Related Experiment Videos
Effect of pH on the morphology of Staphylococcus aureus
Abstract:
Nineteen strains of Staphylococcus aureus (10 sensitive and 9 resistant to oxacillin) were grown for four hours on membranes placed on trypticase soy agar at pH 5, 5.5, 6, 6.5, 7.1, 7.5, 7.8 and 8.3. The morphology was observed by interference phase contrast and by electron microscopy. All strains grown at pH 6 to 7.5 produced cocci of normal size. When grown at pH 5, 5.5, 7.8 and 8.3, however, seven of the oxacillin-resistant strains and seven of the oxacillin-sensitive strains produced bacterial cells 1.5 to 2 micron in diameter. These cells consist of a cluster of staphylococci held together by multiple thick cross walls. Their structure is similar to that of staphylococci grown in the presence of subminimum inhibitory concentrations of beta-lactam antibiotics, which inhibit autolysis of cross walls. It appears that autolysis of cross walls of S. aureus is also inhibited by a low or a high pH.
Insights
Extreme pH levels (5, 5.5, 7.8, 8.3) altered Staphylococcus aureus morphology, causing cells to cluster with thick cross walls. This suggests pH affects bacterial cell wall autolysis, similar to beta-lactam antibiotics.
Area of Science:
- Microbiology
- Bacterial Morphology
- Cell Wall Biology
Background:
- Staphylococcus aureus is a significant human pathogen.
- Bacterial cell wall integrity is crucial for survival.
- Autolysis, the self-digestion of cells, plays a role in bacterial life cycles.
Purpose of the Study:
- To investigate the effect of varying pH on the morphology of Staphylococcus aureus.
- To compare the morphological changes in oxacillin-sensitive and oxacillin-resistant strains.
- To explore the potential role of pH in inhibiting bacterial cell wall autolysis.
Main Methods:
- Culturing 19 Staphylococcus aureus strains (10 oxacillin-sensitive, 9 oxacillin-resistant) on trypticase soy agar across a pH range (5 to 8.3).
- Observing bacterial morphology using interference phase contrast and electron microscopy.
- Analyzing cell size and the presence of cross walls.
Main Results:
- Strains grown at pH 6-7.5 exhibited normal cocci morphology.
- At extreme pH values (5, 5.5, 7.8, 8.3), both sensitive and resistant strains showed enlarged cells (1.5-2 µm) composed of clustered cocci.
- These enlarged cells featured multiple thick cross walls, resembling structures seen when autolysis is inhibited by beta-lactam antibiotics.
Conclusions:
- Both low and high pH conditions inhibit the autolysis of cross walls in Staphylococcus aureus.
- pH-induced morphological changes in S. aureus are similar to those caused by sub-minimum inhibitory concentrations of beta-lactam antibiotics.
- Environmental pH is a critical factor influencing bacterial cell wall dynamics and morphology.