An in vitro resistance study of levofloxacin, ciprofloxacin, and ofloxacin using keratitis isolates of Staphylococcus aureus and Pseudomonas aeruginosa.

PURPOSE: We compared levofloxacin with ciprofloxacin and ofloxacin using the in vitro susceptibilities of Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) keratitis isolates. DESIGN: Retrospective, clinical laboratory study of antibiotic susceptibility among keratitis isolates. PARTICIPANTS: Keratitis isolates from 200 patients with either SA or PA keratitis. METHODS: Minimum inhibitory concentrations (MICs) were determined for levofloxacin, ofloxacin, and ciprofloxacin for 93 SA keratitis isolates (68 fluoroquinolone-resistant and 25 susceptible, as determined by disk diffusion) and 107 PA keratitis isolates (13 fluoroquinolone-resistant and 94 susceptible). National Committee for Clinical Laboratory Standards susceptibilities were determined and analyzed statistically. Time kill studies were determined for fluoroquinolone-susceptible and -resistant isolates to all antibiotics at 8 microg/ml. The killing rates were determined by regression, and the colony count decreases were analyzed. MAIN OUTCOME MEASURES: The susceptibilities and potencies of levofloxacin, ciprofloxacin, and ofloxacin to SA and PA were determined from the MICs. Time kill studies determined the killing rates and decreases in colony counts. RESULTS: The fluoroquinolone-resistant SA susceptibilities to levofloxacin, ofloxacin, and ciprofloxacin were only 22%, 10%, and 3%, respectively. The fluoroquinolone-susceptible SA were 100% susceptible to all antibiotics, with levofloxacin demonstrating the best potency. The fluoroquinolone-resistant PA were resistant to all antibiotics. The fluoroquinolone-susceptible PA isolates were highly susceptible to levofloxacin, ofloxacin, and ciprofloxacin, with ciprofloxacin demonstrating the highest potency. For fluoroquinolone-susceptible SA and PA, the time kill studies determined that the killing rates and decreases in colony counts were equivalent for all three antibiotics tested. The time kill studies demonstrated no colony count decreases for the fluoroquinolone-resistant SA and PA. CONCLUSIONS: Taken together, our susceptibility and time kill data failed to demonstrate convincing differences in the susceptibility of SA and PA keratitis isolates to levofloxacin, ciprofloxacin, and ofloxacin. In general, bacterial isolates that were resistant to ciprofloxacin and ofloxacin were also resistant to levofloxacin.

Evaluation of the shell vial technique for detection of ocular adenovirus. Community Ophthalmologists of Pittsburgh, Pennsylvania.

PURPOSE: The shell vial technique is a cell culture method that uses centrifugation and immunofluorescence to decrease the time required for a positive test. The authors evaluated the shell vial technique as a diagnostic test to detect adenovirus in conjunctival specimens of patients with adenoviral conjunctivitis. DESIGN: Retrospective and prospective case series. PARTICIPANTS: Forty-six patients with adenoviral culture-positive ocular infection. METHODS: The minimum time of incubation (days) that was required for testing clinical isolates with the shell vial was determined with adenovirus serotypes 5 and 8. In a masked retrospective study, 25 true-positive (frozen clinical samples) and 25 true-negative specimens were tested for the presence of adenovirus using the shell vial technique. The 25 true-negative samples included herpes simplex virus, Chlamydia trachomatis, Haemophilus influenzae, Streptococcus pneumoniae, and Staphylococcus aureus. In a prospective study, 21 patients who later tested positive in cell culture for adenovirus were concurrently tested with shell vial. MAIN OUTCOME MEASURES: The time of incubation was determined in days, and the sensitivity, specificity, positive and negative predictive values, and the efficacy of the shell vial test were determined. RESULTS: The minimal time of incubation for testing ocular samples by shell vial was 3 days. In the retrospective study, the sensitivity, specificity, positive predictive value, negative predictive value, and efficacy were 92%, 100%, 100%, 93%, and 96%, respectively. Comparably (P = 0.99), in the prospective study the sensitivity, specificity, positive predictive value, negative predictive value, and efficacy were 95%, 100%, 100%, 96%, and 97%, respectively. The shell vial (93%, 43 of 46) was equivalent (P = 0.42) to cell culture (100%, 46 of 46) for detecting adenovirus, but a positive result was obtained in significantly less time (3 days versus 9.41 +/- 6.23 days) (P = 0.00001). CONCLUSIONS: The shell vial technique was found to be a definitive method for identifying adenovirus from ocular specimens. A clear benefit for the ophthalmologist is that the test can provide a faster positive result (3 days) compared with conventional cell culture, which can take 1 to 3 weeks for adenovirus isolation.

