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Chapter 19
Pathogenic Gram-Positive Cocci and Bacilli
Gram-Positive Pathogens
Stain purple
when properly gram-stained
Can be
categorized into 2 major groups based on their DNA
Low G + C
organisms
Genera of
cocci-shaped organisms- Staphylococcus, Streptococcus, and Enterococcus
Genera of
bacilli-shaped organisms- Bacillus, Clostridium, and Listeria
High G + C
organisms
Genera of bacilli-shaped organisms- Corynebacterium,
Mycobacterium, Propionibacterium, Nocardia, and Actinomyces
Staphylococcus
Normal
members of every humans microbiota
Can be
opportunistic pathogens
Structure and Physiology
Gram-positive
cocci, nonmotile, facultative anaerobes
Cells occur
in grapelike clusters because cells division occurs along different planes and
the daughter cells remain attached to one another
Salt-tolerant-allows
them to tolerate the salt present on human skin
Tolerant of
desiccation-allows survival on environmental surfaces (fomites)
Structure and Physiology
Three
species are commonly associated with staphylococcal diseases in humans
Staphylococcus
aureus-The more virulent strain that can produce a variety of conditions
depending on the site of infection
Staphylococcus
epidermidis-Normal microbiota of human skin that can cause opportunistic
infections in immunocompromised patients or when introduced into the body
Staphylococcus saprophyticus a frequent cause
of urinary tract infections, esp. in young women.
Pathogenicity
Staph infections
result when staphylococci breach the bodys physical barriers
Entry of
only a few hundred bacteria can result in disease
Pathogenicity
results from 3 features
Structures
that enable it to evade phagocytosis
Production
of enzymes
Production
of toxins
Structural Defenses Against
Phagocytosis
Protein A
coats the cell surface
Interferes
with humoral immune responses by binding to class G antibodies
Inhibits the
complement cascade
Bound
coagulase
Converts the
soluble blood protein fibrinogen in insoluble fibrin molecules that form blood
clots
Fibrin clots
hide the bacteria from phagocytic cells
Structural Defenses Against
Phagocytosis
Synthesize
loosely organized polysaccharide slime layers (often called capsules)
Inhibit chemotaxis
of and phagocytosis by leukocytes
Facilitates
attachment of Staphylococcus to artificial surfaces
Enzymes
Cell-free
coagulase
Triggers
blood clotting
Hyaluronidase
Breaks down
hyaluronic acid, enabling the bacteria to spread between cells
Staphylokinase
Dissolves
fibrin threads in blood clots, allowing S.aureus to free itself from clots
Enzymes
Lipases
Digest
lipids, allowing staphylococcus to grow on the skins surface and in cutaneous
oil glands
b-lactamase
Breaks down
penicillin
Allows the
bacteria to survive treatment with b-lactam
antimicrobial drugs
Toxins
Staphylococcus
aureus produces toxins more frequently than S.epidermidis
Cytolytic
toxins
Disrupts the
cytoplasmic membrane of a variety of cells
Leukocidin
can lyse leukocytes specifically
Exfoliative
toxins
Causes the
patients skin cells to separate from each other and slough off the body
Toxins
Toxic-shock-syndrome
toxin
Causes toxic
shock syndrome
Enterotoxins
Stimulate
the intestinal muscle contractions, nausea, and intense vomiting associated
with staphylococcal food poisoning
Staphylococcal Diseases
3 categories
Noninvasive
Disease
Food poisoning
from the ingestion of enterotoxin-contaminated food
Cutaneous
Disease
Various skin
conditions including scalded skin syndrome, impetigo, folliculitis, and
furuncles
Staphylococcal Diseases
Systemic
Disease
Toxic shock
syndrome-TSS toxin is absorbed into the blood and causes shock
Bacteremia-presence
of bacteria in the blood
Endocarditis-occurs
when bacteria attack the lining of the heart
Pneumonia-inflammation
of the lungs in which the alveoli and bronchioles become filled with fluid
Osteomyelitis-inflammation
of the bone marrow and the surrounding bone
Diagnosis, Treatment, and
Prevention
Diagnosis
Detection of
Gram-positive bacteria in grapelike arrangements isolated from pus, blood, or
other fluids
Treatment
Methicillin
is the drug of choice to treat staphylococcal infections
Is a
semisynthetic form of penicillin and is not inactivated by b-lactamase
Diagnosis, Treatment, and
Prevention
Prevention
Hand
