Nonfermentative

Nonfermentative bacteria, or nonfermenters, are a heterogeneous group of Gram-negative bacteria defined by their inability to ferment carbohydrates to acid (and gas) under standard laboratory conditions. Unlike enteric bacteria that ferment glucose and other sugars, most nonfermenters rely on oxidative metabolism of substrates or respiratory pathways for energy. The term is primarily used in clinical microbiology to categorize bacteria that do not belong to the Enterobacterales and that do not produce acid from sugars in fermentation tests.

Nonfermenters display a wide range of biochemical and morphological traits. Many are oxidase-positive and exhibit variable motility and pigment production; others are oxidase-negative and nonmotile. They commonly appear as fastidious or slow-growing Gram-negative rods on routine culture and may require extended incubation. Identification often relies on biochemical panels and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analysis.

Prominent nonfermenters include Pseudomonas species (notably Pseudomonas aeruginosa), Burkholderia species, Stenotrophomonas maltophilia, and Acinetobacter species. They are ubiquitous in soil and water and are frequent causes of opportunistic infections, especially in hospitalized patients, those with cystic fibrosis, or those with weakened immune defenses. Infections include pneumonia, bloodstream infections, wound and urinary tract infections, and device-associated infections.

Management of infections caused by nonfermenters can be challenging due to intrinsic and acquired antibiotic resistance. Empiric therapy often covers nonfermenters in at-risk patients, with definitive treatment guided by susceptibility testing. Prevention focuses on infection control measures in healthcare settings and prompt identification in clinical laboratories.