This multicentric study evaluated prospectively and systematically the phenotypic characteristics and population genetics of MRSA in four Latin American countries of the Andean region. The protocol was designed to include patient isolates consecutively submitted to the clinical laboratory in each hospital under specific guidelines and clinical criteria for collection to avoid the recovery of isolates that were likely to represent colonization. The overall rate of isolation of MRSA was 41%, with important differences between countries. In Colombia, the rate of MRSA in the participating 22 hospitals (from 6 cities across the country) was 45%; this value is similar to a previous multicentric surveillance study (rates of 51%) [31
], indicating that the prevalence of MRSA in Colombia remains high. In contrast, the participating centers and cities involved in the other countries were fewer, making generalizations regarding rates of MRSA in those countries more difficult and raising the possibility that the molecular epidemiology of the organisms recovered may be skewed by the predominance of a particular strain in a given hospital. In Ecuador, for example (unlike the other countries of the region), the local hospital clinical laboratories also receive and process clinical samples from ambulatory services and outpatient clinics which likely influenced the type of isolates that were collected. In fact, the majorities of clinical samples from Ecuador originated from SSTIs and were likely from patients who were not in the hospital. Therefore, the rates of MRSA and the proportions of HA-like vs. CA-like MRSA circulating in the Ecuadorian hospitals are difficult to estimate. Nonetheless, our aim was to determine the population genetics of consecutive isolates submitted to a hospital clinical laboratory and the findings indicate a high circulation of CA-like MRSA in Ecuador. Moreover, the limitations specified above are common in this type of study which included centers from different countries with heterogeneous populations and varied antibiotic prescribing policies.
The most striking finding of our study was that the highly virulent USA300 MRSA-ST8-IV lineage (which includes the MRSA-ST923-IV, a SLV of ST8) was the predominant and almost exclusive CA-like clone in this region of Latin America accounting for ca. 21% of MRSA isolates. We had previously reported the emergence and dissemination of this USA300 clone variant in Colombia, causing severe skin and soft tissue infections in outpatients with important morbidity and mortality [15
]. In this study, we confirmed that the same strain (exhibiting the PFGE banding pattern ComA) has now been established in other Colombian hospitals (accounting for 31% of their MRSA isolates) and also has now been identified in Ecuador and Venezuela (100% and 50% of CA-like MRSA isolates, respectively). The South American USA300 MRSA-ST8-IV has unique characteristics when compared to the USA300-0114 strain: i
) it has a different SCCmec
subtype cassette; ii
) it appears to lack the ACME island and iii
) 41% of isolates exhibited resistance to tetracycline (although minocycline remained active) while the rates of resistance to erythromycin were low. Our findings confirm that a USA300-ST8 derivative genetic lineage has now been established in Latin America and support the hypothesis that a highly virulent ancestral USA300-ST8 methicillin-susceptible S. aureus
strain, related to the USA300-0114, was likely present in this region of the continent and subsequently acquired the SCCmec
independently. Recently, it has been shown that the USA300 lineage is a derivative of a progenitor strain USA500 [32
] and it is tempting to speculate that the South American USA300 variant may also be sublineage derivative of USA500. Our results also indicate that the CA-MRSA lineage prevalent in this area of the continent differs substantially from that of isolates found in the southern cone of South America where MRSA-ST30-IV, and MRSA-ST5-IV derivatives appear to predominate [13
]. A single MRSA-ST22-IV isolate found in Venezuela (with the ComD pattern, ) belongs to one of the pandemic MRSA clones, referred as EMRSA-15 [7
], predominant in United Kingdom hospitals and characterized by a low frequency of multidrug resistance and the presence of SCCmec
IV; this clone has also been recently identified in isolates from non-hospitalized patients in Europe [34
]. Our results also indicate an important variation in the molecular epidemiology of HA-MRSA in the Andean region. The HA Chilean clone (MRSA-ST5-I) has now been successfully established in Colombia, Peru, and Venezuela. This clone was first identified in Chile in the late 1990s [9
], replaced the previously predominant “Pediatric” clone in Colombian hospitals in a span of two years [12
] and now is spreading to the rest of the continent [8
]. Of note, the New York/Japan (MRSA-ST5-II) clone was detected in a few MRSA isolates (3%) from the region, and it is the first time that the presence of this clone is reported in Latin America.
The vancomycin MIC90
of the MRSA isolates from this study was 1 μg/mL, which is identical to that previously reported in Colombia [31
], indicating that an obvious “MIC creep” [35
] has not occurred in MRSA from this region of Latin-America. We also report, for the first time, the emergence of GISA isolates in the northern area of Latin-America (isolates with reduced susceptibility to vancomycin had been previously reported in Brazil) after following a very strict methodology that included three different methods of screening. Of interest, one of the nine VISA isolates exhibited a CA genotype, supporting the finding that this phenotype may also be present in MRSA USA300, as described previously [36
In conclusion, we present evidence that MRSA USA300 genetic lineage has now been established as the almost exclusive CA-like clone in the northern region of South America, and has now entered nosocomial settings in some countries.