Genetic regulation of the ramA locus and its expression in clinical isolates of Klebsiella pneumoniae

Tigecycline resistance has been attributed to ramA overexpression and subsequent acrA upregulation. The ramA locus, originally identified in Klebsiella pneumoniae, has homologues in Enterobacter and Salmonella spp. In this study, we identify in silico that the ramR binding site is also present in Citrobacter spp. and that Enterobacter, Citrobacter and Klebsiella spp. share key regulatory elements in the control of the romA–ramA locus. RACE (rapid amplification of cDNA ends) mapping indicated that there are two promoters from which romA–ramA expression can be regulated in K. pneumoniae. Correspondingly, electrophoretic binding studies clearly showed that purified RamA and RamR proteins bind to both of these promoters. Hence, there appear to be two RamR binding sites within the Klebsiella romA–ramA locus. Like MarA, RamA binds the promoter region, implying that it might be subject to autoregulation. We have identified changes within ramR in geographically distinct clinical isolates of K. pneumoniae. Intriguingly, levels of romA and ramA expression were not uniformly affected by changes within the ramR gene, thereby supporting the dual promoter finding. Furthermore, a subset of strains sustained no changes within the ramR gene but which still overexpressed the romA–ramA genes, strongly suggesting that a secondary regulator may control ramA expression.

Population structure and characterization of viridans group streptococci (VGS) including Streptococcus pneumoniae isolated from adult patients with cystic fibrosis (CF)

A study was undertaken to examine the population structure of viridans group streptococci (VGS) in the sputum of adult patients with cystic fibrosis (CF). Freshly expectorated sputa (n=58) from 45 adult CF patients were examined by selective conventional culture on Mitis-Salivarius agar and yielded 190 isolates of VGS. Sequence analyses of the rpnB and 16-23S rRNA ITS genes identified these isolates to belong to 12 species of VGS and included S. anginosus, S. australis, S. cristatus, S. gordonii, S. infantis, S. mitis, S. mutans, S. oralis, S. parasanguinis, S. pneumoniae, S. salivarius and S. sanguinis. The most frequently VGS organism isolated was S. salivarius (47/190; 24.7%), followed by S. mitts (36/190; 19%), S. sanguinis (25/190; 13.2%), S. oralis (20/190; 11.0%), S. pneumoniae (19/190; 10.0%), S. parasanguinis (16/190; 8.4%), S. infantis (11/190; 5.8%), S. gordonii (7/190; 3.7%), S. anginosus (4/190; 2.1%), S. cristatus (2/190; 1.1%), S. australis (1/190; 0.5%), S. mutans (1/190; 0.5%) and S. agalactiae (1/190; 0.5%). All, but four, patients harboured at least one VGS species, which ranged from one to five streptococcal species, with a mean of 2.85 species per patient. There was no clonality at the subspecies level employing ERIC RAPD PCR. Antibiotic susceptibility was determined by Minimum Inhibitory Concentration (MIC) testing against penicillin, erythromycin and ciprofloxacin. Overall, resistance to penicillin with all VGS was 73/190 (38.4%) and 167/190 (87.9%) for erythromycin. With regard to ciprofloxacin, 27/190 (14.2%) were fully resistant, whilst a further 21/190 (11.1%) showed intermediate resistance, which equated to approximately three quarters (74.7%) of isolates being fully sensitive to this agent. In addition, as a comparator control population, we examined antibiotic susceptibility, as above, in a non-CF population comprising 12 individuals (50 VGS isolates), who were not receiving chronic antibiotics. In comparison, 8% and 38% of VGS isolates from non-CF individuals were resistant by disk susceptibility testing to penicillin and erythromycin, respectively. None of the non-CF VGS organisms were resistant to ciprofloxacin, but 42% showed intermediate resistance. (C) 2010 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.

