Streptococci Flashcards
What is the most pathogenic group of streptococcus?
Group A (Streptococcus pyogenes)
What is the microscopic morphology of streptococci?
-Spherical cells, tend to form pairs or chains of cocci -Gram positive (blurple)
What are the various hemolysis patterns of streptococci types on 5% sheep blood agar?
-alpha = green (some intact red cells) -beta = clear (no intact red cells) -gamma = no hemolysis (intact red cells)
Which hemolysis type does Group A strep have?
-Beta (clear)
What hemolysis type does strep pneumoniae have?
-alpha (Green)
What does the bacitracin susceptibility test reveal about a strep culture, and which hemolytic pattern is it used on?
-used on beta-hemolysis (clear) -Strep pyrogenes is susceptible (group A), the other groups are resistant
What is the important Group D strep species?
-S. gallolyticus [bovis]
What is Lancefield classification?
-developed for strep -immunologic classification based on differences of cell wall carbs -used for beta-hemolytic and non-hemolytic streptococci
How are Group D streptococci identified?
-either alpha or gamma hemolytic -can grow in presence of 40% bile -can hydrolyze esculin (turns black on bile esculin agar) **very sensitive to penicillin
What is the antigenic structure of streptococci?
-capsule (non-antigenic, antiphagocytic) -M-proteins (antiphagocytic) -C-carbohydrate (lancefield groupings) -Peptidoglycan -lipoteichoic acid
How is the capsule of strep non-antigenic?
-probably because it is chemically indistinguishable from hyaluronate in ground substance of connective tissue
How are M-proteins of strep antiphagocytic?
-prevents interaction of organism with complement **antibody to M-protein is protective and imparts long-lasting immunity
What are the extracellular products of Group A strep?
-Pyrogenic exotoxins A -streptolysin O (hemolysin) -Streptokinase -Hyaluronidase -DNAse
Which extracellular product of Group A strep is responsible for a number of the clinical manifestations of toxic strep syndrome?
-Pyrogenic exotoxins
What do pyrogenic exotoxins of strep do?
-superantigens bind directly with class II MHC, leads to clinical manifestations of toxic strep syndrome (releases a bunch of cytokines) -Pyrogenic exotoxin B degrades ECM proteins such as fibronectin & vitronectin (facilitate spread of infection)
What does streptokinase do?
-activates plasminogen to disrupt blood clots -can be used to lyse coronary occlusions *Hypersensitivity reactions occur in patients previously exposed to this antigen.
Why are anti-DNAse titers more useful than Antistreptolysin O (ASO) titer in diagnosing strep A/Rheumatic fever?
-DNAse is not neutralized by cholesterol during skin infections
How does Group A strep cause disease?
-direct damage due to infection itself (acute suppurative disease) -toxin production -immune response (post-streptococcal sequelae)
What is the pathogenesis of acute suppurative diseases caused by Group A strep?
-adherence to skin/mucous membrane by lipoteichoic acid -tendency for local spread, due to enzymes -other enzymes = “thin dishwater pus”
What are common examples of acute suppurative diseases caused by Group A strep?
-Pharyngitis/tonsillitis (strep throat) -Pyoderma (impetigo) -cellulitis/Lymphangitis -erysipelas
What is pyoderma?
-impetigo -discrete skin lesions with a papule-vesicle-pustule crusting sequence
What is erysipelas?
-form of cellulitis -diffuse lymphangitis of skin, infection spreads along lymphatics -well demarcated
What are some common examples of toxin-associated disease caused by Group A strep?
-scarlet fever -Toxic strep syndrome
What is toxic strep/shock syndrome?
-“flesh-eating bacteria” Group A strep (pyrogenic exotoxins) -severe infections, soft tissue, with bacteremia -high mortality -hypotension with multiple organ impairment
What is scarlet fever?
-caused by group A strep -Streptococcal pharyngitis/tonsillitis accompanied by a diffuse, bright scarlet erythema of skin and mucous membranes -rash begins on trunk and neck, then spreads to extremities, sparing the face -due to production of erythrogenic (scarlatiniform) toxin
What are some common post-streptococcal sequelae caused by group A strep?
