Articles on Medical Diseases and Conditions

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 […]

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 […]

Histologic-type stains are used daily in the microbiology laboratory; most often Gram stain and acid-fast stain (Ziehl-Neelsen or its modifications). Both of these stains detect certain bacteria and to some extent help identify them. Other histologic stains perform the same purpose in tissue slide examination; the most common are paraaminosalycylic acid (PAS) and silver stains […]

In many cases, direct detection methods are not possible, are difficult and expensive, are unreliable, or are attempted with negative results. Serologic tests attempt to detect antibodies formed against antigens of an organism being searched for. The majority of organisms have a reasonably predictable antibody response. IgM-type antibodies appear first, most often in 7-14 days […]