Repurposing fusidic acid as an antimicrobial against enterococci with a low probability of resistance development

Drug repurposing constitutes a strategy to combat antimicrobial resistance, by using agents with known safety, pharmacokinetics, and pharmacodynamics. Previous studies have implemented new fusidic acid (FA) front-loading-dose regimens, allowing higher serum levels than those achievable with ordinary doses. As susceptibility breakpoints are affected by serum level, we evaluated the repurposing of FA as an antimicrobial product against enterococci. FA minimum inhibitory concentrations (MICs) against standard enterococci strains; Enterococcus faecalis ATCC 29212 and Enterococcus faecium ATCC 27270 were 2 and 4 µg/mL, respectively. The MIC against 98 enterococcal clinical isolates was ≤ 8 µg/mL; all would be susceptible if categorized according to recalculated breakpoints (≥ 16 µg/mL), based on the serum level achieved using the front-loading regimen. FA administration in vivo, using the BALB/c mouse infection model, significantly reduced bacterial burden by two to three log10 units in the liver and spleen of mice infected with vancomycin-susceptible and -resistant strains. Exposure of the standard enterococcal strains to increasing, but not fixed, FA concentrations resulted in resistant strains (MIC = 128 µg/mL), with thicker cell walls and slower growth rates. Only one mutation (M651I) was detected in the fusA gene of the resistant strain derived from serial passage of E. faecium ATCC 27270, which was retained in the revertant strain after passage in the FA-free medium. In conclusion, FA can be repurposed as an antimicrobial drug against enterococci with a low probability of mutational resistance development, and can be employed for treatment of infections attributable to vancomycin-resistant enterococci.

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.

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.

Extensive expansion of the chemical diversity of fusidane-type antibiotics using a stochastic combinational strategy

Fusidane-type antibiotics, represented by helvolic acid, fusidic acid and cephalosporin P₁, are fungi-derived antimicrobials with little cross-resistance to commonly used antibiotics. Generation of new fusidane-type derivatives is therefore of great value, but this is hindered by available approaches. Here, we developed a stochastic combinational strategy by random assembly of all the post-tailoring genes derived from helvolic acid, fusidic acid, and cephalosporin P₁ biosynthetic pathways in a strain that produces their common intermediate. Among a total of 27 gene combinations, 24 combinations produce expected products and afford 58 fusidane-type analogues, of which 54 are new compounds. Moreover, random gene combination can induce unexpected activity of some post-tailoring enzymes, leading to a further increase in chemical diversity. These newly generated derivatives provide new insights into the structure‒activity relationship of fusidane-type antibiotics. The stochastic combinational strategy established in this study proves to be a powerful approach for expanding structural diversity of natural products.

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.

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.

Biosynthetic Study of Cephalosporin P1 Reveals a Multifunctional P450 Enzyme and a Site-Selective Acetyltransferase

Fusidane-type antibiotics are a group of triterpenoid antibiotics. They include helvolic acid, fusidic acid, and cephalosporin P₁, among which fusidic acid has been used clinically. We have recently elucidated the biosynthesis of helvolic acid and fusidic acid, which share an early biosynthetic route involving six conserved enzymes. Here, we report two separate gene clusters for cephalosporin P₁ biosynthesis. One consists of the six conserved genes, and the other contains three genes encoding a P450 enzyme (CepB4), an acetyltransferase (CepD2), and a short-chain dehydrogenase/reductase (CepC2). Introduction of these three genes into Aspergillus oryzae, which harbors the six conserved genes, produced cephalosporin P₁. Stepwise introduction revealed that CepB4 not only catalyzes stereoselective dual oxidation of C6 and C7, but also monooxygenation of C6 or C7. This led to the generation of five new analogues. Using monohydroxylated products as substrates, we demonstrated that CepD2 specifically acetylates C6-OH, although both C6-OH and C7-OH acetylated analogues have been identified in nature.

