Chapter 11
Characterizing
and Classifying
Prokaryotes
General Characteristics of Prokaryotic Organisms
• Prokaryotes
– Most diverse group of cellular microbes
– Habitats
– From Antarctic glaciers to thermal hot springs
– From colons of animals to cytoplasm of other
prokaryotes
– From distilled water to supersaturated brine
– From disinfectant solutions to basalt rocks
– Only a few capable of colonizing humans and
causing disease
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Figure 11.1 Typical prokaryotic morphologies
Coccus
Spirillum
Coccobacillus
Spirochete
Bacillus
Pleomorphic
Vibrio
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General Characteristics of Prokaryotic Organisms
• Reproduction of Prokaryotic Cells
– All reproduce asexually
– Three main methods
– Binary fission (most common)
– Snapping division
– Budding
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Figure 11.2 Binary fission
Cell replicates its DNA.
Cell wall
Cytoplasmic
membrane
Replicated
DNA
Nucleoid
The cytoplasmic
membrane elongates,
separating DNA
molecules.
Cross wall forms;
membrane
invaginates.
Cross wall forms
completely.
Daughter cells
may separate.
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Figure 11.3 Snapping division-overview
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Figure 11.4 Actinomycetes spores
Spores
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Figure 11.5 Budding
DNA is replicated
One daughter DNA
molecule is moved
into bud
Young bud
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Daughter cell
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Modern Prokaryotic Classification
• Currently based on genetic relatedness of
rRNA sequences
• Three domains
– Archaea
– Bacteria
– Eukarya
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Survey of Bacteria
• Low G+C Gram-Positive Bacteria
– Clostridia
– Rod-shaped, obligate anaerobes, toxin
producing, endospore formers
– Important in medicine and industry
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Bacterial Diseases of the Digestive System
• Bacterial Gastroenteritis: AntimicrobialAssociated Diarrhea
– Signs and symptoms
– Pseudomembranous colitis occurs in severe cases
– Pathogen and virulence factors
– Caused by Clostridium difficile
– Antimicrobial use facilitates overgrowth of C. difficile
– C. difficile produces two toxins
– Pathogenesis
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– Toxins mediate inflammation and pseudomembrane
formation
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Figure 23.9 Pseudomembranous colitis
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Lesions
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Bacterial Diseases of the Digestive System
• Bacterial Gastroenteritis: AntimicrobialAssociated Diarrhea
– Epidemiology
– By-product of modern medicine
– Any antimicrobial can trigger the disease
– Diagnosis, treatment, and prevention
– Diagnosis based on presence of bacterial toxin in
stool
– Treat with antimicrobials
– Avoid unnecessary use of antimicrobials
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Bacterial Diseases of the Skin and Wounds
• Gas Gangrene
– Signs and symptoms
– Blackening of infected muscle
and skin
– Presence of gas bubbles
– Pathogens and virulence
factors
– Caused by several Clostridium
species
– Bacterial endospores survive
harsh conditions
– Vegetative cells secrete 11
toxins
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Bacterial Diseases of the Skin and Wounds
• Gas Gangrene
– Pathogenesis and epidemiology
– Traumatic event must introduce endospores into
dead tissue
– Mortality rate exceeds 40%
– Diagnosis, treatment, and prevention
– Appearance is usually diagnostic
– Rapid treatment is crucial
– Surgical removal of dead tissue
– Administration of antitoxin and penicillin
– Prevent with proper cleaning of wounds
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Survey of Bacteria
• Low G+C Gram-Positive Bacteria
– Low G+C bacilli and cocci
– Bacillus–many common in soil – B. anthracis –
cause of cutaneous and pulmonary anthrax
– Listeria–contaminates milk and meat products–
Listeria monocytogenes
– Causes meningitis of immuno-compromised –
pregnant, newborns, elderly
– Organism can live within cells undetected by
