A comparison of typing methods for Serratia marcescens

Area of Science:

• Microbiology
• Bacteriology
• Epidemiology

Background:

• Accurate strain typing of Serratia marcescens is crucial for tracking hospital-acquired infections.
• Traditional bacteriocine typing methods often require strain induction, adding complexity.
• A simpler, more discriminatory typing method is needed for clinical microbiology.

Purpose of the Study:

• To develop and evaluate a simple bacteriocine typing method for Serratia marcescens without induction.
• To compare the discriminatory power of a novel cross-streaking susceptibility method with mitomycin C induction.
• To assess the utility of bacteriocine typing, combined with O serogrouping, for clinical isolate analysis.

Main Methods:

• A cross-streaking bacteriocine-susceptibility typing method was developed, avoiding mitomycin C induction.
• This method was compared against a susceptibility-typing method using induced, cell-free lysates.
• 178 Serratia marcescens isolates from hospital infections were typed using both methods and O serogrouping.

Main Results:

• The cross-streaking method showed slightly greater discriminatory power than the induction method when appropriate difference rules were applied.
• Both methods yielded acceptable reliability for typing strains within the same O serogroup from distinct infection incidents.
• A hierarchical typing system, combining O serogrouping with cross-streaking bacteriocine typing, offered the highest strain discrimination.

Conclusions:

• Bacteriocine-susceptibility typing without induction is a viable and effective method for Serratia marcescens.
• The cross-streaking technique provides a simple, reliable, and more discriminatory approach compared to induction-based methods.
• Hierarchical typing combining O serogrouping and bacteriocine susceptibility testing is the most effective strategy for clinical strain differentiation.