1. D-2238
48th Interscience Conference on Antimicrobial Agents and Chemotherapy
October 25-28, 2008.
Washington, DC
Evaluation of a Rapid PBP2’ Agglutination Test for Detection of Meticillin Resistance in Coagulase-negative Staphylococci R. Soutar1, M. Wootton1, J. S. Bendle2, Z. E. Thompson2 and R. A. Howe1 1NPHS Microbiology, University Hospital Wales, Cardiff, United Kingdom. 2 Royal Gwent Hospital, Newport, United Kingdom.
Introduction
Materials and Methods
Table: Sensitivity (SN), specificity (SP), positive predictive value (PPV) and negative predictive value (NPV) for Mastalex and Phoenix AST
Coagulase-negative staphylococci (CoNS) are a frequent cause of nosocomial bloodstream infections and can be problematic in immuno-compromised patients. With the spread of meticillin-resistant staphylococci in hospitals and the community, fast and reliable methods for detection of resistance are required. Reliable phenotypic identification of MRSE has been difficult, therefore detection of the mecA gene is recommended. In most diagnostic laboratories genotypic detection is unavailable, however, latex agglutination kits detecting PBP2’ are more common. This rapid method was compared to phenotypic susceptibility testing and mecA PCR
and latex agglutination via MastalexTM kit, using the manufacturer’s instructions. Meticillin resistance was confirmed by mecA PCR. Positive control NCTC and negative control ATCC were used in both tests.
Percentage errors were calculated, with major/minor errors defined as susceptible (S) replacing resistant (R) and R replacing S respectively. Sensitivity (SN), specificity (SP), negative predictive value (NPV) and positive predictive values (PPV) were calculated
Results
Figure 1: mecA PCR
30 out of 48 strains were confirmed as mecA positive by PCR. The SN, SP, NPV and PPV plus percentage correctly classified and major error rate are shown in the Table.
A false negative result was produced for one strain only with both MastalexTM and PhoenixTM susceptibility testing (AST). PhoenixTM AST produced false negative results for five other strains and one false positive result.
MastalexTM produced false negative results for four other strains and one false positive.
The isolates incorrectly classified by MastalexTM were S. epidermidis. The isolates incorrectly classified by PhoenixTM AST were of varied species.
Lanes 1-3, clinical, negative and positive control with mecA, lanes s control.
Conclusions
MastalexTM kit for detecting PBP2’ in S. aureus
The MastalexTM latex agglutination kit for detecting PBP2’ was unreliable for detecting meticillin resistance in CoNS.
Agglutination reactions were noted as weak and poorly reproducible.
Susceptibility testing using PHX was similarly unreliable.
Materials and Methods
48 CoNS were collected, including 6 S. capitis, 7 S. haemolyticus, 26 S. epidermidis, 2 S. chromogenes, 2 S. hominis, 2 S. lugdinensis, 1 S. saprophyticus and 2 S. warneii. Each isolate was subject to susceptibility testing via automated PhoenixTM (BSAC interpretations)
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