Anti-biofilm activities and antibiotic synergy of naturally occurring compounds against drug-resistant rapidly growing mycobacteria.

Some naturally occurring compounds, known for their antimicrobial activities, have been employed as food additives. However, their efficacy in treating infections caused by antibiotic-resistant bacteria is yet to be fully explored. Rapidly growing mycobacteria (RGM), a category within nontuberculous mycobacteria (NTM), are prevalent in various environments and can lead to infections in humans. The rise of antimicrobial resistance within RGM is a documented concern. In this study, we reported that four specific natural compounds effectively inhibited the growth and biofilm formation of three key RGM pathogens M. abscessus, M. fortuitum, and M. chelonae. We screened 12 natural compounds for their effectiveness against antibiotic-resistant clinical strains of RGM. Four compounds showed significant inhibitory effects from the most effective to least: trans-cinnamaldehyde, carvacrol, gentisaldehyde, and phloroglucinaldehyde. In the analysis of time-killing kinetics, gentisaldehyde and phloroglucinaldehyde displayed bactericidal activity while trans-cinnamaldehyde and carvacrol exhibited bacteriostatic effects. At 1× minimal inhibition concentrations, these compounds significantly reduced biofilm formation in all three RGM species to levels between 2.9% and 20.5% relative to controls. Checkerboard assays indicated synergistic interactions between these four compounds and antibiotics such as amikacin, clarithromycin, and linezolid. Of these 12 compound-antibiotic combinations, the pairs of carvacrol-linezolid, carvacrol-amikacin, and gentisaldehyde-clarithromycin demonstrated the most synergy against multiple RGM strains. Moreover, two other compounds citral and geraniol showed synergism with all three test antibiotics. Time-killing assays further confirmed most of synergistic combinations identified in the checkerboard tests. Our research suggests the potential of these essential oils and phenolic aldehydes, both individually and in combination with antibiotics, in treating RGM infections. In addition, this work illuminates applications of these natural compounds in environmental remediation to mitigate bacterial persistence for the control of infectious diseases. IMPORTANCE: The emergence of antimicrobial resistance within rapidly growing mycobacteria (RGM) poses a significant threat to public health. This study investigates the potential of naturally occurring compounds to combat infections caused by antibiotic-resistant RGM including M. abscessus, M. fortuitum, and M. chelonae. We identified four specific natural compounds showing impressive inhibitory effects against antibiotic-resistant clinical strains. These compounds not only inhibited the growth and biofilm formation but also exhibited synergistic interactions with antibiotics against key RGM pathogens. Our findings highlight the alternative treatment strategies for RGM infections and potential environmental applications of these natural compounds in mitigating microbial persistence and controlling infectious diseases.

Distinctive microbial community and genome structure in coastal seawater from a human-made port and nearby offshore island in northern Taiwan facing the Northwestern Pacific Ocean.

Pollution in human-made fishing ports caused by petroleum from boats, dead fish, toxic chemicals, and effluent poses a challenge to the organisms in seawater. To decipher the impact of pollution on the microbiome, we collected surface water from a fishing port and a nearby offshore island in northern Taiwan facing the Northwestern Pacific Ocean. By employing 16S rRNA gene amplicon sequencing and whole-genome shotgun sequencing, we discovered that Rhodobacteraceae, Vibrionaceae, and Oceanospirillaceae emerged as the dominant species in the fishing port, where we found many genes harboring the functions of antibiotic resistance (ansamycin, nitroimidazole, and aminocoumarin), metal tolerance (copper, chromium, iron and multimetal), virulence factors (chemotaxis, flagella, T3SS1), carbohydrate metabolism (biofilm formation and remodeling of bacterial cell walls), nitrogen metabolism (denitrification, N2 fixation, and ammonium assimilation), and ABC transporters (phosphate, lipopolysaccharide, and branched-chain amino acids). The dominant bacteria at the nearby offshore island (Alteromonadaceae, Cryomorphaceae, Flavobacteriaceae, Litoricolaceae, and Rhodobacteraceae) were partly similar to those in the South China Sea and the East China Sea. Furthermore, we inferred that the microbial community network of the cooccurrence of dominant bacteria on the offshore island was connected to dominant bacteria in the fishing port by mutual exclusion. By examining the assembled microbial genomes collected from the coastal seawater of the fishing port, we revealed four genomic islands containing large gene-containing sequences, including phage integrase, DNA invertase, restriction enzyme, DNA gyrase inhibitor, and antitoxin HigA-1. In this study, we provided clues for the possibility of genomic islands as the units of horizontal transfer and as the tools of microbes for facilitating adaptation in a human-made port environment.

