ABSTRACT
The treatment of multidrug-resistant Gram-negative infections is based on colistin. As result, COL-resistance (COL-R) can develop and spread. In Acinetobacter baumannii, a crucial step is to understand COL-R onset and stability, still far to be elucidated. COL-R phenotypic stability, onset modalities, and phylogenomics were investigated in a clinical A. baumannii sample showing a COL resistant (COLR) phenotype at first isolation. COL-R was confirmed by Minimum-Inhibitory-Concentrations as well as investigated by Resistance-Induction assays and Population-Analysis-Profiles (PAPs) to determine: (i) stability; (ii) inducibility; (iii) heteroresistance. Genomics was performed by Mi-Seq Whole-Genome-Sequencing, Phylogenesis, and Genomic Epidemiology by bioinformatics. COLRA. baumannii were subdivided as follows: (i) 3 A. baumannii with stable and high COL MICs defining the "homogeneous-resistant" onset phenotype; (ii) 6 A. baumannii with variable and lower COL MICs displaying a "COL-inducible" onset phenotype responsible for adaptive-resistance or a "subpopulation" onset phenotype responsible for COL-heteroresistance. COL-R stability and onset strategies were not uniquely linked to the amount of LPS and cell envelope charge. Phylogenomics categorized 3 lineages clustering stable and/or unstable COL-R phenotypes with increasing genomic complexity. Likewise, different nsSNP profiling in genes already associated with COL-R marked the stable and/or unstable COL-R phenotypes. Our investigation finds out that A. baumannii can range through unstable or stable COLR phenotypes emerging via different "onset strategies" within phylogenetic lineages displaying increasing genomic mosaicism.
ABSTRACT
Multidrug-Resistant (MDR) and Extensively Drug Resistant (XDR) Acinetobacter baumannii (Ab) represent a serious cause of healthcare-associated infections worldwide. Currently, the available treatment options are very restricted and colistin-based therapies are last-line treatments of these infections, even though colistin resistant (COLR) Ab have rarely been isolated yet. In bacteria, small non-coding RNAs (sRNAs) have been implicated in regulatory pathways of different biological functions, however, no knowledge exists about the sRNA role on the biological adaptation in COLR Ab. Our study investigated two Italian XDR isogenic colistin-susceptible/resistant (COLS/R) Ab strain-pairs to discover new sRNA signatures. Comparative sRNA transcriptome (sRNAome) analyses were carried out by Illumina RNA-seq using both a Tru-Seq and a Short Insert library, whilst Ab ATCC 17978 and ACICU Reference Genome assembly, mapping, annotation and statistically significant differential expression (q-value ≤ 0.01) of the raw reads were performed by the Rockhopper tool. A computational filtering, sorting only similarly statistically significant differentially expressed (DE) sRNAs mapping on the same gene in both COLR Ab isolates was conducted. COLR vs. COLS sRNAome, analyzed integrating the DE sRNAs obtained from the two different libraries, revealed some statistically significant DE sRNAs in COLR Ab. In detail, we found: (i) two different under-expressed cis-acting sRNAs (AbsRNA1 and AbsRNA2) mapping in antisense orientation the 16S rRNA gene A1S_r01, (ii) one under-expressed cis-acting sRNA (AbsRNA3) targeting the A1S_2505 gene (hypothetical protein), (iii) one under-expressed microRNA-size small RNA fragment (AbsRNA4) and its pre-microAbsRNA4 targeting the A1S_0501 gene (hypothetical protein), (iv) as well as an over-expressed microRNA-size small RNA fragment (AbsRNA5) and its pre-microAbsRNA5 targeting the A1S_3097 gene (signal peptide). Custom TaqMan® probe-based real-time qPCRs validated the expression pattern of the selected sRNA candidates shown by RNA-seq. Furthermore, analysis on sRNA ΔA1S_r01, ΔA1S_2505 as well as the over-expressed A1S_3097 mutants revealed no effects on colistin resistance. Our study, for the first time, found the sRNAome signatures of clinical COLR Ab with a computational prediction of their targets related to protein synthesis, host-microbe interaction and other different biological functions, including biofilm production, cell-cycle control, virulence, and antibiotic-resistance.
ABSTRACT
The way viruses interact with cultured cells and their surrounding environment is still a matter of debate. From a technical point of view, 2D cell cultures only partially exhibit the morpho-molecular pattern required for viral tropism, not reflecting the complexity of the microenvironment in vivo. Therefore, 3D cell cultures are envisioned as an alternative approach to study viral replication possibly closer to in vivo conditions than 2D, representing the link between traditional cell culture and in vivo models. The use of cellular spheroids is proving to be useful to optimize and overcome constraints related to conventional in vitro systems for viral isolation. In order to create an advanced 3D in vitro isolation system, we compared the classic 2D shell vial system with the spheroid culture method based on the adhesion inhibition technique with pHema. In this study, we evaluated which of the most common viral cell lines used in our laboratory (A-549, 293 T, CaCo2, KB, HUH-7, VERO, and MRC-5) (Fig. 1) could be grown as 3D cultures and all proved to be able to grow as spheroids. Subsequently, we compared the sensitivity and efficiency of isolation of three viral species of medical interest (Adenovirus, CMV, HSV-1) in 2D and 3D cell cultures obtained from the respective susceptible cells. Our results indicate earlier and more sensitive virus isolation than in traditional 2D shell vial system for all three viruses tested, thus confirming how the establishment of 3D culture systems in the virological field is crucial to the improvement and evolution of more accurate and faster virus isolation protocols.
