Celeste McLean

Virulence Factor Profiles and Antimicrobial Susceptibilities of Ocular Bacillus Isolates

Bacillus causes one of the most rapidly blinding intraocular infections: endophthalmitis. In this study, Bacillus spp. were isolated from ocular infection cases, taxonomically characterized by riboprint analysis, and screened for the presence of putative virulence factors. The ability of these isolates to kill retinal and corneal cells was examined, as were antibiotic susceptibility profiles. The majority of isolates belonged to the B. cereus taxonomic group of microorganisms and were identified as B. cereus (53%) or B. thuringiensis (26%). Toxins were identified in most B. thuringiensis and B. cereus isolates. Most B. cereus and B. thuringiensis killed corneal and retinal cells within 6 h. All isolates were susceptible to most antibiotics tested, with quinolones and vancomycin being the most potent. These findings represent the first report of B. thuringiensis as an important ocular pathogen, demonstrates the potential ocular toxicity of B. cereus and B. thuringiensis isolates, and identifies antibiotics whose efficacy against Bacillus were superior to those used clinically.

Differences in bacteriologic treatment failures in acute otitis externa between ciprofloxacin/dexamethasone and neomycin/polymyxin B/hydrocortisone: results of a combined analysis

ABSTRACT Objective: To compare treatment failure rates for the two major acute otitis externa (AOE) pathogens, Pseudomonas aeruginosa and Staphylococcus aureus, by topical therapy with ciprofloxacin 0.3%/dexamethasone 0.1% (CDex) or neomycin 0.35%/polymyxin B 10 000 IU/mL/hydrocortisone 1% (Cort) based on clinical and microbiological failure in patients positive for these pathogens at baseline. Research design and methods: A combined analysis was conducted from two similar, but non-identical clinical trials involving CDex vs. Cort. Outcomes of the combined efficacy analysis were treatment failure rates and antibiotic susceptibility values for P. aeruginosa and S. aureus. The raw data for the treatment failure rates from the two studies were combined to calculate the overall treatment failure rates of each treatment group. Chi-square tests of independence were conducted to assess differences in treatment failure rates between treatment groups. Results: Of the 789 patients with culture-positive ears prior to the initiation of therapy, 61.0% (n = 481) were positive for P. aeruginosa and 8.9% (n = 70) were positive for S. aureus. While treatment failure rates for S. aureus were similar for the two therapies, CDex had a significantly lower treatment failure rate than Cort (5.1 vs. 13.0%; p = 0.0044) for P. aeruginosa. All of the persisting P. aeruginosa and S. aureus isolates were susceptible to fluoroquinolones and neomycin/polymyxin B. Limitations: The analysis strength is dependent on pooled data from similar studies. Conclusions: Ototopical ciprofloxacin 0.3%/dexamethasone 0.1% more effectively eradicates P. aeruginosa compared to Cort. Eradication of S. aureus by either drug was similar. These results favor CDex as a better first-line choice in the treatment of AOE compared to Cort.

Topical ophthalmic moxifloxacin elicits minimal or no selection of fluoroquinolone resistance among bacteria isolated from the skin, nose, and throat.

PURPOSE To investigate whether moxifloxacin therapy of bacterial conjunctivitis in children changes the moxifloxacin susceptibility of bacterial isolates in eyes, cheeks below eyes, nares, and throat. METHODS Patients (age: 1 to 12 years, n = 105) with bacterial conjunctivitis were treated topically with moxifloxacin three times a day for 7 days. Gender- and age-matched subjects with normal eyes (age: 1 to 12 years, n = 57) served as the control group. Microbiological specimens were collected on days 1 (prior to therapy), 8 (1 day after end of therapy), and 42 (follow-up). Specimens were processed to recover total bacteria and bacteria that grew on fluoroquinolone-selective media. Bacteria were identified to the species level and susceptibility to moxifloxacin and selected other antibiotics determined. RESULTS The primary pathogens recovered from the infected eyes on day 1 before therapy were Haemophilus influenzae, Streptococcus pneumoniae, and Staphylococcus aureus. None of the pre-therapy isolates of H. influenzae and S. pneumoniae were resistant to moxifloxacin. Isolates of these two pathogenic species were also recovered primarily from the nose and eyes. Moxifloxacin-resistant S. aureus isolates (minimum inhibitory concentration 1.0 μg/mL or greater) were recovered from the nose and throat prior to topical dosing on day 1. However, there was no change in the frequency of moxifloxacin-resistant isolates of S. aureus following treatment with moxifloxacin. CONCLUSION Treatment of conjunctivitis with topical ophthalmic moxifloxacin did not select for moxifloxacin resistance in H. influenzae, S. pneumoniae, or S. aureus in the eye or distal body sites.

S218 – Treatment Failures in Acute Otitis Externa

Objectives Understand treatment failure rates of cipro-floxacin/steroid- vs. Neomycin/Polymyxin B/Hydrocortisone (NPH)-containing ear drops against the two major pathogens in acute otitis externa (AOE), Pseudomonas aeruginosa and Staphylococcus aureus. Methods Retrospective analysis of clinical studies involving NPH versus either 0.3% ciprofloxacin/0.1% dexamethasone (CDX)(2 trials, 1998–1999) or 0.2% ciprofloxacin/1% hydrocortisone (CHC) (3 trials, 1994–1996) in the treatment of patients diagnosed with AOE. Patients were randomized to treatment with either CHC, CDX (both bid) or NPH (tid), 3–4 drops per ear for 7 days. Microbiology specimens were collected from infected ears prior to the initiation of therapy, and at exit visit if there were any clinical signs of infection. Results The therapy failure rate of P. aeruginosa for CDX and CHC was 6.7% (20/300) versus NPH at 12.8% (39/306), p = 0.017. The failure rate of S. aureus for CDX and CHC was 9.2% (6/65) vs. NPH at 8.3% (4/48), p = 0.87. In no instance of treatment failure was the pre-therapy pathogen resistant in vitro to the antibiotics used to treat the infection. All of the persisting P. aeruginosa and S. aureus isolates were susceptible to fluoroquinolones and neomycin/polymyxin B. Conclusions Based on data from 5 separate AOE clinical trials, ciprofloxacin-containing ear drops, CDX and CHC, provided significantly greater eradication (93.3%) of P. aeruginosa compared to NPH ear drops (87.2%). There was no significant difference in the rate of eradication of S. aureus between the two groups of ear drops.