Oxidation of Isodrimeninol with PCC Yields Drimane Derivatives with Activity against Candida Yeast by Inhibition of Lanosterol 14-Alpha Demethylase.

Candida species cause an opportunistic yeast infection called Candidiasis, which is responsible for more than 50,000 deaths every year around the world. Effective treatments against candidiasis caused by non-albicans Candida species such as C. glabrata, C. parapsilosis, C. aureus, and C.krusei are limited due to severe resistance to conventional antifungal drugs. Natural drimane sesquiterpenoids have shown promising antifungal properties against Candida yeast and have emerged as valuable candidates for developing new candidiasis therapies. In this work, we isolated isodrimeninol (C1) from barks of Drimys winteri and used it as starting material for the hemi-synthesis of four sesquiterpenoids by oxidation with pyridinium chlorochromate (PCC). The structure of the products (C2, C3, C4, and C5) was elucidated by 1D and 2D NMR spectroscopy resulting in C4 being a novel compound. Antifungal activity assays against C. albicans, C. glabrata, and C. krusei revealed that C4 exhibited an increased activity (IC50 of 75 µg/mL) compared to C1 (IC50 of 125 µg/mL) in all yeast strains. The antifungal activity of C1 and C4 was rationalized in terms of their capability to inhibit lanosterol 14-alpha demethylase using molecular docking, molecular dynamics simulations, and MM/GBSA binding free energy calculations. In silico analysis revealed that C1 and C4 bind to the outermost region of the catalytic site of 14-alpha demethylase and block the entrance of lanosterol (LAN) to the catalytic pocket. Binding free energy estimates suggested that C4 forms a more stable complex with the enzyme than C1, in agreement with the experimental evidence. Based on this new approach it is possible to design new drimane-type sesquiterpenoids for the control of Candida species as inhibitors of 14-alpha demethylase.

Draft Genome Sequence of a Multidrug-Resistant Acinetobacter baumannii Strain from Chile.

Acinetobacter baumannii strain Ab5 was isolated in the year 2007 in Chile, being one of the first multidrug-resistant (MDR) cases reported in the country. Here, we present the very first draft genome sequence of an MDR Chilean strain, which shows the presence of diverse resistance and acquired virulence genes.

Dissemination of multiple carbapenem-resistant clones of Acinetobacter baumannii in the Eastern District of Saudi Arabia.

It has previously been shown that carbapenem-resistant Acinetobacter baumannii are frequently detected in Saudi Arabia. The present study aimed to identify the epidemiology and distribution of antibiotic resistance determinants in these bacteria. A total of 83 A. baumannii isolates were typed by pulsed-field gel electrophoresis (PFGE), and screened by PCR for carbapenemase genes and insertion sequences. Antibiotic sensitivity to imipenem, meropenem, tigecycline, and colistin were determined. Eight different PFGE groups were identified, and were spread across multiple hospitals. Many of the PFGE groups contained isolates belonging to World-wide clone 2. Carbapenem resistance or intermediate resistance was detected in 69% of isolates. The bla VIM gene was detected in 94% of isolates, while bla OXA-23-like genes were detected in 58%. The data demonstrate the co-existence and wide distribution of a number of clones of carbapenem-resistant A. baumannii carrying multiple carbapenem-resistance determinants within hospitals in the Eastern Region of Saudi Arabia.

Variations in IS6 promoters alter the expression of carbapenem resistance in related strains of Acinetobacter baumannii.