-acute rheumatic fever, from cross-reactivity between strep M-proteins & cardiac sarcolemmal proteins -acute glomerulonephritis, from deposition of immune complexes in glomeruli -guttate psoriasis, from superantigenic stimulation of T-cells by pyrogenic exotoxin C
What are the first line treatments for Group A strep infections?
-penicillins & cephalosporins *resistance to these has not yet been described *macrolide can be used in pts with penicillin allergy
How should patients with a history of rheumatic fever be managed long-term? Why?
-long-term penicillin prophylaxis -because they are at an increased risk to develop repeated attacks
What are the two important Strep strains that do alpha-hemolysis?
-Viridans strept -strept pneumo
How do we differentiate viridans strep from strept pneumo?
-Viridans strept is not susceptible to Optochin, strep pneumo are -strep neumo is soluble in bile salts, viridans is not
What do superantigens produced by strep do?
superantigens bind directly with class II MHC, leads to clinical manifestations of toxic strep syndrome (releases a bunch of cytokines)
What does pyrogenic exotoxin B produced by strep do?
Pyrogenic exotoxin B degrades ECM proteins such as fibronectin & vitronectin (facilitate spread of infection)
What are common manifestations of Scarlet Fever caused by Group A strep?
-Strawberry tongue -sandpaper rash
How do we differentiate the malar rash caused by erysipelas and SLE?
-there will be a “step up” upon palpation in erysipelas (group A strep) due to inflammation & lymphatic involvement
What condition always precedes acute rheumatic fever and acute post-strep glomerulonephritis?
Rheumatic fever: -streptococcal pharyngitis (But not skin infections!) Glomerulonephritis: -pharyngitis OR skin infection
What are the major manifestations of Rheumatic fever?
*Fever JONES: Joints (polyarthritis) O (myocarditis) Nodules (subcutaneous nodules) Erythema marginatum Sydenham’s chorea
What are the major manifestations of post-streptococcal glomerulonephritis?
-edema of face & extremeties -hematuria -hypertension -decreased complement levels -abnormal urinary sediment & RBC casts
A 65-year-old man is admitted to the hospital with an acute myocardial infarction. Emergency angiography demonstrates 95% acute occlusion of the left anterior descending coronary artery. Which of the following streptococcal components could be used therapeutically in this man? A. DNAse B B. Streptokinase C. Streptolysin O D. Hyalunonidase
B. Streptokinase
A 20-year-old boy is admitted to LDS Hospital in Salt Lake City with fever, a new heart murmur and joint swelling. His pediatrician suspects acute rheumatic fever. Which test is appropriate? A. Anti-streptolysin O titers (ASO) B. Blood cultures C. Joint fluid PCR for Streptococcus pyogenes D. Optochin susceptibility test
A. Anti-Streptolysin O Titers (ASO)
What streptococcal components is the Lancefield grouping system based on? A. Capsular polysaccharide B. Pyrogenic exotoxins C. C-carbohydrates D. Teichoic acids
C. C-carbohydrates
A 56-year-old man is admitted with necrotizing cellulitis of the left leg. He has a BP=86/65 mmHg, diffuse redness of the skin, abnormal liver enzymes, elevated creatinine and thrombocytopenia. You suspect the toxic strep syndrome. The pathogenesis of this syndrome is suspected to be a result of superantigen production, which includes which one of the following? A. Streptokinase B. Streptolysin O C. Pyrogenic exotoxin A D. DNAse
C. Pyrogenic exotoxin A
A 48-year-old man with COPD is admitted to the MEDVAMC with LLL pneumonia. His sputum grows an -hemolytic streptococcus on the blood agar plates. Which of the following laboratory tests will be used to identify this particular organism? A. Bacitracin susceptibility B. Bile esculin C. Lactose fermentation D. Optochin susceptibility
D. Optochin susceptibility
All of the following components of Streptococcus pyogenes are associated with an antigenic response except: A. Hyaluronic acid B. Streptolysin O C. DNAse D. M-protein
A. Hyaluronic acid
