Bacteria of medical importance I: Gram (-) Rods

pink

Gram (-) Rods color

endotoxin

Lipid A → outer membrane with lipopolysaccharide

Gram negative rods

• large, diverse group of non-spore forming bacteria

• wide range of habitats

• most are not medically important; some are true pathogens, some are opportunists

Aerobes

Pseudomonas and Legionella

Coliforms

Escherichia

Non-coliforms, oxidase-negative

Salmonella, Yersinia

Pseudomonas spp.

• small Gram (-) rods

• free living

  • primarily in soil, sea water, and fresh water; also colonize plants and animals

• important decomposers and bioremediators

• frequent contaminants in homes and clinical settings

• produce oxidase and catalase

Pseudomonas aeruginosa

• common inhabitant of soil and water

• intestinal resident in 10% normal people

• resistant to soaps, dyes, quaternary ammonium disinfectants, drugs, drying

• frequent contaminant of ventilators, IV solutions, anesthesia equipment as biofilms

• opportunistic pathogen

• usually in individuals with cystic fibrosis

• in otistis media

• in burn patients

benefits of biofilm growth

• acts as an absorbent reducing the amount of agent available to interact with bacterial cells in the biofilm

• non-dividing/low metabolically-active bacteria are less susceptible to antimicrobials

Legionella pneumophila

• widely distributed in water

• live in close association with amoebas as facultative intracellular bacteria

• can develop into biofilms in air conditioning and water systems

Enterobacteriaceae family

• enterics

• large family of small, non-spore forming gram (-) rods

• many members inhabit soil, decaying matter, and are common occupants of large bowel of animals including humans

• most frequent cause of diarrhea through enterotoxins

Indole production (SIM Media)

test for: can bacterium degrade tryptophan and produce indole?

positive result: red color when you add Kovac’s reagent

Methyl Red

test for: can bacterium metabolize glucose and produce acidic end products?

positive result: red color when you add methyl red indicator

Voges-Proksauer

test for: can bacterium metabolize glucose and produce non-acidic end products?

positive result: red color when you add Voges Proskauer I and II Indicator

Citrate Test

Test for: does bacterium produce citrate permease to bring citrate (carbon source) into the cell?

positive result: agar slant goes from green to blue color

The analytical profile index (API-20E)

• modern version of IMVIC

• color change tells you (+) or (-)

ETEC

• Enterotoxigenic

• produces enterotoxin (Montezuma’s revenge)

EPEC

Enteropathogenic

actin bundle pedestal formation

• E. coli injects itself so it can attach to itself

EIEC

• Enteroinvasive

• enters via zipper mechanism

• inflammatory disease of large intestine

EHEC

• enterohemorrhagic

• Shiga toxin delivery

• E. coli O157:H7

• hemorrhagic syndrome and kidney disease

Salmonelloses

some gastrointestinal involvement and diarrhea but often affect other systems

Salmonella typhi

most serious pathogen of the genus; cause of typhoid fever; human host

Typhoid Fever

• enters with ingestion of fecally contaminated food or water

• bacteria adhere and enter into the small intestine, which causese invasive diarrhea that leads to septicemia and damage to the intestinal epithelial

• treat with chloramphenicol or sulfatrimethoprim

• 2 vaccines available

Yersinia pestis

• tiny, gram (-) rod, unusualy bipolar staining and capsules

• virulence factors → capsular and envelope proteins protect aganist phagocytosis and foster intracellular growth

  • coagulase

  • endotoxin

contact with wild or semi-domestic animals or infected humans

How do humans develop plague?

flea vectors

bacteria replicates in gut, coagulase causes blood clotting that blocks the esophagus; flea becomes ravenous

bubonic

bacterium multiplies in flea bite, enters lymph, causes necrosis and swelling called a bubo.

septicemic

progression to massive bacterial growth; virulence factors cause intravascular coagulation subcutaneous hemorrhage and purpura → black plague

pneumonic

infection localized to lungs, highly contagious; fatal without treatment