Trends in the Genetic Background of Methicillin-Resistant Clinical Isolates in a South African Hospital: An Institutional-Based Observational Study.

BACKGROUND

This study sought to understand the epidemio-ecological dynamics of MRSA isolates associated with a South African hospital over a period spanning year 2007-8 (a previous study reported in 2009) and year 2010-11 (this study).

METHODS

One hundred and ninety three isolates were characterised by molecular fingerprinting methods including pulsed field gel electrophoresis (PFGE), typing, -typing, SCC-typing, and multilocus sequence typing (MLST). The Vitek-2 automated antibiogram of representative isolates was also performed.

RESULTS

Our data shows that the distribution of MRSA strains among the different clinical conditions was rarely dependent on the genetic backbone or genotype. Compared to the previous survey in 2009, CA-MRSA isolates increased by 31% while HA-MRSA isolates decreased by 17%. An increase in genetic diversity was also revealed including the detection of three pandemic clonal complexes ( type t012-ST36/CC30, type t037-ST239/CC8, type t891-ST22/CC22 and type t1257-ST612/CC8). Majority of the genotypes were classified as Spa Cluster B-SCC I- I 19.2%; (37/193) Spa Cluster A-SCC- I 14.5%; (28/193).

CONCLUSION

This study reveals that increased diversity in MRSA genetic background was associated with resistance to frontline antibiotics. Also, an increase was recorded in the CA-MRSA/HA-MRSA ratio within a 5-year period despite the continuous dominance of the HA-MRSA genotype.