Streptococcus and Enterococcus
Hemolysis (the disintegration of a red blood cells with liberation of hemoglobin) of Streptococcus and Enterococcus species on Sheep Blood Agar.
-Alpha (green/brown) -Beta (clear, colorless zone) -Gamma (no hemolysis)
Strep pneumoniae infections?
-Can be normal flora in upper respiratory tract -Most frequent cause of otitis media in children -Community acquired bacterial pneumonia (the one we worry about and treat aggressively) -Meningitis -Sinusitis
Streptococcus agalactiae infections?
-Colonizer of female genital tract (NORMAL) -Leading cause of meningitis, septicemia, and pneumonia in infants -UTI and bacteremia is elderly and immunocompromised -Post-surgical gynecologic infection
Gamma streptococci
-No hemolysis -There is no such thing as "gamma streptococci"
Enterococcus infections?
-Normal flora of intestinal tract -UTI -Endocarditis -Wound infections
Streptococcus pyogenes infections?
-Pharyngitis, tonsillitis, swollen lymph nodes (strep throat) -Otitis media: middle ear infection -Scarlet fever: strep throat with rash. -Impetigo: an acute contagious staph or strep skin disease characterized by vesicles, pustules, and yellowish crusts -Cellulitis: subcutaneous inflammation of connective tissue, flesh eating bacteria Post-streptococcal sequelae- -Rheumatic fever: auto-immune reaction in heart muscles -Acute glomerulonephritis: auto-immune reaction in renal glomeruli
Viridans group Strep infections?
-Predominant organisms of normal upper respiratory flora -Most common cause of subacute bacterial endocarditis
Streptococcus pneumoniae is classified as what?
Alpha Hemolytic
Viridans group Streptococcus
Alpha hemolytic
The viridans streptococci (i.e., α-hemolytic and nonhemolytic streptococci) are subdivided into five groups. What are the groups and the specific diseases associated with each group?
Anginosus group—abscess formation; mitis group—septicemia in neutropenic patients and endocarditis; salivarius group—endocarditis; mutans group—dental caries; bovis group—bacteremia associated with gastrointestinal cancer and meningitis.
Streptococcus agalactiae (Group B) is classified as what?
Beta Hemolytic
Streptococcus pyogenes (Group A) is classified as what?
Beta Hemolytic
Gram positive or gram negative?
Gram positive cocci, oval or round and usually in chains
Characteristics of Streptococcus and Enterococcus
Normal flora in humans in the oral cavity, nasopharynx, and intestinal tract Most are facultative anaerobes: can survive in anaerobic environments, but they don't like to Catalase negative Nonmotile Non-spore forming (all spore formers are bacilli) Grouped according to appearance of colonies and hemolytic reaction on sheep blood agar.
Antibiotics for Streptococcus
Penicillin Penicillin- resistant S. pneumoniae is treated with vancomycin
Group D Strep
Possible S. bovis group, but strongly associated with GI diseases, especially GI carcinomas.
Alpha streptococci
Produce alpha hemolysis Partial destruction of RBC's around colony, giving green/brown discoloration of medium
Beta streptococci
Produce beta hemolysis RBC completely lysed; giving a clear, colorless zone around colony. Two common toxins produce beta hemolysis -streptolysin O- oxygen labile (causes subsurface hemolysis if the plate has been stabbed) -streptolysin S- oxygen stable (causes surface hemolysis)
Antibiotics for Entercoccus
Resistant to penicillins or cephalosporins when given alone If VRE resistant, can be treated with Synercid or Linezolid (quinolones)
What sites of the human body are normally colonized with Streptococcus pyogenes, Streptococcus agalactiae, and Streptococcus pneumoniae?
S. pyogenes colonizes the oropharynx and skin surface and causes pharyngitis, skin and soft-tissue infections, and nonsuppurative infections (rheumatic fever, glomerulonephritis); S. agalactiae colonizes the female genital tract and causes neonatal infections, as well as infections in pregnant women and older adults; S. pneumoniae colonizes the oropharynx and causes pneumonia, sinusitis, otitis media, and meningitis.
What biochemical properties are used to separate enterococci from the staphylococci and streptococci?
Staphylococci are catalase positive in contrast with streptococci and enterococci; enterococci are PYR positive, whereas most streptococci (except S. pyogenes ) are PYR negative. The microscopic morphology of enterococci (gram-positive cocci in pairs) is also a distinguishing feature (staphylococci are in clusters, and most streptococci are in long chains).
Enterococcus classification
Streptococci of fecal origin or enteric strep Type with Lancefield group D Types responsible for human infection: -E. faecalis -E. faecium Relatively low virulence
Enterococci, like many other bacteria, can cause urinary tract infections but primarily in hospitalized patients. What characteristics of this bacterium are responsible for the predilection for disease in this population?
The bacteria are resistant to many commonly used antibiotics (oxacillin, cephalosporins, aminoglycosides, vancomycin), so infections are most commonly seen in patients hospitalized for prolonged periods and receiving broad-spectrum antibiotics.
