Assessment of disinfectant and antibiotic susceptibility patterns and multi-locus variable number tandem repeat analysis of Staphylococcus epidermidis isolated from blood cultures.

Background and Objectives: Variable number tandem repeat (VNTR) patterns and resistance against three commonly used hospital disinfectants [0.5% (w/w) chlorhexidine digluconate (CHG) and 75% (w/w) alcohol (A), CHG-A; Quaternary ammonium compounds (QACs) and biguanides (B), QAC-B; and 70% (w/w) isopropanol (ISP) and 0.25% (w/w) QACs, ISP-QAC], as well as frequently used antibiotics, were evaluated among 115 Staphylococcus epidermidis blood isolates recovered from a children's hospital in Tehran, Iran.

Materials and Methods: Multi-locus variable number tandem repeat analysis (MLVA) was performed using primers targeting 5 VNTR loci on the genome of S. epidermidis isolates. Micro-broth dilution method and detection of qacA/B and smr genes were carried out for evaluating resistance against the disinfectants.

Results: Out of the 115 isolates, 115 (100%) and 113 (98.3%) were susceptible to linezolid and quinupristin/dalfopristin, respectively. A total of 55.7% of the isolates were found to be multidrug resistant (MDR). All isolates had MICs of CHG-A and ISP-QAC of 8 folds lower and MIC of QAC-B 6 folds lower than that suggested by the manufacturers. The genes qacA/B and smr were found in 28 (24.3%) and 14 (12.2%) isolates, respectively. MLVA typing of the S. epidermidis isolates resulted in 106 VNTR patterns and 102 MLVA types for the 112 S. epidermidis isolates, considering that 3 were not typeable.

Conclusion: MLVA typing of S. epidermidis isolates show a great diversity and that the isolates are still susceptible to the concentrations of disinfectants recommended for use by the manufacturers. In addition, the relatively high percentage of the MDR S. epidermidis isolates could cause MDR infections and act as reservoirs to transfer resistance determinants to S. aureus population. Therefore, it is important that suitable infection control strategies are employed to avoid the distribution of MDR isolates between personnel and patients in this medical centre.