Comparison of ciprofloxacin and ofloxacin using human corneal susceptibility levels.

PURPOSE: We compared the in vitro susceptibility of gram-positive bacteria to ciprofloxacin and ofloxacin using human corneal susceptibility levels. METHODS: The concentrations of ciprofloxacin and ofloxacin that can be attained in 99% of human corneas (Cornea99) after topical administration were calculated statistically from reported data. The minimal inhibitory concentrations (MICs) were determined for 95 corneal isolates of gram-positive bacteria (51 Staphylococcus aureus, 16 Streptococcus pneumoniae, 16 Streptococcus viridans group, and 12 coagulase-negative staphylococci). Susceptibility was interpreted by comparing the MICs with the respective Cornea99 for each antibiotic. Time-kill studies of representative gram-positive bacteria were tested using the Cornea99 and the maximal corneal concentrations reported for ciprofloxacin and ofloxacin. RESULTS: The Cornea99 of ciprofloxacin and ofloxacin were calculated to be 3.57 microg/ml (n = 22) and 2.22 microg/ml (n = 20), respectively. The reported mean corneal concentrations of ciprofloxacin (6.90 +/- 6.20 microg/ml) and ofloxacin (5.71 +/- 6.15 microg/ml) were comparable (p = 0.54). All gram-positive bacteria were equally susceptible to ciprofloxacin and ofloxacin (p = 0.54) based on the Cornea99. The time-kill studies determined that 8-24 h were required for both ciprofloxacin and ofloxacin to reach bactericidal levels. CONCLUSION: Ciprofloxacin and ofloxacin demonstrated comparable penetration into the cornea and provided equivalent in vitro efficacy against representative gram-positive bacteria. Time-kill studies indicated that 8-24 h of continual corneal concentrations of ciprofloxacin and ofloxacin were necessary in this study to reduce susceptible gram-positive bacteria by 99.9%.

Time-kill profiles of Enterococcus to antibiotics used for intravitreal therapy.

BACKGROUND AND OBJECTIVE: To determine and then compare the time-kill profiles of Enterococcus to antibiotics used for intravitreal therapy. PATIENTS AND METHODS: The time-kill profiles of four endophthalmitis isolates of Enterococcus faecalis, one vancomycin-resistant E. faecalis isolate, and three vancomycin-resistant isolates of E. faecium were determined against vancomycin, amikacin, cefazolin, gentamicin, ampicillin, ciprofloxacin, ceftazidime, clindamycin, and the combinations of vancomycin and amikacin, vancomycin and ceftazidime, vancomycin and gentamicin, vancomycin and ampicillin, cefazolin and gentamicin, and ampicillin and gentamicin. RESULTS: No single antibiotic or combination was bactericidal (defined as 99.9% kill) to all isolates of Enterococcus. Gentamicin was bactericidal to all E. faecalis isolates. None of the tested antibiotics were bactericidal to vancomycin-resistant E. faecium. CONCLUSIONS: The time-kill profiles demonstrated that vancomycin and ceftazidime did not produce a 99.9% kill for E. faecalis in this small study. Gentamicin combined with either cefazolin or ampicillin had somewhat better bactericidal activity and should be considered as an alternative therapy. Novel therapy may be necessary to treat endophthalmitis because of vancomycin-resistant Enterococcus, depending on the susceptibility patterns of the individual isolate and the response to initial therapy.

Chlamydia trachomatis can be transmitted by a nonporous plastic surface in vitro.

Chlamydial conjunctivitis is a disease associated with venereal transmission through direct sexual contact or autoinoculation with genital secretions. Appropriate therapy for patients and their sexual partners involves important questions regarding the source of infection and mode of transmission. This study explored the potential role of a fomite, i.e., an environmental surface, as a possible vector of transmission. We determined the in vitro recovery of Chlamydia trachomatis from a nonporous plastic surface under ambient and humid conditions using the standard shell vial technique and confirmation by direct monoclonal immunofluorescence. Under ambient conditions, the TP50 (time at which 50% of samples were positive for Chlamydia) was 5 min, with complete desiccation occurring at 45 min. Under humid conditions, the TP50 was 52.5 min and complete desiccation did not occur up to 3 h. Beyond 45 min, a significantly greater number of positive chlamydial samples were collected under humid conditions (11 of 30) than under ambient conditions (0 of 30) (p = 0.00016). We conclude that a fomite, such as a nonporous plastic surface, may serve as a potential vector for the transmission of chlamydial infection to the eye, especially under humid conditions. This new information may prove useful in counseling patients and their sexual partners.

