A Gram stain showing gram-positive cocci in pairs, or diplococci, is a morphological characteristic of several bacteria. Gram stains can be positive or negative, depending on the cell wall composition of the bacteria. Morphologies in Gram stains include cocci, rods, coccobacilli and spirochetes
The most common gram-positive cocci that form pairs include most Streptococcus species, Listeria and Enterococcus bacteria. All of these organisms can cause infections in humans. Accurate identification of the bacteria is essential for proper antibiotic treatment.
Streptococcal bacteria can cause a variety of infections that target multiple organ systems, including strep throat, pneumonia and necrotizing fasciitis. Along with Listeria monocytogenes, it can also cause meningitis in newborns and those with compromised immune systems. Listeria can be found on contaminated food that has not been properly cleaned prior to ingestion. Both Streptococcus and Listeria have Gram stain morphologies of cocci pairs or short chains.
Enterococcus species look similar to Steptococcus bacteria and both are found naturally in the human intestinal tract. In the past, Enterococci bacteria were classified as Group D Streptococci before being distinguished in their own genus. Enterococcus species have higher rates of antibiotic resistance compared to Streptococcus and Listeria, and typically require more aggressive antibiotic therapies.