MRSA: total war or tolerance?

Rapid screening of pyogenic Staphylococcus aureus for confirmation of genus and species, methicillin resistance and virulence factors by using two novel multiplex PCR

Objectives:

Emergence of methicillin resistant Staphylococcus aureus (MRSA) is a major medical problem of current era. These bacteria are resistant to most drugs and rapid diagnosis can provide a clear guideline to clinicians. They possess specific virulence factors and relevant information can be very useful. We designed this study to develop multiplex PCRs to provide rapid information.

Methods:

We studied 60 Staphylococcus aureus isolates and detected methicillin resistance by cefoxitin sensitivity and targeting of mecA gene. After initial studies with uniplex PCRs we optimized two multiplex PCRs with highly reproducible results. The first multiplex PCR was developed to confirm genus, species and methicillin resistance simultaneously, and the second multiplex PCR was for screening of virulence factors.

Results:

We found 38.33% isolates as methicillin resistant. α -toxin, the major cytotoxic factor, was detected in 40% whereas β-hemolysin was found in 25% cases. Panton Valentine leucocidin was detected in 8.33% and toxic shock syndrome toxin in5% cases. The results of uniplex and multiplex PCRs were highly compatible.

Conclusions:

These two multiplex PCRs when run simultaneously can provide vital information about methicillin resistance and virulence status of the isolate within a few hours as compared to several days needed by routine procedures.

Detection of high levels of resistance to linezolid and vancomycin in Staphylococcus aureus

Both methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) are rapidly overcoming the current array of drugs. One hundred and fifty isolates from a hospital were studied for resistance towards linezolid and vancomycin. Fifty-four (36.0 %) isolates were MRSA. Both MRSA and MSSA showed high resistance towards linezolid when using the disc diffusion method, with the figures being 48.1 and 29.2 %, respectively. The figures for the E-test were 46.3 and 27.0 %, respectively. The vancomycin resistance was remarkable in MRSA (14.8 %), but relatively low in MSSA (3.1 %). The E-test results were 13.0 and 4.16 %, respectively. The cfr gene was detected in 78 % of linezolid-resistant isolates and the vanA operon was detected in 74 % of vancomycin-resistant isolates. This level of resistance against linezolid and vancomycin is unprecedented. These results are alarming and highlight the threat of non-treatable S. aureus strains.

Comparison of different phenotypic and genotypic methods for the detection of methicillin-resistant Staphylococcus aureus

Background:

Staphylococcus aureus is known as a powerful pathogen that causes various infections. Emergence of methicillin-resistant S. aureus (MSRA) is responsible for nosocomial and community-acquired infections worldwide.

Aims:

The present study aimed to evaluate the performance and ability of eight different phenotypic and genotypic methods for the detection of MSRA.

Materials and Methods:

A total of 186 S. aureus isolates were defined as methicillin-susceptible S. aureus (MSSA; 95) and MSRA (91) using polymerase chain reaction (PCR) as the gold standard. Susceptibility to methicillin was investigated using oxacillin, methicillin, cefotetan, cefoxitin, and cefmetazole disks, by oxacillin Adata Tab and strips. For all S. aureus isolates minimal inhibitory concentrations of oxacillin were determined using the broth microdilution method according to Clinical and Laboratory Standards Institute guidelines.

Results:

Among the diagnostic methods studied, broth microdilution and the cefoxitin disk had the highest specificity (98.9 and 94.7%), sensitivity (100 and 98.9%), and concordance with PCR results (98.9 and 93.6%). The cefotetan and cefmetazole disks had the lowest concordance with PCR results.

Conclusion:

Our results suggest that microdilution and cefoxitin disk methods have high sensitivities compared with other methods for detection of MSRA. The cefoxitin disk method may be preferred in clinical laboratories because it is easy to perform and does not require special equipment.