Microbiology
Microbiology
1.
Principles
of bacteriologic lab tests -- specific culture growth requirements:
(pg. 192, 1999 First Aid).
2.
Dermatologic
manifestations of bacterial and viral infections:
a. Primary Syphilis -- painless chancre
b. Secondary syphilis -- maculopapular rash, condylomata lata (flat topped papules -- located at the anus and in skin folds where heat and moisture exist).
c. Rocky Mountain Spotted Fever -- stage 1: erythema chronicum migrans (a red rash that spreads, leaving a clear center -- bulls-eye rash).
d. Menningococcemia --intravascular multiplication of N. meningitidis in the blood can result in a petechial rash (minute hemorrhagic spots the size of a pin that do not blanch when pressed). The rash can enlarge if the organisms multiply in the blood to the leading to fulminant meningoccemia (Waterhouse-Friderichsen syndrome--bilateral hemorrhage into the adrenals).
e. Herpes Zoster (varicella zoster) Virus -- vesicular rash (chicken-pox) that appear on the back of the head and ears then spread to the face, neck, trunk, and extremities. The distinguishing feature from other rashes (small pox) is that lesions will be at different stages (whereas small pox lesions are concentrated on the extremities and are all in the same stage). The lesion are very pruritic (itchy).
f. Coxsackievirus --Coxsackie A: herpangina -- fever, sore throat, and small red-based vesicles over the back of the throat. Hand-foot-mouth disease -- (coxsackie A-16) eruptions of small pearly, gray vesicles on the fingers, toes, palms, and soles often accompanied by painful vesicles and ulceration of the buccal mucous membranes and the tongue with slight fever; disease lasts 4 to 7 days.
3. Common sexually transmitted diseases: (pg. 191 1999 First Aid)
4.
Viral
Gastroenteritis in the pediatric and adult population:
a. Rotavirus -- Group A: cause most infantile disease (most between 6 - 24 months) -- 30-60% of infantile diarrhea. Occurrence is during the winter months (SW to NE spread). Diarrhea, vomiting, and fever for 5-7 days.
Group B: associated with large
epidemic of severe diarrhea (3-5 days) in Adults in
b. Enteric Adenovirus (serotypes 40 & 41) -- 2nd most common cause of diarrhea in children.
Symptoms consist of prolonged diarrhea lasting 5-12 days, vomiting and fever.
c.
Epidemics of vomiting and diarrhea in older children and adults, associated with shellfish,
food or water.
5. Common causes of community-acquired and nosocomial pneumonia: (pg. 190 First Aid)
6. Infections that cause congenital/neonatal complications: ToRCHeS -- all of these organisms can cross the blood-placenta barrier.
a. Toxoplasma gondii -- can cause chorioretinitis, blindness, seizures, mental retardation,
microcephaly, encephalitis, and stillbirth if infections is acquired early in gestation.
b. Rubella (Rubivirus) -- risk is greatest with infection early in fetal development. Heart: PDA,
VSD, and pulmonary artery stenosis. Eye: cataracts, chorioretinitis. CNS: mental
retardation, microcephaly, deafness.
c. CMV -- most common viral cause of mental retardation. Also cause microcephaly, deafness,
seizures.
d. Herpes -- neonate is often infected during delivery. Manifestations vary -- vesicular lesions
or CNS
involvement.
HIV
e. Syphilis -- high rate of mortality (still-birth, spontaneous abortion, and neonatal death).
Survivors will go on to develop Early of Late congenital syphilis.
1. Early: occurs w/in 2 years and is like severe adult secondary syphilis -- widespread
rash and condyloma latum. "Snuffles" -- mucous membrane involvement with
runny nose.
2. Late: similar to adult tertiary syphilis except cardiovascular involvement rarely
occurs.
7. Parasites that
frequently cause disease in the U.S.
a. Entamoeba
histolytica - flask-shaped ulcer in large intestine -
amoebic liver abcesses (liver paste)
b. Trichomonas
vaginalis - strawberry cervix, twitching motility STD
c. Giardia lamblia - non-bloody diarrhea, malabsorption,
trophozoite is “old man with moustache”
d. Cryptosporidium
parvum - diarrhea in immunocompromised
e. Toxoplasma
- acutely like mono. In utero -
hydrocephalus, chorioretinitis, brain calcifications
also
in immunocompromised
f. Pneumocystis
carinii - immunocompromised
g. Enterobius
vermicularis (Pinworm)
h. Ascaris lumbricoides - lives in intestine, pathology in lungs; Toxocara canis (dog Ascaris)
8. Parasites that cause
disease more commonly outside U.S.
