MICROBIOLOGY

• An ovoid Gram-positive coccobacillus [Fig 1], the genus Leuconostoc belongs to the family Leuconostocaceae within the order Lactobacillales.
  • Growth on agar shows colorless colonies [Fig 2] with biofilm slime.
    • Catalase-negative bacteria, glucose gas-producing, form D (-)-lactic acid isomers.
      and are unable to hydrolyze arginine.
    • Able to generate D-lactic acid from glucose, which differs from most other lactic acid bacteria.
    • Traditionally, the most common lab technique for isolation uses de Man, Rogosa and Sharpe media supplemented with 2% CaCO₃ and 30 μg/mL vancomycin for isolation and screening.
      • DNA-based identification is used nowadays and is more reliable.
  • May be misidentified as Viridans streptococci or enterococci.
    • Historically, Leuconostoc was dismissed as nonpathogenic in humans.
  • Widespread in the environment.
    • Found in fermented foods, e.g., a component of sourdough starters; able to ferment sugars to lactate (e.g., cabbage → sauerkraut).
      • Leuconostic species (such as L. mesenteroides subsp. cremoris and L. lactis) are found in cheeses, kefyr and yogurts.
• Coagulase-negative, but importantly, are intrinsically resistant to vancomycin (which is also the case for Lactobacillus).
  • Susceptible to penicillin, ampicillin and amoxicillin
  • Other antibiotics to which the organism is generally susceptible:
    • Azithromycin, cefuroxime, clindamycin, levofloxacin, imipenem/cilastatin and linezolid