Integration of multiscale molecular modeling approaches with the design and discovery of fusidic acid derivatives

Aim: Fusidic acid (FA) is an effective antibiotic against Staphylococcus aureus, but it is metabolically unstable. Methods & results: 14 derivatives were designed and synthesized by blocking the metabolic sites of FA (21-COOH and 3-OH) to maintain antibacterial activity and prolong the half-life. Six derivatives showed good antibacterial activity, and the pharmacokinetic experiments confirmed that two derivatives modified in 21-COOH released FA in vivo and showed longer half-lives than FA. Docking analysis and structure–activity relationships indicated that the 3-glycine derivatives with more hydrogen-bonding acceptor sites and positively charged surface areas were more likely to have good antibacterial activity. Conclusion: The results suggest that introducing groups that block the metabolic sites of FA could maintain antibacterial activity and prolong the half-lives.

Novel antimycobacterial C-21 amide derivatives of the antibiotic fusidic acid: synthesis, pharmacological evaluation and rationalization of media-dependent activity using molecular docking studies in the binding site of human serum albumin

Fusidic acid is a natural product antibiotic used clinically, primarily against staphylococcal infections. It has also exhibited antimycobacterial activity against Mycobacterium species, including Mycobacterium tuberculosis (Mtb). Novel C-21 fusidic acid amides were synthesized and evaluated for antimycobacterial activity in a drug repositioning approach for tuberculosis. The synthesized compounds exhibited good potency in MB7H9/CAS medium albeit showing low to no activity in MB7H9/ADC medium. The fusidic acid ethanamides were, generally, the most potent of the analogues evaluated for antimycobacterial activity (MIC₉₀ < 10 μM) in the MB7H9/CAS medium. The lack of activity in the MB7H9/ADC medium was supported by strong binding interactions in the fusidic acid binding site of the human serum albumin (HSA) protein. The most potent antimycobacterial analogue was the N-(4-sulfamoylbenzyl)fusidic acid amide (1.26) with an MIC₉₀ value of 2.71 μM.

Biosynthesis of clinically used antibiotic fusidic acid and identification of two short-chain dehydrogenase/reductases with converse stereoselectivity

Fusidic acid is the only fusidane-type antibiotic that has been clinically used. However, biosynthesis of this important molecule in fungi is poorly understood. We have recently elucidated the biosynthesis of fusidane-type antibiotic helvolic acid, which provides us with clues to identify a possible gene cluster for fusidic acid (fus cluster). This gene cluster consists of eight genes, among which six are conserved in the helvolic acid gene cluster except fusC1 and fusB1. Introduction of the two genes into the Aspergillus oryzae NSAR1 expressing the conserved six genes led to the production of fusidic acid. A stepwise introduction of fusC1 and fusB1 revealed that the two genes worked independently without a strict reaction order. Notably, we identified two short-chain dehydrogenase/reductase genes fusC1 and fusC2 in the fus cluster, which showed converse stereoselectivity in 3-ketoreduction. This is the first report on the biosynthesis and heterologous expression of fusidic acid.

Activities of Combinations of Antistaphylococcal Antibiotics with Fusidic Acid against Staphylococcal Biofilms in In Vitro Static and Dynamic Models

Staphylococcal biofilms are a major cause of therapeutic failure, especially when caused by multiresistant strains. Oral fusidic acid is currently being redeveloped in the United States for skin, skin structure, and orthopedic infections, in which biofilms play a major role. The aim of this study was to examine the activity of fusidic acid alone or combined with other antistaphylococcal drugs against biofilms made by a reference strain and five clinical isolates of Staphylococcus aureus or Staphylococcus epidermidis in in vitro static and dynamic models (microtiter plates and a CDC reactor) exposed to clinically relevant concentrations. In microtiter plates, antibiotics alone were poorly active, with marked differences among strains. At concentrations mimicking the free-drug human maximum concentration of drug in serum (C_max), the combination of fusidic acid with linezolid, daptomycin, or vancomycin resulted in increased activity against 4 to 5 strains, while the combination with doxycycline, rifampin, or moxifloxacin increased activity against 1 to 3 strains only. In the CDC reactor, biofilms were grown under constant flow and antibiotic concentrations decreased over time according to human elimination rates. A bactericidal effect was obtained when fusidic acid was combined with daptomycin or linezolid, but not with vancomycin. The higher tolerance of biofilms to antibiotics in the CDC reactor is probably attributable to the more complex architecture they adopt when growing under constant flow. Because biofilms grown in the CDC reactor are considered more similar to those developing in vivo, the data support further testing of combinations of fusidic acid with daptomycin or linezolid in models pertinent to chronic skin, skin structure, or orthopedic infections.

