Norihito Kaku

In vitro and in vivo activities of piperacillin-tazobactam and meropenem at different inoculum sizes of ESBL-producing Klebsiella pneumoniae

The inoculum effect is a laboratory phenomenon in which the minimal inhibitory concentration (MIC) of an antibiotic is increased when a large number of organisms are exposed. Due to the emergence of extended-spectrum β-lactamase-producing Klebsiella pneumoniae (ESBL-Kpn) infections, the inoculum effect of ESBL-Kpn on β-lactams was studied in vitro and in vivo using an experimental model of pneumonia. The in vitro inoculum effect of 45 clinical ESBL-Kpn isolates on β-lactams was evaluated at standard (10(5) CFU/mL) and high (10(7) CFU/mL) organism concentrations. The MIC50 of piperacillin-tazobactam, cefotaxime and cefepime was increased eight-fold or more and that of meropenem was increased two-fold. The in vivo inoculum effect was evaluated in an ESBL-Kpn pneumonia mouse model treated with bacteriostatic effect-adjusted doses of piperacillin-tazobactam (1000 mg/kg four times daily, %T>MIC; 32.60%) or meropenem (100 mg/kg twice daily, %T>MIC; 28.65%) at low/standard (10(4) CFU/mouse) and high (10(6) CFU/mouse) inocula. In mice administered a low inoculum, no mice died after treatment with piperacillin-tazobactam or meropenem, whereas all the control mice died. In contrast, in the high inoculum model, all mice in the piperacillin-tazobactam-treated group died, whereas all meropenem-treated mice survived and had a decreased bacterial load in the lungs and no invasion into the blood. In conclusion, meropenem was more resistant to the inoculum effect of ESBL-Kpn than piperacillin-tazobactam both in vitro and in vivo. In the management of severe pneumonia caused by ESBL-Kpn, carbapenems may be the drugs of choice to achieve a successful outcome.

Influence of antimicrobial regimen on decreased in-hospital mortality of patients with MRSA bacteremia

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most important causes of bacteremia. Recently, several epidemiological and microbiological changes have become evident in MRSA infections. The purposes of this study were to assess clinical characteristics of patients with MRSA bacteremia and microbiological changes in MRSA. We conducted a retrospective observational study on patients with MRSA bacteremia who were hospitalized between 2008 and 2011. We used univariate and multivariate analysis to evaluate the predictors associated with 30-day mortality. The 7-day and 30-day mortality rates were 12.0% and 25.3%, respectively. According to multivariate analysis, the independent predictors that associated with 30-day mortality were leukopenia, low serum albumin, high sequential organ failure assessment (SOFA) score, and quinolone use within 30 days. Compared to previous data (2003-2007), the SOFA score of the new data set remained unchanged, but in-hospital mortality decreased significantly. In particular, the mortality associated with use of vancomycin (VCM) was significantly lower. Although the minimum inhibitory concentration of VCM required to inhibit the growth of 90% of organisms (MIC90) had not changed, the trough value of VCM changed significantly; a VCM trough value of 10 or greater was significantly higher compared to previous data. Of the staphylococcal cassette chromosome mec (SCCmec) types, SCCmec II values decreased significantly, and SCCmec I and IV values increased significantly. Our results indicate that changes in VCM usage might contribute to decreased in-hospital mortality.

Azithromycin Attenuates Lung Inflammation in a Mouse Model of Ventilator-Associated Pneumonia by Multidrug-Resistant Acinetobacter baumannii

ABSTRACT Acinetobacter baumannii is one of the main pathogens that cause ventilator-associated pneumonia (VAP) and is associated with a high rate of mortality. Little is known about the efficacy of macrolides against A. baumannii. In order to confirm the efficacy of azithromycin (AZM) against VAP caused by multidrug-resistant A. baumannii (MDRAB), we used a mouse model that mimics VAP by placement of a plastic tube in the bronchus. AZM (10 and 100 mg/kg of body weight) was administered subcutaneously every 24 h beginning at 3 h after inoculation. Phosphate-buffered saline was administered as the control. Survival was evaluated over 7 days. At 48 h postinfection, mice were sacrificed and the numbers of viable bacteria in lungs and bronchoalveolar lavage fluid were compared. Histopathological analysis of lung specimens was also performed. The treatment groups displayed significantly longer survival than the control group (P < 0.05). AZM did not have an antimicrobial effect. Histopathological examination of lung specimens indicated that the progression of lung inflammation was prevented in the AZM-treated groups. Furthermore, total cell and neutrophil counts, as well as cytokine levels, in bronchoalveolar lavage fluid were significantly decreased (P < 0.05) in the AZM-treated groups. AZM may have a role for the treatment of VAP with MDRAB because of its anti-inflammatory effects.

