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Author: Rebecca Buxton​

Citation: Rebecca Buxton. 2007. Examination of gram stains of bacterial skin infections.​

Publication Date: February 2007​

Streptococcus pyogenes/Staphylococcus aureus (Enlarged view)​
Slide 1. Streptococcus pyogenes and Staphylococcus aureus​
This specimen includes gram-positive cocci singly, and in pairs, chains, and clusters. Some are overdecolorized and stain red. To determine whether they are streptococci or staphylococci from the smear is difficult. In fact both grew on the culture, a common occurrence for specimens from skin infections such as impetigo, ecthyma, and some cutaneous abscesses.​

Mixed infection (Enlarged view)​
Slide 2. Mixed infection​

This Gram stain of exudate from a skin ulcer shows many gram-negative coccobacilli; short, plump gram-negative bacilli; and gram-positive cocci singly, in pairs, and in clusters. Because such a mixture of organisms commonly colonizes specimens from skin ulcers, bacterial cultures are not usually diagnostically worthwhile in the absence of cellulites, abscess, or suspicion of cutaneous diphtheria. Only in these circumstances are the bacteria in the ulcer likely to be pathogenic.​

Mixed infection (Enlarged view)​
Slide 3. Mixed infection​

This specimen, from a necrotizing penile infection, includes many gram-negative coccobacilli, gram-negative rods longer than the coccobacilli, gram-positive cocci, and gram-positive bacilli. To identify any organism confidently is difficult. Cultures grew Escherichia coli (the larger gram-negative bacilli), Bacteroides species (the gram-negative coccobacilli), and Clostridium perfringenes (the gram-positive bacilli).​

Corynebacterium diphtheriae (Enlarged view)​
Slide 4. Corynebacterium diphtheriae​

​Material swabbed from a skin ulcer includes gram-negative coccobacilli and a moderate number of gram-positive bacilli, many of which meet at acute ​
angles, a configuration characteristic of "diphtheroids." The culture grew mixed cutaneous flora and Corynebacterium diphtheriae.​

Corynebacterium diphtheriae (Labeled view)​
(Labeled view)​

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