Download USMLE Step 1 Web Prep — Medically Important Bacteria, Part 4

USMLE Step 1 Web Prep — Medically Important Bacteria, Part 4
131125 >>> 0:00:00
SLIDE 1 of 20
Table II-26. Comparison of the Genera Rickettsia, Chlamydia, and
Mycoplasma with Typical Bacteria
Typical
bacteria
(S. aureus)
Chlamydia
Rickettsia
Mycoplasma
Obligate
intracellular
parasite?
Most no
Yes
Yes
No
Make ATP?
Normal ATP
No ATP
Limited ATP
Normal ATP
Peptidoglycan
layer in cell
envelope?
Normal
peptidoglycan
Modified*
peptidoglycan
Normal
peptidoglycan
No
peptidoglycan
*Chlamydial peptidoglycan lacks muramic acid and is considered by some as
modified, by others as absent.
131126 >>> 0:01:25
SLIDE 2 of 20
Table II-27. Infections Caused by Rickettsias and Close Relatives*
Arthropod Reservoir
Group disease
Bacterium
vector
host
Spotted Fevers:
Rocky Mountain Spotted
Fever
Rickettsia rickettsii
Ticks
Rickettsialpox
Rickettsia akari
Mites
Dogs,
rodents,
ticks**
Mice
Typhus Group:
Epidemic
Rickettsia prowazekii
Endemic
Rickettsia typhi
Rickettsia
tsutsugamushi
Scrub
Others:
Human
louse
Fleas
Mites
Humans
Rodents
Rodents
Q fever
Coxiella burnetii
None
Cattle,
sheep, goats
Trench fever, bacillary
angiomatosis
Cat Scratch
Fever,Septicemia in
homeless
Human granulocytic or
monocytic Ehrlichiosis*
Bartonella quintana
(Rochalimaea)
Human
louse
Humans
Bartonella henselae
None
(Rochalimaea)
Ehrlichia
Cats
Ixodes ticks
?
+?
*New tick-borne rickettsial disease caused by Ehrlichia
**Vertical transmission in arthropod ovum
NOTE: Co-infections from a single tick infected with more than one agent may occur:
N East USA: Babesia and B. burgdorferi
N Central USA: B. burgdorferi and Ehrlichia
131127 >>> 0:03:29
SLIDE 3 of 20
Genus: Rickettsia (Rickettsia rickettsii)
 Obligate intracellular bacteria that divide by binary fission (cannot make sufficient
ATP)
 Not seen well on gram-stained smear (too small); but have gram-negative cell
envelope
 Cross reaction of Rickettsia antigens with OX strains of P. vulgaris (Weil-Felix
reaction)
 Reservoir: Small wild rodents and larger wild and domestic animals (dogs)
 Transmission: Hard ticks
 Pathogenesis: Rickettsias invades endothelial lining of capillaries, causing
vasculitis
 Rocky Mountain Spotted Fever: Headache, fever, malaise, myalgias, toxicity,
vomiting, and confusion, rash (maculopapular
petechial) starts (by day 6 of illness)
on ankles and wrists and then spreads to the trunk, palms, soles, and face
(centripetal rash)
 Treatment: Doxycycline
131130 >>> 0:04:53
SLIDE 4 of 20
Genus: Rickettsia (Rickettsia rickettsii)
 Obligate intracellular bacteria that divide by binary
fission (cannot make sufficient ATP)
 Not seen well on gram-stained smear (too small); but
have gram-negative cell envelope
 Cross reaction of Rickettsia antigens with OX strains of
P. vulgaris (Weil-Felix reaction)
 Reservoir: Small wild rodents and larger wild and
domestic animals (dogs)
 Transmission: Hard ticks
 Pathogenesis: Rickettsias invades endothelial lining of
capillaries, causing vasculitis
 Rocky Mountain Spotted Fever: Headache, fever,
malaise, myalgias, toxicity, vomiting, and confusion, rash
(maculopapular
petechial) starts (by day 6 of illness)
on ankles and wrists and then spreads to the trunk,
palms, soles, and face (centripetal rash)
 Treatment: Doxycycline
131131 >>> 0:05:56
SLIDE 5 of 20
Genus: Coxiella(Coxiella burnetii)
 Obligate intracellular bacterium
 Not seen well on gram-stained smear
 Reservoir: Domestic livestock: pregnant animals have high titers
 Transmission: Inhalation of aerosols of urine, feces, amniotic fluid, or placental
tissue
 Survives drying: can be infective miles away
 No significant arthropod vector in human infection
 Q fever: Febrile illness with NO RASH, atypical pneumonia with hepatitis
 Treatment: Doxycycline or erythromycin
131132 >>> 0:07:09
SLIDE 6 of 20
Genus: Ehrlichia





Reservoir: ticks and deer
