Lysostaphin is effective in treating experimental endophthalmitis mediated by MRSA.

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.

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.

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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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Alpha-toxin is a major virulence factor in Staphylococcus aureus keratitis. Active or passive immunization with alpha-toxin toxoid could protect against corneal damage. Results show that either form of immunization did not kill bacteria but did significantly protect against corneal pathology, especially epithelial erosion.

Susceptibility to several ␤-lactams and ␤-lactamase production was investigated in a collection of 20 strains of Pseudomonas otitidis, a new Pseudomonas species that has been recently recognized in association with otic infections in humans. All strains appeared to be susceptible to piperacillin, cefotaxime, ceftazidime, and aztreonam, while resistance or decreased susceptibility to carbapenems was occasionally observed. All strains were found to express metallo-␤-lactamase (MBL) activity and to carry a new subclass B3 MBL gene, named bla POM , that appeared to be highly conserved in this species. P. otitidis, therefore, is the first example of a pathogenic Pseudomonas species endowed with a resident MBL. The POM-1 protein from P. otitidis type strain MCC10330 exhibits the closest similarity (60 to 64%) to the L1 MBL of Stenotrophomonas maltophilia. Expression in Escherichia coli and Pseudomonas aeruginosa revealed that, similar to L1 and other subclass B3 MBLs, POM-1 confers decreased susceptibility or resistance to carbapenems, penicillins, and cephalosporins but not to aztreonam. Expression of the POM MBL in P. otitidis is apparently constitutive and, in most strains, does not confer a carbapenem-resistant phenotype. However, a strong inoculum size effect was observed for carbapenem MICs, and carbapenem-resistant mutants could be readily selected upon exposure to imipenem, suggesting that carbapenem-based regimens should be considered with caution for P. otitidis infections. Pseudomonas otitidis is a newPseudomonas species that has recently been recognized in association with otic infections in humans, including acute otitis externa, acute otitis media, and chronic suppurative otitis media (2). Genotypically and phenotypically, P. otitidis is closely related to Pseudomonas aeruginosa (2), and this similarity likely accounts for the belated identification of this new pathogenic species within the Pseudomonas genus.The susceptibility of P. otitidis was previously investigated with several antimicrobial agents, including aminoglycosides, fluoroquinolones, macrolides, ␤-lactams, tetracycline, chloramphenicol, and polymyxin B, and overall, the behavior of this species appeared to be similar to that of P. aeruginosa (2). However, of ␤-lactams, only piperacillin was tested, while no information is available on the susceptibility of this species to antipseudomonal cephalosporins, aztreonam, and carbapenems.In this work, we investigated the susceptibility of P. otitidis to several ␤-lactams and the production of ␤-lactamase activity by this species. Results revealed that P. otitidis strains constitutively produce a novel subclass B3 metallo-␤-lactamase (MBL), that was named POM (after P. otitidis metallo-␤-lactamase), which is active on carbapenems and other ␤-lactams. MATERIALS AND METHODSBacterial strains. The P. otitidis strains investigated in this work included 19 strains from the collection previously described by Clark et al. (2) and a clinical isolate from South Korea (isolate YMC-Po/06) cultured from the puru...