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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…

Other Neisseria Species

Neisseria gonorrhoeae and N. meningitidis are the 2 most pathogenic Neisseria species. Other Neisseria species are common commensal inhabitants of the upper respiratory tract and oral cavity of humans and other animals, but they have been implicated in clinical disease in occasional cases, particularly in immunocompromised patients. The focus of this chapter is on these other Neisseria species, with mention of species that previously have been…

Neisseria gonorrhoeae

Neisseria gonorrhoeae is a pathogen only of humans. Gonorrhea, one of the oldest known human illnesses, continues to result in significant morbidity; an estimated 87 million cases occur worldwide each year. In the US, gonorrhea is the second most frequently reported communicable disease after Chlamydia trachomatis. The reader is referred to organism- or syndrome-specific chapters for the overall approach to genital tract infections. The major public…

Neisseria meningitidis

Neisseria meningitidis (meningococcus) is an important cause of serious bacterial infections in children, most commonly manifesting as purulent meningitis or septicemia. Asymptomatic pharyngeal colonization is more common than invasive disease, and humans are the only reservoir. Gaspard Vieusseux provided the first clinical description of meningococcal disease during an outbreak in Geneva, Switzerland, as recently as 1805, which was followed by epidemics across Europe for the next…

Other Gram-Positive, Catalase-Negative Cocci: Leuconostoc and Pediococcus Species and Other Genera

Characteristics Of Pathogens Among the gram-positive catalase-negative cocci, streptococci and enterococci cause most human infections. The remaining organisms belong to 5 genera that can be identified according to the criteria proposed by Facklam and colleagues ( Table 124.1 ), and they form colonies that are α hemolytic or nonhemolytic on sheep blood agar and are easily confused with Streptococcus pneumoniae or viridans streptococci. These organisms appear…

Streptococcus pneumoniae

Acknowledgments We acknowledge the contributions of Carrie Byington, MD, Georges Peter, MD and Jerome O. Klein, MD, for their work on this chapter in the previous editions. All references are available online at Elsevier eBooks for Practicing Clinicians . In the introduction to his classic 1938 monograph The Biology of the Pneumococcus, Benjamin White wrote that the “pneumococcus is altogether an amazing cell. Tiny in size,…

Groups C and G Streptococci

The β-hemolytic streptococci can be subdivided on the basis of whether they form large colonies or minute colonies on solid agar. Most notable among those β-hemolytic streptococci that form large colonies are Streptococcus pyogenes (group A) and Streptococcus agalactiae (group B). Among the remaining Lancefield-reactive β-hemolytic streptococci, groups C and G organisms are most commonly associated with human disease. In this chapter, groups C and G…

Viridans Streptococci, Abiotrophia and Granulicatella Species, and Streptococcus bovis Group

The viridans streptococci are genetically diverse organisms that share the propensity to colonize humans and occasionally penetrate local barriers to cause life-threatening disease. Their importance as the predominant cause of endocarditis in children and adults has been known for decades. Improvements in identification and classification led to the recognition that these organisms are a significant cause of other infections as well, including septicemia and infection of…

Enterococcus Species

Historically enterococci, Streptococcus bovis, and S. equinus were grouped together as Lancefield group D streptococci. However, genomic analysis resulted in the reclassification of these organisms, and enterococci now are considered a separate genus ( Table 120.1 ). This chapter focuses on enterococci; the nonenterococcal group D streptococci are discussed in Chapter 121 . TABLE 120.1 Clinical Significance of Enterococci and Group D Streptococci Species Association With…

Streptococcus agalactiae (Group B Streptococcus )

The Pathogen and Pathogenicity Streptococcus agalactiae is the species designation for Lancefield group B Streptococcus (GBS). Colonies appear on sheep blood agar as 3- to 4-mm, grey-white colonies typically with a narrow zone of β-hemolysis; organisms are gram-positive cocci. The group B–specific cell wall carbohydrate antigen is common to all strains, and a surface capsular polysaccharide (CPS) allows classification into serotypes Ia, Ib, II, III, IV,…

Streptococcus pyogenes (Group A Streptococcus )

Acknowledgment The authors acknowledge use of substantial material from this chapter in the previous edition. Group A Streptococcus (GAS) is synonymous with Streptococcus pyogenes, the only species in this group of β-hemolytic streptococci. GAS is a leading pathogenic bacterium affecting children and adolescents, and it is associated with a wide spectrum of infections and diseases. Worldwide, >600 million cases of GAS pharyngitis (“strep throat”) and >700…