Resurgence of penicillin-susceptible Staphylococcus aureus at a hospital in New York State, USA

Sir, I read with interest the article by Nissen et al.1 on the treatment of penicillin-susceptible Staphylococcus aureus (PSSA). Recent articles on S. aureus have tended to focus on the rising resistance to antibiotics, including methicillin.2,3 Indeed, methicillin-resistant S. aureus (MRSA) is now the predominant S. aureus type in most hospitals in North America, and the rise of community-acquired MRSA strains means that patients no longer have to be exposed to the hospital environment to acquire a resistant Staphylococcus. Coincident with the rise of MRSA, however, our hospital has also experienced a resurgence of PSSA (Figure 1). In our 417 bed acute care hospital in upstate New York, PSSA strains have increased to 13% of all S. aureus among patients in ward beds and to 15% among patients in intensive care units (ICUs). Many of the other hospitals in our region have stopped testing S. aureus for susceptibility to penicillin because of the assumption that PSSA has become extinct. The reason for the increase in PSSA strains is unknown, but I suspect that heavy reliance on vancomycin has created a niche for these strains. PSSA appears to have crept back in ‘under the radar’ while our attention has been focused on the more resistant strains. Susceptibility of S. aureus to penicillin G in Erie County Medical Center, Buffalo, NY, USA. The graph shows the increase in the percentage of S. aureus isolates that are susceptible to penicillin. These data are based on patient-unique strains of S. aureus. Data show the percentage of all S. aureus that are susceptible to penicillin, not just the methicillin-susceptible subset of strains. Numbers shown below the year indicate the total number of S. aureus isolates from the two sources for each year. Analysis by the χ2 test for trends was significant (P < 0.01) for both ICU and non-ICU isolates. Linear regression analysis was also significant for both groups. Our clinical experience is that PSSA strains remain quite virulent; therefore, antibiotic susceptibility should not be mistaken for a lack of aggressiveness in vivo. We agree with Nissen et al.1 that penicillin should be considered the drug of choice for PSSA. Clinical microbiology laboratories should be encouraged to test S. aureus strains for susceptibility to penicillin. The observations shown here were part of my routine work as Hospital Epidemiologist and were not grant supported. None to declare.