Francis Tally and the discovery and development of tigecycline: a personal reminiscence.

For Francis Tally, both medicine and science were highly personal undertakings. Tally thought that emotional engagement was important in one's work and one's life, which were inseparable in his case. Indeed, Tally materially participated in no fewer than 4 programs that resulted in the approval and commercialization of novel antibiotics.

Establishment of in vitro susceptibility testing methodologies and comparative activities of piperacillin in combination with the penem {beta}-lactamase inhibitor BLI-489.

The novel bicyclic penem inhibitor BLI-489 has demonstrated activity as an inhibitor of class A, C, and D beta-lactamases. To determine the combination of piperacillin and BLI-489 to be used in susceptibility testing that would most accurately identify susceptible and resistant isolates, a predictor panel of beta-lactamase-producing bacteria was utilized to determine the reliability of the combination of piperacillin-BLI-489 at a constant inhibitor concentration of 2 or 4 microg/ml and at ratios of 1:1, 2:1, 4:1, and 8:1. There were a number of strains that would be falsely reported as susceptible or intermediate if tested with the ratios of 1:1 and 2:1, whereas the constant concentration of 2 microg/ml of BLI-489 and the ratio of 8:1 had a tendency to overpredict resistance.

Late stage antibacterial drugs in the clinical pipeline.

Bacterial resistance to antimicrobial agents is a growing problem worldwide. Not only is issue compounded by the fact that there are fewer pharmaceutical companies conducting research to discover novel antimicrobials than in the past but development time lines have stretched so that a dozen years from discovery to the market is now the standard. Eleven antibacterial drugs in late stage clinical development are discussed.

Transcriptional profiling of a Staphylococcus aureus clinical isolate and its isogenic agr and sarA mutants reveals global differences in comparison to the laboratory strain RN6390.

The production of Staphylococcus aureus virulence factors is under the control of complex regulatory circuits. Most studies aimed at defining these regulatory networks have focused on derivatives of the strain NCTC 8325, most notably RN6390. However, all NCTC 8325 derivatives, including RN6390, possess an 11 bp deletion in rsbU.

Characterization of the Staphylococcus aureus heat shock, cold shock, stringent, and SOS responses and their effects on log-phase mRNA turnover.

Despite its being a leading cause of nosocomal and community-acquired infections, surprisingly little is known about Staphylococcus aureus stress responses. In the current study, Affymetrix S. aureus GeneChips were used to define transcriptome changes in response to cold shock, heat shock, stringent, and SOS response-inducing conditions.

Staphylococcal vaccines and immunotherapy: to dream the impossible dream?

Staphylococcal infections not only remain an important cause of morbidity and mortality in both the community and the clinic, but the emergence of a global pandemic of community-associated methicillin-resistant Staphylococcus aureus, involving what purports to be a more virulent strain of this organism, has also led several in the infectious disease community to call for improved disease prevention strategies (in addition to novel therapeutics) in what could be thought of as the microbiological version of pre-emption. In this case, Staphylococcus aureus possesses "weapons of mass destruction" and appears to be using them effectively as part of anti-immunization insurgency.

Characterization of the Staphylococcus aureus CidR regulon: elucidation of a novel role for acetoin metabolism in cell death and lysis.

The Staphylococcus aureus cid and lrg operons encode a novel regulatory system that affects murein hydrolase activity, stationary-phase survival and antibiotic tolerance. Expression of the lrgAB operon is positively regulated by a two-component regulatory system encoded by the lytSR operon located immediately upstream to lrgAB. By comparison, the cidABC operon lies downstream from the cidR gene, encoding a protein homologous to the LysR-type family of transcriptional regulators.

Characterizing the effect of the Staphylococcus aureus virulence factor regulator, SarA, on log-phase mRNA half-lives.

