dKlebsiella pneumoniae is an important human pathogen associated with a variety of diseases, and the prevalence of multidrugresistant K. pneumoniae (MDRKP) is rapidly increasing. Here we determined the capsular types of 85 carbapenem-resistant K. pneumoniae (CRKP) strains by wzc sequencing and investigated the presence of carbapenemases and integrons among CRKP strains. Ten CRKP strains (12%) were positive for carbapenemase (imipenemase, 6/85 strains; K. pneumoniae carbapenemase, 3/85 strains; Verona integron-encoded metallo-␤-lactamase, 1/85 strains). Capsular type K64 accounted for 32 CRKP strains (38%), followed by K62 (13%), K24 (8%), KN2 (7%), and K28 (6%). Sequence types (STs) were determined by multilocus sequence typing (MLST), and the results indicated that ST11, which accounted for 47% of these CRKP strains (40/85 strains), was the major ST. We further isolated a K64-specific capsule depolymerase (K64dep), which could enhance serum and neutrophil killing in vitro and increase survival rates for K64 K. pneumoniae-inoculated mice. The toxicity study demonstrated that mice treated with K64dep showed normal biochemical parameters and no significant histopathological changes of liver, kidney, and spleen, indicating that enzyme treatment did not cause toxicity in mice. Therefore, the findings of capsular type clustering among CRKP strains and effective treatment with capsule depolymerase for MDRKP infections are important for capsule-based vaccine development and therapy.K lebsiella pneumoniae, a Gram-negative bacillus, causes hospital or community-acquired disease (1-3). Most K. pneumoniae strains harbor chromosome-encoded SHV ␤-lactamase (4). In 1983, the emergence of K. pneumoniae strains producing a mutant of SHV-1 ␤-lactamase that hydrolyzes extended-spectrum cephalosporins was observed in Germany (5); subsequently, K. pneumoniae strains resistant to third-generation cephalosporins were detected in France, and a new ␤-lactamase gene closely related to TEM-1 and TEM-2 was identified (6). In 1989, the CTX-M type was reported as a new extended-spectrum ␤-lactamase (ESBL) family member not belonging to either the TEM type or the SHV type (7), and subsequently it was considered one of the major ESBL types (8). Recent global surveillance data from Europe, North and South America, and Asia revealed that the frequency of ESBL-producing K. pneumoniae was 7.5 to 44% (9). As the prevalence of ESBL-producing isolates increased, carbapenems were used to treat serious infections caused by ESBL-producing K. pneumoniae. However, carbapenem-resistant K. pneumoniae (CRKP) rates have been dramatically increasing worldwide over the past 10 years. In the United States, a significant increase in CRKP prevalence from Ͻ1% in 2000 to 8% in 2007 was reported (10). In addition, data from the National Healthcare Safety Network (NHSN) showed that, in 2006 and 2007, CRKP was reported for up to 10.8% of total isolates associated with certain device-related infections (11). In Italy, CRKP increased rapidly from 1 to 2% in 2006 to 2009...

The genome of the multihost bacteriophage ⌽K64-1, capable of infecting Klebsiella capsular types K1, K11, K21, K25, K30, K35, K64, and K69, as well as new capsular types KN4 and KN5, was analyzed and revealed that 11 genes (S1-1, S1-2, S1-3, S2-1, S2-2, S2-3, S2-4, S2-5, S2-6, S2-7, and S2-8) encode proteins with amino acid sequence similarity to tail fibers/spikes or lyases. S2-5 previously was shown to encode a K64 capsule depolymerase (K64dep). Specific capsule-degrading activities of an additional eight putative capsule depolymerases (S2-4 against K1, S1-1 against K11, S1-3 against K21, S2-2 against K25, S2-6 against K30/K69, S2-3 against K35, S1-2 against KN4, and S2-1 against KN5) was demonstrated by expression and purification of the recombinant proteins. Consistent with the capsular type-specific depolymerization activity of these gene products, phage mutants of S1-2, S2-2, S2-3, or S2-6 lost infectivity for KN4, K25, K35, or K30/K69, respectively, indicating that capsule depolymerase is crucial for infecting specific hosts. In conclusion, we identified nine functional capsule depolymerase-encoding genes in a bacteriophage and correlated activities of the gene products to all ten hosts of this phage, providing an example of type-specific host infection mechanisms in a multihost bacteriophage.IMPORTANCE We currently identified eight novel capsule depolymerases in a multihost Klebsiella bacteriophage and correlated the activities of the gene products to all hosts of this phage, providing an example of carriage of multiple depolymerases in a phage with a wide capsular type host spectrum. Moreover, we also established a recombineering system for modification of Klebsiella bacteriophage genomes and demonstrated the importance of capsule depolymerase for infecting specific hosts. Based on the powerful tool for modification of phage genome, further studies can be conducted to improve the understanding of mechanistic details of Klebsiella phage infection. Furthermore, the newly identified capsule depolymerases will be of great value for applications in capsular typing.KEYWORDS Klebsiella, bacteriophage, capsular type, capsule depolymerase, multiple host T he genus Klebsiella, especially the species Klebsiella pneumoniae, is an important human pathogen that causes a wide range of diseases, including both community and hospital-acquired infections. It is associated with septicemia, pneumonia, and urinary tract infections (1, 2) and also is responsible for a globally emerging disease, pyogenic liver abscess complicated with metastatic meningitis and endophthalmitis (3,4).Klebsiella spp. typically display a layer of thick, polysaccharide-based capsule on their surfaces. The expression of diverse capsule structure caused by different sugar compositions and linkages divide them into distinct serotypes. In addition, genetic