Infective endocarditis by Serratia species: a systematic review

Morbidity and mortality of Serratia marcescens bacteraemia during the substance use epidemic

BACKGROUND

Serratia marcescens (S. marcescens) is an Enterobacterales species present throughout the environment and causes a range of infections. Historically, S. marcescens has been associated with persons who inject drugs (PWID), but literature is scarce. This study aimed to compare treatment characteristics and clinical outcomes between PWID and non-PWID with Serratia marcescens bacteraemia.

METHODS

This was a retrospective cohort study of patients hospitalised with S. marcescens bacteraemia from 1 January 2013 to 31 December 2019 at a tertiary medical centre. Patients were included if they were aged ≥ 18 years and had at least one positive blood culture for S. marcescens.

RESULTS

Of the 67 patients who met inclusion criteria, 14 were identified as PWID (21%) and 53 were non-PWID (79%). Persons who inject drugs were younger (median age: PWID 32 years, non-PWID 67 years) and less likely to have renal disease (PWID 7%, non-PWID 34%). Persons who inject drugs had a higher incidence of infective endocarditis (IE) (PWID 48%, non-PWID 0%) and were more likely to receive combination antimicrobial therapy (PWID 29%, non-PWID 2%). All-cause mortality at 12 months was comparable between groups (PWID 21%, non-PWID 21%).

CONCLUSION

This study demonstrates that long-term outcomes of PWID are comparable with non-PWID, despite PWID being a younger cohort with fewer comorbidities. Clinicians should have high suspicion of IE in PWID with S. marcescens bacteraemia.

ShlA toxin of Serratia induces P2Y2- and α5β1-dependent autophagy and bacterial clearance from host cells

Serratia marcescens is an opportunistic human pathogen involved in antibiotic-resistant hospital acquired infections. Upon contact with the host epithelial cell and prior to internalization, Serratia induces an early autophagic response that is entirely dependent on the ShlA toxin. Once Serratia invades the eukaryotic cell and multiples inside an intracellular vacuole, ShlA expression also promotes an exocytic event that allows bacterial egress from the host cell without compromising its integrity. Several toxins, including ShlA, were shown to induce ATP efflux from eukaryotic cells. Here, we demonstrate that ShlA triggered a nonlytic release of ATP from Chinese hamster ovary (CHO) cells. Enzymatic removal of accumulated extracellular ATP (eATP) or pharmacological blockage of the eATP-P2Y2 purinergic receptor inhibited the ShlA-promoted autophagic response in CHO cells. Despite the intrinsic ecto-ATPase activity of CHO cells, the effective concentration and kinetic profile of eATP was consistent with the established affinity of the P2Y2 receptor and the known kinetics of autophagy induction. Moreover, eATP removal or P2Y2 receptor inhibition also suppressed the ShlA-induced exocytic expulsion of the bacteria from the host cell. Blocking α5β1 integrin highly inhibited ShlA-dependent autophagy, a result consistent with α5β1 transactivation by the P2Y2 receptor. In sum, eATP operates as the key signaling molecule that allows the eukaryotic cell to detect the challenge imposed by the contact with the ShlA toxin. Stimulation of P2Y2-dependent pathways evokes the activation of a defensive response to counteract cell damage and promotes the nonlytic clearance of the pathogen from the infected cell.

Serratia endocarditis, uncommon organism, with significant complications

Serratia marcescens is an aerobic, Gram-negative bacillus predominantly seen in patients with intravenous drug use, immunosuppression, previous antibiotic exposure, and indwelling catheterization. Gram-negative organism causing infective endocarditis (IE) is rare. Serratia marcescens IE is uncommon and is reported to be seen in 0.14% of all cases. In this report, we discuss in detail about a 38-year-old man with a history of intravenous drug abuse presenting with S. marcescens related prosthetic valve IE.

Infective Endocarditis by Pasteurella Species: A Systematic Review

Pasteurella spp. are non-motile, facultative anaerobic, Gram-negative coccobacilli that are commonly found in the oral cavity and the gastrointestinal tract of some animals and are known to be the cause of infections. Usually, infections by Pasteurella spp. in humans is more common in the context of an animal bite leading to a skin and soft tissue infection (SSTI). Infective endocarditis (IE) is rarely caused by Pasteurella spp.; however, it can pose diagnostic and therapeutic dilemmas due to its rarity. The aim of the present study was to systematically review all cases of IE by Pasteurella spp. in the literature. A systematic review was performed of PubMed, Scopus and the Cochrane Library (through 20 December 2021) for studies providing data on epidemiology and clinical and microbiological characteristics as well as data on treatment and outcomes of IE by Pasteurella spp. A total of 28 studies containing data for 28 patients were included. Prosthetic valve was present in 21.4% of patients. The aorta was the most commonly involved intracardiac site. Fever, sepsis, septic shock and heart failure were the most common clinical presentations. Cephalosporins, aminopenicillins and penicillin were the antimicrobials used most commonly. Overall mortality was 17.9%.