You saw a 13-year-old boy in the Medicine/Pediatrics Clinic yesterday with a sore throat, fever, cervical adenopathy, and tonsillar exudates on examination. The laboratory called this morning to tell you that there is a Beta-hemolytic organism growing on the blood agar plates from the throat swab. The diagnostic test that they will run to differentiate the different Beta-hemolytic organisms is: A. Optochin susceptibility B. Bile solubility C. Bacitracin susceptibility D. Penicillin susceptibility
C. Bacitracin susceptibility
Two siblings came to the HMO this morning with sore throats accompanied by tonsillar exudates and a diffuse rash that had the characteristic of fine sandpaper. Their problem was caused by: A. Streptococcus agalactiae B. Streptococcus salivarius C. Streptococcus pneumoniae D. Streptococcus pyogenes
D. Streptococcus pyogenes
Treatment for Strep with tonsillar exudates and diffuse sandpaper rash caused by Strep pyogenes is:
Amoxicillin
You are volunteering on a medical mission trip in Jamaica. Several children have been seen with cellulitis in the last month. Today, a child comes in with diffuse anasarca. He has a BP = 145/98 mm Hg and his urine is foamy. When you do a urine dipstick, there is 4+ protein and 2+ blood. The pathophysiological mechanism responsible for his disease is: A. Cross reacting Abs to renal tubular antigens; B. Immune complex deposition in renal glomeruli; C. Activated T-cells attacking renal glomerular cells; D. Emboli to renal arteries
B. Immune complex deposition in renal glomeruli;
What is the scientific name of Group B streptococci?
-Streptococcus agalactiae
What is the epidemiology of Group B strep?
-normal inhabitants of the bowel and vagina (5-40%)
How is immunity to group B streptococci mediated?
-antibodies to a type-specific carbohydrate **in absence of antibody, mothers and neonates may become infected during labor and birth
What are the risk factors for developing infection from group B strep?
-no maternal or fetal antibodies to type-specific antibodies -Young age of mother, premature rupture of membranes, prolonged labor -in adults, significant underlying illnesses (DM, cirrhosis, cancer, decubitus ulcers, or GU disorders)
Distinguish the time-frame and presentation of early vs late onset neonatal disease caused by Group B strep.
Early: -7 days -Bacteremia, pneumonia, or meningitis Late: -7 days to 3 months -Bacteremia with meningitis
How to post-partum women present with group B strep infection?
-chorioamnionitis -endometritis -bacteremia
What are the common illnesses caused by Group B Strep?
OB/GYN infections**** Skin & soft tissue infections** Bacteremia* UTI* Pneumonia
What is the treatment for diseases caused by Group B strep?
-susceptible to penicillins & cephalosporins
How are infections by group B strep prevented?
-Immunization (Type III capsular polysaccharide) -Prenatal screening -Intrapartum antibiotic prophylaxis/pre-emptive treatment
There is very strong association between bacteremia or endocarditis caused by ______________ and lesions of the gastrointestinal tract, particularly colonic neoplasms.
S. gallolyticus [bovis] **infected patients require colonoscopy to screen for cancer
How do we treat S. Gallolyticus [bovis] infection?
penicillin
What are the most important of the enterococcus species?
E. faecalis & E. faecium **constitute a substantial portion of normal bowel flora
Who is at greatest risk for enterococcal infection?
Hospitalized patients
What factors predispose patients to enterococcal colonization?
-prior antibiotic therapy -surgery -invasive procedures
(T/F) Enterococci are not as intrinsically virulent as the other streptococci.
T *cause infections usually in areas that have been previously damaged
What infections are commonly caused by enterococcal infections?
-endocarditis -UTI -Intra-abdominal, pelvic, & wound -Spontaneous peritonitis -Nosocomial bacteremia
What does nosocomial mean?
Hospital-acquired
How do we treat Enterococcal infections?
-Ampicillin & vancomycin (will inhibit growth) -combine with gentamicin or streptomycin to kill
Why are enterococci so resistant to antibiotics?
