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H. Mino de Kaspar, T.C. Kreutzer, V. Klauss, A. Kampik; Counts of Colony Forming Units as an Effective Semi Quantitative Method to Specify Changes in Amounts of Bacteria on the Conjunctiva . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1884.
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To evaluate counts of colony forming units on solid culture media as a semi–quantitative against a non–quantitative method (broth media), to substantiate effect of prophylactic measures.
Prospective, randomized evaluation of 140 patients/eyes (Group I, control group, n = 70 eyes; Group II, study group, n = 70 eyes). At baseline (T0), and after one week (T1) culture swabs were taken from the conjunctival sacs (slow and complete rotation of the moistened cotton swab) from both groups of patients. Eyes of Group II received topical antibiotic, one drop of 0.5% levofloxacin 4 times a day starting one day prior to collection of swab. Eyes in Group I did not receive any antibiotic. Exclusion criteria comprised of active ocular infection and any antibiotic treatment 30 days prior to inclusion. The presence of bacteria was determined non–quantitative in thioglycolate broth (THIO) and semi–quantitative in counting colony forming units (CFUs) on solid aerobic–microaerophilic blood agar (BAG) and anaerobic chocolate agar (CHOCO) cultured media. Cultures were incubated at 37°C for 7, 3 and 5 days respectively.
Culture results of 132 patients were evaluated. In Group I cultures in thioglycolate broth (THIO) showed positive results in 55 of 65 eyes (84.6%) at baseline (T0) compared with 57 of 65 eyes (87.7%) at T1 (P = 0.612). In Group II results showed positive culture growth in THIO at T0 in 55 of 67 eyes (82%) as opposed to 50 of 67 (74.6%) at T1 (study group) (P = 0.294). Mean amounts of CFUs on BAG in Group I were 26.42 (Range 0 – 302) at T0 compared with 15.8 (Range 0 – 200) at T1 (P = 0.257) and 12.22 (Range 0 – 101) as opposed to 1.9 (Range 0 – 38) in Group II, respectively (P < 0.001). On CHOCO mean amounts of CFUs were 10.48 (Range 0 – 100) at T0 and 9.05 (Range 0 – 130) at T1 in Group I (P = 0.897) compared with 6.9 (Range 0 – 72) at T0 and 3.13 (Range 0 – 58) at T1 in Group II (P = 0.002). There was no significant difference in amounts of CFUs on BAG and CHOCO as well as in positive cultures in THIO at baseline between the groups (P = 0.302, P = 0.789 and P = 0.697).
While thioglycolate broth seems to be highly effective in detecting even very small amounts of bacteria on the conjunctiva it is less effective determining quantitative reduction. Counts of colony forming units on solid culture plates could be an effective semi–quantitative method to assess these changes. With appropriate technique of swab collection this method was sensitive enough to detect small amounts of bacteria on the conjunctiva.
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