nonlactosefermenting

Nonlactosefermenting refers to microorganisms that do not metabolize lactose to acid or gas under standard laboratory conditions. In microbiology, lactose fermentation is a common phenotypic trait used to differentiate Gram-negative bacteria, particularly on lactose-containing media such as MacConkey agar. Nonlactosefermenting organisms typically produce colorless or pale colonies on such media, whereas lactose fermenters produce acid that changes the medium to pink.

Testing for lactose fermentation involves inoculating carbohydrate-containing media and observing acid and gas production. In addition to lactose, other sugars can be tested to determine a fermentation profile. Biochemical and enzymatic tests help distinguish nonlactosefermenters within Gram-negative groups. Many nonlactosefermenters are oxidase-positive (for example, Pseudomonas spp.) or nonfermentative in biochemical panels, which can aid identification.

Examples of nonlactosefermenting organisms include Salmonella enterica and Shigella spp., which are typically nonfermenters on MacConkey agar; Proteus spp. are also generally nonlactose fermenters. Other nonlactosefermenters encountered in clinical microbiology include Pseudomonas aeruginosa, Acinetobacter spp., Stenotrophomonas maltophilia, and Burkholderia cepacia complex. Many of these organisms are environmental or hospital-associated pathogens and can cause opportunistic infections.

Clinical relevance: Distinguishing nonlactosefermenters from lactose-fermenters is part of routine bacterial identification and can influence empirical therapy and infection control decisions, as nonlactosefermenters include several significant pathogens. The lactose fermentation phenotype is one of multiple phenotypic traits used to narrow down possibilities before definitive methods such as biochemical panels or molecular diagnostics are employed.