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

Coccobacillus

Bacillus

Vibrio

Spirillum

Spirochete

Pleomorphic

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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.

Nucleoid

Cell wallCytoplasmicmembraneReplicatedDNA

The cytoplasmicmembrane elongates,separating DNAmolecules.

Cross wall forms;membraneinvaginates.

Cross wall formscompletely.

Daughter cellsmay 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 DNAmolecule is movedinto bud

Young bud

Daughter cell10/1/11 8MDufilho

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: Antimicrobial-Associated 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– Toxins mediate inflammation and pseudomembrane

formation10/1/11 11MDufilho

Figure 23.9 Pseudomembranous colitisLesions

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Bacterial Diseases of the Digestive System

• Bacterial Gastroenteritis: Antimicrobial-Associated 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 wounds10/1/11 15MDufilho

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 withpharyngitis

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– 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– Early diagnosis is difficult because symptoms are

nonspecific

– Treat with clindamycin and penicillin10/1/11 22MDufilho

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

0–200

201–400

401–600

601–800

801–1000

1000

0

0

3

19

1717

31

27

27

69 31

25

58

1

31

119

24

53

26

842

52

32

16748

34189

164

650116228

61448

6

52

218

314

780

563541589

265

853

231

871

1711

14964382

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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– Genetic probes used to diagnose asymptomatic

infection

– Treat with broad-spectrum cephalosporins

– Prevent with safe sex practices10/1/11 41MDufilho

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 larvaehatch from egg, crawl upvegetation, and wait to jumpon passing animal.

Uninfected eggs

Infected larvaedevelop into8-legged nymphsthat remaininfected.

Larvae

Nymph

Infected nymphsfeed on animals orhumans, introducingBorrelia.

Adult ticks feedon deer and mate.Infected female tickslay uninfected eggs.

Nymphs developinto adult ticks.

Larvae become infected withBorrelia when the larvae feedon small mammals or birds.After feeding, they drop off.

Borreliamultipliesin infectedlarvae.

Winter

Fall

Summer

Spring

Spring

(Year 1)

(Year 2)

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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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