Exam Review 1 Flashcards
What are the 3 types of exotoxins?
- A-B toxins (cholera, tetanus toxins); 2. Membrane disrupting toxins (hemolysins, alpha toxin); 3. Superantigens (TSS)
What kind of bacteria can make spores?
Gram positive (gram negatives can’t make spores!)
What is LPS?
Essential component of Gram Negative bacterial survival and replication; Messes stuff up in the human body!
How is peptidoglycan made?
- Synthesis of water soluble, nucleotide-linked precursor in the cytoplasm; 2. Transfer of precursors to the membrane lipid; 3. addition of prefabricated block to the glycan chain; 4. Cross-linking to adjacent chain via transpeptidation
What are the typical bacterial reservoirs?
Endogenous (normal flora): skin, colon, oropharynx; Exogenous: water, air, food, ticks
What is the difference in the outbreak curve between common source outbreak and propagated epidemic?
Onset epidemic begins almost immediately, has a sharp peak, and comes back down (this is due to common source like food poisoning); propagated epidemic is more parabolic
Define: Infection
The ability of an organism to invade host tissue, replicate, and stimulate an immune response
Define: Intoxication
Agents that cause disease by elaboration of toxin sometimes without the presence of viable bacteria
Define: Incubatory stage of human infection
Subject incubating but w/out symptoms of disease - subject may be infectious
Define: Latent stage of human infection
Pathogen persists in tissue w/out symptoms for much of the time (eg HIV, TB, HSV)
What is horizontal transmission?
Transmission from infected individual to others through air, water, food, contact vectors, etc
What is vertical transmission?
Transmission to offspring through ovum, sperm, placenta, milk, contact
What is required for pathogen to establish infection?
Opportunity, adherence to and colonization of host surfaces, evasion of host defense mechanisms, adaptation to the host environment, invasion of tissue both locally or systemically (dissemination), host response (often responsible for tissue damage)
What are the differences in hemolysis for the streps?
S. Pyogenes is b hemolytic (complete), viridans strep is a hemolytic, enterocci are g hemolytic (no hemolysis)
Which strep grows in 6.5% NaCl? Bile esculin? Which is bacitracin susceptible? Optochin susceptible?
6.5% NaCl and bile: E. Faecalis; Bile: Nonenterococcal Gp D; nothing: strep viridans; Bacitracin susceptible: S pyogenes; Optochin: S pneumo
What is Group A Strep?
Strep pyogenes - what you think of as Strep Throat
What makes Group A strep virulent?
Hyaluronic acid capsule (anti-phagocytic); Gram + (peptidoglycan); Pili M protein type (VERY important in causing disease)
What does M Protein do?
Antigenic variations in M proteins are used to type Group A strep; strains lacking M protein are avirulent; M protein is anti-phagocytic and inhibits activation of complement via the alternate pathway
What are clinical features of Group A Strep pharyngitis?
Sore throat, sudden onset, fever, pain with swallowing, headache, lymphadenitis, tonsillar exudates, soft palate petechiae; sequelae can include abscess, sepsis, metastatic seeding
What findings are NOT suggestive of Group A Strep?
Conjunctivitis, nasal discharge, cough, diarrhea
How is Group A Strep diagnosed?
Culture is gold standard, rapid strep antigen kids can be used (treat if positive, confirm if negative), anti-streptolysin O reflects past (not present) infection
What is the epidemiology of Group A Strep Pharyngitis?
Humans are natural reservoir, mostly seen in 5-15 year olds, most common in temperate/cold climates (occurs in water, early spring), asymptomatic carriage is common, spread through droplets or nasal secretions (can also be foodborne)
What is the pathogenesis of Group A Strep?
Adhere to epithelial cells using adhesins (protein F1 and lipoteichoic acid), susceptibility to infection is determined by the presence or absence of type-specific antibody to M protein
What are nonsupperative sequelae of Group A Strep pharyngitis?
Rheumatic fever - carditis, polyarthritis, erythema marginatum, subcutaneous nodules, chorea; glomulonephritis
What is streptococcal TSS?
