Definition Chlamydiae are obligate intracellular bacteria that cause a variety of human and animal diseases and much morbidity. Within the Chlamydia genus are now 11 validated species: C. trachomatis, C. pneumoniae, C. psittaci , C. abortus , C. avium , C. caviae , C. felis , C. gallinacea , C. muridarum , C. pecorum , and C. suis . C. trachomatis is classified into a trachoma…
Mycoplasma pneumoniae Definition Mycoplasma organisms of the class Mollicutes are ubiquitous as pathogens and colonizing agents in the plant, animal, and insect kingdoms. They represent the smallest known free-living forms, but because they have fastidious growth requirements, they are difficult to culture. The presence of several species of Mycoplasma as commensals in animals and on human oral and genital mucosa frequently results in contamination of cell…
Definition Granuloma inguinale, also known as donovanosis, is a chronic and progressive bacterial ulcerative disease that predominantly affects the skin and mucous membranes of the genital, inguinal, perirectal, and anal regions, often associated with sexual transmission. The Pathogen Donovanosis is caused by Klebsiella granulomatis , which is a gram-negative, facultatively aerobic coccobacillus that is intracytoplasmic, immobile, and can be encapsulated. In lesions, these microorganisms are found…
Definition Bartonella are vector-borne bacteria responsible for a wide spectrum of human acute and chronic diseases. More than 40 different bacterial species from this genus have been isolated from animals and humans. The human infections linked to these different bacteria include cat-scratch disease, Oroya fever, verruga peruana, trench fever, endocarditis, bacillary angiomatosis, and peliosis hepatis. The Pathogen Bartonella species belong to the α-2 subgroup of Proteobacteria…
Definition Legionellosis refers to two clinical syndromes caused by Legionella bacteria: pneumonia and Pontiac fever. Legionella pneumonia (legionnaires disease) can be episodic or occur in outbreaks, and it can be acquired in the community or in health care settings. Pontiac fever is an acute, self-limited febrile illness caused by inhalation or aspiration of Legionella spp. Legionella extrapulmonary infections include meningitis, cellulitis, and skin and soft tissue…
Definition Whooping cough, also known as pertussis, is a toxin-mediated, highly contagious respiratory illness that affects all age groups and is characterized by distinctive, violent, paroxysmal coughing episodes, which end in the classic inspiratory whoop that gives the disease its name. Each paroxysm may last several minutes, and patients often feel entirely normal between paroxysms. Severe and fatal disease is concentrated among infants, in whom pertussis…
The genus Yersinia currently contains 26 officially recognized species, of which three are known to be important human pathogens, Yersinia pestis, Y. enterocolitica, and Y. pseudotuberculosis . The remaining species are generally considered nonpathogenic and are most frequently isolated from environmental sources. Two possible exceptions are Y. intermedia and Y. frederiksenii, which have been isolated from clinical samples, thereby suggesting a possible role as rare human…
Definition Tularemia is an infectious zoonosis caused by Francisella tularensis , which is an aerobic, pleomorphic, gram-negative bacillus. Many animal species harbor this organism, most prominently rabbits, squirrels, and muskrats. Humans acquire the infection by various means, including direct contact with infected animal tissues, ingestion of contaminated water or meat, the bite of an infected tick or deer fly, or inhalation of aerosolized bacteria. F. tularensis…
Definition Brucellosis, previously known as Malta fever, Mediterranean fever, or undulant fever, is a zoonotic disease caused by bacteria of the genus Brucella . Human infection, which has protean manifestations, is acquired via direct contact, ingestion, or inhalation. Most disease is acquired by eating unpasteurized dairy products or undercooked meat. Occupational infection typically occurs by inhalation, inadvertent exposure to live attenuated vaccines, or through contamination of…
Definition Shigellosis results from inflammation of the large intestine due to infection with bacteria of the genus Shigella . Clinical presentation is either with acute watery diarrhea or bloody diarrhea, known as dysentery, and is commonly accompanied by fever. Shigellosis is a major global health problem compounded by increasing levels of antimicrobial resistance. It is the most common cause of diarrheal deaths for which no vaccine…
