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Gram Negative Rods

Erin Westcott Bacteriology ASCLS Englisch

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Gram Negative Rods

Glucose Fermenters
- Enterobacteriaceae
  - Facultative anaerobes, non spore-forming, catalase positive, oxidase negative, reduce nitrate to nitrite
    - Opportunistic Pathogens
      - Lactose Fermenters
        Motile
        Escherichia coli
        Strains
        ETEC
        Enterotoxigenic E. coli: causes traveler's diarrhea, enterotoxins stimulate hypersecretion of fluids and electrolytes. Strains must have fimbriae.
        EPEC
        Enteropathogenic E. coli: causes infantile diarrhea, involves disruption of normal microvilli structure, resulting in malabsorption and diarrhea
        EAEC
        Enteroaggregative E. coli: causes infant diarrhea, rods adhere like stacked bricks causing shortening of microvilli, mononuclear infiltration, hemorrhage, and decreased fluid absorption
        STEC/EHEC
        Shiga-toxin/Enterohemorrhagic E. coli: causes hemorrhagic colitis and hemolytic uremic syndrome. Cytotoxic shiga toxins disrupt protein synthesis
        EIEC
        Enteroinvasive E. coli: causes dysentery- necrosis, ulceration, and inflammation of the large intestine. Organism invades enterocytes, leading to destruction of epithelial cells lining the colon.
        Virulence Factors
        O Antigen
        Somatic Antigen
        K Antigen
        Capsule Antigen
        H Antigen
        Flagellar Antigen
        F Antigen
        Fimbrial Antigen
        LPS
        Lipopolysaccharide; major cell wall component
        Type III Secretion System
        Used by bacteria to secrete effector proteins into host cells to promote virulence and colonization.
        Enterotoxins
        Hemolysin
        Inserts into the plasma membrane and causes cytoplasmic leakage.
        Indole: P Citrate: N
        Causes UTIs, neonatal meningitis, traveler's diarrhea, pneumonia, wound infections, and gastroenteritis.
        Citrobacter
        C. freundii
        Indole: N H2S: P Ornithine: N
        C. koseri
        Indole: P H2S: N Ornithine: P
        C. amalonaticus
        50% Delayed Lactose Positive
        Enterobacter
        E. aerogenes
        E. cloacae
        E. agglomerans
        Indole: N Ornithine: P Citrate: P Motility: P
        Common nosocomial infection
        Serratia
        S. marcescens
        S. liquifaciens
        Delayed Lactose Positive
        DNase: P Citrate: P Ornithine: P Indole: N
        20% produce a red pigment
        Non-motile
        Klebsiella
        K. pneumoniae
        Indole N
        K. oxytoca
        Indole P
        Citrate: P Ornithine: N
        All utilize citrate except E. coli
      - Lactose Non-Fermenters
        Proteus Tribe
        All PAD Positive
        Proteus
        P. vulgaris
        Indole: P Ornithine: N
        P. mirabilis
        Indole: N Ornithine: P
        H2S: P Urease: P Swarming Motility
        Causes nosocomial infections, UTIs, and wound infections
        Morganella
        M. morganii
        H2S: N Urease: P Ornithine: P Citrate: N
        Providencia
        P. stuartii
        P. rettgeri
        P. alcalificans
        H2S: N Ornithine: N Citrate: P Urease: Variable
        Edwardsiella
    - Primary Pathogens
      - Salmonella enterica
        Causes gastroenteritis
        Serotype: Typhi
        Causes typhoid fever
        Subspecies
        Enterica (I)
        Salamae (II)
        Arizonae (IIIa)
        Diarizonae (IIIb)
        Indica (IV)
        Houtenae (VI)
        Lactose: N Sucrose: N H2S: P Citrate: P Ornithine: P Motility: P Urease: N PAD: N
        Black colonies on HEA agar
      - Shigella
        Group A: S. dysenteriae
        Most severe form: causes ulceration of the bowels through the destruction of epithelial cells
        Group B: S. flexneri
        Group C: S. boydii
        Group D: S. sonnei
        Most common in US
        Causes bacillary dysentery (shigellosis)
