Biology subjects

O'Connor, P. M.

Publications and source records attributed to O'Connor, P. M..

5 recordsLinked to original sources

bioRxiv2022

Mass red blood cell extravasation and tubular uptake results in toxic injury to the tubules during kidney ischemia from venous clamping

Vascular congestion is common in ischemic acute kidney injury (AKI) and represents densely packed red blood cells (RBC) in the kidney circulation. In this study we tested the hypothesis that vascular congestion directly promotes tubular injury. Studies were performed in male and female Wistar-Kyoto rats. Vascular congestion and tubular injury were examined between renal venous clamping, arterial clamping and venous clamping of blood perfused and blood free kidneys. Vessels were occluded for either 15 or 45 minutes without reperfusion. We found that venous clamping resulted in greater vascular congestion than arterial clamping, particularly in the outer-medullary region (P<0.001). Venous clamping resulted in significant tubular injury, including cell swelling, tubular degeneration and luminal cast formation following as little as 15 minutes of occlusion. Tubular injury was significantly less following arterial clamping (P<0.001). Numerous red droplets were observed within tubular cells which were most prominent following venous clamping. Electron microscopy and immunohistochemistry identified these as derived from RBCs and indicated that RBCs from congested renal capillaries were extravasated and phagocytosed by tubular cells. CD235a staining confirmed tubular uptake and secretion of RBCs. Cast formation and tubular swelling were absent from blood free kidneys following venous clamping (P<0.001). Our data demonstrate that congestion of the kidney results in the rapid, mass extravasation and uptake of RBCs by tubular cells causing toxic injury to the tubules. Tubular toxicity from extravasation of RBCs appears to be a major component of tubular injury in ischemic AKI which has not previously been recognized.

physiology↗

bioRxiv2022

Nisin G is a novel nisin variant produced by a gut-derived Streptococcus salivarius

Fusobacterium nucleatum is an emerging human pathogen associated with a number of intestinal conditions including colorectal cancer (CRC) development. Screening for gut-derived strains that exhibit anti-F. nucleatum activity revealed Streptococcus salivarius DPC6487 as a strain of interest. Whole genome sequencing analysis of DPC6487 resulted in the identification of a gene predicted to encode a novel nisin variant designated nisin G. The structural nisin G peptide differs from the prototypical nisin A with respect to seven amino acids (Ile4Tyr, Ala15Val, Gly18Ala, Asn20His, Met21Leu, His27Asn and His31Ile), including differences that have not previously been associated with a natural nisin variant. The nisin G gene cluster consists of nsgGEFABTCPRK with transposases encoded between the nisin G structural gene (nsgA) and nsgF. The cluster lacked an equivalent to the nisI immunity determinant. S. salivarius DPC6487 exhibited a narrower spectrum of activity compared to the nisin A producer, Lactococcus lactis NZ9700, when assessed through deferred antagonism-based assays. Such narrow spectrum activity is desirable as it is less likely to lead to collateral damage to gut commensals. Ultimately, this is the first report of a nisin variant produced by a representative of a species that is frequently a focus for probiotic development. The production of this bacteriocin by a gut-derived S. salivarius and its narrow spectrum activity against F. nucleatum indicates that this strain merits further attention to determine its potential for probiotic-related applications.

microbiology↗

bioRxiv2020

Validation of a Lysis Buffer Containing 4 M Guanidinium Thiocyanate (GITC)/ Triton X-100 for Extraction of SARS-CoV-2 RNA for COVID-19 Testing: Comparison of Formulated Lysis Buffers Containing 4 to 6 M GITC, Roche External Lysis Buffer and Qiagen RTL Lysis Buffer

The COVID-19 pandemic has resulted in increased need for diagnostic testing using reverse transcriptase real-time PCR (RT-PCR). An exponential increase in demand has resulted in a shortage of numerous reagents in particular those associated with the lysis buffer required to extract the viral RNA. Herein, we describe a rapid collective effort by hospital laboratory scientists, academic researchers and the biopharma industry to generate a validated lysis buffer. We have formulated a 4M Guanidinium thiocyanate (GITC)/ Triton X-100 Lysis buffer which provides comparable results with the recommended reagents. This buffer will ease the burden on hospital labs in their heroic efforts to diagnose a large population of patients.

molecular biology↗

bioRxiv2019

Production of multiple bacteriocins, including the novel bacteriocin gassericin M, by Lactobacillus gasseri LM19, a strain isolated from human milk

Bacteriocins are antimicrobial peptides produced by bacteria and their production by health-promoting microbes is regarded as a desirable probiotic trait. We found that Lactobacillus gasseri LM19, a strain isolated from human milk, exhibits antagonistic activity against different enteropathogens and produces several bacteriocins, including a novel bacteriocin, gassericin M. These bacteriocins were purified from culture and synthesised to investigate their activity and potential synergy. L. gasseri LM19 was tested in a complex environment mimicking human colon conditions where it not only survived but expressed the seven bacteriocin genes and produced short chain fatty acids. Metagenomic analysis of these in vitro colon cultures showed that co-inoculation of L. gasseri LM19 with Clostridium perfringens gave profiles with more similarity to controls than to vessels inoculated with C. perfringens alone. This makes L. gasseri LM19 an interesting candidate for further study for maintaining homeostasis in the gut environment.

microbiology↗

bioRxiv2019

First evidence of production of the lantibiotic nisin P

Nisin P is a natural nisin variant, the genetic determinants for which were previously identified in the genomes of two Streptococcus species, albeit with no confirmed evidence of production. Here we describe Streptococcus agalactiae DPC7040, a human fecal isolate, which exhibits antimicrobial activity against a panel of gut and food isolates by virtue of producing nisin P. Nisin P was purified, and its predicted structure was confirmed by nanoLC-MS/MS, with both the fully modified peptide and a variant without rings B and E being identified. Additionally, we compared its spectrum of inhibition and minimum inhibitory concentration (MIC) with that of nisin A and its antimicrobial effect in a fecal fermentation in comparison with nisin A and H. We found that its antimicrobial activity was less potent than nisin A and H, and we propose a link between this reduced activity and the peptide structure.

microbiology↗