In vivo efficacy of biapenem with ME1071, a novel metallo-β-lactamase (MBL) inhibitor, in a murine model mimicking ventilator-associated pneumonia caused by MBL-producing Pseudomonas aeruginosa

ME1071, a maleic acid derivative, is a novel, specific inhibitor of metallo-β-lactamases (MBLs). In vitro, ME1071 can potentiate the activity of carbapenems against MBL-producing Pseudomonas aeruginosa. To confirm the clinical efficacy of ME1071 in ventilator-associated pneumonia (VAP) caused by MBL-producing P. aeruginosa, a mouse model that mimics VAP by placement of a plastic tube in the bronchus was used. Biapenem (100 mg/kg) or ME1071 plus biapenem (each 100 mg/kg) was administered intraperitoneally every 12 h beginning at 12 h after inoculation. Survival was evaluated over 7 days. At 30 h post infection, mice were sacrificed and the numbers of viable bacteria in the lungs and bronchoalveolar lavage fluid (BALF) were compared. Histopathological analysis of lung specimens was also performed. The pharmacokinetics of ME1071 was analysed after initial treatment. The ME1071 plus biapenem combination group displayed significantly longer survival compared with the control and biapenem monotherapy groups (P<0.05). Furthermore, the number of viable bacteria in the lungs was significantly lower in the combination group (P<0.05). Histopathological examination of lung specimens indicated that progression of lung inflammation was prevented in the combination group. Furthermore, total cell and neutrophil counts, as well as cytokine levels, in BALF were significantly decreased (P<0.05) in the combination group. The percentage time above the MIC (%T>MIC) for biapenem without ME1071 was 0% in plasma; however, this value was elevated to 10.8% with ME1071. These results suggest that ME1071 is potent and effective for treatment of VAP caused by MBL-producing P. aeruginosa.

Azithromycin inhibits MUC5AC induction via multidrug-resistant Acinetobacter baumannii in human airway epithelial cells

Acinetobacter baumannii is one of the main pathogens that cause ventilator-associated pneumonia (VAP). Hypersecretion of mucin in the airway is associated with the onset of VAP. Furthermore, macrolides are known to accelerate the resolution of VAP. However, this mechanism has not been elucidated. We examined whether macrolides inhibit MUC5AC production that is induced by multidrug-resistant A. baumannii (MDRAB). MUC5AC production in bronchial cells after MDRAB stimulation was analyzed by enzyme-linked immunosorbent assay and quantitative reverse transcription-polymerase chain reaction. For the inhibition study, cells were treated with azithromycin (AZM) or clarithromycin (CAM) simultaneously along with MDRAB stimulation. Western blotting was performed was performed to determine potential rules for signal modules. MDRAB induced MUC5AC production and gene expression. The EGFR-ERK/JNK-NF-κB pathway was involved in MDRAB-induced MUC5AC production. AZM but not CAM inhibited MUC5AC production. AZM suppressed the phosphorylation of ERK/JNK and the nuclear translocation of NF-κB. Our results suggest that the efficacy of macrolides against VAP may be due to the inhibition of mucin production.

