Genetic typing and susceptibility testing of strains from Staphylococcus aureus keratitis or conjunctivitis patients

Abstract

Objective: To study the relationship between genetic typing and the antibiotic susceptibility of staphylococcus aureus (SA) isolated from keratitis or conjunctivitis patients. Methods: Experimental study. Thirty-four (34) strains of Staphylococcus aureus were isolated from 34 cases of keratitis or conjunctivitis. The genomic DNA was extracted and amplified with PCR. With the method of multi locus sequences typing (MLST), gene fragments from 7 house-keeping genes were amplified and the products were sequenced. The results were submitted to the MLST website (www.pubmlst.org). In comparison with the allele of the corresponding gene, the allele spectrums of the strain were obtained with 7 housekeeping genes. At last, the MLST genotypes of the isolated strains were determined. With the START software, the evolutionary tree was established with UPGMA method. With the microdilution method, the MIC(90) of 13 antimicrobial agents was determined. The MIC(90) value of antimicrobial agents among different genotypes of Staphylococcus aureus was comparatively analyzed. Results: Ten (10) genotypes were obtained from 34 strains of Staphylococcus aureus. The dominant types were ST239, ST2592 and ST188. The clustering of genotyping was relatively concentrated, mainly in group Ⅰ (25 strains of SA, 83.3% of the total), and followed by group Ⅱ (5 strains of SA, 16.7%). The conjunctival isolates were distributed in the subgroup A of group Ⅰ. The cornea isolates were concentrated in subgroup B and group Ⅱ. With the exact probability method, the R×C chi square tests were used as statistic analysis method. The difference between the bacterial genotyping of two sources was statistically significant (P=0.011). Twenty-four strains of SA in group Ⅰ was sensitive to Vancomycin, Rifampicin and Amikacin (sensitivity ratio was 24/24, 20/24 and 20/24, respectively), and was generally resistant to other antibiotics. The values of MIC(90) of ciprofloxacin, ofloxacin, gatifloxacin and moxifloxacin to Staphylococcus aureus in subgroup A (0.16±0.07, 0.51±0.42, 0.31±0.14, 0.22±0.33) were significantly lower than the values in subgroup B(0.74±0.11, 0.84±0.45, 0.67±0.03, 0.68±0.26). The difference was statistically significant (P=0.004, 0.026, 0.034, 0.001). There was no significant difference between the MIC(90) values of the other 9 kinds of antibiotics in the subgroup A and in the subgroup B of Staphylococcus aureus (P value 0.047-0.561). Conclusion: The genotype of Staphylococcus aureus of corneal isolations and conjunctival isolations were different. The conjunctival isolates were distributed in the subgroup A of group Ⅰ and the corneal isolates were concentrated in subgroup B and group Ⅱ. There is a significant correlation between the MLST genotypes and antibiotic sensitivity. (Chin J Ophthalmol, 2018, 54:767-774).