Characterization of RarA, a Novel AraC Family Multidrug Resistance Regulator in Klebsiella pneumoniae

Transcriptional regulators, such as SoxS, RamA, MarA, and Rob, which upregulate the AcrAB efflux pump, have been shown to be associated with multidrug resistance in clinically relevant Gram-negative bacteria. In addition to the multidrug resistance phenotype, these regulators have also been shown to play a role in the cellular metabolism and possibly the virulence potential of microbial cells. As such, the increased expression of these proteins is likely to cause pleiotropic phenotypes. Klebsiella pneumoniae is a major nosocomial pathogen which can express the SoxS, MarA, Rob, and RamA proteins, and the accompanying paper shows that the increased transcription of ramA is associated with tigecycline resistance (M. Veleba and T. Schneiders, Antimicrob. Agents Chemother. 56:4466-4467, 2012). Bioinformatic analyses of the available Klebsiella genome sequences show that an additional AraC-type regulator is encoded chromosomally. In this work, we characterize this novel AraC-type regulator, hereby called RarA (Regulator of antibiotic resistance A), which is encoded in K. pneumoniae, Enterobacter sp. 638, Serratia proteamaculans 568, and Enterobacter cloacae. We show that the overexpression of rarA results in a multidrug resistance phenotype which requires a functional AcrAB efflux pump but is independent of the other AraC regulators. Quantitative real-time PCR experiments show that rarA (MGH 78578 KPN_02968) and its neighboring efflux pump operon oqxAB (KPN_02969_02970) are consistently upregulated in clinical isolates collected from various geographical locations (Chile, Turkey, and Germany). Our results suggest that rarA overexpression upregulates the oqxAB efflux pump. Additionally, it appears that oqxR, encoding a GntR-type regulator adjacent to the oqxAB operon, is able to downregulate the expression of the oqxAB efflux pump, where OqxR complementation resulted in reductions to olaquindox MICs.

Tigecycline Resistance Can Occur Independently of the ramA Gene in Klebsiella pneumoniae

Tigecycline resistance in Klebsiella pneumoniae results from ramA upregulation that causes the overexpression of the efflux pump, AcrAB-TolC. Tigecycline mutants, derived from Ecl8?ramA, can exhibit a multidrug resistance phenotype due to increased transcription of the marA, rarA, acrAB, and oqxAB genes. These findings support the idea that tigecycline or multidrug resistance in K. pneumoniae, first, is not solely dependent on the ramA gene, and second, can arise via alternative regulatory pathways in K. pneumoniae. © 2012, American Society for Microbiology.

Role of AcrR and ramA in fluoroquinolone resistance in clinical Klebsiella pneumoniae isolates from Singapore

The MICs of ciprofloxacin for 33 clinical isolates of K. pneumoniae resistant to extended-spectrum cephalosporins from three hospitals in Singapore ranged from 0.25 to >128 microg/ml. Nineteen of the isolates were fluoroquinolone resistant according to the NCCLS guidelines. Strains for which the ciprofloxacin MIC was >or=0.5 microg/ml harbored a mutation in DNA gyrase A (Ser83-->Tyr, Leu, or IIe), and some had a secondary Asp87-->Asn mutation. Isolates for which the MIC was 16 microg/ml possessed an additional alteration in ParC (Ser80-->IIe, Trp, or Arg). Tolerance of the organic solvent cyclohexane was observed in 10 of the 19 fluoroquinolone-resistant strains; 3 of these were also pentane tolerant. Five of the 10 organic solvent-tolerant isolates overexpressed AcrA and also showed deletions within the acrR gene. Complementation of the mutated acrR gene with the wild-type gene decreased AcrA levels and produced a two- to fourfold reduction in the fluoroquinolone MICs. None of the organic solvent-tolerant clinical isolates overexpressed another efflux-related gene, acrE. While marA and soxS were not overexpressed, another marA homologue, ramA, was overexpressed in 3 of 10 organic solvent-tolerant isolates. These findings indicate that multiple target and nontarget gene changes contribute to fluoroquinolone resistance in K. pneumoniae. Besides AcrR mutations, ramA overexpression (but not marA or soxS overexpression) was related to increased AcrAB efflux pump expression in this collection of isolates.

