Nocardia keratitis: amikacin nonsusceptibility, risk factors, and treatment outcomes

Abstract

Purpose To report the increasing trends in Nocardia keratitis species diversity and in vitro antibiotic susceptibility, to demonstrate contact lens wear as a risk factor, and to report visual acuity outcomes after treatment. Methods A retrospective clinical case series was performed at a single academic referral center which identified 26 patients with culture-confirmed Nocardia keratitis between 2014 and 2021. A combination of conventional microbiology and molecular techniques were used to identify isolates. Antibiotic susceptibilities were determined using both commercial and in-house laboratory methods. Microbiology and electronic medical records were used to characterize patients’ clinical profiles. Results Patients’ median age was 32.5 years with a 2:1 male to female ratio. Eighty-four percent (n = 21/25) of patients were diagnosed within two weeks of symptom onset. Nocardia amikacinitolerans (n = 11/26) was the most recovered Nocardia isolate among study patients. Sixty-four percent (n = 16/25) of all isolates, including all 11 N. amikacinitolerans isolates, were resistant to amikacin. All isolates were susceptible to trimethoprim sulfamethoxazole. Contact lens wear was the leading identified risk factor (n = 23/26) in this population. Median time to resolution was 44 days (n = 23, range: 3–190 days). Seventy-one percent of patients (n = 15/21) had a final visual acuity of 20/40 or better. Conclusion Amikacin resistant Nocardia isolates were the majority in the current study. Trimethoprim sulfamethoxazole may be the preferred alternative antibiotic treatment based on in vitro susceptibilities. Contact lens wear was the major risk factor for Nocardia keratitis in South Florida. Overall visual acuity treatment outcomes of patients were favorable.

Nocardia infection following ocular surface surgery

“…Susceptibility testing is crucial to determine the most effective drugs for ocular Nocardia infections. All of the Nocardia strains were susceptible to amikacin in this current study, consistent with the largest-sample-size surveillance study on Nocardia strains and nocardiosis throughout China [ 20 ]. However, all the patients responded poorly to amikacin in this current study.…”

Whole Genome Sequencing Highlights the Pathogenic Profile in Nocardia Keratitis

“…Furthermore, 13 strains displayed resistance to rifampin, showcasing peculiar antimicrobial resistance profiles that differed from previous studies. [36][37][38] Combining with the whole genome sequences online, most of the same species of 141 strains of Nocardia from different sources were harbored in the same clade suggesting the accuracy and precision of our whole-genome phylogenetic analysis. Among the strains studied, 32 of 34 strains of N. farcinica and all strains of N. puris were isolated from China, suggesting certain species of Nocardia were restricted in specific regions with the influence of climate and environmental factors.…”

“…In this cohort, Nocardia keratitis had a longer mean presentation time (20.50 ± 2.86 days) and resolution time (33.00 ± 7.07 days) compared to other forms of bacterial or infectious keratitis (4.0-14.0 days [31][32][33] and 5.8-14.0 days [33][34][35] ), and consistent with the previous cohorts of Nocardia keratitis. 36,37 Among the various strains, N. puris was the most common isolate, followed by N. abscessus, N. cyriacigeorgica, and N. farcinica. Despite the genetic similarities observed among the corneal Nocardia isolates, there were variations in terms of antimicrobial resistance properties of the strains, the clinical characteristics, severity, and outcomes of Nocardia keratitis.…”