Discovery and development of new antimicrobial agents

Potential role of Manilkara Zapota L in treating bacterial infection

The increasing problem of antibiotic resistance in bacteria leads to an urgent need for new antimicrobial agents. Alternative treatments for bacterial infections need to be explored to tackle this issue. Plant-based substances are emerging as promising options. Manilkara zapota L. contains compounds with antibiotic activities, and anti-inflammatory, antitumor, antipyretic, and antioxidant properties. It has medicinal properties and contains bioactive compounds, like tannins, flavonoids, and triterpenoids. This review aimed to comprehensively evaluate the existing literature on the potential medicinal and therapeutic benefits of M. zapota in bacterial infections by utilizing data from in vivo and in vitro studies. M. zapota has the potential to be a nutritional source of antimicrobial food. Numerous preclinical studies have demonstrated the antibacterial activities of M. zapota and its components. The antibacterial mechanisms of this fruit could interact with bacterial cell structures such as cell walls or membranes.

Computational Screening of Approved Drugs for Inhibition of the Antibiotic Resistance Gene mecA in Methicillin-Resistant Staphylococcus aureus (MRSA) Strains

Antibiotic resistance is a critical problem that results in a high morbidity and mortality rate. The process of discovering new chemotherapy and antibiotics is challenging, expensive, and time-consuming, with only a few getting approved for clinical use. Therefore, screening already-approved drugs to combat pathogens such as bacteria that cause serious infections in humans and animals is highly encouraged. In this work, we aim to identify approved antibiotics that can inhibit the mecA antibiotic resistance gene found in methicillin-resistant Staphylococcus aureus (MRSA) strains. The MecA protein sequence was utilized to perform a BLAST search against a drug database containing 4302 approved drugs. The results revealed that 50 medications, including known antibiotics for other bacterial strains, targeted the mecA antibiotic resistance gene. In addition, a structural similarity approach was employed to identify existing antibiotics for S. aureus, followed by molecular docking. The results of the docking experiment indicated that six drugs had a high binding affinity to the mecA antibiotic resistance gene. Furthermore, using the structural similarity strategy, it was discovered that afamelanotide, an approved drug with unclear antibiotic activity, had a strong binding affinity to the MRSA-MecA protein. These findings suggest that certain already-approved drugs have potential in chemotherapy against drug-resistant pathogenic bacteria, such as MRSA.

Bioassay-Guided Isolation of Antimicrobial Components and LC/QToF Profile of Plumeria obtusa: Potential for the Treatment of Antimicrobial Resistance

The methanolic fraction (M-F) of the total extract (TE) of Plumeria obtusa L. aerial parts showed promising antibacterial effects against the MDR (multidrug-resistant) gram-negative pathogens Klebsiella pneumoniae and Escherichia coli O157:H7 [Shiga toxin-producing E. coli (STEC)]. In addition, M-F had a synergistic effect (in combination with vancomycin) against the MDR gram-positive strains MRSA (methicillin-resistant Staphylococcus aureus) and Bacillus cereus. After treating the K. pneumoniae- and STEC-infected mice with M-F (25 mg/kg, i.p.), the level of IgM and TNF-α was decreased and the severity of pathological lesions were reduced better than that observed after administration of gentamycin (33 mg/kg, i.p.). Thirty-seven compounds including 10 plumeria-type iridoids and 18 phenolics, 7 quinoline derivatives, 1 amino acid, and 1 fatty acid were identified in TE using LC/ESI-QToF. Furthermore, five compounds; kaempferol 3-O-rutinoside (M1), quercetin 3-O-rutinoside (M2), glochiflavanoside B (M3), plumieride (M4), and 13-O-caffeoylplumieride (M5) were isolated from M-F. M5 was active against K. pneumoniae (MIC of 64 μg/mL) and STEC (MIC of 32 μg/mL). These findings suggested that M-F and M5 are promising antimicrobial natural products for combating MDR K. pneumoniae and STEC nosocomial infections.

Design, Synthesis, Characterization, and Analysis of Antimicrobial Property of Novel Benzophenone Fused Azetidinone Derivatives through In Vitro and In Silico Approach

A sequence of novel 2-(4-benzoyl-2-methyl-phenoxy)-N-(3-chloro-2-oxo-4-phenyl-azetidin-1-yl)-acetamide analogues 9(a−n) were synthesized by multistep synthesis. The newly synthesized compounds were well characterized, and their antimicrobial activities were carried out by disc diffusion and broth dilution methods. Further, all the novel series of compounds (9a−n), were tested against a variety of bacterial and fungal strains in comparison to Ketoconazole, Chloramphenicol, and Amoxicillin as standard drugs, respectively. Compounds 9a, 9e, and 9g as a lead molecule demonstrated a good inhibition against tested strains. Further, molecular docking studies have been performed for the potent compounds to check the three-dimensional geometrical view of the ligand binding to the targeted proteins.

