By performing multiplex PCR, they can count categories such as 'A not B', 'A and B', and 'B plus A'.The particular A's and B's are degenerate primers targeting bacterial 16S ribosomal RNA and a key enzyme for some termite endosymbionts, FTHFS. The 16S rRNA primers have very broad specificity, whereas the FTHFS primers are specific to a subtype called 'clone H'.