Linezolid Versus Vancomycin for the Treatment of Methicillin-Resistant Staphylococcus aureus Keratitis in Rabbits

Topical Vancomycin is More Efficient than Povidone-Iodine Treatment in Controlling Bacterial Growth in Methicillin-Resistant Staphylococcus Aureus Keratitis Model in Rabbits

To evaluate the efficacy of topical vancomycin and povidone iodine (PI) application on methicillin-resistant Staphylococcus aureus (MRSA) keratitis model in rabbits.

MRSA keratitis was induced by injecting 0.1 mL MRSA containing 1000 colony-forming units (CFU) into central cornea of right eyes of 24 New Zealand White rabbits. Animals were divided into four groups (n = 6): control (treated with balanced salt solution), 50 mg/mL topical vancomycin, 5% topical PI, and combination; examined before and after treatment, and corneal tissues were harvested for analysis at 9th hour of treatment.

Bacterial load was determined as: 7.63 ± 0.82 log10 CFU/g in control group, 6.95 ± 1.66 log10 CFU/g in PI group, 4.67 ± 0.77 log10 CFU/g in combination group, and 4.33 ± 0.71 log10 CFU/g in vancomycin group (p = 0.001). Median of total clinical score increased significantly from 7 [range: 5-8] to 11.5 [range: 11-15] (p = 0.001) in control group, did not change (6 [range: 5-8] to 7 [range: 5-7]; p = 0.695) in vancomycin group, increased significantly from 7 [range: 5-8] to 12.5 [range: 10-14] (p < 0.001) in PI group, increased significantly from 6.5 [range: 5-7] to 8 [range: 7-9] in combination group (p = 0.002). Post-treatment clinical scores for chemosis, conjunctival injection, iritis, hypopyon, epithelial erosion, and corneal infiltrate were significantly lower in vancomycin-treated groups compared to others (p < 0.05). In PI-treated groups, especially scores for chemosis, conjunctival injection, epithelial erosion and corneal infiltrate were significantly higher than vancomycin (p < 0.05).

Topical vancomycin significantly inhibited bacterial growth in MRSA keratitis. However, PI was ineffective in controlling this growth; additionally, exerted toxic effect on ocular surface. When vancomycin was combined with PI, no additional increase in efficacy of treatment was detected compared to only vancomycin.

Temporal impacts of topical ceftazidime and tobramycin-vancomycin mixtures on the ocular surface microbiota in rabbits

Antibiotics are one of the important factors that can alter the diversity and composition of ocular surface microbiota. At present, there are a few studies about the antibiotic effect on ocular surface microbiota, including its time-dependent changes. However, these limited studies have revealed various results, and more experiments are required. In this study, we used 16 S rRNA sequencing method to investigate the effects of topical ceftazidime and tobramycin-vancomycin mixtures on the ocular surface microbiota and the temporal changes of the microbiota after discontinuing antibiotic treatment in rabbits. Seventeen healthy rabbits were treated with 5% ceftazidime and a mixture of 0.3% tobramycin-5% vancomycin (CTV) eye drops on one eye four times a day for 7 days. Swab samples of conjunctiva sacs were collected before antibiotic treatment (D0), 12 h after the last antibiotic treatment (D8) and two further time points on Day 15 (D15) and Day 30 (D30). We found that the species diversity of the ocular surface microbiota increased significantly at D8 and was restored at D15, namely, one week after antibiotic cessation. The community structure of the ocular surface microbiota changed after treatment with CTV but recovered at D30. At D8, the relative abundances of 13 bacterial phyla of the initial top 20 phyla and 11 bacterial genera of the initial top 20 genera were significantly different from the relative abundances of the phyla and genera at D0. Furthermore, the relative abundance of the dominant phylum Epsilonbacteraeota obviously decreased, while Proteobacteria and Bacteroidetes markedly increased. For dominant genera, the relative abundance of Helicobacter notably decreased, while Acinetobacter and Pasteurella greatly increased. Thirteen altered bacterial phyla and 7 of 11 altered bacterial genera recovered to preantibiotic levels at D30. In addition, there was a group of nondominant and rare bacteria enriched at D8, and most of them were restored at D30. In conclusion, the species diversity, community structure and composition of the ocular surface microbiota changed greatly after exposure to CTV, but they tended to be restored within weeks after discontinuing antibiotic treatment.

