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Klebsiella pneumoniae and the closely related species K. variicola and K. quasipneumoniae are common causes of health care-associated infections, and patients frequently become infected with their intestinal colonizing strain. To assess the association between Klebsiella colonization density and subsequent infections, a case-control study was performed. A multiplex quantitative PCR (qPCR) assay was developed and validated to quantify Klebsiella (K. pneumoniae, K. variicola , and K. quasipneumoniae combined) relative to total bacterial DNA copies in rectal swabs. Cases of Klebsiella infection were identified based on clinical definitions and having a clinical culture isolate and a preceding or coincident colonization isolate with the same wzi capsular sequence type. Controls were colonized patients without subsequent infection and were matched 2:1 to cases based on age, sex, and rectal swab collection date. qPCR from rectal swab samples was used to measure the association between the relative abundance of Klebsiella and subsequent infections. The Klebsiella relative abundance by qPCR was highly correlated with 16S sequencing (ρ = 0.79; P  < 0.001). The median Klebsiella relative abundance was higher in cases (15.7% [interquartile range {IQR}, 0.93 to 52.6%]) ( n  = 83) than in controls (1.01% [IQR, 0.02 to 12.8%]) ( n  = 155) ( P < 0.0001). Adjusting for multiple clinical covariates using inverse probability of treatment weighting, a Klebsiella relative abundance of >22% was associated with infection overall (odds ratio [OR], 2.87 [95% confidence interval {CI}, 1.64 to 5.03]) ( P = 0.0003) and with bacteremia in a secondary analysis (OR, 4.137 [95% CI, 1.448 to 11.818]) ( P  = 0.0084). Measurement of colonization density by qPCR could represent a novel approach to identify hospitalized patients at risk for Klebsiella infection. IMPORTANCE Colonization by bacterial pathogens often precedes infection and offers a window of opportunity to prevent these infections in the first place. Klebsiella colonization is significantly and reproducibly associated with subsequent infection; however, factors that enhance or mitigate this risk in individual patients are unclear. This study developed an assay to measure the density of Klebsiella colonization, relative to total fecal bacteria, in rectal swabs from hospitalized patients. Applying this assay to 238 colonized patients, a high Klebsiella density, defined as >22% of total bacteria, was significantly associated with subsequent infection. Based on widely available PCR technology, this type of assay could be deployed in clinical laboratories to identify patients at an increased risk of Klebsiella infections. As novel therapeutics are developed to eliminate pathogens from the gut microbiome, a rapid Klebsiella colonization density assay could identify patients who would benefit from this type of infection prevention intervention.

Carbapenemases have become a significant mechanism for broad-spectrum β-lactam resistance in Enterobacteriaceae and other Gram-negative bacteria such as Pseudomonas and Acinetobacter spp. Intestinal carriage of carbapenemase-producing organisms (CPOs) is an important source of transmission. Isolation of carriers is one strategy that can be used to limit the spread of these bacteria. In this review, we critically examine the clinical performance, advantages, and disadvantages of methods available for the detection of intestinal carriage of CPOs. Culture-based methods (Centers for Disease Control and Prevention [CDC] protocols, chromogenic media, specialized agars, and double-disk synergy tests) for detecting carriage of CPOs are convenient due to their ready availability and low cost, but their limited sensitivity and long turnaround time may not always be optimal for infection control practices. Contemporary nucleic acid amplification techniques (NAATs) such as real-time PCR, hybridization assays, loop-mediated isothermal amplification (LAMP), or a combined culture and NAAT approach may provide fast results and/or added sensitivity and specificity compared with culture-based methods. Infection control practitioners and clinical microbiologists should be aware of the strengths and limitations of available methods to determine the most suitable approach for their medical facility to fit their infection control needs., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

