Polymorphisms in the type A gene as determinants of the cefazolin inoculum effect in .

Plasmids containing the wild-type (WT) or mutant type A () gene (mutations at codons 226, 229, or both 226 and 229) were constructed and transformed into RN4220, yielding the strains WT-blaZ, M226-blaZ, M229-blaZ, and MB-blaZ. The high-inoculum cefazolin MIC was significantly lower in MB-blaZ and M226-blaZ than in WT-blaZ but not in M229-blaZ, suggesting that the single nucleotide polymorphism at codon 226 in contributes to the cefazolin inoculum effect.