Current and Emerging Topical Antibacterials and Antiseptics: Agents, Action, and Resistance Patterns

Bacterial skin infections represent some of the most common infectious diseases globally. Prevention and treatment of skin infections can involve application of a topical antimicrobial, which may be an antibiotic (such as mupirocin or fusidic acid) or an antiseptic (such as chlorhexidine or alcohol). However, there is limited evidence to support the widespread prophylactic or therapeutic use of topical agents. Challenges involved in the use of topical antimicrobials include increasing rates of bacterial resistance, local hypersensitivity reactions (particularly to older agents, such as bacitracin), and concerns about the indiscriminate use of antiseptics potentially coselecting for antibiotic resistance. We review the evidence for the major clinical uses of topical antibiotics and antiseptics. In addition, we review the mechanisms of action of common topical agents and define the clinical and molecular epidemiology of antimicrobial resistance in these agents. Moreover, we review the potential use of newer and emerging agents, such as retapamulin and ebselen, and discuss the role of antiseptic agents in preventing bacterial skin infections. A comprehensive understanding of the clinical efficacy and drivers of resistance to topical agents will inform the optimal use of these agents to preserve their activity in the future.

A Randomized Study Evaluating Oral Fusidic Acid (CEM-102) in Combination With Oral Rifampin Compared With Standard-of-Care Antibiotics for Treatment of Prosthetic Joint Infections: A Newly Identified Drug-Drug Interaction

BACKGROUND

 Fusidic acid (FA) has been used for decades for bone infection, including prosthetic joint infection (PJI), often in combination with rifampin (RIF). An FA/RIF pharmacokinetic interaction has not previously been described.

METHODS

 In a phase 2 open-label randomized study, we evaluated oral FA/RIF vs standard-of-care (SOC) intravenous antibiotics for treatment of hip or knee PJI. Outcome assessment occurred at reimplantation (week 12) for subjects with 2-stage exchange, and after 3 or 6 months of treatment for subjects with hip or knee debride and retain strategies, respectively.

RESULTS

 Fourteen subjects were randomized 1:1 to FA/RIF or SOC. Pharmacokinetic profiles were obtained for 6 subjects randomized to FA/RIF. FA concentrations were lower than anticipated in all subjects during the first week of therapy, and at weeks 4 and 6, blood levels continued to decline. By week 6, FA exposures were 40%-45% lower than expected.

CONCLUSIONS

 The sponsor elected to terminate this study due to a clearly illustrated drug-drug interaction between FA and RIF, which lowered FA levels to a degree that could influence subject outcomes. Optimization of FA exposure if used in combination with RIF should be a topic of future research.

CLINICAL TRIALS REGISTRATION

 NCT01756924.

Activity of Fusidic Acid Tested against Staphylococci Isolated from Patients in U.S. Medical Centers in 2014

Fusidic acid (FA) activity was evaluated against 2,002 clinical staphylococcal isolates collected in U.S. hospitals during 2014. FA (MIC50/90, 0.12/0.12 μg/ml) inhibited 99.8% of Staphylococcus aureus isolates at ≤1 μg/ml. Only four S. aureus isolates displayed FA values of >2 μg/ml (three strains with fusC and one with an L461K substitution in fusA), and they were isolated from patients in four states. In conclusion, FA demonstrated sustained, potent activity against this recent collection of U.S. staphylococci.

Fusidic Acid: A Bacterial Elongation Factor Inhibitor for the Oral Treatment of Acute and Chronic Staphylococcal Infections

