Biology subjects

Salipante, S.

Publications and source records attributed to Salipante, S..

5 recordsLinked to original sources

bioRxiv2022

Identifying indels from WGS short reads of haploid genomes distinguishes variant-calling algorithms

Identification of clinically relevant strains of bacteria increasingly relies on whole genome sequencing. The downstream bioinformatics steps necessary for calling variants from short read sequences are well-established but seldom validated against haploid genomes. We devised an in silico workflow to introduce single nucleotide polymorphisms (SNP) and indels into bacterial reference genomes, and computationally generate sequencing reads based on the mutated genomes. We then applied the method to Mycobacterium tuberculosis H37Rv and used the synthetic reads as truth sets for evaluating several popular variant callers. Insertions proved especially challenging for most variant callers to correctly identify, relative to deletions and single nucleotide polymorphisms. With adequate read depth, however, variant callers that use high quality soft-clipped reads and base mismatches to perform local realignment consistently had the highest precision and recall in identifying medium-length insertions and deletions.

bioinformatics↗

bioRxiv2021

A Population-level Strain Genotyping Method to Study Pathogen Strain Dynamics in Human Infections

A hallmark of chronic bacterial infections is the long-term persistence of one or more pathogen species at the compromised site. Repeated detection of the same bacterial species can suggest that a single strain or lineage is continually present. However, infection with multiple strains of a given species, strain acquisition and loss, and changes in strain relative abundance can occur. Detecting strain-level changes and their effects on disease is challenging as most methods require labor intensive isolate-by-isolate analyses, thus, only a few cells from large infecting populations can be examined. Here we present a population-level method for enumerating and measuring the relative abundance of strains called "PopMLST". The method exploits PCR amplification of strain-identifying polymorphic loci, next-generation sequencing to measure allelic variants, and informatic methods to determine whether variants arise from sequencing errors or low abundance strains. These features enable PopMLST to simultaneously interrogate hundreds of bacterial cells that are either cultured en masse from patient samples, or are present in DNA directly extracted from clinical specimens without ex vivo culture. This method could be used to detect epidemic or super-infecting strains, facilitate understanding of strain dynamics during chronic infections, and enable studies that link strain changes to clinical outcomes.

microbiology↗

bioRxiv2019

Identification of a novel tedizolid resistance mutation in rpoB of methicillin-resistant Staphylococcus aureus

A tedizolid-resistant isolate of MRSA was selected by serial passage. Whole genome sequencing revealed only a single nucleotide variant in rpoB. Cross-resistance to linezolid, chloramphenicol, and quinupristin-dalfopristin was observed but susceptibility to other drugs including rifampin was unchanged. Models of the RNA-polymerase-ribosomal complex revealed that the mutated residue was unlikely to interact directly with the oxazolidinone binding site. This is the first time that rpoB mutation has been associated with resistance to the PhLOPSa antimicrobials.

microbiology↗

bioRxiv2019

Sensitive detection of highly fragmented cytomegalovirus nucleic acid in human cfDNA

Congenital human cytomegalovirus (CMV) infections are the leading cause of newborn hearing and central nervous system impairments worldwide. Currently, routine prenatal screening for congenital CMV is not performed in the United States and confirmation in suspected perinatal cases requires invasive sampling by amniocentesis. We hypothesized that detection of CMV from maternal cell-free DNA (cfDNA) plasma could provide a non-invasive indicator of congenital CMV infection. We analyzed sequence data from 2,208 individuals undergoing routine non-invasive prenatal aneuploidy screening at the University of Washington. CMV reads were identified in 117 (5.3%) samples. Positive samples were stratified based on CMV reads per million sample reads (RPM), resulting in ten samples being classified as strong positive (RPM > 0.3) and 107 as intermediate positive (0.01<RPM<0.3). Subsequent qPCR testing identified CMV in 9/10 strong positive samples and 2/32 intermediate positive samples. Median cfDNA insert size derived from CMV was significantly shorter than cfDNA derived from human chromosomes (103 vs 172 bp, p<0.0001), corresponding to the 3rd percentile of human cfDNA insert size. In addition, CMV cfDNA fragment lengths were distributed over a wider range than human cfDNA reads. These studies reveal the highly fragmented nature of CMV cfDNA and offer precise measurements of its length: these features likely explain discrepancies in serum CMV viral loads measurements determined by different qPCR assays, despite widespread efforts to standardize results. More work is required to determine how detection of CMV from maternal cfDNA can be best used as tool for congenital CMV screening or diagnosis.

microbiology↗

bioRxiv2019

Occurrence of cross-resistance and beta-lactam seesaw effect in glycopeptide, lipopeptide, and lipoglycopeptide-resistant MRSA correlates with membrane phosphatidylglycerol levels

Treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections is challenging and is associated with high rates of therapeutic failure. The glycopeptide (GP) vancomycin and the lipopeptide (LP) daptomycin are still relied upon to manage invasive MRSA infections; however, resistance to these antibiotics has emerged and there is evidence of cross-resistance between them. It has been observed that the susceptibility of MRSA to beta-lactams increases as susceptibility to GPs and LPs decreases, a phenomenon termed the seesaw effect. Recent efforts to understand the mechanism underlying the seesaw effect have focused on the penicillin binding proteins (PBPs). However, while daptomycin resistance is largely mediated by remodeling of membrane lipid composition, the role of membrane lipids in producing cross-resistance and the seesaw effect has not yet been investigated. Here, we evaluate the lipid profiles, cross susceptibilities, and beta-lactam susceptibilities of a collection of isogenic MRSA strains selected against daptomycin, vancomycin or dalbavancin (a lipoglycopeptide; LGP) to assess the relationship between membrane composition, cross-resistance, and the seesaw effect. We found that modification of membrane composition occurs not only in daptomycin-selected strains, but also vancomycin- and dalbavancin-selected strains. Significantly, we observed that typically the levels of short-chain phosphatidylglycerols (PGs) negatively correlate with MICs of GP/LP/LGP and positively correlate with MIC of certain beta-lactams, the latter being dependent on the primary PBP target of the particular beta-lactam. Furthermore, changes to certain PGs with long-chain fatty acids correlate well with presence of the seesaw effect. These studies demonstrate a major association between membrane remodeling and the seesaw effect.

microbiology↗