a. Trypanosoma
brucei - Africa - sleeping sickness, Winterbottom’s sign
b. Trypanosoma
cruzi - S. America - reduviid
bug, Chaga’s disese, arrhythmias, CHF
c. Leishmania
tropica (Asia) and mexicana
(C. and S. America) - sandfly, cutaneous ulcers
1. L. braziliensis
(C. and S. America) - also mucocutaneous involvement
2. L. donovani
(Asia and S. America) - visceral involvement
d. Plasmodium malariae
(least common), falciparum (most common, most
deadly), vivax and ovale (both have latent liver phase) - Anopheles mosquito
e. Chlonorchis
sinensis - SE Asia - cholangiocarcinoma
f. Paragonimus
westermani - SE Asia - causes hemoptysis,
CNS involvement in 1%
g. Schistosomas
- all cause liver granulomata, cirrhosis
1. S. haemotobium
- Africa - adults in bladder-squamous cell carcinoma,
no Katayama fever
2. S. japonicum
- SE Asia - adults in superior mesenteric vein, Katayama fever
3. S. mansoni
- all but developed world - adults in inferior mesenteric vein, Katayama fever
h. Onchocerca
volvulus - Africa and S. America - black fly, river
blindness
i.
Wucheria bancrofti/Brujia malayi - Aedes/Culex mosquitos, elephantiasis
*Note: All other parasites seen
worldwide, but can easily be avoided
9. Herpes Simplex
(HSV-1) encephalitis is the most common cause of viral encephalitis
a. Brain tissue swelling, cell death
(medial temporal lobe lesion)
b. Fever, focal neurological
abnormalities, mental status changes
c. Treat with Acyclovir
(one of the few treatable viral encephalitides)
10. Tests for diagnosis of
viral infections
a. Culture (gold standard) - examine
for cytopathic effect (CPE)
- takes a few days to two weeks
1. Can add red cells to check for hemagglutinins
2. 100% specificity (for showing a
virus is there, not specific ID), poor sensitivity
3. Without antigen detection (shell
vial technique) can only make presumptive ID of virus
b. Antigen detection - can do on cell
specimens from patient or on culture (shell vial technique)
1. Immunofluorescence
assay - Ab labeled w/ fluorescing compound - use UV
microscope
2. ELISA, immunoperoxidase
- Ab labeled w/ enzyme that changes substrate color
c. Serology for IgG (four-fold rise of
two specimensis diagnostic), IgM
- single result is diagnostic
d. DNA probes/PCR
e. Electron microscopy for ID of viral
particles - expensive, insensitive
11. Know the microscopic
appearance of organisms - too difficult to summarize here, easier to see
12. Fever patterns - a. Roseola (HHV-6) - very high fever for 3-5 days, comes down
w/ a rash for 1-3 days
b. Plasmodia - spiking fevers- P. malariae (q 72 hrs.); vivax, ovale (q 48 hrs.), falciparum
(varies)
c. Brucellosis
- undulant fever - fever increases to peak in evening, declines to normal by
morning
Immunology
1.
Some Immunologic Tests – ELISA – see above
a.
Coombs test – anti-Ig Ab is added to red cells to
look for agglutination
·
Direct -
looks for Ab bound to rbc’s
·
indirect –
looks for Ab in serum – serum added to naked rbc’s, then anti-Ig added
b.
Complement-fixation
tests – utilize Ig’s ability to fix complement to
look for various antigens
2.
Immune
complex diseases (Type III hypersensitivity)
a.
Serum
sickness – circulating foreign Ag leads to Ab formation and deposition of Ag-Ab
complexes (in arteries, glomeruli, synovia) that activate complement to cause tissue damage
(arthritis, rash, fever)
b.
Arthus reaction – vasculitis from Ag injection into
skin – Ag-Ab complexes form at injection site
c.
SLE – DNA-anti-DNA
complexes in kidneys, vessels to cause glomerulonephritis,
vasculitis
d.
Post-streptococcal
GN – Strep Ag deposits in kidney, Ab binds (Arthus-type reaction)
A. VDJ recombination
1. the heavy chain of the immunoglobulin is made up of a variable (V), diversity (D), and junctional/joining (J) segment.
2. The gene possesses greater than 200 V, 20 D, and 6 J coding sequences.
3. During B cell development the sequences between the V, D, and J sequences are removed via recombination to provide for a single open reading frame.
4. Heavy chain recombination precedes light chain rearrangement.
5. The light chains can utilize either the kappa or lambda genes for generation of a functional Ig protein.
6. Light chain possesses V and J segments: No D
7. During B cell development, the sequence between the V segment (more than 100 coding sequences) and the J segment (1 or more J segments, depending on the light chain) is removed via recombination to provide for a single open reading frame.
B. Class switching
1. Only the heavy chain
2. The isotype is defined by those sequences (known as the constant region, i.e. codes for IgG, IgM etc.) that are invariable and downstream of the VDJ recombination.
