A microbiologist used Gram staining method in a laboratory to identify different types of infectious bacteria in four different samples (I, II, III and IV). The given table shows the results.Based on the results of sample I and IV, he infers that the cell walls of Escherichia coli and Salmonella typhi have

Explanation

Gram staining is a method used to classify bacteria into two major groups: Gram-positive and Gram-negative, based on the structure of their cell walls. Gram-negative bacteria, such as Escherichia coli and Salmonella typhi, have a thin peptidoglycan layer located between the cell membrane and an outer membrane composed of lipopolysaccharides, lipoproteins, and phospholipids. This structure is significant in determining the bacteria's response to Gram staining, where Gram-negative bacteria do not retain the crystal violet stain and instead take up the counterstain (safranin), appearing pink. Thus, the inference that the cell walls of E. coli and S. typhi have a thin peptidoglycan layer is correct. Other options either incorrectly describe the cell wall structure of Gram-negative bacteria or are partially correct.