Pyrogenic exotoxins A-C have been implicated; similar mechanism of action to staph TSS (superantigen), but frequently also includes presence of infection; presentations w/ necrotizing fasciitis appear to be linked w/ specific M types
How is S pyogenes treated?
Penicillin; clindamycin can be added in invasive infections; soft tissue infections often require debridement; prophylactic antibiotics can also be given; NO VACCINE
What is strep pneumonaie/pneumococcus?
Gram + lancent-shaped diplococci; form a hemolytic colonies on blood agar; encapsulated; naturally competent (uptakes naked DNA from environment)
What is the epidemiology of strep pneumo?
Primarily causes diseases in the very young or very old; colonizes the nasopharynx of 5-10% of adults and 20-40% of children; transmitted by extensive close contact; often occurs in winter; mortality remains high
How does pneumococcal pneumonia invade?
Increased capsule expression, pneumolysin (cholesterol-dependent cytotoxin present in most invasive strains); adhere to alveolar type II cells and initiate an inflammatory response due to the cell wall; also has secretory IgA protease
What are the differences between the pneumococcal vaccines?
Children should get the polysaccharide protein conjugate vaccine (T cell dependent, more effective in infants
How do you identify the difference b/w staph and strep w/out a Gram stain?
Staph is catalase +, strep is catalase -
What are rifamycins?
Aka Rifampin! They block mRNA synthesis by binding to the bacterial DNA-dependent RNA polymerase; used in combo w/ other antimicrobials (only used alone as prophylaxis for N. Meningitidis)
How is sensitivity to a particular antibiotic determined?
Sensitivity is determined by the interpretation of the minimum inhibitory concentration
What is the minimum inhibitory concentration of antibiotics?
The lowest concentration of antibiotic that prevents visible bacterial growth after 24h of incubation in the appropriate culture media; it is organism and drug specific
What does susceptible mean?
Implies that the concentration of antibiotic that can be achieved at the site of infection is >MIC
What are the common causes of community acquired pneumonia?
1 is strep pneumo; “atypical organisms” are mycoplasma, chlamydia, etc; can also be viral
What can cause CAP in early childhood?
Group B Strep, gram negative enteric bacilli, cytomegalovirus, Listeria, HSV, Pertussis, RSV
What are weird exposures that relate to CAP?
Bats: histoplasma capsulatum; birds: chlamydophila psittaci, cryptococcus neoformans; contact with farm animals or outdoor cats: coxiella burnetii; exposure to rabbits: francisella tularensis; travel to southwest USA: coccidiodes immitis
What are common complaints in pneumonia?
Dyspnea (shortness of breath), fever, cough (productive or not), chills, chest pain, myalgia, headache
What are common physical exam findings in pneumonia?
Rales (clicking, rattling, and crackling noise), tactile fremitus (palpable vibration), decreased breath sounds, rhonchi (course rattling), grunting, nasal flaring
What are the major risk factors for pneumococcal pneumonia?
Alcohol, smoking, asthma, hyposplenism or splenectomy, immunocompromised, antecedent influenza, defects in humoral immunity
What are risk factors for resistance to beta lactams?
Age >65, recently taking antibiotics w/in 3 months, alcoholism, immune suppression, multiple medical co-morbidities, exposure to child in daycare
How do you diagnose S. Pneumoniae?
Blood culture, urine antigen test, sputum culture (hard to get from a child); antimicrobial susceptibility testing is key!
How do you treat s. Pneumonia in a child?
Ampicillin or ceftriaxone (if resistant)
How do you treat S. Pneumonia in an adult?
Macrolide; if co-morbidity, fluoroquinolone or beta-lactam plus macrolide
What is different about mycoplasma?
Doesn’t have a cell wall; membrane contains sterols not present in other bacteria; lab cultures are rarely done (diagnosis usually by serology)
What is a vector?
An animal, most often an arthropod, which picks
up a pathogen and transmits it to a susceptible
individual
What is a reservoir?
an ecological niche where a pathogen
survives, lives and multiples (can serve as a
source of infection)