The prevalence, population structure and screening test specificity of penicillin-susceptible Staphylococcus aureus bacteremia isolates in Malmö, Sweden.
The objectives of this study were to examine the prevalence of penicillin-susceptible bacteremic Staphylococcus aureus in the Malmö area in 2014, to re-evaluate the phenotypic methods of penicillinase detection on these isolates, and to investigate the clonal distribution of penicillin-susceptible isolates.



All non-redundant S. aureus from blood in the Malmö catchment area in southern Sweden 2014 were screened for penicillin susceptibility using PcG 1U disk diffusion, E-test PcG and the nitrocefin test. All isolates screened as likely susceptible were subjected to PCR for detection of penicillinase (blaZ) and spa-typing.



Almost one out of three bacteremic isolates (80/257; 31.1%) were susceptible to penicillin. All screening methods except for the nitrocefin test alone had a low proportion of isolates falsely tested as susceptible, but no method used in the study had perfect specificity compared with PCR. Penicillin-susceptible isolates had a distinct phylogenetic distribution, and two clonal complexes (CC5 and CC45) constituted half of the isolates.



Almost one third of S. aureus isolated from blood in southern Sweden in 2014 was susceptible to penicillin. Considering that intravenous penicillin has theoretical advantages compared with the standard treatment in the study area, we argue that routine testing of penicillin susceptibility should be reconsidered.
Infectious Diseases Unit, Department of Clinical Sciences, Lund University, Malmö, Sweden; Riesbeck Lab, Clinical Microbiology, Department of Translational Medicine, Lund University, Malmö, Sweden. Electronic address: fredrik.resman@med.lu.se.
Fredrik
F
Resman
Riesbeck Lab, Clinical Microbiology, Department of Translational Medicine, Lund University, Malmö, Sweden.
John
J
Thegerström
Infectious Diseases Unit, Department of Clinical Sciences, Lund University, Malmö, Sweden.
Fredrik
F
Månsson
Infectious Diseases Unit, Department of Clinical Sciences, Lund University, Malmö, Sweden; Riesbeck Lab, Clinical Microbiology, Department of Translational Medicine, Lund University, Malmö, Sweden.
Jonas
J
Ahl
Infectious Diseases Unit, Department of Clinical Sciences, Lund University, Malmö, Sweden; Riesbeck Lab, Clinical Microbiology, Department of Translational Medicine, Lund University, Malmö, Sweden.
Johan
J
Tham
Riesbeck Lab, Clinical Microbiology, Department of Translational Medicine, Lund University, Malmö, Sweden.
Kristian
K
Riesbeck
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016470:Bacteremia / Q000453:epidemiology* / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D010403:Penicillin Resistance; D010406:Penicillins / Q000494:pharmacology*; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D015995:Prevalence; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D013548:Sweden / Q000453:epidemiology; D001618:beta-Lactamases / Q000235:genetics
D000900:Anti-Bacterial Agents; D010406:Penicillins; D001618:beta-Lactamases
Bacteremia; Penicillin; Staphylococcus aureus; Susceptibility testing