In Vitro and In Vivo Activities of OP0595, a New Diazabicyclooctane, against CTX-M-15-Positive Escherichia coli and KPC-Positive Klebsiella pneumoniae.

Gram-negative bacteria are evolving to produce ß-lactamases of increasing diversity that challenge antimicrobial chemotherapy. OP0595 is a new diazabicyclooctane serine ß-lactamase inhibitor which acts also as an antibiotic and as a ß-lactamase-independent ß-lactam "enhancer" against Enterobacteriaceae Here we determined the optimal concentration of OP0595 in combination with piperacillin, cefepime, and meropenem, in addition to the antibacterial activity of OP0595 alone and in combination with cefepime, in in vitro time-kill studies and an in vivo infection model against five strains of CTX-M-15-positive Escherichia coli and five strains of KPC-positive Klebsiella pneumoniae An OP0595 concentration of 4 µg/ml was found to be sufficient for an effective combination with all three ß-lactam agents. In both in vitro time-kill studies and an in vivo model of infection, cefepime-OP0595 showed stronger efficacy than cefepime alone against all ß-lactamase-positive strains tested, whereas OP0595 alone showed weaker or no efficacy. Taken together, these data indicate that combinational use of OP0595 and a ß-lactam agent is important to exert the antimicrobial functions of OP0595.

Investigations on yearly changes in tebipenem susceptibility of bacterial isolates from pediatric patients -A post-marketing surveillance of tebipenem pivoxil granules for pediatric.

We conducted the post-marketing surveillance of tebipenem pivoxil (Orapeneme fine granules 10% for pediatric), an oral carbapenem antibacterial agent, to investigate changes in bacterial susceptibility against tebipenem (TBPM). Bacterial strains used in this surveillance were methicillin-susceptible Staphylococcus aureus (MSSA: 303 strains), Streptococcus pneumoniae (554 strains), other Streptococcus spp. (242 strains: including Streptococcus pyogenes 133 strains), Moraxella catarrhalis (306 strains) and Haemophilus influenzae (506 strains) isolated from pediatric patients in 15 medical facilities in Japan between April 2010 and March 2015. Investigation was conducted three times (April 2010-March 2011, April 2012-March 2013 and April 2014-March 2015), and in any of these investigation periods, there were a large number of isolates from infants in terms of the frequency of isolates by age. The MIC90s of TBPM against MSSA, S. pneumoniae, other Streptococcus spp., M. catarrhalis and H. influenzae in these investigations were 0.015-0.03, 0.06, 0.008-0.015 (0.002 for S. pyogenes), 0.03 and 0.5-1 µg/mL, respectively, which were less than 2-fold, and a remarkable increase in MIC90 was not shown. On the other hand, the MIC50s of carbapenems including TBPM and penicillins against S. pneumoniae decreased to 1/4-1/8 during the investigation periods, and decreased gPRSP*¹ (48.7% - 26.1%) and increased gPISP (2x)*² (24.1% -+ 46.8%) were suggested to be involved in these changes in susceptibility. In S. pneumoniae, a decrease of macrolides-resistant strains due to mefA*³ (38.5% - 18.8%) and an increase of macrolides-resistant strains due to ermB*4 (41.7% - 62.4%) were noted. In H. influenzae, the frequencies of gBLNAR*5 and ß-lactamase-producing strains were about 60-70% and 7-9%, respectively, and a remarkable change in susceptibility was not shown. As a result of investigations in the susceptibility of clinical isolates collected from pediatric patients as post-marketing surveillance, there was no decrease in TBPM susceptibility noted.

[Effect of diet on the pharmacokinetics of tebipenem pivoxil fine granules in healthy male volunteers].

Tebipenem pivoxil (TBPM-PI), a novel oral carbapenem antibiotic, is a prodrug of tebipenem (TBPM). We assessed the pharmacokinetics of TBPM-PI fine granules at 250 mg as potency in healthy male volunteers in fasting and non-fasting states. Cmax of TBPM in the non-fasting state was lowered to approximately 60% of that in the fasting state, however AUC(0-infinity) and urinary excretion of TBPM in the non-fasting state were almost equivalent to those in the fasting state when TBPM-PI fine granules were administered. In conclusion, the absorption rate of TBPM-PI was reduced in the non-fasting state after the administration of TBPM-PI fine granules, but intake of food had little influence on the absorption amount of TBPM. Thus the effect of diets on the pharmacokinetics of TBPM-PI would raise no problem in clinical use of TBPM-PI.

