Heterogeneous oxacillin-resistant phenotypes and production of PBP2A by oxacillin-susceptible/mecA-positive MRSA strains from Africa.
Recent surveillance of MRSA colonizing patients and healthcare workers in two African countries (Angola and São Tomé and Príncipe) reported the frequent recovery of oxacillin-susceptible MRSA (OS-MRSA): Staphylococcus aureus strains that gave positive results with the mecA DNA probe, but had low oxacillin MIC values characteristic of susceptible S. aureus. This apparent dissociation of the drug-resistant phenotype from mecA-the primary genetic determinant of resistance-prompted us to perform a more detailed analysis on nine of the African OS-MRSA strains.



Oxacillin MIC values were determined by Etest and population analysis profiles with and without induction of the stringent stress response by mupirocin. Biochemical profiling using SDS-PAGE followed by western blotting was used for the detection of PBP2A protein produced.



Cultures of the African MRSA strains (ST88-IVa and ST8-V) showed heterogeneous oxacillin resistance in which the majority of cells exhibited low oxacillin MICs (≤0.75 mg/L), but highly resistant subpopulations were also present with oxacillin MIC values up to several hundred mg/L and with frequencies of 10(-4) to 10(-6). The same strains after induction of the stringent stress response by mupirocin 'converted' the heterogeneous phenotypes into a more homogeneous and higher level resistance. After induction by oxacillin and mupirocin, each of the nine African OS-MRSA strains produced PBP2A-the protein product of mecA.



The resistant phenotype of OS-MRSA resembles the phenotypes of historically early MRSA clones. The nature of genetic determinants responsible for the heterogeneous phenotypes of OS-MRSA remains to be determined.
Laboratory of Microbiology & Infectious Diseases, The Rockefeller University, New York, NY 10065, USA.
Marilyn
M
Chung
Laboratory of Microbiology & Infectious Diseases, The Rockefeller University, New York, NY 10065, USA.
Choon Keun
CK
Kim
Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica António Xavier (ITQB), Universidade Nova de Lisboa (UNL), Oeiras, Portugal.
Teresa
T
Conceição
Escola Superior de Saúde da Cruz Vermelha Portuguesa (ESSCVP), Lisboa, Portugal.
Marta
M
Aires-De-Sousa
Laboratory of Microbiology & Infectious Diseases, The Rockefeller University, New York, NY 10065, USA Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica António Xavier (ITQB), Universidade Nova de Lisboa (UNL), Oeiras, Portugal.
Hermínia
H
De Lencastre
Laboratory of Microbiology & Infectious Diseases, The Rockefeller University, New York, NY 10065, USA tomasz@rockefeller.edu.
Alexander
A
Tomasz
D000349:Africa / Q000453:epidemiology; D000810:Angola / Q000453:epidemiology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics; D004591:Electrophoresis, Polyacrylamide Gel; D062665:Epidemiological Monitoring; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification* / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D010068:Oxacillin / Q000494:pharmacology*; D046915:Penicillin-Binding Proteins / Q000096:biosynthesis* / Q000235:genetics; D010641:Phenotype; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology; D018440:beta-Lactam Resistance / Q000235:genetics
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; D010068:Oxacillin