Interspecies recombination, not de novo mutation, maintains virulence after β-lactam resistance acquisition in Streptococcus pneumoniae.

As opposed to de novo mutation, β-lactam resistance in S. pneumoniae is often conferred via homologous recombination during horizontal gene transfer. We hypothesize that β-lactam resistance in pathogenic streptococci is restricted to naturally competent species via intra-/interspecies recombination due to in vivo fitness trade-offs of de novo penicillin-binding protein (PBP) mutations.

A genome-wide atlas of antibiotic susceptibility targets and pathways to tolerance.

Detailed knowledge on how bacteria evade antibiotics and eventually develop resistance could open avenues for novel therapeutics and diagnostics. It is thereby key to develop a comprehensive genome-wide understanding of how bacteria process antibiotic stress, and how modulation of the involved processes affects their ability to overcome said stress. Here we undertake a comprehensive genetic analysis of how the human pathogen Streptococcus pneumoniae responds to 20 antibiotics.

Pneumolysin: Pathogenesis and Therapeutic Target.

is an opportunistic pathogen responsible for widespread illness and is a major global health issue for children, the elderly, and the immunocompromised population. Pneumolysin (PLY) is a cholesterol-dependent cytolysin (CDC) and key pneumococcal virulence factor involved in all phases of pneumococcal disease, including transmission, colonization, and infection. In this review we cover the biology and cytolytic function of PLY, its contribution to pathogenesis, and its known interactions and effects on the host with regard to tissue damage and immune response.

Molecular and genetic basis of azole antifungal resistance in the opportunistic pathogenic fungus Candida albicans.

Candida albicans is an opportunistic yeast and the major human fungal pathogen in the USA, as well as in many other regions of the world. Infections with C. albicans can range from superficial mucosal and dermatological infections to life-threatening infections of the bloodstream and vital organs.

Impact of the Major Candida glabrata Triazole Resistance Determinants on the Activity of the Novel Investigational Tetrazoles VT-1598 and VT-1161.

VT-1161 and VT-1598 are promising investigational tetrazole antifungals that have shown and activity against and other fungi. is a problematic opportunistic pathogen that is associated with high mortality in invasive infection, as well as both intrinsic and rapidly acquired antifungal resistance. The MICs of VT-1161 and VT-1598 were determined by CLSI methodology to evaluate their activities against clinical isolates and strains containing individual deletions of the zinc cluster transcription factor genes and as well as the efflux transporter genes , , and Overall, both tetrazoles demonstrated relative activities comparable to those of the tested triazole antifungals against clinical isolates (MIC range, 0.

Activities of the Novel Investigational Tetrazoles VT-1161 and VT-1598 Compared to the Triazole Antifungals against Azole-Resistant Strains and Clinical Isolates of .

The fungal Cyp51-specific inhibitors VT-1161 and VT-1598 have emerged as promising new therapies to combat fungal infections, including spp. To evaluate their activities compared to other azoles, MICs were determined by Clinical and Laboratory Standards Institute (CLSI) method for VT-1161, VT-1598, fluconazole, voriconazole, itraconazole, and posaconazole against 68  clinical isolates well characterized for azole resistance mechanisms and mutant strains representing individual azole resistance mechanisms. VT-1161 and VT-1598 demonstrated potent activity (geometric mean MICs ≤0.

A Systematic Screen Reveals a Diverse Collection of Medications That Induce Antifungal Resistance in Species.

The increasing incidence of and high mortality rates associated with invasive fungal infections (IFIs) impose an enormous clinical, social, and economic burden on humankind. In addition to microbiological resistance to existing antifungal drugs, the large number of unexplained treatment failures is a serious concern. Due to the extremely limited therapeutic options available, it is critical to identify and understand the various causes of treatment failure if patient outcomes are to improve.

Contribution of Clinically Derived Mutations in the Gene Encoding the Zinc Cluster Transcription Factor Mrr2 to Fluconazole Antifungal Resistance and Expression in .

Mutations in genes encoding zinc cluster transcription factors (ZCFs) such as , , and play a key role in azole antifungal resistance. Artificial activation of the ZCF Mrr2 has shown increased expression of the gene encoding the Cdr1 efflux pump and resistance to fluconazole. Amino acid substitutions in Mrr2 have recently been reported to contribute to fluconazole resistance in clinical isolates.

The Evolution of Azole Resistance in Sterol 14α-Demethylase (CYP51) through Incremental Amino Acid Substitutions.

Recombinant CYP51 (CaCYP51) proteins containing 23 single and 5 double amino acid substitutions found in clinical strains and the wild-type enzyme were expressed in and purified by Ni-nitrilotriacetic acid agarose chromatography. Catalytic tolerance to azole antifungals was assessed by determination of the concentration causing 50% enzyme inhibition (IC) using CYP51 reconstitution assays. The greatest increase in the IC compared to that of the wild-type enzyme was observed with the five double substitutions Y132F+K143R (15.

Abrogation of Triazole Resistance upon Deletion of in a Clinical Isolate of .

has rapidly emerged as a health care-associated and multidrug-resistant pathogen of global concern. In this work, we examined the relative expression of the four genes with the highest degree of homology to and among three triazole-resistant clinical isolates as compared to the triazole-susceptible genome reference clinical isolate. We subsequently utilized a novel Cas9-mediated system for genetic manipulations to delete and in both a triazole-resistant clinical isolate and a susceptible reference strain and observed that MICs for all clinically available triazoles decreased as much as 128-fold in the deletion strains.

Loss of Upc2p-Inducible Transcription Is Sufficient To Confer Niche-Specific Azole Resistance without Compromising Candida albicans Pathogenicity.

Inactivation of sterol Δ-desaturase (Erg3p) in the prevalent fungal pathogen is one of several mechanisms that can confer resistance to the azole antifungal drugs. However, loss of Erg3p activity is also associated with deficiencies in stress tolerance, invasive hyphal growth, and attenuated virulence in a mouse model of disseminated infection. This may explain why relatively few -deficient strains have been reported among azole-resistant clinical isolates.

Loss of C-5 Sterol Desaturase Activity Results in Increased Resistance to Azole and Echinocandin Antifungals in a Clinical Isolate of Candida parapsilosis.

Among emerging non- species, is of particular concern as a cause of nosocomial bloodstream infections in neonatal and intensive care unit patients. While fluconazole and echinocandins are considered effective treatments for such infections, recent reports of fluconazole and echinocandin resistance in indicate a growing problem. The present study describes a novel mechanism of antifungal resistance in this organism affecting susceptibility to azole and echinocandin antifungals in a clinical isolate obtained from a patient with prosthetic valve endocarditis.

Azole Antifungal Resistance in and Emerging Non- Species.

Within the limited antifungal armamentarium, the azole antifungals are the most frequent class used to treat infections. Azole antifungals such as fluconazole are often preferred treatment for many infections as they are inexpensive, exhibit limited toxicity, and are available for oral administration. There is, however, extensive documentation of intrinsic and developed resistance to azole antifungals among several species.

Isavuconazole: Pharmacology, Pharmacodynamics, and Current Clinical Experience with a New Triazole Antifungal Agent.

Coinciding with the continually increasing population of immunocompromised patients worldwide, the incidence of invasive fungal infections has grown over the past 4 decades. Unfortunately, infections caused by both yeasts such as Candida and molds such as Aspergillus or Mucorales remain associated with unacceptably high morbidity and mortality. In addition, the available antifungals with proven efficacy in the treatment of these infections remain severely limited.