Anaerobic Media

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Initial processing of anaerobic specimens involves inoculation of appropriate media. Table 43-4 lists commonly used anaerobic media. Primary plates should be freshly prepared or used within 2 weeks of preparation. Plates stored for longer periods accumulate peroxides and become dehydrated; this results in growth r

Organism

Virulence Factors

Spectrum of Disease and Infections

Clostridium perfringans

Produces several exotoxins; a-toxin is most important and mediates destruction of host cell membranes; enteroioxin inserts and disrupts membranes of mucosal cells

Gas gangrene, a life-threatening, toxin-mediated destruction of muscle and other tissues following traumatic introduction of the organism. Food poisoning caused by release of the toxin after ingestion of large quantities of organism. Disease is usually self-limiting and benign and Is manifested by abdominal cramps, diarrhea, and vomiting

Clostridium tetani

Produces tetanospasmin, a neurotoxic exotoxin that disrupts nerve impulses to muscles

Tetanus (also commonly known as lockjaw/). Organism establishes a wound infection and elaborates the potent toxin that mediates generalized muscle spasms. If untreated, spasms continue to be triggered by ever« minor stimuli, leading to exhaustion and, eventually, respiratory failure

Clostridium botulinum

Produces extremely potent neurotoxins

The disease botulism results from ingestion of preformed toxin In nonacldiei vegetable or mushroom foodstuffs. Absorption of the toxin leads to nearly complete paralysis of respiratory and other essential muscle groups. Other forms of botulism can occur when the organism elaborates the toxin after it has colonized the gastrointestinal tract c infants (i.e„ intent botulism). Wound botulism is more rare than the otherforms, and occurs when C, botuiinum produces the toxin from an Infected wound site

Clostridium difficile

Produces toxin A, which is an enterotoxin that is thoughtto be primarily responsible for the gastrointestinal disease caused by this organism. Toxin B, a cytotoxin, has a less clear role in C. Arte Infections

Organism requires diminution of normal gut flora by the activity of various antimicrobial agents to become established In the gut of hospitalized patients. Once established, elaboration of toxlnfs) results in diarrhea (i.e., antibiotic-associated diarrhea) or potentially life-threatening inflammation of the colon. When the surface of the inflamed bowel is overlaid with a "pseudomembrane" composed of necrotic debris, white blood cells, and fibrin, the disease Is referred to as pseudo-membranoo^ colitis

Actinomyces spp., inducting A israelii A. meyeri A naeslundii Aodontolyb'cus

No well-characterized virulence factors. Infections usually require disruption of protective mucosal surface of the oral cavity, respiratory tract, gastrointestinal tract, and/or female genitourinary tract

Usually involved in mixed oral or cervicofacial, thoracic, pelvic, and abdominal infections caused by patient's endogenous strains; certain species (A wscasusand A. naeslundii) also involved in periodontal disease and dental carles

Propionibacterium spp.

No definitive virulence factors known

Associated with inflammatory process in acne but only rarely implicated In infections of other body sites. As part of normal skin flora they arete most common anaerobic contaminants of blood cultures

---------a.

Bifidobacterium spp.

No definitive virulence factors known

Not commonly found In clinical specimens. Usually encountered in mixed Infections of pelvis or abdomen

Eubacterium spp.

No definitive virulence factors known

Usually associated with mixed infections of abdomen, pelvis, or genitourinary tract

Mobiluncus spp.

No definitive virulence factors known

Organisms are found in the vagina and have been associated with bac lajj vaginosis, but their precise role in gynecologic infections is unclear., Rarely encountered in infections outside the female genital tract

Bactmides fragilisgmp, other Bacteroidesspp., Bacterotdes gracilis, Bacteroidesureolyticus, Prevotella spp., Porpbyromonasspp., Fusobacterium nudeatum, and other Fusobacterium spp.

These anaerobic gram-negative bacilli produce capsules, endotoxin, and succinic acid, which inhibit phagocytosis, and various enzymes that mediate tissue damage. Most infections still require some breach of mucosal integrity that allows the organisms to gain access to deeper tissues

Organisms most commonly encountered in anaerobic infections. Infection^ are often mixed with other anaerobic and facultatively anaerobic organisms. Infections occur throughout the body, usually as localized of 1 enclosed abscesses, and may involve the cranium, periodontium, thorax, peritoneum, liver, and female genital tract May also cause bacteremia, aspiration pneumonia, septic arthritis, chronic sinusitis, decubitus uicer^ and other soft tissue infections. The hallmark of most, but not all, infections is the production of a foul odor. In general, infections caused If B. fragllls group occur below the diaphragm; pigmented Prevoteila spp.. Porphyromonas spp., and F. nudeatum generally are involved In head al^j neck and pleuropulmonary Infections

Rnegoldia magna, Micromonas micros

No definitive virulence factors known

Most often found mixed with other anaerobic and facultatively anaerobic bacteria in cutaneous, respiratory, oral, or female pelvic infections

Veillonella spp.

