Staphylococci and Streptococci are often confused with each other, with a lot of people using both terms interchangeably to refer to certain pathogenic bacteria, which is an incorrect practice. However, similar to staphylococci, certain group and strains of streptococcus are also pathogenic to humans. On the other hand, certain strains are known to be useful and even beneficial. A close relative of the lactic acid bacteria, Strep bacteria shape is spherical and the bacterial organisms that comprise this genus are all gram positive organisms. As many as 27 different species of bacteria are grouped under the Streptococcus genus.
Strep Bacteria and Humans
While a lot of Streptococcus species are pathogenic and are responsible for causing a number of bacterial diseases and infections such as pneumonia, meningitis, inflammation of the endocardium (inner surface layer of the heart), sepsis (or bacteremia), flesh-eating disease, bacterial pharyngitis, etc. A lot of Streptococcus species are a part of the naturally occurring microbial flora of the mouth, intestines, skin and respiratory tract of humans and various other mammals.
There are also certain Streptococcus species that are of great use to humanity. You may be surprised to know that the poriferous Emmental cheese which is the signature, world-famous Swiss cheese variety, uses Strep (Streptococcus thermophilus, to be specific) as one of its basic ingredients! Let's take a look at the pathogenic side of certain species of this genus of bacteria in the following segment.
Some of the most common infections and diseases caused by Streptococcus bacteria species include dental caries, strep throat (bacterial pharyngitis), meningitis, scarlet fever, rheumatic fever, Glomerulonephritis (the small blood vessels present in the kidneys become inflamed, causing a lot of discomfort and may also result in partial to complete renal failure in advanced cases), bacteremia (presence of bacteria in blood), urinary tract infection, etc. The Streptococcus thermophilus species can be broadly classified under three elementary categories - Alpha Hemolytic, Beta Hemolytic and Gamma Hemolytic.
Before I proceed to get into further details of these three categories, let me tell you what alpha and beta hemolysis means, first. A bacterial strain is said to be alpha hemolytic if its reaction with a blood agar sample causes the contents of the agar plate to turn dark greenish. A bacterial strain is said to be beta hemolytic if its reaction with a blood agar sample causes the latter to turn light yellowish and transparent. Gamma hemolytic bacteria do not cause any change of color to blood agar plate contents on coming in contact with the same. Now, going back to the categories, the alpha and beta hemolytic bacteria are further classified into various sub groups.
Streptococcus bacteria are sub categorized as Pneumococci and Viridans. The former group comprises just one species, the Streptococcus Pneumoniae, which causes bacterial pneumonia. The Viridans group consists of six Streptococcus species out of which only one, Streptococcus mutans, is somewhat pathogenic to humans as it causes dental cavities.
Streptococcus bacteria are further classified as Group A, Group B, Group C and Group G, of which only the first three are primarily pathogenic in case of humans. Streptococcus agalactiae, which is a Group B beta hemolytic bacteria, is the most commonly found strep bacteria in urine samples which indicates towards possible UTI and bacterial colonization in the female reproductive tract and intestinal recesses. Bacteriemia, which is caused by invasion of bloodstream by pathogenic bacteria, is most frequently caused by Streptococcus pyogenes, a beta hemolytic Group A strep in blood, though Group B Streps have also been known to be responsible for this condition. Group C and Group G species of Streptococcus do not normally make humans sick, although infection may be contacted from other infected animals, especially from canines and equines.
Streptococci are predominantly non pathogenic and do not usually cause diseases. However, opportunistic pathogenesis in immunocompromised individuals or organisms may occur, though this is rare.
Based upon the type of infection or disease and particular species of strep pathogen causing it, the pathophysiology of strep symptoms and indications differ from case to case. For instance, a person suffering from meningitis (inflammation of the meninges, which are outer membranes that protect the brain) will exhibit very different symptoms when compared to a person suffering from strep throat. However, fever, loss of appetite and malaise are typically present in all kinds of strep infections, be it strep throat, scarlet, meningitis, UTI or sepsis.