antisepsis is the most important measure in preventing nosocomial infections
Also
important is the proper cleansing of wounds and surgical openings, aseptic use
of catheters or indwelling needles, an appropriate use of antiseptics
Streptococcus
Gram-positive
cocci, arranged in pairs or chains, that are facultative anaerobes
Often
categorized based on the Lancefield classification (Rebecca Lancefield
1895-1981)
Divides the
streptococci into serotype groups based on the bacterias antigens
Lancefield
groups A and B include the significant streptococcal pathogens of humans
Group A Streptococcus: Streptococcus
pyogenes
S. pyogenes
forms white colonies surrounded by zone of beta-hemolysis on blood agar plates
Pathogenic
strains often form a capsule
Group A
streptococci generally only cause disease in the following situations:
Normal
microbiota are depleted
Large
inoculum enable the streptococci to establish themselves before antibodies are
formed against them
Specific
immunity is impaired
Pathogenicity
Structural
components
Protein M,
which interferes with opsonization and lysis of the bacteria and a hyaluronic
acid capsule, which acts to camouflage the bacteria
Enzymes
Streptokinases,
deoxynucleases, and C5a peptidase all facilitate the spread of streptococci
through tissues
Pyrogenic
toxins that stimulate macrophages and helper T cells to release cytokines
Streptolysins
lyse red blood cells, white blood cells, and platelets
Group A Streptococcal Diseases
Pharyngitis
(strep throat)-inflammation of the pharynx
Scarlet
fever-rash that begins on the chest and spreads across the body
Pyoderma-confined,
pus-producing lesion that usually occurs on the face, arms, or legs. Can become
erysipelas if surrounding lymph nodes involved
Streptococcal
toxic shock syndrome-bacteremia and severe multisystem infections
Group A Streptococcal Diseases
Necrotizing
fasciitis-toxin production destroys tissues and eventually muscle and fat
tissue
Rheumatic
fever-inflammation that leads to damage of heart valves muscle
Glomerulonephritits-inflammation
of the glomeruli and nephrons which obstruct blood flow through the kidneys
Diagnosis, Treatment, and
Prevention
Diagnosis
Observation
of Gram-positive bacteria in short chains or pairs or immunological tests that
identify the presence of group A streptococcal antigens
Streptococci
are normally in the pharynx so their presence in a respiratory sample is of little
diagnostic value
Diagnosis, Treatment, and
Prevention
Treatment
Penicillin
is very effective
Prevention
Antibodies
against M protein provide long-term protection against future infection of S.
pyogenes, but only if it is the same strain
Group B Streptococcus: Streptococcus
agalactiae
Gram-positive
cocci that divide to form chains
Distinguished
from group A streptococcus by its buttery colonies and smaller zone of
beta-hemolysis on blood agar plates and its resistance to bacitracin
Normally
colonizes the lower gastrointestinal, genital, and urinary tracts
Pathogenicity and Diseases
Pathogenicity
Often
infects newborns who have not yet formed type-specific antibodies and whose
mothers are uninfected (and so do not provide passive immunity)
Produces
various enzymes whose roles in causing disease is not yet understood
Diseases
Most often
associated with neonatal bacteremia, meningitis, and pneumonia
Immunocompromised
older patients are at risk from group B streptococcal infections
Prevention
Prophylactic
administration of penicillin at birth to children whose mothers urinary tracts
are colonized with group B streptococci
Immunization
of women against group streptococci to prevent infection of future children
Alpha-Hemolytic Streptococci: The
Viridans Group
One of the
causes of dental caries and dental plaques
If enter the
blood can cause meningitis and endocarditis
Streptococcus pneumoniae
Gram-positive
cocci that most commonly forms pairs but may also form chains
Normally
colonizes the mouths and pharynx but can cause disease if travels to the lungs
Disease is
highest in children and the elderly
Pathogenicity
Polysaccharide
capsule-protects the bacteria from digestion after phagocytosis
Diseases
Pneumococcal
pneumonia-bacteria multiply in the alveoli causing damage to the alveolar
lining and an inflammatory response
Sinusitis