Transmitted by the Lone Star Tick (Amblyoma)
Infects monocytes and macrophages
Human monocytic ehrlichiosis
Similar to Rocky Mountain Spotted Fever
131135 >>> 0:07:41
SLIDE 7 of 20
Genus: Chlamydia (Chlamydia trachomatis)
 Obligate intracellular bacterium; cannot make ATP
 Infective form: inactive, extracellular elementary body
 Found in cells as metabolically active, replicating
reticulate bodies
 Not seen on gram stain; peptidoglycan layer lacks
muramic acid
 Reservoir: Human genital tract and eyes
 Transmission: Sexual contact and at birth. Trachoma is
transmitted by hand-to-eye contact
 Trachoma: Serotypes A, B, Ba, and C
 STD: Serotypes D-K (This is the most common
bacterial STD in U.S; Herpes and HPV are more
common)
 Nongonococcal urethritis, cervicitis, PID and major
portion of infertility
 Inclusion conjunctivitis
 Inclusion conjunctivitis and/or pneumonia in
neonates/infants (staccato cough)
 Lymphogranuloma venereum: (Serotypes L1, 2, 3)
STD, swollen lymph nodes (bubo) leading to genital
elephantiasis in late stages
131140 >>> 0:09:22
SLIDE 8 of 20
Genus: Chlamydia (Chlamydia trachomatis)
 Obligate intracellular bacterium; cannot make ATP
 Infective form: inactive, extracellular elementary
body
 Found in cells as metabolically active, replicating
reticulate bodies
 Not seen on gram stain; peptidoglycan layer lacks
muramic acid
 Reservoir: Human genital tract and eyes
 Transmission: Sexual contact and at birth.
Trachoma is transmitted by hand-to-eye contact
 Trachoma: Serotypes A, B, Ba, and C
 STD: Serotypes D-K (This is the most common
bacterial STD in U.S; Herpes and HPV are more
common)
 Nongonococcal urethritis, cervicitis, PID and major
portion of infertility
 Inclusion conjunctivitis
 Inclusion conjunctivitis and/or pneumonia in
neonates/infants (staccato cough)
 Lymphogranuloma venereum: (Serotypes L1, 2, 3)
STD, swollen lymph nodes (bubo) leading to genital
elephantiasis in late stages
131145 >>> 0:10:00
SLIDE 9 of 20
Genus: Chlamydia (Chlamydia
trachomatis)
 Obligate intracellular bacterium; cannot make
ATP
 Infective form: inactive, extracellular
elementary body
 Found in cells as metabolically active,
replicating reticulate bodies
 Not seen on gram stain; peptidoglycan layer
lacks muramic acid
 Reservoir: Human genital tract and eyes
 Transmission: Sexual contact and at birth.
Trachoma is transmitted by hand-to-eye contact
 Trachoma: Serotypes A, B, Ba, and C
 STD: Serotypes D-K (This is the most
common bacterial STD in U.S; Herpes and HPV
are more common)
 Nongonococcal urethritis, cervicitis, PID and
major portion of infertility
 Inclusion conjunctivitis
 Inclusion conjunctivitis and/or pneumonia in
neonates/infants (staccato cough)
 Lymphogranuloma venereum: (Serotypes L1,
2, 3) STD, swollen lymph nodes (bubo) leading
to genital elephantiasis in late stages
131150 >>> 0:10:59
SLIDE 10 of 20
Genus: Chlamydia (Chlamydia trachomatis)
 Obligate intracellular bacterium; cannot make ATP
 Infective form: inactive, extracellular elementary body
 Found in cells as metabolically active, replicating
reticulate bodies
 Not seen on gram stain; peptidoglycan layer lacks
muramic acid
 Reservoir: Human genital tract and eyes
 Transmission: Sexual contact and at birth. Trachoma is
transmitted by hand-to-eye contact
 Trachoma: Serotypes A, B, Ba, and C
 STD: Serotypes D-K (This is the most common
bacterial STD in U.S; Herpes and HPV are more
common)
 Nongonococcal urethritis, cervicitis, PID and major
portion of infertility
 Inclusion conjunctivitis
 Inclusion conjunctivitis and/or pneumonia in
neonates/infants (staccato cough)
 Lymphogranuloma venereum: (Serotypes L1, 2, 3)
STD, swollen lymph nodes (bubo) leading to genital
elephantiasis in late stages
131155 >>> 0:11:35
SLIDE 11 of 20
Genus: Chlamydia (Chlamydia trachomatis)
 Obligate intracellular bacterium; cannot make ATP
 Infective form: inactive, extracellular elementary body