The emergence of multidrug-resistant (MDR) Klebsiella pneumoniae has resulted in a more frequent reliance on treatment using colistin. However, resistance to colistin (Col(r)) is increasingly reported from clinical settings. The genetic mechanisms that lead to Col(r) in K. pneumoniae are not fully characterized. Using a combination of genome sequencing and transcriptional profiling by RNA sequencing (RNA-Seq) analysis, distinct genetic mechanisms were found among nine Col(r) clinical isolates. Col(r) was related to mutations in three different genes in K. pneumoniae strains, with distinct impacts on gene expression. Upregulation of the pmrH operon encoding 4-amino-4-deoxy-L-arabinose (Ara4N) modification of lipid A was found in all Col(r) strains. Alteration of the mgrB gene was observed in six strains. One strain had a mutation in phoQ. Common among these seven strains was elevated expression of phoPQ and unaltered expression of pmrCAB, which is involved in phosphoethanolamine addition to lipopolysaccharide (LPS). In two strains, separate mutations were found in a previously uncharacterized histidine kinase gene that is part of a two-component regulatory system (TCRS) now designated crrAB. In these strains, expression of pmrCAB, crrAB, and an adjacent glycosyltransferase gene, but not that of phoPQ, was elevated. Complementation with the wild-type allele restored colistin susceptibility in both strains. The crrAB genes are present in most K. pneumoniae genomes, but not in Escherichia coli. Additional upregulated genes in all strains include those involved in cation transport and maintenance of membrane integrity. Because the crrAB genes are present in only some strains, Col(r) mechanisms may be dependent on the genetic background., (Copyright © 2015, American Society for Microbiology. All Rights Reserved.)

Genome sequencing of carbapenem-resistant Klebsiella pneumoniae isolates from regional U.S. hospitals was used to characterize strain diversity and the bla(KPC) genetic context. A phylogeny based on core single-nucleotide variants (SNVs) supports a division of sequence type 258 (ST258) into two distinct groups. The primary differences between the groups are in the capsular polysaccharide locus (cps) and their plasmid contents. A strict association between clade and KPC variant was found. The bla(KPC) gene was found on variants of two plasmid backbones. This study indicates that highly similar K. pneumoniae subpopulations coexist within the same hospitals over time., (Copyright © 2014, American Society for Microbiology. All Rights Reserved.)

The STP oncoproteins of the herpesvirus saimiri (HVS) subgroup A strain 11 and subgroup C strain 488 are now found to be stably associated with tumor necrosis factor receptor-associated factor (TRAF) 1, 2, or 3. Mutational analyses identified residues of PXQXT/S in STP-A11 as critical for TRAF association. In addition, a somewhat divergent region of STP-C488 is critical for TRAF association. Mutational analysis also revealed that STP-C488 induced NF-kappaB activation that was correlated with its ability to associate with TRAFs. The HVS STP-C488 P10-->R mutant was deficient in human T-lymphocyte transformation to interleukin-2-independent growth but showed wild-type phenotype for marmoset T-lymphocyte transformation in vitro and in vivo. The STP-C488 P10-->R mutant was also defective in Rat-1 fibroblast transformation, and fibroblast cell transformation was blocked by a TRAF2 dominant-negative mutant. These data implicate TRAFs in STP-C488-mediated transformation of human lymphocytes and rodent fibroblasts. Other factors are implicated in immortalization of common marmoset T lymphocytes and may also be critical in the transformation of human lymphocytes and rodent fibroblasts.

Two hundred fifty clinical isolates of anaerobic bacteria were tested for suceptibility to cefoperazone, cefamandole, cefoxitin, carbenicillin, clindamycin, and chloramphenicol. Anaerobic gram-positive cocci were susceptible to all of the antibiotics tested. Clindamycin was the most active agent against Bacteroides species, followed by chloramphenicol and then cefoxitin. Cefoperazone was less active than cefoxitin and equal in activity to carbenicillin. Cefamandole was the least active antibiotic against Bacteroides. B. distasonis, B. vulgatus, B. thetaiotaomicron, and B. ovatus were more resistant to the antibiotics than B. melaninogenicus, B. oralis, or B. bivius. Clindamycin was the most active agent against Clostridium species, followed by chloramphenicol; the three cephalosporins and carbenicillin were about equal in activity. Clindamycin was the most active antibiotic against Fusobacterium species, followed by chloramphenicol, carbenicillin, and cefoperazone (which were about equally active) and then cefamandole.