and otitis media-bacteria invade the sinuses or middle ear, often following a
viral infection
Bacteremia and
endocarditis-bacteria in the bloodstream or in the lining of the heart
Pneumococcal
meningitis-bacteria that have spread to the meninges
Diagnosis, Treatment, and
Prevention
Diagnosis
Gram strain
of sputum smears
Treatment
Penicillin
Prevention
Vaccine made
from purified capsular material
Provides
long lasting immunity in normal adults but is not as effective in children, the
elderly, or AIDS patients
Enterococcus
Previously
classified as group D streptococci but differed enough to be reclassified as a
separate genus
Form short
chains and pairs and lack a capsule
Found in the
human colon but are rarely pathogenic at this site
Can cause
disease if they are introduced into other parts of the body, such as the
urinary tract or bloodstream
Important
cause of nosocomial infections
Treatment is
difficult because enterococci are often resistant to antimicrobials
Prevention
is difficult, especially in a health care setting, where patients often have
weakened immune systems
Bacillus
Gram-positive
bacilli, that occurs singly, in pairs, or in chains
Forms
endospores
Bacillus
anthracis is a strict pathogen of animals and humans
Primarily a
disease of herbivores, but humans can contract the disease from infected
animals
Humans
contract the bacteria via on of three routes
Inhalation
of spores
Inoculation
of spores into the body through a break in the skin
Ingestion of
spores
Pathogenicity and Diseases
Pathogenicity
Anthrax
toxin
Diseases
Anthrax is
the only disease caused by Bacillus anthracis
Anthrax can
have three clinical manifestations
Gastrointestinal
anthrax
Rare in
humans
Intestinal
hemorrhaging and eventually death
Pathogenicity and Diseases
Cutaneous
anthrax
Produces a
ulcer called an eschar and toxemia
Inhalation
anthrax
Rare in
humans
Spores
germinate in the lungs and secrete toxins that are absorbed into the
bloodstream
High
mortality rate
Diagnosis, Treatment, and
Prevention
Diagnosis
Presence of
large, nonmotile, Gram-positive bacilli in clinical samples of the lungs or
skin
Treatment
Ciproflaxacin
and many other antimicrobials are effective against B.anthracis
Prevention
Control the
disease in animals
An anthrax
vaccine is available but requires multiple doses and boosters
Clostridium
Gram-positive,
anaerobic, endospore-forming bacillus
Ubiquitous
in soil, water, and the gastrointestinal tracts of animals and humans
The presence
of endospores allows for survival in harsh conditions
Clostridium perfringens
Commonly
grows in the digestive tracts of animals and humans
Produces 11
toxins that have various effects on the body and can result in irreversible
damage
Clostridium perfringens
Diseases
Food
poisoning
Benign
disease characterized by abdominal cramps and watery diarrhea
Gas gangrene
Endospores
are introduced into the body through some traumatic event
The
endospores germinate and cause necrosis that is often accompanied by
foul-smelling gaseous bacterial waste products
Diagnosis, Treatment, and
Prevention
Diagnosis
The presence
of more than 105 bacteria in a gram of food or 106 cells
per gram of feces indicates the involvement of Clostridium in food
poisoning
Gas gangrene
is usually diagnostic by itself
Treatment
Food
poisoning is self-limited
Gas gangrene
is treated by removing the dead tissue and administering large doses of
penicillin
Prevention
Difficult to
prevent because it is so common
Proper
cleaning of wounds can often prevent gas gangrene
Clostridium difficile
Common
member of the intestinal microbiota
Opportunistic
pathogen in patients treated with broad-spectrum antimicrobial drugs
Minor
infections can result in a self-limiting explosive diarrhea
Serious
cases can cause pseudomonas colitis
Can result
in perforation of the colon, leading to massive internal infection by fecal
bacteria and eventual death
Clostridium botulinum
Anaerobic,
endospore-forming, Gram-positive bacillus
Common in
soil and water
Botulism
results when the endopsores germinate and produce botulism toxin
The
different botulism toxins are the deadliest toxins known
Diseases
Botulism is
not an infection, but an intoxification caused by the botulism toxin
3 forms of
botulism
Food-borne
botulism
Usually
occurs due to the consumption of toxin in home-canned foods or preserved fish