Diabetes and obesity and risk of pyogenic liver abscess.

Few literatures discussed the relationship of glycemic control and body mass index (BMI) with the risk of pyogenic liver abscess. We conducted a population-based cohort study using participants of a community-based health screening program in Taiwan from 2005 to 2008 (n = 125,865). Information on fasting plasma glucose (FPG), BMI, and other potential risk factors of liver abscess were collected at baseline. Incidence of pyogenic liver abscess was ascertained using inpatient records from the National Health Insurance database. During a median 8.6 years of followed up, 192 incident cases of pyogenic liver abscess were reported. The incidence rate of pyogenic liver abscess was 70.2 and 14.7 per 100,000 in the diabetic and non-diabetic population respectively. In multivariable Cox regression analysis, the adjusted hazard ratio (HR) was 2.18 (95% confidence interval (CI) 1.22-3.90) in patients with diabetes with good glycemic control (FPG ≤ 130 mg/dl) and 3.34 (95% CI 2.37-4.72) in those with poor glycemic control (FPG > 130 mg/dl), when compared with non-diabetics. In the dose-response analysis, the risk of liver abscess increased monotonically with increasing FPG. After adjusting for diabetes and other comorbidities, overweight (25 ≤ BMI < 30) (adjusted HR: 1.43, 95% CI 1.05-1.95) and obese (BMI ≥ 30) (adjusted HR: 1.75, 95% CI 1.09-2.81) populations had a higher risk of liver abscess when compared to people with normal weight. Diabetes, especially poorly controlled disease, and high BMI were associated with higher risk of pyogenic liver abscess. Improving glycemic control and weight reduction may reduce the risk of developing pyogenic liver abscess.

A hexasaccharide from capsular polysaccharide of carbapenem-resistant Klebsiella pneumoniae KN2 is a ligand of Toll-like receptor 4.

Klebsiella pneumoniae serotype KN2 is a carbapenem-resistant strain and leads to the health care-associated infections, such as bloodstream infections. Its capsular polysaccharide (CPS) was isolated and cleaved by a specific enzyme from a bacteriophage into a hexasaccharide-repeating unit. With GC-MS, NMR, and Mass analyses, the structure of KN2 CPS was determined to be {→3)-ß-D-Glcp-(1→3)-[α-D-GlcpA-(1→4)-ß-D-Glcp-(1→6)]-α-D-Galp-(1→6)-ß-D-Galp-(1→3)-ß-D-Galp-(1→}n. We demonstrated that 1 µg/mL CPS could stimulate J774A.1 murine macrophages to release tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in vitro. Also, we proved that KN2 CPS induced the immune response through Toll-like receptor 4 (TLR4) in the human embryonic kidney (HEK)-293 cells. Strikingly, the hexasaccharide alone shows the same immune response as the CPS, suggesting that the hexasaccharide can shape the adaptive immunity to be a potential vaccine adjuvant. The glucuronic acid (GlcA) on other polysaccharides can affect the immune response, but the GlcA-reduced KN2 CPS and hexasaccharide still maintain their immunomodulatory activities.

Identification of three podoviruses infecting Klebsiella encoding capsule depolymerases that digest specific capsular types.