Novel Polyhydroquinoline-Hydrazide-Linked Schiff's Base Derivatives: Multistep Synthesis, Antimicrobial, and Calcium-Channel-Blocking Activities

Polyhydroquinoline (PHQ) are the unsymmetrical Hantzsch derivatives of 1,4-dihydropyridines with several biological applications. In this work, twenty-five (3-27) new Schiff's base derivatives of polyhydroquinoline hydrazide were synthesized in excellent to good yields by a multi-component reaction. The structures of the synthesized products (1-27) were deduced with the help of spectroscopic techniques, such as 1H-, 13C -NMR, and HR-ESI-MS. The synthesized products (1-27) were tested for their antibacterial and in vitro calcium -channel-blocking (CCB) potentials using the agar-well diffusion method, and isolated rat aortic ring preparations, respectively. Among the series, sixteen compounds were found to inhibit the growth of Escherichia coli and Enterococcus faecalis. Among them, compound 17 was observed to be the most potent one at a dose 2 µg/mL, with an 18 mm zone of inhibition against both bacteria when it was compared with the standard drug amoxicillin. Eight compounds showed CCB activity of variable potency; in particular, compound 27 was more potent, with an EC50 value of 0.7 (0.3-1.1) µg/mL, indicating their CCB effect.

Antimicrobial activities of amphiphilic cationic polymers and their efficacy of combination with novobiocin

Today, drug-resistant bacteria represent a significant problem worldwide. In fact, bacteria are becoming resistant even to newly developed antibiotics. Therefore, there is an urgent need to develop antibiotics to which bacteria cannot become resistant. In this study, antimicrobial polymers to which bacteria cannot develop resistance were prepared from 6-aminohexyl methacrylamide and N-isopropyl acrylamide. The polymers with molecular weights of the order of 10⁵ showed little antimicrobial activity against Staphylococcus aureus and Escherichia coli as well as low toxicity. On the other hand, polymers with lower molecular weights (of the order of 10⁴) did show antimicrobial activity against S. aureus and E. coli. These polymers were combined with novobiocin to investigate the combined usage effects against E. coli. The combined usage of novobiocin and the low-molecular-weight polymers reduced the minimum inhibitory concentration, which was less than 0.0625 μg/mL against E. coli. This result indicates that the combination is useful for increasing the efficacy of antibiotics and broadening their antimicrobial spectrum. Furthermore, the results showed the possibility that the antimicrobial polymers serve not only as antibiotics to which bacteria have not developed resistance but also as adjuvants for other antibiotics.

Two antibacterial spiro compounds from the roots of Artemisia pallens wall: evidence from molecular docking

Bioassay-guided isolation from acetone extract of the roots of Artemisia pallens Wall yielded two spiro compounds (1 and 2). The structures of these compounds were determined on the basis of spectroscopic techniques such as IR, MS, 1 D and 2 D- NMR. The acetone extract, fractions and the isolated two compounds were investigated for their antibacterial activity against two gram negative (E. coli, P. aeruginosa) and two gram positive (S. aureus, B. subtilis) bacterial strains. Compound (2) showed the best spectra of activity with IC₅₀ and MIC values between 2.48-3.08 and 12.78 - 21.77 µM and Compound (1) with 2.57-3.69 and 38.17 - 80.57 µM, respectively, for the four bacterial strains, whereas inactive against Mycobacterium tuberculosis. Molecular docking study could further help in understanding the various interactions between these compounds and DNA gyrase active site in detail and thereby could provide valuable insight into the mechanism of action.

Evaluation and Docking Study of Pyrazine Containing 1, 3, 4-Oxadiazoles Clubbed with Substituted Azetidin-2-one: A New Class of Potential Antimicrobial and Antitubercular

BACKGROUND

Tuberculosis (TB) caused by Mycobacterium tuberculosis is one of the main killers of people all over the world. The major hurdles with existing therapy are the lengthy regimen and appearance of multi drug resistant (MDR) and extensively drug resistant (XDR) strains of M.tuberculosis.

AIMS

The present work was aimed to synthesize and determine antitubercular and antimicrobial potential of some novel 3-chloro-4-aryl-1-[4-(5-pyrazin-2-yl[1,3,4]oxadiazole-2-ylmethoxy)-phenyl]-azetidin-2-one derivatives 7: (A: -H: ) from pyrazinoic acid as precursor, which is a well-established antitubercular agent. Here we report the synthesis of a new class of heterocyclic molecules in which pyrazine, 1, 3, 4-oxadiazole and azetidinone moieties were present in one frame work.

METHODS

Pyrazinoic acid (1: ) was esterified first (2: ) followed by amination to produce hydrazide (3: ) which was refluxed with POCl3 to obtain 2-chloromethyl-5pyrazino-1, 3, 4-oxadiazole (4: ). This was then further reacted with 4-amino phenol to obtain 4-[5-pyrazino-1, 3, 4-oxadiazol-2-yl-methoxy]-phenyl amine (5: ) which on condensation with various aromatic aldehydes afforded a series Schiff's bases 6(A-H): . Dehydrative annulations of 6(A-H): in the presence of chloroacetyl chloride and triethylamine yielded 3-chloro-4-aryl-1-[4-(5-pyrazin-2-yl-[1, 3, 4]oxadiazole-2-ylmethoxy)-phenyl]-azetidin-2-one derivatives 7(A-H): . Antibacterial, antifungal and antitubercular potential of all the synthesized compounds were assessed. Docking study was performed using the software VLife Engine tools of Vlifemds 4.6 on the protein lumazine synthase of M. tuberculosis (PDB entry code 2C92).

RESULTS

The present studies demonstrated that synthesized oxadiazole derivatives have good antimicrobial activity against the various microorganisms. Among the synthesized derivative, 7B: and 7G: were found to be prominent compounds which have potential antibacterial, antifungal and antitubercular activity (with MIC 3.12 µg/ml and high dock score ranging from -59.0 to -54.0) against Mycobacterium tuberculosis.