No definitive virulence factors known

May be involved In mixed infections but rarely play a significant role JS1

Nlium

Components/Comments

Primary Purpose

Anaerobic blood agar

May be prepared with Columbia, Schaedler, CDC, Brucella, or brain-heart infusion base supplemented with 5% sheep blood, 0.5% yeast extract, hemin, L-cystine, and vitamin K,

Nonselective medium for isolation of anaerobes and facultative anaerobes

i Sacteroides bile esculin agar (BBE)

Trypticase soy agar base with ferric ammonium citrate and hemin; bile salts and gentamicin act as inhibitors

Selective and differential for Bacteroldes fragills group; good for presumptive identification

Laked kanamycin-vancomycin blood agar (LKV) ------

Brucella agar base with kanamycin (75 ng/ mL), vancomycin (7.5 pg/mL), vitamin K„ (10 (ig/mL), and 5% laked blood

Selective for isolation of Prevotella and Bacteroides spp.

Anaerobic phenylethyl alcohol agar (PEA)

Nutrient agar base, 5% blood, phenylethyl alcohol

Selective for inhibition of enteric gram-negative rods and swarming by some Clostridia

Egg-yolk agar (EYA)

Egg yolk base

Nonselective for determination of lecithinase and lipase production by Clostridia and fusobacteria

Cycloserine cefoxitin fructose agar (CCFA) —-—---

Egg yolk base with fructose, cycloserine (500 mg/L), and cefoxitin (16 mg/L); nrutral red indicator

Selective for Clostridium difficile

jEooked meat (also called chopped meat) broth t-—---

Solid meat particles initiate growth of bacteria; reducing substances lower oxidation-reduction potential (Eh)

Nonselective for cultivation of anaerobic organisms; with addition of glucose, can be used for gas-liquid chromatography

, Peptone-yeast extract glucose broth (PYG)

Peptone base, yeast extract, glucose, cysteine (reducing agent), resazurin (oxygen tension indicator), salts

Nonselective for cultivation of anaerobic bacteria for gas-liquid chromatography

Thloglycollate broth --—

Pancreatic digest of casein, soy broth, and glucose enrich growth of most bacteria. Thioglycollate and agar reduce Eh. May be supplemented with hemin and vitamin K,

Nonselective for cultivation of anaerobes, as well as facultative anaerobes and aerobes

"Sure 43-5 Gloveless anaerobe chamber. (Courtesy Anaerobe Systems, Morgan Hill, Calif.)

Figure 43-6 Prereduced, anaerobically sterilized (PRAS) plated media. (Courtesy Anaerobe Systems, Morgan Hill, Calif.)

"Sure 43-5 Gloveless anaerobe chamber. (Courtesy Anaerobe Systems, Morgan Hill, Calif.)

Inhibition. Reduction of media in an anaerobic environment eliminates dissolved oxygen but has no effect on the peroxides. Prereduced, anaerobically sterilized fPRAS) media are produced, packaged, shipped, and ored under anaerobic conditions. They are commercially available from Anaerobe Systems (Morgan Hill, Calif) (Figure 43-6) and have an extended shelf life of UP to 6 months.

Figure 43-6 Prereduced, anaerobically sterilized (PRAS) plated media. (Courtesy Anaerobe Systems, Morgan Hill, Calif.)

prevention

A multiple-dose vaccine is available for prevention of tetanus.1 The immunogen is adsorbed tetanus toxoid and is generally administered with diphtheria toxoid and pertussis vaccine as a triple antigen called DTP. Single boosters of diphtheria and tetanus (DT) or tetanus alone are recommended every 10 years. Immunoprophylaxis in wound management is based on the type of wound. Completely immunized individuals with minor and/or uncontaminated wounds do not need any specific treatment. However; completely immunized individuals with major and/or contaminated wounds should get a booster of tetanus toxoid if they have not had one in the previous 5 years. Finally, a partially immunized individual or one who has never been immunized should receive a dose of tetanus toxoid immediately. In addition, passive immunization with human tetanus immune globulin (TIG) should be given if the individual has a major wound or a wound contaminated with soil that contains animal feces.

Individuals who have eaten food suspected of containing botulinum toxin should be purged with cathartics (laxatives), have their stomach pumped, and be given high enemas.

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