3. Isotype switching utilizes recombination to remove such constant region sequences so as to allow the VDJ sequence to be placed upstream of different C regions.
C. Affinity maturation
1. After the B cells have been activated and class switched, a portion are found that migrate to the spleen and lymph nodes. Two things happen:
a) rapid proliferation, every 6-12 hours=1 division
b) B cells sustain somatic mutation at Ig chains.
2. Aim of this process is to create Ig with higher affinity for antigen
3. Those B cells that lose affinity for antigen are eliminated.
A. Immune system evasion and antigenic variation
1. Inhibition of complement activation
a) Capsules with sialic acid residues that prohibit alternative pathway activation
b) Group B and Group A streptococcal C5a-ase
2. Presence of antiphagocytic factors
a) Capsular polysaccharide
b) M-proteins
3. Genetic variation of surface proteins
a) Pilli of GC
4. Inhibit phagolysosome fusion- mycobacteria
5.
Scavenge reactive oxygen species- glycolipid of M. leprae
6.
Block killing- hemolysins
of L monocytogenes
A.
Transient
physiologic hypogammaglobulinemia occurs in infants
between the ages of approximately 3 and 6
months. Although infants born
with adult levels of placentally transferred IgG, a
low level of IgG results from:
1.
The disappearance of maternal antibody which has a
half life of 22-28 days
2.
The infants low early rate of synthesis of secretable immunoglobulins
B.
Congenital agammaglobulinemia (Bruton’s
disease) is a sex-linked (male) disorder that affects infants between the
ages of 5 and 6 months. These patients
have an apparently normal thymus and CMI.
1.
Clinical features include:
a)
Recurrent pyogenic
infections
b)
digestive tract disorders
2.
Cause—may occur in the transition from pre-B to B
cells and involves the loss of a tyrosine kinase
gene. The pre-B cells are normal
3.
Diagnosis is made by noting the absence of tonsils
(on examination), germinal centers (on lymph node biopsy), and B cells (on
peripheral smear) Serum immunoglobulins levels of less that 10% also suggest the
disease.
4.
Treatment—passive transfer of adult serum immunoglobulin can be administered prophylactically
to diminish infections.
C.
Dysgammaglobulinemia.
Patients of varying age present with a selective immunoglobulin
class deficiency.
1.
Diagnosis—Most patients have decreased IgA levels with 1:600-800 of those patients having levels
of less than 5mg/dl
2.
Immunologic features
include:
a)
Loss of mucosal surface
protection
b)
Failure of IgA bearing
cells to differentiate into secreting plasma cells, although their numbers are
normal
c)
increased susceptibility to autoimmune
disease
D.
Congenital thymic aplasia (DiGeorge syndrome) is characterized by hypocalcemia, tetany and an
absence of T cells
1.
Cause—Not hereditary. It is caused by unknown intrauterine injury
to the third and fourth pharyngeal pouches that occurs between the third and
sixth weeks of gestation
2.
Clinical Features:
a)
Thymus and parotid glands are not developed
b)
Depressed CMI permits
opportunistic infections (Candida, Pneumocystis,
viruses)
c)
Apparently normal germinal centers, plasma cells,
and serum immunoglobulin
3.
Treatment—These patients die early
a)
Vaccination with live vaccines (measles) is
contraindicated
b)
The transplantation of fetal thymic
tissue is experimental and may be complicated by a graft-versus-host reaction.
E.
Chronic mucocutaneous candidiasis is
a highly specific T cell disorder that is characterized by an absence of
immunity to Candida.
Patients have apparently normal T cell absolute numbers and
functions. Approximately 50% of patients
with this disorder also have endocrine dysfunctions
(hypothyroidism)
F.
Wiskott-Aldrich
syndrome is a sex-linked (male) disorder occurring mainly in children. The syndrome has three main features 1) thrombocytopenia (bleeding), eczema, and recurrent
infections. An increased incidence of lymphoreticular malignancies or lymphomas occur.
1.
Immunologic features
include:
a)
Depressed CMI and a low
serum IgM level, but normal IgG and IgA levels
b)
Poor response to bacterial capsular polysaccharide
antigens.
2.
Cause—May be an absence of specific glycoprotein receptors on T cells and platelets.
3.
Treatment—Bone marrow transplantation may be effective
G.
Severe
combined immunodeficiency disease (SCID) is a rare disorder characterized by a genetic
defect in stem cells that results in the absence of the thymus gland and t and
b cells. Affected children are extremely
susceptible to infections and have a very short life span.
1.
Immunologic features—A
deficiency in the enzyme adenosine deaminase (ADA) occurs in 50% of patients. This deficiency results in the accumulation
of toxic deoxyadenosine triphosphate
(DATP), which inhibits ribonucleotide
reductase and prevents DNA synthesis. A mutation in the g chain of the IL-2
receptor gene is found in other patients with SCID
2.
