Micologia, Virologia e Microbiologia Clínica 03/03

Summary

In this lesson, the speaker discusses staphylococci, specifically focusing on coagulase-negative staphylococci (CoNS). The lecture covers the significance of these bacteria, which were once thought to be contaminants but are now recognized as potential pathogens, particularly in immunocompromised patients. The two main species, *Staphylococcus epidermidis* and *Staphylococcus saprophyticus*, are explored, with emphasis on their ability to form biofilms and cause infections such as urinary tract infections and endocarditis. Additionally, the process for laboratory identification of these bacteria, including tests like catalase, coagulase, and automated systems, is explained.

Takeaways

• 😀 Staphylococcus coagulase-negative species were once considered contaminants, but it was later discovered they can cause infections, especially in immunocompromised patients.
• 😀 Staphylococcus epidermidis, part of our normal skin and mucosal flora, can cause wound infections, systemic infections, urinary tract infections, and endocarditis.
• 😀 Staphylococcus saprophyticus is commonly associated with urinary tract infections in sexually active young women.
• 😀 The ability of Staphylococcus species to form biofilms is a key virulence factor that contributes to their ability to cause persistent infections.
• 😀 The diagnostic process for Staphylococcus species starts with Gram staining to identify Gram-positive cocci and inform the choice of culture medium.
• 😀 The catalase test is used to differentiate Staphylococci (catalase-positive) from Streptococci (catalase-negative).
• 😀 Coagulase testing is critical in identifying whether the Staphylococcus species is coagulase-positive (e.g., Staphylococcus aureus) or coagulase-negative (e.g., Staphylococcus epidermidis, Staphylococcus saprophyticus).
• 😀 The use of automated laboratory systems helps with the identification and antimicrobial susceptibility testing of microorganisms, increasing efficiency in high-volume laboratories.
• 😀 Identification in the laboratory can also involve testing for resistance or sensitivity to bacitracin, which aids in differentiating species within the Staphylococcus genus.
• 😀 Automated systems in microbiology labs provide more precise results in shorter timeframes, helping in faster diagnosis and treatment, especially in large-scale clinical settings.

Q & A

What are coagulase-negative staphylococci (CoNS)?

Coagulase-negative staphylococci (CoNS) are staphylococci species that lack the enzyme coagulase. This makes them different from coagulase-positive staphylococci like Staphylococcus aureus.

Why were coagulase-negative staphylococci initially considered contaminants?

CoNS were initially considered contaminants because they are part of the normal human microbiota, specifically found on the skin and mucous membranes. Their presence in cultures was often thought to be an accidental contamination rather than a sign of infection.

How has the understanding of coagulase-negative staphylococci changed over time?

Over time, it was realized that coagulase-negative staphylococci can cause infections, especially in immunocompromised patients or those with invasive medical devices like catheters and prostheses.

What are the main species of coagulase-negative staphylococci discussed in the lesson?

The two main species discussed are Staphylococcus epidermidis and Staphylococcus saprophyticus.

What is the role of biofilm formation in infections caused by Staphylococcus epidermidis?

Staphylococcus epidermidis has a strong ability to form biofilms, which are complex communities of microorganisms that adhere to surfaces, including medical devices. This biofilm formation contributes to the bacteria's ability to cause persistent infections.

What kind of infections can Staphylococcus epidermidis cause?

Staphylococcus epidermidis can cause a variety of infections, including wound infections, systemic infections, urinary tract infections, endocarditis, and osteomyelitis.

How is Staphylococcus saprophyticus associated with urinary tract infections (UTIs)?

Staphylococcus saprophyticus is commonly associated with urinary tract infections, particularly in sexually active young women. It has a preference for epithelial tissue and can ascend through the urethra to the bladder, causing cystitis and urethritis.

What are the general steps involved in the laboratory identification of staphylococci?

The laboratory identification begins with Gram staining to classify the bacteria. Then, tests like catalase and coagulase are performed. Coagulase-negative staphylococci are further differentiated using tests for antibiotic resistance, such as the bacitracin test, and by observing biofilm formation and sugar fermentation.

What is the significance of the coagulase test in staphylococcal identification?

The coagulase test differentiates between coagulase-positive staphylococci (e.g., Staphylococcus aureus) and coagulase-negative staphylococci. A positive result indicates Staphylococcus aureus, while a negative result suggests a coagulase-negative species.

How does automated microbiology work in identifying staphylococcal species?

Automated microbiology systems use panels of tests that are inoculated with a sample. After incubation, the system identifies the species of bacteria and determines its sensitivity to antibiotics. This process provides fast and accurate results, especially useful in large laboratories handling many samples.