How do I determine if a certain bacterium is colonized?

From the Guidelines

To determine if a certain bacteria has colonized, you should collect and analyze appropriate samples from the suspected colonization site, with the most recent and highest quality study suggesting the use of rectal surveillance cultures for carbapenem-resistant Enterobacteriaceae (CRE) as part of a comprehensive infection control program 1.

Methods for Determining Colonization

• Swabbing the area (such as nasal passages, skin, or wounds) and sending the sample to a laboratory for culture testing
• Using rapid screening tests, such as those for MRSA, which can provide results within hours
• PCR testing, which detects bacterial DNA rather than waiting for cultures to grow
• Regular surveillance cultures in healthcare settings to monitor for colonization of concerning bacteria such as VRE or CRE

Importance of Understanding Colonization

• Colonization (presence of bacteria without causing infection) differs from active infection, which would show symptoms like inflammation, pain, or fever
• If you suspect bacterial colonization, consult with a healthcare provider who can recommend appropriate testing based on your specific situation and the bacteria of concern

Key Considerations

• The distinction between pathogen and colonizer is facilitated by detection of pathogenic organisms as the dominant flora on direct Gram-negative stain or their recovery in respiratory secretions in moderate or heavy growth 1
• Quantitative cultures of bronchoscopic or other specimens from lower airways may also facilitate the distinction between colonizing bacteria and pathogens 1

From the Research

Determining Bacterium Colonization

To determine if a certain bacterium is colonized, several factors and methods can be considered:

• The type of bacterium: Different bacteria have different colonization patterns and risks. For example, Staphylococcus aureus is a common cause of bacteremia and endocarditis 2, 3, 4.
• The site of colonization: Bacteria can colonize different parts of the body, such as the skin, respiratory tract, or oral cavity. The oral cavity is a common site for Staphylococcus aureus colonization 3.
• The presence of antibiotic resistance: The presence of antibiotic resistance genes, such as the vanA gene, can indicate colonization with a resistant bacterium 3, 4.
• The use of antimicrobial susceptibility testing: This can help determine the effectiveness of different antibiotics against the colonizing bacterium 3, 5.
• The clinical presentation: The presence of symptoms such as fever, infection, or sepsis can indicate colonization with a pathogenic bacterium 2, 5.

Methods for Detecting Colonization

Several methods can be used to detect colonization, including:

• Culture: This involves taking a sample from the suspected site of colonization and growing the bacteria in a laboratory setting 2, 3, 5.
• Polymerase chain reaction (PCR): This is a molecular technique that can be used to detect the presence of specific genes, such as the vanA gene 3, 4.
• Antimicrobial susceptibility testing: This involves testing the effectiveness of different antibiotics against the colonizing bacterium 3, 5.

Considerations for Specific Bacteria

Different bacteria have different considerations for determining colonization:

• Staphylococcus aureus: This bacterium is commonly colonized in the oral cavity and can cause bacteremia and endocarditis 2, 3, 4.
• Group B streptococcus: This bacterium is commonly colonized in the genital and gastrointestinal tracts and can cause infection in pregnant women and newborns 6.