-they are relatively sexually promiscuous (acquire resistant DNA copies)
What is there to know about group C strep?
-recognized as common causes of infection in animals -occasionally cause pharyngitis & maybe nephritis in humans
What is there to know about Group G strep?
-part of the normal flora of the pharynx, skin, GI tract, & vagina -infections include: localized abscesses, puerperal sepsis, pleuropulmonary, skin & soft tissue infections, endocarditis, bone & joint infections and bacteremia.
What major diseases are caused by Viridans group streptococci?
-dental caries -sometimes most common cause of infective endocarditis, usually involving abnormal valves
Where do viridans group strep usually live?
-major part of the human oral and bowel flora -normally adhere to teeth, buccal mucosa, and tongue
Tell me about Microaerophilic streptococci.
=Milleri -normally live in human bowel -cause disease when spread to normally sterile areas -cause abscesses (brain, hepatic, empyema(pleural))
Tell me about Strep iniae.
-fish pathogen, causes subcute abscesses in amazon fish -infected some canadians in the 90’s from touching raw fish
Tell me about anaerobic streptococci.
-normal constituents of microbial flora of GI and female GU tract -cause problems when they end up in normally sterile areas **septic abortion, endometritis, ovarian abscess, diabetic foot ulcers
A 48-year-old man with COPD is admitted to the MEDVAMC with LLL pneumonia. His sputum grows an alpha-hemolytic streptococcus on the blood agar plates. Which of the following laboratory tests will be used to identify this particular organism? A. Bacitracin susceptibility B. Bile esculin C. Lactose fermentation D. Optochin susceptibility
D. Optochin susceptibility Bacitracin for group A (beta-hemolysis)
A 5-day-old infant was delivered from a 16-year-old G1P1 woman who was in labor for 22 hours and had no prenatal care. The baby now has lethargy and bulging fontanels. You suspect meningitis due to: A. Streptococcus pneumoniae B. Streptococcus agalactiae C. Streptococcus pyogenes D. Streptococcus mitis
B. Streptococcus agalactiae
A 76-year-old woman is admitted to Baylor St. Luke’s Medical Center with a hip fracture and undergoes internal fixation. She had a Foley urinary catheter placed on admission. Five days after surgery, she develops delirium, fever and cloudy urine. The urine culture is most likely to grow which of the following organisms? A. Streptococcus pyogenes B. Peptostreptococcus magnus C. Enterococcus faecalis D. Streptococcus constellatus
C. Enterococcus faecalis
A 73-year-old woman is admitted with low-grade fevers and a murmur of mitral insufficiency that has not previously been documented in her chart. She has had some weight loss for the last year and has an iron deficiency anemia with a positive stool for occult blood. Two sets of blood cultures are positive for a group D streptococcus. You suspect she has: A. Infective endocarditis due to E. faecium. B. Infective endocarditis due to S. pneumoniae. C. Liver abscess due to S. constellatus. D. Infective endocarditis due to S. gallolyticus.
D. Infective endocarditis due to S. gallolyticus. **deficiency anemia likely from colon cancer
A 56-year-old homeless man was admitted to BTGH with fever and seizures. CT of the head demonstrated an enhancing mass suspected to be an abscess. Blood cultures are growing gamma-hemolytic gram-positive cocci in chains which do not have a (+) bile esculin test. This organism is most likely: A. Streptococcus pneumoniae B. Streptococcus intermedius C. Streptococcus pyogenes D. Enterococcus faecalis
B. Streptococcus intermedius =strep milleri
A 34-year-old man works in the meat department at Kroger. Yesterday, while cutting up some tilapia (which, of course, was farm raised), he cut his hand. This morning he noted the onset of redness and pain that had started to progress up his arm. Which of the following is most likely responsible for his problem? A. Streptococcus intermedius B. Streptococcus agalactiae C. Streptococcus iniae D. Streptococcus salivarius
C. Streptococcus iniae
A 68-year-old woman has a history of mitral stenosis. She presented to her PCP with a 2-month history of fatigue, intermittent low-grade fevers and mild symptoms of congestive heart failure, which are new. Three sets of blood cultures are positive in both the aerobic and anaerobic bottles for alpha-hemolytic, Gram-positive cocci. The organism is most likely: A. Streptococcus pneumoniae B. Streptococcus pyogenes C. Streptococcus sanguis D. Streptococcus agalactiae
C. Streptococcus sanguis =viridans group strep
A 56-year-old man was admitted with fevers and chills. Two sets of blood cultures are growing Streptococcus constellatus. Which of the following tests is most likely to be helpful? A. Transthoracic echocardiogram B. Transesophageal echocardiogram C. Computerized tomographic scan of the chest & abdomen D. Ultrasound of the kidneys E. Urine culture
C. Computerized tomographic scan of the chest & abdomen
A 78-year-old man has been on the rehabilitation ward with an indwelling Foley catheter for months. A urine culture done for surveillance purposes is growing a vancomycin-resistant Enterococcus faecium, but there is no pyuria on urinalysis. The most appropriate approach to this man is: A. Place him in contact isolation. B. Treat him with PO linezolid, to which the organism is susceptible. C. Treat him with IV daptomycin, to which the organism is susceptible. D. Change the Foley to a suprapubic catheter.
