Increase In Excision Research Articles

Changes in Burn Surgery Operative Volume and Metrics due to COVID-19.

Due to COVID-19, hospitals underwent drastic changes to operating room policy to mitigate the spread of the disease. Given these unprecedented measures, we aimed to look at the changes in operative volume and metrics of the burn surgery service at our institution. A retrospective review was conducted for operative cases and metrics for the months of March to May for 2019, 2020, and 2021, which correspond with pre-COVID, early COVID (period without elective cases), and late COVID (period with resumed elective cases). Inclusion criteria were cases related to burns. Case types and operative metrics were compared amongst the three time periods. Compared to the hospital, the burn service had a smaller decrease in volume during early COVID (28.7% vs. 50.1%) and exceeded pre-pandemic volumes during late COVID (+21.8% vs. -4.6%). There was a significant increase in excision and grafting cases in early and late COVID periods (p < .0001 and p < .002). There was a significant decrease in laser scar procedures that persisted even during late COVID (p < .0001). The projected and actual lengths of cases significantly increased and persisted into late COVID (p < .01). COVID-19 related operating room closures led to an expected decrease in the number of operative cases. However, there was no significant decline in the number of burn specific cases. The elective cases were largely replaced with excision and grafting cases and this shift has persisted even after elective cases have resumed. This change is also reflected in increased operative times.

Biology and engineering of integrative and conjugative elements: Construction and analyses of hybrid ICEs reveal element functions that affect species-specific efficiencies.

Integrative and conjugative elements (ICEs) are mobile genetic elements that reside in a bacterial host chromosome and are prominent drivers of bacterial evolution. They are also powerful tools for genetic analyses and engineering. Transfer of an ICE to a new host involves many steps, including excision from the chromosome, DNA processing and replication, transfer across the envelope of the donor and recipient, processing of the DNA, and eventual integration into the chromosome of the new host (now a stable transconjugant). Interactions between an ICE and its host throughout the life cycle likely influence the efficiencies of acquisition by new hosts. Here, we investigated how different functional modules of two ICEs, Tn916 and ICEBs1, affect the transfer efficiencies into different host bacteria. We constructed hybrid elements that utilize the high-efficiency regulatory and excision modules of ICEBs1 and the conjugation genes of Tn916. These elements produced more transconjugants than Tn916, likely due to an increase in the number of cells expressing element genes and a corresponding increase in excision. We also found that several Tn916 and ICEBs1 components can substitute for one another. Using B. subtilis donors and three Enterococcus species as recipients, we found that different hybrid elements were more readily acquired by some species than others, demonstrating species-specific interactions in steps of the ICE life cycle. This work demonstrates that hybrid elements utilizing the efficient regulatory functions of ICEBs1 can be built to enable efficient transfer into and engineering of a variety of other species.

85 Changes in Burn Surgery Operative Volume and Metrics Due to COVID-19

IntroductionDue to COVID-19, hospitals have had to undergo drastic changes to operating room (OR) policy to mitigate the spread of the disease. Elective surgeries were cancelled, and some ORs were repurposed to help withstand a surge of COVID-19 patients. Given these unprecedented measures, we aim to look at the changes in operative volume and metrics of the burn surgery service at our institution.MethodsAn IRB-approved single-institution retrospective review was conducted by querying our institutional OR database. We obtained case lists and OR metrics for the months of March to May for 2019, 2020, and 2021, which correspond with pre-COVID, early COVID (period without elective cases), and late COVID (period with resumed elective cases). Inclusion criteria were cases related to burns. These cases were then divided into the following groups: excision only, grafting only, excision and grafting, laser scar procedures, secondary reconstruction without grafting or flaps, secondary reconstruction with grafting, and secondary reconstruction with flaps. Types of cases and operative metrics were compared amongst the three time periods.ResultsThe total number of cases performed by the entire hospital during 2019, 2020, and 2021 was 2375, 1184, and 2265 respectively. During those times, the burn surgery service performed 174, 124, and 212 total cases (138, 103, and 114 burn related cases) respectively. Compared to the hospital, the burn service had a smaller decrease in volume during early COVID (28.7% vs. 50.1%) and exceeded pre-pandemic volumes during late COVID (+21.8% vs. -4.6%). There was a significant increase in excision and grafting cases in early and late COVID periods (41, 84, 74 respectively; p < .0001 and p < .002). There was a significant decrease in laser scar procedures that persisted even during late COVID (69, 0, 14 respectively; p < .0001). The projected and actual lengths of cases significantly increased and persisted into late COVID (p < .01). The average length pre-COVID and late COVID were 109.9 ± 78.5 and 138.2 ± 79.2 minutes.ConclusionsCOVID-19 related OR closures lead to an expected decrease in the number of overall cases and elective cases. However, there was no significant decline in the number of burn specific cases performed. The elective cases were largely replaced with excision and grafting cases and this shift has persisted even after elective cases have resumed. This change is also reflected in increased operative times.

