Articles on Medical Diseases and Conditions

There are other mycobacteria besides Mycobacterium tuberculosis, some of which are frequently pathogenic for humans and some of which rarely cause human infection. The nontuberculous mycobacteria were originally called “atypical mycobacteria.” The first useful classification was that of Runyon, who subdivided the nontuberculous mycobacteria into four groups, depending on growth speed and colony characteristics (Table […]

Tuberculosis is caused by Mycobacterium tuberculosis (MTB), a rod-shaped bacterium that requires special media for culture and that has the peculiarity of “acid-fastness” (resistance to decolorization by strong acidic decolorizing chemicals such as acid alcohol after being stained by certain stains such as carbol fuchsin). Tuberculosis is still very important and common despite advances in […]

The three major sources of anaerobic organisms are the dental and mouth area, the lower intestinal tract (ileum and colon), and the female external genital tract (vagina and vulva area). Anaerobes comprise about 95% of the bacterial flora of the colon and outnumber aerobes in the mouth and vagina. From the mouth the organisms can […]

Listeria monocytogenes Listeria monocytogenes is a short gram-positive rod. Although most gram-positive rods of medi- cal importance are anaerobes, Listeria is an aerobic (rather than anaerobic) organism. It is found widely in soil, sewage, and various animals, as well as in the feces of about 15% (range, 2%-60%) of asymptomatic adults. Infection in children and […]

Pseudomonas These gramegative rods are not classified with the Enterobacteriaceae, although they may be found normally in the GI tract. The most important is Pseudomonas aeruginosa. Pseudomonas is less common in community-acquired infection than with most of the major Enterobacteriaceae but becomes more frequent in hospital-acquired infections (about 10% of nosocomial infections). The conditions for […]

Enteric bacilli form a large family of gramegative rods (see Table 37-6). As their name implies, most are found primarily in the intestinal tract. These include species such as Salmonella, Shigella, Escherichia coli, Enterobacter, Klebsiella, Proteus, and several others (see Table 37-6). Many are normal inhabitants and cause disease only if they escape to other […]

Other venereal diseases include lymphogranuloma venereum (caused by a subspecies of C. trachomatis different from the one that causes nongonococcal urethritis), syphilis, granuloma inguinale, trichomoniasis, chancroid, herpesvirus type 2, molluscum contagiosum, and condyloma acuminatum. Most of these will be discussed elsewhere. Gardnerella vaginalis This organism (also called Corynebacterium vaginalis and Haemophilus vaginalis) is a small […]

Gramegative diplococci include several Neisseria species, such as meningococci and gonococci; and Branhamella catarrhalis. Branhamella catarrhalis (formerly Neisseria catarrhalis) is a member of the genus Moraxella but closely resembles neisseriae in many respects, including microscopic appearance. B. catarrhalis, as well as some of the neisseriae, is normally found in the upper respiratory tract. Although usually […]

Streptococci Streptococci are gram-positive cocci that, on Gram stain, typically occur in chains. Streptococci are subclassified in several ways. The three most useful classifications are by bacterial oxygen requirements, by colony appearance on blood agar, and by specific carbohydrate from the organism. Depending on clinical oxygen environment associated with disease, streptococci may be considered aerobic, […]

The most useful laboratory classification of bacteria involves a threefold distinction: the Gram stain characteristics (gram positive or gram negative), morphology (coccus or bacillus), and oxygen requirements for growth (aerobic or anaerobic). Species exist that are morphologic exceptions, such as spirochetes; others are intermediate in oxygen requirements; still others are identified by other techniques, such […]