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transient bacteremia
minor mucocutaneous breaches allowing acces by normal microbiota or pathogens
- brushing/flossing
- BM, hemorrhoids
- endoscopy
- GI infection
- UTI
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intermittent bactermia
showering of bloodstream from established localized but severe infection
- staphylococcal abscess
- pneumococcal pnemonia
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continuous bacteremia
source of infection with direct access to blood
- infective endocarditis
- IV catheter/line infection
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Microbial products stimulate host response in sepsis
- Pathogen-associated molecular patterns: (PAMPs)
- Endotoxin/ lipopolysaccharide (LPS) in Gram -
- teichoic acids in gram +
- peptidoglycan in most bacteria
- glucans in fungi
Superantigens: toxic shock syndrome toxins (TSST), produced by some staphylococcal and streptococcal species and strains
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Host response in sepsis
- complement cascade --> inflammation
- kinins--> hypotension
- coagulation cascade --> DIC
- Cellular responses --> stimulation of pattern recognition receptors by PAMPs, cytokines --> fever, innate and adaptive immune responses
- hyperstimulation may be follow by hypoactivity
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microbes commonly isolated from "true positive " BC's
- Escherichia coli and other enterobacteriaceae
- staphylococci
- streptococci
- pseudomonas
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most common isolates from nosocomial infections
- coagulase negative staphylococci including staphylococcus epidermidis
- staphylococcus aureus
- enterococci
- candida
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multiorgan failure
- acidosis- blood pH <7.35
- lung- pulmonary edema, cyanosis
- kidney- oliguria, anuria
- lier- jaundice
- heart- CHF, septic shock usually characterized by high cardiac output at start
- CNS- altered mental status
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contamination of blood draw
- common on skin: can contaminate sample
- staphylococci
- streptococci
- pseudomonas
higher probability of IV being contaminated
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neonate infections
- Vaginal microbes: during delivery
- group B strep (streptococcus agalactia)
- -leading cause of neonatal sepsis and meningitis, can have neurological deficits after
- e coli
- enterococcus spp
- neisseria gonorrhoeae
- chalmydia trachomatis
- salmonella
- transplacental transmission: with or w/o symptoms
- listeria monocytogenes (foodborne)
- toxoplasma gondii
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granulocytes
- Neutrophils: PMN
- responsible against infection
- produced in bone marrow, migrate to tissues where needed
- phagocytic, form pus, first to inflammation via chemotaxis
- eosinophils: allergies and parasites
- basophils: WBC releases histamine
- natural modulator of inflammatory response
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lymphocyte
- Natural Killer cells: patrol body for pathogens
- binds to enemy cells and releases perforins, granzymes. destroys compromised host cells
- T cells: mature in the thymus
- recognize antigens presented by APC's
- Helper T cells: nonspecific defense and humoral and cellular immunity
- recognize antigen fragments from APC's with MHCII proteins, secrete interleukins that activate B, Tc, and NK cells
- Cytotoxic T cells: cellular immunity, directly attach and destroy enemy cells
- recognized MHCI cells
- B cells: identifies pathogens by its antibodies, serve as APC, produces antibodies in response
- B cell receptor (immunoglobulin, antibody) is secreted
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Innate immunity
- immediate response, initial defense
- non-specific, no memory, not enhanced by immunization
- includes cellular components- neutrophils, macrophages, dendritic cells, NK cells and humoral components - complement, cytokines, antimicrobial peptides
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Adaptive immunity
- slower response, antigen specific
- enhanced by immunization, generates memory, rapid response on subsequent exposures
- includes T and B lymphocytes and antibodies
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Monocytes/macrophages
- migrate to tissues and become macrophages and includes dendritic cells
- antigen presenting cells in T cell activation by phagocytizing microbes, processing antigen, and presenting it
- MHC class II
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Plasma cells
- develop from B cells that have been activated by helper T cells
- synthesize and secrete antibodies
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Dendritic cells
