Which bacteria have a thick cell wall with several layers of peptidoglycan and teichoic acid?

The correct option is Staphylococcus aureus.

To determine which bacterium has a cell wall with a thick peptidoglycan layer and teichoic acid, we can analyze the structural differences between Gram-positive and Gram-negative bacterial cell walls:
1. Gram-Positive Bacteria: These organisms possess a thick cell wall composed of multiple layers (up to 40 layers) of peptidoglycan, which accounts for up to 90% of the cell wall's dry weight. Polymeric molecules called teichoic acids (and lipoteichoic acids) are covalently linked to the peptidoglycan or the cell membrane, spanning the thick layer to provide structural support and aid in cell wall maintenance.
2. Gram-Negative Bacteria: In contrast, Gram-negative bacteria have a much thinner, single-layered peptidoglycan cell wall (making up only about 10% of the cell wall) surrounded by an outer membrane containing lipopolysaccharides (LPS). They do not contain teichoic acids.

Let's classify each of the options based on their Gram staining characteristics:
• Salmonella enterica: Gram-negative rod-shaped bacterium.
• Staphylococcus aureus: Gram-positive sphere-shaped (coccus) bacterium.
• Pseudomonas aeruginosa: Gram-negative rod-shaped bacterium.
• Escherichia coli: Gram-negative rod-shaped bacterium.

Thus, among the choices provided, only the Gram-positive bacterium Staphylococcus aureus has a thick cell wall rich in peptidoglycan layers and teichoic acid.