In this episode I’ll discuss the treatment of coagulase-negative staphylococci infection.

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Shout out to “Pharmacy Ben” for leaving a review on my book A Pharmacist’s Guide to Inpatient Medical Emergencies at Amazon. Ben wrote: Good, practical, concise review of critical care pharmacy. Who this book would be great for: new hospital pharmacists, recent PGY1 graduating pharmacists, and pharmacists uncomfortable with critical care. Who this book may not be great for: PGY2 graduate critical care pharmacists…

Coagulase-negative staphylococci

Coagulase-negative staphylococci are typically considered part of the normal flora. They are found on the skin and mucous membranes. There are dozens of coag-negative staph species. The more common species are Staph epidermidis, Staph saprophyticus, Staph lugdunensis, and Staph haemolyticus.

Contaminant vs pathogen

When coag-negative staph grows in a culture it is usually considered a contaminant. Occasionally, coag-negative staph can be a pathogen. This is more likely if the patient is immunocompromised or has an implanted device. Coag-negative staph forms a biofilm on implanted devices, allowing it to adhere well to the device.

How can you tell if coag-negative staph are pathogenic? If only 1 blood culture is positive for coag-negative staph, it is most likely a contaminant. If 2 or more blood cultures are positive, or if significant growth is detected from a device culture, it is most likely a pathogen.

Resistance

Shout out to “Pharmacy Stephen” whose question in the pharmacy nation slack group on coag-negative staph resistance led to this topic. You can signup at pharmacynation.org to join in real-time messaging with other clinicians about patient care issues.

The majority of coag-negative staph are resistant to methicillin. But strains reported as oxacillin sensitive may not be. This is because coag-negative staph displays heterotypic resistance. In heterotypic resistance, a minority of the bacterial population are resistant. Due to the low inoculum used in standard susceptibility testing, heterotypic resistance may result in a culture with methicillin-resistant coag-negative staph being reported as methicillin susceptible. For this reason, an antibiotic with activity against methicillin-resistant coag-negative staph should be used, even if a single culture of coag-negative staph is reported to be methicillin sensitive.

Treatment

If coag-negative staph is considered pathogenic, vancomycin is the preferred treatment. Second-line alternatives that are also active in the setting of methicillin resistance such as telavancin, linezolid, or daptomycin may be considered based on patient factors and the site of infection. Rifampin may be added for enhanced biofilm penetration but cannot be used as monotherapy. My Johns Hopkins Antibiotic Guide recommends that methicillin sensitive coag-negative staph should only be considered if multiple isolates are identified as methicillin sensitive.

Treatment involves source control when possible. The duration of antibiotic therapy may be several weeks depending on the site of infection (ex: 6 weeks for endocarditis but 1 week for a peripheral line infection).

Species

Your laboratory may need to be contacted to speciate the coag-negative staph. Knowing the exact species does not usually change treatment. Here are some things to know about some of the more common species of coag-negative staph:

Staph epidermidis

This is both the most common contaminant and the most common pathogen of all the coag-negative staph. Use the number of positive blood cultures or amount of growth from device cultures to determine pathogen vs contaminant.

Staph haemolyticus

Often causes neonatal infection.

Staph saprophyticus

Second only to E. coli as a cause of UTI in young, sexually active females.

Staph lugdunensis

This is the most virulent of the coag-negative staph species. Interestingly, it is also usually sensitive to methicillin. Staph lugdunensis has been in the news lately due to the discovery of the compound ‘lugdunin.’ Lugdunin is produced by Staph lugdunensis, and in mice and rats it has been found to kill methicillin-resistant Staph aureus. Expect lugdunin to be developed for human use as a new antibiotic.

If you like this post, check out my book – A Pharmacist’s Guide to Inpatient Medical Emergencies: How to respond to code blue, rapid response calls, and other medical emergencies.

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