- branched, mobile APC's of the skin, mucous membranes and lymphatic tissues
- internalize antigen, migrate to lymph node and present to Th and Tc cells
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MHC proteins
- proteins on APC surface that are unique to each person labeling those cells as yours
- MHCI: found on surface of all nucleated host cells
- recognized by CD8 T lymphocytes
- recognized by cytotoxic T cells
- presents endogenous cytosolic antigens (viral antigens, tumor antigens)
- MHCII: found on surface of host APC's
- presents exogenous antigens in endocytic pathway (phagocyosed particle antigens)
- recognized by CD4 T lymphocytes
- recognized by T helper cells
- foreign antibodies
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Active vs passive immunity
- Natrually acquired active is infection
- Naturally acquired passive is transplacental, colostrum, or receiving ab
- Artificial active is vaccine
- Artificial passive is ab injections, immunoglbulin tx for autoimmune,
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Immunoglobulin
- IgG: 4 subclasses
- predominant in serum, also in secretions, only one that crosses placenta
- monomeric
- IgM: appears early in immune response, dominant one in it
- strong agglutinating and complement fixation abilities
- can be pentameric
- IgA: 2 subclasses
- found in mucosal secretions and surfaces as well as serum
- dimeric or large polymers
- IgE: monomer
- attaches to mast cells and basophils
- stimulates histamine release
- important in parasite immunity
- IdD: monomer
- activation of B cells by antigens
- antibodies exert effects via
- neutralization: blocking viral adhesion, inactivating bacterial toxin
- opsonization: promoting phagocytosis
- complement activation: causing lysis via mAC, promoting phagocytosis
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inflammation
- microbe stimulates macrophages and activates complement
- macrophage produces cytokines, chemokines, and other mediators
- complement activation results in production of C3a, C5a - both anaphylatoxins and chemotaxins
- cardinal signs are redness, swelling, heat, and pain
- begins with vasoconstriction, followed by increase in vascular permeability
- upregulation of surface adhesion molecules on endothelium and PMN
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complement
- microbe stimulates macrophages and activates complement
- proteins that promote phagocytosis and cytolysis of pathogens
- activate and attract PMN's and macrophages
- stimulate basophils and mast cells to secrete inflammatory chemicals
- 3 pathways: classical, alternative, lectin
- classical- antibody molecule, specific immunity, Ag-Ab exposes complement binding sites
- alternative- C3b binds to targets, triggers cascade, non-specific, spontaneous
- lectin- plasma proteins bind to carbs (microbe surface), sets off cascade leading to C3b production
- products of complement activation
- C3a and C5a- anaphylatoxins (mast cell degredation, histamine release) and chemotaxins (attracts WBC's)
- C3b- opsonization - opsonin coats particle and facilitates uptake by phagocytes
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integirin
protein that links outside of cell with its interior
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interleukin
produced mainly by T cells, and macrophages to stimulate other leukocytes
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epitope
- found on surface of antigen
- determines specificity of antibody reaction and where antibody binds
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therapeutic index
vancomycin and aminoglycosides have toxic level close to therapeutic level
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antibiotic spectrum of activity
 - Narrow spectrum: isoniazid
- broad: amoxicillin
- tetracycline
- chloamphenicol
- very broad: metronidazole
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Sensitivity
- Proportion of individuals with disease that are correctly identified
- TP/ (TP+FN)
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Specificity
- Proportion of individuals without disease correctly identified
- TN/ (TN +FP)
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Positive predicative value
Negative predictive value
- Reliability of a positive test to identify diseased individual
- TP / All positives
- Negative is reverse
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cultures
- some obligate intracellular microbes may be cultured in host cells in tissue culture
- some viruses
- chalmydia
- syphilis can grow in rabbit
- mycobacterium leprae (leprosy) grow in armadillos
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agglutination tests
- streptococcus pneumoniae- urinary antigen
- cryptococcal antigen- csf, serum
