Clinical ID Flashcards
viruses
- 20-30 nm
- obligate intracellular
- dependent on host cell metabolism for replication
- classified by the nucleic acid content of their core and shape of their protein capsid or coat
- cause acute illnesses
- capable of lifelong latency and of long term reactivation or of giving rise to chronic disease
- ex. ebola, herpes
chlamydiae
- 200-100 nm
- obligate intracellular
- Can cause GU infections, conjunctivitis, respiratory infections & STDs
- obligate intracellular pathogens that divide by binary fission, are susceptible to antibiotics, but lack certain cell structures
rickettsiae
- 300-1200 nm
- obligate intracellular
- Transmitted by insect vectors (lice, ticks, mites) and can cause Rocky Mountain Spotted Fever, Q Fever, ehrlichiosis &scrub typhus
- obligate intracellular pathogens that divide by binary fission, are susceptible to antibiotics, but lack certain cell structures
mycoplasmas
- 125-350nm
- Tiniest free-living organism known and can cause atypical pneumonia & nongonococcal urethritis
- obligate intracellular pathogens that divide by binary fission, are susceptible to antibiotics, but lack certain cell structures
fungi imperfecti
2-200um
-Possess thick cell walls
-Growth patterns include budding yeast and slender tubes called hyphae
-Hyphae produce fruiting bodies called conidia
Infect superficial layers of skin (Tinea)
-Deep fungal infections can spread systemically (some species limited to geographic regions eg. Blastomyces, -Histoplasma, Coccidioides)
-Opportunistic fungi that normally colonize the body may cause disease in immunosuppressed patients such as lethal pneumonia & tissue necrosis
protozoa
- 1-50 um
- Parasitic, single-celled organisms with motility, pliable plasma membranes and complex cytoplasmic organelles
- Can be transmitted:
- sexually (Trichomonas)
- via the fecal-oral route (Giardia)
- by blood – sucking insects (Leishmania)
- by contact with infected cats or eating cyst ridden, undercooked meat (Toxoplasma gondii)
helminths
- 3mm-10m
- Parasitic worms that are highly differentiated multicellular organisms
- Complex life cycles
- Most are dependent on an intermediary host or vector for asexual reproduction
- Disease is often caused by host inflammatory responses (ex. Schistosomiasis) and in proportion to the number of infecting organisms
- 3 classes: roundworms, flatworms, and flukes
prions
- composed of modified host proteins (prion protein)
- cause transmissible spongiform encephalopathies
- assoc with neurodegenerative diseases such as kuru, mad cow disease CJD
bacteriophages, plasmids, and transposons
- mobile genetic elements that encode bacterial virulence factors = plasmids and transposons
- include adhesins, toxins or enzymes that confer antibiotic resistance
- they can infect bacteria and incorporat themselves into their genome
bacteria
- prokaryotes that lack nuclei and ER
- capable of synthesizing own DNA, RNA and proteins but rely heavily on host for favorable growth conditions
- grow both extracellularly and intracellularly
round worms
nematodes
- collagenous tegument and non-segmented structure (hookworms & Trichinella)
- larvae penetrate skin (often through bare feet), are carried to lungs, go through respiratory tract to mouth, are swallowed, and eventually reach the small intestine. Cycle takes about a week.
flatworms (cestodes)
- gutless worms
- heads sprout a ribbon of flat segments (tapeworms)
flukes (trematodes)
-primitive leaflike worms with syncytial integument (schistosomes
ectoparasites
- Arthropods (lice, ticks, bedbugs, fleas)
- Attach and live on skin
- May be vectors for other pathogens such as deer ticks transmitting Lyme disease, babesia and ehrlichia while the dog ticks are harmless
breeches to host barriers by commensal bacteria
- skin bacteria can cause infection after etering through cuts
- GI system- virulent organisms can penetrate the intact mucosal barriers and cause infection
spread and dissemination of mibcrobes
- The major manifestations of infectious disease may arise at sites distant from those of entry (eg. Chickenpox and measles enter through airways but manifest as skin rash
- Bloodstream invasion is a common event for both non-virulent and virulent microbes.
- The placental-fetal route is an important mode of transmission.
how microorganisms cause disease
- direct cell death
- endo/exotoxins
- secondary response through host immune response
mechanisms of viral injury
- Viruses inhibit host cell DNA, RNA or protein
synthesis. - Viral proteins insert into host cell’s plasma
membrane. - Viruses replicate efficiently and lyse host cells.
- Viral proteins on the surface of the host cells are
recognized by immune systems and host
lymphocytes attack the viral infected cells. - Viruses damage cells involved in secondary
infections. - Viral killing of one cell type causes the death
of another. - Slow virus infection and latency.