CONCLUSIONS

Derivatives 7B: and 7G: would be effective lead candidates for tuberculosis therapy.

A Novel Small Molecule, 1,3-di-m-tolyl-urea, Inhibits and Disrupts Multispecies Oral Biofilms

An imbalance of homeostasis between the microbial communities and the host system leads to dysbiosis in oral micro flora. DMTU (1,3-di-m-tolyl-urea) is a biocompatible compound that was shown to inhibit Streptococcus mutans biofilm by inhibiting its communication system (quorum sensing). Here, we hypothesized that DMTU is able to inhibit multispecies biofilms. We developed a multispecies oral biofilm model, comprising an early colonizer Streptococcus gordonii, a bridge colonizer Fusobacterium nucleatum, and late colonizers Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans. We performed comprehensive investigations to demonstrate the effect of DMTU on planktonic cells and biofilms. Our findings showed that DMTU inhibits and disrupts multispecies biofilms without bactericidal effects. Mechanistic studies revealed a significant down regulation of biofilm and virulence-related genes in P. gingivalis. Taken together, our study highlights the potential of DMTU to inhibit polymicrobial biofilm communities and their virulence.

Epidemiology of resistance and phenotypic characterization of carbapenem resistance mechanisms in Klebsiella pneumoniae isolates at Sahloul University Hospital-Sousse, Tunisia

Objective

To assess the prevalence of ESBL producing and carbapenem resistant Klebsiella pneumoniae isolated from in-come and out-come patients at Sahloul-university hospital.

Methods

A retrospective study over a 3 years period (January 2012 and December 2014) focused on 2160 strains of Klebsiella pneumoniae. Statistical analysis was carried out using SPSS program. ESBL detection was performed using a double disc diffusion method and carbapenemase detection was realized by Rosco-Disk kit.

Results

A total of 2160 Klebsiella pneumoniae strains were isolated during the period of the study, 26.2% (n=566) were ESBL-producers and 15.8% (n=342) showed resistance to carbapenem. The wards most affected by these strains were basically urology and intensive care units. Eighty four percent of studied strains (203/241) were resistant to temocillin, which correlate with the production of a class D (OXA-48-like) carbapenemase and 7% (17/241) showed sensitivity to EDTA and dipicolinic acid, which indicate the production of metallo-enzyme. The rate of resistance to colistin remains low.

Conclusion

Resistance of Enterobacteriaceae, including K. pneumoniae, to third generation cephalosporins (3rd GC) and carbapenem through the mechanism of ESBL and carbapenemases production is becoming increasingly worrying. This suggests a more rational use of antibiotics, as well as the rigorous application of hygiene measurement.

A Review on Antibiotic Resistance: Alarm Bells are Ringing

Antibiotics are the 'wonder drugs' to combat microbes. For decades, multiple varieties of antibiotics have not only been used for therapeutic purposes but practiced prophylactically across other industries such as agriculture and animal husbandry. Uncertainty has arisen, as microbes have become resistant to common antibiotics while the host remains unaware that antibiotic resistance has emerged. The aim of this review is to explore the origin, development, and the current state of antibiotic resistance, regulation, and challenges by examining available literature. We found that antibiotic resistance is increasing at an alarming rate. A growing list of infections i.e., pneumonia, tuberculosis, and gonorrhea are becoming harder and at times impossible to treat while antibiotics are becoming less effective. Antibiotic-resistant infections correlate with the level of antibiotic consumption. Non-judicial use of antibiotics is mostly responsible for making the microbes resistant. The antibiotic treatment repertoire for existing or emerging hard-to-treat multidrug-resistant bacterial infections is limited, resulting in high morbidity and mortality report. This review article reiterates the optimal use of antimicrobial medicines in human and animal health to reduce antibiotic resistance. Evidence from the literature suggests that the knowledge regarding antibiotic resistance in the population is still scarce. Therefore, the need of educating patients and the public is essential to fight against the antimicrobial resistance battle.

Recent developments in the synthesis of condensed β-lactams

β-Lactams are important heterocycles with diverse pharmacological profiles and have emerged as useful organic synthons.

The use of platensimycin and platencin to fight antibiotic resistance

Infectious diseases are known as one of the most life-threatening disabilities worldwide. Approximately 13 million deaths related to infectious diseases are reported each year. The only way to combat infectious diseases is by chemotherapy using antimicrobial agents and antibiotics. However, due to uncontrolled and unnecessary use of antibiotics in particular, surviving bacteria have evolved resistance against several antibiotics. Emergence of multidrug resistance in bacteria over the past several decades has resulted in one of the most important clinical health problems in modern medicine. For instance, approximately 440,000 new cases of multidrug-resistant tuberculosis are reported every year leading to the deaths of 150,000 people worldwide. Management of multidrug resistance requires understanding its molecular basis and the evolution and dissemination of resistance; development of new antibiotic compounds in place of traditional antibiotics; and innovative strategies for extending the life of antibiotic molecules. Researchers have begun to develop new antimicrobials for overcoming this important problem. Recently, platensimycin - isolated from extracts of Streptomyces platensis - and its analog platencin have been defined as promising agents for fighting multidrug resistance. In vitro and in vivo studies have shown that these new antimicrobials have great potential to inhibit methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and penicillin-resistant Streptococcus pneumoniae by targeting type II fatty acid synthesis in bacteria. Showing strong efficacy without any observed in vivo toxicity increases the significance of these antimicrobial agents for their use in humans. However, at the present time, clinical trials are insufficient and require more research. The strong antibacterial efficacies of platensimycin and platencin may be established in clinical trials and their use in humans for coping with multidrug resistance may be allowed in the foreseeable future.

