What type of bacteria is classified as gram positive rods?

The classification of bacteria into gram-positive or gram-negative is based on their cell wall structure, as determined by the Gram staining technique. Gram-positive bacteria, which appear purple after gram staining, have a thick peptidoglycan layer in their cell wall and lack an outer membrane.

Among the options provided, diphtheria is indeed associated with the bacterium Corynebacterium diphtheriae, which is classified as a gram-positive rod. This characteristic is critical for identifying the organism in clinical microbiology, especially given its role in causing diphtheria, a serious respiratory disease.

The other options are either classified as gram-negative or do not fit the description of rod-shaped bacteria. Neisseriae and Haemophilus influenzae are both gram-negative cocci, while Escherichia coli is a gram-negative rod. Understanding these classifications helps in diagnosing infections and determining appropriate antibiotic therapies. Thus, diphtheria stands out as the correct choice reflecting gram-positive rods in this context.