Impact of specific pbp5 mutations on expression of beta-lactam resistance in Enterococcus faecium.
We tested the impact of individual PBP 5 mutations on expression of ampicillin resistance in Enterococcus faecium using a shuttle plasmid designed to facilitate expression of cloned pbp5 in ampicillin-susceptible E. faecium D344SRF. Substitutions that had been implicated in contributing to the resistance of clinical strains conferred only modest levels of resistance when they were present as single point mutations. The levels of resistance were amplified when some mutations were present in combination. In particular, a methionine-to-alanine change at position 485 (in close proximity to the active site) combined with the insertion of a serine at position 466 (located in a loop that forms the outer edge of the active site) was associated with the highest levels of resistance to all beta-lactams. Affinity for penicillin generally correlated with beta-lactam MICs for the mutants, but these associations were not strictly proportional.
Medical and Research Services, Louis Stokes Cleveland VA Medical Center, Cleveland, Ohio 44106, USA. louis.rice@med.va.gov
Louis B
LB
Rice
Samuel
S
Bellais
Lenore L
LL
Carias
Rebecca
R
Hutton-Thomas
Robert A
RA
Bonomo
Patrick
P
Caspers
Malcolm G P
MG
Page
Laurent
L
Gutmann
D000668:Ampicillin Resistance / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics* / Q000502:physiology*; D002352:Carrier Proteins / Q000235:genetics* / Q000502:physiology*; D018360:Crystallography, X-Ray; D016984:Enterococcus faecium / Q000187:drug effects* / Q000235:genetics*; D005822:Genetic Vectors / Q000235:genetics; D006602:Hexosyltransferases / Q000235:genetics* / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D002267:Muramoylpentapeptide Carboxypeptidase / Q000235:genetics* / Q000502:physiology*; D009154:Mutation / Q000235:genetics* / Q000502:physiology*; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000378:metabolism; D010458:Peptidyl Transferases / Q000235:genetics* / Q000502:physiology*; D010957:Plasmids / Q000235:genetics; D011485:Protein Binding; D018440:beta-Lactam Resistance / Q000235:genetics*
D001426:Bacterial Proteins; D002352:Carrier Proteins; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002267:Muramoylpentapeptide Carboxypeptidase