Subtle variation within conserved effector operon gene products contributes to T6SS-mediated killing and immunity.

Type VI secretion systems (T6SS) function to deliver lethal payloads into target cells. Many studies have shown that protection against a single, lethal T6SS effector protein requires a cognate antidote immunity protein, both of which are often encoded together in a two-gene operon. The T6SS and an effector-immunity pair is sufficient for both killing and immunity. HereIn this paper we describe a T6SS effector operon that differs from conventional effector-immunity pairs in that eight genes are necessary for lethal effector function, yet can be countered by a single immunity protein. In this study, we investigated the role that the PefE T6SS immunity protein plays in recognition between two strains harboring nearly identical effector operons. Interestingly, despite containing seven of eight identical effector proteins, the less conserved immunity proteins only provided protection against their native effectors, suggesting that specificity and recognition could be dependent on variation within an immunity protein and one effector gene product. The variable effector gene product, PefD, is encoded upstream from pefE, and displays toxic activity that can be countered by PefE independent of T6SS-activity. Interestingly, while the entire pef operon was necessary to exert toxic activity via the T6SS in P. mirabilis, production of PefD and PefE alone was unable to exert this effector activity. Chimeric PefE proteins constructed from two P. mirabilis strains were used to localize immunity function to three amino acids. A promiscuous immunity protein was created using site-directed mutagenesis to change these residues from one variant to another. These findings support the notion that subtle differences between conserved effectors are sufficient for T6SS-mediated kin discrimination and that PefD requires additional factors to function as a T6SS-dependent effector.

Tianeptine-involved emergency department visits, fatal overdoses, and substance seizures in Tennessee, 2021-2023.

Background: Tianeptine is an antidepressant that acts as an agonist to the mu-opioid receptor and enhances serotonin reuptake. Tianeptine has been legally sold as an antidepressant in some countries but is not approved for any medical use by the U.S. Food and Drug Administration (FDA). Tianeptine is not a federally controlled substance, but became a schedule II substance in Tennessee on July 1, 2022. This publication aims to describe the prevalence of tianeptine-involved emergency department visits, fatal overdoses, and substance seizures in Tennessee from 2021 to 2023. Methods: We conducted a study to examine the prevalence of tianeptine-involved emergency department visits and fatal overdoses in Tennessee using data for 2021 to 2023 from the Tennessee Electronic Surveillance System for the Early Notification of Community based Epidemics (ESSENCE) database and the Tennessee State Unintentional Drug Overdose Reporting System (SUDORS). Substance seizure data from National Forensic Laboratory Information System (NFLIS) are included. Results: Our search of ESSENCE, SUDORS, and NFLIS yielded 50 tianeptine-involved emergency department visits, 6 tianeptine-involved fatal overdoses, and 19 tianeptine substance seizures respectively. Demographic information is provided for the emergency department visits and tianeptine-involved fatal overdoses. Discharge diagnosis and clinical symptomology information are provided for the emergency department visits. Conclusion: Emergency department visits and fatal overdoses involving tianeptine have occurred in Tennessee despite tianeptine becoming a schedule II substance. Among emergency department visits, tianeptine use is most commonly associated with gastrointestinal and psychological symptoms. All fatal cases where tianeptine was detected involved other substances, suggesting tianeptine plays a role in polysubstance use.