The RT-PCR analysis also revealed the possibility of downregulation of both ompK35 and ompK36 expression in the C-S isolates (except ompK35 in one isolate) when compared with a wild-type K. pneumoniae BIBF 1120 supplier isolate, and a further decrease in ompK35 expression in at least some of the C-NS isolates. Numerous studies reviewed by Martínez-Martínez (2008) indicated
the role of OmpK35 deficiency alone or concomitant with that of OmpK36 in increasing the resistance of ESBL- or AmpC-producing K. pneumoniae to various cephalosporins and reducing susceptibility to carbapenems. It has also been proposed that OmpK35 deficiency may create a favorable background for the selection of other resistance mechanisms (Martínez-Martínez,
2008). The effects observed might have contributed to the resistance of all the isolates studied to β-lactams, including carbapenems in the C-NS isolates. Sequencing of the ompK35 gene in the C-S and C-NS isolates did not reveal any changes when compared with the wild-type gene including its promoter (Crowley et al., 2002); therefore, no promoter-down mutations could be responsible for the reduced levels of ompK35 mRNA (Doumith et al., 2009). It is possible that another, yet unknown regulatory mechanism was responsible for this phenomenon (Martínez-Martínez, 2008). Almost all of the C-NS isolates represented different Talazoparib in vitro PFGE types or subtypes, which, together with differences in their β-lactamase content and different types of ompK36 alterations, supports rather the hypothesis of their independent emergence by the possible in vivo evolution. Regardless of the differences, all of the isolates belonged to the same K. pneumoniae clone ST11 that is spread internationally
and is a founder of the clonal complex CC11 (http://www.pasteur.fr). Methocarbamol Its wide dissemination facilitates the acquisition of various resistance determinants in particular locales, for example in Hungary, K. pneumoniae ST11 has been identified with the CTX-M-15 ESBL or VIM-4 metallo-β-lactamase (Damjanova et al., 2008; Kristóf et al., 2010). Klebsiella pneumoniae ST11 with SHV-5 had been recorded in the hospital in Plzeň in 2006 (Hrabák et al., 2009a), which suggests its persistence and wider presence in this environment, creating a background for clonal and phenotypic diversification. Because of the lack of the comparative typing data in other works, it is impossible to determine at present whether particular K. pneumoniae clones may evolve more easily toward carbapenem nonsusceptibility via porin alterations combined with the ESBL and/or AmpC production. With the results obtained in this study, it is difficult to explain all of the observations regarding the resistance phenotypes of the isolates.
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