Definition Many of the more than 2500 serovars (also called serotypes) of Salmonella enterica subspecies enterica infect humans and cause a range of clinical conditions from asymptomatic intestinal carriage to intestinal infection to invasive disease with extraintestinal complications. Each serovar designation follows the species name (e.g., Salmonella enterica subspecies enterica serovar Typhimurium) and is frequently abbreviated as simply Salmonella followed by the serovar name (e.g., Salmonella…
Acinetobacter Spp Definition The Pathogen Acinetobacter spp are gram-negative, aerobic, coccobacillary bacteria, which are generally non–lactose-fermenting, nonfastidious, catalase positive, oxidase negative, and nonmotile, though their description of being “nonmotile” is questioned. The Gram stain appearance of Acinetobacter spp is highly dependent on the life cycle. In the early growth phases, Acinetobacter spp appear rod shaped. In the stationary phase, they acquire a coccobacillary morphology. A. baumannii…
Pseudomonas Infection Definition Infections due to Pseudomonas spp are caused by members of the family Pseudomonadaceae. The Pseudomonadaceae is a group of gram-negative rods, including P. aeruginosa , the most frequently recovered human pathogen in the family. Other Pseudomonas s pp include P. putida, P. alcaligenes, P. fluorescens, P. luteola, P. mendocina, P. oryzihabitans, P. pseudoalcaligenes, P. stutzeri, P. chlororaphis, P. delafieldii, P. kingii, P. pertucinogena…
Definition The Enterobacterales are an order of gram-negative bacilli that are responsible for a broad range of infections in humans and in animals. They may be motile or nonmotile, depending on the species. They are aerobic or facultatively anaerobic in growth and have a predilection for inhabiting the gastrointestinal tract. Only extragastrointestinal manifestations of disease are discussed in this chapter. Enteric infections caused by Escherichia coli…
Definition Bacteria belonging to the species Escherichia coli are a normal component of the intestinal microbiota ( Chapter 257 ). The majority of E. coli are harmless commensals, but specific isolates have acquired pathogenicity genes that enable them to cause diseases, including urinary tract infections, bacteremia, meningitis, and diarrheal illness. One particular challenge to the clinician and microbiology laboratory is how to distinguish these pathogenic E.…
Definition Campylobacter jejuni is one of the most commonly recognized bacterial causes of diarrhea in developed and underresourced nations. More than 95% of campylobacter isolated in developed countries are C. jejuni or C. coli . However, other Campylobacter species are also associated with human disease. The Pathogen Campylobacter organisms are motile, curved, gram-negative rods that are found in domestic and wild animals—especially poultry—all over the world.…
Cholera Definition Cholera is a dreaded epidemic diarrheal disease caused by Vibrio cholerae serogroup O1 and, since 1992, by the new serogroup O139. The disease is characterized by acute, large-volume watery diarrhea. In its more severe form, a person may be severely dehydrated and in hypovolemic shock; the patient may die in a matter of a few hours after contracting the infection if treatment is not…
Haemophilus Influenzae Definition Haemophilus refers to the bacteria’s requirement for specific blood components for growth. In the respiratory tract, which is the primary site of colonization for most Haemophilus species, the most common infections include otitis media, sinusitis, bronchitis, and pneumonia. Serious invasive diseases (e.g., epiglottitis, bacteremia, endocarditis, meningitis, septic arthritis) may occur, particularly in susceptible older adults and infants ( Table 277-1 ). TABLE 277-1…
Definition Chancroid is a sexually transmitted disease that is characterized by painful genital ulcers and inguinal lymphadenitis caused by Haemophilus ducreyi . H. ducreyi also is a major cause of nonsexually transmitted cutaneous ulcers in children who live in regions of the South Pacific and Africa where yaws ( Chapter 295 ), which is a nonsyphilitic treponematosis that causes a disfiguring and debilitating childhood infectious disease,…
Definition Neisseria gonorrhoeae , which is predominantly a sexually transmitted infection, is a common cause of urethral discharge in men and cervical discharge in women. Because N. gonorrhoeae may infect mucosal epithelial cells, it also may cause pharyngeal and rectal infection in adults and conjunctival infection in the newborn. Complications of N. gonorrhoeae infections include epididymitis in males and pelvic inflammatory disease in females. Chronic or…