 Found in cells as metabolically active, replicating
reticulate bodies
 Not seen on gram stain; peptidoglycan layer lacks
muramic acid
 Reservoir: Human genital tract and eyes
 Transmission: Sexual contact and at birth. Trachoma is
transmitted by hand-to-eye contact
 Trachoma: Serotypes A, B, Ba, and C
 STD: Serotypes D-K (This is the most common
bacterial STD in U.S; Herpes and HPV are more
common)
 Nongonococcal urethritis, cervicitis, PID and major
portion of infertility
 Inclusion conjunctivitis
 Inclusion conjunctivitis and/or pneumonia in
neonates/infants (staccato cough)
 Lymphogranuloma venereum: (Serotypes L1, 2, 3)
STD, swollen lymph nodes (bubo) leading to genital
elephantiasis in late stages
131160 >>> 0:12:05
SLIDE 12 of 20
Genus: Chlamydia (Chlamydia trachomatis)
Lab Diagnosis
 DNA probes in US
 Cytoplasmic inclusions seen on Giemsa-, iodine-, or
fluorescent-antibody-stained smear or scrapings
 Serodiagnosis: complement fixation or
microimmunofluorescence test
131165 >>> 0:12:15
SLIDE 13 of 20
Genus: Chlamydia (Chlamydia trachomatis)
Lab Diagnosis
 DNA probes in US
 Cytoplasmic inclusions seen on Giemsa-, iodine-, or
fluorescent-antibody-stained smear or scrapings
 Serodiagnosis: complement fixation or
microimmunofluorescence test
131170 >>> 0:12:39
SLIDE 14 of 20
Genus: Chlamydia (Chlamydia trachomatis)
Lab Diagnosis
 DNA probes in US
 Cytoplasmic inclusions seen on Giemsa-, iodine-, or
fluorescent-antibody-stained smear or scrapings
 Serodiagnosis: complement fixation or
microimmunofluorescence test
131175 >>> 0:12:42
SLIDE 15 of 20
Genus: Chlamydia (Chlamydia
trachomatis)
Lab Diagnosis
 DNA probes in US
 Cytoplasmic inclusions seen on Giemsa-,
iodine-, or fluorescent-antibody-stained smear or
scrapings
 Serodiagnosis: complement fixation or
microimmunofluorescence test
131180 >>> 0:12:57
SLIDE 16 of 20
Genus: Chlamydia (Chlamydia trachomatis)
Lab Diagnosis
 DNA probes in US
 Cytoplasmic inclusions seen on Giemsa-, iodine-, or
fluorescent-antibody-stained smear or scrapings
 Serodiagnosis: complement fixation or
microimmunofluorescence test
131181 >>> 0:13:44
SLIDE 17 of 20
Chlamydia pneumoniae
 Respiratory infections. Atypical pneumonia (single lobe) is very common
 Infect smooth muscle, endothelial cells of coronary artery and macrophages
 Potential association with atherosclerosis
131182 >>> 0:14:13
SLIDE 18 of 20
Chlamydia psittaci
 Chlamydia that is associated with birds
 No glycogen in the inclusion bodies
 Reservoir: Birds- parrots (psittacine), turkeys, others
 Transmission: Dust of dried bird secretions and feces
 Psittacosis (Atypical Pneumonia) :Cough may be absent; when present, nonproductive initially then scant mucopurulent
 Cytoplasmic inclusions seen on Giemsa or fluorescent-antibody-stained sputum or
biopsy
 Organism can be isolated from sputum in tissue culture, but this is rarely done
 Serodiagnosis by complement fixation test
131185 >>> 0:15:04
SLIDE 19 of 20
Genus: Mycoplasma (Mycoplasma
pneumoniae)
 Smallest free-living (extracellular) bacteria
 No cell wall and not seen on gram-stained smear
 Membrane with cholesterol but does not synthesize
cholesterol; requires cholesterol for in vitro culture
 Reservoir: Human respiratory tract
 Transmission: Respiratory droplets. Close contact:
families, military recruits, medical school classes, college
dorms
 Fried egg colonies on Mycoplasma or Eaton’s media
(require sterols) in 10 days
 Positive cold agglutinins (autoantibody to red blood
cells) test is not very specific and positive in only 65%
 Complement fixation test for antibodies to Mycoplasma
pneumoniae is more specific
 Treatment: Erythromycin, azithromycin, clarithromycin.
No cephalosporins nor penicillin
131186 >>> 0:17:39
SLIDE 20 of 20
Ureaplasma urealyticum




Belongs to the Mycoplasma family
Produces a urease
Urethritis (half of the non-Neisserial, non-Chlamydial), prostatitis
Can cause renal calculi