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Mindy Miller-Kittrell,
North Carolina
State University
CHAPTER
19
Pathogenic
Gram-Positive
Rods
© 2014 Pearson Education, Inc.
Gram-Positive Bacilli
Two Groups:
 Endospore-forming


Bacillus – aerobic; found in soil
Clostridium - anaerobes; found in soil, water, sewage & GI
tract of animals & humans
 Nonendospore-forming

Corynebacterium


Many species are normal flora of mucus membranes
Listeria monocytogenes


Found in soil and water
Some animals have bacteria
Bacillus anthracis
 Description
Gram-positive rods,
Endospore-forming
Aerobic
 Pathogenicity (virulence
factors)
 Capsule
 Anthrax toxin

Figure 19.11
http://animal.discovery.com/tv/killer-outbreaks/
Bacillus anthracis
Transmission
 Humans contract disease primarily from
infected animal by-products
 Three routes of transmission
1. Inhalation of spores
2. Inoculation of spores into the body
through a break in the skin
3. Ingestion of spores
Bacillus anthracis
Diseases – clinical manifestations
Gastrointestinal anthrax –
•
•
rare in humans but common in animals
intestinal hemorrhaging and eventually
death
Cutaneous anthrax -Most common
•
•
Ulcer with black necrotic center (eschar)
20% mortality if toxemia develops
Inhalation anthrax – Woolsorter’s Disease
•
Inhaled spores germinate in the lungs and
secrete toxins into the bloodstream
• Early signs – fatigue, malaise, fever aches
• Late stage – toxemia, difficulty breathing;
High mortality rate
Characteristic black eschar of
cutaneous Bacillus anthracis
Bacillus anthracis
http://www.cdc.gov/anthrax/basics/index.html
 Diagnosis –

presence of large, nonmotile, Gram-positive bacilli

in clinical samples of the lungs or skin
 Treatment –

Penicillin, doxycycline, ciprofloxacin

Antitoxin
 Prevention –

Control the disease in animals

Via vaccination & proper disposal of carcasses

Human anthrax vaccine requires multiple doses
and boosters
Clostridium perfringens
 Description


gram positive, endospore forming anaerobic
rod
normal flora of the intestinal tract
 Pathogenicity (virulence factors)

Produces 11 toxins that cause irreversible
damage by:




Lysing RBC & WBC
Killing host cells
Increasing vascular permeability
Reducing blood pressure
Clostridium perfringens
http://www.cdc.gov/foodsafety/clostridium-perfingens.html
Diseases – typically non-invasive
 Mild food poisoning from ingestion of
contaminated meat
 abdominal cramps, watery diarrhea; lasts
24 hrs; NO fever, nausea or vomiting
 Treatment - typically self-limiting as pathogens
& toxins are eliminated through watery stool
 Prevention
– refrigerate foods to prevent toxin
formation; thoroughly reheat foods to destroy
toxins
Clostridium perfringens
http://www.nlm.nih.gov/medlineplus/ency/article/000620.htm
• Gas Gangrene – trauma introduces endospores into body
•
•
•
•

Treatment –





Toxins induce swelling & tissue death
Myonecrosis – death of muscle and connective tissue
Foul smelling gases produced by growing bacterial waste
Shock, kidney failure & death often within one week of
infection
fatal without treatment; 40% mortality
with treatment
Penicillin & antitoxins
amputation of necrotic tissue;
hyperbaric chamber saturates tissue
with oxygen
Prevention - prompt wound cleaning
Figure 19.13
Clostridium difficile
http://www.michigan.gov/documents/mdch/Clostridium_difficile_Infection_
101_385953_7.pdf
 Normal intestinal flora in 3-5% of adults
 Pathogenicity (virulence factors)
Toxin A & Toxin B
 Diseases
 Opportunistic pathogen in patients treated with longterm broad-spectrum antimicrobial drugs
 Minor infections result in a self-limiting explosive
diarrhea
 Serious cases can cause pseudomembranous
colitis resulting in perforation of the colon