Fusidic acid is an oral antistaphylococcal antibiotic that has been used in Europe for more than 40 years to treat skin infections as well as chronic bone and joint infections. It is a steroidal antibiotic and the only marketed member of the fusidane class. Fusidic acid inhibits protein synthesis by binding EF-G-GDP, which results in the inhibition of both peptide translocation and ribosome disassembly. It has a novel structure and novel mode of action and, therefore, there is little cross-resistance with other known antibiotics. Many mutations can occur in the FusA gene that codes for EF-G, and some of these mutations can result in high-level resistance (minimum inhibitory concentration [MIC] > 64 mg/L), whereas others result in biologically unfit staphylococci that require compensatory mutations to survive. Low-level resistance (<8 mg/L) is more common and is mediated by fusB, fusC, and fusD genes that code for small proteins that protect EF-G-GDP from binding fusidic acid. The genes for these proteins are spread by plasmids and can be selected mostly by topical antibiotic use. Reports of resistance have led to combination use of fusidic acid with rifampin, which is superseded by the development of a new dosing regimen for fusidic acid that can be used in monotherapy. It consists of a front-loading dose to decrease the potential for resistance development followed by a maintenance dose. This dosing regimen is now being used in clinical trials in the United States for skin and refractory bone and joint infections.

Skin Commensal Staphylococci May Act as Reservoir for Fusidic Acid Resistance Genes

We analyzed the occurrence and mechanisms of fusidic acid resistance present in staphylococci isolated from 59 healthy volunteers. The fingers of the volunteers were screened for the presence of staphylococci, and the collected isolates were tested for resistance to fusidic acid. A total of 34 fusidic acid resistant staphylococcal strains (all were coagulase-negative) were isolated from 22 individuals (22/59, 37.3%). Examination of the resistance genes revealed that acquired fusB or fusC was present in Staphylococcus epidermidis, Staphylococcus capitis subsp. urealyticus, Staphylococcus hominis subsp. hominis, Staphylococcus warneri and Staphylococcus haemolyticus. Resistance islands (RIs) carrying fusB were found in S. epidermidis and S. capitis subsp. urealyticus, while staphylococcal chromosome cassette (SCC)-related structures harboring fusC were found in S. hominis subsp. hominis. Genotypic analysis of S. epidermidis and S. hominis subsp. hominis indicated that the fus elements were disseminated in diverse genetic strain backgrounds. The fusC elements in S. hominis subsp. hominis strains were highly homologous to SCCfusC in the epidemic sequence type (ST) 239/SCCmecIII methicillin-resistant S. aureus (MRSA) or the pseudo SCCmec in ST779 MRSA. The presence of acquired fusidic acid resistance genes and their genetic environment in commensal staphylococci suggested that the skin commensal staphylococci may act as reservoir for fusidic acid resistance genes.

The effect of fusidic acid on Plasmodium falciparum elongation factor G (EF-G)

Inhibition of growth of the malaria parasite Plasmodium falciparum by known translation-inhibitory antibiotics has generated interest in understanding their action on the translation apparatus of the two genome containing organelles of the malaria parasite: the mitochondrion and the relic plastid (apicoplast). We report GTPase activity of recombinant EF-G proteins that are targeted to the organelles and further use these to test the effect of the EF-G inhibitor fusidic acid (FA) on the factor-ribosome interface. Our results monitoring locking of EF-G·GDP onto surrogate Escherichia coli ribosomes as well as multi-turnover GTP hydrolysis by the factor indicate that FA has a greater effect on apicoplast EF-G compared to the mitochondrial counterpart. Deletion of a three amino acid (GVG) sequence in the switch I loop that is conserved in proteins of the mitochondrial EF-G1 family and the Plasmodium mitochondrial factor, but is absent in apicoplast EF-G, demonstrated that this motif contributes to differential inhibition of the two EF-Gs by FA. Additionally, the drug thiostrepton, that is known to target the apicoplast and proteasome, enhanced retention of only mitochondrial EF-G on ribosomes providing support for the reported effect of the drug on parasite mitochondrial translation.

In vitro activity of CEM-102 (fusidic acid) against prevalent clones and resistant phenotypes of Staphylococcus aureus

Clinical development of CEM-102 (fusidic acid) has recently begun in the United States for chronic oral treatment of prosthetic joint infections. To support this development, the in vitro activity of fusidic acid against important Staphylococcus aureus clones and resistance phenotypes was determined. Against 51 such isolates, the modal fusidic acid MIC was 0.12 μg/ml (range, 0.06 to 0.25 μg/ml for 49 isolates). This level of in vitro fusidic acid activity underscores the potential clinical utility of this compound in the United States.