Can result
in a progressive paralysis that results in death due to the inability to inhale
Infant
botulism
Results from
the ingestion of endospores, which germinate, and colonize the gastrointestinal
tract due to the lack of sufficient numbers of normal microbiota
Symptoms
include constipation and failure to thrive, but paralysis and death are rare
Wound
botulism
Wound
becomes contaminated with endospores
Symptoms are
the same as with food-borne botulism
Diagnosis, Treatment, and
Prevention
Diagnosis
Symptoms of botulism
are diagnostic
Confirm
diagnosis by culturing the organism from food, feces, or the patients wound
Treatment
Can involve
three approaches
Repeated
washing of the intestinal tract to remove Clostridium
Administer
antibodies against botulism toxin to neutralize toxin in the blood
Administer
antimicrobials drugs to kill clostridia in infant botulism cases
Prevention
Proper
canning of food to prevent contamination
Infants
should not consume honey under the age of 1
Clostridium tetani
Endospore-forming,
obligately anaerobic, Gram-positive cocci
Ubiquitous
in soil, dust, and the GI tract of animals and humans
Tetanus
results when the bacterial endopsores germinate and produce tetanus toxin
Tetanus
results in spasms and contractions that can result in death because patients
cant exhale
Diagnosis, Treatment, and
Prevention
Diagnosis
Characteristic
muscular contraction
The bacteria
is rarely isolated from clinical samples because it grows slowly and is
sensitive to oxygen
Treatment
Thorough
cleaning of wounds to remove endospores
Passive
immunization with immunoglobulin directed against the toxin
Administration
of antimicrobials
Active immunization
with tetanus toxoid
Prevention
Immunization
with tetanus toxoid
Listeria
Gram-positive
non-spore-forming, coccobacillus
Found in
soil, water, mammals, birds, fish, and insects
Enters body
in contaminated food and drink
Listeria
produces no toxins or enzymes
Virulence is
directly related to the bacterias ability to live within cells
Diagnosis, Treatment, and
Prevention
Diagnosis
Presence of
the bacteria in the cerebrospinal fluid
Rarely seen
by Gram-staining because so few Listeria cells are required to produce
disease
Treatment
Most
antimicrobial drugs inhibit Listeria
Prevention
Difficult
because the organism is ubiquitous
At risk
individuals should avoid undercooked vegetables, unpasteurized milk,
undercooked meat, and all soft cheeses
Corynebacterium
Ubiquitous
on plants and in animals and humans
Colonizes
the skin and the respiratory, gastrointestinal, urinary, and genital tract
Corynebacterium
diphtheriae, the cause of diphtheria, is the most widely known
Transmitted
from person to person via respiratory droplets or skin contact
Endemic in
poor parts of the world that lack adequate immunization
Diphtheria
toxin is responsible for the signs and symptoms of diphtheria
Disease
Diphtheria
toxin inhibits polypeptide synthesis which results in cell death
Infections
are asymptomatic or produce mild respiratory disease in immune or partially
immune individuals
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
The
pseudomembrane can completely occlude the respiratory passages and cause
suffocation
Cutaneous
diphtheria causes cell death and formation of a pseudomembrane on the skin
Diagnosis, Treatment, and
Prevention
Diagnosis
Initial
diagnosis is based on the presence of pseudomembrane
Absolute
identification is based on the Elek test
Antibodies
against the toxin react with toxin in a sample of fluid from the patient
Treatment
Administration
of antitoxin to neutralize toxin before it binds to cells
Penicillin
and erythromycin kills the bacteria
Prevention
Immunization
with the DPT vaccine
Mycobacterium
Cell wall
contains a waxy lipid called mycolic acid
The unusual
cell wall results in a number of unique characteristics
Slow growth
Protection
from lysis once the bacteria are phagocytized
Capacity for
intracellular growth
Resistance
to Gram-staining, detergents, many antimicrobial drugs, and dessication
3 main
mycobacterial diseases
Tuberculosis
Leprosy
Opportunistic
infections in AIDS patients
Tuberculosis (TB)
Respiratory
disease cause by Mycobacterium tuberculosis
Cases are
declining in the United States but it is pandemic in other parts of the world
