Flashcards in L23 Streptococci and Enterococci Deck (89):
Streptococci can be classified in two different ways - what are they?
1. Serological properties (Lancefield groupings)
2. Hemolytic properties
What are the Lancefield groupings based upon and what are the 5 groups?
Group specific carbohydrates
A, B, C, F, G
What are the 3 hemolytic groupings?
1. Beta: complete hemolysis
2. Alpha: incomplete hemolysis
3. Gamma: no hemolysis
What are the 4 genera of streptococcaceae?
1. Peptostreptococcus anaerobes
3. Enterococcus Group D
4. Other genera
What are the 3 classes of streptococcus?
1. Pyogenic beta Lancefield groups
2. Pneumococci (alpha)
3. Viridans group (alpha/gamma)
What is Group A strep?
What is Group B strep?
A 15 year old girl presents to an urgent care clinic. She describes sore throat, pain on swallowing, and she has a temperature. She has a negative rapid antigen test for strep throat. What is the diagnosis?
Acute pharyngitis caused by S. pyogenes
What are classic symptoms of acute pharyngitis caused by S. pyogenes?
Fever, sore throat, headache, cervical lymphadenopathy (swollen lymph nodes), exudate
Acute pharyngitis caused by S. pyogenes is difficult to differentiate from ___ infection.
___% of people are asymptomatic carriers of S. pyogenes.
How is S. pyogenes transmitted?
True or false - rapid antigen testing is not 100% sensitive.
What is the sensitivity and specificity of rapid antigen tests? What can it be used for?
Rapid rule-in for pediatrics and adults
What is the sensitivity and specificity of NAATs (PCR-based antigen tests)? What can it be used for?
Rapid rule-out for pediatrics and adults
What is the sensitivity and specificity of culture? What can it be used for?
Rule out for pediatrics (adults?)
What are the adherence, evasion, and destruction tools used by streptococci?
Adhere: M protein, F protein
Evade: M protein, capsule
Destroy: exotoxins and enzymes
What is the function of the M protein virulence factor of S. pyogenes?
M protein binds to epidermal cells and allow bacteria to survive. It is anti-phagocytic and degrades C3b.
M protein has over ___ (#) serotypes.
True or false - strains without M protein are still virulent.
False - they are avirulent.
What are two infections associated with S. pyogenes?
What is erysipelas?
Infection with S. pyogenes that causes spreading erythema with a well-demarcated edge on the face; often presents with fever and lymphadenopathy, often with accompanying streptococcal pharyngitis
Historically, erysipelas affects the face primarily. Today, the ___ are most affected.
What is impetigo?
Pyoderma associated with trauma/insect bites; pustules have a yellow crust; appears on face or extremities; frequently seen in young children, during warm months, and/or with poor hygiene.
True or false - the strains of S. pyogenes that cause impetigo are the same as those that cause pharyngitis.
False - they are different strains
What is streptokinase?
A destructive enzyme virulence factor of S. pyogenes that cleaves fibrinogen and fibrin, facilitating spread in infected tissues.
What are the two primary hemolysins of S. pyogenes and what do they do
Streptolysin S and Streptolysin O; lyse RBCs, leukocytes, kill phagocytic cells, spread bacteria in tissues
An 8 year old boy presents to his pediatrician. He has a low-grade fever and a diffuse erythematous rash over his chest that developed 2 days after he complained of a painful sore throat. An exudate was present over the tonsillar area of his throat and covered his tongue. He has a positive rapid antigen test. What is the diagnosis?
Scarlet fever is a complication of streptococcal ___. Describe its progression.
Pharyingitis; a rash first appears as tiny red bumps on the the chest and abdomen. The rash is fine, red, and rough-textured; it blanches upon pressure. It appears 12-48 hours after fever. It generally starts on the chest, armpits, and behind the ears. It spares the face, though some circumoral pallor is characteristic.
What are the characteristic features of scarlet fever?
1. Sore throat
3. Strawberry tongue
4. Rash that fades after 3-4 days, followed by desquamation
A 35 year old man presents to the emergency department. He reports 3 days of malaise, diffuse myalgia, and low grade fever. Over the next several hours, the pain became excruciating. Extensive necrotizing faciitis was present on surgical exploration. What is the diagnosis?
Necrotizing fasciitis caused by S. pyogenes
What happens in necrotizing fasciitis caused by S. pyogenes?
It is a strep infection that occurs deep in the subcutaneous tissues; it spreads along the fascial planes and destroys muscle and fat.
Describe toxic shock-like syndrome caused by S. pyogenes.
Multisystem organ failure (heart, respiratory tract, kidney) caused by SPE toxins (similar to TSST-1). Unlike patients with staph toxic shock, cultures are usually positive for Group A strep.
Streptococcal pyrogenic exotoxin (SPE) involves three distinct heat labile toxins (A, B, C). They cause strep toxic shock-like syndrome. They are also responsible for the rash in ___.
What are two important post-streptococcal sequelae?
1. Rheumatic fever
2. Acute glomerulonephritis
What is rheumatic fever?
Non-suppurative inflammatory disease that occurs 1-5 weeks after strep pharyngitis.
What are the symptoms of rheumatic fever?
Fever, carditis, subcutaneous nodules, chorea, polyarthritis (attacks reoccur into adulthood)
Describe the characteristic cardiac lesions of rheumatic fever.
Aschoff bodies and valvular damage that leads to possible endocarditis later in life
What are the symptoms of acute glomerulonephritis?
Edema, hypertension, hematuria, proteinuria; results from antigen + antibody + complement deposited in glomeruli
An infant male was delivered spontaneously at term. Examinations were normal during the first week of life. On day 13, the baby was admitted to the hospital with generalized seizures. CSF was collected by lumbar puncture and a Gram positive coccus was isolated by culture in lab. What is the diagnosis?