Early stage efficacy and toxicology screening for antibiotics and enzyme inhibitors

The rise in organisms resistant to existing drugs has added urgency to the search for new antimicrobial agents. Aspartate β-semialdehyde dehydrogenase (ASADH) catalyzes a critical step in an essential microbial pathway that is absent in mammals. Our laboratory is using fragment library screening to identify efficient and selective ASADH inhibitors. These preliminary agents are then tested to identify compounds with desired antimicrobial properties for further refinement. Toward this end, we have established a microplate-based, dual-assay approach using a single reagent to evaluate antibiotic activity and mammalian cell toxicity during early stage development. The bacterial assay uses nonpathogenic bacteria to allow efficacy testing without a dedicated microbial laboratory. Toxicity assays are performed with a panel of mammalian cells derived from representative susceptible tissues. These assays can be adapted to target other microbial systems, such as fungi and biofilms, and additional mammalian cell lines can be added as needed. Application of this screening approach to antibiotic standards demonstrates the ability of these assays to identify bacterial selectivity and potential toxicity issues. Tests with selected agents from the ASADH inhibitor fragment library show some compounds with antibiotic activity, but as expected, most of these early agents display higher than desired mammalian cell toxicity.

Drosophila and Galleria insect model hosts: new tools for the study of fungal virulence, pharmacology and immunology

Over recent years we have witnessed the emergence of several non-vertebrate mini-hosts as alternative pathosystems for the study of fungal disease. These heterologous organisms have unique advantages, as they are economical, ethically expedient, and facile to use. Hence, they are amenable to high-throughput screening studies of fungal genomes for identification of novel virulence genes and of chemical libraries for discovery of new antifungal compounds. In addition, because they have evolutionarily conserved immunity they offer the opportunity to better understand innate immune responses against medically important fungi. In this review, we discuss how the insects Drosophila melanogaster and Galleria mellonella can be employed for the study of various facets of host-fungal interactions as complementary hosts to conventional vertebrate animal models.

A rapid in situ procedure for determination of bacterial susceptibility or resistance to antibiotics that inhibit peptidoglycan biosynthesis

Background

Antibiotics which inhibit bacterial peptidoglycan biosynthesis are the most widely used in current clinical practice. Nevertheless, resistant strains increase dramatically, with serious economic impact and effects on public health, and are responsible for thousands of deaths each year. Critical clinical situations should benefit from a rapid procedure to evaluate the sensitivity or resistance to antibiotics that act at the cell wall. We have adapted a kit for rapid determination of bacterial DNA fragmentation, to assess cell wall integrity.

Results

Cells incubated with the antibiotic were embedded in an agarose microgel on a slide, incubated in an adapted lysis buffer, stained with a DNA fluorochrome, SYBR Gold and observed under fluorescence microscopy. The lysis affects the cells differentially, depending on the integrity of the wall. If the bacterium is susceptible to the antibiotic, the weakened cell wall is affected by the lysing solution so the nucleoid of DNA contained inside the bacterium is released and spread. Alternatively, if the bacterium is resistant to the antibiotic, it is practically unaffected by the lysis solution and does not liberate the nucleoid, retaining its normal morphological appearance. In an initial approach, the procedure accurately discriminates susceptible, intermediate and resistant strains of Escherichia coli to amoxicillin/clavulanic acid. When the bacteria came from an exponentially growing liquid culture, the effect on the cell wall of the β-lactam was evident much earlier that when they came from an agar plate. A dose-response experiment with an E. coli strain susceptible to ampicillin demonstrated a weak effect before the MIC dose. The cell wall damage was not homogenous among the different cells, but the level of damage increased as dose increased with a predominant degree of effect for each dose. A microgranular-fibrilar extracellular background was evident in gram-negative susceptible strains after β-lactam treatment. This material was digested by DNase I, hybridised with a specific whole genome probe, and so recognized as DNA fragments released by the bacteria. Finally, 46 clinical strains from eight gram-negative and four gram-positive species were evaluated blind for susceptibility or resistance to one of four different β-lactams and vancomycin, confirming the applicability of the methodology.

Conclusion

The technique to assess cell wall integrity appears to be a rapid and simple procedure to identify resistant and susceptible strains to antibiotics that interfere with peptidoglycan biosynthesis.

