A sample of pus collected from a 4-year-old boy diagnosed with pleural empyema complicating lobar pneumonia was received in the microbiology laboratory. Gram- stained smears of the pus showed intracellular and extracellular small Gram-positive diplococci. Cultures were done on sheep blood agar and incubated at 37 degrees in the presence of 5-10% carbon-dioxide, After overnight incubation, alpha hemolytic small (0.5-1mm) dome-shaped glistening colonies appeared on the blood agar medium.
Further study of the colonies showed that the isolate was oxidase and catalase negative, fermented various carbohydrates with acid production, and was bile soluble and sensitive to optochin. The organism was resistant to penicillin with minimum inhibitory concentration (MIC) of >8mcg/ml. It was sensitive to vancomycin and resistant to erythromycin and cephalosporin.
The high resistance to penicillin shown by the isolate is most likely to be due to which of the following mechanisms?
1. Alteration in the penicillin binding proteins 2. Production of chromosomal beta-lactamase 3. Efflux pump activity 4. Change in porin channels 5. Production of plasmid-mediated beta-lactamase