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"Methicillin-resistant Staphylococcus aureus (MRSA) is a type of antibiotic-resistant bacteria that is becoming increasingly important in both hospital and community settings. This bacterium develops resistance to antibiotics by acquiring genes from other bacteria or from the surrounding environment. Beta-lactam antibiotics, which target the penicillin-binding proteins (PBPs) in Staphylococcus aureus, inhibit cell wall synthesis and bacterial replication. However, MRSA has a mutated cell-wall protein called PBP2a, encoded by the mecA gene, which reduces its affinity for penicillins. The presence of mecA gene can be detected using polymerase chain reaction (PCR), while the presence of PBP2a can be detected using a latex agglutination technique. Although both methods are highly sensitive for identifying methicillin resistance, they are relatively expensive.

To determine the effectiveness of more affordable methods for rapidly detecting MRSA in resource-limited settings, researchers compared the sensitivity and specificity of mecA PCR with the standard and cost-effective disk-diffusion method, as shown in Figure 1. In the disk-diffusion method, an antibiotic disk is placed in a petri dish containing MRSA. After 18 hours of incubation, the area of bacterial clearance around the disk is measured.

The researchers tested 500 Staphylococcus aureus isolates and found that 300 of them were methicillin-resistant based on mecA probe results. Among the 300 resistant isolates, 270 were detected using the disk-diffusion method. Additionally, 150 mecA-negative isolates were correctly identified as negative using the disk-diffusion method. Based on these findings, the researchers concluded that the disk-diffusion method is a viable approach for detecting MRSA in laboratories with limited resources."