Anaerobic and Aerobic Culture and Gram Stain

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Turnaround Time: 4 - 7 days
CPT Code:

87070, 87075, 87205

Test Type: 0.5 mL pus, or other fluid or tissue


Isolate and identify anaerobic pathogenic organisms; determine susceptibility of isolates (extra charge). When actinomycetes are suspected a specific request must be made. Anaerobic cultures are indicated particularly when suspected infections are related to gastrointestinal tract, pelvic organs, associated with malignancy, related to use of aminoglycosides; or occur in a setting in which the diagnosis of gas gangrene or actinomycosis is considered. Anaerobic culture is especially indicated when an exudate has a foul odor or if the exudate has a grayish discoloration and is hemorrhagic. Frequently, more than one organism is recovered from an anaerobic infection.

The only sources for specimens with established validity for meaningful anaerobic culture in patients with pleuropulmonary infections are blood, pleural fluid, transtracheal aspirates, transthoracic pulmonary aspirates, and specimens obtained at thoracotomy. Pleural fluid is preferred for patients with empyema.1 Blood cultures yield positive results in <5% of cases of anaerobic pulmonary infection. Specimens received in anaerobic transport containers are not optimal for aerobic fungus cultures. Mycobacterium sp or Nocardia sp, which may cause abscesses, will not be recovered even if present, since extended incubation periods, aerobic incubation, and special media are necessary for their isolation. Cultures for these organisms should be specifically requested.

IUDs will be cultured for Actinomyces sp only.

Bronchoscopically obtained specimens are not ideal as the instrument becomes contaminated by organisms normally contaminating the oropharynx during insertion. Culture of specimens from sites harboring endogenous anaerobic organisms or contaminated by endogenous organisms may be misleading with regard to etiology and selection of appropriate therapy.

In open wounds, anaerobic organisms may play an etiologic role, whereas aerobes may represent superficial contamination. Serious anaerobic infections are often due to mixed flora that are pathologic synergists. Anaerobes frequently recovered from closed postoperative wound infections include Bacteroides fragilis, approximately 50%; Prevotella melaninogenica, approximately 25%; Peptostreptococcus prevotii, approximately 15%; and Fusobacterium sp, approximately 25%. Anaerobes are seldom recovered in pure culture (10% to 15% of cultures). Aerobes and facultative bacteria when present are frequently found in lesser numbers than the anaerobes. Anaerobic infection is most commonly associated with operations involving opening or manipulating the bowel or a hollow viscus (eg, appendectomy, cholecystectomy, colectomy, gastrectomy, bile duct exploration, etc). The ratio of anaerobes to facultative species is normally about 10:1 in the mouth, vagina, and sebaceous glands and at least 1000:1 in the colon. Biopsy culture is particularly useful in establishing the diagnosis of anaerobic osteomyelitis,2 clostridial myonecrosis, intracranial actinomycosis, and pleuropulmonary infections. Anaerobic infections of soft tissue include anaerobic cellulitis, necrotizing fasciitis, clostridial myonecrosis (gas gangrene), anaerobic streptococcal myositis or myonecrosis, synergistic nonclostridial anaerobic myonecrosis, and infected vascular gangrene. These infections, particularly clostridial myonecrosis, necrotizing fasciitis, and nonclostridial anaerobic myonecrosis, may be fulminant and are frequently characterized by the presence of gas and foul-smelling necrotic tissue.3 Empiric therapy based on likely pathogens should be instituted as soon as appropriate cultures are collected.

Clinical symptoms suggestive of anaerobic infection include:

• Foul-smelling discharge

• Location of infection in proximity to a mucosal surface

• Necrotic tissue, gangrene, pseudomembrane formation

• Gas in tissues or discharges

• Endocarditis with negative routine blood cultures

• Infection associated with malignancy or other process producing tissue destruction

• Septic thrombophlebitis

• Bacteremic picture with jaundice

• Infection resulting from human or other bites

• Black discoloration of blood-containing exudates (may fluoresce red under ultraviolet light in P melaninogenica infections)

• Presence of “sulfur granules” in discharges (actinomycosis)

• Classical clinical features of gas gangrene

• Clinical setting suggestive for anaerobic infection (septic abortion, infection after gastrointestinal surgery, genitourinary surgery, etc)

See table.