- In addition to causing injury, viruses induce cell
proliferation and transformation which can lead
to neoplasms.
bacterial virulence
Depends on ability of bacteria to adhere, invade, & deliver toxic moieties
bacterial adherence
- Adhesins are bacterial surface molecules that bind to host cells
- lipoteichoic acids, M proteins of S. pyogenes
- Fimbriae or pili on surface of gram-negative bacteria
- Entry into macrophages – directed by receptors that recognize antibodies or complement on surface of bacteria
- Entry into epithelial cells – dependent on interactions between bacterial surface and epithelial cell receptor such as integrins
bacterial endotoxin
Lipopolysaccharide (LPS): structural component of outer cell wall in gram negative bacteria; induces host cytokine release to cause fever, activate macrophages & B cells
bacterial exotoxin
Toxins released by bacteria that interfere with cellular metabolism & allow bacteria to outgrow competing bacteria (ex. Diphtheria toxin, Vibrio cholera toxin, anthrax toxin)
immune evasion by microbes
1) Being inaccessible to the immune response
2) Resisting complement-mediated lysis and phagocytosis
3) Varying or shedding antigens
4) Causing specific & non-specific immuosuppression
spectrum of inflammatory responses to infection
A. Suppurative (Polymorphonuclear) Inflammation
B. Mononuclear and Granulomatous Inflammation
C. Cytopathic-Cytoproliferative Inflammation
D. Necrotizing Inflammation
E. Chronic Inflammation and Scarring
suppurative (polymorphonuclear) inflammation
- Caused by pyogenic bacteria
- Characterized by increased vascular permeability and leukocytic infiltration by neutrophils
- Bacteria recruit neutrophils:
- Directly by release of chemoattractive peptides
- Indirectly by release of endotoxin which stimulates macrophages to release cytokines that chemoattract neutrophils
Mononuclear and Granulomatous Inflammation
- Diffuse, predominantly mononuclear interstitial infiltrates form in response to pathogens
- Include lymphocytes (syphilis chancres) and macrophages (mycobacterium granulomas) depending on the pathogen and host responses
- Granulomatous inflammation occurs when aggregates of altered macrophages form or fuse to form giant cells
Cytopathic-Cytoproliferative Inflammation
- Reactions characteristic of virus-mediated damage to individual host cells in the absence of host inflammatory responses
- Result in:
- Inclusion bodies (CMV)
- Polykaryons following cell fusion (measles)
- Blisters due to cell damage (Herpesvirus)
- Morphologic lesions (venereal warts/HPV)
- Dysplastic changes & cancers
Necrotizing Inflammation
- Rapid and severe tissue damage with predominant cell death in the absence of inflammatory infiltrates
- Caused by uncontrolled viral infections, secreted bacterial toxins or cytolysis of host cells in protozoa infections (eg. Necrotizing fasciitis caused by Group A streptococcus)
Chronic Inflammation and Scarring
- Chronic inflammation can lead to either complete healing or to extensive scarring
- Several inert organism cause damage by the scarring response (ex. schistosome eggs)
poliovirus
virus
obligate intracellular
= poliomyelitis
-Chlamydia trachomatis
= trachoma
clamydiae
obligate intracellular
-rickettsia prowazekii
== typhus fever
obligate intracellular
-mycoplasma pneumoniae
-extracellular
== atypical pneumonia
staphylococcus epidermidis
bacteria
= wound infection,
cutaneous
vibrio cholerae
bacteria
cholera
mucosal
streptoccocus pneumoniae
bacteria
extracellular
pneumonia
mycobacterium tuberculosis
bacteria
tuberculosis
facultative intracellular
trichophyton sp
fungi imperfecti
-cutaneouse
= tinea pedis
canadida albicans
fungi imperfecta
-mucosal
= thrush
sporothrix schenckii
fungi imperfecta
-extracellular
= sporotrichosis
histoplasma capsulation
fungi imperfecta
-facultative intracellular
= histoplasmosis
giardia lambi
protozoa
-mucosal
= giardiasis
-
tyrpanosoma gambiense
protozoa
-extracellular
= sleeping sickness
trypanosome cruzi
protozoa
-facultative intracellular
= chagas disease
leishmania donovani
protozoa
obligate intracellular
= kala-azar
enterobias vermicularis
helminths
-mucosal
= oxyuriasis
wuchereria bancrofti
helminths
-extracellular
= filariasis
trichinella spiralis
helminths
-intracellular
= trichinosis
