Slide 2. Streptococcus agalactiae (group B streptococcus)
Large, round, gram-positive cocci are found singly and in pairs, chains, and clumps. The cocci are larger and rounder than pneumococci, which rarely, if ever form chains of more than four cocci in sputum. Various nonpneumococcal streptococci cannot be differentiated by their appearance on a Gram stain. When chains of streptococci overlap, they can resemble clusters of staphylococci, making differentiation of these two kinds of bacteria difficult.

Slide 3. Staphylococcus aureus
Numerous gram-positive cocci, round and large, are visible as single organisms, pairs, and grape-like clusters. The clusters strongly suggest that the organisms are staphylococci. The red strands of mucus in the background are common in good sputum specimens.

Slide 4. Nocardia asteroides
Nocardia asteroides are branching, beaded, gram-positive bacilli. Actinomyces look the same, and Streptomyces species are also long, branching gram-positive rods, but usually are not beaded.

Slide 5. Nocardia asteroides
When stained with a modified acid-fast technique, as this specimen is, most Nocardia are acid fast, but Actinomyces and Streptomyces species are not. The presence of branching, red rods on the blue background confirms that the organism is acid fast and thus most likely Nocardia.

(Labeled view)