Klebsiella pneumoniae is an important human pathogen causing opportunistic nosocomial and community-acquired infections. A major public health concern regarding K. pneumoniae is the increasing incidence of multidrug-resistant strains. Here, we isolated three novel Klebsiella bacteriophages, KN1-1, KN3-1 and KN4-1, which infect KN1, KN3 and K56, and KN4 types respectively. We determined their genome sequences and conducted a comparative analysis that revealed a variable region containing capsule depolymerase-encoding genes. Recombinant depolymerase proteins were produced, and their enzymatic activity and specificity were evaluated. We identified four capsule depolymerases in these phages that could only digest the capsule types of their respective hosts. Our results demonstrate that the activities of these capsule depolymerases were correlated with the host range of each phage; thus, the capsule depolymerases are host specificity determinants. By generating a capsule mutant, we demonstrate that capsule was essential for phage adsorption and infection. Further, capsule depolymerases can enhance bacterial susceptibility to serum killing. The discovery of these phages and depolymerases lays the foundation for the typing of KN1, KN3, KN4 and K56 Klebsiella and could be useful alternative therapeutics for the treatment of K. pneumoniae infections.

A Novel Role for the Klebsiella pneumoniae Sap (Sensitivity to Antimicrobial Peptides) Transporter in Intestinal Cell Interactions, Innate Immune Responses, Liver Abscess, and Virulence.

Klebsiella pneumoniae is an important human pathogen causing hospital-acquired and community-acquired infections. Systemic K. pneumoniae infections may be preceded by gastrointestinal colonization, but the basis of this bacterium's interaction with the intestinal epithelium remains unclear. Here, we report that the K. pneumoniae Sap (sensitivity to antimicrobial peptides) transporter contributes to bacterial-host cell interactions and in vivo virulence. Gene deletion showed that sapA is required for the adherence of a K. pneumoniae blood isolate to intestinal epithelial, lung epithelial, urinary bladder epithelial, and liver cells. The ΔsapA mutant was deficient for translocation across intestinal epithelial monolayers, macrophage interactions, and induction of proinflammatory cytokines. In a mouse gastrointestinal infection model, ΔsapA yielded significantly decreased bacterial loads in liver, spleen and intestine, reduced liver abscess generation, and decreased mortality. These findings offer new insights into the pathogenic interaction of K. pneumoniae with the host gastrointestinal tract to cause systemic infection.

Using the Chinese herb Scutellaria barbata against extensively drug-resistant Acinetobacter baumannii infections: in vitro and in vivo studies.

BACKGROUND: No animal model studies have been conducted in which the efficacy of herbal compounds has been tested against multidrug-resistant Acinetobacter baumannii infections. Very few antibiotics are available for the treatment of pulmonary infections caused by extensively drug-resistant Acinetobacter baumannii (XDRAB). To find alternative treatments, traditional Chinese herbs were screened for their antimicrobial potential. METHODS: The present study screened 30 herbs that are traditionally used in Taiwan and that are commonly prescribed for heat clearing and detoxification. The herbs with antibacterial activities were analysed by disc diffusion assays, time-kill assays and a murine lung infection model. RESULTS: Of the 30 herbs tested, only Scutellaria barbata demonstrated 100% in vitro activity against XDRAB. Furthermore, we compared the antibacterial effect of the S. barbata extract with that of colistin, and the S. barbata extract showed better antibacterial effect. In the XDRAB pneumonia murine model, we compared the antimicrobial effects of the orally administered S. barbata extract (200 mg/kg, every 24 h), the intratracheally administered colistin (75,000 U/kg, every 12 h), and the control group. The bacterial load in the lungs of the treatment group that received the oral S. barbata extract showed a significant decrease in comparison to that in the lungs of the control group. In addition, histopathological examinations also revealed better resolution of perivascular, peribronchial, and alveolar inflammation in the oral S. barbata extract-treated group. CONCLUSIONS: Our in vitro and in vivo data from the animal model support the use of S. barbata as an alternate drug to treat XDRAB pulmonary infections. However, detailed animal studies and clinical trials are necessary to establish the clinical utility of S. barbata in treating XDRAB pulmonary infections.

Imipenem represses CRISPR-Cas interference of DNA acquisition through H-NS stimulation in Klebsiella pneumoniae.