A. Place him in contact isolation.
This 75-year-old man with benign prostatic hypertrophy is admitted with fevers and chills. Three sets of blood cultures are growing Enterococcus faecalis. Echocardiogram shows a bicuspid aortic valve with vegetations. You diagnose infective endocarditis. What is the most appropriate antimicrobial therapy? A. IV ampicillin B. IV vancomycin C. IV ampicillin + IV gentamicin D. IV vancomycin + IV gentamicin E. IV ceftriaxone
C. IV ampicillin + IV gentamicin
Which strep (-like) organisms will display gama hemolysis on blood agar?
-Strep gallolyticus [bovis] = group D -enterococcus -some “milleri” group streptococci
What pattern of hemolysis does viridans group strep show?
Alpha-hemolysis (do optochin susceptability to distinguish from Strep pneumo
“honey-crusted”
=Impetigo -S. pyogenes and/or S. aureus
“Thin dishwater pus”
-Strep pyogenes
“B hemolysis & bacitracin susceptible”
Strep pyogenes
“cellulitis/erysipelas after saphenous vein graft or mastectomy”
Strep pyogenes
Strep gallolyticus! Get that man a________!
colonoscopy to look for colon adenocarcinoma
“Strawberry tongue & sandpaper rash”
Scarlet fever by Group A Strep. pyogenes
What portion of the streptococcal cell wall is used for lancefield grouping?
C carbohydrate
What is the major virulence factor of the Group A strep pyogenes cell wall? What does it do?
-M-protein -inhibits activation of complement and phagocytosis **antibodies against it are protective
What enzyme produced by Group A strep is responsible for it being B hemolytic?
Streptolysin O (used for ASO titer)
What bugs can cause necrotizing fasciitis?
-Group A Strep pyogenes -Staph -Clostridium -Gm (-) enterics -mixed infection
What is fornier’s gangrene?
-necrotizing fasciitis involving the male genital area and perineum -often caused by mixed organisms
“Puffy-faced, pediatric, with dark urine” and had a sore throat or skin infection a week ago.
-acute post-streptococcal glomerulonephritis
How can we distinguish endocarditis caused by Viridans group strep vs Staph?
Viridans: -subacute =slow piling of bacteria on heart valve -low grade fevers (Group D and enterococcus is also subacute) Staph: -Acute, rapid onset -2’ to IV drug use -abrupt onset of shaking, chills, high spiking fevers, and rapid valve destruction
What type of viridans strep is known to cause abscesses in the brain and abdominal organs?
Strep milleri
What infections are commonly caused by Enterococcus (faecalis and faecium)?
-UTI -biliary tract infections -subacute endocarditis Nosocomial!
Enterococcus and viridans strep can both grow in something, what is it? And how can we easily distinguish enterococcus from viridans?
-Both grow in 40% bile -ONLY enterococcus grows well in 6.5% NaCl *Group D strep gallolyticus can also grow in bile, not salt.
