Microbiology - Block 2 - Part 3

davidwurbel7's version from 2015-07-06 02:00


Question Answer
Positive catalase testStaphylococcus
Negative catalase testStreptococcus and Enterococcus
Positive coagulase testStaphylococcus aureus
Negative coagulase testStaphylococcus epidermidis and Staphylococcus saprophyticus
GPC clusters, catalase +, coagulase + , Highly salt tolerantStaphylococcus aureus
On culture media produce golden yellow colonies, beta-hemolytic on blood agar, Mannitol salt agar – ferment mannitolStaphylococcus aureus
Reservoir is the anterior naresStaphylococcus aureus
Transmission by contaminated hands and hospital staff transmit staph because of poor hand-washing. Leading cause of hospital-acquired infections. Eating contaminated food - custard pies, potato salad, canned meatsStaphylococcus aureus
Drug resistance to PenicillinPenicillinase producing Staphy aureus
Resitance to MethicillinMRSA
Resistance to VancomycinVRSA
Infections with this bacteria cannot be treated with Beta-lactam drugsMRSA
Carries mecA gene – encodes PBP2a (modified Penicillin-binding Protein)MRSA
Hospital-acquired MRSA drug of choiceVancomycin
Primary drug of choice for treating VRSAQuinupristin-Dalfopristin (Streptogramins)
Secondary drug of choice for treating VRSALinezolid
Tertiary drug of choice for treating VRSA Daptomycin
Binds Fc portion of IgG and inhibits phagocytosisProtein A
Enhances fibrin deposition and abcess formationCoagulase Enzyme
Converts H2O2 to water and O2Catalase Enzyme
Causes food poisoningEnterotoxin (A-F)
Desquamation of skin – split the stratum corneum causing separation of the superficial layers of the epidermisExfoliative toxins (ETA & ETB)
Exfoliative toxin producing sloughing of the skin which makes it look like the skin was burnedStaphylococcal scalded skin syndrome (SSSS)
Diagnostic marker for Community-acquired MRSA (absent in hospital-acquired MRSA strains)Panton-Valentine Leukocidins
Those with this are prone to repeated infections by some catalase+ bacteria esp. Staph aureus. Recurrent skin infections and respiratory tract infectionsChronic Granulomatous Disease
Activation of large numbers of helper T cells no-specifically → Stimulates release of cytokines → leakage of endothelial cells. Hypovolemic shock → multi-organ failure → deathToxic Shock Syndrome Toxin-1 (TSST-1)
Begins as a erythematous rash followed by diffuse epidermal exfoliation (desquamation of skin). Positive Nikolsky’s sign. Bullae (fluid does not contain the bacteria or leukocytes – culture negative. Condition is due to Exfoliative A & B Toxin). Usually occurs occurs in neonates and children (below age 6)Staphylococcal Scalded Skin Syndrome
Localized form of SSSS. Bullae fluid contains bacteria (culture positive). Nikolsky’s sign not seen.Bullous Impetigo
Ingestion of heat-stable preformed enterotoxin. Foods associated with ham, salted pork, custard-filled pastries, potato salad, ice-cream. Symptoms include nausea, severe vomitting, diarrhea. Rapid onset – 2 to 6 hours after ingestion. Resolves in 24 hours.Staphylococcal Food Poisoning
Acute onset, fever, low BP (<90mmHg). Rash with subsequent desquamation (esp palms & soles). Sore throat, headache, vomitting, diarrhea. Signs of multisystem organ failure. HypotensionStaphylococcus aureus – Toxin Shock Syndrome
Risk factors include tampon use, surgical packing and wound infectionsStaphylococcus aureus – Toxin Shock Syndrome
Prolonged Staph bacteremia is associated withEndocariditis
Bulky vegetations found on the tricuspid value and/or to a lesser extent the tricuspid valueAcute Endocariditis
Staphy aureus IE is commonly seen in this group due to sharing of needlesIntravenous Drug Users
Post-influenza pneumonia Ventilator–associated pneumonia are associated withStaphylococcus aureus
Those with Cystic fibrosis and Chronic granulomatous disease are predisposed to this infection with Staph aureusPneumonia
Lobar pneumonia has high rate ofAbcess Formation
Due to hematogenous spread from staph skin infection that effects metaphyses of long bones which causes fever and pain in childrenOsteomyelitis
Due to hematogenous spread from staph skin infection that effects flat bones (vertebrae) causing back pain and fever in adultsOsteomyeliis
Most common cause of osteomyelitisStaphylococcus aureus
In those with sickle cell disease, thalassemia this bacteria is the leading cause of osteomyelitis.Salmonella (GNB)
Infection of the joint – synovial fluid purulent/turbid. Painful erythematous joint with purulent material on aspiration. Large joints usually involved – shoulder, hip, knee, elbow. Associated with intraarticular injections, infected prosthetic jointsSeptic Arthritis
MCC of septic arthritis in young children and adults over 50 yrsStaphylococcus aureus
MCC of septic arthritis among sexually active age group.Neisseria gonorrhea
Gram positive cocci (clusters). Normal skin flora. Catalase positive. Coagulase negative. Non-hemolytic (gamma-hemolytic) on blood agar. MSA – does not ferment mannitol - forms pink colonies. Novabiocin sensitiveStaphylococcus epidermidis
Gram positive cocci (clusters). Normal skin flora. Catalase positive. Coagulase negative. Non-hemolytic (gamma-hemolytic) on blood agar. MSA – does not ferment mannitol - forms pink colonies. Novabiocin insensitiveStaphylococcus saprophyticus
Infect prosthetic heart valves causing subacute endocarditisStaphylococcus epidermidis
Organism introduced at time of valve replacement. Signs and symptoms develop after a year. Course is indolent (slow and does not cause too much trouble, but can cause valve failure)Subacute Endocarditis
Most common cause of infections due to adherence to catheter & shunt. Produce slime (polysaccharide capsule) that binds to catheters/shunts → biofilm that antibiotics cannot penetrateStaphylococcus epidermidis
Localized pain & reduced mobility of joint. Only treatment is replacement of infected jointProsthetic Joint Infections
This bacteria is the second most common cause of urinary tract infections in young, sexually active women. Dysuria (pain on urination) & pyuria. Nitrite negative on urine dipsticksStaphylococcus saprophyticus


