omp33 disruption. (a) Schematic representation of the strategy used to construct the omp33 mutant by gene disruption (omp33::TOPO). The oligonucleotides used (small arrows) are listed in Table 2. The boxes indicated by A and A' represent the original and the cloned internal fragment of the omp33 gene, respectively. See Materials and Methods for details. (b) Screening of omp33 A. baumannii mutants generated by gene disruption. The numbers at the top are bacterial colony numbers. All PCR products with 697 bp and 798 bp (amplified with primer pairs 33extFW + SP6 and T7 + 33extRV, respectively) were sequenced to confirm omp33 gene disruption. Lambda DNA-Hin d III and ϕX174 DNA-Hae III Mix (Finnzymes) was used as a size marker (M). The wild-type strain (WT) was used as a negative control. The lengths of PCR products and of some molecular size marker fragments are also indicated.