Late-onset group B strep neonatal disease
When does early onset neonatal disease occur and what are three causes?
First week of life; bacteremia, pneumonia, or meningitis
When does late onset neonatal disease occur and what is frequently seen?
1 week to 3 months of age; bacteremia with meningitis
S. agalctiae are part of normal flora in what locations?
Throat, vaginal, GI tract
S. agalctiae often cause infections in what patient population?
Pregnant women (though it can still infect men and non-pregnant women)
What are some illnesses associated with S. agalctiae?
Neonatal pneumonia, sepsis, meningitis, skin/wound infections in adult diabetic patients, endocarditis
How do babies get exposed to S. agalctiae?
Maternal colonization of vagina or rectum exposes baby at delivery; lack of protective maternal Ab
___ on the polysaccharide capsule of S. agalctiae inhibits complement, allowing the organism to multiply.
How can perinatal GBS disease be prevented?
Culture should be performed on vaginal/rectal swabs collected at 35-37 weeks gestation
How should the lab test for GBS to prevent perinatal GBS disease?
Combined vaginal/rectal swab (improved isolation rates over vaginal swab alone); use selective enrichment broth to increase isolation by 50%
What are the three other groups of beta hemolytic strep?
Group C, F, G
What are three diseases associated with Group C strep?
1. Veterinary infections
2. Pharyngitis in college age patients
Group F strep is associated with ___.
Group G strep is associated with ___, and ___ in neonates and elderly.
A 68 year old female presents to the ED. She developed fever, chills, weakness, and a productive cough with pleuritic chest pain 3 days prior to admission. At the time of admission, she was febrile and in moderate respiratory distress. Chest radiograph showed bilateral infiltrates with pleural effusions. What is the diagnosis?
Pneumonia caused by S. pneumoniae
True or false - S. pneumoniae are part of the normal flora of the human upper respiratory tract.
Patients with pneumoniae caused by S. pneumoniae usually have a these two symptoms.
1. Productive cough
2. Chest pain (pleurisy)
True or false - a culture for someone with pneumoniae caused by S. pneumoniae is not always useful.
What is the most common cause of community acquired acute bacterial pneumonia?
What are 5 conditions that predispose patients to bacterial infection with S. pneumoniae?
2. Diabetes mellitus
3. Chronic lung disease
4. Chronic renal disease
5. Certain malignancies
There are more than ___ known serotypes of S. pneumoniae.
What is an important virulence factor of S. pneumoniae and what does it do?
Polysaccharide capsule; prevents phagocytosis
What is pneumolysin?
S. pneumoniae virulence factor that damages ciliated cells and activates alternative complement pathways
___ is the most common clinical presentation of pneumococcal disease among children younger than 2 years.
Pneumococcal disease is the most common cause of ___ in the United States.
What are 9 pneumococcal diseases?
Paranasal sinusitis, otitis media, meningitis, osteomyelitis, septic arthritis, endocarditis, peritonitis, cellulitis, brain abscesses
Viridans streptococci are either ___ or ___ hemolytic.
How are viridans streptococci different from beta strep?
They lack hemolysins and the toxins of beta strep
Viridans streptococci are normally found in the flora of the ___.
Upper respiratory tract
Viridans streptococci are a major cause of what three things?
Dental caries; endocarditis; sepsis in neutropenic cancer patients
What are the 4 groups of viridans streptococci?
Sanguis, Mitis, Mutans, Salivarius
The bovis group streptococci cause what 3 issues?
3. Native and prosthetic-valve endocarditis
Isolation of strep bovis group S. gallolyticus ss. gallolyticus from the blood is associated with ___.
Carcinoma of the colon
Anginosus group streptococcus involves ___ formation in deep tissue.
Anginosus group strep comes from what 4 groups?
C, F, G, U
Anginosus group strep are usually commensals isolated from what 4 locations?
Mouth, oropharynx, GI tract, vagina
A 65 year old man has been hospitalized for several weeks post-surgery. He develops symptoms consistent with UTI, including pain and fever. He was recently catheterized as part of a post-surgical complication. A Gram positive coccus is recovered from his urine on culture in the laboratory. What is the diagnosis?
Catheter associated urinary tract infection (CAUTI) caused by enterococcus faecalis
What is the most common site of infection with Enteroccocus faecalis?
Enterococcus species formally belong to Group ___ streptococci.
What is the most common vancomycin resistant enteroccci in the US?
What are the three Van phenotypes?
1. Van A - plasmid mediated (high level resistance)
2. Van B - plasmid mediated (high or low level resistance)
3. Van C - chromosomal (intrinsic resistance)
What 3 lab tools can be used to diagnose strep?
1. Gram stain
2. Group specific carbohydrate
Compare and contrast staph and strep as it relates to catalase.
Staph: catalase +
Strep: catalase -
Compare and contrast staph and strep as it relates to cocci.
Staph: cocci in clusters
Strep: cocci in paris and chains
Compare and contrast staph and strep as it relates to growth media.
Staph: grows in minimal media at 35-37 C
Strep: requires complex media at 35-37 C
Compare and contrast staph and strep as it relates to preferred atmosphere.
Strep: anaerobic or CO2
S. pneumoniae and enterococcus are Gram ___ (+/-) ___ (shape).
Positive; cocci (usually diplocci)
What are some lab features of S. pneumoniae?
1. Produces a capsule
3. Inhibited by optochin
4. Bile soluble
What is the PYR test?
Quick spot test for enterococcus and Group A strep