Genetic Diversity in MRSA Isolates from Chile Characterized: Study

   The genetic lineages CC5 and CC8/239 were the most common among clinical Staphylococcus aureus isolates from Chile, according to a study presented at the 51st Interscience Conference on Antimicrobial Agents and Chemotherapy, in Chicago.

   Rosa Del Campo, MD, PhD, of the Hospital Ramin y Cajal in Madrid, and colleagues presented the first molecular typing of hospital and community acquired clones of methicillin-resistant S. aureus (MRSA) clones in northern Chile.

   Surveillance of MRSA clones and SCCmec elements is required to understand the epidemiology of the disease. Few studies, however, have reported on the S. aureus population structure in Latin America. The investigators used molecular typing techniques to analyze a clinical collection (collected 2009 – 2010) of S. aureus isolates from a single hospital in Antofagasta, Chile. They found high genetic diversity in the region.

   Antibiotic resistance of the isolates was tested by agar dilution methods. Many of the 56 S. aureus isolates were methicillin resistant (64.3%) as well as resistant to other antibiotics such as ciprofloxacin (100%), erythromycin (91%), gentamycin (73%), amikacin (70%), and cotrimoxazol (11%).

   Polymerase chain reaction (PCR) was used to determine the presence of mecA and pvl genes. The mecA gene was found in all 36 isolates whereas the pvl genes were only detected in eight MRSA isolates (22%). SSCmec type was further analyzed with a multiplex PCR scheme. The most frequent SCCmec element was type I (50%) followed by type IVc (25%), type II (17%), and finally type III (8%). Spa-typing (guidelines results were grouped into Cluster 1 (38%), t149,  and t8354; Cluster 2 (21%), t002, and t067; Cluster 3 (13%), t037, and t8353, and the singletons (28%) t008, t078, t148, t197, and t3221.

   Pulsed-field gel electrophoresis patterns were also assigned to the isolates. One isolate per pulsotype (20 in total) were further typed by multi-locus sequence typing (MLST). The researchers found a high concordance among spa typing and MLST, they reported.