gram-positive
UK[ˌɡræm ˈpɒzətɪv]US[ˌɡræm ˈpɑːzətɪv]
adj
(of bacteria) retaining a violet stain after being treated with Gram's method, typically having a thick cell wall.
Morpheme Breakdown
gram
positive
gram
name
positive
property
Etymology
The term is a scientific eponym, formed in the late 19th century from the surname of the Danish physician Hans Christian Gram. He developed the differential staining technique in 1884 to classify bacteria based on their cell wall structure. The word 'positive' derives from Latin positivus, meaning 'settled' or 'affirmative', and here indicates the bacteria's property of retaining the primary crystal violet stain. Thus, 'gram-positive' literally means 'affirmative for (the test of) Gram', describing bacteria identifiable by his specific staining protocol.
Analysis
Structure: gram (name) + positive (property)
- gram: A proper name, from Hans Christian Gram, a Danish bacteriologist. It functions as a bound root specifying the method.
- positive: From Latin positivus, meaning 'formally laid down, settled, affirmative'. It functions as an adjective indicating a result or property.
Examples
Penicillin is particularly effective against gram-positive bacteria like streptococci.
The laboratory report identified the infection as being caused by a gram-positive coccus.
A key difference between the two major bacterial classes is that gram-positive cells have a thicker peptidoglycan layer.