Synthesis, antimicrobial activity and cytotoxicity of novel oxadiazole derivatives

In the present study, 5-substituted-1,3,4-oxadiazolin-2-thiones (1a-b) were synthesized via the ring closure reactions of appropriate acid hydrazides with carbon disulphide. N-(Benzothiazol-2-yl)-2-[[5-substituted-1,3,4-oxadiazol-2-yl]sulfanyl]acetamide derivatives (3a-j) were obtained by the nucleophilic substitution reactions of 5-substituted-1,3,4-oxadiazolin-2-thiones (1a-b) with N-(benzothiazol-2-yl)-2-chloroacetamides. The chemical structures of the compounds were elucidated by IR, (1)H NMR, (13)C NMR and FAB(+)-MS spectral data and elemental analyses. The synthesized compounds were screened for their antimicrobial activities against Micrococcus luteus, Bacillus subtilis, Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, Listeria monocytogenes and Candida albicans. All compounds except compound 3h exhibited the highest antibacterial activity against P. aeruginosa. Among all compounds (3a-j), the compounds bearing 4-methoxyphenoxymethyl moiety on oxadiazole ring (3a-e) exhibited the highest inhibitory activity against C. albicans. Although compound 3j did not possess 4-methoxyphenoxymethyl moiety on oxadiazole ring, this derivative also exhibited the same level of anti-candidal activity. The compounds were also investigated for their cytotoxic effects using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. Compound 3a exhibited the highest cytotoxic activity, whereas compound 3g possessed the lowest cytotoxic activity against NIH/3T3 cells.

Production, purification and characterization of serraticin A, a novel cold-active antimicrobial produced by Serratia proteamaculans 136

AIM

This study focuses on the production, purification and characterization of serraticin A, a novel cold-active antimicrobial produced by Serratia proteamaculans 136.

METHODS AND RESULTS

A Ser. proteamaculans strain producing a novel cold-active antimicrobial was isolated from Isla de los Estados, Argentina. Antimicrobial production was optimized in a BIOFLO 101 bioreactor under batch culture mode, with temperature, pH and dissolved oxygen controlled conditions. A purification protocol was developed including activated charcoal adsorption, solid-phase C18 extraction (SPE) and semi-preparative HPLC. The molecular weight was determined by LC/QTOF/MS/MS mass analysis.

CONCLUSIONS

Serratia proteamaculans 136 produces a cold-active low molecular bacteriocin-like compound named serraticin A. In this work, it has been laboratory-scale produced, purified and partially characterized. Cross-immunity test revealed that serraticin A is very different from other well-known microcins assayed, with a wide inhibitory spectrum, showing an interesting biotechnology potential to be applied as a control agent against pathogenic bacteria.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study is the first report of a cold-active compound with antimicrobial activity from Ser. proteamaculans. The work also highlights that cold environments could be a suitable source of micro-organisms with ability to produce cold-active biomolecules of biotechnological interest.

Broad-spectrum antibiotic activity of the arylomycin natural products is masked by natural target mutations

Novel classes of broad-spectrum antibiotics are needed to treat multidrug-resistant pathogens. The arylomycin class of natural products inhibits a promising antimicrobial target, type I signal peptidase (SPase), but upon initial characterization appeared to lack whole-cell activity against most pathogens. Here, we show that Staphylococcus epidermidis, which is sensitive to the arylomycins, evolves resistance via mutations in SPase and that analogous mutations are responsible for the natural resistance of Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. We identify diverse bacteria lacking these mutations and demonstrate that most are sensitive to the arylomycins. The results illustrate that the arylomycins have a broad-spectrum of activity and are viable candidates for development into therapeutics. The results also raise the possibility that naturally occurring resistance may have masked other natural product scaffolds that might be developed into therapeutics.

Chromobacterium violaceum and its important metabolites--review

C. violaceum appeared as important bacterium in different applications and mainly these aspects are related to the production of violacein. This review discusses the last reports on biosynthetic pathways, production, genetic aspects, biological activities, pathological effects, antipathogenic screening through quorum sensing, environmental effects and the products of C. violaceum with industrial interest. An important discussion is on biological applications in medicine and as industrial products such as textile and in cosmetics.

2-Azetidinone--a new profile of various pharmacological activities

2-azetidinone, a β-lactam four member heterocyclic compound involved in research aimed to evaluate new products that possess interesting biological activities. These compounds reported for their antimicrobial and antifungal activities. Successful introduction of aztreonam as a potent inhibitor of cephalosporinase and ezetimibe as a cholesterol absorption inhibitor proved potential of 2-azetidinone moiety. Subsequently 2-azetidinones were highlighted as a potent mechanism based inhibitor of several enzymes like human tryptase, chymase, thrombin, leukocyte elastase, human cytomegalovirus protease and serine protease enzyme. These derivatives also known to possess antitubercular, anti-inflammatory, antitumor, anti-HIV, antiparkinsonian, antidiabetic and vasopressin V1a antagonist activity. The present review article focuses on the pharmacological profile of 2-azetidinones with their potential activities.

Small molecules with antimicrobial activity against E. coli and P. aeruginosa identified by high-throughput screening

BACKGROUND AND PURPOSE

New antimicrobials are needed because of the emergence of organisms that are resistant to available antimicrobials. The purpose of this study was to evaluate a high-throughput screening approach to identify antibacterials against two common disease-causing bacteria, and to determine the frequency, novelty, and potency of compounds with antibacterial activity.

EXPERIMENTAL APPROACH

A high-throughput, turbidometric assay of bacterial growth in a 96-well plate format was used to screen a diverse collection of 150,000 small molecules for antibacterial activity against E. coli and P. aeruginosa. The statistical Z'-factor for the assay was > or = 0.7.

KEY RESULTS

Screening for inhibition of E. coli growth gave a 'hit' rate (> 60% inhibition at 12.5 microM) of 0.025%, which was more than 5-fold reduced for P. aeruginosa. The most potent antibacterials (EC50 < 0.5 microM) were of the nitrofuran class followed by naphthalimide, salicylanilide, bipyridinium and quinoazolinediamine chemical classes. Screening of > 250 analogs of the most potent antibacterial classes established structure-activity data sets.