Inactivation of PbTopo IIIβ causes hyper‐excision of the Pathogenicity Island HAI2 resulting in reduced virulence of Pectobacterium atrosepticum

Topoisomerase III enzymes are present only in a limited set of bacteria and their physiological role remains unclear. Here, we show that PbTopo IIIβ, a homologue of topoisomerase III encoded on the chromosome of Pectobacterium atrosepticum strain SCRI1043 (Pba SCRI1043), is involved in excision of HAI2, a discrete ~100 kb region, from the Pba SCRI1043 chromosome. HAI2 is a Pathogenicity Island (PAI) that encodes coronafacic acid (Cfa), a major virulence determinant required for infection of potato. PAIs are horizontally acquired genetic elements that in some instances are able to excise from the chromosome of their host cell to form a circular episome prior to transfer to a recipient bacterium. We demonstrate excision of HAI2 from the chromosome, a process that is independent of growth phase and that results in the production of a circular intermediate. Inactivation of PbTopo IIIβ causes a 10(3) - to 10(4) -fold increase in excision, leading to reduced fitness in vitro and a decrease in the virulence of Pba SCRI1043 on potato. These results suggest that PbTopo IIIβ is required for stable maintenance of HAI2 in the chromosome of Pba SCRI1043 and may control as yet unidentified genes involved in viability and virulence of Pba SCRI1043 on potato.

End Modification of a Linear DNA Duplex Enhances NER-Mediated Excision of an Internal Pt(II)-Lesion

The study of DNA repair has been facilitated by the development of extract-based in vitro assay systems and the use of synthetic DNA duplexes that contain site-specific lesions as repair substrates. Unfortunately, exposed DNA termini can be a liability when working in crude cell extracts because they are targets for DNA end-modifying enzymes and binding sites for proteins that recognize DNA termini. In particular, the double-strand break repair protein Ku is an abundant DNA end-binding protein that has been shown to interfere with nucleotide excision repair (NER) in vitro. To facilitate the investigation of NER in whole-cell extracts, we explored ways of modifying the exposed ends of synthetic repair substrates to prevent Ku binding and improve in vitro NER efficiency. Replacement of six contiguous phosphodiester linkages at the 3'-ends of the duplex repair substrate with nuclease-resistant nonionic methylphosphonate linkages resulted in a 280-fold decrease in binding affinity between Ku and the modified duplex. These results are consistent with the published crystal structure of a Ku/DNA complex [Walker et al. (2001) Nature 412, 607-614] and show that the 3'-terminal phosphodiester linkages of linear DNA duplexes are important determinants in DNA end-binding by Ku. Using HeLa whole-cell extracts and a 149-base pair DNA duplex repair substrate, we tested the effects of modification of exposed DNA termini on NER-mediated in vitro excision of a 1,3-GTG-Pt(II) intrastrand cross-link. Methylphosphonate modification at the 3'-ends of the repair substrate resulted in a 1.6-fold increase in excision. Derivatization of the 5'-ends of the duplex with biotin and subsequent conjugation with streptavidin to block Ku binding resulted in a 2.3-fold increase excision. By combining these modifications, we were able to effectively reduce Ku-derived interference of NER excision in vitro and observed a 4.4-fold increase in platinum lesion excision. These modifications are easy to incorporate into synthetic oligonucleotides and may find general utility whenever synthetic linear duplex DNAs are used as substrates to investigate DNA repair in whole-cell extracts.

Mismatch dependent uracil/thymine-DNA glycosylases excise exocyclic hydroxyethano and hydroxypropano cytosine adducts.

Exocyclic adducts of DNA bases, such as etheno- and hydroxyalkano- ones, are generated by a variety of bifunctional agents, including endogenously formed products of lipid peroxidation. In this work we selectively modified cytosines in the 5'-d(TTT TTT CTT TTT CTT TTT CTT TTT T)-3' oligonucleotide using: chloroacetaldehyde to obtain 3,N(4)-alpha-hydroxyethano- (HEC) and 3,N(4)-etheno- (epsilonC), acrolein to obtain 3,N(4)-alpha-hydroxypropano- (HPC) and crotonaldehyde to obtain 3,N(4)-alpha-hydroxy-gamma-methylpropano- (mHPC) adducts of cytosine. The studied adducts are alkali-labile which results in oligonucleotide strain breaks at the sites of modification upon strong base treatment. The oligonucleotides carrying adducted cytosines were studied as substrates of Escherichia coli Mug, human TDG and fission yeast Thp1p glycosylases. All the adducts studied are excised by bacterial Mug although with various efficiency: epsilonC >HEC >HPC >mHPC. The yeast enzyme excises efficiently epsilonC>HEC>HPC, whereas the human enzyme excises only epsilonC. The pH-dependence curves of excision of eC, HEC and HPC by Mug are bell shaped and the most efficient excision of adducts occurs within the pH range of 8.6-9.6. The observed increase of excision of HEC and HPC above pH 7.2 can be explained by deprotonation of these adducts, which are high pK(a) compounds and exist in a protonated form at neutrality. On the other hand, since epsilonC is in a neutral form in the pH range studied, we postulate an involvement of an additional catalytic factor. We hypothesize that the enzyme structure undergoes a pH-induced rearrangement allowing the participation of Lys68 of Mug in catalysis via a hydrogen bond interaction of its epsilon-amino group with N(4) of the cytosine exocyclic adducts.