Virulent
strains of M.tuberculosis contain the cell wall component, cord factor,
that is necessary to cause disease
3 types of
tuberculosis
Primary TB
Results from
the initial infection with M.tuberculosis
Secondary TB
Reestablishment
of an active infection after a period of dormancy
Disseminated
TB
Results when
the infection spreads throughout the body
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
Prevention
Prophylactic
use of antibacterial drugs 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
Inmmunization
with BCG vaccine is used in countries where TB is common
Leprosy
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
Diagnosis, Treatment, and
Prevention
Prevention
Primarily
prevented by limiting exposure to the pathogen
BCG vaccine
provides some protection
Mycobacterial Infections in AIDS
Patients
Mycobacterium
avium-intracellulare is the most common mycobacterial infection among AIDS
patients in the United States
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
Propionibacterium
Small,
Gram-positive rods that are often found on the skin
Propionibacterium
acnes is the species most commonly involved in human infections
Causes much
of the acne of adolescents and young adults
May also be
an opportunistic pathogen
Treatment
often involves the use of antimicrobial drugs though many cases require no
treatment
Nocardia asteroides
Common
inhabitant of soils rich in organic matter
Produces
opportunistic infections in numerous sites
Pulmonary
infections
Develop from
inhalation of the bacteria
Produce
pneumonia
Cutaneous
infections
Result form
introduction of the bacteria into wounds
Produce mycetoma,
a painless, long-lasting infection characterized by swelling, pus production,
and draining sores
Nocardia asteroides
Central
Nervous system infections
Result from
the spread of the bacteria in the blood
Prevention
of nocardial disease involves avoiding exposure to the bacterium in soil
Actinomyces
Normal
member of the surface microbiota of human mucous membranes
Produces
opportunistic infections of the respiratory, gastrointestinal, urinary, and
female genital tracts
Actinomycosis
results when the bacteria enters breaks in the mucous membrane
Disease is
characterized by the formation of many abscesses connected by channels in the
skin or mucous membranes
Diagnosis of
actinomycosis can be difficult because other organisms cause similar diseases
Chapter 20
Pathogenic Gram-Negative Cocci and Bacilli
Gram-Negative Bacteria
Neisseria,
Enterobacteriaceae (E.coli, Klebsiella, Serratia, Proteus, Salmonella, Shigella, Yersinia)
Pasteurella,
Haemophilus, Brucella, Bordetella
Pseudomonas,
Moraxella, Francisella, Legionella
Bacteroides
Gram-Negative Bacteria
Constitute
the largest group of human pathogens
Due in part
to the presence of lipid A in the bacterial cell wall
Triggers
fever, vasodilation, inflammation, shock, and disseminated intravascular coagulation
(blood clots within blood vessels)
Almost every
Gram-negative bacterium that can breach the skin or mucous membranes, grow at
37°C, and evade the immune system can cause disease and
death in humans
Neisseria
Only genus
of Gram-negative cocci that regularly causes diseases in humans
Nonmotile,
aerobic bacteria often arranged as diplococci
Distinguished
from many other Gram-negative pathogens by being oxidase positive
2 species
are pathogenic to humans
The gonococcus, N. gonorrhoeae
The meningococcus, N. meningitides
Neisseria gonorrhoeae
Causes
gonorrhea, a sexually transmitted disease
Gonococci
adhere to epithelial cells of the mucous membranes lining the genital, urinary,
and digestive tracts of humans spreading to deeper tissue as they multiply
Gonorrhea in
men
Usually
symptomatic producing inflammation that causes painful urination and pus-filled
discharge
Gonorrhea in
women
Often
asymptomatic
Can infect
the cervix and other parts of the uterus, including the Fallopian tubes
Can result
in pelvic inflammatory disease (PID)
Can result
in ectopic pregnancy or sterility
Gonococcal
infection of children can occur during childbirth producing inflammation of the
cornea and sometimes blindness
Diagnosis, Treatment, and
Prevention
Diagnosis
Gonorrhea in
men can be identified by the presence of Gram-negative diplococci in pus from
an inflamed penis
