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Agents of Chromoblastomycosis

Chromoblastomycosis (chromomycosis) is a chronic, localized fungal infection of the skin and subcutaneous tissue that produces raised scaly lesions, usually of the lower extremities. The lesions of chromoblastomycosis are frequently warty or cauliflower-like in appearance, with pathognomonic muriform cells (also called “copper penny” or sclerotic bodies) found at histologic examination. This disease of tropical and subtropical distribution is produced by inoculation of the infecting fungi in…

Sporothrix schenckii

Mycology Sporothrix schenckii sensu lato (meaning in the broadest sense) is a dimorphic fungus that exists in a hyphal form in vitro at temperatures less than 37°C. Colonies are initially white but gradually become brown to black due to the production of pigmented conidia. In vivo or at 37°C on rich media such as brain heart infusion agar, the organism converts to an oval- or cigar-shaped…

Agents of Mucormycosis and Entomophthoramycosis

The disappearance of the class Zygomycetes from current taxonomy has made the term zygomycosis obsolete. The term zygomycosis encompassed both mucormycosis and entomophthoramycosis. These two infections are so different that no new name has been proposed to include both infections. Most of this chapter discusses mucormycosis, a group of filamentous fungi in the subphylum Mucoromycotina that belong to the order Mucorales. Mucorales can cause life-threatening infections…

Aspergillus Species

Revised August 7, 2021 Invasive aspergillosis (IA) remains a major cause of morbidity and mortality in the immunosuppressed population. This infection is caused by Aspergillus , a hyaline mold, and is responsible for a variety of noninvasive or semiinvasive conditions. These syndromes range from colonization, such as a fungus ball due to aspergillosis (also known as aspergilloma); allergic responses to Aspergillus , including allergic bronchopulmonary aspergillosis…

Candida Species

Revised April 26, 2022 Written descriptions of oral lesions that were probably thrush date to the time of Hippocrates and Galen. Langenbeck, in 1839, found fungi in oral lesions of a patient. In 1861, Zenker described the first well-documented case of deep-seated Candida. The first case of Candida -induced endocarditis was described in 1940. The most interesting period in the history of Candida infections began in…

Introduction to Mycoses

The advent of the human immunodeficiency virus epidemic and the ever-increasing use of immunosuppressive drugs has dramatically increased the incidence of deep mycoses and substantially broadened the range of fungi causing potentially lethal disease. Clinicians caring for highly immunosuppressed patients are rarely able to ignore a fungal isolate because the species is not “pathogenic.” An additional complication is that the rapidly moving field of diagnostic microbiology…

Agents of Actinomycosis

Actinomycosis is an indolent, slowly progressive infection caused by anaerobic or microaerophilic bacteria, primarily from the genus Actinomyces, that normally colonize the mouth, colon, and vagina. Disruption of mucosa may lead to infection of virtually any site. When the organisms invade tissue, they form tiny, sometimes visible clumps, called grains or “sulfur granules,” named for their yellow color. Lesions of actinomycosis are purulent foci surrounded by…

Nocardia Species

Nocardia is a genus of aerobic actinomycetes responsible for localized or disseminated infections in animals and humans. The genus is named after Edmond Nocard, who in 1888 described the isolation of an aerobic actinomycete from cattle with bovine farcy. The first human case of nocardiosis was reported by Eppinger in 1890. Cases of human disease have increased substantially in the past 2 decades, in association with…

Infections Caused by Nontuberculous Mycobacteria Other Than Mycobacterium avium Complex

Revised March 30, 2021 Overview The recent advances in mycobacterial culture techniques and the increasing utility of modern molecular techniques for identification of previously unidentified organisms have produced a major resurgence of interest in disease caused by the nontuberculous mycobacteria (NTM). In addition, there has been an increasing appreciation of the defects in lung structure and immune response that predispose to NTM. This group of mycobacteria…

Mycobacterium avium Complex

Mycobacterium avium complex (MAC) is the most common of all the nontuberculous mycobacteria (NTM) to cause human infection and pulmonary infection. MAC contains genetically diverse strains with different reservoirs and pathogenicity for humans. The three most common are M. avium, M. intracellulare, and M. chimaera. M. avium and M. intracellulare are often not microbiologically separated and are referred to as M. avium-intracellulare (MAI). Two major disease…

Leprosy ( Mycobacterium leprae )

