Plasmid-Mediated Antibiotic Resistance and Virulence in Gram-negatives: the Klebsiella pneumoniae Paradigm

Abstract

Plasmids harbor genes coding for specific functions including virulence factors and antibiotic resistance that permit bacteria to survive the hostile environment found in the host and resist treatment. Together with other genetic elements such as integrons and transposons, and using a variety of mechanisms, plasmids participate in the dissemination of these traits resulting in the virtual elimination of barriers among different kinds of bacteria. In this article we review the current information about physiology and role in virulence and antibiotic resistance of plasmids from the gram-negative opportunistic pathogen Klebsiella pneumoniae. This bacterium has acquired multidrug resistance and is the causative agent of serious communityand hospital-acquired infections. It is also included in the recently defined ESKAPE group of bacteria that cause most of US hospital infections.

Keywords: Klebsiella; eskape; gram-negative; xer recombination.

Fig. 1

Small plasmids. a, General genetic organization of small ColE1-type plasmids from K. pneumoniae and other Enterobacteriaceae. b, Alignment of the nucleotide sequences of the replication regions of K. pneumoniae ColE1-type plasmids using CLUSTAL W (143). c, Alignment of the nucleotide sequences of Xer site-specific recombination sites of K. pneumoniae ColE1-type plasmids using CLUSTAL W. The ARG box, XerC and XerD binding sites are shown in color and the central regions are boxed. Blue capital letters indicate the most important conserved nucleotides in the ARG box. Downward pointing arrowhead shows the conserved T nucleotide that its found substituted by a C in several Xer site-specific recombination sites (76, 81, 88).

Fig. 2

Comparison of pFPBT1 and pJHCMW1. The black lines, which represent regions of homology (coordinates 463-3361 in pJHCMW1), are drawn at scale. The Tn3-like transposons, Tn1331 and Tn3/DeltaTn1723, as well as the dots indicating oriT and the Xer target sites are shown at the correct locations but are not drawn to scale. The replication regions (REP) share 97% homology. The numbers indicate the coordinates in the GenBank database (pJHCMW1, accession number AF479774; pFPBT1, accession number AJ634602). The location of the similar but not identical Xer site-specific recombination sites (81) is indicated.

Fig. 3

Effect of changes in osmolarity of the culture medium on Xer site-specific recombination at mwr. Schematic representation of the possible chain of events that lead to a higher efficiency of Xer site-specific recombination at the K. pneumoniae plasmid pJHCMW1 site mwr. A decrease in the NaCl concentration in the growth medium (L broth containing 0.5% NaCl added to no NaCl added) is correlated with an increase in supercoiling density, which facilitates interaction of ArgR with the substandard mwr ARG box leading to a more efficient formation of a productive synaptic complex and Holliday junction (78). Molecular models of the interwrapped synaptic complex are available at the following references (146-148). The two strands are shown only in the core recombination site (red and green lines), blue lines represent the accessory sequences.

Fig. 4

Genetic maps comparison of the K. pneumoniae pIP843 and the E. coli pE66An. The shadowed areas show regions of homology (6681/6701 identities and 6 gaps in the region with 99% homology). The ColE1-type replication region is schematically shown on top of the pIP843 map. The semicircle in pE66An represents the region encompassing nucleotides 6697 – 79713.

Fig. 5

Multiple alignment of pLVPK, pK2044 and pKCTC2242. The nucleotide sequences of pLVPK (accession number AY378100.1)(112), pK2044 (accession number AP006726.1)(116), and pKCTC2242 (accession number CP002911.1)(117) were compared using the MAUVE aligner version 2.3.1 (149). Different colors represent local LCBs. Inside each block there is a similarity profile of the sequence, the height corresponds to the average level of conservation. Completely white areas are not aligned and most probably contain sequences specific to the particular molecule. In pKCTC2242 the LCBs drawn below the black line are inverted with respect to their homologs in pLVPK and pK2044. Some genes or clusters present in these blocks are identified by name. The terZ gene has been reported as “truncated” (112). The truncation is a consequence of an extra T in the sequence that could also be a sequencing error. The terBCDE genes are sufficient for the tellurite resistance phenotype (Te^R). The ter cluster is also responsible for the phage inhibition (Phi) and colicin resistance (PacB) phenotypes (150). Copper (pco), silver (sil), lead (pbr), and tellurite (ter) resistance related genes; IUS, iron uptake system.

Fig. 6

Multiple alignment of pNDM-MAR, pTR3/4, pNDM-HN380, pNDM-KN, and pNDM10469. The nucleotide sequences of pNDM-MAR (accession number JN420336) (72), pTR3/4 (accession number JQ349086) (151), pNDM-HN380 (accession number JX104760) (152), pNDM-KN (accession number JN157804) (153), and pNDM10469 (accession number JN861072) were compared using the MAUVE aligner version 2.3.1 (149). The bla_NDM-1 gene is represented in red, genes ble_MBL and trpF are represented in light blue and light brown, respectively. Plasmids pTR3 and pTR4, originally thought to be similar but not identical were later proved to be identical and renamed pTR3/4 (151). a. The comparison of the complete nucleotide sequence is shown with LCBs represented in blocks of different colors. b. Zoom in the region including the bla_NDM-1 gene.

Fig. 7

Genetic map of the Tn1331: :Tn4401 region in the _{K. pneumoniae} plasmid pBK692.