Gram Positive Bacteria

    Gram positive bacteria have a cell wall composed of approximately 90% peptidoglycan bound by transpeptide linkages. This structure is associated with teichoic acids, which maintain a low pH with respect to the surrounding environment.  The cell wall lies above the cell membrane, and there is no outer membrane.  These cells stain purple as the crystal violet primary stain and iodine mordant form an insoluble precipitate which is trapped as the acetone-alcohol destain dehydrates the cell wall.
 
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Bacillus subtilis (1000X).  This is an example of a typical streptobacillus.  Note the clear endospores inside the chains of cells.  B. subtilis is a common inhabitant of soil and is thermoduric (can withstand high temperatures). Some strains of this species produce the antibiotic bacitracin, a cell wall inhibitor used as a topical chemotheraputic agent.
 
 

Staphylococcus aureus (1000X).  This is a organism which exhibits the typical staphylococcus (grape-like cluster) arrangement of cells.  S. aureus is a halotolerant (salt tolerant) organism associated with the nasal mucosa of mammals which has both benign and pathogenic strains. Illnesses associated with this organism include toxic shock syndrome (TSS), scalded skin syndrome in infants, intoxication-based gastroenteritis, pimples, boils, and other inflammations.  It is a nosocomial (hospital-borne) agent of infection.
 
 

Staphylococcus epidermidis (1000X).  Another staphylococcus, though this organism is a nonpathogenic normal microflora component of the skin.  Like S. aureus, it is a halotolerant microorganism.
 
 

Micrococcus luteus (1000X).  This soil and air-borne contaminant of media forms groups of two to four cocci, is catalase positive like the staphylococci, and forms distinct yellow pigmented colonies which are circular with entire margins.
 
 


Corynebacterium xerosis (1000X).  This slightly curved rod is a normal flora component of the skin of mammals which has arrangements of two, fours, V formations or palisades.  This species does not form spores and is commonly referred to by the generic term "diptheroid", which is based on its relation to C. diptheriae, the etiologic agent of diptheria.
 
 

Streptococcus pyogenes (1000X).  This streptococcus is an inhabitant of the oral cavities of mammals and is the etiologic agent of with strep throat (pharyngitis), Scarlet fever, Erysipelas, Pneumonia, bacteremia, necrotizing fasciaitis (IGAS; Invasive Group A Streptococcus), and other systemic infections.
 
 

Streptococcus pneumoniae (1000X). This streptococcus is a major agent of bacterial pneumonia. The pathogenic strains form capsules which can be visuallized with a capsule stain.
 
 

Enterococcus faecalis (1000X). This enterococcus is a normal flora inhabitant of the gastrointestinal tract of mammals, and is an opportunistic pathogen associated with pyogenic infections. Recently, strains of vancomycin resistant enterococci have begun to appear which are probably spread by the nosocomial route.

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