Analysis of the genome of Klebsiella pneumoniae NTUH-K2044 strain revealed the presence of two clustered regularly interspaced short palindromic repeats (CRISPR) arrays separated with CRISPR-associated (cas) genes. Carbapenem-resistant K. pneumoniae isolates were observed to be less likely to have CRISPR-Cas than sensitive strains (5/85 vs. 22/132). Removal of the transcriptional repressor, H-NS, was shown to prevent the transformation of plasmids carrying a spacer and putative proto-spacer adjacent motif (PAM). The CRISPR-Cas system also decreased pUC-4K plasmid stability, resulting in plasmid loss from the bacteria with acquisition of new spacers. Analysis of the acquired proto-spacers in pUC-4K indicated that 5'-TTN-3' was the preferred PAM in K. pneumoniae. Treatment of cells by imipenem induced hns expression, thereby decreasing cas3 expression and consequently repressed CRISPR-Cas activity resulted in increase of plasmid stability. In conclusion, NTUH-K2044 CRISPR-Cas contributes to decrease of plasmid transformation and stability. Through repression of CRISPR-Cas activity by induced H-NS, bacteria might be more able to acquire DNA to confront the challenge of imipenem.

Identification of a capsular variant and characterization of capsular acetylation in Klebsiella pneumoniae PLA-associated type K57.

Klebsiella pneumoniae can cause community-acquired pyogenic liver abscess (PLA). Capsular polysaccharide (CPS) is important for its virulence. Among 79 capsular (K) types discovered thus far, K57 is often associated with PLA. Here, we report the identification of a K57 variant. Cps gene locus sequencing revealed differences between the K57 reference strain 4425/51 (Ref-K57) and a variant, the PLA isolate A1142. While Ref-K57 cps contained orf13 encoding a putative acetyltransferase, the insertion of a putative transposase-encoding gene at this position was detected in A1142. This variation was detected in other K57 clinical strains. Biochemical analyses indicated that A1142 was deficient in CPS acetylation. Genetic replacement and complementation verified that orf13 was responsible for CPS acetylation. Acetylation increased CPS immunoreactivity to antiserum and enhanced K. pneumoniae induction of pro-inflammatory cytokines through JNK and MAPK signaling. While acetylation diminished the serum resistance of bacteria, it promoted adhesion to intestinal epithelial cells possibly via increasing production of type I fimbriae. In conclusion, acetylation-mediated capsular variation in K57 was observed. Capsular acetylation contributed to the variety and antigenic diversity of CPS, influenced its biological activities, and was involved in K. pneumoniae-host interactions. These findings have implications for vaccine design and pathogenicity of K. pneumoniae.

The Klebsiella pneumoniae YfgL (BamB) lipoprotein contributes to outer membrane protein biogenesis, type-1 fimbriae expression, anti-phagocytosis, and in vivo virulence.

Klebsiella pneumoniae is an opportunistic pathogen that causes several kinds of infections, including pneumonia, bacteremia, urinary tract infection and community-acquired pyogenic liver abscess (PLA). Adhesion is the critical first step in the infection process. Our previous work demonstrated that the transcellular translocation is exploited by K. pneumoniae strains to migrate from the gut flora into other tissues, resulting in systemic infections. However, the initial stages of K. pneumoniae infection remain unclear. In this study, we demonstrated that a K. pneumoniae strain deleted for yfgL (bamB) exhibited reduced adherence to and invasion of host cells; changed biogenesis of major ß-barrel outer membrane proteins; decreased transcriptional expression of type-1 fimbriae; and increased susceptibility to vancomycin and erythromycin. The yfgL deletion mutant also had reduced ability to against neutrophil phagocytosis; exhibited decreased induction of host IL-6 production; and was profoundly attenuated for virulence in a K. pneumoniae model of bacteremia. Thus, the K. pneumoniae YfgL lipoprotein mediates in outer membrane proteins biogenesis and is crucial for anti-phagocytosis and survival in vivo. These data provide a new insight for K. pneumoniae attachment and such knowledge could facilitate preventive therapies or alternative therapies against K. pneumoniae.

Genetic analysis of capsular polysaccharide synthesis gene clusters in 79 capsular types of Klebsiella spp.