        Lactose: N Sucrose: N H2S: N Citrate: N Ornithine: N Indole: N Motility: N Urease: N PAD: N
      - Yersinia
        Y. enterocolitica
        Causes acute gastroenteritis and mesenteric lymphadenitis
        Motile at 25C Non-motile at 36C
        Selective medium: Cefsulodin-Irgasan-Novobiocin
        Urease: P
        "Safety pin" Gram stain due to bipolar staining
        Y. pestis
        Causitive agent of the bubonic plague. Spread via vector by fleas carried on rodents.
HACEK Group
- Haemophilus
  - H. influenzae
    - Requires X and V factor
    - NF in URT and conjunctiva
    - Causes pneumoniae, croup, meningitis (only type b), septicemia, epiglottitis, and ear/eye infections
    - Virulence factors
      - Capsule serotypes a-f
      - IgA protease cleaves secretory IgA
    - Forms satellite colonies around S. aureus, S. pneumoniae, and Neisseria species
  - H. parainfluenzae
    - Requires V factor
  - H. haemolyticus
    - Requires X and V factor
  - H. aphrophilus
    - Does not require X or V
  - H. ducreyi
    - Requires X factor
  - All species Oxidase P and Catalase P except H. ducreyi, which is N for both
- Aggregatibacter
  - A. aphrophilus = H. aphrophilus
- Cardiobacterium
- Eikenella corrodens
  - Normal oral and GI flora
  - Found in human bite and fist fight infections; can form bone abscesses in face and neck
  - NG on MAC, small colonies on SBA
  - Oxidase: P Catalase: N
  - Non-oxidizer
  - Bleach odor
- Kingella
Environmental Pathogens
- Vibrio
  - Halophilic
    - V. cholerae
      - Motile via polar flagella
      - Causes Cholera: accurate diarrheal disease
      - Secretes enterotoxins that result in hypersecretion
      - Acquired from contaminated water
      - Sucrose P: Yellow colonies on TCBS
  - Not halophilic. Sucrose N: blue-green colonies on TCBS
    - V. parahaemolyticus
      - Acquired from contaminated seafood or swimming in contaminated ocean water with an open wound
      - Causes enteritis and cellulitis
    - V. vulnificus
      - Ctrl + V (V. parahaemolyticus)
  - Oxidase P
  - Plated on TCBS: Thiosulfate Citrate Bile salts Sucrose
- Campylobacter jejuni
  - "Gull wings" gram stain
  - Most common cause of gastroenteritis in US
  - Microaerophilic and capnophile
  - Grows at 42C
- Helicobacter pylori
  - Causes 80% of peptic ulcers and 90% of duodenal ulcers
  - May predispose ppl to gastric cancer
  - S-shaped GNR with polar flagella
  - Virulence factors
    - Urease: causes increase in pH
    - Protein that inhibits acid production
    - Flagella enable burrowing into mucus lining
    - Adhesins facilitate binding to epithelial cells
    - Enzymes that inhibit phagocytic killing
  - LAB ID
    - Gastric biopsy
    - Urea breath test
    - Serological tests
- Aeromonas hydrophilia Plesiomonas shigelloids
  - Ubiquitous in the environment
  - NF
  - Opportunistic pathogens: cause gastroenteritis
  - Resemble Enterobacteriaceae: large gray mucoid colonies on SBA
Sugar Non-fermenters
- Oxidizers
  - Utilize sugars through aerobic respiration. Prefer peptones on TSI.
    - Burkholderia
      - B. cepacia
        Formally classified as Pseudomonas cepacia; causes pneumonia in CF patients
        Oxidase: P
      - B. mallei
        Potential bioterrorist agent
      - B. pseudomallei
        Causes glanders disease
    - Pseudomonas
      - P. aeruginosa
        Ubiquitous, causes infections in burn patients, UTIs, respiratory tract infections, cystic fibrosis patients, necrotizing skin rash, and ear infections.
        Virulence Factors
        Adhesins
        Attachment to host epithelial cells; enhance pili adherence
        Alginate production
        Forms mucoid layer that protects bacteria from phagocytosis and facilitates adherence to host cells
        Exotoxin A
        Inhibits host protein synthesis and produces tissue damage
        Exoenzyme S
        Inhibits host protein synthesis and interferes with phagocytic killing
        Elastolytic activity
        Degrades elastin; causes direct damage to lung tissue and vessels
        Phospholipase C
        Mediates tissue damage