Treatment of Severe Acute Bacterial Keratitis in Rabbits Using Continuous Topical Ocular Instillation with Norvancomycin

Purpose

Efficacy of norvancomycin (NVCM) through continuous topical ocular instillation drug delivery (CTOIDD) system for treating severe acute bacterial keratitis infection with Staphylococcus aureus was investigated.

Methods

Rabbits with bacterial keratitis were treated using CTOIDD with NVCM (n=13), topical NVCM eye drops (n=11), and CTOIDD with saline (n=8). Clinical signs of keratitis in all groups were assessed consecutively for a week. Bacterial quantification of excised corneas was counted on the fourth and eighth days. Histopathologic examinations were performed to assess inflammatory cell infiltration on the eighth day.

Results

All signs of bacterial keratitis were alleviated in CTOIDD with NVCM according to criteria, and the CTOIDD-NVCM group had significantly less inflammation than CTOIDD-saline (p<0.05), and eye drop-NVCM (p<0.05). Two eyes in the eye drop-NVCM group, four eyes in the CTOIDD-saline group had corneal perforation (CP), while none of the rabbits showed CP in the CTOIDD-NVCM group. Bacterial counts were significantly less in the CTOIDD with NVCM group in comparison to the eye drop-NVCM (p<0.05), and CTOIDD-saline (p<0.05) groups. Severe inflammation and marked inflammatory cell infiltration were found in histopathologic examinations in the CTOIDD-saline and eye drop-NVCM groups, while significantly less inflammation was documented in the CTOIDD-NVCM (p<0.05) group.

Conclusion

CTOIDD with NVCM effectively reduced the severity and treated acute bacterial S. aureus keratitis infection in a rabbit model. The presented approach of CTOIDD with NVCM appears to be a promising therapeutic approach for severe acute bacterial keratitis.

Vancomycin-loaded niosomes integrated within pH-sensitive in-situ forming gel for treatment of ocular infections while minimizing drug irritation

Objectives

The aim of the current study was to minimize ocular irritation and prolong the pharmacological action of vancomycin via formulation into nanosized spherical niosomes loaded into pH-sensitive in-situ forming gel.

Methods

Stability and rheological behaviour of the various gelling systems were evaluated. The ability of the selected system to eradicate methicillin-resistant Staphylococcus aureus (MRSA) infections was examined in vitro and in vivo. Draize technique was also used to assess ocular irritation in rabbits.

Key findings

Nanosized spherical niosomes loaded with vancomycin at high entrapment efficiency were prepared and integrated into polymeric solution that forms gel in situ upon instillation into the eye, to allow for a further increase in the ocular residence time. In MRSA-infected rabbits, there were 180- and 2.5-fold increases in the antibacterial efficacy after treatment with the vancomycin niosomal gels in comparison with the untreated animals and the animals treated with the vancomycin free drug solution, respectively.

Conclusions

The developed formulations demonstrated promising in-vivo biocompatibility and antibacterial efficacy, signifying their potential application as ophthalmic preparation to overcome ocular infections induced by resistant bacterial strains while minimizing drug irritation and improving patient compliance.

Comparing the ocular surface effects of topical vancomycin and linezolid for treating bacterial keratitis

BACKGROUND

Vancomycin is the gold standard in combination therapy for severe and resistant gram-positive keratitis and in particular for Methicillin-resistant Staphylococcus aureus (MRSA) infections. The aim of this study was to report the ocular surface toxicity and scoring in patients whose treatment shifted to topical linezolid/ceftazidime from topical vancomycin/ceftazidime due to their vancomycin intolerance.