- legionella- urinary antigen
- c diff toxin- stool
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limulus amebocyte lysate (LAL) assays
- For gram neg LPS endotoxin or fungal beta glucan
- non-invasive, serum
- PAMPs are targets of innate immune
- gram neg bacteria or fungi including CANDIDA
- sensitivity up to 90
- specificity 84-100
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Gram pos/neg
- Positive: bacteria
- staphylococcus
- steptococcus
- bacilli
- clostridium
- listeria
- bacillus
- Neg: bacteria
- e. coli
- salmonella
- shigell
- enterobacteriaceae
- pseudomonas
- heliobacter
- NEISSERIA GONORRHOEAE
- MENINGITIS
- MORAXELLA CATARRHALIS
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Visualization
- microscopy, istopathology, staining, bright field microscopy
- gram stain for routine bacteria
- ziehl-neelsen stain for acid-fast mycobacteria
- silver stain for fungi
- KOH prep for fungi
- saline wet mount for motile trichomonas vaginalis
- auramine stain for mycobacteria
- calcofluor white stain for fungie
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Prevalence
- Rate at which a disease is found in a population
- TP + FN / everything
- PPV is higher for a test with higher prevalence. NPV is higher for lower prevalence
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Clostridium difficile
- Anaerobic gram pos sporulating rod
- found in soil, water, some normal gut microbiota
- clinical range: for C diff
- Asymptomatic
- enteric infection- diarrhea, cramps, fever
- pseudomembranous colitis- severe colitis, bloody diarrhea, ulcers, perfs, toxic megacolon, life threatening
- Diagnose: c diff
- PMN's in stool from inflammation
- aerobic stool culture negative for other causes
- anaerobic stool culture when done right may be positive
- Leukocytosis (elevated WBC)
- Stool sample pos for c diff toxins by ELISA or toxin genes by PCR
- Treatment: for C diff diarrhea
- discontinue previous abx
- add new treatment with another abx- metronidazole for mild to moderate, vancomycin for more severe (but save for MRSA)
- add probiotic therapy
- Treatment: for C diff with pseudomembranous colitis
- donor stool transplant
- partial or complete colectomy
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abx targets
- Cell wall synthesis: targets peptidoglycan cell wall that we don't have
- d-cycloserine
- vancomycin
- bacitracin
- penicillins
- cephalosporins
- cephamycins
- Protein synthesis: 50S inhibitors and 30S inhibitors
- erythromycin
- choramphenoicol
- cindamycin
- lincoycin
- 30- tetracyclines
- aminoglycosides- gentamiciin, kanamycin, streptomycin, tobramycin
- RNA polymerase: rifampicin
- DNA synthesis: metronidazole
- cytoplasmic membrane/phospholipid: polymyxins
- Folate synthesis: TMP/sulfa
- Fatty acid synthesis: isoniazid
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Threatening bacteria
- Urgent: clostridium difficile
- carbapenem- resistant enterobacteriaceae
- drug resistant neisseria gonorrhoeae
- Concerning: vancomycin resistant staphyloccoccus aureus
- erthromycin resistant group A strep
- clindamycin resistant group B strep
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UTI - agents of descending infection
- hematogenous spread: from blood
- staphylococcus aureus
- candida albicans
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Lower UTI vs upper UTI
- cystitis: of the bladder
- dysuria
- frequency
- urgency
- sometimes suprapubic pain
- pyelonephritis: kidneys
- flank and CVA pain
- fever sometimes
- perineal pain in men (prostatisi)
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epitope
- found on surface of antigen
- determines specificity of Ab rxn and where it will bind
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abx information
- Aminoglycosides: low therapeutic index
- Vancomycin: low therapeutic index
- attacks cell wall synthesis
- Isoniazid: narrow range
- fatty acid synthesis
- Amoxicillin: broad range
- tetracycline: broad range
- chloramphenicol: broad range
- 50S inhibitor, affects protein synthesis
- metronidazole: very broad range
- used to treat c diff
- attacks DNA synthesis
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microbe info
- clostridium difficile: main cause of abx
- associated diarrhea
- ANAEROBIC GRAM POSITIVE SPORULATING ROD
- Staphylococcus aureus: can cause ADD
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Pulmonary aspergillosis
25-30% have no symptoms usually due to neutropenia and lack of host response
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UTI ascending infection
- E coli- gram negative rod
- other: enterobacteriaceae
- proteus spp
- profidencia
- kelbsiella
- serratia
- Vaginal colonizers
- staphylococcos saprophyticus
- enterococcus
- candida albicans
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