the role of the ppGpp signaling system in translation in bacteria is conserved in the translation system of chloroplasts.

Characterization of two malaria parasite organelle translation elongation factor G proteins: the likely targets of the anti-malarial fusidic acid

Malaria parasites harbour two organelles with bacteria-like metabolic processes that are the targets of many anti-bacterial drugs. One such drug is fusidic acid, which inhibits the translation component elongation factor G. The response of P. falciparum to fusidic acid was characterised using extended SYBR-Green based drug trials. This revealed that fusidic acid kills in vitro cultured P. falciparum parasites by immediately blocking parasite development. Two bacterial-type protein translation elongation factor G genes are identified as likely targets of fusidic acid. Sequence analysis suggests that these proteins function in the mitochondria and apicoplast and both should be sensitive to fusidic acid. Microscopic examination of protein-reporter fusions confirm the prediction that one elongation factor G is a component of parasite mitochondria whereas the second is a component of the relict plastid or apicoplast. The presence of two putative targets for a single inhibitory compound emphasizes the potential of elongation factor G as a drug target in malaria.

[Antibiotic resistance dynamics and isolation rate of staphylococci and enterococci from patients of reconstructive surgery units]

The dynamics of isolation of staphylococci and enterococci from clinical material of patients and their antibiotic susceptibility within a 5-year period (2005-2009) was analysed. 5990 isolates were tested: 1250 isolates of Staphylococcus aureus, 3268 isolates of S. epidermidis, 1005 isolates of Enterococcus faecalis and 467 isolates of E. faecium. Grampositive infections were shown to be prevailing within the last 2-3 years, the nosocomial epidermal staphylococci more and more replacing S. aureus (the ratio of S. epidermidis and S. aureus in 2009 was 3.3). The isolation rate of E. faecalis significantly increased (by 3.5 times) and the ratio of E. faecalis and E. faecium in 2009 was 4.3. The microflora composition with respect to the isolation source was analysed and its clinical significance was estimated. The study of the antibiotic susceptibility showed that oxacillin had its own specific niche, while antibiotics active against resistant grampositive cocci, such as rifampicin, fusidic acid, fluoroquinolones (moxifloxacin), cefoxitin, as well as amoxicillin/clavulane in infections due to E. faecalis, might be considered as the drugs of choice. In the treatment of nosocomial infections, when the etiological role of MRSA or VRE is suspected or confirmed, the complex therapy should obligatory include the most active antibiotics (vancomycin or linezolid among them).

Utility of antimicrobial susceptibility-based algorithms for the presumptive identification of genotypically-defined community-associated methicillin-resistant Staphylococcus aureus at a London teaching hospital

PURPOSE

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains are classically characterised by susceptibility to most non-β-lactam antimicrobial agents. We sought to determine whether antimicrobial susceptibility (AMS)-based algorithms could be used to presumptively identify CA-MRSA in a hospital MRSA collection.

METHODS

Over a three-month period, all MRSA were tested for AMS, staphylococcal cassette chromosome mec (SCCmec) type, presence of the Panton-Valentine leukocidin (PVL) genes and spa type. CA-MRSA isolates were defined genotypically using a combination of spa and SCCmec type. AMS based algorithms were developed and tested for their sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV).

RESULTS

Ciprofloxacin susceptibility (p < 0.001) and fusidic acid resistance (p  = 0.044) were independent predictors of CA-MRSA in a multivariate model. Although 98.5% of HA-MRSA were ciprofloxacin resistant, so too were 36.6% of CA-MRSA. Algorithms based on ciprofloxacin-susceptibility and fusidic acid resistance performed best, with specificity and NPV >90% and sensitivity and PPV >70%.

CONCLUSIONS

Our data indicate that while ciprofloxacin-susceptible isolates are likely to be CA-MRSA, the use of ciprofloxacin-susceptibility as a marker of CA-MRSA would miss approximately one third of CA-MRSA isolates. Therefore, AMS patterns have limited utility for the identification of genetically-defined CA-MRSA in our setting.

Characterization of crosslinking effects on the physicochemical and drug diffusional properties of cationic hydrogels designed as bioactive urological biomaterials

This study examined the effects of concentration and type of crosslinker (tetraethyleneglycol diacrylate, TEGDA; diethyleneglycol dimethacrylate, DEGDMA; and polyethyleneglycol dimethacrylate, PEGDMA) on the mechanical and drug diffusional properties of hydrogels that had been selected as candidate coatings for bioactive medical devices. Hydrogels (dimethylaminoethylmethacrylate-covinylpyrrolidone; 1:1) were prepared by free radical polymerization and characterized using tensile analysis, dynamic contact angle analysis and analysis of swelling at pH 6.0. The release of fusidic acid and chlorhexidine was evaluated using buffered medium at pH 6.0 and, in addition, using dissolution medium that had been buffered to pH 9 in the presence and absence of elevated concentrations of calcium, representative of urinary encrustation. Crosslinker concentration, but not type, affected the advancing and receding contact angles. Conversely, both crosslinker type and concentration affected the mechanical and swelling properties of the hydrogels. Maximum swelling and elongation at break were associated with the PEGDMA-crosslinked hydrogels whereas TEGDA-crosslinked hydrogels exhibited the maximum ultimate tensile strength and Young's modulus. Drug release from all systems occurred by diffusion. The mass of chlorhexidine and fusidic acid released was dependent on crosslinker type and concentration, with hydrogels crosslinked with PEGDMA offering the greatest mass of drug released at each sampling period. The mass of fusidic acid but not chlorhexidine released at pH 9.0 in a calcium augmented medium was lower than that released in the same medium devoid of elevated calcium, due to the formation of the poorly soluble calcium salt. In conclusion, this study has uniquely examined the effects of crosslinker type and concentration on physicochemical and drug release properties essential to the clinical and non-clinical performance of bioactive hydrogels for medical device application.

