Background: The emerging pks‐positive (pks⁺) strains have aroused great public concern recently. Colibactin, encoded by pks gene cluster, has been reported to be involved in DNA damage and increased virulence. Little is known about its prevalence among Klebsiella pneumoniae‐induced bloodstream infections (BSIs). Therefore, the aim of this study was to investigate the prevalence of pks gene cluster, and molecular and clinical characteristics of K pneumoniae‐induced BSIs.Methods: A total of 190 non‐duplicate K pneumoniae bloodstream isolates were collected at a university hospital in China from March 2016 to March 2018. Molecular characteristics including capsular types, virulence, and pks genes were detected by polymerase chain reaction (PCR). Clinical characteristics and antimicrobial susceptibility were also investigated.Results: Overall, 21.6% (41/190) of K pneumoniae bloodstream isolates were hypervirulent K pneumoniae(hvKP). The prevalence of pks gene cluster was 26.8% (51/190). The positive rates of K1, K57, and genes associated with hypervirulence, that is, rmpA, wcaG, mrkD, allS, ybtS, kfu,and iucA, were significantly higher in the pks⁺isolates than the pks‐negative (pks⁻) isolates (P < 0.05), while the pks⁺ isolates were significantly less resistant to 11 antimicrobial agents than the pks⁻ isolates. Multivariate analysis showed diabetes mellitus, and K1 and K20 capsular types as independent risk factors for pks⁺ K pneumoniaebloodstream infections.Conclusions: The pks⁺ K pneumoniae was prevalent in individuals with bloodstream infections in mainland China. The high rates of hypervirulent determinants among pks⁺ K pneumoniaerevealed the potential pathogenicity of this emerging gene cluster. Diabetes mellitus, and K1 and K20 capsular types were identified as independent risk factors associated with pks⁺ K pneumoniaebloodstream infections. This study highlights the significance of clinical awareness and epidemic surveillance of pks⁺strains.

The objectives of this study were to determine CTX-M-producing Escherichia coli ST131 strain prevalence in stool specimens from healthy subjects in central China and to molecularly characterize clonal groups. From November 2013 to January 2014, stool specimens from healthy individuals in Hunan Province were screened for ESBL-producing E. coli using chromogenic medium and CTX-M genotypes and phylogenetic groups were determined. ST131 clonal groups were detected by PCR and characterized for antibiotic resistance, fimH, gyrA and parC alleles, plasmid-mediated quinolone resistance determinants, virulence genotypes and PFGE patterns. Among 563 subjects, 287 (51.0%) exhibited the presence of faecal ESBL-producing E. coli, all of which produced CTX-M enzymes. The most common CTX-M genotypes were CTX-M-14 (48.4%), CTX-M-15 (27.5%) and CTX-M-27 (15.0%). Of the 287 CTX-M-producing isolates, 32 (11.1%) belonged to the ST131 clone. O16-ST131 isolates were dominant (75%) and contained the fimH41 allele. The remaining eight (25%) ST131 isolates were of the O25b subgroup and contained fimH30 or fimH41. Ciprofloxacin resistance was found in 100% of the O25b-ST131 isolates, whereas only 8% of the O16-ST131 isolates were resistant. All of the O25b-ST131 isolates except one showed gyrA1AB and parC1aAB mutations; most of the O16-ST131 isolates had gyrA1A and parC1b mutations. The virulence genotypes of O16-ST131 resembled those of the O25b-ST131 isolates. The 32 ST131 isolates formed one large group at the 64% similarity level. They comprised 15 PFGE groups (defined at ≥85% similarity). O16-ST131 isolates have emerged as the predominant type of ST131 isolate in faecal CTX-M-producing E. coli in healthy individuals in China.

Dissemination of hypervirulent and carbapenem-resistant Klebsiella pneumoniae (CRKP) has been reported worldwide, posing a serious threat to antimicrobial therapy and public health. Outer membrane vesicles (OMVs) act as vectors for the horizontal transfer of virulence and resistance genes.

Clostridium difficile toxin B (cdtB) is a critical virulence factor characterized with potential cytotoxicity and pro-inflammatory activity. This study aims to investigate anti-tumor effects of cdtB on breast cancer development. Clostridium difficile strain was cultured and cdtB recombinant protein (rcdtB) was synthesized. Breast cancer cell line, MDA-MB-231, was divided into Normal control, rcdtB 50, 100, 200 and 400 ng/ml group in vitro. Mice were divided into Normal control and rcdtB treatment group (400 ng/ml) in vivo. 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay was performed to evaluate inhibitive effects of rcdtB on cell growth. Flow cytometry and transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) were employed to examine apoptosis in vitro and in vivo, respectively. Cell cycle distribution was analyzed by utilizing commercial kit. B-cell lymphoma-2 (Bcl-2) and Bcl-2-associated X protein (Bax) were examined using western blot. Inflammatory response was detected using haematoxylin and eosin (HE). Erythroblastic leukemia viral oncogene homolog 2 (C-erbB-2) and cyclooxygenase-2 (Cox-2) were examined using immunohistochemical and immunofluorescence assay, respectively. The results indicated that rcdtB significantly induced MDA-MB-231 death, inhibited growth and decreased S-phase cells compared to Normal control group (P < 0.05). rcdtB significantly induced early and late apoptosis, and decreased Bcl-2 levels compared to Normal control group (P < 0.05). rcdtB significantly inhibited cell migration compared to Normal control group (P < 0.05). rcdtB significantly inhibited tumor growth and activated inflammation of breast cancer model compared to Normal control group (P < 0.01). rcdtB significantly reduced C-erbB-2 and Cox-2 in tumor tissues compared to Normal control group (P < 0.01). In conclusion, rcdtB treatment inhibited tumor growth and induced apoptosis through inhibiting Bcl-2 expression, inflammatory responses, and activating C-erbB-2 and Cox-2 expression in breast cancer mouse model.