Gram Negative Rods

Gram Negative Rods

1. 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.

2. 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

3. 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

4. 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

5. 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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