CONCLUSIONS AND IMPLICATIONS

Our results validate and demonstrate the utility of a growth-based phenotype screen for rapid identification of small-molecule antibacterials. The favourable efficacy and structure-activity data for several of the antibacterial classes suggests their potential development for clinical use.

Fishing for new antimicrobials

The discovery of antibiotics and other antimicrobial agents in the 1930s is arguably the most significant therapeutic advance in medical history. Penicillin and the sulfa drugs touched off the search for and discovery of countless derivative compounds and several new antibiotic classes. However, the pace of discovery has slowed down, and there is growing appreciation that much of the low-lying fruit accessible to traditional methods of antimicrobial discovery has been harvested. Combating emerging drug-resistant strains of infectious agents may require the adoption of fresh approaches to drug target validation, small-molecule discovery and safety assessment. The recent development of several infectious disease models in zebrafish raises the possibility of a new paradigm in antimicrobial discovery.

Ex vivo analysis of antineoplastic agents in precision-cut tissue slices of human origin: effects of cyclooxygenase-2 inhibition in hepatocellular carcinoma

Cultures of precision-cut tissue slices allow the investigation of substance effects on human tissues under in vivo-like conditions over a limited time span. We have adapted the model for direct analyses of antineoplastic substances on tumor tissues. We have recently demonstrated that selective cyclooxygenase-2 (COX-2) inhibitors strongly suppress growth of human hepatocellular carcinoma (HCC) cells in vitro and nude mouse HCC implants by inducing apoptosis and reducing proliferation. We have now analyzed the effects of COX-2 inhibition on human tumor tissue. Three hundred micrometer slices of tumorous and non-tumorous liver tissue from three surgically resected HCCs were cultured with increasing concentrations of the selective COX-2 inhibitor Meloxicam (20-200 microM) for 6, 12, 24, and 48 h. The cultured tissue slices were analysed morphologically and by immunohistology for proliferation (Ki-67), apoptosis (M30), and COX-2 expression. COX-2 was expressed in all HCCs and in the non-tumorous liver tissue. Cytoplasmic COX-2 immunoreactivity in HCCs increased during culturing time. In two of three cases, COX-2 inhibition significantly increased tumor cell apoptosis in HCCs, whereas the low basal apoptosis rate in the non-tumorous liver parenchyma did not change. Tumor cell proliferation was mildly reduced, but the changes did not reach statistical significance. These results demonstrate that the precision-cut tissue slice culture model is a useful tool to analyze directly drug-dependent antitumorous or unwanted organ-specific effects. The analysis of COX-2 inhibition lends further support to the antineoplastic effects previously demonstrated in vitro and in animal models.

The importance of the development of antibiotic resistance in Staphylococcus aureus

Hospital- and community-acquired Staphylococcus aureus infections pose a substantial burden in terms of morbidity, mortality and health care costs. The introduction of new antibiotics to counter this pathogen has frequently been closely followed by the emergence of resistant strains. Most significantly, S. aureus isolates resistant to beta-lactams have become common, and many of these are also resistant to beta-lactamase-resistant penicillins. The rapid spread of methicillin-resistant S. aureus (MRSA) clones across the world often results in hospital outbreaks, but implementation of appropriate control measures usually reduces prevalence to sporadic levels. However, the recent emergence of MRSA infections in the community, affecting patients with no established risk factors for MRSA acquisition, is likely to impact significantly on future strategies for control of nosocomial MRSA. In contrast to other antibiotic classes, S. aureus resistance to glycopeptides did not emerge until nearly 40 years after their clinical introduction, and as a result this drug class has remained the mainstay of treatment for MRSA infections. However, a number of vancomycin-intermediate S. aureus isolates have emerged worldwide and four fully resistant S. aureus isolates have been reported in the USA. This raises the concern that the current first-line treatment for MRSA infection may become ineffective in an increasing proportion of cases in the near future. New classes of antibiotic are urgently needed to treat infections with this growing population of multidrug-resistant S. aureus, and the recently introduced oxazolidinone linezolid and the cyclic lipopeptide daptomycin are welcome additions to the ever-narrowing range of therapies effective against this pathogen.

Preclinical evaluation of novel antibacterial agents by microbiological and molecular techniques

The defining property of an antibacterial agent is its ability to selectively interfere with bacterial growth and/or survival. Consequently, a considerable and crucial part of the preclinical evaluation of any novel antibacterial drug involves judging and characterising its effects on bacteria in vitro. These critical stages in drug development are sometimes made to appear somewhat trivial, sandwiched as they are between the highly demanding antibacterial discovery process and the formidable task of demonstrating safety and efficacy in vivo. However, careful biological evaluation in vitro is key to quantifying and understanding the basis of the antibacterial activity, providing preliminary indications and evaluations of therapeutic potential, assessing the likelihood for the development of bacterial resistance, guiding chemical refinement and assisting subsequent stages of the appraisal of any new antibacterial drug. This review covers concepts in, and strategies for, the in vitro microbiological and molecular evaluation of antibacterial drug candidates.

