Antibiotic resistant Staphylococcus aureus: a paradigm of adaptive power

Abstract

Nothing documents better the spectacular adaptive capacity of Staphylococcus aureus than the response of this important human and animal pathogen to the introduction of antimicrobial agents into the clinical environment. The effectiveness of penicillin introduced in the early 1940s was virtually annulled within a decade because of the plasmid epidemics that spread the ss-lactamase gene through the entire species of S. aureus. In 1960 within one to two years of the introduction of penicillinase resistant ss-lactams (methicillin), methicillin resistant S. aureus (MRSA) strains were identified in clinical specimens. By the 1980s, epidemic clones of MRSA acquired multidrug resistant traits and spread worldwide to become one of the most important causative agents of hospital acquired infections. In the early 2000s, MRSA strains carrying the Tn1546 transposon-based enterococcal vancomycin resistant mechanism were identified in clinical specimens, bringing the specter of a totally resistant bacterial pathogen closer to reality. Then, in the late 1990s, just as effective hygienic and antibiotic use policies managed to bring down the frequency of MRSA in hospitals of several countries, MRSA strains began to show up in the community.

Figure 1

Genetic organization of SCCmec types I – VI (Maria Miragaia, Ph.D. thesis, Universidade Nova de Lisboa, 2006).

Figure 2

“SCCmec IV multiplex PCR” (Adapted with permission from reference [24]. Pannel A - Genetic organization of the subtypes of SCCmec type IV. Pannel B – Amplification patterns obtained with the SCCmec multiplex IV PCR for the prototype strains of SCCmec IV subtypes. M, DNA molecular size marker (1 Kb DNA Ladder Plus, Invitrogen Life Technologies, Carlsbad, USA).