Biology subjects

Chowdhury, N.

Publications and source records attributed to Chowdhury, N..

3 recordsLinked to original sources

bioRxiv2018

Novel cholera toxin variant and ToxT regulon in environmental Vibrio mimicus strains: potential resources for the evolution of Vibrio cholerae hybrid strains

Atypical El Tor strains of Vibrio cholerae O1 harboring variant ctxB genes of cholera toxin (CT) are gradually becoming a major cause of recent cholera epidemics. Vibrio mimicus occasionally contains virulence factors associated with cholera, e.g., CT, encoded by ctxAB on CTX[FE] genome; and TCP, the CTX[FE]-specific receptor. This study carried out extensive molecular characterization of CTX[FE] and ToxT regulon in ctx+ve strains of V. mimicus isolated from the Bengal coast. Southern hybridization, PCR, and DNA sequencing of virulence related-genes revealed the presence of an El Tor type CTX prophage (CTXET) carrying a novel ctxAB, tandem copies of environmental type pre-CTX prophage (pre-CTXEnv), and RS1 elements, which were organized in an array of RS1-CTXET-RS1-pre-CTXEnv-pre-CTXEnv. Additionally, a novel variant of tcpA and toxT respectively, showing clonal lineage to a phylogenetic clade of V. cholerae non-O1/O139, was identified. The V. mimicus strains lacked the RTX and TLC elements, and Vibrio seventh pandemic islands of the El Tor strains, but contained five heptamer (TTTTGAT) repeats in ctxAB promoter region like some classical strains of V. cholerae O1. PFGE analysis showed all the ctx+ve V. mimicus strains were clonally related. However, their in vitro CT production and in vivo toxigenecity were variable, which could be explained by differential transcription of virulence genes along with ToxR regulon. Taken together, our findings strongly suggest that environmental V. mimicus strains act as potential reservoir of atypical virulence factors, including variant CT and ToxT regulon, and may contribute to the evolution of V. cholerae hybrid strains.\n\nIMPORTANCENatural diversification of CTX[FE] and ctxAB genes certainly influences disease severity and shifting patterns in major etiological agents of cholera, e.g., the overwhelming emergence of hybrid El Tor variants, replacing the prototype El Tor strains of V. cholerae. This study showing the occurrence of CTXET comprising a novel variant of ctxAB in V. mimicus points out a previously unnoticed evolutionary event, independent to that of the El Tor strains of V. cholerae. Identification and cluster analysis of the newly-discovered alleles of tcpA and toxT indicates their horizontal transfer from an uncommon clone of V. cholerae. The genomic content of ToxT regulon, and tandemly arranged multiple pre-CTX[FE]Env and a CTX[FE]ET in V. mimicus probably act as salient raw materials inducing natural recombination among the hallmark virulence genes of hybrid V. cholerae strains. This study will facilitate deeper understanding of the evolution of new variant CT and ToxT regulon, influencing cholera epidemiology.

microbiology↗

bioRxiv2017

Viable But Non-Culturable Cells Are Persister Cells

Bacteria have two dormant phenotypes: the viable but non-culturable (VBNC) state and the persister state. Both resting stages arise without mutation and both have been linked to chronic infections; however, persister cells revive rapidly whereas the cell population called VBNC is reported to not resuscitate. Here we investigated the relatedness of the two stress-induced phenotypes at the single-cell level by using transmission electron microscopy and fluorescent microscopy to examine cell morphology and by quantifying cell resuscitation. Using the classic starvation conditions to create VBNC cells, we found that the majority of the remaining Escherichia coli population are spherical, have empty cytosol, and fail to resuscitate; however, some of the spherical cells under these classic VBNC-inducing conditions resuscitate immediately (most probably those with dense cytosol). Critically, all the culturable cells became persister cells within 14 days of starvation. We found that the persister cells initially are rodlike, have clear but limited membrane damage, can resuscitate immediately, and gradually become spherical by aging. After 24 h, only rod-shaped persister cells survive, and all the spherical cells lyse. Both cell populations formed under the VBNC-inducing conditions and the persister cells are metabolically inactive. Therefore, the bacterial population consists of dead cells and persister cells in the VBNC-inducing conditions; i.e., the non-lysed particles that do not resuscitate are dead, and the dormant cells that resuscitate are persister cells. Hence, \"VBNC\" and \"persister\" describe the same dormant phenotype.

microbiology↗

bioRxiv2017

Stability of Commonly Used Haematological Parameters in Samples Stored at 33°C, 22°C and 4°C

AimThis study aimed to investigate the analytical bias and imprecision in haematological parameters induced by storage at 4{degrees}C, 22{degrees}C and 33 {degrees}C.\n\nMethodsThree K2EDTA anticoagulated vials of blood were collected from each of twenty blood donors and stored at 4{degrees}C, 22{degrees}C and 33{degrees}C respectively. Readings from each vial were taken at 0, 4, 6, 12, 24, 48 and 72 hours after collection on the Sysmex XP-100 analyser. The mean and median shift of the parameters relative to the baseline and the coefficient of variation for each time-temperature combination were calculated. The shift was compared to the maximum acceptable bias.\n\nResultsHaemoglobin, Red Blood Cell Count, White Blood Cell Count, Mean Corpuscular Haemoglobin were stable for at least twenty four hours at 33{degrees}C. Haematocrit, Mean Corpuscular Volume and Platelet Counts were stable for less than four hours at 33{degrees}C. All the above parameters were stable for longer at 22{degrees}C and 4{degrees}C. The three-part differential count showed instability within four hours at 33 {degrees}C.\n\nConclusionsStrict pre-analytical control is needed at 33{degrees}C or above due to the marked instability of most parameters. However, Haemoglobin, Red Blood Cell Count, White Blood Cell Count and Mean Corpuscular Haemoglobin remain relatively stable even at 33{degrees}C.\n\nKey MessageHaematology samples exposed to temperatures of 33{degrees}C or above show rapid change in MCV, HCT,MCHC, RDW, Platelet Counts and three-part differential counts. Settings where prolonged exposure to these temperatures cannot be avoided should rely on the more stable parameters of Haemoglobin, RBC Counts, MCH and WBC Counts.

pathology↗