Bacterial pathogens regulate virulence factor expression at both the level of transcription initiation and mRNA processing/turnover. Within Staphylococcus aureus, virulence factor transcript synthesis is regulated by a number of two-component regulatory systems, the DNA binding protein SarA, and the SarA family of homologues. However, little is known about the factors that modulate mRNA stability or influence transcript degradation within the organism.

Transcription Profiling of the mgrA Regulon in Staphylococcus aureus.

MgrA has been shown to affect multiple Staphylococcus aureus genes involved in virulence and antibiotic resistance. To comprehensively identify the target genes regulated by mgrA, we employed a microarray method to analyze the transcription profiles of S. aureus Newman, its isogeneic mgrA mutant, and an MgrA-overproducing derivative.

Characterization of a strain of community-associated methicillin-resistant Staphylococcus aureus widely disseminated in the United States.

A highly stable strain of Staphylococcus aureus with a pulsed-field gel electrophoresis type of USA300 and multilocus sequence type 8 has been isolated from patients residing in diverse geographic regions of the United States. This strain, designated USA300-0114, is a major cause of skin and soft tissue infections among persons in community settings, including day care centers and correctional facilities, and among sports teams, Native Americans, men who have sex with men, and military recruits. The organism is typically resistant to penicillin, oxacillin, and erythromycin (the latter mediated by msrA) and carries SCCmec type IVa.

Use of ribotyping to retrospectively identify methicillin-resistant Staphylococcus aureus isolates from phase 3 clinical trials for tigecycline that are genotypically related to community-associated isolates.

A retrospective study was performed to identify methicillin-resistant Staphylococcus aureus (MRSA) isolates obtained from patients enrolled in phase 3 clinical trials for tigecycline that were genotypically similar to known community-associated MRSA (CA-MRSA) strains. The clinical trials were double-blind comparator studies for complicated skin and skin structure infections or complicated intra-abdominal infections. We obtained 85% of the MRSA isolates from patients with complicated skin and skin structure infections.

Differential proteomic analysis of bronchoalveolar lavage fluid in asthmatics following segmental antigen challenge.

Allergic asthma is characterized by persistent airway inflammation and remodeling. Bronchoalveolar lavage conducted with fiberoptic bronchoscopy has been widely used for investigating the pathogenesis of asthma and other lung disorders. Identification of proteins in the bronchoalveolar lavage fluid (BALF) and their expression changes at different stages of asthma could provide further insights into the complex molecular mechanisms involved in this disease.

A novel MATE family efflux pump contributes to the reduced susceptibility of laboratory-derived Staphylococcus aureus mutants to tigecycline.

Tigecycline, an expanded-broad-spectrum glycylcycline antibiotic is not affected by the classical tetracycline resistance determinants found in Staphylococcus aureus. The in vitro selection of mutants with reduced susceptibility to tigecycline was evaluated for two methicillin-resistant S. aureus strains by serial passage in increasing concentrations of tigecycline.

Comparative genomics of Staphylococcus aureus musculoskeletal isolates.

Much of the research aimed at defining the pathogenesis of Staphylococcus aureus has been done with a limited number of strains, most notably the 8325-4 derivative RN6390. Several lines of evidence indicate that this strain is unique by comparison to clinical isolates of S. aureus.

Effect of mild acid on gene expression in Staphylococcus aureus.

During staphylococcal growth in glucose-supplemented medium, the pH of a culture starting near neutrality typically decreases by about 2 units due to the fermentation of glucose. Many species can comfortably tolerate the resulting mildly acidic conditions (pH, approximately 5.5) by mounting a cellular response, which serves to defend the intracellular pH and, in principle, to modify gene expression for optimal performance in a mildly acidic infection site.

Small molecules for small minds? The case for biologic pharmaceuticals.

Biologic pharmaceuticals are gaining in both market share and clinical utility compared with small molecule therapeutics. This market growth is, in part, reflective of a field of science entering its toddlerhood, where with increased maturity, both development timelines and costs of manufacturing for these complex molecules will decrease, further enhancing the profitability side of the equation. Although a firm understanding of the rules governing toxicity (especially antibody responses to therapeutic proteins) remains to be defined, it is clear that proteins are less prone to much of the idiosyncratic toxicity associated with small molecule drug candidates.