http://www.youtube.com/watch?v=gsdMxDmzOMM&feature=related
Clostridium difficile
 Diagnosis
 by isolating the organism from feces
 by demonstrating the presence of toxins via
immunoassay
 Minor infections are usually resolved by discontinuing
use of the antimicrobial drug
 Serious cases are treated with antibiotics: Vancomycin
 Fecal transplant
 Proper hygiene is critical for limiting nosocomial
infections
http://youtu.be/rehwXEcUKms
http://www.sciencedaily.com/releases/2013/10/131004105253.htm
http://youtu.be/JcEbgEn7SA0
Clostridium botulinum
http://www.cdc.gov/nczved/divisions/dfbmd/diseases/botulism
• Description - gram positive anaerobic spore forming bacillus
• Pathogenicity (virulence factors)
– 7 antigenic types (desginated A-G) of botulism toxin (Botox)
– Extremely potent; among deadliest toxins known
– Toxin inhibits release of neurotransmitter
http://youtu.be/_Eo54f6Lc4c
Figure 19.14 - Overview
Clostridium botulinum
Disease – Botulism
– Infant botulism
• ingestion of endospores that
germinate and colonize GI tract
because lack sufficient normal
flora
• constipation and “failure to thrive”;
paralysis and death are rare
http://www.infantbotulism.org/gener
al/faq.php?printable=1
– Wound botulism
• 4 or more days following
contamination of wound by
endospores
• symptoms are the same as with
food-borne botulism
Clostridium botulinum
Disease – Botulism
• Intoxication
• caused by the botulism toxin;
not an infection
• Food-borne botulism – ingest toxin in canned foods
or preserved fish
– weakness, dizziness, blurred
vision, dry mouth, dilated
pupils, constipation &
abdominal pain
– can lead to progressive
paralysis
http://youtu.be/A-_QTgKwHEw
Clostridium botulinum
 Treatment

Repeated washing of the intestinal tract to remove
Clostridium


large doses of antitoxin will neutralize circulating neurotoxin
supportive care

infant botulism - antimicrobials drugs to kill bacteria
 Prevention




Proper canning techniques
Prevent germination of endospores in food via
refrigeration or acidic environment
Toxin is destroyed by heating (80oC 20 min.)
Honey source of endospores so do not feed to infants
under age 1
Clostridium tetani
http://youtu.be/AzCDKC06WLw
 Description
gram positive anaerobic terminal endosporeforming bacillus
 found in soil, dust & GI tract of animals & humans
 Pathogenicity (virulence factors)
 potent tetanus toxin
(neurotoxin)
 Transmission
 via puncture into tissue
 from soil contaminated with
animal feces
 IV drug users
Figure 19.15

Clostridium tetani
Disease

Tetanus (lockjaw)




Typically starts
with tight jaw &
neck muscles
Neurotoxin blocks
relaxation pathway
Hyperactive
spasms & muscle
contractions
Respiratory
spasms – inability
to exhale leads to
death
http://youtu.be/L2Dr929zjY4
Figure 19.16 - Overview
Clostridium tetani
 Causes irreversible damage at each synapse
 50% mortality rate; > 90% mortality in neonatal
tetanus
 Treatment
Clean wounds to
remove endospores
 Antitoxin - tetanus
immunoglobulin
 Antibiotics – penicillin
 Prevention
 DPT vaccine (Toxoid)

Figure 19.17
Listeria monocytogenes
 Description - Gram-positive non-spore-
forming bacillus


Found in soil, water, mammals, birds, fish,
and insects
Enters body in contaminated food and drink
 Pathogenicity (virulence factors)


Listeria produces no toxins or enzymes
Virulence is directly related to the bacteria’s
ability to live within cells
http://youtu.be/iXQOwCfZQek
Listeria monocytogenes
Figure 19.18
Listeria monocytogenes
 Diseases
 Meningitis that can lead to death in pregnant women,
fetuses, newborns, the elderly & immunocompromized
patients
 Human to human transmission only from pregnant women to
fetuses
 Treatment
 Penicillin and erythromycin
 Resistant to tetracycline & trimethoprim
 Prevention
(Outbreaks) http://www.cdc.gov/listeria/outbreaks/
http://youtu.be/drfmt5dqbrs


Difficult because the organism is ubiquitous
At risk individuals should avoid undercooked vegetables,
unpasteurized milk, undercooked meat, and all soft cheeses
Corynebacterium diptheriae
 Description
gram-positive, non-endospore forming
pleomorphic bacillus
 Colonize skin, respiratory, gastrointestinal,
urinary & genital tracts