        Pyocyanin
        Mediates tissue damage through production of toxic oxygen radicals (hydrogen peroxide, superoxide, and hydroxyl radicals)
        Antibiotic Resistance
        Lipid A
        Causes fever, vasodilation, inflammation, and shock
        Growth at 42C
      - P. fluorescens
        NG at 42C
      - P. stutzeri
        Very wrinkled colonies
    - Stenotrophomonas maltophilia
      - Grows on MAC
      - Oxidase: N Catalase: P
      - Glucose: P Maltose: P
- Non-Oxidizers
  - Cannot utilize any sugars: nonsaccharolytic.
    - Alcaligenes
      - Alcaligenes faecalis Alcaligenes denitrificans
      - Growth on MAC: dry feathery colonies
      - Oxidase: P Catalase: P
      - Glucose: N Maltose: N
      - Sweet apple smell
- Cause opportunistic infections in compromised hosts. Found in wounds, UTIs, blood, and CSF. All Catalase Positive.
- O/F Variable
  - Acinetobacter
    - Cause of nosocomial URTIs
    - Lactose N on MAC; purple pigmentation
    - Oxidase: N Catalase: P
    - A. baumanii
      - Glucose: P Maltose: N
      - Carbapenem resistant strains
    - A. lwofi
      - Glucose: N Maltose: P/N
  - Elizabethkingia meningosepticum
    - Poor to NG on MAC
    - Oxidase: P Catalase: P
    - O/F rxns variable
Fastidious Organisms
- Capnocytophaga
- Pasteurella multocida
  - Acquired from cat/dog bites and scratches
  - NG on MAC
  - Growth on SBA
  - Fermentative on TSI: weak butt rxn
  - Weak Oxidase P
- Brucella
  - B. melitensis (humans)
  - B. abortus (cattle)
  - B. suis (pig)
  - Causes spontaneous abortions in cattle
  - Causes undulant fever in humans
  - Intracellular parasite
    - Phagocytized by macrophages and monocytes
      - Causes lesions in spleen, liver, bone marrow, lymph nodes, and kidneys
- Francisella tularensis
  - Causes tularemia
    - Acute, febrile, granulomatous inflammation, fever
  - Capable of penetrating unbroken skin
  - <10 organisms required for infection
  - Acquired via
    - Handling the carcasses or skin of infected animals
    - Touching your eyes with contaminated skin or water
    - Tick bites
  - Intracellular parasite
- Legionella pneumophilia
  - Causes Legionnaire's disease
  - Lives inside the protozoan Hartmanella vermiforms
  - Grows on BCYE agar: buffered charcoal yeast extract with iron salts and cysteine added
  - Identified using DFA from sputum and pulmonary secretions
- Bordetella
  - B. pertussis
  - B. parapertussis
  - Toxins
    - Pertussis toxin
      - Increased mucus production
    - Tracheal cytotoxin
      - Inhibits movement of cilia and causes expulsion of cells lining the trachea
    - Adenylate cyclase toxin
      - Mucus production, immune system inhibition
    - Dermonecrotic toxin
      - Localized constriction and hemorrhage of blood vessels
  - Phases of Infection
    - Incubation
      - 7-10 days, bacteria multiply, no symptoms
    - Catarrhal
      - Resembles the common cold, 1-2 weeks, most infectious phase
    - Paroxysmal
      - 2-4 weeks, severe coughing fits
    - Convalescent
      - 3-4 weeks, number of bacteria decreases, secondary infections in damaged epithelium can occur
  - Whooping cough: "100 day cough"
  - Regan-Lowe transport medium necessary. Contains horse blood, charcoal, and cephalexin
  - Primary Plating Media
    - Bordet-Gengou
      - SBA + potato and glycerol extract
    - CHB: charcoal horse blood
  - Colonies look like droplets of mercury
  - Can be ID'd using direct fluorescent antibodies
  - B. bronchioseptica
    - Occasional respiratory pathogen and non-fastidious
- Bartonella henslae
  - Causes cat scratch disease
- Gardnerella vaginalis
  - NF in 70% of healthy females
  - Cultured on human blood tween agar
  - Non-hemolytic on SBA
  - Gram stain shows clue cells

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Beschreibung: ASCLS Bacteriology Mindmap am Gram Negative Rods, erstellt von Erin Westcott am 18/08/2026.
Erstellt von: Erin Westcott
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Gram Negative Rods

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