Treatment—Gene therapy with ADA
is experimental
H.
Chronic granulomatous disease (CGD)
results from a genetic defect in the nicotimamide adenine
dinucleotide phosphate (NADPH)
oxidase system in neutrophils. Patients are susceptible to infections by age
2 years, especially organisms of low virulence.
1.
Immunologic
features—Neutrophils bactericidal activity (respiratory burst) is defective because
of depressed NADPH oxidase,
superoxide dismutase
activity and decreased hydrogen peroxide levels
2.
Diagnosis is based on failure of neutrophils and
macrophages to reduce a nitroblue tetrazolium
dye
3.
Treatment with IFN-g has
been successful
I.
Absence of
spleen can be due to surgical removal after a trauma, treatment of certain hematologic diseases or as a result of infarction in sickle
cell disease.
1.
Increased susceptibility to encapsulated organisms
such as Streptococcus pneumoniae
2.
The spleen is required for induction of protective humoral immune responses to the thymus-independent capsular
polysaccharide antigens of such organisms.
1.
Familial
inheritance
a)
Many alleles of class I and class II molecules are
present at each locus on chromosome 6.
b)
Haplotypes from both
parents are inherited and expressed codominantly.
2.
Disease
associations
a)
DR4 Rheumatoid arthritis
b)
DR3, DR4 IDDM
c)
DR3 Sjogren’s syndrome
d)
B27 ankylosing spondylitis
3.
Transplant
compatibility
a)
Matching the donor and recipient at the HLA locus improves graft acceptance
b)
Both the donor and recipient are typed for HLA profiles using DNA sequence analysis of the HLA genes or more than 200 specific anti-HLA antisera
c)
HLA antigens on allographs stimulate recipient CD4+ T cells while respond
by secreting cytokines and by inducing adhesion molecules
(1)
IL-2 activates CD8+ T cells to a state of cytotoxicity, thus releasing effector
molecules such as perforins
(2)
IFN-g
activates monocytes/macrophages to expresses delayed
type hypersensitivity, resulting in increased lysosomal
activity, phagocytosis, respiratory burst and release of TNF-a
(3)
Activated selectins,
integrins, intercellular adhesion molecules (ICAM)
and vascular cell adhesion molecules (VCAM) promote
leukocyte extravasion into the graft bed.
d)
Acute
rejection
(1)
Within weeks
e)
Chronic
rejection
(1)
Episodic bouts of rejection, occurring months to
years after transplantation
f)
Hyperacute rejection
(1) Within minutes—graft never takes because of pre-existing sensitivity
1. Penicillin
2. Procaine
3. Insect venom
4. Pollen
5. Molds
6. Foreign serum
7. Fungal spores
8. House dust
9. Animal dander
1. Excess IgE antibody is produced and binds avidly via its FC domain to its receptor on the surface of mast cells and basophils
2. When antigen is reintroduced into the sensitized host, it binds to and aggregates several cell-bound IgE antibody molecules, forming the complex
3. The resulting membrane perturbation causes degranulation of the mast cells and release of histamine, leukotrienes, serotonin, bradykinin, etc.
4. These agents rapidly contract smooth muscle, increase vascular permeability and secretions, change coagulability, and induce hypotension
1. A hyposensitive state is achieved by repeated injection of the agent into subliminal doses
2. Parenteral exposure favors the synthesis of IgG which combines avidly with the allergen in the circulation, thus blocking union with cell-associated IgE and mediator release
1. Occur if the antigen persists in the tissues and continues to stimulate host reactivity
2. Chronic stimulation by intracellular organisms releases chemotactic agents (e.g. IL-1, IL-8) leading to an inflammatory cell influx
3. IL-4 and IFN-g promote the retention of macrophages and cause the fusion of monocytes at the site, leading to an epithelioid cell granuloma derived from macrophages, histocytes, and epithelioid cells
B. Foreign body vs. immune
C. Caseating versus non-caseating
D. Common causes
1. Live attenuated vaccines permit replication in the hose, increasing antigenic stimulation. Weakened so as to not cause illness, but still stimulate immune system
2. Killed vaccines have been inactivated. Multiple doses must be given and adjuvants might be required
a) Adjuvants are substances added to increase immunogenicity (aluminium hydroxide gel)
3. Recombinant vaccines requires identification of an epitope and synthesis of the antigen
1. Phagocytosis
2. Cytokine production
3. Antigen presenting cell
4. Principle effector of CMI—Activated by antigen-stimulated T-cells to more efficiently perform microbicidal functions
5. Participate in humoral immune responses, because they bind opsonized particles much more avidly that non-opsonized particles
1. Lack the specific TCR for antigen recognition
2. Kill target cells that display decreased expression of self class I MHC molecule or cells with specific IgG