Genome Sequence of Klebsiella pneumoniae Ecl8, a Reference Strain for Targeted Genetic Manipulation

We report the genome sequence of Klebsiella pneumoniae subsp. pneumoniae Ecl8, a spontaneous streptomycin-resistant mutant of strain ECL4, derived from NCIB 418. K. pneumoniae Ecl8 has been shown to be genetically tractable for targeted gene deletion strategies and so provides a platform for in-depth analyses of this species.

Elucidating the Regulon of the Multidrug Resistance Regulator RarA in Klebsiella pneumoniae

RarA is an AraC-type regulator in Klebsiella pneumoniae, which, when overexpressed, confers a low-level multidrug-resistant (MDR) phenotype linked to the upregulation of both the acrAB and oqxAB efflux genes. Increased rarA expression has also been shown to be integral in the development of tigecycline resistance in the absence of ramA in K. pneumoniae. Given its phenotypic role in MDR, microarray analyses were performed to determine the RarA regulon. Transcriptome analysis was undertaken using strains Ecl8?rarA/pACrarA-2 (rarA-expressing construct) and Ecl8?rarA/pACYC184 (vector-only control) using bespoke microarray slides consisting of probes derived from the genomic sequences of K. pneumoniae MGH 78578 (NC_009648.1) and Kp342 (NC_011283.1). Our results show that rarA overexpression resulted in the differential expression of 66 genes (42 upregulated and 24 downregulated). Under the COG (clusters of orthologous groups) functional classification, the majority of affected genes belonged to the category of cell envelope biogenesis and posttranslational modification, along with genes encoding the previously uncharacterized transport proteins (e.g., KPN_03141, sdaCB, and leuE) and the porin OmpF. However, genes associated with energy production and conversion and amino acid transport/metabolism (e.g., nuoA, narJ, and proWX) were found to be downregulated. Biolog phenotype analyses demonstrated that rarA overexpression confers enhanced growth of the overexpresser in the presence of several antibiotic classes (i.e., beta-lactams and fluoroquinolones), the antifungal/antiprotozoal compound clioquinol, disinfectants (8-hydroxyquinoline), protein synthesis inhibitors (i.e., minocycline and puromycin), membrane biogenesis agents (polymyxin B and amitriptyline), DNA synthesis (furaltadone), and the cytokinesis inhibitor (sanguinarine). Both our transcriptome and phenotypic microarray data support and extend the role of RarA in the MDR phenotype of K. pneumoniae.

Klebsiella pneumoniae subverts the activation of inflammatory responses in a NOD1-dependent manner

Klebsiella pneumoniae is an important cause of community-acquired and nosocomial pneumonia. Subversion of inflammation is essential for pathogen survival during infection. Evidence indicates that K. pneumoniae infections are characterized by lacking an early inflammatory response although the molecular bases are currently unknown. Here we unveil a novel strategy employed by a pathogen to counteract the activation of inflammatory responses. K. pneumoniae attenuates pro-inflammatory mediators-induced IL-8 secretion. Klebsiella antagonizes the activation of NF-?B via the deubiquitinase CYLD and blocks the phosphorylation of mitogen-activated protein kinases (MAPKs) via the MAPK phosphatase MKP-1. Our studies demonstrate that K. pneumoniae has evolved the capacity to manipulate host systems dedicated to control the immune balance. To exert this anti-inflammatory effect, Klebsiella engages NOD1. In NOD1 knock-down cells, Klebsiella neither induces the expression of CYLD and MKP-1 nor blocks the activation of NF-?B and MAPKs. Klebsiella inhibits Rac1 activation; and inhibition of Rac1 activity triggers a NOD1-mediated CYLD and MKP-1 expression which in turn attenuates IL-1ß-induced IL-8 secretion. A capsule (CPS) mutant does not attenuate the inflammatory response. However, purified CPS neither reduces IL-1ß-induced IL-8 secretion nor induces the expression of CYLD and MKP-1 thereby indicating that CPS is necessary but not sufficient to attenuate inflammation.