Protostane and fusidane triterpenes: a mini-review

Protostane triterpenes belong to a group of tetracyclic triterpene that exhibit unique structural characteristics. Their natural distribution is primarily limited to the genus Alisma of the Alismataceae family, but they have also been occasionally found in other plant genera such as Lobelia, Garcinia, and Leucas. To date, there are 59 known protostane structures. Many of them have been reported to possess biological properties such as improving lipotropism, hepatoprotection, anti-viral activity against hepatitis B and HIV-I virus, anti-cancer activity, as well as reversal of multidrug resistance in cancer cells. On the other hand, fusidanes are fungal products characterized by 29-nor protostane structures. They possess antibiotic properties against staphylococci, including the methicillin-resistant Staphylococcus aureus (MRSA). Fusidic acid is a representative member which has found clinical applications. This review covers plant sources of the protostanes, their structure elucidation, characteristic structural and spectral properties, as well as biological activities. The fungal sources, structural features, biological activities of fusidanes are also covered in this review. Additionally, the biogenesis of these two types of triterpenes is discussed and a refined pathway is proposed.

Optimizing combination rifampin therapy for staphylococcal osteoarticular infections

Staphylococcus spp. causes more than half of all osteoarticular infections of native structures or implanted material. The ability of Staphylococcus spp. to persist within infected bone tissue and to produce a bacterial biofilm, most notably in infections of implanted material, can lead to treatment failures and microbiological relapses. Rifampin is a cornerstone of the treatment of staphylococcal osteoarticular infections, particularly those of implanted material. Rifampin is a bactericidal antibiotic that diffuses very well within bone tissue and bacterial biofilms. The mechanism of action is inhibition of bacterial DNA transcription to mRNA independently from bacterial division, which results in activity against even dormant Staphylococcus spp. organisms. However, the high risk of emergence of rifampin-resistant mutants requires the concomitant administration of another antibiotic. Several antibiotics are recommended in the French guidelines issued by the French-Speaking Society for Infectious Diseases (Société de Pathologie Infectieuse de Langue Française [SPILF]). Here, we discuss the results from in vitro, animal, and clinical studies that explain the advantages and drawbacks of each antibiotic used with rifampin to treat osteoarticular infections due to Staphylococcus spp.

Comparison of Disk Diffusion and Etest Methods to Determine the Susceptibility of Staphylococcus aureus Circulating in Riyadh, Saudi Arabia to Fusidic Acid

Fusidic acid is a common therapy for staphylococcal infections in Saudi Arabia, but reports have suggested high rates of resistance among clinical isolates. Susceptibility testing of S. aureus to fusidic acid is further complicated by the lack of consensus on mean inhibitory concentrations (MIC) and disk diffusion cutoffs to determine resistance. The purpose of this study was to determine the correlation between disk diffusion and Etest determined MIC susceptibility results in clinical isolates of S. aureus from a large academic hospital in Riyadh, Saudi Arabia. Our data demonstrate excellent correlation between Etest determined MIC and disk diffusion susceptibility data, using either previously proposed zone sizes of ≥21 mm as susceptible and ≤18 mm as resistant or the EUCAST recommended zone size of ≤24 mm for resistance, in an area with relatively high rates of fusidic acid resistance.

Antibiotics in development targeting protein synthesis

The resolution of antibiotic-ribosomal subunit complexes and antibacterial-protein complexes at the atomic level has provided new insights into modifications of clinically relevant antimicrobials and provided new classes that target the protein cellular apparatus. New chemistry platforms that use fragment-based drug design or allow novel modifications in known structural classes are being used to design new antibiotics that overcome known resistance mechanisms and extend spectrum and potency by circumventing ubiquitous efflux pumps. This review provides details on seven antibiotics in development for treatment of moderate-to-severe community-acquired bacterial pneumonia and/or acute bacterial skin and skin structure infections: solithromycin, cethromycin, omadacycline, CEM-102, GSK1322322, radezolid, and tedizolid. Two antibiotics of the oxazolidinone class, PF-02341272 and AZD5847, are being developed as antituberculosis agents. Only three antibiotics that target the protein cellular machinery, TP-434, GSK2251052, and plazomicin, have a spectrum that encompasses multidrug-resistant Gram-negative pathogens. These compounds provide hope for treating key pathogens that cause serious disease in both the community and the hospital.