An in vitro comparison of the susceptibilities of bacterial isolates from patients with conjunctivitis and blepharitis to newer and established topical antibiotics.

This retrospective study compared new and established topical antibiotics with regard to the in vitro susceptibility of bacterial isolates recovered from patients with conjunctivitis (n = 385) and blepharitis (n = 173) using the National Committee for Clinical Laboratory Standards-approved disk diffusion method. The percent susceptibility of recovered isolates to single antibiotic agents or combinations were ranked from greatest to least: chloramphenicol, bacitracin/polymyxin B, ofloxacin, sulfa, ciprofloxacin, trimethoprim/polymyxin B, norfloxacin, gentamicin, bacitracin, trimethoprim, tobramycin, neomycin, erythromycin, and polymyxin B. We determined that none of the available topical antibiotics provided 100% broad spectrum coverage in vitro. Established antibiotics often provided coverage comparable to the newer drugs. Due to the unproven value of in vitro testing as a predictor of clinical outcome in bacterial blepharitis and conjunctivitis, the ophthalmologist should choose therapy based on clinical experience, ongoing critical evaluation of available antibiotics, and cost-effectiveness.

Evaluation of the polymerase chain reaction test for detecting chlamydial DNA in adult chlamydial conjunctivitis.

PURPOSE: A new polymerase chain reaction (PCR) test (Amplicor, Diagnostics, Branchburg, NJ) was evaluated for its ability to detect chlamydial DNA from previously obtained adult conjunctival specimens. METHODS: The sensitivity of this PCR test was determined on 42 adult conjunctival specimens that were culture-positive for Chlamydia. The specificity was determined by testing 40 true-negative specimens that included 10 normal conjunctival samples and 20 ocular specimens that were culture-positive for herpes simplex virus or adenovirus. The remaining ten samples consisted of ocular bacterial pathogens in chlamydial transport media. RESULTS: Amplicor was 88% (37/42) sensitive and 100% (40/40) specific. CONCLUSIONS: The authors conclude that PCR testing for chlamydial DNA from ocular specimens may be useful, especially when conditions in transport might reduce the yield of positive cultures.

Evaluation of vitrectomy machines as a source of false-positive culture contamination in endophthalmitis.

PURPOSE: We sought to determine whether a venturi-aspiration vitrectomy machine could contaminate a vitrectomy culture. METHODS: Ninety vitrectomies were simulated in a hospital operating room and were cultured with standard techniques. An additional 90 control specimens were cultured in the exact same manner, but the vitrectomy machine was not used. Instead, the control specimens were placed directly into a sterile vitrectomy cassette. Contamination rates in the two groups were compared. RESULTS: Contamination occurred in four of 90 vitrectomy-simulation cultures and in three of 90 control cultures. This difference in contamination rate was not statistically significant. CONCLUSIONS: Although the result of a culture of the vitrectomy effluent can be false-positive, the source of contamination is not likely to be the vitrectomy machine.

Clinical characteristics of corneal foreign bodies and their associated culture results.

A prospective study was performed to investigate the clinical characteristics of corneal foreign bodies and to determine if these characteristics were related to the culture results of the foreign body. The clinical characteristics included the type of foreign body, the mechanism of injury, the time present in the cornea, and the presence of a rust ring or an infiltrate. Sixty-three foreign bodies were removed from corneas and cultured for bacteria, and 14.3% cultured positive for bacteria. The major pathogen was coagulase-negative Staphylococcus. The majority of foreign bodies were metallic, and mechanisms of injury were similar for both culture-positive and culture-negative groups. There was no significant correlation between the mean time present in the cornea and the culture results. The presence of a rust ring or an infiltrate was not found to be significant when predicting culture results. No clinical features readily distinguished culture-negative foreign bodies from culture-positive foreign bodies.

The role of ciprofloxacin in endophthalmitis therapy.

Ciprofloxacin has been proposed for the systemic treatment of endophthalmitis. We studied the role of therapy based on the susceptibility of actual bacterial isolates and developed a system for assessing this susceptibility in endophthalmitis. Susceptibility testing was performed on 68 bacterial isolates from 66 patients with endophthalmitis. Our results indicated that, on the basis of a vitreous ciprofloxacin concentration of 0.25 microgram/ml, only 41 of 68 isolates (60%) would be inhibited by systemic therapy. All gram-negative bacteria (six of six) would be inhibited, whereas gram-positive bacterial susceptibility was variable. We concluded that systemic ciprofloxacin alone should not be administered empirically but it could provide an adjunct for treating selective cases of bacterial endophthalmitis. Bacterial susceptibility should be assessed on a blood serum standard of 0.25 microgram/ml instead of 1.0 microgram/ml.