Klebsiella pneumoniae outer membrane protein A is required to prevent the activation of airway epithelial cells

Outer membrane protein A (OmpA) is a class of proteins highly conserved among the Enterobacteriaceae family and throughout evolution. Klebsiella pneumoniae is a capsulated Gram-negative pathogen. It is an important cause of community-acquired and nosocomial pneumonia. Evidence indicates that K. pneumoniae infections are characterized by a lack of an early inflammatory response. Data from our laboratory indicate that K. pneumoniae CPS helps to suppress the host inflammatory response. However, it is unknown whether K. pneumoniae employs additional factors to modulate host inflammatory responses. Here, we report that K. pneumoniae OmpA is important for immune evasion in vitro and in vivo. Infection of A549 and normal human bronchial cells with 52OmpA2, an ompA mutant, increased the levels of IL-8. 52145-?wca ompA, which does not express CPS and ompA, induced the highest levels of IL-8. Both mutants could be complemented. In vivo, 52OmpA2 induced higher levels of tnfa, kc, and il6 than the wild type. ompA mutants activated NF-?B, and the phosphorylation of p38, p44/42, and JNK MAPKs and IL-8 induction was via NF-?B-dependent and p38- and p44/42-dependent pathways. 52OmpA2 engaged TLR2 and -4 to activate NF-?B, whereas 52145-?wca ompA activated not only TLR2 and TLR4 but also NOD1. Finally, we demonstrate that the ompA mutant is attenuated in the pneumonia mouse model. The results of this study indicate that K. pneumoniae OmpA contributes to attenuate airway cell responses. This may facilitate pathogen survival in the hostile environment of the lung. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.

Role of Bacterial Surface Structures on the Interaction of Klebsiella pneumoniae with Phagocytes

Phagocytosis is a key process of the immune system. The human pathogen Klebsiella pneumoniae is a well known example of a pathogen highly resistant to phagocytosis. A wealth of evidence demonstrates that the capsule polysaccharide (CPS) plays a crucial role in resistance to phagocytosis. The amoeba Dictyostelium discoideum shares with mammalian macrophages the ability to phagocytose and kill bacteria. The fact that K. pneumoniae is ubiquitous in nature and, therefore, should avoid predation by amoebae, poses the question whether K. pneumoniae employs similar means to counteract amoebae and mammalian phagocytes. Here we developed an assay to evaluate K. pneumoniae-D. discoideum interaction. The richness of the growth medium affected the threshold at which the cps mutant was permissive for Dictyostelium and only at lower nutrient concentrations the cps mutant was susceptible to predation by amoebae. Given the critical role of bacterial surface elements on host-pathogen interactions, we explored the possible contribution of the lipopolysaccharide (LPS) and outer membrane proteins (OMPs) to combat phagoyctosis by D. discoideum. We uncover that, in addition to the CPS, the LPS O-polysaccharide and the first core sugar participate in Klebsiella resistance to predation by D. discoideum. K. pneumoniae LPS lipid A decorations are also necessary to avoid predation by amoebae although PagP-dependent palmitoylation plays a more important role than the lipid A modification with aminoarabinose. Mutants lacking OMPs OmpA or OmpK36 were also permissive for D. discoideium growth. Except the LPS O-polysaccharide mutants, all mutants were more susceptible to phagocytosis by mouse alveolar macrophages. Finally, we found a correlation between virulence, using the pneumonia mouse model, and resistance to phagocytosis. Altogether, this work reveals novel K. pneumoniae determinants involved in resistance to phagocytosis and supports the notion that Dictyostelium amoebae might be useful as host model to measure K. pneumoniae virulence and not only phagocytosis. © 2013 March et al.