Gram Positive Cocci- Streptococci PDF

Gram Positive Cocci- Streptococci Hiba J. A. Barqawi 2023 College of Medicine University of Sharjah United Arab Emirates Optochin sensitive Optochin resistant Streptococci Optochin sensitive Optochin resistant  Gram Positive Cocci Sta...

Gram Positive Cocci- Streptococci Hiba J. A. Barqawi 2023 College of Medicine University of Sharjah United Arab Emirates Optochin sensitive Optochin resistant Streptococci Optochin sensitive Optochin resistant  Gram Positive Cocci Staphylococci – S. aureus – S. epidermidis – S. saprophyticus Streptococci – S. pyogenes (Group A) – S. agalactiae (Group B) – S. pneumoniae – Viridans Streptococci Enterococci – Enterococcus faecalis – Enterococcus faecium  Streptococci Gram positive cocci Chains or pairs Usually capsulated Non-motile Non-spore forming Facultative anaerobes Fastidious Catalase negative  Classification of Streptococci Three different but overlapping schemes: α -hemolysis 1. Serological Grouping – Lancefield Grouping β -hemolysis – (A-W) 2. Hemolysis – Complete (Beta-hemolysis) – Partial (Alpha-hemolysis) – None (Gamma-hemolysis) ϒ - hemolysis 3. Biochemical properties  Classification- Lancefield In 1927 Rebecca Lancefield discovered the ability to group streptococci based upon differences in streptococcal cell wall polysaccharides She found the species in each ‘group’ shared significant clinical properties Groups A, B, C, D, F, and G were the primary groups likely to form human infections Lancefield later determined that viridans strep and pneumococci did NOT possess antigens that reacted with her antisera  Streptococci of Medical Significance Streptococcus pyogenes (Group A) Streptococcus agalactiae (Group B) Streptococcus pneumaniae (Non-groupable) Viridans Group (Non-groupable)  S. pyogenes Transient colonisation in upper respiratory tract and skin Person-to-person spread by respiratory droplets (pharyngitis) or through breaks in skin after direct contact Diseases by S. pyogenes: – Superficial/deep infections: Pharyngitis, invasive infections (cellulitis, bacteraemia, pneumonia, necrotizing fasciitis) – Immunologic illnesses: Acute post-streptococcal glomerulonephritis, rheumatic fever – Toxin-mediated diseases: Streptococcal toxic-shock syndrome, necrotizing fasciitis  Disease caused by S. pyogenes Suppurative (characterized by an abscess formation) – Non-Invasive Pharyngitis (“strep throat”) 90% Skin infections, Impetigo – Invasive Erysipelas Scarlet fever Pyoderma Erysipelas Cellulitis Necrotizing fasciitis Cellulitis Non Suppurative (immune mediated) – Rheumatic fever – Glomerulonephritis  Necrotizing fasciitis caused by S. pyogenes The patient presented with a 3-day history of malaise, diffuse myalgia, and low-grade fever. Over 3 hours, the pain became excruciating and was localized to the calf Note the two small, purple bullae (arrows) over the calf Extensive necrotizing fasciitis present on surgical exploration The patient died despite aggressive surgical and medical management  Streptococcus agalactiae These belong to Lancefield Group B streptococci Normal flora of upper respiratory and female genital tract Cause neonatal disease (meningitis, pneumonia and bacteremia), infections in pregnant women (endometritis, wound infections, UTIs), infections in other adult patients (bacteremia, pneumonia, bone and joint infections, SSTIs) Typically are beta-hemolytic Positive CAMP test CDC recommendation: Vaginal/ rectal swab to detect GBS colonization at 35-37 weeks (prophylactic penicillin at labour) Penicillin G is drug of choice – For high-risk babies, penicillin given at least 4 hours before delivery  Streptococcus pneumoniae Gram positive diplococci possessing a polysaccharide capsule Alpha-hemolytic In adults, most common cause of community- acquired pneumonia and bacterial meningitis Etiological agent