Leprosy, or Hansen disease, is a curable infectious disease caused by Mycobacterium leprae. Widespread implementation of multidrug antibiotic therapy for leprosy in the 1980s dramatically decreased the burden of leprosy worldwide. There is no indication for physical or social isolation of people with leprosy. Sequelae of leprosy, including nerve damage, muscle weakness, and physical deformity, are related to delayed diagnosis and pathologic immune reactions that complicate…

Mycobacterium tuberculosis

Revised March 31, 2020 Revised March 29, 2021 and June 6, 2021 The term tuberculosis describes a broad range of clinical illnesses caused by Mycobacterium tuberculosis (or, less commonly, Mycobacterium bovis ). Tuberculosis (TB) is the leading cause of death due to a single infectious agent worldwide, and ranks ninth among all causes of death. In 2014 the World Health Assembly embraced a resolution to reduce…

Anaerobic Cocci and Anaerobic Gram-Positive Nonsporulating Bacilli

Both anaerobic cocci and anaerobic gram-positive nonsporulating bacilli belong to the commensal microbiota of the digestive tract, and some are members of the microbiota of the urogenital tract and skin. When the environment changes due to trauma, immunosuppression, or antimicrobial therapy, they can cause damage in a susceptible host and result even in life-threatening infections. The major genera of anaerobic cocci and gram-positive anaerobic nonsporulating bacilli…

Bacteroides, Prevotella, Porphyromonas, and Fusobacterium Species (and Other Medically Important Anaerobic Gram-Negative Bacilli)

Overview The genera Bacteroides, Porphyromonas, Prevotella, and Fusobacterium account for most infections caused by gram-negative anaerobic rods (GNARs). Bilophila and Sutterella also cause human infections, although they are less frequently encountered in clinical practice. These obligately anaerobic gram-negative bacteria colonize the oropharynx, gastrointestinal tract, and urogenital tract of humans. Several species from some of these genera are useful symbiotic bacteria, facilitating host metabolism and favorably shaping…

Diseases Caused by Clostridium

The genus Clostridium includes over 200 described species. Members of this genus participate in a variety of invasive and toxigenic infections. They can cause disease that is strictly toxin mediated, such as antibiotic-associated colitis (AAC) and foodborne botulism, or contribute to invasive infections, including bacteremia, clostridial myonecrosis (gas gangrene), and other suppurative infections driven by histotoxins and enzymes that destroy soft tissue. Historically, clostridial infections were…

Botulism (Clostridium botulinum)

Botulism and tetanus result from intoxication with the protein neurotoxins elaborated by two related species of Clostridium. The toxins are very similar in structure and function but differ dramatically in their clinical effects because they target different cells in the nervous system. Botulinum neurotoxins predominantly affect the peripheral neuromuscular junction and autonomic synapses and primarily manifest as weakness. In contrast, although tetanus toxin can affect the…

Tetanus (Clostridium tetani)

History Tetanus was well known to the ancients; descriptions by Egyptian and Greek physicians survive to the present. They recognized the frequent relationship between injuries and the subsequent development of fatal spasms. Gowers provided the quintessential description of tetanus in 1888. Tetanus is a disease of the nervous system characterized by persistent tonic spasm, with violent brief exacerbations. The spasm almost always commences in the muscles…

Clostridioides difficile (Formerly Clostridium difficile ) Infection

Revised June 20, 2022 Reviewed for currency November 8, 2020 The administration of antibiotics can be complicated by a number of unintended consequences, among which gastrointestinal side effects are quite common. Gastrointestinal symptoms occur in up to 25% to 50% of patients depending on the specific antimicrobial agent, patient population, and epidemiology. While the majority of these side effects are mild, consisting of minor antibiotic-associated diarrhea…

Anaerobic Infections: General Concepts

Anaerobic bacteria are a major component of the normal human microbiota (formerly termed the normal flora ) residing on mucous membranes and predominate in many infectious processes, particularly those arising from mucosal sites. These organisms generally cause disease after the breakdown of mucosal barriers and the leakage of indigenous flora into normally sterile sites. The predominance of anaerobes in certain clinical syndromes can be attributed to…

Lyme Disease (Lyme Borreliosis) Due to Borrelia burgdorferi

Revised November, 2019 Lyme disease or Lyme borreliosis, which is caused by the tick-borne spirochete Borrelia burgdorferi (sensu lato), occurs in temperate regions of North America, Europe, and Asia. It is now the most common vector-borne disease in the United States and Europe. The illness usually begins in summer (stage 1) with a characteristic expanding skin lesion, called erythema migrans (EM), which occurs at the site…