Immunomodulatory Effect of Linezolid on Methicillin-Resistant Staphylococcus aureus Supernatant-Induced MUC5AC Overexpression in Human Airway Epithelial Cells

ABSTRACT Linezolid is the first member of the oxazolidinones and is active against drug-resistant Gram-positive pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA). Additionally, linezolid shows an immunomodulatory effect, such as inhibition of inflammatory cytokine production. In this study, we examined the effect of linezolid on MRSA-induced MUC5AC overexpression in airway epithelial cells. In this study, an MRSA supernatant was used to avoid the direct effect of linezolid on MRSA. MUC5AC protein production was significantly increased with a 40-fold dilution of MRSA supernatant. At the mRNA level, MUC5AC gene expression was significantly increased 6 and 9 h after stimulation. In an inhibition study, linezolid significantly reduced MRSA-induced MUC5AC protein and mRNA overexpression at concentrations of 5 and 20 μg/ml, which were the same as the trough and peak concentrations in human epithelial lining fluid. In an analysis of cell signaling, among the mitogen-activated protein kinase inhibitors, only the extracellular signal-regulated protein kinase 1/2 (ERK1/2) inhibitor reduced the MUC5AC protein production to the same level as that of the control; on Western blot analysis, only ERK1/2 was phosphorylated by the MRSA supernatant. In addition, the ERK1/2 phosphorylation was inhibited by linezolid. MUC5AC and MUC5B are the major barrier that traps inhaled microbial organisms, particulates, and foreign irritants. However, in patients with chronic respiratory diseases, pathogen-induced MUC5AC overexpression causes many problems, and control of the overexpression is important. Thus, this study revealed that linezolid showed a direct immunomodulatory effect in airway epithelial cells.

Antimicrobial and immunomodulatory effects of tedizolid against methicillin-resistant Staphylococcus aureus in a murine model of hematogenous pulmonary infection.

Tedizolid (TZD) is a second-generation oxazolidinone and demonstrates potent in-vitro activity against multidrug-resistant Gram-positive bacteria. Phase III studies in patients with acute bacterial skin and skin structure infections (ABSSSI) have demonstrated the non-inferiority of TZD to linezolid (LZD). However, there are only a few studies that show the effect of TZD in pulmonary infections. In this study, we investigated the effect of TZD in a murine model of hematogenous pulmonary infection caused by methicillin-resistant Staphylococcus aureus (MRSA). The mice were treated either twice daily with saline (control), 25mg/kg of vancomycin (low-VAN), 110mg/kg of vancomycin (high-VAN), 120mg/kg of LZD or once daily with 20mg/kg of TZD. As compared to the control, the low- and high-VAN treatment groups, LZD and TZD significantly improved the survival rate, reduced the bacterial count in the lungs. Furthermore, TZD decreased the area of central bacterial colony zone (CBCZ) at 36h post-inoculation, compared with the control. In addition, we investigated the immunomodulatory effect of TZD by evaluating the plasma concentrations of the inflammatory cytokines. Although there were no significant differences in the bacterial count in the lungs amongst the drugs at 26h post-inoculation, TZD and LZD significantly improved the plasma concentrations of TNF-alpha, IL-6 and MIP-2, in comparison with the control. In this study, both TZD and LZD demonstrated antimicrobial and immunomodulatory efficacy in a murine model of hematogenous pulmonary infection caused by MRSA.

Strong influence of human leukocyte antigen-DP variants on response to hepatitis B vaccine in a Japanese population

Genome-wide association studies (GWASs) have reported that human leukocyte antigen (HLA) variants are associated with chronic hepatitis B, spontaneous hepatitis B virus (HBV) clearance, and response to hepatitis B vaccine. Single nucleotide polymorphisms (SNPs) in HLA-DP (rs9277535 and rs3077) and HLA-DQ (rs2856718 and rs7453920) have been repeatedly associated with chronic hepatitis B and spontaneous HBV clearance. However, the data on the SNPs associated with response to hepatitis B vaccine are inconclusive. The objective of this study was to determine whether these four HLA SNPs that have been identified as risk loci for chronic HBV infection are associated with response to hepatitis B vaccine in a Japanese population. We enrolled 278 medical students who received hepatitis B vaccination and measured anti-hepatitis B surface (HBs) antibody titers 1month after a three-dose vaccination series. We found that rs9277535 and rs3077 in HLA-DP were strongly associated with response to hepatitis B vaccine (odds ratio [OR]=0.31 and 0.32, P=0.004 and 0.010, respectively). These two SNPs were significantly associated with anti-HBs titers in an allele-dependent manner. On the other hand, rs2856718 and rs7453920 in HLA-DQ were not associated with response to hepatitis B vaccine. These results indicate that rs9277535 and rs3077 in HLA-DP are the major determinants of response to hepatitis B vaccine, whereas rs2856718 and rs7453920 in HLA-DQ have little effect on the immune response to hepatitis B vaccine.

