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EXAM 2 MLT 124
MLT 124:MEDICAL MICRO PT 1 (LECTURES 6-9)
| Question | Answer |
|---|---|
| What exotoxin is responsible for causing scarlet fever? | Streptococcal pyogenic exotoxins (SPE) |
| Which enzyme in S. pyogenes is oxygen liable, meaning that it will only be found in anaerobic conditions | Streptolysin O |
| Describe Impetigo | localized skin disease caused by S. aureus or S. pyogenes that causes small vesicles to develop into weeping lesions. Typically affects 2-5 year olds |
| What virulence factor in S. pyogenes aid in resisting phagocytosis and increasing adherence to the upper respiratory tract's mucosal cells? | M Protein |
| True or false: S. pyogenes is resistant to bacitracin | false; S. pyogenes is susceptible to bacitracin |
| True or false: weak positives for catalase testing results are not indicative of Staph spp. | true |
| What virulence factor in S. pyogenes prevents the bacteria from succumbing to antibiotic destruction | Hyaluronic acid capsule |
| What Streptococci spp. are beta hemolytic? | S. pyogenes (A), S. agalactiae (B) |
| If a bacteria is neg. catalase, beta hemolytic, resistant to bacitracin, but tested positive to the CAMP test, what Streptococci spp. do we have? | Group B (S. agalactiae) |
| What Streptococcal localized infections target the body's extremities at various degrees? | Impetigo (weeping lesions) Erysipelas (superficial to subcutaneous) Cellulitis (deeper Strept invasion) |
| What systemic S. pyogenes infection causes skin and tissue necrosis? | Necrotizing fasciitis |
| Strep throat, known professionally as (blank) can evolve into scarlet fever following exposure from (blank) | Pharyngitis; SPE |
| What systemic infection is caused by virulent strains of exotoxin-producing Strep species that not only affect tissue function due to necrosis, but also can cause renal and respiratory failure? | Streptococcal Toxic Shock Syndrome |
| What's another complication (ASIDE FROM SCARLET FEVER/ACUTE GLOMERULONEPHRITIS) that can occur following Group A pharyngitis infection? What causes it? | Rheumatic Fever; antibody-antigen complexes build up in heart tissue to combat the Strep infection, which causes mechanical and immunological damage to the cardiac tissue |
| Why is Rheumatic Fever so dangerous for the body? | Because the body is damaging heart tissue, it can result in a chronic degradation of heart valves, making it difficult for blood to flow properly |
| Describe Acute Glomerulonephritis | this is a S. pyogenes-complication that causes the antibody-antigen complexes to get deposited into the glomerulus, shedding through it and causing inflammation that will impede on proper kidney function; often identified by blood in urine |
| What affect does Group A Step have on neonates? | it can cause pneumonia or meningitis with bacteremia in newborns |
| What are two ways that S. aureus is able to nullify phagocytosis? | 1) Coagulase that hides bacteria from phagocytes by forming clots 2) Protein A, which binds to IgG to block phagocytosis |
| What is known as the "spreading factor" enzyme used by S. aureus? | Hyaluronidase |
| Hemolysins are cytolytic toxins meant to destroy | RBCs and all WBCs |
| What is an enterotoxin? | An exotoxin that causes food poisoning |
| Describe furuncle | folliculitis that is able to further develop, forming raised nodules from dead/necrotizing tissue (boils) |
| If S. aureus is able to burrow deeper into subcutaneous tissue, a patient with furuncle will see their condition develop into | carbuncle |
| What systemic infection is typically associated with post-surgical/nosocomial infection? | Toxic Shock Syndrome |
| In Scalded Skin Syndrome, a disease that mainly affects (blank) the epidermis of the skin is sloughed off by (blank), which is produced by S. aureus | neonates; Staphylococcal exfoliative toxin |
| Which CONS is the most common, opportunistic pathogen that can contaminate skin, causing nosocomial infections? | S. epidermidis |
| How do we reach the conclusion that S. saprophyticus has caused a UTI? (Describe the Staph biocehmical test chart) | GPC, catalase positive, coagulase negative, oxidase/bacitracin resistant, novobiocin resistant (less than 16mm growth) |
| Which SSNA is known for causing UTIs in sexually active females? How would it respond to oxidase/bacitracin and novobiocin testing? | oxidase (negative/no color), bacitracin (R), novobiocin (R- 16mm> growth) |
| How would we the conclusion that we have Micrococcus spp. on a skin culture? | catalase (+), coagulase (-), oxidase (positive/purple or blue color) OR bacitracin (S) |
| What test results determine S. aureus presence | Beta hemolytic, Catalase and Coagulase (+), MSA (growth in 7.5% NaCl plus yellow - ferments mannitol sugar), or DNase (visible clearing=positive) |
| If we have a patient urine sample that is resistant to bacitracin, but is susceptible to novobiocin, how would we categorize this? | SSNA |
| Which type of bacteria will grow on MAC plate? | Gram negatives |
| Why would S. aureus be beta hemolytic? | it contains hemolysins that eat RBCs |
| True or false: A GPC that can cause a catalase positive reaction contributes to its level of virulence | false |