A total of 79 capsular types have been reported in Klebsiella spp., whereas capsular polysaccharide synthesis (cps) regions were available in only 22 types. Due to the limitations of serotyping, complete repertoire of cps will be helpful for capsular genotyping. We therefore resolved the rest 57 cps and conducted comparative analysis. Clustering results of 1,515 predicted proteins from cps loci categorized proteins which share similarity into homology groups (HGs) revealing that 77 Wzy polymerases were classified into 56 HGs, which indicate the high specificity of wzy between different types. Accordingly, wzy-based capsular genotyping could differentiate capsule types except for those lacking wzy (K29 and K50), those sharing identical wzy (K22 vs. K37); and should be carefully applied in those exhibited high similarity (K12 vs. K41, K2 vs. K13, K74 vs. K80, K79 vs. KN1 and K30 vs. K69). Comparison of CPS structures in several capsular types that shared similarity in their gene contents implies possible functions of glycosyltransferases. Therefore, our results provide complete set of cps in various types of Klebsiella spp., which enable the understandings of relationship between genes and CPS structures and are useful for identification of documented or new capsular types.

Klebsiella pneumoniae translocates across the intestinal epithelium via Rho GTPase- and phosphatidylinositol 3-kinase/Akt-dependent cell invasion.

Klebsiella pneumoniae is an important pathogen that causes hospital-acquired septicemia and is associated with the recent emergence of community-acquired pyogenic liver abscess (PLA). Clinical typing suggests that K. pneumoniae infections originate from the gastrointestinal reservoir. However, the underlying mechanism remains unknown. Here, we have sought to determine how K. pneumoniae penetrates the intestinal barrier. We identified that bacteremia and PLA clinical isolates adhered to and invaded intestinal epithelial cells. Internalization of K. pneumoniae in three different human colonic cell lines was visualized by confocal microscopy and three-dimensional (3D) imaging. Using a Transwell system, we demonstrated that these K. pneumoniae isolates translocated across a polarized Caco-2 monolayer. No disruptions of transepithelial electrical resistance and altered distribution of tight junction protein ZO-1 or occludin were observed. Therefore, K. pneumoniae appeared to penetrate the intestinal epithelium via a transcellular pathway. Using specific inhibitors, we characterized the host signaling pathways involved. Inhibition by cytochalasin D and nocodazole suggested that actin and microtubule cytoskeleton were both important for K. pneumoniae invasion. A Rho inhibitor, ML141, LY294002, and an Akt1/2 inhibitor diminished K. pneumoniae invasion in a dose-dependent manner, indicating that Rho family GTPases and phosphatidylinositol 3-kinase (PI3K)/Akt signaling were required. By a mouse model of gastrointestinal colonization, in vivo invasion of K. pneumoniae into colonic epithelial cells was demonstrated. Our results present evidence to describe a possible mechanism of gastrointestinal translocation for K. pneumoniae. Cell invasion by manipulating host machinery provides a pathway for gut-colonized K. pneumoniae cells to penetrate the intestinal barrier and access extraintestinal locations to cause disease.

Identification of capsular types in carbapenem-resistant Klebsiella pneumoniae strains by wzc sequencing and implications for capsule depolymerase treatment.

Klebsiella pneumoniae is an important human pathogen associated with a variety of diseases, and the prevalence of multidrug-resistant 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-ß-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.

Isolation of a bacteriophage and its depolymerase specific for K1 capsule of Klebsiella pneumoniae: implication in typing and treatment.

BACKGROUND: Klebsiella pneumoniae causing community-acquired pyogenic liver abscess complicated with metastatic meningitis and endophthalmitis has emerged recently, most frequently associated with the K1 capsular type. METHODS: A bacteriophage (NTUH-K2044-K1-1) that infects K. pneumoniae NTUH-K2044 (capsular type K1) was isolated and characterized. RESULTS: The phage infected all K1 strains, and none of the strains with other capsular types. Capsule deletion mutants were not lysed by this phage, suggesting that the capsule was essential for phage infection. Complete genome sequencing revealed the phage was a novel phiKMV-like virus. The gene-encoding capsule depolymerase was identified. The recombinant enzyme demonstrated specific lysis of the K1 capsule. Treatment with the phage or the recombinant enzyme provided significantly increased survival in mice infected with NTUH-K2044 strain, including one treated after the detection of a neck abscess by imaging. No obvious disease was observed after administration of this phage in mice. Phage was retained at detectable levels in liver, spleen, brain, and blood 24 hours after administration in mice. CONCLUSIONS: These results demonstrate this phage and its capsule depolymerase exhibit specificity for capsular type K1 and can be used for the diagnosis and treatment of K1 K. pneumoniae infections.