Fluoroquinolone resistance in extended-spectrum β-lactamase-producing Klebsiella pneumoniae in a Japanese tertiary hospital: silent shifting to CTX-M-15-producing K. pneumoniae

Purpose. Fluoroquinolone resistance (FQ‐r) in extended‐spectrum β‐lactamase (ESBL) producers is an urgent health concern in countries where ESBL‐producing K. pneumoniae (ESBL‐Kpn) is prevalent. We investigated FQ‐r in Japan where ESBL‐Kpn is less prevalent. Methodology. Clinical ESBL‐Kpn isolates from 2011 to 2013 were collected in Nagasaki University Hospital. The ESBL genotypes included CTX‐M‐15, and the mechanisms of FQ‐r through plasmid‐mediated quinolone resistance (PMQR) and mutations in quinolone resistance‐determining regions (QRDRs) were examined. Clonality was analysed by enterobacterial repetitive intergenic consensus (ERIC)‐PCR and multi‐locus sequence typing was performed on selected isolates. Results/Key findings. Thirty ESBL‐Kpn isolates, including seven levofloxacin‐resistant isolates, were obtained from different patients. An increase in CTX‐M‐15‐producing strains was observed during the study period (0/11 in 2011, 3/8 in 2012, and 5/11 in 2013). PMQR was detected in 53.3% of the isolates and aac‐(6′)‐Ib‐cr was the most common (36.7 %). ST15 was observed in 60.0% of the isolates, and for the most predominant ERIC‐PCR profiles, 62.5% of the isolates possessed the CTX‐M‐15 genotype and 71.4% were levofloxacin‐resistant. Levofloxacin‐resistance was significantly more common in CTX‐M‐15 isolates (62.5 %) compared to non‐CTX‐M‐15 isolates (9.1 %). Three QRDR mutations and aac(6′)‐Ib‐cr, but not qnrB and qnrS, were significantly enriched in the CTX‐M‐15 isolates (100.0 %) compared to the non‐CTX‐M‐15 isolates (13.6 %). Conclusion. Cumulatively, these results indicate that the epidemic strain, the CTX‐M‐15‐producing K. pneumoniae ST15, is covertly spreading even when ESBL producers are not prevalent. Monitoring these epidemic strains and ESBLs in general is important for quickly identifying health crises and minimizing future risks from FQ‐r ESBL‐Kpn.

TNF-α inhibits the growth of Legionella pneumophila in airway epithelial cells by inducing apoptosis.

BACKGROUND TNF-α plays an important role in the pathogenesis of Legionella pneumophila (Lp)-induced pneumonia. Patients undergoing anti-TNF-α therapy are at an increased risk of Lp infection. Lp infects both phagocytic and non-phagocytic cells such as airway epithelial cells; however, the role of TNF-α in airway epithelial cells is unknown. METHODS Human airway epithelial cell line NCI-H292 was infected with Lp NUL1 strain. After infection, both intracellular growth of Lp and cell death were evaluated after treating the cells with or without TNF-α. Apoptosis was examined by performing activated caspase-3/7 staining and by using a pan-caspase inhibitor. RESULTS Lp infected and replicated in NCI-H292 cells in a time-dependent manner, and TNF-α treatment of Lp-infected NCI-H292 cells inhibited Lp replication. Inhibitory effects of TNF-α on Lp replication were suppressed after treatment with a TNF-α-neutralizing antibody. Lp infection increased extracellular lactate dehydrogenase levels and decreased the number of living cells. Increased number of Lp-infected NCI-H292 cells showed caspase-3/7 activation, indicating they underwent apoptosis. TNF-α treatment inhibited Lp replication by increasing the apoptosis of NCI-H292 cells. CONCLUSIONS Thus, our results suggested that airway epithelial cells were involved in the pathogenesis of Lp infection and that TNF-α played a protective role by inhibiting the intracellular replication of Lp and by increasing the apoptosis of Lp-infected airway epithelial cells. However, Lp infection should be investigated further in patients undergoing anti-TNF-α therapy who develop pneumonia.