There have been several reports related to antimicrobial usage and an increase in resistant bacteria, yet this is the first describing evidence of the co-selection of PMQR genes in this manner. Both qnrB and qnrS demonstrated significant copy number increases between Day 0 and Day 7. Yet, none of the individuals enrolled in this study were treated with fluoroquinolones and instead were prescribed amoxicillin/clavulanic acid, macrolides or cephalosporins. This increase in copy number over the two time points, apparently via exposure to these antimicrobials, particularly amoxicillin/clavulanic acid or amoxicillin/clavulanic acid combined with a cephalosporin, substantiates our co-selection hypothesis. Indeed, additional selection is the most likely mechanism, as PMQR plasmids frequently contain other resistance genes, particularly determinants encoding resistance to b-lactams. Our currently unpublished data related to PMQR plasmids and the genetic background of qnrS1 containing mobile elements in HCMC reveals a predominant qnrS1-containing transposon type carrying the blaLAP-2 gene, which also encodes resistance to b-lactams. Additional reports have also shown an intimate association between qnrA and qnrB with ESBL genes. Our results clearly show a major shift in qnr gene copy numbers after antimicrobial therapy, yet our findings are limited by a lack of control group who did not receive antimicrobials. The results presented here warrant asking additional questions related to the effect of antimicrobials on the presence and maintenance of qnr genes and other antimicrobial resistance genes in the gut flora. We are currently Gefitinib longitudinally following a cohort of children in HCMC over a two-year period with and without antimicrobial treatment to address natural fluctuations of resistance genes and changes in Enterobacteriaceae. In conclusion, our data demonstrate an increasing prevalence of qnrB and an increasing quantity of the qnrB and qnrS genes in the stools of children with ARIs between enrolment and after seven days treatment with non-fluoroquinolone antimicrobials. This is the first study describing an association between the use of nonquinolone antimicrobials and the increasing relative prevalence in qnr gene copy number in the gut flora. Our work highlights the rampant nature of PMQR genes in this locality and suggests aggressive co-selection of these resistance determinants through the use of unrelated and potentially unnecessary antimicrobial treatment regimes. As well as cloning one desired multi-component construct, many projects require degenerate cloning or mutagenesis to make combinatorial libraries of gene variants. The OmniChange technique, which simultaneously saturates five independent codons, has therefore been developed to generate full-length gene libraries with degenerate NNK-codons while avoiding PCRamplification. Large libraries of genetic sequences can be derived from oligonucleotides synthetized in a microarray, and later pooled in libraries from which more complex sequences can be derived. By combining linear DNA amplification and PCR, DNA libraries with hundreds to thousands of members can be synthesized. PCR methods themselves can have certain limitations, such as difficulties in amplifying GC-rich DNA targets. One study optimized polymerase chain assembly and ligase chain reaction methods for the construction of two GC-rich gene fragments implicated in tumorigenesis, IGF2R and BRAF. They found that LCR was superior and benefited from the addition of DMSO and betaine.