the immune system
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Bacterial Diseases of the Skin and Wounds
• Cutaneous Anthrax
– Caused by Bacillus
anthracis
– Characterized by an
eschar
– Black, painless, ulcer
– Treated with
antimicrobial drugs
– Prevention requires
control of the disease in
animals
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Survey of Bacteria
• Low G+C Gram-Positive Bacteria
– Low G+C bacilli and cocci
– Lactobacillus–grows in the body but rarely causes
disease
– Streptococcus and Enterococcus–cause
numerous diseases
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Bacterial Diseases of the Upper Respiratory System, Sinuses, and Ears
• Streptococcal Respiratory Diseases
– Signs and symptoms
– Sore throat and difficulty swallowing
– May progress to scarlet or rheumatic fever
– Pathogen and virulence factors
– Caused by group A streptococci (S. pyogenes)
– Variety of virulence factors
– M proteins, hyaluronic acid capsule,
streptokinases, C5a peptidase, pyrogenic toxins,
streptolysins
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Streptococcal Pharyngitis (Strep Throat): pus pockets on tonsils
Pus pockets on tonsils
The reddened appearance and pus pockets of a throat with
pharyngitis
Bacterial Diseases of the Upper Respiratory System, Sinuses, and Ears
• Streptococcal Respiratory Diseases
– Pathogenesis
– Occurs when normal microbiota are depleted,
large inoculum is introduced, or adaptive immunity
is impaired
– Epidemiology
– Spread via respiratory droplets
– Occurs most often in winter and spring
– Diagnosis, treatment, and prevention
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– Often confused with viral pharyngitis
– Penicillin is an effective treatment
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Bacterial Diseases of the Skin and Wounds
• Necrotizing Fasciitis
– Pathogen and virulence factors
– Most cases caused by S. pyogenes
– Various enzymes facilitate invasion of tissues
– Exotoxin A and streptolysin S are also secreted
– Pathogenesis and epidemiology
– S. pyogenes enters through breaks in the skin
– Usually spread person-to-person
– Diagnosis, treatment, and prevention
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– Early diagnosis is difficult because symptoms are
nonspecific
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– Treat with clindamycin
and penicillin
Figure 19.6 Necrotizing fasciitis
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Survey of Bacteria
• Low G+C Gram-Positive Bacteria
– Low G+C bacilli and cocci
– Staphylococcus–one of the most common
inhabitants of humans – S. aureus
– Can cause food poisoning – produces 5 toxins
– Endocarditis, styes, pneumonia, skin infections
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Bacterial Diseases of the Skin and Wounds
• Staphylococcal Scalded Skin Syndrome
– Pathogen and virulence factors
– Some Staphylococcus aureus strains
– One or two different exfoliative toxins cause SSSS
– Pathogenesis
– No scarring because dermis is unaffected
– Death is rare but may be due to secondary infections
– Epidemiology
– Disease occurs primarily in infants
– Transmitted by person-to-person spread of bacteria
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Figure 19.3 Staphylococcal scalded skin syndrome
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Bacterial Diseases of the Skin and Wounds
• Staphylococcal Scalded Skin Syndrome
– Diagnosis, treatment, and prevention
– Diagnosed by characteristic sloughing of skin
– Treated by administration of antimicrobial
drugs
– Widespread presence of S. aureus makes
prevention difficult
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Bacterial Diseases of the Skin and Wounds
• Impetigo (Pyoderma) and Erysipelas
– Pathogens and virulence factors
– Most cases are caused by S. aureus
– Some cases are caused by Streptococcus
pyogenes
– Gram-positive coccus, arranged in chains
– Virulence factors similar to those of S. aureus
– M protein
– Hyaluronic acid
– Pyrogenic toxins
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Figure 19.4 Impetigo
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Figure 19.5 Erysipelas
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Bacterial Diseases of the Skin and Wounds
