Gram positive organisms, descried by Gram in 1884 are the organism which retain the primary stain of crystal violet and do not get decolorized and do not take counterstain like carbol fuchsin or safranin. There are factors which make them gram positive like acidic protoplasm and addition of iodine helps to fix the stain, cell wall is more mucoid as compared to gram negative.
Staphylococcus sp are gram positive which are seen as ovoid or spherical (0.8-0.9 µm) grape like clusters with staining, coagulase positive and ferments carbohydrates. It can be differentiated by Micrococcus sp due to tetrad arrangement, coagulase negative and it ferments carbohydrate oxidatively. Other important sp is Staphylococcus saprophyticus, and Staphylococcus epidermidis.
Staphylococcus are further divided based on pigmentation into three types of Staphylococcus . Staphylococcus aureus which produces golden yellow colonies and are pathogenic, Staphylococcus albus produces white colony which may be non-pathogenic, Staphylococcus citreus produces lemon yellow colonies which may also be nonpathogenic. Staphylococcus can also be divided into sub-groups (I-VI) depending upon the biochemical reaction like coagulase, phosphatase, acid from glucose, arabinose, lactose, mannitol, acetoin and pigment production.
Pathogenic strains of Staphylococcus is production of coagulase ,mannitol fermentation ,beta haemolysis,golden yellow pigmentation, liquefies gelatin,produces phosphatase, hydrolyses urea, reduces nitrate to nitrite , causes tellurite reduction, deoxyribose nuclease enzyme production.
Staphylococcus may cause pyogenic lesions like carbuncles, furuncles, styes, boiles,abscess,impetigo,pemphigus neonatorum.It can also cause deep infections like acute osteomyelitis,tonsillitis,pharyngitis,sinusitis,pneumonia,pulmonary abcess,breast abcess, meningitis,endocarditis,renal abcess and sepsis It can also cause scalded skin syndrome, toxic shock syndrome, and food poisoning.
Staphylococcus saprophyticus is coagulase negative and resistant to Novobiocin. It is known to cause urinary tract infection and may cause endocarditis in patients undergoing cardiac surgery.
Streptococcus sp are ( 0.5-1µm) gram positive cocci seen in pairs or chains which can be long or short They are classified according to growth on blood agar plate as alpha haemolytic (partial green lysis of RBC ), Beta haemolytic (2-4mm complete lysis of RBC clear zone )The beta haemolytic streptococci are further classified into Lancefield group on basis of polysaccharide-C hapten in cell wall. Streptococcus Lancefield A, Streptococcus pyogenes is further divided into Griffith typing(80 types).
Streptococcus pyogenes may cause sepsis and invasive infections as compared to Staphylococcus sp.
Streptococcus pyogenes may cause Tonsillitis, pharyngitis, Spread can occur to otitis media,mastoiditis, Ludwig angina, and supparative adenitis , Scarlet fever (erythrogenic toxin leading to rash).Meningitis, broncho-pneumonia, empyema may also occur. In the skin, it may cause wounds, burns, lymphangitis and cellulitis. Impetigo is caused in young children leading to glomerulonephritis. Erysipelas diffuse infection of the superficial lymphatic system. Other organs like genital tract puerperal sepsis and brain, lungs, liver, and kidney infections may be affected. Nonsuppurative complications like Acute Rheumatic fever and acute glomerulonephritis.
Streptococcus agalactiae may cause puerperal infection, sepsis, meningitis, osteomyelitis, endocarditis, meningitis, arthritis, sepsis, pyoderma.
Alpha haemolytic Streptococcus like Streptococcus mitis, Streptococcus salivarius, Streptococcus viridans cause bacterial endocarditis.
Enterococcus sp , gram positive alpha haemolyticngram positive cocci , ability to grow in 6.5%sodium chloride and 40 %bile and 45 ᵒC . It can cause urinary tract infection, wound infection, infective endocarditis, biliary tract infection, peritonitis, suppurative abdominal lesions, and septicemia.
Anaerobic Streptococcus like Peptococcus, Streptococcus, petostreptococcus may lead to Puerperal sepsis, and puerperal septicemia, brain abscess, and other suppurative and gangrenous lesions.
Streptococcus pneumonia are 1 µm gram-positive lanceolate (one end broad, one end pointed, flame-shaped ) diplococci and are capsulated . On blood agar flat, umbonated colonies showing alpha hemolysis. They are optochin sensitive and bile soluble. They cause lobar pneumonia, bronchopneumonia, meningitis, and other suppurative lesions like empyema, pericarditis, otitis media, sinusitis, conjunctivitis, and peritonitis.