Lysostaphin is effective in treating experimental endophthalmitis mediated by MRSA.

The aim of this study was to determine the pathogenic role of alpha-, beta-, and gamma-toxins in a rabbit model of Staphylococcus aureus keratitis. S. aureus strains 8325-4, Newman, and their isogenic mutants were intrastromally injected into rabbit corneas. Eyes were scored for pathology by slit lamp examination (SLE), histologic examination, and bacterial colony-forming units (CFU) per cornea were determined. Rabbits were immunized against alpha-toxin and subsequently challenged with S. aureus strain 8325-4 or Newman. All strains grew equivalently to approximately 7 log CFU/cornea at 25 h postinfection. SLE scores at 15, 20, and 25 h postinfection revealed that alpha-toxin - producing strains caused greater corneal pathology than strains deficient in alpha-toxin. A beta-toxin - deficient mutant produced significantly less ocular edema than its parent or rescued strains. The gamma-toxin-deficient mutant, relative to its parent strain or genetically rescued strain, had reduced virulence. These results demonstrate that the virulence of S. aureus involves mainly alpha-toxin and to a lesser extent gamma-toxin, with beta-toxin mediating minimal corneal pathology.

The purpose of this study was to quantitatively compare, in a rabbit keratitis model, the levels of effectiveness of moxifloxacin, levofloxacin, and ciprofloxacin for the treatment of Staphylococcus aureus isolates of diverse antibiotic susceptibilities. Rabbit eyes were intrastromally injected with approximately 100 CFU of methicillinsensitive or methicillin-resistant S. aureus (MSSA or MRSA, respectively) organisms that were either sensitive or resistant to ofloxacin. One drop of moxifloxacin (0.5%), levofloxacin (0.5%), or ciprofloxacin (0.3%) was topically applied hourly from 4 to 9 (early) or 10 to 15 (late) h postinfection. At 1 h after cessation of therapy, the corneas were harvested, and the number of CFU per cornea was determined. For the ofloxacin-sensitive strains, early treatment of MSSA or MRSA with moxifloxacin, levofloxacin, or ciprofloxacin produced approximately a 5-log decrease in CFU per cornea relative to that in untreated eyes (P < 0.0001). For late therapy of ofloxacin-sensitive strains, moxifloxacin, levofloxacin, and ciprofloxacin produced approximately 5-, 4-, and 2-to 3-log reductions in CFU per cornea, respectively (P < 0.0001). Early treatment of the ofloxacin-resistant strains with either moxifloxacin or levofloxacin produced a >4-log or >3-log decrease, respectively, in the MSSA or MRSA strains (P < 0.0001), whereas ciprofloxacin treatment produced a 1-log decrease in CFU per cornea relative to that in untreated eyes (P ‫؍‬ 0.1540). For late treatment of ofloxacin-resistant strains, levofloxacin and ciprofloxacin failed to significantly reduce the number of CFU per cornea (P > 0.3627), whereas moxifloxacin produced a significant reduction in CFU per cornea of approximately 1 log (P < 0.0194). Therefore, for three of the four treatments tested, moxifloxacin demonstrated greater effectiveness than either levofloxacin or ciprofloxacin.

A novel Pseudomonas species, for which the name Pseudomonas otitidis sp. nov. is proposed, was identified from clinical specimens of infected human ears. Forty-one pseudomonads (34 from patients with acute otitis externa, six from patients with acute otitis media with otorrhoea and one from a patient with chronic suppurative otitis media) were recovered that did not match any known species. On the basis of genetic analyses and biochemical characterization, these isolates were shown to belong to the genus Pseudomonas. 16S rRNA gene sequence analysis and DNA–DNA hybridization studies indicated that this novel bacterium is closely related to, but different from, Pseudomonas aeruginosa. A description of this species is based on polyphasic studies of 11 clinical isolates. The type strain of Pseudomonas otitidis is MCC10330T (=ATCC BAA-1130T=DSM 17224T).

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