The aim of this work was to investigate the role of the IS6 family of insertion sequences present upstream of blaOXA-58 in two clonally related carbapenem-resistant Acinetobacter baumannii isolates obtained from paediatric cancer patients in Egypt. To determine their relatedness, the isolates were typed by pulsed-field gel electrophoresis (PFGE), and the intrinsic blaOXA-51-like gene was amplified and sequenced. Minimum inhibitory concentrations (MICs) to imipenem and meropenem was determined according to British Society of Antimicrobial Chemotherapy (BSAC) guidelines. PCR and sequencing of blaOXA-58 and the upstream and downstream regions was performed to determine the genetic environment. The two isolates were positive for the intrinsic blaOXA-64 gene, and the MICs for isolates AB-14298 and AB-P67 were 8mg/L and 64mg/L for imipenem and 2mg/L and 16mg/L for meropenem, respectively. The blaOXA-58 gene in AB-14298 was flanked by ISAba3 interrupted with IS1006, whereas AB-P67 had ISAba3 interrupted by IS1008, both belonging to the IS6 family of insertion sequences. In conclusion, both IS1006 and IS1008 provided suitable promoter sequences for expression of the downstream blaOXA-58 gene.

OXA-type carbapenemases in Acinetobacter baumannii in South America.

Acinetobacter baumannii is an opportunistic pathogen that is frequently involved in outbreaks of infection, occurring mostly in intensive care units. The increasing incidence of carbapenem resistance in A. baumannii worldwide is a concern since it limits drastically the range of therapeutic alternatives. The most important mechanism of carbapenem resistance is the enzymatic hydrolysis mediated by carbapenemases. In A. baumannii these enzymes are usually OXA-type carbapenemases, and belong to class D according to the classification of Ambler. The OXA-type carbapenemases are divided into five subgroups, four of which correspond to acquired carbapenemases, which accounts for the distribution of genes blaOXA in different geographic areas. In this work we review the different types of OXA-type carbapenemases present in A. baumannii, emphasizing the current situation in South America with special mention to the findings in Chile.

Plasmid-encoded PER-7 ß-lactamase responsible for ceftazidime resistance in Acinetobacter baumannii isolated in the United Arab Emirates.

OBJECTIVES: To investigate the mechanism of ceftazidime resistance in two isogenic Acinetobacter baumannii strains from the United Arab Emirates. METHODS: Two A. baumannii strains, NM55 and NM128, were isolated 4 months apart from a 6-year-old patient in the United Arab Emirates. Genotypic characterization was performed by PFGE and the MIC of ceftazidime was determined by the agar dilution method. Detection of bla(OXA) and metallo-ß-lactamase genes was performed by multiplex PCR. Analysis of bla(PER-7), ISAba1, bla(ADC) and the ISCR1 element was carried out by standard PCR. Plasmid analysis was achieved by Southern blotting. RESULTS: Strain NM55 was resistant to ceftazidime, whereas strain NM128 was susceptible. Both isolates carried the bla(OXA-23) and bla(OXA-64) genes and were identical according to their PFGE patterns. ISAba1 was present upstream of the bla(OXA-23) gene, but absent upstream of bla(ADC-26), in both strains. Strain NM55 possessed a bla(PER-7) gene with the presence of gst, a fragment of the abc transporter and a transposase gene downstream of it. The entire structure was part of an ISCR1 element and was located on an ≈ 200 kb plasmid in strain NM55, while the ceftazidime-susceptible NM128 strain carried an ≈ 180 kb plasmid without the bla(PER-7) gene. CONCLUSIONS: Ceftazidime resistance was mediated by a PER-7 ß-lactamase encoded in an ISCR1 element located on a plasmid. This represents the first detection of a PER-7 ß-lactamase encoded by a plasmid in A. baumannii.

[Multi-drug efflux pumps and antibiotic resistance in Acinetobacter baumannii]. / Bombas de expulsión multidrogas en Acinetobacter baumannii y resistencia a antimicrobianos.

Bacterial multi-drugs systems contribute to the development of multi-resistance patterns of Acinetobacter baumannii, a nosocomial pathogen of increasing importance due to its emerging resistance to carbapenems. The multi-resistance phenomena is generated by a combination of mechanisms, one of which the efflux pump system. Many of these multiresistant isolates of A. baumannii harbor genes for the AdeABC multi-drug efflux system, related with resistance to various groups of antibacterial agents, including tygecicline and meropenem. Inhibition of these systems would allow to increase the efficacy of this antimicrobial. This review focuses on the multi-drug efflux pump system of A. baumannii with special emphasis in the AdeABC system.