The art of war is simple enough. Find out where your enemy is. Get at him as soon as you can. Strike him as hard as you can, and keep moving on.
—Ulysses S. Grant
Since the discovery of antibiotics, there has been a conflict between antibiotics and bacterial mutations and resistance. This has led to an arms race of sorts in which bacteria have undergone modifications that facilitate the development of resistance to progressive generations of antibiotics. Staphylococcus aureus, a bacterium frequently found in the nose and skin of patients, is now noted to be one of the most common causes of hospital-based infections and contamination of postsurgical wounds. Bacteria such as S aureus rapidly developed resistance to the penicillins, which led to the development of the so-called β-lactamase-resistant penicillins such as methicillin. However, with the emergence of methicillin-resistant S aureus (MRSA), bacteria have now developed resistance to all β-lactam antibiotics.
The review article by Mah et al. (pages 1894–1908) looks at the current medical literature and describes many of the challenges of ocular MRSA infections and also recommends ways to identify, treat, and reduce the overall problems associated with MRSA.
Methicillin-resistant S aureus is a potential widespread problem in ophthalmology as S aureus is now reported to be the second-most-common pathogen causing bacterial keratitis worldwide. Methicillin-resistant S aureus infections have also been reported following a wide variety of corneal or anterior segment procedures, such as penetrating keratoplasty and lamellar keratoplasty, in addition to MRSA keratitis. These complications have been reported after laser in situ keratomileusis as well as photorefractive keratectomy. The issue of bacterial resistance is particularly troubling in the setting of cataract surgery. Studies evaluating the presence of bacteria on the ocular surface have found that Staphylococcus epidermidis as well as S aureus are isolated frequently in patients having cataract surgery. More troubling is the fact that MRSA accounts for almost 50% of S epidermidis isolates and almost 30% of S aureus isolates. As bacteria on the ocular surface are the most common source for postoperative infections including endophthalmitis, the rapid rise of MRSA may lead to potential problems with these resistant bacteria.
Treatment of MRSA infections is problematic given the relative resistance to many antibiotics that are commonly used following cataract surgery, including the so-called third- and fourth-generation fluoroquinolones. However, extremely high doses of antibiotics to which bacteria show a resistance on sensitivity testing can possibly eradicate MRSA. These include topical antibiotics such as cefazolin and the later-generation fluoroquinolones. Ophthalmology is relatively unusual in that following routine ophthalmic surgery, antibiotics can be placed on the surface of the eye in very high doses, which may increase the concentration to a higher level than can be attained with oral or intravenous dosing. This may allow topical or intracameral antibiotics to which bacteria are resistant to reach a therapeutic level to treat potential MRSA infections in ophthalmology. Finally, antibiotics such as vancomycin in which no resistance of gram-positive pathogens has been reported are still available. This makes vancomycin an excellent antibiotic for the treatment of MRSA infections. However, there are many recommendations to limit the routine use of vancomycin for MRSA to minimize the potential risk for resistance.
A more important topic is the actual prevention of MRSA infections. Recommendations to prevent the colonization of MRSA on patients or in the ophthalmic clinic include rigorous hand washing as well as regular cleaning of surfaces in the clinic itself. The prevention of surgical infections is critical and starts with the antisepsis of the ocular surface on which many bacteria that can cause ocular infections reside. Many products for eyelid cleaning are commercially available. One of the most effective methods of sterilizing the eyelid surface is the use of povidone–iodine. This agent has been found to reduce the bacterial load on the eyelid margin. When dilute povidone–iodine is placed on the ocular surface prior to cataract surgery, more than 95% of bacteria can be eradicated. Proper patient draping to isolate the lids and lashes from the surgical field is critical. Finally, the proper use of antibiotics preoperatively, intraoperatively, and postoperatively is important to ensure that the antibiotic agents are used in a concentration and a regimen to allow a high tissue concentration compared with the minimal inhibitory concentration required to kill bacteria. Proper concentration and dosing allow the maximum possible response to the antibiotic while lowering the risk for the development of antibiotic resistance. Antibiotics should not be prescribed fewer than 4 times per day and should be discontinued abruptly with no tapering or long-term use.
As stated in a previous editorial regarding the increasing problem of antibiotic resistance,1 “the use of the optimal antibiotic in the optimal dose for the optimal period of time is essential to prevent the development of resistance to fluoroquinolone antibiotics and hopefully extend the useful lifetime of these medications.” This statement is even more true today.
1. Mamalis N. The increasing problem of antibiotic resistance [editorial]. J Cataract Refract Surg