Related Experiment Videos
Autolysis of methicillin-resistant and -susceptible Staphylococcus aureus
J E Gustafson1, B Berger-Bächi, A Strässle
1Department of Biological Sciences, Illinois State University, Normal 61761.
Abstract:
The autolytic activities, including unstimulated, Triton X-100-stimulated, and daptomycin-induced, of various sets of methicillin-resistant and related methicillin-susceptible strains were compared. Faster rates of autolysis were noted in two heterogeneous methicillin-resistant transductants than in their methicillin-susceptible parental recipients, in a heterogeneous resistant strain than in a susceptible derivative created by chemical mutagenesis, and in a homogeneous resistant strain than in a derivative that had decreased methicillin resistance and was created by transposon Tn551 mutagenesis. These results suggest that the presence of the methicillin resistance region, mec, either directly or indirectly through an interaction with other host genes, confers a faster rate of autolysis on strains. Various auxilliary genes are known to affect methicillin resistance expression, and one of these genes, femA, was necessary for the expression of this faster rate of autolysis. These differences in autolytic activities were not observed in isolated crude cell walls retaining autolytic activities, suggesting different modes of regulation of autolysins in intact cells and isolated walls. In contrast, one homogeneous, highly resistant strain, DU4916, had a lower autolytic activity than did derived heterogeneous resistant and susceptible strains created by chemical mutagenesis and a strain that had decreased resistance and was created by transposon mutagenesis. Our observations suggest that methicillin resistance expression is associated with an enhanced rate of autolysis, in heterogeneous resistant strains at least.
Insights
Methicillin resistance in bacteria is linked to faster cell wall breakdown (autolysis), particularly in heterogeneous strains. This enhanced autolysis requires specific genes like femA and differs between intact cells and isolated components.
Area of Science:
- Microbiology
- Bacterial Physiology
- Antibiotic Resistance
Background:
- Methicillin resistance in Staphylococcus aureus (MRSA) is a significant public health concern.
- Bacterial autolysis, the self-digestion of cell walls, plays a role in cell viability and antibiotic response.
- The relationship between methicillin resistance and autolytic activity is not fully understood.
Purpose of the Study:
- To compare the autolytic activities of various methicillin-resistant and methicillin-susceptible bacterial strains.
- To investigate the role of the methicillin resistance (mec) region and auxiliary genes (e.g., femA) in autolysis.
- To determine if autolysis regulation differs in intact cells versus isolated cell walls.
Main Methods:
- Comparison of unstimulated, Triton X-100-stimulated, and daptomycin-induced autolytic activities.
- Analysis of heterogeneous and homogeneous methicillin-resistant strains and their susceptible derivatives.
- Mutagenesis studies using chemical methods and transposon Tn551 to create resistant and susceptible strains.
- Assessment of autolytic activity in isolated crude cell walls.
Main Results:
- Faster autolysis rates were observed in heterogeneous methicillin-resistant strains compared to their susceptible counterparts.
- The presence of the mec region and the femA gene were associated with enhanced autolysis.
- Differences in autolytic activity were not evident in isolated cell walls, suggesting regulation in intact cells.
Conclusions:
- Methicillin resistance expression is generally associated with an enhanced rate of autolysis, especially in heterogeneous strains.
- Specific genes, including femA, are necessary for this accelerated autolysis.
- Autolysin regulation appears to differ between intact bacterial cells and isolated cell wall preparations.