PowerPoint Contents
Author: Rebecca Buxton
Citation: Rebecca Buxton. 2007. Examination of gram stains of miscellaneous tissue infections.
Publication Date: February 2007
Streptococcus anginosus (Enlarged view)
Slide 1. Brain abscess
In this aspirate, gram-positive cocci form chains with peculiar configurations resembling balls of yarn. Organisms of the Streptococcus anginosus group (historically known as Streptococcus milleri) grew on this culture. The S. anginosus group is commonly isolated from brain abscesses.
Clostridium perfringenes (Enlarged view)
Slide 2. Gangrene of the leg caused by Clostridium perfringenes
This aspirate shows many gram-positive bacilli, some with square ends. Because Clostridium perfringenes produces a potent phospholipase that lyses neutrophils, few neutrophils are present on the slide. The size of C. perfringenes is usually uniform, and many have square ends. C. perfringenes can decolorize readily to appear gram variable or gram negative.
Streptococcus anginosus (Enlarged view)
Slide 3. Osteomyelitis caused by the Streptococcus anginosus group
This bone aspirate contains a few neutrophils and gram-positive cocci singly, in pairs, and in chains. Organisms are often sparse in bone aspirates. Gram-negative bacteria can be particularly difficult to detect within the reddish background material.
Corynebacterium species (Enlarged view)
Slide 4. Osteomyelitis caused by Corynebacterium species
This sternal aspirate contains only a few neutrophils and many small gram-positive bacilli that resemble diphtheroids. Because of their method of division, corynebacteria tend to form sharp angles with one another, many of the configurations are said to resemble "Chinese characters.
Streptococcus pyogenes (Enlarged view)
Slide 5. Septic arthritis caused by Streptococcus pyogenes
In this aspirate of a knee joint are chains of intracellular gram-positive cocci. S. pyogenes cannot be differentiated from other chaining streptococci by its appearance on Gram stain. Microaerophilic streptococci, for example, could look like this.
Moraxella osloensis (Enlarged view)
Slide 6. Moraxella osloensis conjunctivitis
Material swabbed from an eye contains many short, fat gram-negative bacilli. Their structure and the source of the specimen suggest that Moraxella caused the infection. Many organisms are paired, and since they may also be nearly circular, they may resemble Neisseria.
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