MMSC 428 Final 2024 (100% Accurate Answers)
Staphylococcus aureus correct answers -gram positive cocci in clusters
-facultative aerobe (prefers O2)
-halotonic
-ferment mannitol (yellow on MSA plate)
-catalase +
-*coagulase +*
-clumping factor +
-medium sized b-hemolytic white colonies
-serological tests for TSST-1 and DNA probes are the best diagnosis methods
-most clinically significant staphylococcus
-important cause of nosocomial infection
staphylococcus aureus virulence mechanisms correct answers -protein A: virulent cell wall
protein that binds to IgG antibodies and prevents them from being active
-hemolysins: produce B-hemolysis of RBCs
-exfoliatin: causes epidermal layer of skin to peel off
-pyrogenic toxin: causes fever
-toxic shock syndrome toxin 1 (TSST-1): super antigen over stimulates the T cells and produces
cytokine storm
-panton valentine leukocidin (PVL): lyses WBCs, platelets and RBCs
-staphycoagulase: activates fibrin to cause clotting and prevent WBCs from reaching the bacteria
-hyaluronidase: breaks down hyaluronic acid in tissue to spread bacteria
-lipases & proteases: destroy host tissues and spread bacteria
staphylococcus aureus clinical manifestations correct answers -furuncle: large raised suppurative
dome shaped boil due to infection of oil gland or hail follicle
-carbuncle: a furuncle that progresses and infects a deeper level of the skin, infection causes
systemic symptoms of fever and chills
-impetigo: bullous (>5 mm) domed fluid filled pustules surrounded by zone of erythema, mainly
seen in children
-cellulitis: inflammatory infection of connective tissue
-staphylococcal scalded skin syndrome (SSS): release of exfoliatin exotoxin causes exfoliative
dermatitis with red peeling skin that resembles a burn, mainly in children and newborns
-toxic shock syndrome (TSS): release of TSST-1 and enterotoxin B cause systemic symptoms
including fever, liver and kidney damage, vomiting, diarrhea, muscle aches and rash, menstrual
and non-menstrual forms
-endocarditis
-intoxication food poisoning: food is contaminated with enterotoxins (no actual bacteria) and
causes vomiting and diarrhea
-nosocomial infections: wound infections, osteomyelitis, biofilm on body implants
-childhood infections: SIDS, head and neck infection
staphylococcus aureus drug resistance correct answers -penicillin resistant due to acquiring beta-
lactamase genes
,-MRSA: methicillin resistant staphylococcus aureus
-VISA: vancomycin intermediate staphylococcus aureus
-VRSA: vancomycin resistance staphylococcus aureus
staphylococcus epidermidis correct answers -gram positive cocci in clusters
-nonmotile
-facultative anaerobe (prefer O2)
-smooth, round, non-hemolytic white colonies on BSA
-staphycoagulase - (indicated by the fact that it is nonhemolytic)
-clumping factor -
-PYR -
-ODC d+
-is part of the normal biota, only causes opportunistic infections
-hospital acquired infections: biofilms, septicemia, osteomyelitis, catheter associated UTI
staphylococcus lugdunensis correct answers -gram positive cocci in clusters
-staphycoagulase -
-clumping factor d+
-PYR +
-*ODC +* (very strong and fast)
-mannitol -
-nonhemolytic
-oxacillin resistant (mecA gene)
-highly virulent
-equally clinically significant as Staphylococcus aureus, just isolated less frequently
-community and hospital acquired infections: skin abscess, meningitis, septicemia, septic shock,
UTI
-endocarditis: very aggressive and fatal
staphylococci characteristics correct answers -gram positive cocci that grow in clusters
-*catalase +* (good to differentiate from streptococcus)
-non-motile, lack flagella
-facultative anaerobes (prefer O2)
-lysostaphin sensitive
-glucose fermentation +
-modified oxidase test -
-bacitracin resistant
-produce a sticky glycocolyx that allow them to establish a biofilm
-important causes of hospital acquired infections
micrococcus correct answers -gram positive cocci in pairs, tetrads or clumps
-related to staphylococci, but less clinically significant
-*lysostaphin resistant* (would only be able to lyse staphylococcus cells)
-glucose fermentation -
-modified oxidase (cytochrome C oxidase) +
-bacitracin sensitive
,streptococcus pyogenes (group A strep) correct answers -gram positive cocci in chains
-lancefield group A cell wall antigens
-aerotolerant anaerobe (fermentation only)
-modified oxidase test -
-catalase -
-*PYR +* (the only B-hemolytic strep that is)
-B-hemolytic