Capsular types of Klebsiella pneumoniae revisited by wzc sequencing.

Capsule is an important virulence factor in bacteria. A total of 78 capsular types have been identified in Klebsiella pneumoniae. However, there are limitations in current typing methods. We report here the development of a new genotyping method based on amplification of the variable regions of the wzc gene. Fragments corresponding to the variable region of wzc were amplified and sequenced from 76 documented capsular types of reference or clinical strains. The remaining two capsular types (reference strains K15 and K50) lacked amplifiable wzc genes and were proven to be acapsular. Strains with the same capsular type exhibited ≧94% DNA sequence identity across the variable region (CD1-VR2-CD2) of wzc. Strains with distinct K types exhibited <80% DNA sequence identity across this region, with the exception of three pairs of strains: K22/K37, K9/K45, and K52/K79. Strains K22 and K37 shared identical capsular polysaccharide synthesis (cps) genes except for one gene with a difference at a single base which resulted in frameshift mutation. The wzc sequences of K9 and K45 exhibited high DNA sequence similarity but possessed different genes in their cps clusters. K52 and K79 exhibited 89% wzc DNA sequence identity but were readily distinguished from each other at the DNA level; in contrast, strains with the same capsular type as K52 exhibited 100% wzc sequence identity. A total of 29 strains from patients with bacteremia were typed by the wzc system. wzc DNA sequences confirmed the documented capsular type for twenty-eight of these clinical isolates; the remaining strain likely represents a new capsular type. Thus, the wzc genotyping system is a simple and useful method for capsular typing of K. pneumoniae.

Isolation of a bacteriophage specific for a new capsular type of Klebsiella pneumoniae and characterization of its polysaccharide depolymerase.

BACKGROUND: Klebsiella pneumoniae is one of the major pathogens causing hospital-acquired multidrug-resistant infections. The capsular polysaccharide (CPS) is an important virulence factor of K. pneumoniae. With 78 capsular types discovered thus far, an association between capsular type and the pathogenicity of K. pneumoniae has been observed. METHODOLOGY/PRINCIPAL FINDINGS: To investigate an initially non-typeable K. pneumoniae UTI isolate NTUH-K1790N, the cps gene region was sequenced. By NTUH-K1790N cps-PCR genotyping, serotyping and determination using a newly isolated capsular type-specific bacteriophage, we found that NTUH-K1790N and three other isolates Ca0507, Ca0421 and C1975 possessed a new capsular type, which we named KN2. Analysis of a KN2 CPS(-) mutant confirmed the role of capsule as the target recognized by the antiserum and the phage. A newly described lytic phage specific for KN2 K. pneumoniae, named 0507-KN2-1, was isolated and characterized using transmission electron microscopy. Whole-genome sequencing of 0507-KN2-1 revealed a 159 991 bp double-stranded DNA genome with a G+C content of 46.7% and at least 154 open reading frames. Based on its morphological and genomic characteristics, 0507-KN2-1 was classified as a member of the Myoviridae phage family. Further analysis of this phage revealed a 3738-bp gene encoding a putative polysaccharide depolymerase. A recombinant form of this protein was produced and assayed to confirm its enzymatic activity and specificity to KN2 capsular polysaccharides. KN2 K. pneumoniae strains exhibited greater sensitivity to this depolymerase than these did to the cognate phage, as determined by spot analysis. CONCLUSIONS/SIGNIFICANCE: Here we report that a group of clinical strains possess a novel Klebsiella capsular type. We identified a KN2-specific phage and its polysaccharide depolymerase, which could be used for efficient capsular typing. The lytic phage and depolymerase also have potential as alternative therapeutic agents to antibiotics for treating K. pneumoniae infections, especially against antibiotic-resistant strains.

