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Shigella Species

Shigella species usually cause acute gastrointestinal tract infection, a clinical syndrome named shigellosis. , The term dysentery denotes colitis manifested as frequent, painful passage of stools containing blood or mucus; bacillary dysentery is caused by a number of invasive bacteria including Shigella . Shigellosis has substantial public health importance, especially in resource-limited settings, with a global estimate of 188–269 million cases and 164,300–212,440 deaths annually. ,…

Salmonella Species

Nontyphoidal Salmonella species are found widely in animals and cause a broad spectrum of clinical infections that include asymptomatic carriage, gastroenteritis, bacteremia, and metastatic focal infections. In contrast, Salmonella serotypes Typhi and Paratyphi A, B, and C are human-specific pathogens that cause typhoid or enteric fever, a protracted febrile illness with myriad manifestations. Description of The Pathogen Salmonella species are gram-negative bacilli that belong to the…

Serratia Species

Microbiology The genus Serratia, family Yersiniaceae fam.nov, order Enterobacterales ord.nov (former family Enterobacteriaceae), contains at least 15 species. Serratia marcescens is the primary pathogenic species in humans, but a few cases of human infections are caused by S. liquefaciens , S. rubidaea , S. plymuthica , S. odorifera , S. ficaria , and S . fonticola , which are diverse groups containing several biogroups based on…

Proteus, Providencia, and Morganella Species

Microbiology and Epidemiology Organisms belonging to the genera Proteus, Providencia, and Morganella are phylogenetically related members of the family Morganellaceae fam.nov , order Enterobacterales ord.nov. (former family Enterobacteriaceae) and are often referred to as the Proteeae. All members of these genera have phenylalanine deaminase activity, and most have urease activity and motility. Organisms can be isolated readily in the laboratory on enriched media, such as blood…

Plesiomonas shigelloides

Plesiomonas shigelloides is a common inhabitant of surface water and fish and is a cause of acute gastroenteritis, mainly in travelers to tropical regions, and uncommonly of severe extraintestinal infections in children. Description of Pathogen Microbiology P. shigelloides is the only species in the genus Plesiomonas . Based on phenotypic characteristics, P. shigelloides was formerly classified in the Vibrionaceae family. However, sequence analysis indicates its phylogenetic…

Less Commonly Encountered Enterobacterales

Microbiology, Epidemiology, Clinical Manifestations, and Treatment More than 99% of Enterobacterales recovered in clinical laboratories belong to a few dozen species. Three species— Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae —made up of more than 90% of isolates, and several other well-recognized species account for most of the remaining clinical isolates. Some less common genera have well described, clinically important member species, whereas others are newly…

Citrobacter Species

Microbiology And Epidemiology The genus Citrobacter has undergone significant taxonomic revision through the use of newer techniques based on DNA relatedness. The genus contains 13 named species: Citrobacter freundii, C. koseri (formerly C. diversus ) , C. amalonaticus, C. youngae, C. farmeri, C. braakii, C. werkmanii, C. sedlakii, C. gillenii, C. murliniae, C. rodentium, C. pasteurii , and C. europaeus. All species except C. rodentium (pathogenic…

Enterobacter, Cronobacter, and Pantoea Species

Microbiology And Epidemiology The recent taxonomic re-classification of the former Enterobacteriaceae family places the genera Enterobacter and Cronobacter as members of the Enterobacteriaceae family, while Pantoea has been reassigned to the Erwinaceae family. The genus Enterobacter has undergone significant taxonomic revision. Although there are more than 15 named species, molecular techniques likely will identify additional species. Many former members of the genus Enterobacter have been transferred…

Klebsiella granulomatis : Granuloma Inguinale (Donovanosis)

Granuloma inguinale, also known as donovanosis, is a chronic, slowly destructive, ulcerative disease of the skin and subcutaneous tissues caused by Klebsiella (formerly Calymmatobacterium ) granulomatis . , Uncommon in industrialized countries, donovanosis historically has been seen among adolescents and adults (and rarely among children) in some tropical and developing regions, including Papua New Guinea, central Australia, South Africa, Brazil, and regions of India. Sporadic cases…

