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Neisseria meningitidis

Revised December, 2019 Definition and History Neisseria meningitidis (the meningococcus) is the cause of epidemic cerebrospinal fever, clusters and sporadic cases of acute bacterial meningitis, mild bacteremia to devastating septicemia, pneumonia, and, less commonly, septic arthritis, pericarditis, chronic bacteremia, conjunctivitis, epiglottitis, otitis, sinusitis, urethritis, and proctitis. Historically, half a million cases of invasive meningococcal disease occur worldwide each year, but incidence is declining owing to the…

Whipple Disease

Reviewed for currency January 14, 2021 Whipple disease (WD) is a rare systemic infectious disorder caused by the actinomycete Tropheryma whipplei. This chronic disease, first described by Whipple as “intestinal lipodystrophy,” preferentially affects middle-aged white men, who may present with weight loss, arthralgia, diarrhea, and abdominal pain. Various other clinical patterns, such as involvement of the heart, lung, or central nervous system (CNS), are frequent. In…

Erysipelothrix rhusiopathiae

Erysipelothrix rhusiopathiae is a thin, pleomorphic, nonsporulating gram-positive rod. First isolated from mice by Robert Koch in 1878 and from swine by Louis Pasteur in 1882, it was established as the etiologic agent of swine erysipelas in 1886 by Löffler and as a human pathogen in 1909 when Rosenbach isolated it from a patient with localized cutaneous lesions. Rosenbach coined the term erysipeloid to avoid confusion…

Bacillus Species and Related Genera Other Than Bacillus anthracis

Microbiology Bacteria of the genus Bacillus are well adapted to their normal environment of soil. This includes Bacillus anthracis, discussed elsewhere in this text (see Chapter 207 ). These gram-positive or gram-variable, aerobic or facultatively anaerobic, rod-shaped bacilli have rounded or squared-off ends, form endospores, tolerate extremes of temperature and moisture, and are ubiquitous. They are found in superficial lake and ocean sediment, even in deep…

Bacillus anthracis (Anthrax)

Anthrax has never been a cause of the massive loss of life associated with cholera, plague, or smallpox, but it has played a prominent role in the history of infectious diseases. While much of the industrialized world is focused on anthrax as an agent of bioterrorism, anthrax remains a significant cause of animal deaths as well as more limited numbers of human cases in much of…

Listeria monocytogenes

Definition Listeria monocytogenes is a gram-positive bacillus and zoonotic and foodborne pathogen found worldwide that causes listeriosis. Listeriosis spans the clinical spectrum from self-limited febrile gastroenteritis in immunocompetent people to more severe and invasive disease that mostly affects pregnant women, newborn infants, older adults, and individuals with cell-mediated immunodeficiencies. It is a rare but important pathogen because of the populations it infects and its high rates…

Other Coryneform Bacteria, Arcanobacterium haemolyticum, and Rhodococci

Coryneform Bacteria Other Than Corynebacterium diphtheriae Corynebacterium was proposed as a genus by Lehmann and Neumann in 1896, who derived the name from the Greek koryne, which means “club,” and bacterion, meaning “little rod.” The coryneforms are a diverse group of organisms. Corynebacterium diphtheriae serves as the type species, leading to the term diphtheroids to describe other bacteria sharing similar morphologic features. Also known as coryneform…

Corynebacterium diphtheriae (Diphtheria)

A primary series of vaccination with diphtheria toxoid affords protective immunity in children and adults. To counter the effect of waning immunity, booster doses should be administered every 10 years to older children and adults who have completed the primary vaccination series. Close contacts and Corynebacterium diphtheriae carriers should be treated with a course of antibiotics until microbiologic clearance is documented and should also undergo primary…

Streptococcus anginosus Group

The Streptococcus anginosus (milleri) group is a subgroup within the viridans-group streptococci that includes three separate streptococcal species: S. anginosus, S. constellatus, and S. intermedius. These viridans-group streptococci are part of the normal flora of the human oropharynx and urogenital and gastrointestinal tracts, but tend to be more virulent than other viridans streptococci and are known to cause serious infections. Microbiologically, members of this group are…

Viridans Streptococci, Nutritionally Variant Streptococci, and Groups C and G Streptococci

Overview The viridans group streptococci (VGS) are a diverse group of organisms and are the predominant microbiota in the oropharynx and gastrointestinal (GI) tract. The viridans streptococci cause a significant percentage of all cases of infective endocarditis (IE). Streptococcus mutans is responsible for dental caries. Several typing schemes for the VGS have been proposed. There are at least 30 recognized species of VGS, which are classified…

