“Influenza” is a generic term that describes a large host of variant viruses that are closely related. These viruses are not differentiated, as bacteria are, by genus and species but rather through a complex naming process that first distinguishes between the three major types of influenza viruses, either A, B, or C, and then the differentiation continues through the identification of proteins on the surface of the virus, which is denoted by the use of the letters H and N followed by a number. In epidemiology, descriptions continue to include the host species (i.e. human, avian, swine, equine, or canine), geographic information regarding where first isolated, and the year of isolation. These details mean little, in most cases, to the general public and usually do not convey meaningful information about prevention.
Vibrio is a genus of bacteria that includes several species that are important causes of human disease. The most infamous of these diseases is caused by Vibrio cholerae, which causes cholera. Other significant species causing illness in humans are Vibrio vulnificus and Vibrio parahaemolyticus. Globally, these infections sicken many people and are sometimes fatal.
Streptococcus pyogenes refers to a specific genus and species pair which shares many common characteristics with a wide range of microorganisms in the same genus. For sake of convenience at the expense of scientific specificity, we will refer to Streptococcus pyogenes from here on out simply as strep, although this is understood to apply only for the purposes of this post. Using the term to refer to all other species is misleading and inaccurate.
While there are many bacteria that could be abbreviated as “strep,” Streptococcus pyogenes is easily one of the most clinically significant, causing a variety of human illnesses that range from the distressing to the life-threatening. Strep is quite infamous as the causative agent of the aptly named “strep throat” infection common in children and adults alike. About 700 million infections are estimated to occur worldwide each year and of those, 650,000 are severe with a death rate of about 25%.
Recent news reports have highlighted the potentially serious, and usually deadly, risk of the fungal disease known as mucormycocis. While Mucor refers to a specific genus of fungi with thousands of species included, the disease is not exclusively caused by the Mucor genus; other genus of fungi may be implicated.
While mucormycosis is rare it is almost always deadly. The infection is usually associated with underlying conditions, most commonly uncontrolled diabetes, but other problems including certain cancers, burns, or any condition that suppresses the immune system, and/or which lowers the white blood cell count can predispose someone to the infection. In the earlier days of the HIV and AIDS epidemics, patients with advanced disease sometimes developed mucormycosis and the fatality rate was almost 100%. Outcomes for most anyone with the disease are generally poor and if survival is possible, the disfigurement common from the surgeries necessary to preserve life is permanent and pronounced.
Staphylococcus is the genus name of a very large group of closely related bacteria, some of which are commonly found on and in the human body, and some of these bacteria are notorious causes of infection and disease. Among the most common of these bacteria that are capable of causing disease are Staphylococcus aureus and Staphylococcus epidermidis. Other species have been associated with infection and disease in humans, but the vast majority of such infections are associated with the two species identified above. These bacteria, and the infections they cause, are most commonly referred to as “Staph” and “staph infections,” and while not scientifically accurate, we will follow this common convention throughout. Continue reading
Shigella is a genus group of bacteria that contains four species, S. dysenteriae, S. flexneri, S. boydii, and S. sonnei. While these are frequently referred to as “species,” it is probably more scientifically correct to refer to them as biotypes of Escherichia, but because of the important medical differences between infections with Shigella versus most Escherichia the naming convention remains. As is also true of Salmonella species, there are numerous serotypes found within the different Shigella species, with the notable exception of S. sonnei which has only one serotype. Serotyping is important for scientific, especially epidemiological, studies, but is not likely to be relevant to most people.
Serratia is the genus name of a group of relatively common bacteria, the most common of which is Serratia marcescens. There are other species within the genus, a few of which have on rare occasion caused disease in humans, but the vast majority of infections with the Serratia occur with Serratia marcescens, and from this point forward, any mention of Serratia is understood to refer specifically to S. marcescens.
Salmonella is the genus name of a large group of bacteria which however contains only two distinct species. Unlike many bacterial genus groups the distinctions among the many, at last count 2,501, individually recognized types of Salmonella are not species but instead are known as serovars, or serological variants. These variants are recognized by differing antigens expressed on the surface of the bacteria instead of the variations in DNA sequence that mark different species. Serovars are generally named for the geographic location of their first isolation. The differing serovars, with a few important exceptions, are not relevant to the vast majority of people as they rarely change the course of the infection and subsequent disease, again, there are several important exceptions, but they are of critical value to epidemiologists and others who track and combat the large scale outbreak forms of these infections which occur in the United States on a yearly basis.
Pseudomonas is the genus name of a large group of bacteria, some of which can infect and sicken humans. The number of bacteria assigned to Pseudomonas has declined in recent years as the advent and widespread adoption of genetic testing of bacteria has caused many former members of Pseudomonas to be moved to existing, or in many cases completely new, genus groups. Of the remaining members of the genus Pseudomonas, only a few have been implicated in human illnesses and of those by far the most common culprit is Pseudomonas aeruginosa. From this point forward, for our purposes, any mention of Pseudomonas is understood to refer specifically to P. aeruginosa.
Listeria monocytogenes is one specific genus and species pair of bacteria. There are five additional species within the Listeria genus, but only one of these, L. ivanovii, in addition to L. monocytogenes, is considered to be a pathogen, or capable of causing disease. L. ivanovii is not nearly as common an infection however and it is nowhere near as great a concern as L. monocytogenes, which is an organism of great public health concern as it often occurs in large scale outbreaks, sometimes spanning multiple states, due to its association with contaminated fresh and processed food. Because most all references to Listeria are linked specifically to L. monocytogenes, from this point forward this specific organism will be referred to by the shorthand of Listeria.