Asymptomatic
cases can identified with commercially available genetic probes
Treatment
Complicated
due to resistant gonococcal strains
Broad-spectrum
antimicrobial drugs are often used
Prevention
Most
effective prevention is sexual abstinence
Neisseria meningitidis
Humans are
the only natural carrier of N. meningitides
Can be
member of the normal microbiota of the upper respiratory tract
Causes
life-threatening disease when the bacteria invade the blood or cerebrospinal
fluid
Most common
cause of meningitis in individuals under 20
Respiratory
droplets transmit the bacteria among people living in close contact, especially
students living in dormitories
Meningococcal
meningitis can result in death as early as 6 hours after initial symptoms
Meningococcal
septicemia, blood poisoning, can also be life threatening
Can produce
blood coagulation and the formation of minute hemorrhagic lesions
Diagnosis, Treatment, and
Prevention
Diagnosis
Presence of
Gram-negative diplococci in phagocytes of the central nervous system
Treatment
Penicillin,
administered intravenously, is the drug of choice
Prevention
Eradication
is unlikely due to the presence of asymptomatic carriers
Enterobacteriaceae
Members of
the intestinal microbiota of most animals and humans
Ubiquitous
in water, soil, and decaying vegetation
Enteric
bacteria are the most common Gram-negative pathogens of humans
Coccobacilli
or bacilli
Diagnosis, Treatment, and
Prevention
Diagnosis
Enterobacteriaceae
are cultured using selective and differential media
Commercially
available biochemical tests can rapidly identify enteric bacteria
Treatment
Treatment of
diarrhea involves treating the symptoms with fluid and electrolyte replacement
Antimicrobial
drugs are not usually needed since diarrhea is self-limited
Prevention
Preventing
enteric infections is almost impossible since they are a major component of the
normal microbiota
Good
personal hygiene and proper sewage control are important in limiting the risk
of infection
Enterobacteriaceae Classification
Pathogenic
Enterobacteriaceae are often classified into three groups
Coliforms,
which rapidly ferment lactose, are part of the normal microbiota, and may be
opportunistic pathogens
Noncoliform
opportunists, which do not ferment lactose
True
pathogens
Coliform Opportunistic
Enterobacteriaceae
Aerobic or
facultatively anaerobic, Gram-negative, rod-shaped bacteria
Commonly
found in soil, on plants, and on decaying vegetation
Colonize the
intestinal tracts of animals and humans
Presence of
coliforms in water is indicative of impure water and of poor sewage treatment
Escherichia coli
The most common
and important of the coliforms
Virulent
strains have genes located on virulence plasmids that allow the bacteria to
colonize human tissue
Gastroenteritis
is the most common disease associated with E.coli
Often
mediated by exotoxins that produce the symptoms associated with gastroenteritis
Most common
cause of non-nosocomial urinary tract infections
E.coli
O157:H7 is the most prevalent strain of pathogenic E.coli in developed
countries
Causes
diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome, a severe kidney
disorder
Most
epidemics associated with undercooked ground beef or unpasteurized milk or
juice
Produces a
Shiga-like toxin that aids in the virulence of the bacteria
Klebsiella
Found in the
digestive and respiratory systems of humans and animals
Can cause
opportunistic infections
Produce a
capsule that protect the bacteria from phagocytosis
K.pneumoniae
is the most commonly isolated pathogenic species
Causes
pneumonia
May be
involved in bacteremia, meningitis, wound infections, UTIs
Serratia
Produce a
red pigment when grown at room temperature
Can grow on
catheters, in saline solutions, and other hospital supplies
Can cause
life-threatening opportunistic infections in the urinary and respiratory tracts
of immunocompromised patients
Difficult to
treat due to resistance to various antimicrobial drugs
Noncoliform Opportunistic
Enterobacteriaceae
Include a
number of opportunistic pathogens
Proteus
Gram-negative,
facultative anaerobe
Proteus
mirabilis is the most common species associated with human disease
Can cause
urinary tract infections in patients with long-term urinary catheters
Infection-induced
kidney stones can develop
