Verocytotoxin-producing Escherichia coli infection: The Hong Kong experience

Population-Based Clinical Studies Using Routinely Collected Data in Hong Kong, China: A Systematic Review of Trends and Established Local Practices

Background: Routinely collected health data are increasingly used in clinical research. No study has systematically reviewed the temporal trends in the number of publications and analyzed different aspects of local research practices and their variations in Hong Kong, China, with a specific focus on research ethics governance and approval.

Methods: PubMed was systematically searched from its inception to March 28, 2023, for studies using routinely collected healthcare data from Hong Kong.

Results: A total of 454 studies were included. Between 2000 and 2009, 32 studies were identified. The number of publications increased from 5 to 120 between 2010 and 2022. Of the investigator-led studies using the Hospital Authority (HA)’s cross-cluster data (n = 393), 327 (83.2%) reported receiving ethics approval from a single cluster/university-based REC, whereas 50 studies (12.7%) did not report approval from a REC. For use of the HA Data Collaboration Lab, approval by a single hospital-based or University-based REC is accepted. Repeated submission of identical ethics applications to different RECs is estimated to cost HK$4.2 million yearly.

Conclusions: Most studies reported gaining approval from a single cluster REC before retrieval of cross-cluster HA data. Substantial cost savings would result if repeated review of identical ethics applications were not required.

A newly discovered verotoxin variant, VT2g, produced by bovine verocytotoxigenic Escherichia coli

A new verotoxin (VT) variant, designated vt2g, was identified from a bovine strain of verocytotoxigenic Escherichia coli (VTEC) serotype O2:H25. When vt2g was aligned with published sequences of vt2 and vt variants, it exhibited the highest DNA sequence homology with vt2 and vt2c. However, vt2g was not detected by vt2-specific primers and probes, although it was partially neutralized by an antiserum to the VT2A subunit. VT2g was cytotoxic for Vero and HeLa cells and was not activated by mouse intestinal mucus. The vt2g gene was detected in 3 of 409 (0.7%) bovine VTEC strains, including serotypes O2:H25, O2:H45 and Ont:H-.

Polyclonal antibodies to glutathione S-transferase--verotoxin subunit a fusion proteins neutralize verotoxins

The A1 subunits of verotoxin-1 (VT1) and VT2 genes were cloned into pGEX-4T-2 for the expression of glutathione S-transferase (GST) fusion proteins. The N-terminal and the transmembrane regions of the A1 subunits were excluded from the constructs in order to increase the product yields. Polyclonal anti-VT1A1 and anti-VT2A1 antibodies were produced by immunizing rabbits with GST-VT1A1 and GST-VT2A1 fusion proteins, respectively. The antibodies were tested for their ability to neutralize active toxins from 45 VT-producing Escherichia coli (VTEC) strains. The antibodies had significantly high neutralizing activities against their homologous toxins. The average percentages of neutralization of VT1 by anti-GST-VT1A1 and anti-GST-VT2A1 were 76.7% +/- 7.9% and 3.6% +/- 2.3%, respectively, and those of VT2 were 1.7% +/- 2.3% and 82.5% +/- 13.9%, respectively. VT2 variant toxin was neutralized by anti-GST-VT2A1, with cross neutralization being a possible consequence of sequence homology between VT2 and a VT2 variant. To our knowledge, this is the first report on the production of polyclonal antibodies from GST-VT fusion proteins. The antibodies were shown to exhibit specific toxin neutralizing activities and may be useful for immunological diagnosis of VTEC infections.

Detection of RTX toxin gene in Vibrio cholerae by PCR

A PCR that amplifies a recently discovered Vibrio cholerae RTX (repeat in toxin) toxin gene was developed. Among 166 clinical and environmental isolates of V. cholerae causing epidemics and sporadic cases of cholera in various parts of the world, all were found to be toxigenic by both PCR and HEp-2 cell cytotoxicity assay. Standard strains of the classical biotype containing a deletion within the gene cluster exhibited negative results by both assays. This is the first rapid genotyping method for differentiation of V. cholerae O1 classical biotype strains from El Tor biotype strains as well as strains of other non-O1 serogroups including serogroup O139. The PCR assay that was developed also specifically detects RTX toxin genes in V. cholerae, as clinical isolates of Vibrio parahaemolyticus, diarrheagenic Escherichia coli, Aeromonas species, and Plesiomonas species were all negative by the RTX toxin-specific PCR as well as the HEp-2 cytotoxicity assay. These findings highlight the characteristics of the RTX toxins in V. cholerae. Their role in the pathogenicity of the bacterium requires further investigation.