Principle Types of Anaerobic Infections



Type of Infection

Head and neck

Brain abscess


Chronic sinusitis

Chronic otitis

Odontogenic and oropharyngeal space infections

Respiratory tract

Aspiration pneumonia

Necrotizing pneumonia

Lung abscess

Empyema (adults)

Gastrointestinal tract


Intra-abdominal abscess

Liver abscess

Female genital tract

Tubo-ovarian abscess

Salpingitis (30% to 50% of cases)

Septic abortion and endometritis

Bartholin gland abscess

Bacterial vaginosis

Skin and soft tissue

Crepitant cellulitis

Necrotizing fasciitis

Myonecrosis (gas gangrene)

Decubitus ulcer

Diabetic foot ulcer

Bite wounds

Adapted from Styrt B, Gorbach SL. Recent developments in the understanding of the pathogenesis and treatment of anaerobic infections. N Engl J Med. 1989 Jul 24; 321(4):240-246.

1. Bartlett JG. Anaerobic bacterial infections of the lung. Chest. 1987 Jun; 91(6):901-909. PubMed 3556058

2. Hall BB, Fitzgerald RH Jr, Rosenblatt JE. Anaerobic osteomyelitis. J Bone Joint Surg Am. 1983 Jan; 65(1):30-35. PubMed 6848532

3. Finegold SM, George LW, Mulligan ME. Anaerobic infections. Part II. Dis Mon. 1985 Nov; 31(11):1-97. PubMed 3914407

Collection Details:

Patient Preparation:

Sterile preparation of the aspiration site is imperative.

Collection Instructions:

The test request form must state specific site of specimen, age of patient, current antibiotic therapy, clinical diagnosis, and time of collection. If an unusual organism is suspected, such as Actinomyces, this information must be specifically noted on the test request form. For extended incubation use Aerobic Culture, Extended Incubation [180803] or Anaerobic Culture, Extended Incubation [008900]. Aspirations are preferable to swabs. A thin smear for Gram stain prepared at the time of specimen collection may better represent the flora present than one prepared in the laboratory several hours after specimen collection. Culture samples must be collected to avoid contamination with indigenous anaerobic flora from skin and mucous membranes. Because of resident anaerobic flora, the following sites are inappropriate for anaerobic cultures and will be rejected: throat and nasopharynx, sputum, bronchoscopy specimens, gastrointestinal contents, voided or catheterized urine, urogenital swabs (eg, vaginal and/or cervical), and specimens from superficial wounds.

Aerobic/anaerobic bacterial swab transport containing gel medium or anaerobic transporter and one prepared smear in slide carrier; ESwab™ transport.

Some anaerobes will be killed by contact with molecular oxygen for only a few seconds. Overlying and adjacent areas must be carefully disinfected to eliminate contamination with indigenous flora. Ideally, pus or other fluid obtained by needle aspiration through intact skin or mucosal surface that has been cleaned with antiseptic should be collected. Sampling of open lesions is enhanced by deep aspiration using a sterile plastic catheter. Curettings of the base of an open lesion are optimal. If irrigation is necessary, nonbacteriostatic sterile normal saline may be used. Lower respiratory samples must be obtained by transtracheal percutaneous needle aspiration, transbronchial biopsy, transthoracic needle biopsy, or open lung biopsy by physicians trained in these procedures. If swabs must be used, collect two, use one for Gram stain and one for culture. Anaerobic transports must be used for swabs and for aspirates. Specimens are to be collected from a prepared site using sterile technique. Contamination with normal flora from skin, rectum, vaginal tract, or other body surfaces must be avoided.

Specimens for anaerobic culture should be maintained at room temperature. Under these conditions, aerobes and anaerobes will survive 24 to 72 hours when properly collected in the anaerobic transport tube. Storage of specimens in the ESwab™ transport at room temperature for greater than 48 hours may result in diminished recovery of certain anaerobic species.