Micro| Gram Negative Bacteria

3.04 Gram Negative Bacteria Microbiology review for the USMLE Step 1 Exam. Gram negative bacteria are characterized by a thin cell wall surrounded by a lipid outer membrane They do not retain the violet gram stain and appear pink after staining Gram negative bacteria can be classified by shape: cocci, coccobacilli, bacilli, and spirals Gram negative cocci include Neisseria species, which can be further categorized as maltose fermenters or non maltose fermenters Gram negative coccobacilli include: Bordetella pertussis, Haemophilus influenzae, Pasteurella, Francisella tularensis, Brucella, and Acinetobacter Gram negative bacilli can be divided into lactose fermenting and non lactose fermenting categories Lactose fermenting gram negative bacilli include: Escherichia coli, Klebsiella, Enterobacter, Citrobacter, and Serratia Non lactose fermenting gram negative bacilli can be further divided into oxidase positive and oxidase negative Oxidase positive non lactose fermenting gram negative bacilli include Pseudomonas Oxidase negative non lactose fermenting gram negative bacilli include Shigella, Yersinia, and Salmonella Gram negative spirals can be divided into oxidase positive and oxidase negative categories Oxidase positive gram negative spirals include Vibrio species, Helicobacter pylori, and Campylobacter jejuni Oxidase negative gram negative spirals include Borrelia burgdorferi (cause of lyme disease) and Treponema pallidum (cause of syphilis)