Question Answer
Gram positive cocci (in chains). Catalase-negativeStreptococcus
S.pyogenes and S. agalactiae on blood agarBeta-Hemolytic
S.pneumoniae and Viridans Strep on blood agarAlpha-Hemolytic
Viridans Strep and Strep bovis (group D)Gamma-Hemolytic
Group A Strep (GAS), GPC chains, Catalase negative, Beta-hemolytic on Blood agar, Bacitracin sensitive, PYR positive (pyrrolidonyl arylamidase)Streptococcus pyogenes
Group A Strep (GAS), GPC chains, Catalase negative, Beta-hemolytic on Blood agar, Bacitracin insensitive, PYR positive (pyrrolidonyl arylamidase)Streptococcus agalactiae
M protein, Streptolyin O, Streptokinase, Streptodornases, Hyaluronidase, C5a Peptidase, Streptococcal pyrogenic exotoxinsStreptococcus pyogenes Virulence Factors
Virullence factor the binds Fc portion of antibodies and prevents Complement C3 from binding to the surface preventing the bacteria from being phagocytizedM Protein

Streptococcus pyogenes

Question Answer
Lyses fibrous clots to allow motility from the bacteriaStreptokinase
Breaks down the nucleic acids of dead cells liquefying pus to allow motility for the bacteriaStreptodornases
Cleaves the chemattractive chemical of the complement systemC5a Peptidase
Cleaves the ground substance in connective tissue to allow motility for the bacteriaHyaluronidase
Oxygen labile and antigenic. Lyses RBCs, leukocytes, plateletsStreptolysin O
Oxygen stable and Non-antigenic. Lyses RBCs, leukocytes & platelets. Responsible for beta-hemolysisStreptolysin S
Cause the rash of scarlet fever. Produced by Streptococcal TSS strains functioning as a superantigenStreptococcal Pyrogenic Exotoxins (SPEs)
Streptococcal ASO test detects recent throat infection with S.pyogenes important in diagnosis ofRheumatic Fever
Occurs in children – 5-15 yrs. Abrupt onset of sore throat, fever, malaise, headache, possibly exudative cervical lymphadenopathy. Rapid swab antigen test – 15 minutes Pharyngitis
Untreated cases of pharyngitis may developAcute Rheumatic Fever
Leading cause of bacterial pharyngitisStreptococcus pyogenes
A complication of streptococcal pharyngitis. Caused by GAS producing pyrogenic toxin. Begins a couple of days after start of throat infection. Erythematous rash – upper chest and spreads to extremeties. Tongue has an initial yellowish-white coating which later sheds to show a red raw surface “strawberry tongue”Scarlet Fever
Purulent infection of the skin. Seen in kids 2-5 yrs old in summer months. Often in association with Saph aureus. Honey-crusted lesions.Impetigo
Spreading acute inflammation of the deep dermis and upper subcutis by streptococci. Local pain and erythema, lymphadenopathy, chills, fever, leukocytosis. Lesions are red and raised and painful and clearly demarcated from unaffected skinErysipelas
Deep skin infection. No clearly demarked separation between normal and infected skin. Both local and systemic signsCellulitis
May arise following minor trauma, or hematogenous spread from GAS throat infection to site of blunt trauma/muscle strain. Bacteria spreads along superficial and deep fascial planes. Vascular occlusion, tissue ishemia, and necrosis extensive destruction of muscle and fatNecrotizing Fasciitis
