The severity of ocular inflammation correlates with genomic bacterial load in ocular tuberculosis

Abstract

Purpose : In the past, it has been shown that necrosis correlates with severity of inflammation in tuberculosis. Irrespective of severity of inflammation, ocular tuberculosis is considered as paucibacillary disease. To correlate Mycobacterium Tuberculosis genome levels with severity of ocular tuberculosis, we made an attempt to determine extent of necrosis, the bacterial genome levels and presence of acid-fast bacteria (AFB) in ocular biopsy submitted with clinical diagnosis of tuberculosis.

Methods : Formalin-fixed, paraffin-embedded ophthalmic tissues of 27 cases with clinical diagnosis of ocular TB were processed for Auramine-rhodamine and Ziehl-Neelsen AFB staining and qPCR using specific TB primer (IS6110 gene). All cases were divided into five groups based on the extent of necrotic area in the inflammation and the necrotic area was measured by SPOT digital camera software.

Results : Of the 27 cases, eight cases were positive with both AFB staining and qPCR. In addition, six cases that were negative with the staining were positive with qPCR. Of these 14 PCR positive cases, 10 cases showed necrosis and 4 cases showed non-necrotizing granulomatous inflammation. Area of necrosis varied from 0 to 33.9 mm². The genomic bacterial load varied from 50 to 550,000 in 20-µm thick paraffin embedded tissue. Correlation analysis showed the genomic bacterial loads were high in cases with large area of necrosis and minimal in cases with small or no necrosis. The genomic bacterial load correlated positively with the extent of necrosis (Spearman correlation coefficient =0.927, p-value <0.001) and AFB staining reveled presence of bacteria mostly in cases with large necrosis.

Conclusions : Above results show that severity of tuberculous ocular inflammation depends on the bacterial genome levels; mild ocular tuberculosis is paucibacillary whereas severe disease is multibacillary. Thus, ocular tuberculosis can present either as paucibacillary or multibacillary disease suggesting duration of treatment can be variable depending on severity of the inflammation.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

The H&E stained section of each case was scanned with digital microsope system, Aperio. Area of necrosis was measured with SPOT digital camera software.

 

Genomic bacterial load was positively correlated with the extent of necrosis