The presence of antibiotic resistance related to Integrative Conjugative Elements (ICEs) in oral streptococci are increasingly being reported. This study investigates the prevalence, diversity and stability of one family of ICEs, Tn916-Tn1545 in blood isolates collected in Norway.. Prevalence and diversity of Tn916-Tn1545 ICEs in oral streptococci in Norway

The Tn916-Tn1545 family of Integrative Conjugative Elements (ICEs) are Mobile Genetic Elements (MGEs) that play a role in the spread of antibiotic resistance genes in bacteria. Tn916, the progeny of this family of ICEs harbors the tetracycline resistance gene (tet M) and possess the ability to transpose within and between bacteria. With each transposition event, the levels of tetracycline resistance in the bacterial population are increased. This ICE has been reported in various bacterial species including oral streptococci. The increase in the levels of tetracycline resistance among oral streptococci is of great concern primarily due to the abundance of these species in the oral cavity and their ability to act as reservoirs for antibiotic resistance genes. In this current study, we screened 100 Norwegian clinical oral streptococci isolates for the presence of Tn916-Tn1545 family elements. We investigated the presence of Tn916-Tn1545 family by Digital Droplet PCR (ddPCR) and the diversity was assessed by Restriction Fragment Length Polymorphism (RFLP) and Next Generation Sequencing (NGS). In addition, we investigated the ability of the bacteria to transfer the element and the associated transfer frequencies. It was found that 21 isolates harboured the Tn916-Tn1545 family of which two of these elements are the novel Tn6815 and Tn6816. The most prevalent member of the Tn916 -Tn1545 family observed in the Norwegian clinical oral streptococci isolates was the wild type Tn916. The minimum inhibitory concentration of the isolates harbouring Tn916-Tn1545 family ranged between 2-96 µg/mL and the observed rate of transfer per recipients ranged from non-detectable transfer to 3.5 (± 6.0) × 100 per recipient. The detection of other members of this family of ICE and varying transfer frequencies suggests high versatility of the Tn916 element in oral streptococci in Norway.