In vitro and in vivo activities of the diazabicyclooctane OP0595 against AmpC-derepressed Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a common cause for healthcare-associated infections, which have been historically treated by antipseudomonal ß-lactam agents in the clinical setting. However, P. aeruginosa has evolved to overcome these ß-lactam agents via multiple endogenous resistance mechanisms, including derepression of the chromosomal cephalosporinase (AmpC). In this article, we investigated the effective concentration of OP0595 for combination with piperacillin, cefepime or meropenem in in vitro susceptibility tests, and the antibacterial activity of cefepime in combination with OP0595 in both in vitro time-kill studies and in vivo murine thigh infection model study with AmpC-derepressed P. aeruginosa. The sufficient combinational concentration of OP0595 was a 4 µg ml-1 with all these three ß-lactam agents. OP0595 increased the antibacterial activity of cefepime in both in vitro and in vivo studies against all strains tested. Taken together, OP0595 is the diazabicyclooctane serine ß-lactamase inhibitor with activity against AmpC-derepressed P. aeruginosa and its combinational use with a ß-lactam agent will provide a new approach for the treatment of P. aeruginosa infections.

[Antimicrobial activity of fosfomycin under various conditions against standard strains, beta-lactam resistant strains, and multidrug efflux system mutants].

The purpose of this study was to evaluate the possible benefit of fosfomycin (FOM) as prophylactic antibiotic in terms of antimicrobial activity and the potential of inducibility of beta-lactamase, compared with cefazolin, cefotiam, cefmetazole, and piperacillin that are commonly used as perioperative agents. The in vitro activity of FOM against aerobic Gram-negative bacteria using Mueller-Hinton agar or nutrient agar supplemented with glucose-6-phosphate (G6P) as tested medium increased within a range from 2 to 256 times the activity in the medium without G6P. However, the susceptibility of Gram-positive bacteria to FOM remained largely unchanged with or without G6P. There was no aerobic- or anaerobic-bacteria which changed susceptibility against beta-lactam antibiotics under various tested medium conditions. FOM demonstrated strong bactericidal activity against Escherichia coli and Pseudomonas aeruginosa in a dose dependent manner, and decreased viable cell counts of Staphylococcus aureus. In the case of P. aeruginosa, transmission electron micrographs study revealed that numerous lysed cells were present 2 hours after treatment with FOM at four times the MIC. First and second generation cephalosporins induced AmpC-type beta-lactamase in a dose dependent manner among beta-lactamase inducible strains of P. aeruginosa and Enterobacter cloacae. On the other hand, inducible activity of FOM on beta-lactamase production was less than 1/25 to 1/65 compared with those of cephalosporins. In addition, FOM maintained strong antimicrobial activity for over then 20 years after marketing, because of the excellent stability against various types of beta-lactamase produced by plasmid-carrying bacteria and clinical isolates. FOM was not extruded by four types of efflux systems, such as MexAB-OprM, MexCD-OprJ, MexXY/ OprM and MexEF-OprN, however beta-lactam antibiotics were substrates of MexAB-OprM and MexCD-OprJ. In conclusion, FOM provides adequate coverage for both aerobic Gram-positive and Gram-negative bacteria causing postoperative infections. Further, FOM would not select/concentrate beta-lactamase producing bacteria in the clinical fields and would not be a substrate for multidrug efflux system of P. aeruginosa.

[Activity of fosfomycin against Escherichia coli O157:H7--morphological changes and production of Shiga toxins].

We examined the effects of fosfomycin (FOM), norfloxacin (NFLX), kanamycin (KM), chloramphenicol (CP), and ampicillin (ABPC) on the morphology of E. coli O157:H7, and the accumulation (cell fraction) and release (medium fraction) of Shiga toxins (Stxs: Stx1 and Stx2) in E. coli O157:H7 three hours after treatment with the antibiotics. For each drug, 16 MIC was used for measurement of the activity at a high drug concentration and 1/4 MIC at a low concentration. At 16 MIC, cell wall synthesis inhibitors, FOM and ABPC, strongly induced lysis of the cell of E. coli KU3342, a strain of E. coli O157:H7. The release of Stx1 was observed, but there was no accumulation of Stxs. Nucleic acid synthesis inhibitor NFLX and protein synthesis inhibitor KM induced partial lysis and short filamentation of the cell, and the accumulation and release of Stxs were low. No morphological change was observed after treatment with protein synthesis inhibitor CP, but the accumulation and release of Stxs by CP were low. At 1/4 MIC, FOM induced strong lysis of the cell, and the release of Stx1 was observed, but there was no accumulation of Stxs. ABPC and NFLX had weak lytic reaction, but induced filamentation of the cell, and the accumulation and release of Stxs were observed. In particular, NFLX significantly induced accumulation and release of Stx2. KM and CP had no effect on the morphology of the cells, and the accumulation of Stx1 was not observed, but there was no release of Stxs. The above-mentioned results support the clinical efficacy of FOM in the control of enterohoemorhagic E. coli infections.

