A hypervirulent Klebsiella pneumoniae (hvKp) pathotype is undergoing global dissemination. In contrast to the usual health care-associated epidemiology of classical K. pneumoniae (cKp) infections, hvKp causes tissue-invasive infections in otherwise healthy individuals from the community, often involving multiple sites. An accurate test to identify hvKp strains is needed for improved patient care and epidemiologic studies. To fill this knowledge gap, clinical criteria or random blood isolates from North American and United Kingdom strain collections were used to assemble hvKp-rich (n = 85) and cKp-rich (n = 90) strain cohorts, respectively. The isolates were then assessed for multiple candidate biomarkers hypothesized to accurately differentiate the two cohorts. The genes peg-344, iroB, iucA, plasmid-borne rmpA gene (_prmpA), and _prmpA2 all demonstrated >0.95 diagnostic accuracy for identifying strains in the hvKp-rich cohort. Next, to validate this epidemiological analysis, all strains were assessed experimentally in a murine sepsis model. peg-344, iroB, iucA, _prmpA, and _prmpA2 were all associated with a hazard ratio of >25 for severe illness or death, additionally supporting their utility for identifying hvKp strains. Quantitative siderophore production of ≥30 μg/ml also strongly predicted strains as members of the hvKp-rich cohort (accuracy, 0.96) and exhibited a hazard ratio of 31.7 for severe illness or death. The string test, a widely used marker for hvKp strains, performed less well, achieving an accuracy of only 0.90. Last, using the most accurate biomarkers to define hvKp, prevalence studies were performed on two Western strain collections. These data strongly support the utility of several laboratory markers for identifying hvKp strains with a high degree of accuracy.

Primary Klebsiella pneumoniae liver abscess complicated with metastatic meningitis or endophthalmitis is a globally emerging infectious disease. Its pathogenic mechanism remains unclear. The bacterial virulence factors were explored by comparing clinical isolates. Differences in mucoviscosity were observed between strains that caused primary liver abscess (invasive) and those that did not (noninvasive). Hypermucoviscosity correlated with a high serum resistance and was more prevalent in invasive strains (52/53 vs. 9/52; P < 0.0001). Transposon mutagenesis identified candidate virulence genes. A novel 1.2-kb locus, magA, which encoded a 43-kD outer membrane protein, was significantly more prevalent in invasive strains (52/53 vs. 14/52; P < 0.0001). The wild-type strain produced a mucoviscous exopolysaccharide web, actively proliferated in nonimmune human serum, resisted phagocytosis, and caused liver microabscess and meningitis in mice. However, magA⁻ mutants lost the exopolysaccharide web and became extremely serum sensitive, phagocytosis susceptible, and avirulent to mice. Virulence was restored by complementation using a magA-containing plasmid. We conclude that magA fits molecular Koch's postulates as a virulence gene. Thus, this locus can be used as a marker for the rapid diagnosis and for tracing the source of this emerging infectious disease.

Background. Since 1986, researchers have noted a syndrome of Klebsiella pneumoniae pyogenic liver abscess that is complicated by endophthalmitis or central nervous system infections. There are limited data regarding the role of bacterial genotype in the pathogenesis of this syndrome.

Nosocomial infections caused by antibiotic-resistantKlebsiella pneumoniaeare emerging as a major health problem worldwide, while community-acquiredK. pneumoniaeinfections present with a range of diverse clinical pictures in different geographic areas. In particular, an invasive form ofK. pneumoniaethat causes liver abscesses was first observed in Asia and then was found worldwide. We are interested in how differences in gene content of the same species result in different diseases. Thus, we sequenced the whole genome ofK. pneumoniaeNTUH-K2044, which was isolated from a patient with liver abscess and meningitis, and analyzed differences compared to strain MGH 78578, which was isolated from a patient with pneumonia. Six major types of differences were found in gene clusters that included an integrative and conjugative element, clusters involved in citrate fermentation, lipopolysaccharide synthesis, and capsular polysaccharide synthesis, phage-related insertions, and a cluster containing fimbria-related genes. We also conducted comparative genomic hybridization with 15K. pneumoniaeisolates obtained from community-acquired or nosocomial infections using tiling probes for the NTUH-K2044 genome. Hierarchical clustering revealed three major groups of genomic insertion-deletion patterns that correlate with the strains' clinical features, antimicrobial susceptibilities, and virulence phenotypes with mice. Here we report the whole-genome sequence ofK. pneumoniaeNTUH-K2044 and describe evidence showing significant genomic diversity and sequence acquisition amongK. pneumoniaepathogenic strains. Our findings support the hypothesis that these factors are responsible for the changes that have occurred in the disease profile over time.

Background. Taiwan established a nationwide surveillance system for human immunodeficiency virus (HIV) infection in 1989 and adopted a policy to prov

The severe acute respiratory syndrome–associated coronavirus (SARS-CoV) is thought to be transmitted primarily through dispersal of droplets, but little is known about the load of SARS-CoV in oral droplets. We examined oral specimens, including throat wash and saliva, and found large amounts of SARS-CoV RNA in both throat wash (9.58 x 102 to 5.93 x 106 copies/mL) and saliva (7.08 x 103 to 6.38 x 108 copies/mL) from all specimens of 17 consecutive probable SARS case-patients, supporting the possibility of transmission through oral droplets. Immunofluorescence study showed replication of SARS-CoV in the cells derived from throat wash, demonstrating the possibility of developing a convenient antigen detection assay. This finding, with the high detection rate a median of 4 days after disease onset and before the development of lung lesions in four cases, suggests that throat wash and saliva should be included in sample collection guidelines for SARS diagnosis.