The role of Klebsiella pneumoniae rmpA in capsular polysaccharide synthesis and virulence revisited.

Klebsiella pneumoniae community-acquired pyogenic liver abscess (PLA) is an emerging infectious disease. The rmpA gene (for regulator of mucoid phenotype A) has been reported to be associated with PLA in prevalence studies. NTUH-K2044, a K1 PLA isolate, carries three rmpA/A2 genes: two large-plasmid-carried genes (p-rmpA and p-rmpA2) and one chromosomal gene (c-rmpA). In this study, we re-examined the role of rmpA/A2 in PLA pathogenesis to clarify the relationship of rmpA/A2 and capsular serotype to virulence. Using isogenic gene deletion strains and complemented strains of NTUH-K2044, we demonstrated that only p-rmpA enhanced expression of capsular polysaccharide synthesis (cps) genes and capsule production. Nevertheless, the lethal dose and in vivo competitive index indicated that p-rmpA does not promote virulence in mice. The prevalence of these three rmpA/A2 and capsular types in 206 strains was investigated. This revealed a correlation of rmpA/A2 with six PLA-related capsular types (K1, K2, K5, K54, K57 and KN1). However, the correlation of rmpA/A2 with K1 strains from the West was less obvious than with the strains from Asia (17/22 vs 39/39, P = 0.0019). Among the three rmpA/A2 genes, p-rmpA was the most prevalent. Due to the strong correlation with PLA-related capsular types, p-rmpA could serve as a surrogate marker for PLA. We found an association of p-rmpA with three widely spaced loci in a large plasmid (30/32). Therefore, rmpA could be co-inherited together with virulence genes carried by this plasmid.

Use of a Dictyostelium model for isolation of genetic loci associated with phagocytosis and virulence in Klebsiella pneumoniae.

Phagocytosis resistance is an important virulence factor in Klebsiella pneumoniae. Dictyostelium has been used to study the interaction between phagocytes and bacteria because of its similarity to mammalian macrophages. In this study, we used a Dictyostelium model to investigate genes for resistance to phagocytosis in NTUH-K2044, a strain of K. pneumoniae causing pyogenic liver abscess that is highly resistant to phagocytosis. A total of 2,500 transposon mutants were screened by plaque assay, and 29 of them permitted phagocytosis by Dictyostelium. In the 29 mutants, six loci were identified; three were capsular synthesis genes. Of the other three, one was related to carnitine metabolism, one encoded a subunit of protease (clpX), and one encoded a lipopolysaccharide O-antigen transporter (wzm). Deletion and complementation of these genes showed that only ΔclpX and Δwzm mutants became susceptible to Dictyostelium phagocytosis, and their complementation restored the phagocytosis resistance phenotype. These two mutants were also susceptible to phagocytosis by human neutrophils and revealed attenuated virulence in a mouse model, implying that they play important roles in the pathogenesis of K. pneumoniae. Furthermore, we demonstrated that clpP, which exists in an operon with clpX, was also involved in resistance to phagocytosis. The transcriptional profile of ΔclpX was examined by microarray analysis and revealed a 3-fold lower level of expression of capsular synthesis genes. Therefore, we have identified genes involved in resistance to phagocytosis in K. pneumoniae using Dictyostelium, and this model is useful to explore genes associated with resistance to phagocytosis in heavily encapsulated bacteria.

Possible DNA viral factors of human breast cancer.

Viruses are considered to be one of the high-risk factors closely related to human breast cancer. However, different studies of viruses in breast cancer present conflicting results and some of these works remain in dispute. DNA viruses, such as specific types of human papillomaviruses (HPV), Epstein-Barr virus (EBV), human cytomegalovirus (HCMV), herpes simplex virus (HSV), and human herpes virus type 8 (HHV-8), have emerged as causal factors of some human cancers. These respective exogenous viruses and the possibility of multiple viral factors are discussed in this review.