Genetic strategies for antibacterial drug discovery

The availability of genome sequences is revolutionizing the field of microbiology. Genetic methods are being modified to facilitate rapid analysis at a genome-wide level and are blossoming for human pathogens that were previously considered intractable. This revolution coincided with a growing concern about the emergence of microbial drug resistance, compelling the pharmaceutical industry to search for new antimicrobial agents. The availability of the new technologies, combined with many genetic strategies, has changed the way that researchers approach antibacterial drug discovery.

The future challenges facing the development of new antimicrobial drugs

The emergence of resistance to antibacterial agents is a pressing concern for human health. New drugs to combat this problem are therefore in great demand, but as past experience indicates, the time for resistance to new drugs to develop is often short. Conventionally, antibacterial drugs have been developed on the basis of their ability to inhibit bacterial multiplication, and this remains at the core of most approaches to discover new antibacterial drugs. Here, we focus primarily on an alternative novel strategy for antibacterial drug development that could potentially alleviate the current situation of drug resistance--targeting non-multiplying latent bacteria, which prolong the duration of antimicrobial chemotherapy and so might increase the rate of development of resistance.

Pulse and continuous oral norfloxacin treatment of experimentally induced Escherichia coli infection in broiler chicks and turkey poults

Experimental colibacillosis was produced in 40 healthy, 7-day-old broiler chickens and turkeys by intratracheal injection of 1 x 10(8) CFU/chick and 1.23 x 10(9) CFU/poult bacteria of an O1:F11 strain of Escherichia coli, respectively. Two days before E. coli challenge all chicks were vaccinated with a live attenuated strain of infectious bronchitis virus (H-52). This model of infection--at least in chicken--proved to be useful for evaluating the efficacy of antimicrobial medication, by recording mortality, body weight gain, pathological alterations and frequency of reisolation of E. coli. Using this model, the efficacy of two different dosing methods of norfloxacin (continuous and pulse dosing) was evaluated. The once-per-day pulse dosing of norfloxacin administered via the drinking water at 15 mg/kg body weight proved to be more efficacious than the continuous dosing method of 100 mg/L for 5 days in chickens, while there were no convincing differences between the two treatment regimens in turkeys. The results confirmed earlier observations on the pharmacokinetic properties of norfloxacin in chicks and turkeys (Laczay et al., 1998).

In vitro models to study hepatotoxicity

Drug discovery and development consists of a series of processes starting with the demonstration of pharmacological effects in experimental cell and animal models and ending with drug safety and efficacy studies in patients. A main limitation is often the unacceptable level of toxicity with the liver as the primary target organ. Therefore, approaches to study hepatic toxicity in the early phase of drug discovery represent an important step towards rational drug development. A variety of in vitro liver models have been developed in the past years. Next to their use in drug development, they can also be applied to study environmental toxins and their hepatotoxicity. The 3 main approaches are ex vivo isolated and perfused organ models, precision-cut liver slices and cell culture models. Although the advantage of whole organ perfusions is based on the assessment of physiologic parameters such as bile production and morphologic parameters such as tissue histology, cell culture models can be efficiently used to assess cellular metabolism, cytotoxicity and genotoxicity. The advantage of precision-cut liver slices is based on the juxtaposition of cellular assays and tissue morphology. None of these models can be compared as they all focus on different fields of hepatoxicology. For the future, the ideal setup for testing the hepatic toxicity of a new compound could of primary studies in cell or slice cultures to assess cellular effects and secondary studies using ex vivo perfused organs to examine gross organ function parameters and histology.

Treatment of experimentally induced Pasteurella multocida infections in broilers and turkeys: comparative studies of different oral treatment regimens

Experimental fowl cholera was induced in 60 healthy 10-week-old broiler chickens and 8-week-old turkeys by intramuscular inoculation with approximately 80 colony-forming units (cfu) of Pasteurella multocida X-73 strain and with approximately 70 cfu of P. multocida P-1059 strain, respectively. This method of infection proved to be useful for evaluating the efficacy of anti-microbial medication, by measuring mortality, weight gain, pathological responses and frequency of re-isolation of P. multocida. The efficacies of two different dosing methods, continuous and pulse dosing, were compared. Using the continuous-dosing method, norfloxacin was administered to drinking water at 100 mg/l for 5 days in chickens. Efficacies were slightly improved compared with pulse dosing at 15 mg/kg bodyweight for the same length of time. The opposite was observed in turkeys, to the degree of control of mortality and maintenance of weight gain.

Susceptibility testing. Phenotypic and genotypic tests for bacteria and mycobacteria

Genotypic-based methods hold promise for the rapid and accurate detection or confirmation of antimicrobial resistance; however, phenotypic methods will continue to have an advantage when resistance to the same antimicrobial agent may be caused by several different mechanisms. The diversity of genetic mechanisms may exceed the capabilities of current molecular technology. Genotypic assays have the ability to detect resistance but not susceptibility. Although resutls can be obtained rapidly, many molecular methods are labor-intensive, expensive, and lack standardization. Clinical studies will be required to validate the genotypic approach to detection of antimicrobial resistance. Molecular assays are also at risk for false-positive results because of contamination of specimens by other specimens that carry the DNA targeted for the assay, or carryover of amplified target DNA (amplicons) from a previous PCR assay during sample preparation. Detection of certain genetic resistance loci in clinical specimens must be interpreted with caution, because organisms in normal flora may also harbor the same loci. All these factors must be taken into consideration when introducing a genotypic method in the clinical laboratory. Other considerations include cost, turnaround time, and assay performance. It must be emphasized that the bedside assessment of the patient should always be considered in addition to the results of antimicrobial susceptibility tests (whether phenotypic or genotypic) so that the best outcome is assured for the patient.