Streptococcus agalactiae (Group B Streptococci)

Reviewed for currency January 14, 2021 Historical Perspective Group B streptococci (GBS; Streptococcus agalactiae ) were reported as human pathogens in 1938 by Fry, who described three cases of fatal puerperal sepsis. Infections in humans were reported infrequently until the 1960s, when it became evident that disease was occurring more commonly. By the 1970s, GBS emerged as the predominant pathogens causing septicemia and meningitis in neonates…

Enterococcus Species, Streptococcus gallolyticus Group, and Leuconostoc Species

Revised January 7, 2021 Historical Background The first time that the term entérocoque was used appears to have been in an article in the French literature in 1899. The article was referring to a diplococcus found in the gastrointestinal (GI) tract that had the potential to become pathogenic for humans. The first clinical and pathologic description of an enterococcal infection was published the same year (1899)…

Streptococcus pneumoniae

Revised July 1, 2020 Long recognized for causing asymptomatic colonization and as a prominent cause of pneumonia, bacteremia, meningitis, sinusitis, and otitis media, Streptococcus pneumoniae is likely the most common cause of serious bacterial respiratory infection in both children and adults worldwide. Antimicrobials and vaccines have substantially reduced the incidence of, and morbid outcomes from, pneumococcal infection. However, acquisition of antibiotic resistance, the more limited impact…

Nonsuppurative Poststreptococcal Sequelae: Rheumatic Fever and Glomerulonephritis

Reviewed for currency November 8, 2020 Rheumatic Fever Acute rheumatic fever (ARF) is a disease characterized by nonsuppurative inflammatory lesions involving primarily the heart, joints, subcutaneous tissues, and central nervous system. In its classic form, ARF is acute, febrile, and largely self-limited. However, damage to heart valves may occur, and such damage may be chronic and progressive and lead to severe cardiac failure, total disability, and…

Streptococcus pyogenes

Revised December, 2019 Streptococcus pyogenes (group A Streptococcus; [GAS]) is one of the most important bacterial pathogens of humans. This ubiquitous organism is the most frequent bacterial cause of acute pharyngitis, and it also gives rise to a variety of cutaneous and systemic infections. Its unique place in medical microbiology stems from its propensity to initiate two nonsuppurative sequelae: acute rheumatic fever and poststreptococcal glomerulonephritis. The…

Staphylococcus epidermidis and Other Coagulase-Negative Staphylococci

The genus Staphylococcus, with more than 80 recognized species and subspecies ( ) is one of the most abundant microbes inhabiting normal human skin and mucous membranes. They infrequently cause primary invasive disease and are most commonly encountered by clinicians as contaminants of microbiologic cultures. However, because of relatively recent changes in the practice of medicine and changes in underlying host populations, coagulase-negative staphylococci, most…

Staphylococcus aureus (Including Staphylococcal Toxic Shock Syndrome)

Revised July 1, 2020 Staphylococcus aureus is a highly successful opportunistic pathogen. It is a frequent colonizer of the skin and mucosa of humans and animals (it is present in the anterior nares of up to 30% of the healthy human population) and can produce a wide variety of diseases. These diseases encompass relatively benign skin infections, such as folliculitis and furunculosis, and life-threatening conditions, including…

Introduction to Bacteria and Bacterial Diseases

Bacteria, the oldest forms of life on earth, are remarkably diverse and exist in astounding numbers. Diseases caused by bacteria include some of the most common infections in the world and some of the most important human scourges, past, present, and probably future. At the same time, each of us is colonized by as many bacterial cells as we have human cells in our bodies. In…

Ehrlichia chaffeensis (Human Monocytotropic Ehrlichiosis), Anaplasma phagocytophilum (Human Granulocytotropic Anaplasmosis), and Other Anaplasmataceae

Until 1987, infections by members of the family Anaplasmataceae, including the genera Ehrlichia, Anaplasma, and Neorickettsia, were known mainly as veterinary diseases ( Table 192.1 ). Canine ehrlichiosis was first described in 1935 by Donatien and Lestoquard in Algeria. This disease is produced by Ehrlichia canis, which is transmitted to dogs by Rhipicephalus sanguineus ticks. The disease is characterized by fever associated with the presence of…