Evidence for recombination among the alleles encoding TEM and SHV β-lactamases

The objective of this research was to determine whether recombination occurs in class A beta-lactamases. We performed chi(2) analysis of the observed and expected numbers of times that beta-lactamases from the TEM, SHV and CTX-M groups co-occurred. Additionally, we performed phylogenetic analysis to detect independent occurrences of silent mutations in bla(TEM) and bla(SHV) variants. We found that the distribution of co-occurring bla(TEM), bla(SHV) and bla(CTX-M) alleles in clinical microbial populations is consistent with the regular occurrence of recombination among alleles within the groups. We also found that the distribution of silent mutations in bla(TEM) and bla(SHV) alleles is inconsistent with spontaneous point mutations. Our findings indicate that recombination has an important effect on the sequence evolution and population distribution of the alleles that encode class A beta-lactamases.