| What is the principle of the catalase test? | Assess whether or not bacteria is able to produce catalse to break down hydrogen peroxide into oxygen and water, forming bubbles |
| What is the principle of the coagulase test? | Assess if bacteria can produce coagulase (clumping factor) to convert fibrinogen into fibrin, forming clots |
| Why must a free-coagulase tube be checked for clotting at 4 hours of incubation and at 18 hours of overnight incubation? | hyaluronidase can break down the previously formed clots, |
| What is free coagulase? | coagulase in a free environment that forms a complex similar to thrombin, which indirectly converts fibrinogen to fibrin |
| Why must a Coagulase tube test be assess within 4 hours and 18 hours? | Hyaluronidase enzyme will eventually break down the clots previously made at 18hrs |
| What would a positive result on a modified oxidase test look like? | Purple/blue |
| What is the principle of the modified oxidase test? | To differentiate micrococci from most staphylococci |
| What affect does bacitracin have on susceptible bacteria (eg. Micrococcus spp.) What would a positive result look like? | it inhibits cell wall synthesis; any clear zone of inhibition |
| When a novobiocin disc be used? | determining Stap presence in a urine specimen, particularly S. saprophyticus |
| SSNA that do not ferment mannitol on a MSA plate can be referred to as | non-halophilic |
| True or false: MSA plates are selective and differential | true |
| What is the principle of the VP test? What would color would be indicative of a positive result? | presence of acetoin, an end product of glucose fermentation; red color |
| True or false: CNA with sheep blood afar is selective for gram positives, but differentiates based on hemolytic ability | true |
| PEA inhibits the growth of | gram negatives |
| Why might an oxacillin-infused MSA plate aid in identifying S. aureus presence? | Only S. aureus can grow in the presence of oxacillin |
| Group A stept= | S. pyogenes |
| Group B stept= | S. agalctiae |
| Where are streptococci spp. usually found in? When can they be life threatening? | respiratory tract normal flora; if they enter sterile sights |
| What are the two main virulence factors in S. pyogenes? What do they do? | M Protein: resists phagocytosis and adheres to the mucosal cells in the respiratory tract Capsule: hides antigens, preventing antibiotic destruction |
| Which enzyme in S. pyogenes is active in anaerobic environments, or is labile? | Streptolysin O |
| Streptolysin S is stable, meaning that it activates in | oxygen-abundant environments |
| What localized infection can cause S. pyogenes to reach subcutaneous tissue? | Erysipelas |
| What is a common S. pyogenes infection that targets the throat? | Pharyngitis/strept throat |
| What determines S. pyogenes presence in a patient sample? | GPC, catalase negative, Beta hemolytic on BAP, susceptible to bacitracin |
| If a Streptococci is Bacitracin resistant, what test(s) can be done next? | CAMP/Hippurate Hydrolysis test |
| What is the principle of the CAMP test? | detect production of Camp Factor, which produces an arrow of zone inhibition upon contact with S. aureus |
| What Group of Strept would prove a positive CAMP test? | Group B (S. agalactiae) |
| What agent is used to visualize the color change reaction in a Hippurate Hydrolysis test? | Ninhydrin |
| A positive Hippurate Hydrolysis test would be | purple |
| What can S. pneumoniae appear like on a BAP? | mucoid in appearance due to its capsule |
| Optochin sensitivity is used on (blank). A zone of inhibition greater than 14mm is indicative of (blank) | alpha hemolytic strept; S. pneumoniae |
| What plate/broth test can be done to distinguish S. pneumoniae from other alpha-hemolytic strept? | Bile solubility; pneumococcal colonies will get lysed and disintegrate on a plate; cloudy broth for this test would be positive (due to the colonies dissolving) |
| What is the principle of the Quellung test? What organism from test positive? | serotypes the capsule of bacteria and swells it for microscopy; S. pneumoniae |
| What are the biochemical test results to determine Viridans stretococcus? | Resistant to Optochin, Negative bile esculin |
| What are the biochemical results to determine Enterococcus species? | bile esculin positive, PYR positive/6.5% NaCl positive |
| What is the principle of the bile esculin test? What does it differentiate? | assesses organism's ability to hydrolyze glucoside esculin; differentiates Enterococcus spp. from other strept |
| What is the principle of the PYR test? What does it differentiate between? | assess if bacteria has the enzymes to break down chemicals to produce a bright red/pink color; differs between Enterococcus spp. and Group D strept |
| What microorganisms would produce positive PYR results? | Group A Strept and Enterococcus spp. |
| What makes Enterococcus so virulent? | it can live in extreme conditions, and produce enzymes that adhere to unwanted areas (eg. heart valves, renal epithelial tissue) |
| A majority of Enterococcus spp. possess which hemolytic reaction(s) | alpha or gamma |
| True or false: Enterococcus spp. is commonly seen with nosocomial infections, particularly causing UTIs | True |
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