Q: What are some of the trends in the TRUST data? Are there any troubling emerging trends regarding microbial resistance?

A: "Having done this for three years, we"ve seen consistent susceptibility patterns among these eye pathogens," says Penny Asbell, M.D., of Mount Sinai School of Medicine in New York.
The Ocular Tracking Resistance in U.S. Today (TRUST) program benefits from its size and focus, says Dr. Asbell. "Ocular TRUST is one study with more than 50 centers across the U.S. and one single reference lab-it has a much larger sample size than just one site could collect." As Ocular TRUST was launched in 2005, it also provides current data, adds Dr. Asbell.

Over the three years of surveillance, susceptibility profiles for Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae have been relatively stable for all of the antibiotics tested. "We know from The Surveillance Network data that more and more of the S. aureus infections we encounter are due to methicillin-resistant S. aureus (MRSA)."

In 2008, Ocular TRUST collected and examined 152 Staphylococcus aureus isolates. Of these, 48.1% were methicillin-resistant (MRSA), and the rest were methicillin-sensitive or susceptible (MSSA).

In 2006, 16.8% of S. aureus isolates were MRSA and 83.2% were MSSA.1 "TRUST has actually shown since 2000 that the number of MRSA isolates is steadily rising, while MSSA is steadily decreasing," notes Dr. Asbell.

Likewise, when it comes to coagulase-negative S. epidermidis, the 2008 findings demonstrated only a 38% methicillin-susceptibility rate--the rest were methicillin-resistant, says Dr. Asbell.

So, what drugs are effective? If you"re dealing with a case of MSSA, then the fourth-generation fluoroquinolones gatifloxacin, levofloxacin and moxifloxacin are all equally effective, but not as effective as tobramycin or trimethoprim, the most effective drug, according to Ocular TRUST 2 data, says Dr. Asbell.2 Indeed, 95% of MRSA ocular isolates were susceptible to trimethoprim, while 50% were susceptible to tobramycin and only 18% were susceptible to each fluoroquinolone.

When Streptococcus pneumoniae was analyzed, the three fourth-generation fluoroquinolones were each 100% effective, followed by ciprofloxacin with a susceptibility rate of 92%. Haemophilus influenza was even more susceptible to an array of antibiotics, completely resisting only penicillin (used as a control) and demonstrating only 15% resistance to trimethoprim.2

"The take-home message is that fluoroquinolones continue to be effective against many organisms," says Dr. Asbell. "The other message: MRSA is a marker for multi-drug resistance."

But, other aspects of antibiotics also need to be evaluated to verify efficacy in the eye-such as penetration into the cornea and the drug"s persistence (i.e., how long it remains in the eye), Dr. Asbell notes.
 
1. Ta CN, Sahm DF. Methicillin-susceptible Staphylococcus aureus and methicillin-resistant Staphylococcus aureus: findings of Ocular TRUST. Poster presented at ASCRS/ASOA Symposium, San Diego, Calif; 2007.
2. Asbell PA, Sahm DF. Longitudinal nationwide antimicrobial susceptibility surveillance in ocular isolates: results from Ocular TRUST 2. Presentation at ASCRS/ASOA Symposium, Chicago; 2008.