Endophthalmitis most often caused by Staphylococcus

Endophthalmitis is most often caused by coagulase-negative Staphylococcus, and the antibiotics vancomycin and ceftazidime seem to perform well in treating it.

That was one of the findings of a 25-year retrospective study conducted by Dr Ronald C. Gentile, of the New York Eye and Ear Infirmary, and his colleagues in New York City and San Antonio, Texas, USA. The researchers set out to look for trends related to pathogens and antibiotics over the past 25 years. They reported their results in Ophthalmology.

Other findings:

• Many antibiotics, among them cephalosporins and methicillin, are associated with a statistically significant trend in increasing microbial resistance.
• A significant trend toward decreasing microbial resistance against aminoglycosides and imipenem also exists.

The researchers studied 911 eyes with a total of 988 consecutive culture-positive endophthalmitis isolates that had been collected from 1987 to 2011. The pathogens they most frequently found were coagulase-negative Staphylococcus (39.4%), Streptococcus viridans species (12.1%) and Staphylococcus aureus (11.1%). Gram-negative organisms accounted for 10.3% of all isolates and fungi accounted for 4.6% of them.

Two isolates, Enterococcus faecium and Nocardia exalbida, were not susceptible to vancomycin, but the rest of the 725 gram-positive bacteria they tested were susceptible. The researchers tested 94 gram-negative organisms against ceftazidime and found that 2 were of intermediate sensitivity and 6 were resistant.

The researchers found that microbial resistance was associated with 8 antibiotics as time went on. Those 8 were ampicillin, cefazolin, cefotetan, ceftriaxone, cephalothin, clindamycin, erythromycin and methicillin/oxacillin. They saw increasing microbial susceptibility with 3 antibiotics: gentamicin, imipenem and tobramycin.

To read the abstract of the study click here.