 Pathogenicity
(virulence factors)
 diphtheria toxin – only
lysogenic phage
infected bacteria;
strains without phage
are avirulent
Figure 19.19
Corynebacterium diptheriae
 Diseases
 Severe respiratory
infections of
nonimmune patients
produce the signs
and symptoms of
diphtheria
 Pseudomembrane
results from fluid that
has thickened and
adheres throughout
the respiratory tract
http://youtu.be/Vjq9jRBEklg
Corynebacterium diptheriae
 Transmission
Humans are only known hosts
 Very contagious- via respiratory droplets
or skin contact
 Endemic in poor parts of the world that
lack adequate immunization
 Treatment
 antitoxin to neutralize toxin before it binds
to cells
 Penicillin and erythromycin kills the bacteria
 Prevention
 Immunization with the DTaP vaccine


http://www.cdc.gov/vaccines/vpd-vac/diphtheria/fs-parents.html
Mycobacterium tuberculosis
• Description
–
–
–
–
–
Acid-fast rod
Occurs in clumps
Very slow to grow
Aerobic
Thick waxy outer wall
• Pathogenicity
– Resistant to drying
– Survives phagocytosis
• Transmission
• from human to
human
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
http://youtu.be/u7o93nmgp1E
Tuberculosis (TB)
 Primary TB (Latent)
 Results from the initial infection with
M.tuberculosis
 Secondary TB (Active)
 Reestablishment of an active infection after a
period of dormancy
 Can spread throughout the body
http://www.cdc.gov/tb/topic/basics/default.htm
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Primary Tuberculosis (Latent)
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 19.22a
Secondary Tuberculosis (Active)
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 19.22b
Screening for Tuberculosis
• Tuberculin skin test
– (+) = current or
previous infection
– Followed by X-ray or
CT, acid-fast staining
of sputum, culturing
bacteria
• Acid-fast staining
– All Mycobacterium
species are positive
http://www.cdc.gov/tb/topic/testing/default.htm
Diagnosis, Treatment, and Prevention
 Diagnosis
 Tuberculin skin test identifies individuals with
previous exposure to M. tuberculosis by the
presence of a hard, red swelling at the test site
 Chest x-rays are used to identify individuals with
active disease
 Treatment
 Treatment with common antimicrobials is difficult
because the bacteria grow slowly and can live
within macrophages
 Combination therapy must be used for a number
of months to treat the disease
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Diagnosis, Treatment, and Prevention
 Treatment
 Primary line: Isoniazid and rifampin
http://www.cdc.gov/tb/topic/treatment/default.htm
 Prevention
 Prophylactic use of antibacterial drugs (Isoniazid) is
used to treat patients who have shown a conversion
from a negative to a positive skin test or were exposed
to active cases of tuberculosis
 Immunization with BCG vaccine is used in countries
where TB is common
http://www.cdc.gov/tb/topic/basics/default.htm
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Leprosy
http://youtu.be/5EBQq6iFayM
 Caused by Mycobacterium leprae
 Bacteria have never been grown in cell-free
culture
 Cases of leprosy are becoming relatively rare
 Transmission is via person-to-person contact or
through a break in the skin
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Diagnosis, Treatment, and Prevention
 Diagnosis
 Based on the signs and symptoms of the disease
 Loss of sensation in skin lesions in the case of
tuberculoid leprosy
 Disfigurement in the case of lepromatous leprosy
 Treatment
 Treatment with a combination of antimicrobial drugs
 Lifelong treatment is sometimes needed
 Prevention
 Primarily prevented by limiting exposure to the pathogen
 BCG vaccine provides some protection
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings
Other Mycobacterial Infections in AIDS
Patients
 Mycobacterium avium-intracellulare
mycobacterial infection seen in AIDS patients
and other immunocompromised patients
 Infections are a result of ingestion of
contaminated food or water
 Infections can simultaneously affect almost every
organ and result in massive organ failure
 Treatment is difficult due to the disseminated
nature of the infection
http://www.cdc.gov/ncidod/dbmd/diseaseinfo/mycobacteriumavium_t.htm
Copyright © 2007 Pearson Education, Inc. publishing as Benjamin Cummings