Antigen detection tests These tests are 60-90% sensitive, 98-99% specific compared to the culture methods. Serology A rise in the titer of antibodies to many group A streptococcal antigens can be estimated. Such antibodies as antisterptolysin O (ASO) mainly in respiratory disease. A high titer (ASO > 250 units) indicate recent or repeated infection and found mostly in rheumatic fever individuals. anti-DNAase and anti hyaluronidase mainly in skin infection
Treatment All S. pyogenes are susceptible to penicillin G. Antimicrobial drugs have no effect on glomerulonephritis and rheumatic fever. So penicillin need to be taken for 10 days for pharyngitis. This extensive therapy is necessary because large number of Streptococci persist in the pharynx even after 3-4 days of treatment. Erythromycin and cephalosporins are used
streptococcus pneumoniae (pneumococcus) Pneumococci are normal inhabitants of the upper respiratory tract of 5-40% of humans and cause pneumonia, sinusitis, otitis, bronchitis. Bacteremia, meningitis and other infections. Morphological characteristics Cultural characteristicsAerobic and facultatively anaerobic, grow best with 5-10% CO2.Colonies on blood agar are small, round low convex and produce partial hemolysis (α hemolysis) of blood. differentiated from α hemolytic Streptococci colonies by being sensitive to optochin test and bile solubility test positive (soluble in bile).
Epidemiology and control Strep. Pneumoniae account for about 60% of all bacterial pneumonia. Healthy carrier is more important in disseminating Pneumococci than the sick patients. A polysaccharide vaccine containing 23 types licensed in united state used for elderly and immunosuppressed individuals. Treatment Penicillin is the drug of choice, but 5-10% of Pneumococci are penicillin resistant. Resistance to erythromycin and tetracycline occur. High resistant strains are treated by Vancomycin and moderate resistant strains by third cephalosporins.
Streptococcus agalactiae (group B Streptococci).Are β hemolytic and produce zone of hemolysis about1-2mm in diam. around the colony.Considered part of the normal vaginal flora in 5-25% of women, and an important cause of neonatal sepsis, meningitis and lung infection.Hydrolyze sodium hippurate and give a positive CAMP test (Christie, Alkins, Munch, Peterson).Ampicillin is the drug of choice for treatment..
Enterococci (group D)Are part of enteric flora, they react with group D antisera. Enterococcus faecalis is the most common species that cause enterococcal infection.the most common cause of nosocomial infection mainly in ICU.transmitted from patient to another primarily on the hands of hospital personnel. The common sites of infection are urinary tract, wounds, biliary tract and blood, and may cause meningitis and bacteremia in neonates and endocarditis in adults. nonhemolytic and occasionally α hemolytic, PYR positive, grow in the presence of bile, hydrolyze esculin and grow in 6.5% Nacl.
Antibiotic resistanceIntrinsic resistance intrinsically resistant to cephalosporins, pencillinase resistant pencillins and monbactum, low-level resistance to aminoglycosides, intermediate resistant or susceptible to fluoroquinolones and less susceptible than Streptococci to penicillin and ampicillin. Resistance to aminoglycosideCombination of penicillin or vancomycin plus an aminoglycoside is used for severe enterococcal infections.Enterococci have intrinsic low level resistance to aminoglycosides. Some enterococci have high level resistance to aminoglycosides and are not susceptible to the synergism. Vancomycin resistance Resistance to vancomycin have increased in frequency, and certain strains are not synergistically susceptible to vancomycin+ aminoglycosides.β- lactamase production and resistance to β- lactams. Gen encoding for β- lactamase is the same gen as found in S. aureus. Trimethoprim- sulfamethoxazole (TMP-SMZ) resistance.
Viridance streptococciInclude many species as S. mitis an S. mutans.α hemolytic but may be non hemolytic.Not inhibited by optochin and colonies are not soluble in bile (bile solubility test).prevalent members of the normal flora of the upper respiratory tract.associated with dental caries and they are the leading cause of subacute bacterial endocarditis in persons with abnormal valve due to congenital heart diseases and rheumatic lesions.