AUTHOR=Yang Ye , Zhang Hui , Zhao Rongqing , Qiu Xuedan , Ye Jinglu , Lu Wenjun , Li Qingcao , Wu Guangliang 

TITLE=Distribution diversity and expression regulation of class 1 integron promoters in clinical isolates of Morganella morganii

JOURNAL=Frontiers in Microbiology

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2024.1459162

DOI=10.3389/fmicb.2024.1459162

ISSN=1664-302X

ABSTRACT=<sec id="sec1"><title>Background</title><p><italic>Morganella morganii</italic> is an emerging nosocomial opportunistic pathogen with increasing multidrug resistance. Antibiotic resistance, driven primarily by the horizontal transfer of resistance genes, has become a global health crisis. Integrons, mobile genetic elements, are now understood to facilitate the transfer of these genes, contributing to the rapid proliferation of resistant strains. Understanding the regulatory role of integrons in drug resistance gene expression is crucial for developing novel strategies to combat this pressing public health issue.</p></sec><sec id="sec2"><title>Objective</title><p>To investigate the distribution of promoter types in the variable regions of class 1 integrons isolated from clinical isolates of <italic>M. morganii</italic> and their regulatory role in the expression of downstream drug resistance gene cassettes.</p></sec><sec id="sec3"><title>Methods</title><p>Ninety seven clinical isolates of <italic>M. morganii</italic> were screened for the presence of class 1 integrons (<italic>intI1</italic>) using polymerase chain reaction (PCR). Gene cassettes within the variable regions of positive isolates were characterized, and the gene cassette promoter Pc variants and downstream auxiliary promoter P2 were identified. Enterobacterial repetitive intergenic consensus (ERIC)-PCR was employed for homology analysis. Recombinant plasmids containing different variable region promoters and gene cassettes were constructed to evaluate drug resistance genes and integrase (<italic>intI1</italic>) expression levels using reverse transcription-quantitative PCR (RT-qPCR) and antimicrobial susceptibility testing.</p></sec><sec id="sec4"><title>Results</title><p>Of the clinical isolates, 28.9% (<italic>n</italic> = 28/97) were positive for class 1 integrons. 24.7% (<italic>n</italic> = 24/97) of these isolates carried gene cassettes encoding resistance to aminoglycosides and trimethoprim. Three Pc promoter types (PcH1, PcS, and PcW) were identified, while all P2 promoters were inactive with a 14-base pair spacing between the −35 and −10 regions. ERIC-PCR analysis classified the integron-positive strains into 6 genotypes, with high consistency in promoter types and gene cassettes within each genotype. RT-qPCR and antimicrobial susceptibility testing demonstrated that strong promoters significantly enhanced the expression of downstream drug resistance gene cassettes compared to weak promoters. Additionally, RT-qPCR revealed a negative correlation between <italic>intI1</italic> expression and Pc promoter strength.</p></sec><sec id="sec5"><title>Conclusion</title><p>Class 1 integrons are prevalent in <italic>M. morganii</italic>. The promoter types within these integrons are diverse, and promoter strength is closely linked to downstream gene cassette expression. Integron-positive strains exhibit high homology, suggesting horizontal gene transfer and dissemination in clinical settings.</p></sec>