of sinusitis, otitis media, bacteremia Respiratory droplet transmission Disease is more common in cool months Optochin Test- – S. pneumoniae: optochin-sensitive – Other α-hemolytic streptococci e.g. Streptococcus viridans: resistant Vaccines available: – pneumococcal conjugate vaccine (PCV13 –infants) – pneumococcal polysaccharide vaccine (PPSV 23- adults)  Viridans Streptococci Viridans streptococci include several species: S. mitis, S. mutans, S. salivarius, S. sanguis and S. anginosus Typically they are alpha-hemolytic, but they may be non-hemolytic The viridans streptococci are the most prevalent members of normal microflora of the upper respiratory tract May reach the bloodstream as a result of trauma or dental procedures. Principal cause of endocarditis on abnormal heart valves (prophylaxis antibiotics) Diseases associated with Viridans streptococci: – Abscess formation in deep tissues (S. anginosus) – Septicaemia in neutropenic patients (S. mitis) – Subacute infective endocarditis (S. mitis and S. salivarius) – Dental caries (S. mutans) due to biofilm formation – Malignancies of GI tract (S. bovis) – Meningitis (S. suis and S. mitis)  Gram Positive Cocci Staphylococci – S. aureus – S. epidermidis – S. saprophyticus Streptococci – S. pyogenes (Group A) – S. agalactiae (Group B) – S. pneumoniae – Viridans Streptococci Enterococci – Enterococcus faecalis – Enterococcus faecium Enterococci  Enterococci Gram positive cocci arranged in pairs and short chains Grow both aerobically and non-aerobically Previously classed as Group D Streptococci but then reclassified into a new genus Complex nutritional needs but enriched sheep blood agar supports their growth Large, non-hemolytic colonies after 24 hours incubation Can grow in presence of high conc. of NaCl and bile salts 6.5% NaCl and 40% bile Diseases include urinary tract infections, wound infections (particularly intraabdominal and usually polymicrobic) and bacteraemia and endocarditis  Enterococci Enterococci either inherently resistant to many commonly used antibiotics or have acquired resistance genes All strains carry some drug resistance Enteric bacteria recovered in faeces of humans and animals – E. faecalis found in the large intestine in large concentrations and in the genitourinary tract (bile/salt tolerance allows survival in bowel and gall bladder) – Distribution of E. faecium similar to that of E. faecalis but the organisms are found less frequently Enterococci not commonly isolated in the respiratory tract or on skin surface except in hospitalised patients who have been treated with broad- spectrum antibiotics (allows the spread from the intestinal tract to other mucosal and skin surfaces) Bile Esculin Agar (BEA) for identification of Enterococci Gram stain of blood culture with Enterococcus faecalis Which GPC would be most likely responsible for the following conditions? – Pharyngitis in young adult – Streptococcus pyogenes (Group A Streptococci) – Scalded Skin Syndrome (Ritter’s Disease) in neonate – Staphylococcus aureus – Neonatal meningitis – Streptococcus agalactiae (Group B Streptococci) – Septicaemia in a hospitalized patient in the ICU – Staphylococcus epidermidis – Toxic Shock Syndrome in a 30-year-old female – Staphylococcus aureus – Urinary tract infection in a 25-year-old female – Staphylococcus saprophyticus – Dental caries – Streptococcus mutans (Viridans Streptococci) – Pneumonia in 32-year-old male – Streptococcus pneumoniae – Impetigo in a 4-year-old child – Staphylococcus aureus and Streptococcus pyogenes – Necrotizing fasciitis – Streptococcus pyogenes (Group A Streptococci) – Endocarditis in patient with artificial heart valve – Viridans Streptococci – Urinary tract infection in a hospitalized patient in the ICU – Staphylococcus epidermidis – Cellulitis – Staphylococcus aureus and Streptococcus pyogenes