Antibiotic Resistance in the Treatment of Staphylococcus aureus Keratitis

Abstract

Purpose We compared the resistance patterns of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible Staphylococcus aureus (MSSA) keratitis isolates to common topically applied ophthalmic antimicrobials. Methods We reviewed the antibiotic susceptibility results of 122 MRSA and 276 MSSA keratitis isolates from January 1993 to November 2012. In vitro susceptibility testing of each SA isolate was performed using Kirby-Bauer disk diffusion based on modified serum interpretations for cefoxitin, bacitracin, cefazolin, ciprofloxacin, gatifloxacin, gentamicin, moxifloxacin, ofloxacin, polymyxin B, sulfamethoxazole, tobramycin, and trimethoprim. Results MRSA represented 30.7% (122 of 398) of the total SA isolates. All SA isolates were susceptible to vancomycin, while less susceptible to the fluoroquinolones than to the non-fluoroquinolones. In comparison to MSSA, MRSA was significantly more resistant to all antibiotics tested other than polymyxin B (both equally resistant) and vancomycin (both equally susceptible) (p<0.001). Besides vancomycin, MRSA demonstrated the best susceptibilities to sulfamethoxazole (94.3%), bacitracin (89.3%), trimethoprim (88.5%), and gentamicin (86.1%). Additionally, MRSA was found to be significantly more resistant to the second-generation fluoroquinolones (ciprofloxacin and ofloxacin) than to the fourth-generation fluoroquinolones (moxifloxacin and gatifloxacin). An increase in resistance to the fourth-generation fluoroquinolones was detected for both MRSA and MSSA over the study period. Conclusions The in vitro susceptibilities of commonly used topical antibiotics differ for MRSA and MSSA isolates, thus successful treatment of bacterial keratitis should be supported with laboratory studies. Vancomycin remains the treatment of choice for MRSA keratitis. The empiric use of second-generation fluoroquinolones appears to be contraindicated in the treatment of MRSA keratitis.

Trends of Bacterial Keratitis Culture Isolates in Jerusalem; a 13- Years Analysis

“…In our study the percentage of MRSA isolates decreased from 18% in the first study period of 2002–2005 to 0% in the last study period of 2010–2014 with a non-statistical decrease in trend. This differs significantly from frequencies reported in the literature [4,6,7,17,25]. Furthermore, much higher frequencies of MRSA isolates from corneal cultures have been reported in other studies, ranging from 42–45%[6,7].…”

Bacteriophages: the possible solution to treat infections caused by pathogenic bacteria

“…Moreover, 95% of nosocomial infections are caused by resistant staphylococci (National Center for Health Statistics 2009). Hospital-and community-acquired methicillin-resistant Staphylococcus aureus (MRSA) were found to be resistant to many classes of antibiotics, including the 4th-generation fluoroquinolones, and can cause systemic infections with a mortality rate of 50% (Kollef and Micek 2005;Rubinstein et al 2008;Roberts et al 2013;Chang et al 2015). Other pathogenic bacteria such as Pseudomonas, Campylobacter, and Listeria show similar trends of antibiotic resistance (Ozbey and Tasdemi 2014;Pobiega et al 2014;Komba et al 2015;Obaidat et al 2015).…”

Challenges of corneal infections

“…S. aureus is a leading cause of keratitis worldwide. From 1993–2012, S. aureus accounted for 25.2% of 1576 bacterial keratitis isolates with other staphylococcus species comprising 9.5% [36]. S. aureus possesses a number of factors that allow for increased host adhesion, cytolytic activity against host cells, and the ability to evade the innate immune system and is therefore considered the most virulent of the Staphylococcus species [36].…”

“…Treatment with a fortified antibiotic (cefazolin 5% and tobramycin or gentamicin 1.4%) [45] is often initiated prior to receiving results of bacterial smears or cultures. This is common in instances for ulcers less than 2 mm in dimension, when broad-spectrum antibiotics may be started if smears are negative and before culture reports are available [36]. Because of their broad-spectrum anti-bacterial activity and relatively low toxicity, topical fluoroquinolones, particularly gatifloxacin and moxifloxacin have become important treatment options for common ocular bacterial infections [46].…”

“…Unfortunately, these concentrations are quickly diminished by reflex tearing and blinking after instillation. Since there is currently no standard to measure efficacy of topical therapies, it must be assumed that antibiotic concentrations reached in the ocular tissues are at an equal or greater concentration than would be seen in the serum [36]. Studies have been done in animal and human models to determine PK concentration of topical antibiotics used in ocular disease.…”