METHODS

A retrospective, interventional case series of bacterial keratitis was treated with topical linezolid (one drop of 0.2% solution per eye), administered hourly until epithelization and then gradually decreased. The number and extent of punctate epithelial erosions were noted across the entire surface of the cornea. Ocular discomfort was assessed by means of (a) patient-reported pain upon instillation of the medication (vancomycin/linezolid), (b) reported burning sensation between doses and (c) reported foreign-body sensation. No ocular surface toxicity related to linezolid use was noted. Patients were followed for at least 2 months after treatment between April and December 2013.

RESULTS

Of the seven patients included in the study (age range: 2-88 years; five females, two males), complete epithelization and resolution was achieved in five patients. One patient was treated with linezolid after penetrating keratoplasty. The second culture of another patient with impending perforation despite linezolid/ceftazidime therapy yielded Fusarium spp., so he underwent tectonic keratoplasty. The mean ocular surface score was 9.4 ± 1.6 during vancomycin treatment and 5.9 ± 1.3 during linezolid treatment after discontinuation of vancomycin. The topical linezolid score was significantly lower (p = 0.027).

CONCLUSIONS

Topical linezolid may be better tolerated, according to the mean ocular surface score, than topical vancomycin by some patients and can be considered an alternative for patients who do not well tolerate vancomycin.

New therapy option for treatment of methicillin-resistant Staphylococcus aureus keratitis: tigecycline

PURPOSE

The aim of the present study was to evaluate the effectiveness of topically applied tigecycline for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) in a rabbit model.

METHODS

Experimental bacterial keratitis was induced in rabbits by a corneal intrastromal injection of 100 colony-forming units (CFUs) of MRSA bacteria. Sixteen hours after the injection, 28 rabbits were randomly divided into 4 treatment groups of 7 rabbits each. In each group, the rabbits' eyes were treated topically with 19 doses of topical tigecycline (10 or 50 mg/mL), vancomycin (50 mg/mL), or isotonic saline. Slit lamp examinations were performed before and after the inoculation by two observers masked to the study for the determination of clinical severity. Corneas were harvested for bacterial quantitation and histopathologic examination.

RESULTS

No significant differences were observed in the clinical scores between pretreatment and posttreatment in the 4 groups (P>0.05). The mean difference between the pretreatment and posttreatment clinical scores from the 4 treatment groups was also not significant (P>0.05). All treatment groups had significantly lower CFUs compared with the control group. There were no significant differences in the bacterial load among the treatment groups. The minimum inhibitory concentration (MIC) for tigecycline was 0.12 μg/mL, whereas the MIC for vancomycin was 2.2 μg/mL. The tigecycline 10 mg/mL group had the lowest mean epithelial erosion values among the treatment groups.

CONCLUSIONS

Topical tigecycline significantly reduced the bacterial load in infected rabbit corneas and may be as effective as vancomycin for the topical treatment of MRSA keratitis.

Efficacy of daptomycin on experimental methicillin-resistant Staphylococcus aureus keratitis in rabbits

PURPOSE

We aimed to compare the efficacy of topical daptomycin (DAP) with that of vancomycin (VA) in the treatment of keratitis caused by methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

One hundred colony-forming unit MRSA bacteria were injected intrastromally into both corneas of 28 rabbits. Sixteen hours after injection, the rabbits' eyes were treated with 1 drop of topical DAP (10 or 50 mg/mL), VA (50 mg/mL), or isotonic saline for 19 doses. Their eyes were examined for clinical severity before and after treatment.

RESULTS

The minimum inhibitory concentration values of VA and DAP against the bacterial strain were found to be 2 and 0.5 μg/mL, respectively. The mean pre- and post-treatment clinical scores of the eyes did not differ significantly among the groups. However, the mean difference between the post- and pretreatment clinical scores was significantly lower in the 50 mg/mL DAP group than in the other groups (P=0.042). A marked decrease in bacterial load was detected in all treatment groups compared to the control group (P=0.002). Although there were no significant differences in bacterial load among the treatment groups, the 50 mg/mL DAP group showed the greatest decrease. The mean % epithelial erosion rate tended to be higher in the 50 mg/mL VA group than in the other groups (P=0.31).

CONCLUSIONS

Topical DAP significantly reduced the bacterial load and showed activity against MRSA comparable to that of fortified VA in this experimental model.