• Impetigo (Pyoderma) and Erysipelas
– Pathogenesis
– The bacteria invade where the skin is
compromised
– Epidemiology
– Transmitted by person-to-person contact or
via fomites
– Impetigo occurs most in children
– Erysipelas can also occur in the elderly
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Bacterial Diseases of the Skin and Wounds
• Impetigo (Pyoderma) and Erysipelas
– Diagnosis, treatment, and prevention
– The presence of vesicles is diagnostic for
impetigo
– Treat with penicillin and careful cleaning of
infected areas
– Prevent with proper hygiene and cleanliness
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Survey of Bacteria
• High G+C Gram-Positive Bacteria
– Mycobacterium
– Aerobic rods that sometimes form filaments
– Slow growth partly due to mycolic acid in its cell walls
– Mycobacterium tuberculosis - tuberculosis
– Actinomycetes
– Form branching filaments resembling fungi
– Important genera include Actinomyces, Nocardia,
Streptomyces
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Survey of Bacteria
• Gram-Negative Proteobacteria
– Largest and most diverse group of bacteria
– Many have extensions called prosthecae
– Used for attachment and to increase surface
area for nutrient absorption
– Alphaproteobacteria
– Pathogenic alphaproteobacteria
– Rickettsia
– Brucella
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Bacterial Diseases of the Skin and Wounds
• Rocky Mountain Spotted Fever
– Signs and symptoms
– Non-itchy spotted rash on trunk and appendages
– Pathogen and virulence factors
– Caused by Rickettsia rickettsii
– Pathogen avoids digestion in phagosome
– Pathogenesis
– Disease follows damage to blood vessels
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Disease at a Glance 19.2 Rocky Mountain Spotted Fever-overview
Bacterial Diseases of the Skin and Wounds
• Rocky Mountain Spotted Fever
– Epidemiology
– Transmitted via bite of infected tick
– Diagnosis, treatment, and prevention
– Diagnosed with serological testing
– Treated with various antimicrobials
– Prevented with the use of tick repellents and
avoidance of tick-infested areas
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Figure 19.9 Number of cases of Rocky Mountain spotted fever in the U.S., 1999-2009
3
27
6
1
26
19
31
31
8
58
53
119
17
27
17
69
25
31
42
25
218
314
167
48 780
24
1711
32
4382
1496
853 871
563
189
589 541
34
231
164
265 52
48
14
6
228
116
650
0
0
0–200
201–400
401–600
601–800
801–1000
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Survey of Bacteria
• Gram-Negative Proteobacteria
– Betaproteobacteria
– Pathogenic betaproteobacteria
– Neisseria
– Bordetella
– Burkholderia
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Bacterial STDs
• Gonorrhea – 2-5 days
– Signs and symptoms
– Men experience painful urination
and a purulent discharge
– Women are often asymptomatic
– Pelvic inflammatory disease my
develop
– Pathogen and virulence factors
– Caused by Neisseria gonorrhoeae
– Virulence factors include fimbriae,
capsule, and endotoxin
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Bacterial STDs
• Gonorrhea
– Pathogenesis
– Bacteria attach to epithelial cells of the mucous
membranes
– Epidemiology
– Gonorrhea occurs only in humans
– Risk increases with frequency of sexual encounters
– Diagnosis, treatment, and prevention
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– Genetic probes used to diagnose asymptomatic
infection
– Treat with broad-spectrum cephalosporins
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– Prevent with safe sex
practices
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Figure 24.5 Incidence of civilian gonorrhea in the U.S.-overview
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Survey of Bacteria
• Gram-Negative Proteobacteria
– Gammaproteobacteria
– Purple sulfur bacteria
– Intracellular pathogens
– Legionella
– Coxiella
– Methane oxidizers
– Glycolytic facultative anaerobes
– Family Enterobacteriaceae
– Pseudomonads
– Pseudomonas
– Azotobacter
– Azomonas
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Bacterial Diseases of the Skin and Wounds
• Pseudomonas Infection
– Pathogen and virulence factors
– Pseudomonas aeruginosa is the
causative agent
– Found in soil, decaying matter,