Resistant to
many antimicrobial drugs
Truly Pathogenic Enterobacteriaceae
Important
members of this group almost always pathogenic due to numerous virulence
factors
All are lactose negative in sugar fermentation studies
Salmonella
Gram-negative,
motile, bacilli
Found in the
intestines and feces of most birds, reptiles, and mammals
Most
salmonella infections in humans are the result of consumption of food
contaminated with animal feces
Poultry and
eggs are particularly common sources of Salmonella
2 important
pathogens
S.typhimurium-causes salmonellosis
S.typhi-causes
typhoid fever
Salmonella typhi
Humans are
the only host
Causes
typhoid fever
Infection
occurs via ingestion of food or water contaminated with sewage containing
bacteria from carriers
Bacteria can
pass through the intestines into the bloodstream and into the liver, spleen,
bone marrow, and gall bladder
Bacteria
from the gall bladder can reinfect the intestines, producing gastroenteritis
and a recurrence of bacteremia
In some
patients the bacteria ulcerate and perforate the intestinal wall causing
peritonitis
Treatment is through the use of antimicrobial drugs
Vaccines are
available to provide temporary protection to individuals traveling to areas
where typhoid fever is endemic
Shigella
Gram-negative,
nonmotile bacteria
Primarily a
parasite of the digestive tract of humans
Produce a
diarrhea-inducing enterotoxin
Cause a
severe form of dysentery called shigellosis
4
well-defined species
S.boydii
S.sonnei-most
commonly isolated in industrialized nations
S.
flexneri-most commonly isolated in developing countries
S.dysenteriae-produces
a more serious disease than the other species
Shigellosis
is treated with fluid and electrolyte replacement
Yersinia
Normal
pathogens of animals
3 important
species
Y.enterocolitica
Acquired via consumption of food or water contaminated
with animal feces
Causes inflammation of the intestinal tract
Y.pseudotuberculosis
Similar to Y.enterocolitica
but produces a less severe intestinal inflammation
Y.pestis
Bubonic plague-characterized by high fever and swollen,
painful lymph nodes called buboes
Pneumonic
plague-rapidly developing infection of the lungs
Diagnosis, Treatment, and
Prevention
Diagnosis
and treatment must be rapid due to the fast progression and deadliness of the
plague
Diagnosis
Characteristic
symptoms are usually sufficient for diagnosis
Treatment
Many antibacterial drugs are effective against Yersinia
Pasteurellaceae
Most are
small, nonmotile, facultative anaerobes
Require heme
or cytochromes for growth = fastidious
Pasteurella
Normal
microbiota in the oral and nasopharyngeal cavities of animals such as cats and
dogs
Humans are
typically infected via animal bites and scratches or via inhalation of aerosols
from animals
Most cases
produce localized inflammation and swelling of the lymph nodes at the site of
infection
Diagnosis is
by the identification of the bacteria in specimens collected from the patient
Antibacterial
drugs are an effective treatment
Haemophilus
Small,
pleomorphic bacilli
Obligate
parasites due to their requirement of heme and NAD+ for growth
Colonize the
mucous membranes of humans and some animals
Haemophilus influenzae
Most strains
have a polysaccharide capsule that resists phagocytosis and is used in
classification of the bacteria
H.influenzae
type b is the most significant
Was the most
common form of meningitis in infants prior to the use of an effective vaccine
Can cause a
number of other diseases in young children
Use of the Hib vaccine has eliminated much of the
disease caused by H.influenzae b
Other
strains still cause a variety of diseases
Other Species of Haemophilus
H.ducreyi
Causes a
sexually transmitted disease
Results in the
formation of a genital ulcer called a chancroid
Often
asymptomatic in women but in men the chancroid is often painful
H.aphrophilus
causes a rare type of endocarditis
Other
species primarily cause opportunistic infections
Brucella
Small,
nonmotile, aerobic coccobacilli
Can infect
animals or humans
Causes
brucellosis
Often an
asymptomatic or mild disease
Illness is
characterized by a fluctuating fever
Humans
become infected by coming in contact with contaminated dairy products or from
infected animal parts
Bordetella
Small,
aerobic, nonmotile coccobacillus
B.