Association between the use of avilamycin for growth promotion and the occurrence of resistance among Enterococcus faecium from broilers: epidemiological study and changes over time

This study describes the changes in the occurrence of resistance to avilamycin among Enterococcus faecium from broilers in Denmark and the epidemiological association between usage of avilamycin for growth promotion and the occurrence of avilamycin-resistant E. faecium on broiler farms. The consumption of avilamycin for growth promotion increased from 10 kg in 1990 to 2,740 kg 1996 and decreased in the following years to only 7 kg in 1998. Most of this has been used for broilers. As part of the nationwide monitoring program for antimicrobial resistance, a total of 473 E. faecium isolates from broilers and 290 isolates from pigs have been tested for their susceptibility to avilamycin from 1995 to 1998. A very limited number of isolates from pigs were resistant to avilamycin, whereas the occurrence of resistance among isolates from broilers increased from 63.6% at the end of 1995 to a maximum of 80.7% during the last half of 1996. Since then, the occurrence of resistance has decreased to 23.3% in the last half of 1998. The epidemiological association between consumption of avilamycin and occurrence of resistant E. faecium fecal droppings were examined on 10 poultry farms that had not used avilamycin for growth promotion during 1996 or 1997 and eight farms that had used avilamycin during 1997. We tested a total of E. faecium isolates from the exposed farms and 104 from the nonexposed farms for their susceptibility to avilamycin. Resistant isolates were found on all eight exposed farms, and on seven of 10 nonexposed farms. Sixty-four isolates (72%) from the exposed farms were resistant, compared with 24 (23%) of the isolates from nonexposed farms. The adjusted chi-square p value equaled 0.01065, and showed a significant association between use of avilamycin and occurrence of resistance. The national monitoring program showed a decrease in the occurrence of resistance following a decreased use of avilamycin in Denmark, and the epidemiological study showed a statistically significant association between the use of avilamycin for growth promotion and the occurrence of avilamycin-resistant E. faecium on broiler farms.

Association between decreased susceptibility to a new antibiotic for treatment of human diseases, everninomicin (SCH 27899), and resistance to an antibiotic used for growth promotion in animals, avilamycin

The emergence of multiresistant bacteria has increased the need for new antibiotics or modifications of older antibiotics. One promising agent might be the everninomicin SCH 27899, an oligosaccharide antibiotic recently developed by Schering Plough. However, another oligosaccharide, avilamycin, that is structurally very similar has been used as a growth promoter for food animals in the EU for several years, and a very frequent occurrence of resistance to avilamycin has been found among Enterococcus faecium isolates from broilers in Denmark. This study was conducted to investigate whether the resistance to avilamycin was associated with decreased susceptibility to everninomicin. From broilers, a total of 31 avilamycin susceptible and 55 avilamycin resistant (MIC >16 microg/mL) E. faecium isolates were selected. From pigs, 21 avilamycin-susceptible and eight avilamycin-resistant Enterococcus faecalis and 50 avilamycin-susceptible and two avilamycin-resistant E. faecium isolates were selected. All isolates were tested for susceptibility to everninomicin by E-test. The avilamycin-susceptible enterococci isolates had MICs to everninomicin from 0.064 to 0.75 microg/mL (MIC50 = 0.38 microg/mL) and the avilamycin-resistant isolates had MICs from 1.5 to 16 microg/mL (MIC50 = 3 microg/mL). Complete agreement between decreased susceptibility to avilamycin and everninomicin was found. This study showed that the use of avilamycin as a growth promoter for broilers and pigs has created a reservoir of E. faecium and E. faecalis isolates with decreased susceptibility to everninomicin among food animals already before this antibiotic have been finally developed for human use.

Mining bacterial cell wall biosynthesis with new tools: multitarget screens

The cytoplasmic steps of peptidoglycan synthesis remain underexplored for the discovery of novel antibiotics. Pathway screens are well suited to screen for novel inhibitors because several targets are tested at once. Whole-cell based assays are easier to set up but they tend to favor identification of compounds that inhibit enzymes that are at the limiting rate in the pathway. Screens that use purified enzymes are optimized to detect with similar probability inhibitors of any of the targets in the pathway. This approach is being used to identify novel promising molecules. Copyright 1999 Harcourt Publishers Ltd.

In vitro activity of eight fluoroquinolones against clinical isolates of Brucella melitensis

Since fluoroquinolones have generated much interest because of their excellent in vitro and in vivo activity, their pharmacokinetic propertiesm oral dosing and intracellular penetration, we tested the susceptibility of 146 recent clinical isolated of Brucella melitensis agaist eight 4-quinolone drugs and five conventional drugs. The drugs tested included ciprofloxacin, norfloxacin, temafloxacin, sparfloxacin, fleroxacin, pefloxacin, lomefloxacin, CI-960, tetracycline, gentamicin, streptomycin rifampicin and trimethoprim-sulfamethoxazole. All the isolates were susceptible to the eight quinolones tested, with an MIC-90 ranging between 0.12 mg/L to 2.0 mg/L depending on the drug. Lowest MCIs were observed with CI-960 and highest temafloxacin and sparfloxacin. One isolate which had developed resistance to ciprofloxacin while the patient was being treated with this drug exhibited cross-resistance to all the members of the family.