Klebsiella and Raoultella Species

Microbiology And Epidemiology The genus Klebsiella , family Enterobacteriaceae, order Enterobacterales, contains at least five Klebsiella species and three Raoultella species: K. pneumoniae, K. oxytoca, K. granulomatis, K. variicola, K. singaporensis, R. terrigena, R. ornithinolytica, and R. planticola . These organisms are gram-negative, facultative anaerobic rods or coccobacilli. Like other members of the Enterobacteriaceae family, they ferment glucose and are oxidase negative. Enterobacter aerogenes is now…

Escherichia coli

Escherichia coli is a genetically diverse species comprising nonpathogenic gut commensals and strains responsible for intestinal and extraintestinal infections in humans. Commensal E. coli is the predominant facultative anaerobe of the human gut microbiota, and it colonizes the gastrointestinal (GI) tract within hours after birth. E. coli is a gram-negative bacillus and oxidase-negative organism of the family Enterobacteriaceae. It grows well aerobically and anaerobically, preferably at…

Nocardia Species

Since the first report of Nocardia as a pathogen in 1888, multiple species have been recognized as serious human pathogens. Molecular analysis has identified to date 92 species in the Nocardia genus with 54 species shown to be clinically significant on the basis of at least one published report. The evolving taxonomy of Nocardia spp. will require ongoing attention and modifications to our understanding of diagnosis…

Mycobacterium Nontuberculosis Species

The growing importance of nontuberculous mycobacteria (NTM) in the past 2 decades prompted development of sophisticated microbiologic techniques that enable more rapid and accurate identification of older species and those that are emerging as human pathogens. More than 180 species of mycobacteria are currently recognized. Epidemiology NTM species are ubiquitous in soil, water, foodstuffs, and domestic and wild animals. Human strains of Mycobacterium avium and M.…

Mycobacterium tuberculosis

The genus Mycobacterium consists of a diverse group of acid-fast bacilli (AFB) with a lipid-rich cell wall. The bacilli are aerobic, non–spore-forming, nonmotile, and slightly curved or straight organisms. Mycobacteria take up stain poorly but retain specific dyes despite treatment with acid-alcohol solutions. This acid-fast property is demonstrated with fuchsin stain techniques, such as the Ziehl-Neelsen and Kinyoun methods, or the more sensitive fluorochrome method using…

Other Gram-Positive Bacilli

A number of pleomorphic, non-sporulating, and gram-positive bacilli have been identified in the past as “diphtheroids” or “coryneform” bacteria and dismissed as contaminants. However, many of these organisms can cause endocarditis and other serious infections, especially in immunocompromised patients. For this reason, coryneform bacteria isolated from clinical specimens should be identified as a matter of routine, particularly if they are found in pure culture, from multiple…

Listeria monocytogenes

Acknowledgment The author acknowledges the substantial contributions to this chapter from previous editions of the textbook and the skillful work that created Fig. 132.2 . The bacterium Listeria monocytogenes is a rare but important cause of severe illness in neonates, pregnant women, older adults, and people with impaired cell-mediated immunity. It often manifests as a life-threatening bloodstream infection (BSI) and meningoencephalitis or as less severe febrile…

Corynebacterium diphtheriae

Diphtheria is a toxicosis caused by infection with Corynebacterium diphtheriae. The genus and species names are derived from Greek roots: korynee (“club”) after the microscopic appearance of the organisms and diphtheria (“leather hide”) for the pseudomembrane that is the hallmark of respiratory tract infection. Once a major cause of childhood death, diphtheria was among the first infectious diseases to be controlled using modern principles of microbiology,…

Bacillus Species (Including Anthrax)

Bacillus species, ubiquitous in the environment, are found in soil, water, dust, and air. With the exception of B. anthracis, which causes anthrax, Bacillus spp. previously have been considered nonpathogenic when isolated from clinical specimens. However, nonanthrax species are increasingly recognized as pathogens in immunosuppressed people and in patients with indwelling devices. Isolates are more likely to be significant if the organism is present on a…

Arcanobacterium haemolyticum

Arcanobacterium haemolyticum was first identified as Corynebacterium haemolyticum in 1946 in pharyngeal cultures of World War II soldiers and Pacific Islanders with pharyngitis that was indistinguishable clinically from infection caused by group A Streptococcus . Epidemiology Humans are the primary reservoir of A. haemolyticum , where the organism is found in the pharynx and on the skin. A. haemolyticum has been implicated increasingly in association with…