The structure of the ribosome with elongation factor G trapped in the posttranslocational state

Elongation factor G (EF-G) is a guanosine triphosphatase (GTPase) that plays a crucial role in the translocation of transfer RNAs (tRNAs) and messenger RNA (mRNA) during translation by the ribosome. We report a crystal structure refined to 3.6 angstrom resolution of the ribosome trapped with EF-G in the posttranslocational state using the antibiotic fusidic acid. Fusidic acid traps EF-G in a conformation intermediate between the guanosine triphosphate and guanosine diphosphate forms. The interaction of EF-G with ribosomal elements implicated in stimulating catalysis, such as the L10-L12 stalk and the L11 region, and of domain IV of EF-G with the tRNA at the peptidyl-tRNA binding site (P site) and with mRNA shed light on the role of these elements in EF-G function. The stabilization of the mobile stalks of the ribosome also results in a more complete description of its structure.

[Analysis on the susceptibility of fusidic acid for common gram positive bacteria]

OBJECTIVE

To assess in vitro susceptibility of the fusidic acid, vancomycin, tobramycin and ofloxacin for 8 kinds of ocular gram-positive bacteria.

METHODS

It was an experimental study. One hundred strains of ocular gram-positive bacterial isolates selected from Beijing Institute of Ophthalmology, cultivated and identified by the routine, were tested for their susceptibilities to fusidic acid, vancomycin, tobramycin and ofloxacin, with in vitro by the Kirby-Bauer disk diffusion method. Significant differences between groups were evaluated by SPSS 11.5 chi-square test of four-fold table.

RESULTS

In the study, the percentage of susceptibility for in vitro gram-positive bacterial isolates to tobramycin, ofloxacin, vancomycin and fusidic acid was 55.0%, 65.0%, 98.0% and 53.0%. The susceptibility to vancomycin was significantly higher than to tobramycin, ofloxacin and fusidic acid (chi(2) = 51.425, 36.113, 54.737; P < 0.05). The susceptibility of common staphylococci to fusidic acid (85.5%) was just lower than to vancomycin (100.0%) (chi(2) = 6.605, P < 0.05), but was significantly higher than to tobramycin (58.2%) and ofloxacin (54.5%) (chi(2) = 10.106, 12.511; P < 0.05). The susceptibility of common streptococcus to fusidic acid (0.0%) was lower than to vancomycin (100.0%) and ofloxacin (85.0%) (chi(2) = 40.000, 29.565; P < 0.05), but the susceptibility to fusidic acid and tobramycin (15.0%) were equivalent (chi(2) = 1.441, P > 0.05). The gram-positive bacilli and nocardia showed significantly lower susceptibility to fusidic acid (24.0%) than that to the other three antibiotics (tobramycin 80.0%, ofloxacin 72.0%, vancomycin 92.0%) (chi(2) = 23.727, 22.430, 11.538; P < 0.05).

CONCLUSION

The in vitro susceptibility of fusidic acid to staphylococci is higher, while to streptococcus and gram-positive bacilli is obviously lower than other three kinds of antibiotics.

Single-molecule structural dynamics of EF-G--ribosome interaction during translocation

EF-G catalyzes translocation of mRNA and tRNAs within the ribosome during protein synthesis. Detection of structural states in the reaction sequence that are not highly populated can be facilitated by studying the process one molecule at a time. Here we present single-molecule studies of translocation showing that, for ribosomes engaged in poly(Phe) synthesis, fluorescence resonance energy transfer (FRET) between the G' domain of EF-G and the N-terminal domain of ribosomal protein L11 occurs within two rapidly interconverting states, having FRET efficiencies of 0.3 and 0.6. The antibiotic fusidic acid increases the population of the 0.6 state, indicating that it traps the ribosome.EF-G complex in a preexisting conformation formed during translation. Only the 0.3 state is observed when poly(Phe) synthesis is prevented by omission of EF-Tu, or in studies on vacant ribosomes. These results suggest that the 0.6 state results from the conformational lability of unlocked ribosomes formed during translocation. An idling state, possibly pertinent to regulation of protein synthesis, is detected in some ribosomes in the poly(Phe) system.

Current options for the treatment of impetigo in children

Impetigo contagiosa is a common, superficial, bacterial infection of the skin characterised by an inflamed and infected epidermis caused by Staphylococcus aureus, Streptococcus pyogenes or both. The less common bullous impetigo is characterised by fragile fluid-filled vesicles and flaccid blisters, and is invariably caused by pathogenic strains of S. aureus. In bullous impetigo, exfoliative toxins are produced, although these are restricted to the area of infection and bacteria can be cultured from the blister contents. In the rare variant, staphylococcal scalded skin syndrome, the exfoliative toxins are spread haematogenously from a localised source causing widespread epidermal damage at distant sites.