In the last several issues, we have been discussing staphylococcal infections and their importance to you as Residents, students, and clinicians. Make no mistake about it, you must know your staph and you must know several different agents used to treat it. Learn it now and keep learning it (and forget about Ciprofloxacin, please!).
Now we will move on to streptococcal species, the other very common organisms often causing infections in our patients (remember those flesh eating bacteria?). Since most group B and C streptococci are universally sensitive to penicillins of all varieties as well as other common agents like clindamycin and cephalexin, there is not much more that we need to discuss about their therapy. Nonetheless, Group D streptococci are somewhat different. These are the enterococci, often found in the gut but increasingly more frequent in the foot of diabetic patients. Years ago, this organism was often felt to be an innocuous contaminant that could usually be ignored. Not anymore. We frequently see this pathogen complicating many patients with diabetic foot infections.
Enterococcus is "special" because it is not sensitive to cephalosporins, clindamycin, doxycycline, or fluoroquinolones. Classically, ampicillin is the drug of choice for this organism, although other penicillins are also effective. We have seen this organism as the primary pathogen not only in diabetic foot ulcers (DFU), but in bacteremia as well as osteomyelitis in the diabetic foot. There are two strains of this organism that you must remember. The most common is Enterococcus faecalis . This pathogen frequently accompanies other more common organisms in the diabetic host such as staphylococcus aureus or beta-hemolytic streptococci. Perhaps they have a synergistic effect on its pathogenicity. This is the strain that I prefer to treat with ampicillin, amoxicillin, or ampicillin/sulbactam to which it is usually sensitive. The more difficult strain to manage is Enterococcus faecium , since this is typically vancomycin resistant and almost always requires treatment with linezolid or daptomycin. It is an important distinction to make, since the therapies must often be very different. Vancomycin resistant enterococci (VRE), unfortunately, complicate many of our diabetic foot infections. This mutation, due to prior antimicrobial pressure, confers resistance to either of the two aforementioned strains, making them obviously resistant to vancomycin. VRE is a reportable organism that we usually refer to our infectious disease specialist to treat. These patients, like those with MRSA, must be isolated and contact precautions must always be implemented to prevent the spread to hospital staff, other patients, and visitors. Luckily, these pathogens are usually susceptible to common antimicrobial agents such as linezolid or daptomycin (sometimes even ampicillin!).
Although not as common as methicillin resistant staphylococcus aureus (MRSA), enterococcal infections should be recognized as requiring special considerations for their therapy as previously discussed. (See Table 1 for suggested antimicrobial therapies). You cannot treat this organism with the usual cephalosporin or clindamycin as you would other streptococci. Most residents miss this point and prescribe inappropriate therapy, just prolonging or exacerbating the severity of infection in the diabetic host. While not difficult to treat, it is your job as physicians to make the right call and the right prescription.
| Oral | Parenteral |
| Ampicillin | Ampicillin |
| Amoxicillin | Ampicillin/Sulbactam |
| Amoxicillin/Clavulanate | Piperacillin/Tazobactam |
| Linezolid | Vancomycin |
| Linezolid*§ | |
| Daptomycin*§ | |
| Doripenem, Imepenem | |
| Aminoglycosides |
|
* also used to treat Enterococcus faecium § used to treat Vancomycin Resistant Enterococcus (VRE) |
See you next time.
Robert Frykberg, DPM, MPH
PRESENT Editor,
Diabetic Limb Salvage
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References:
- Joseph, Warren S: Handbook of Lower Extremity Infections, 3rd Edition Data Trace Publishing, 2009
- Gilbert DN et al: The Sanford Guide to Antimicrobial Therapy 2012, 42nd Edition Antimicrobial Therapy, Inc., Sperryville, VA
- Lipsky BA, Berendt AR, Cornia PB, et al. 2012 Infectious Diseases Society of America clinical practice guideline for the diagnosis and treatment of diabetic foot infections. Clin Infect Dis. Jun 2012;54(12):e132-173.
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