Global gene expression in Staphylococcus aureus biofilms.

We previously demonstrated that mutation of the staphylococcal accessory regulator (sarA) in a clinical isolate of Staphylococcus aureus (UAMS-1) results in an impaired capacity to form a biofilm in vitro (K. E. Beenken, J.

Hydrophobic acetal and ketal derivatives of mannopeptimycin-alpha and desmethylhexahydromannopeptimycin-alpha: semisynthetic glycopeptides with potent activity against Gram-positive bacteria.

The effect of introducing hydrophobic groups onto the disaccharide portion of the mannopeptimycins has been examined. Under acid-catalyzed conditions dimethyl acetals and ketals react on the terminal mannose of the disaccharide moiety of mannopeptimycin-alpha and the cyclohexylalanyl analogue 2. The preferentially formed monofunctionalized 4,6-acetals and -ketals display potent antibacterial activities against Gram-positive microorganisms, including MRSA, PRSP, and VRE pathogens.

Comparison of tetracycline and tigecycline binding to ribosomes mapped by dimethylsulphate and drug-directed Fe2+ cleavage of 16S rRNA.

Objectives: The new antibiotic tigecycline (9-t-butylglycylamido-minocycline; GAR-936) overcomes most of the known tetracycline resistance mechanisms. Here we analyse its mode of antibiotic action by probing 70S ribosomes of Escherichia coli with dimethylsulphate (DMS) and Fe(2+)-mediated cleavage to identify binding sites of tetracycline and tigecycline.

Methods: Fe(2+)-mediated cleavage makes use of the ability of Fe2+ to replace the Mg2+ ion complexed with tetracyclines.

Effect of srtA and srtB gene expression on the virulence of Staphylococcus aureus in animal models of infection.

Objective: The role that the surface proteins anchored by the srtA and srtB gene products play in the ability of Staphylococcus aureus bacteria to establish infection was investigated in several animal models.

Methods: Wild-type and corresponding mutants with deletions of the srtA and/or srtB genes were used in murine acute lethal infection, septic arthritis, kidney infection and rat endocarditis models.

Results: The LD(50) of the wild-type and srtB- knockout were comparable and approximately two- to four-fold lower than the required inoculum of the srtA- and srtA-B- strains.

Why is big Pharma getting out of antibacterial drug discovery?

Since the advent of the antibiotic era in the late 1940s drug discovery and development has evolved into an expensive, time consuming, cumbersome and bureaucratic process involving multiple interest groups such as pharmaceutical manufacturers, governmental regulatory authorities, patent officers, academic and clinical researchers and trial lawyers. It would seem that the least involved among the interest groups are the consumers of health care themselves. Politicians and the public alike complain loudly about drug prices although fewer and fewer new therapies are being developed.

Recurrent episodes of shock-like syndrome caused by the same strain of vancomycin-resistant Enterococcus faecium in a pediatric patient.

We present the case of a hospitalized pediatric patient with short bowel syndrome who was dependent upon total parenteral nutrition for 17 months. Shortly after admission she became colonized with vancomycin-resistant Enterococcus faecium (VRE) and developed 12 distinct episodes of serious infection associated with it. The course of VRE colonization and infections in this patient was studied through analysis of 40 representative isolates obtained from different sites during distinct episodes of infection.

Inactivation of mprF affects vancomycin susceptibility in Staphylococcus aureus.

A chemically generated mutant of Staphylococcus aureus RN4220, GC6668, was isolated that had a fourfold increase in resistance to vancomycin. This phenotype reverted back to susceptibility by insertional mutagenesis with Tn917. In a selected set of revertants, Tn917 insertion was mapped to a unique chromosomal region upstream of mprF, a recently described gene that determines staphylococcal resistance to several host defense peptides.