pertussis is the most important
Causes
pertussis, also called whopping cough
Most cases
of disease are in children
Produce
various adhesins and toxins, including pertussis toxin, that mediate the disease
Bacteria are
first inhaled in aerosols and multiply in epithelial cells
Then
progress through four stages of disease
Diagnosis, Treatment, and
Prevention
Diagnosis
Symptoms of
pertussis are usually diagnostic
Treatment
Primarily
supportive
Antibacterial
drugs have little effect on the course of the disease
Prevention
Immunization with the DPT vaccine
Cases in the
United States have increased due to a refusal by some parents to have their
children immunized
Pseudomonads
Gram-negative,
aerobic bacilli
Ubiquitous
in soil, decaying organic matter, and almost every moist environment
Problematic
in hospitals because they can be found in numerous locations
Opportunistic
pathogens
Pseudomonas aeruginosa
Rarely part
of the normal microbiota
Opportunistic
pathogen of immunocompromised patients
Can colonize
almost every organ and system and result in various diseases
Often
infects the lungs of cystic fibrosis patients
The bacteria
form a biofilm that protects them from phagocytosis
Increases the
likelihood of death in these patients
Diagnosis
can be difficult as the presence of bacteria may represent contamination of the
sample
Treatment is
difficult because P. aeruginosa is resistant to many antibacterial drugs
Moraxella
Aerobic,
short, plump, bacilli
Moraxella
catarrhalis can cause opportunistic infections of the sinuses, bronchi,
ears, and lungs
Originally
called Neisseria catarrhalis. Virginia Branham did extensive cell-wall
and fatty acid analysis to distinguish this organism. Her work resulted in a
new genus Branhamella.
Type species was B. catarrhalis.
However, her
work led others to do more work. Branhamella was found to really belong in the
genus Moraxella.
M. catarrhalis may cause clinical syndromes indistinguishable
from those caused by gonococci, and so it is important to distinguish these
organisms from one another. Many strains produce ί-lactamase
Francisella tularensis
Nonmotile,
strictly aerobic coccobacillus
Found living
in water as an intracellular parasite of animals
Causes the
zoonotic disease tularemia
Spread to
humans occurs mainly through the bite of an infected tick or by contact with an
infected animal
The bacteria
can spread through unbroken skin and mucous membranes, making it highly infectious
Tularemia
produces symptoms common to other bacterial and viral diseases and may be
misdiagnosed
A vaccine is
available to at risk individuals
Preventing
infection is done by avoiding the major reservoirs of the bacteria
Legionella pneumophila
Aerobic,
slender, pleomorphic bacteria
Universal
inhabitants of water
Humans
acquire the disease by inhaling the bacteria in aerosols from various water
sources
Intracellular
parasites
Causes
Legionnaires disease
Results in
pneumonia
Immunocompromised
individuals are more susceptible
Elimination
of the bacteria is not feasible but reducing their number is a successful
control measure
Pathogenic, Gram-Negative,
Anaerobic Bacilli
Anaerobic
bacteria are the predominant microbiota of the gastrointestinal, urinary,
reproductive, and lower respiratory tracts
Important
for human health
Inhibit the
growth of most pathogens, synthesize necessary vitamins, and aid in digestion
of food
Cause
disease only when they are introduced into other parts of the body by trauma or
surgery
Bacteroides
Normal
microbiota of the intestinal tract and the upper respiratory tract
Bacteroides
fragilis is the most important
Can be
involved in abdominal infections, genital infections in women, and wound
infections of the skin
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Chapter 21
Miscellaneous Bacterial Pathogens: Mycoplasmas,
Rickettsias, Chlamydias, Spirochetes, and Slightly Curved Bacilli
Miscellanous Bacterial Pathogens
Stain pink in
a Gram stain but differ from typical Gram-negative organisms
Have
different morphology, growth habits, or reproductive strategies
Traditionally
discussed separately due to their unique features
Mycoplasmas
Smallest
free-living microbes
Lack
cytochromes, enzymes of the Krebs cycle, and cell walls
Can colonize
the mucous membranes of the respiratory and urinary tracts
Mycoplasma pneumoniae
Attaches
specifically to receptors located at the bases of cilia on epithelial cells
lin