Microbiology 10: Introduction to Pathogenic Bacteria
- Staphylococci and streptococci both Gram + cocci
- Escherichia coli is Gram – enteric bacteria
- Tubercle bacillus (Mycobaterium tuberculosis) is acid-fast bacteria
- 2 large categories
o “typical” bacteria – rods and cocci (Gram + and -)
o Those not in first category
- Isolates from different hosts of 1 specis = strains
o E. coli strain in research = K12
“Typical” Bacteria
- Gram stain = presence of outer membrane in Gram - bacteria and murein layer in Gram + bacteria
o Subdivided into rods or cocci
o Gram + -> appear dark violet; Gram - -> appear red
o Gram + cocci and Gram – rods are most common infections
- Gram-Positive Cocci
o Streptococci
§ Chains of spherical cells (strings of pearls)
§ β-hemolytic streptococci -> lyse RBCs with clear area around
· main pathogens (A through T)
o group A strep = S. pyogenes (cause strep throat, infections with rheumatic fever or glomerulonephritis)
§ α-hemolytic streptococci -> green around colony
· S. pneumoniae (bacterial pneumonia)
§ Some strains contribute to production of cheese
§ Do not carry out respiration only fermentation
· Most are oxygen-tolerant anaerobes
o Staphylococci
§ S. aureus and S. saprophyticus look like bunches of grapes
§ Withstand many chemical and physical agents
§ Aerobes
§ Found esp on skin (pus, osteomyelitis, endocarditis)
§ Secrete coagulase
- Gram-Negative Cocci
o Neisseria -> genus includes gonococcus (gonorrhea) and meningococcus (meningitis and severe septicemia)
o Outer membranes contain endotoxin (lipopolysaccharide)
- Gram-positive Rods
o Abundant in environment
o Diphtheria -> Corynebacterium diphtheriae (relatives are diphtheroids)
§ Common inhabitant of skin and mucous membranes
o Most common -> spore-forming rods (large)
§ Aerobic Bacillus anthracis
§ Strict anaerobes (Clostridium)
· C. botulinum (botulism), C. tetani (tetanus), C. perfringens (gas gangrene)
· Symptoms caused by exotoxins
· C. difficile (pseudomembranous colitis from antibiotic use)
· Listeria monocytogenes (immunocompromised and pregnancy infection)
- Gram-negative Rods
o Enteric bacteria = Echerichia coli, Salmonella (typhoid fever, food poisoning), Shigellea (bacillary dysentery)
§ Do not for spores, many are motile
§ Some ferment lactose (E. coli and others) and some don’t (Shigella and Salmonella)
§ Distant relatives = Vibrio, Pseudomonas (found in aqueous environments), Campylobacter jejuni (infectious diarrhea), Helicobacter pylori (gastritis, gastric ulcer/cancer)
o Fastidious and Small Gram-negative rods = Haemophilus (pneumonia and meningitis), Bordetella (whooping cough), Brucella (brucellosis), Francisella (tularemia), Bartonella (cat scratch fever), Legionella (in soil, water)
o Strictly Anaerobic Gram-negative Rods = Bacteroides (intestinal flora, stimulus for proper tissue development)
§ May be harmful if deposited into deep tissues (peritonitis)
Not So Typical Bacteria
- Acid-Fast Bacteria
o Synonymous with Mycobacterium (tubercle bacillus [M. tuberculosis] and leprosy bacillus [M. leprae])
o Withstand many chemicals (waxy envelope)
§ Penetrated by dyes if bacteria heated or treated with detergent = Ziehl-Neelsen technique (red dye fuschsin with detergents + 3% HCl + blue dye)
· “Red bugs” visible against blue background
o Environmental species = atypical acid-fast bacilli (Mycobacterium avium-intracellulare)
o Sometimes form branches like fungi (myco)
§ Relatives -> Nocardia [aerobic] and Actinomyces [anaerobes] and Streptomyces (make antibiotics [streptomycin, tetracycline, etc])
- Spirochetes
o Helical (spring)
o Treponema pallidum (syphilis) -> do not dye
o Leptospira (icterohemorrhagic fever), Borrelia recurrentis (relapsing fever), Borrelia burgdorferi (Lyme disease)
- Chlamydiae
o Intracellular bacteria (don’t grow on media) -> in phagocytes
o Chlamydia trachomatis (STD), C. pneumonia (pneumonia, atherosclerosis)
- Rickettsiae
o Intracellular obligate parasites, rod-shaped
o Cause typhus and Rocky Mountain spotted fever
§ Transmitted by bite of arthropod (except Coxiella burnetii [Q fever] inhaled)
o Ehrlichia (infect WBCs)
- Mycoplasmas
o Lack rigid cell wall (aka murein)
§ Resistant to penicillin
§ Resemble regular L bacteria
o Need sterols for nutrition
o Mycoplasma pneumoniae, Ureaplasma ureae
o Grow in hypertonic mediums
- Tropheryma whipplei (Whipple disease) -> diarrhea and intestinal bleeding, lymphadenopathy
o IDed by PCR and 16S rRNA analysis