-bacitracin sensitive
-fastidious
-requires blood to be cultured
-small, transparent, dry colonies
-the most virulent streptococci
-usually detected using antigen detection or serology
streptococcus pyogenes (group A strep) virulence mechanisms correct answers -streptolysin O:
hemolysin that is active in anaerobic conditions, produces B-hemolysis
-streptolysin S: hemolysin that is active in aerobic conditions, produces B-hemolysis
-M protein: virulent protein that aids attachment to host cells and evades WBC phagocytosis
-hyaluronic acid capsule: weakly immunogenic, body does not fight it off
-pili: adhesion
-streptokinase: anti-clotting factor that breaks down clots so bacteria can spread
-hyaluronidase: breaks down skin and allows more bacterial spreading
-streptodornoase: breaks down extracellular DNA from lysed host cells and uses it to make its
own nucleic acids
streptococcus pyogenes (group A strep) clinical manifestations correct answers -pharyngitis:
strep throat with malaise, fever, headache, nausea and vomiting, mainly seen in children under
15 due to protective M-protein antibodies that adults have
-scarlet fever: untreated strep throat leads to release of erythrogenic toxins and breaks down
RBCs causing rash and damage to blood vessels that causes "strawberry tongue", mainly seen in
developing countries where strep does not get treated
-purpural fever (child bed fever): infection of infant that is inoculated with bacteria during birth
and leads to bacteremia/ sepsis
-impetigo: nonbullous (<5 mm) lesions that leak and then crust over, mainly seen on the face of
children
-erysipelas: infection of dermis and subcutaneous tissue that causes inflamed lesions on the skin,
mainly in elderly individuals
-necrotizing fasciitis: "flesh eating bacteria" skin infection that rapidly progresses to
inflammation and necrosis of skin, fat and fascia membrane around muscle
-wound and burn infections, cellulitis
-streptococcal toxic shock syndrome: cold like symptoms progress to flu-like symptoms and a
fatal pneumonia
-sinusitis and OME common in children
streptococcus pyogenes culture correct answers -throat swab for sample
, -techniques are not well standardized between clinics
-SBA: can be used but normal biota would over populate
-selective strep agar (SSA): inhibits normal biota
Post-streptococcal sequelae (streptococcus pyogenes/ group A strep) correct answers -acute
glomerulonephritis: antibodies bind to streptococcus pyogenes in the blood and form large
immune complexes which become trapped in the small vessels of the kidneys, body attempts to
clear our the immune complexes using complement, WBCs, etc. and causes a type 3
hypersensitivity response that damages the kidneys
-acute rheumatic fever: body produces antibodies against M proteins that cross react and attack
antigens on the heart, leading to a type 1 hypersensitivity response that causes valve damage
-both treated with penicillin
streptococcus algalactaiae (group B strep) correct answers -gram positive cocci in chains
-aerotolerant anaerobe (fermentation only)
-lancefield group B cell wall antigens
-*CAMP test +*
-hippurate hydrolysis +
-fastidious
-requires blood to be cultured
-small colonies with small zone of B-hemolysis
-normal biota of vaginal mucosa
-weakly virulent, only able to infect newborns (important cause of perinatal infections)
-detected via culture or PCR
streptococcus algalactaiae (group B strep) virulence mechanisms correct answers -CAMP factor:
toxic to humans
-sialic acid capsule: weak immunogen, doesn't trigger immune system
-super antigen: carbohydrate that functions similarly to endotoxin (LPS) to overstimulate the
immune system
streptococcus algalactaiae (group B strep) clinical manifestations correct answers -early onset
perinatal infection: baby is inoculated with bacteria during brith and within first 7 days of
delivery bacteremia and pneumonia occur
-late onset perinatal infection: baby is inoculated during birth and within 3-8 weeks will progress
from bacteremia to bacterial meningitis
streptococcus algalactaiae (group B strep) culture correct answers -prenatal vaginal or urine
sample is obtained
-lim broth: suppresses normal biota of vagina
-granada agar & carrot broth: colonies will appear orange
streptococcus pneumoniae correct answers -gram positive diplococci
-alpha hemolytic (pnuemolysin)
-NO lancefield antigens (no lancefield group)
-bile (optochin) sensitive