moist environments
– Virulence factors
– Adhesins, toxins, and a polysaccharide capsule
– Pathogenesis
– Infection can occur in burn victims
– Bacteria grow under the surface of the burn
– The bacteria kills cells, destroys tissue, and triggers
shock
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Figure 19.8 Pseudomonas aeruginosa infection
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Survey of Bacteria
• Gram-Negative Proteobacteria
– No human pathogens
– Desulfovibrio – sulfate reducer
– Bdellovibrio – pathogen of Gram neg. bacteria
– Myxobacteria -
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Survey of Bacteria
• Gram-Negative Proteobacteria
– Epsilonproteobacteria
– Campylobacter
– Helicobacter – cause of peptic ulcers
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Survey of Bacteria
• Other Gram-Negative Bacteria
– Chlamydias
– Chlamydia
– Spirochetes
– Treponema
– Borrelia
– Bacteroids
– Bacteroides
– Cytophaga
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Bacterial STDs
• Syphilis
– Signs and symptoms
– Four phases of syphilis
– Primary syphilis
– Secondary syphilis
– Latent syphilis
– Tertiary syphilis
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Figure 24.6 The later lesions of syphilis-overview
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Bacterial STDs
• Syphilis
– Pathogen and virulence factors
– Treponema pallidum causes syphilis
– Lives only in humans
– Virulence factors have been difficult to identify
– Pathogenesis
– Transmitted mostly via sexual contact
– Sometimes transmitted from mother to child
– Most individuals do not develop tertiary syphilis
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Bacterial STDs
• Syphilis
– Epidemiology
– Syphilis occurs worldwide
– Virulence factors have been difficult to identify
– Diagnosis, treatment, and prevention
– Diagnose primary, secondary, and congenital
syphilis with antibody test
– Tertiary syphilis is difficult to diagnose
– Penicillin G used to treat all but tertiary syphilis
– Prevent with safe sex practices
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Figure 24.7 The incidence of syphilis in the U.S.-overview
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Bacterial Cardiovascular and Systemic Diseases
• Lyme Disease
– Signs and symptoms
– Three phases in untreated
patients
– Bull's-eye rash at infection site
– Neurological symptoms
– Severe arthritis
– Pathogen and virulence factors
– Caused by the spirochete Borrelia burgdorferi
– Use of manganese instead of iron circumvents host
defense
– Avoids immune detection by altering membrane proteins
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Figure 21.9 The life cycle of the deer tick Ixodes
Uninfected 6-legged larvae
hatch from egg, crawl up
vegetation, and wait to jump
on passing animal.
Spring
(Year 1)
Uninfected
eggs
Larvae
Spring
(Year 2)
Infected larvae
develop into
8-legged nymphs
that remain
infected.
Infected nymphs
feed on animals or
humans, introducing
Borrelia.
Nymph
Winter
Larvae become infected with
Borrelia when the larvae feed
on small mammals or birds.
After feeding, they drop off.
Summer
Nymphs develop
into adult ticks.
Adult ticks feed
on deer and mate.
Infected female ticks
lay uninfected
eggs.
Borrelia
multiplies
in infected
larvae.
Fall
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Bacterial Cardiovascular and Systemic Diseases
• Lyme Disease
– Diagnosis, treatment, and prevention
– Based on the signs and symptoms of the disease
– Bacterium rarely detected in the blood
– Antimicrobial drugs are used in the early phases
– Treatment of later phases is difficult
– Symptoms often caused by the immune system
– Prevent with repellents containing DEET and
protective clothing
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Bacterial Cardiovascular and Systemic Diseases
• Lyme Disease
– Epidemiology
– One of the most reported vector-borne diseases
in U.S.
– Two events contributed to an increase in Lyme
disease
– Movement of human populations into woodland
areas
– Protection of the deer population
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Figure 21.10 The occurrence of Lyme disease in the United States-overview
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