Effect of prophylactic antibiotics on antimicrobial resistance of viridans streptococci in the normal flora of cataract surgery patients.

PURPOSE: To evaluate the effect of prophylactic treatment including vancomycin in the irrigating solution and topical chloramphenicol on antimicrobial resistance in viridans-group streptococci in the normal flora of patients having cataract surgery. SETTING: Department of Ophthalmology, Turku University Central Hospital and Antimicrobial Research Laboratory, National Public Health Institute, Turku, Finland. METHODS: Minimal inhibitory concentrations (MICs) of 15 antimicrobials were determined for 529 viridans streptococci isolated from throat, nasopharyngeal, and conjunctival swabs of 23 patients on 4 sampling occasions: before cataract surgery and 1 day, 1 month, and 3 months after surgery. Resistance mechanisms of erythromycin-resistant isolates were studied by the double-disk test and polymerase chain reaction of resistance genes. RESULTS: No statistically significant changes occurred in the proportions of isolates with elevated MICs between different sampling occasions. Resistance to vancomycin or chloramphenicol was not found. Resistance to tetracycline, erythromycin, penicillin, quinupristin-dalfopristin, clindamycin, levofloxacin, and moxifloxacin was found on different sampling occasions in 27.9% to 38.7%, 13.1% to 21.8%, 11.5% to 19.4%, 8.9% to 16.9%, 2.3% to 5.6%, 0% to 2.4%, and 0% to 2.2% of the isolates, respectively. Of the erythromycin-resistant isolates, 80.8% had the M phenotype and mefA gene and 19.2% has the macrolide-lincosamide-streptogramin B phenotype and ermB gene. CONCLUSIONS: Development of resistance of viridans streptococci in the normal flora to vancomycin and chloramphenicol during prophylactic use with uneventful cataract surgery is unlikely; the effect on resistance patterns of other antimicrobials is minor. Routine use of prophylactic vancomycin is discouraged, however, because of the lack of scientific proof of its efficacy in preventing postoperative endophthalmitis.

Antimicrobial susceptibility patterns and macrolide resistance genes of viridans group streptococci from normal flora.

OBJECTIVES: Our aim was to study the antimicrobial susceptibilities and macrolide resistance mechanisms of viridans group streptococci isolated from the normal flora. METHODS: In vitro susceptibilities of 16 antimicrobials were studied for 161 viridans streptococci (on average 5.8 isolates per person) from the normal flora of 28 elderly persons. Resistance mechanisms of erythromycin-resistant isolates were studied by the double disc test and PCR. RESULTS: In all, 16.8% of the isolates were non-susceptible (MIC > or =0.25 mg/L) to penicillin, but none showed high-level resistance (MIC > or =4 mg/L). Resistance to erythromycin, tetracycline, quinupristin/dalfopristin, levofloxacin and moxifloxacin was found in 22.4, 27.3, 13.0, 1.9 and 1.9% of the isolates, respectively. Combined resistance to erythromycin and tetracycline was found in 13.0% of the isolates. Erythromycin-resistant isolates were isolated from 57% of the study persons. Of the erythromycin-resistant isolates 80.6% were of the M phenotype and 19.4% were of the macrolide-lincosamide-streptogramin B (MLSB) phenotype (one isolate with constitutive and six with inducible expression). Isolates with the M phenotype were the least susceptible to telithromycin, a new ketolide. The mef(A) gene was found in the isolates with the M phenotype and the erm(B) gene in the isolates with the MLSB phenotype. CONCLUSIONS: The distribution of phenotypes among the viridans streptococci resembles that found in Streptococcus pyogenes, with predominance of the M phenotype. However, the coding gene for the MLSB phenotype, erm(B), is the same in viridans streptococci as in Streptococcus pneumoniae. Viridans group streptococci carrying different resistance traits provide a pool of resistant bacteria that may transfer resistance determinants to more pathogenic organisms.

Evaluation of a new cellulose sponge-tipped swab for microbiological sampling: a laboratory and clinical investigation.

A new type of swab (Cellswab; Cellomeda, Turku, Finland), utilizing a highly absorbent cellulose viscose sponge material, was compared to some traditional swabs. The survival of 14 aerobic and 10 anaerobic and microaerophilic bacterial species in the Cellswab, two commercial swab transport systems (Copan, Brescia, Italy, and Orion Diagnostica, Espoo, Finland), and one Dacron swab (Technical Service Consultants Ltd. [TSC], Heywood, United Kingdom) was evaluated. Bacteria were suspended in broth, into which the swabs were dipped. The Cellswab absorbed 1.3 times more fluid and released 3.5 times more fluid upon plating than the other swabs. Aerobic bacteria were stored in dry tubes, the others in transport medium, at 4 degrees C and room temperature (RT), for up to 14 days. Swab samples were transferred to plates at 0, 1, 2, 4, 7, and 14 days. For 10 strains the Cellswab yielded > or =10% of the original CFU for longer than all the other swabs. In the clinical study, the ability of the Cellswab to detect beta-hemolytic streptococci from throat samples (n = 995) was compared to that of the TSC Dacron swab. The swabs performed equally, both when their samples were transferred to plates immediately and after storage for 1 day at 4 degrees C or RT. The changes in normal microbiota after storage were also similar. The Cellswab was found to perform at least as well as ordinary swabs. It was better at storing fastidious strains, and at keeping bacteria viable for long storage times; it might well be a useful replacement or complement to ordinary swabs.