Exercise 2 Neisseria and Spirochetes

The sexually transmitted diseases are perhaps the most important infections acquired through the urogenital tract, from the social as well as medical points of view. Three frequent infectious diseases of this type are gonorrhea, syphilis, and chlamydial urethritis/cervicitis. All three infections are caused by bacteria. Gonorrhea is caused by Neisseria gonorrhoeae; syphilis by Treponema pallidum, a spirochete; and chlamydial infection by Chlamydia trachomatis. Neisseria gonorrhoeae can be grown on special laboratory culture media, but chlamydiae are obligate intracellular parasites (once considered viruses, in part for this reason) and require special laboratory techniques for isolation (see Exercise 30). Treponema pallidum, on the other hand, has not yet been grown in any laboratory culture system and is cultivated only in certain animals, such as the rabbit.

The bacterial groups to which these sexually transmitted agents belong contain other pathogenic species associated with nonsexually transmitted disease, that is, infections acquired through other entry portals. Still other species of Neisseria and Treponema are nonpathogenic, including some that are frequent members of the normal flora of various mucous membrane surfaces, particularly of the respiratory tract.

EXPERIMENT 27.1 Neisseria

The genus Neisseria contains two pathogenic species and a number of others that are commonly found in the normal flora of the upper respiratory tract. The two medically important species are N. gonorrhoeae, the agent of gonorrhea, and N. meningitidis, an agent of bacterial meningitis. All Neisseria are gram-negative diplococci, indistinguishable from each other in microscopic morphology. The pathogenic species are obligate human parasites and quite fastidious in their growth requirements on artificial media. On primary isolation, they require an increased level of CO2 during incubation at 35° C. The nonpathogenic commensals of the upper respiratory tract are not fastidious and grow readily on simple nutrient media. Some of the respiratory flora, for example, N. subflava and N.flavescens, have a yellow pigment, but most Neisseria produce colorless colonies. All Neisseria are oxidase positive (see colorplate 13), which helps to distinguish them from other genera, but not from each other. Biochemically, the Neisseria species are most readily identified on the basis of their differing patterns of carbohydrate degradation. The cultural differentiation of a few Neisseria species, including the two pathogenic species, is shown in table 27.1-1. Recently, nucleic acid probe tests and gene amplification assays for detecting N. gonorrhoeae directly in patient specimens have become available (see Exercise 19). These tests can be completed within 2 to 4 hours and thus diagnostic results are available the day the specimen is taken.

Table 27.1-1 Differentiation of Some Neisseria species

Name of Organism

Pathogenicity

Growth on Enriched

Media (in CO2)

Growth on Simple

Nutrients (in Air)

Yellow Pigment

Oxidase

Acid Production from*

G

M

S

N. gonorrhoeae

Gonorrhea

+

-

-

+

+

-

-

N. meningitidis

Meningitis

+

-

-

+

+

+

-

N. sicca

Normal flora

respiratory tract

+

+

±

+

+

+

+

N. flavescens

Normal flora

respiratory tract

+

+

+

+

-

-

-

Morello-Mizer-Granato: I III. Diagnostic I 10. Microbiology of the I I © The McGraw-Hill

Laboratory Manual and Microbiology in Action Urinary and Genital Tracts Companies, 2003

Workbook in Microbiology, 7/e

Figure 27.1 Diagram of a microscopic field showing intracellular diplococci within polymorphonuclear cells. In cervical smears, organisms of the normal flora may be numerous, but these are extracellular.

Figure 27.1 Diagram of a microscopic field showing intracellular diplococci within polymorphonuclear cells. In cervical smears, organisms of the normal flora may be numerous, but these are extracellular.

Microbiology Neisseria

Isolation of the organism in culture is still considered the standard test, however, and is always used for potential medical-legal cases such as suspected sexual abuse of children.

Gonorrhea usually begins as an acute, local infection of the genital tract. In the male, the urethra is initially involved and exudes a purulent discharge. When the exudate is smeared on a microscope slide and Gram stained, it is seen to contain many polymorphonuclear cells (phagocytic white blood cells), some of which contain intracellular, gram-negative diplococci (see color-plate 4). In the female, acute infection usually begins in the cervix. Smears of the exudate show the same intracellular diplococci as seen in males, except that there are often many more extraneous organisms present in specimens collected from females (see fig. 27.1). Indeed, the abundant normal flora of the vagina may mask the presence of gonococci (N.gonorrhoeae) in smears or cultures from females. For many women, initial infection may be asymptomatic. In them, gonococci cannot be demonstrated in smears, and, therefore, culture or other detection techniques, such as nucleic acid probes, or gene amplification assays must be used for laboratory diagnosis. Asymptomatic infection also occurs in a smaller percentage of infected males. Demonstration of N. gonorrhoeae in culture or by a probe or gene amplification test provides definitive proof of infection. For culture, specimens may be taken from the cervix, urethra, anal canal, or throat and one or more of these sites should be swabbed for culture when disease is suspected in women. For male patients, with a urethral discharge, Gram-stained smears of the exudate revealing typical gram-negative intracellular diplococci are considered presumptively diagnostic, and cultures are generally not taken. Figure 27.2 outlines the recommendations of the Centers for Disease Control and Prevention, U.S. Public Health Service, regarding smears and cultures from males and females, indicating all necessary steps to confirm the diagnosis of gonorrhea by these methods.

When swab cultures are taken, a suitable agar medium should be inoculated directly with the swab, the culture placed in a candle jar or CO2 incubator, and incubated at 35°C pending laboratory examination. Media enriched with hemoglobin and other growth factors are in common use (modified Thayer-Martin and NYC medium are examples). Antimicrobial agents are added to suppress the normal flora of mucous membranes and to make these media more selective for gonococci. Following suitable incubation, laboratory identification of N. gonorrhoeae is made by the criteria shown in table 27.1-1 (see colorplate 37).

Meningitis, an inflammation of the meninges of the brain, may be caused by a variety of microbial agents. Chief among them is Neisseria meningitidis, a gram-negative diplococcus. The usual portal of entry for these organisms is the upper respiratory tract. They may colonize harmlessly there in the immune individual. When they enter susceptible hosts who cannot keep them localized, they may cause invasive disease, either by finding their way into the bloodstream and then to deep tissues, or by direct extension through the membranous bony structures posterior to the pharynx and sinuses. When they localize on the meninges (the thin membranes that cover the brain), meningococci (N. meningitidis) induce an acute, purulent local infection that may have far-reaching effects in the central nervous system. The laboratory diagnosis of N. meningitidis infections is made by recovering the

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Bacterial Vaginosis Facts

Bacterial Vaginosis Facts

This fact sheet is designed to provide you with information on Bacterial Vaginosis. Bacterial vaginosis is an abnormal vaginal condition that is characterized by vaginal discharge and results from an overgrowth of atypical bacteria in the vagina.

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