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Alteration in expression of Serratia marcescens porins associated with decreased outer membrane permeability
T Hashizume1, M Sanada, S Nakagawa
1Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd., Tsukuba, Japan.
Abstract:
The porin expression of two clinical isolates of Serratia marcescens, which overproduced cephalosporinase and had decreased outer membrane permeability, were studied in comparison with those of reference strains. Separation of the porin proteins assessed by SDS-PAGE containing urea revealed that both clinical isolates overexpressed a single porin of 44 and 43 kilodalton (kDa), respectively. In contrast, the in-vitro porin deficient mutant, which was derived from the reference strain IFO3736 as latamoxef-resistant, showed decreased outer membrane permeability, but produced low levels of all three peptidoglycan associated porins of 45, 44 and 43 kDa, and overexpressed 39 kDa OmpA protein. These observations suggested that the clinical isolates had a different mechanism of latamoxef resistance compared with the mutant and overexpressed possible narrow transport channels of 44 or 43 kDa. The 45 kDa porin may facilitate a more effective channel than the other two proteins. Heterogeneity of porin profiles between biotypes was also suggested. The two isolates were also resistant to penicillins and cephalosporins tested, but imipenem was the most active agent and inhibited the isolates at 1.56 mg/L.
Insights
Two Serratia marcescens clinical isolates showed distinct porin expression linked to cephalosporin resistance. Their unique porin profiles suggest novel resistance mechanisms compared to laboratory mutants.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Serratia marcescens is an opportunistic pathogen known for antibiotic resistance.
- Outer membrane proteins, particularly porins, play a crucial role in bacterial antibiotic susceptibility.
- Understanding porin expression is vital for elucidating resistance mechanisms in clinical isolates.
Purpose of the Study:
- To investigate and compare the porin expression profiles of two clinical Serratia marcescens isolates with those of reference strains.
- To elucidate the role of porin expression in the cephalosporin and latamoxef resistance of these clinical isolates.
- To compare the resistance mechanisms of clinical isolates with a laboratory-derived porin-deficient mutant.
Main Methods:
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with urea was used to separate and analyze porin proteins.
- Outer membrane permeability was assessed in clinical isolates and a reference strain mutant.
- Antibiotic susceptibility testing was performed, including determining the minimum inhibitory concentration (MIC) for imipenem.
Main Results:
- Clinical isolates overexpressed single porins of 44 kDa and 43 kDa, respectively, and exhibited decreased outer membrane permeability.
- A laboratory-derived mutant showed decreased permeability, low levels of three porins (45, 44, 43 kDa), and overexpression of OmpA protein (39 kDa).
- Clinical isolates displayed resistance to penicillins and cephalosporins, with imipenem showing high activity (MIC = 1.56 mg/L).
Conclusions:
- Clinical Serratia marcescens isolates possess distinct porin expression patterns compared to laboratory mutants, suggesting different resistance mechanisms.
- Overexpression of 44 kDa or 43 kDa porins in clinical isolates may represent narrow transport channels contributing to resistance.
- The 45 kDa porin might function as a more effective channel, and heterogeneity in porin profiles across biotypes is suggested.