High degree of pain. Erythema (diffuse or localized). Fever, malaise, myalgias, diarrhea, and anorexia may be present.Necrotizing Fasciitis
Caused by strains that produce prominent capsule and SPEs. Initial infection with pain, fever, chills, malaise, vomiting, diarrhea. Patients are bacteremicStreptococcal Toxic Shock Syndrome
Rheumatic fever and acute glomerulonephritisNon-Suppurative Post-streptococcal Sequelae
Anti-Streptococcal antibodies cross-react with self tissues of the heart valuesRheumatic Fever
This positive serologic tests reflects antecedent (recent) Strep pharyngitisASO
This condition occurs after a severe episode of ARF or many attacks of ARF. 10-20 years after these ARF episodes. Due to damage to the mitral and aortic valves which leads to stenosisRheumatic Heart Disease
Immune-complex disease. Edema, hypertension, hematuria, proteinuriaAcute glomerulonephritis
Follows cutaneous infection, or pharyngitis. 1-2 weeks after infection. Smoky/coal-coloured urine. Moderate proteinuriaAcute Glomerulonephritis
Positive ASOAcute Rheumatic Fever
Positive anti-DNAse B and ASO testAcute Glomerulonephritis
Group A Strep treatmentOral Penicillin / Amoxicillin
Impetigo with Strep A and Staph aureus treatmentNafcillin
MC overall cause of IEViridans Streptococcus
2nd MC overall cause of IE and MCC of IE in IVDAStaphylococcus aureus
MC cause of IE after prosthetic valve and MC cause of IE from intravenous cathetersStaphylococcus epidermidis
MC cause of IE in ulcerative colitis or colorectal cancerStreptococcus bovis
MC valve affected by IEMitral Valve
2nd MC valve affected by IEAortic Valve
3rd MC valve affected by IETricuspid Valve
Last common valve affected by IEPulmonary Valve
Retinal hemorrhage with pale center due to immune complex vasculitisRoth's Spot
Inflammatory reactions involving the heart, joints, basal ganglia and other tissues after a bacteria infectionAcute Rheumatic Fever

Streptococcus agalactiae

Question Answer
Gram positive cocci (chains), Catalase negative, weak beta-hemolysis on blood agar. Resistant to bacitracin. CAMP test positive. Hydrolyze hippurateStreptococcus agalactiae
MCC of neonatal meningitisStreptococcus agalactiae
Increased risk of infection with prolonged labor after premature rupture of membranesStreptococcus agalactiae
High fever. Bulging fontanelle (soft spot on top of head). Irritability, poor feeding, stiffness in body or neckNeonatal meningitis
Treatment of this penicillin/ampicillin plus aminoglycoside, or cephalosporin (cefotaxime)Neonatal Meningitis
Empirical treatment for Neonatal meningitisCefotaxime
2nd MCC cause of meningitis in neonates (birth to 1 month)Escherichia coli
Least MCC cause of meningitis in neonates (birth to 1 month)Listeria monocytogenes
Screening for GBS colonization at 35-37 weeks pregnancyVaginal-Rectal Screening
If Vaginal-Rectal Screening is positive this is recommendedIntra-Partum Prophylaxis
Intra-Partum prophylaxis is done by IV infusion ofPenicillin

Recent badges