Preventive and protective effects of guanethidine against MRSA endophthalmitis in rabbits

Authors:Liang Qian, Shao Zheng,Fan Zheng, Wang Weina, Huang Yusen

Corresponding author:Huang Yusen, Email:huang_yusen@126.com

Published:2026-07-10

DOI:10.3760/cma.j.cn115989-20240612-00150

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ABSTRACT 

Objective To establish a rabbit model of methicillin-resistant Staphylococcus aureus (MRSA) endophthalmitis and to investigate the regulatory effects of the sympatholytic agent guanethidine on the inflammatory response in endophthalmitis.

Methods Six male New Zealand white rabbits of about 2.5 kg were selected and injected intravitreally with 50 μl of the MRSA bacterial suspension containing 1.5×10 ⁴ and 1.5×10 ⁵ colony forming units (CFU), respectively, with 3 rabbits in each group to establish the stable infection concentration for the MRSA endophthalmitis model. Additionally, thirty-six New Zealand white rabbits were included and randomly divided into control group, dexamethasone group, guanethidine group and prophylactic treatment group, with 9 rabbits in each group. The control group, the dexamethasone group, and the guanethidine group were injected with 50 μl of sterile physiological saline, 4 mg/ml dexamethasone sodium phosphate injection, and 5 mg/ml guanethidine, intravitreally 1 day after unilateral modeling, respectively. The prophylactic treatment group was injected with 50 μl of 5 mg/ml guanethidine intravitreally one hour before modeling. The subsequent treatments were identical to those in the guanethidine group. Drug treatment was administered on alternate days starting on day 1 after successful modeling. On days 1, 3, 5, 7, 9, and 11 after modeling, the inflammatory reactions of each group were observed and scored using a slit lamp microscope. On days 1, 3 and 5 after modeling, the intraocular bacterial load of each group was measured using standard gradient dilution method and bacterial plate counting method. On day 5 after modeling, the ocular tissue structure of each group was observed by hematoxylin-eosin staining. The growth of MRSA in each group was observed by the in vitro antibacterial test of guanethidine. Animal experiments were conducted in strict accordance with the Statement on the Use of Animals in Vision and Ophthalmic Research issued by the Association for Research in Vision and Ophthalmology and were approved by the Ethics Committee of Qingdao Eye Hospital, Affiliated to Shandong First Medical University (No. SDSYKYJS-20210419).

Results Intravitreal injection of 1.5×10 ⁴ CFU of MRSA into rabbit eyes resulted in a phenotypically stable model of MRSA endophthalmitis. After modeling, in the control group, inflammation continued to progress, leading to corneal opacity, the formation of corneal neovascularization, and the disappearance of the red reflex in the fundus, replaced by yellow opacity. In the dexamethasone group, inflammation in the anterior segment was milder, while inflammation in the posterior segment gradually progressed, and the red reflex disappeared. In the guanethidine group, the iris vessels persistently congested and swelled. The prophylactic treatment group exhibited the mildest inflammation, with a clear and transparent cornea and a good red reflex. There was a statistically significant overall difference in inflammation scores at different time points after modeling among various groups ( F _group=20.72, P<0.001; F _time=9.66, P<0.001). Specifically, the inflammation scores in the prophylactic treatment group on days 3, 9 and 11 were all lower than those in the control group, dexamethasone group and guanethidine group at the corresponding time points, the inflammation scores in the prophylactic treatment group on day 7 were lower than those in the control group at the corresponding time points, the inflammation scores in the dexamethasone group and methamphetamine group on day 9 were lower than those in the control group at the corresponding time points, showing statistically significant differences (all P<0.05). Compared with the first day within the group, the inflammation scores in the control group increased significantly on days 7, 9, and 11, the inflammation scores in the dexamethasone group increased significantly on days 3 and 11, and the inflammation scores in the mezzanine group increased only on day 11, with statistically significant differences (all P<0.05). On days 1, 3, and 5 after modeling, abundant Staphylococcus aureus colonies appeared in the control, dexamethasone, and guanethidine groups, while the prophylactic treatment group remained free of colony growth throughout the experiment. There was a significant overall difference in CFU at different time points after modeling across groups ( F _group=15.73, P<0.001; F _time=9.45, P<0.001). Specifically, the CFU on days 3 and 5 in the preventive treatment group were lower than that in the dexamethasone group at the corresponding time points, and the CFU on day 5 in the dexamethasone group were higher than that in the control group and the guanethidine group at the corresponding time points, with statistically significant differences (all P<0.05). CFU in the dexamethasone group continued to increase after modeling, and there were significant pairwise differences in the comparison of CFU on days 1, 3 and 5 (all P<0.05). On day 5 after modeling, inflammatory exudate and inflammatory cell infiltration, with severe destruction of retinal structure were observed in the control and dexamethasone groups. In the guanethidine group, inflammatory cell infiltration and exudate were reduced, and the various retinal layers were faintly visible. In the prophylactic treatment group, the retinal structure remained intact, with no obvious exudate or inflammatory cell infiltration. In the in vitro antibacterial assay of guanethidine, MRSA in the control group entered the logarithmic growth phase at 6 hours and reached a peak at 16 hours. Bacterial growth in the guanethidine group was similar to that in the cefuroxime group, with the absorbance values of the bacterial suspensions remaining at a low level, near 0, throughout the experiment.

Conclusions Prophylactic use of the sympatholytic agent guanethidine effectively reduces intraocular inflammatory responses, inflammatory cell infiltration, and damage to retinal tissue structure following MRSA infection.

KEYWORDS：

Endophthalmitis, bacterial; Methicillin-resistant Staphylococcus aureus ; Inflammatory response; Sympathoinhibitor;Guanethidine

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Authors Info & Affiliations 

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