Staphylococcus pseudintermedius's PBP4 Is Directly Associated with the Dissociated Oxacillin and Cefoxitin Phenotype

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Molecular Biology

Background:

• Staphylococcus pseudintermedius is a significant pathogen in veterinary and human medicine.
• The rise of multidrug-resistant strains, including methicillin-resistant S. pseudintermedius (MRSP), complicates treatment.
• Current laboratory methods using cefoxitin disks are insufficient for detecting MRSP's beta-lactam resistance.

Purpose of the Study:

• To investigate the molecular mechanisms behind the differing resistance patterns to oxacillin and cefoxitin in MRSP.
• To understand why cefoxitin disk tests fail to accurately detect methicillin resistance in S. pseudintermedius.

Main Methods:

• Analysis of Penicillin-Binding Proteins (PBP) profiles in MRSP.
• Assessment of PBP affinity for various beta-lactam antibiotics.
• Sequencing of PBP genes to identify resistance-associated mutations.

Main Results:

• Penicillin-Binding Protein 4 (PBP4) retains affinity for cefoxitin in MRSP.
• This retained affinity of PBP4 for cefoxitin interferes with the accurate phenotypic detection of resistance.
• The study identified PBP4 as the key factor in the dissociated oxacillin and cefoxitin resistance phenotype.

Conclusions:

• Staphylococcus pseudintermedius PBP4 is directly implicated in the discordant oxacillin and cefoxitin resistance.
• Understanding this mechanism is crucial for accurate diagnosis and effective treatment of MRSP infections.
• This finding highlights the need for revised diagnostic strategies for MRSP in clinical microbiology.