Can anaerobic bacteria be part of a normal oropharyngeal (throat) culture?

From the Guidelines

Yes, anaerobes can be part of the normal throat microbiota. The human throat naturally harbors various anaerobic bacteria, including species of Peptostreptococcus, Actinomyces, Fusobacterium, and Prevotella, which coexist with aerobic and facultative anaerobic organisms 1. These anaerobes typically live in the deeper recesses of the tonsillar crypts and posterior pharyngeal areas where oxygen levels are lower. In healthy individuals, these anaerobic bacteria exist in a balanced state with other microorganisms and don't cause disease. However, standard throat cultures performed in clinical settings typically don't detect these anaerobes because they require special collection techniques, transport media, and culture conditions. Conventional throat cultures focus on identifying potential pathogens like Group A Streptococcus using aerobic culture methods. If anaerobic infections are suspected, specific anaerobic culture techniques must be requested, which involve immediate inoculation into anaerobic transport media and processing in an oxygen-free environment. This distinction is important because while anaerobes are normal inhabitants of the throat, they can become pathogenic in certain conditions like peritonsillar abscess, retropharyngeal abscess, or following aspiration pneumonia.

Some key points to consider:

• Anaerobes are part of the normal throat microbiota, but standard throat cultures may not detect them due to the lack of anaerobic culture conditions 1.
• Specific anaerobic culture techniques are required to detect anaerobes, which involve immediate inoculation into anaerobic transport media and processing in an oxygen-free environment 1.
• Anaerobes can become pathogenic in certain conditions, such as peritonsillar abscess, retropharyngeal abscess, or following aspiration pneumonia 1.
• The presence of anaerobes in the throat can be significant in certain clinical contexts, such as in the diagnosis of Lemierre's syndrome, which is caused by Fusobacterium necrophorum 1.

In terms of clinical practice, it is essential to consider the possibility of anaerobic infections in patients with symptoms of pharyngitis, especially if they do not respond to standard antibiotic therapy. In such cases, specific anaerobic culture techniques should be requested to detect the presence of anaerobes. Additionally, clinicians should be aware of the potential for anaerobes to cause disease in certain conditions and take appropriate measures to prevent and treat these infections.

From the Research

Anaerobes in Normal Throat Culture

• Anaerobes are a predominant component of the normal human oropharyngeal bacterial flora 2
• They are common in the upper respiratory tract and can be found in the throat, making them a part of normal throat culture 3, 2
• The oral cavity harbors more than 300 different bacterial species, with anaerobic bacteria outnumbering aerobic bacteria by 10:1 in saliva 4
• Anaerobes such as gram-positive bacilli, gram-negative bacilli, Veillonella, and gram-positive cocci are found in the healthy gingival sulcus, marginal plaque, and plaque from the tooth surface 5

Prevalence of Anaerobes in the Throat

• Anaerobes are invariably present in adults, but their prevalence varies with age and specific sites sampled in the oral cavity 5
• In the saliva, Veillonella are the most numerous anaerobes, while in the gingival crevice, large concentrations of gram-negative rods are recovered 5, 4
• The concentrations of anaerobic bacteria in the throat can be high, with bacterial concentrations in gingival scrapings reaching 10(11) to 10(12) cfu/ml 4

Importance of Anaerobes in Throat Culture

• Anaerobes can be a cause of endogenous bacterial infections in the upper respiratory tract, including tonsillitis and deep oral and neck infections 3, 2
• They can produce the enzyme beta-lactamase, which can "shield" non-beta-lactamase-producing bacteria from penicillins, leading to clinical failures if not adequately treated 2
• Appropriate methods of collection, transportation, and cultivation of specimens are required to isolate anaerobes from the throat 2