Microbiology Chapters 19 + 20: Bacteria (Outliers) + Proteobacteria

proteobacteria

The largest and most diverse group of bacteria: over 2,000 species assigned to 500+ genera

5 lineages

Genus Rickettsia

Class Alphaproteobacteria

Genuses Rickettsia and Coxiella

Both are parasitic

grow in vertebrate erythrocytes, macrophages, and vascular endothelial cells

also live in blood-sucking arthropods (i.e. fleas and ticks), which serve as vectors or primary hosts

Genus Coxiella

Class Gammaproteobacteria

Rickettsia life cycle

enters host by phagocytosis



escapes phagosome



reproduces in cytoplasm



host cell bursts

Coxiella life cycle

enters host by phagocytosis



remains in phagosome



reproduces in phagolysosome



host cell bursts

typhus fever

is an infectious disease caused by Rickettsia prowazekii typhi – typhus fever, characterized by high fever, rash, and severe headache.

Transmitted by lice and fleas.

Rocky Mountain Spotted Fever

Rickettsia rickettsii

Most severe tickborne illness in the United States

Incubation period 5-10 days

Initial symptoms include fever, nausea, vomiting, lack of appetite, and severe headache

Prolonged symptoms include rash, abdominal and joint pain, and diarrhea

Q fever

Coxiella burnetti

Excreted in milk, urine, and feces of infected animals

Organisms shed in high numbers in amniotic fluid and placenta

Humans inhale organisms from the air

Symptoms: high fever, confusion, chills, sweats, vomiting, diarrhea

Considered a potential terrorist threat

Class Betaproteobacteria

Two genera with important human pathogens:

Neisseria and Bordetella

Genus Neisseria

Found in the mucous membranes of mammals

gonorrhea

Neisseria gonorrhoeae, Common ST

meningitis

Neisseria meningitidis

Inflammation of the membranes that cover the brain and spinal cord

Can be caused by bacteria or virus (fatal)

Symptoms include high fever, headache, and stiff neck

Genus Bordetella

Multiplies in respiratory epithelial cells

e.g., Bordetella pertussis

Non-motile, encapsulated species

Causes whooping cough

whooping cough

pertussis. Highly contagious respiratory tract infection

Hallmark symptom: hacking cough followed by a high-pitched intake of breath (“whoop”)

Class Gammaproteobacteria

Contains Pseudomonas aeruginosa

Pseudomonas aeruginosa

• Produces blue-green pigment (later pus)

• Opportunistic pathogen

• Exploits a break in host defenses to initiate an infection

• Almost never infects uncompromised tissues

• Serious problem in patients with cancer, AIDS, and cystic fibrosis (mortality rate ~50%)

• Invades burns and wounds

• Problem in hospitals

• Can grow on equipment

• Growing resistance to antibiotics

Genus Legionella

• discovered in 1976

• “Legionnaires’ disease”

• Can colonize water lines and air conditioning systems

• Causes disease when contaminated water droplets are inhaled

• Not spread from person-to-person

• Produces pneumonia

Genus Vibrio

V. cholerae and V. parahaemolyticus

V. cholerae

Causative agent of cholera

Causes extreme diarrhea

Without treatment, death can occur in hours

With treatment, < 1% of patients die

V. parahaemolyticus

Caused by… eating raw/undercooked shellfish

Causes a less severe gastroenteritis

Escherichia coli

Inhabitant of intestinal tracts of many animals

Used as indicator organisms for testing water for fecal contamination

Some strains are pathogenic

O157:H7

E. coli pathogenic strain. Can cause Gastroenteritis and UTIs

Class Deltaproteobacteria

Genus Bdellovibrio

Genus Bdellovibrio

Predator

Attaches to other gram-negative bacteria

Penetrates into the periplasmic space (between the outer membrane and plasma membrane)

Inhibits host DNA, RNA, and protein synthesis

Predator rapidly grows into a long filament

Then divides into many smaller, flagellated progeny

Host cell lyses and releases newly formed cells

Class Epsilonproteobacteria

Contains two pathogenic genera

Campylobacter and Helicobacter

Campylobacter fetus

Causes abortions in cattle and sheep

Septicemia and enteritis in humans

Septicemia: pathogens or toxins in the blood

Enteritis: Inflammation of the intestinal tract

Septicemia

pathogens or toxins in the blood

Enteritis

Inflammation of the intestinal tract

Campylobacter jejuni

• Abortion in sheep

• Enteritis diarrhea in humans

  • Leading cause of bacterial diarrheal illness in the U.S.

Helicobacter pylori

Causes gastritis and peptic ulcer disease

Produces large quantities of urease

Urea hydrolysis produces ammonia, creating an alkaline environment

Associated with virulence

Symptoms: burning pain in the abdomen, vomiting, and frequent burping

Spread through untreated water and person-to-person through saliva or fecal matter