[Combined effects of arbekacin with biapenem against in vitro and in vivo model of a mixture of MRSA and Pseudomonas aeruginosa].

Combined effects of arbekacin (ABK) with biapenem (BIPM) were examined on both in vitro and in vivo model of a mixture of MRSA and Pseudomonas aeruginosa. As a result, significant effect in vitro was observed in combined use of ABK (1/2 MIC) with BIPM (1/4 and 1/2 MIC) against MRSA as compared with ABK or BIPM alone. Against P. aeruginosa combined effect was also observed, showing reduction of viable cells to the limitation of detection within 2 hours. Moreover, with respect to the protective effect on mixed systemic infection of MRSA and P. aeruginosa, the combined treatment with ABK and BIPM showed more excellent efficacy as compared with the single use of each drug.

[Bactericidal activity of biapenem against various efflux system mutants of Pseudomonas aeruginosa].

The bactericidal activity of biapenem, a new carbapenem, against various efflux-mutants of Pseudomonas aeruginosa was compared with those of imipenem, panipenem, meropenem and ceftazidime. The bactericidal activity of biapenem against P. aeruginosa KG5001, a strain deficient in MexAB-OprM, MexCD-OprJ and MexXY-OprM, was very strong compared with those of imipenem and meropenem. In terms of bactericidal activities, biapenem and imipenem had similar activities against P. aeruginosa KG5003, a strain overexpressing MexAB-OprM, as against P. aeruginosa KG5001, however meropenem and ceftazidime had weaker activities against KG5003 than KG5001. The bactericidal activity against P. aeruginosa KG5007, a strain overexpressing MexCD-OprJ, was observed only by biapenem. The bactericidal activity of biapenem was strong and not influenced by all of these three efflux systems.

Pharmacokinetic and pharmacodynamic properties of biapenem, a carbapenem antibiotic, in rat experimental model of severe acute pancreatitis.

OBJECTIVES: It is known that prophylaxis with imipenem reduces the risk of infection accompanying severe acute pancreatitis. In this study,we modified a rat experimental model of severe acute pancreatitis for antibiotic evaluation, and the effect of biapenem was compared with that of imipenem to determine the usefulness of biapenem. METHODS: Severe acute pancreatitis was induced by 5% sodium taurocholate. Antibiotics were subcutaneously administered at 3 and 6 hours and evaluated at 12 hours after the pancreatitis induction. For pharmacokinetic evaluation, antibiotics were subcutaneously administered at 3 hours after the pancreatitis induction. RESULTS: From 3 hours after the induction, bacteria were detected from the pancreas. The total bacterial count increased in a time-dependent manner for 12 hours. Biapenem administration reduced the total bacterial count in the pancreas, as observed in imipenem administration. The plasma concentration of biapenem was almost equivalent to that of imipenem; however, the pancreatic penetration of biapenem was approximately twice that of imipenem in this model. CONCLUSIONS: Biapenem was suggested to be effective in prophylactic treatment of infectious complications as much as imipenem because of its superior penetration to the pancreas in severe acute pancreatitis.

CP5484, a novel quaternary carbapenem with potent anti-MRSA activity and reduced toxicity.

A new series of 1beta-methyl carbapenems possessing a 6,7-disubstituted imidazo[5,1-b]thiazol-2-yl group directly attached to the C-2 position of the carbapenem nucleus was prepared, and the activities of these compounds against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated. To study the effect of basic moieties on anti-MRSA activity, we introduced an amino, or imino, or amidino group at the 6-position of imidazo[5,1-b]thiazole in place of the carbamoylmethyl moiety of CP5068. Anti-MRSA activities of almost all basic group-substituted carbapenems were improved, though some of the compounds showed stronger acute toxicity in mice than IPM. In order to decrease the toxicity without decreasing the activity, we introduced various additional functionalities around the basic moiety. Finally, we obtained CP5484, which has excellent anti-MRSA activity and low acute toxicity.

In vitro short-time killing activity of povidone-iodine (Isodine Gargle) in the presence of oral organic matter.

In order to estimate the clinical efficacy of a povidone-iodine oral antiseptic (PVP-I) on oral bacterial infectious diseases, we studied the effect of oral organic matter on the in vitro killing activity of PVP-I. In addition, we compared the in vitro short-time killing activity of PVP-I with those of other oral antiseptics using mouth-washing and gargling samples collected from healthy volunteers. When any of the mouth-washing and gargling samples was used, the standard (0.23-0.47%) or lower concentrations of PVP-I killed methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, including multidrug-resistant strains, within 15-60 s in the presence of oral organic matter. 0.02% benzethonium chloride (BEC) and 0.002% chlorhexidine gluconate (CHG) did not show effects against MRSA and P. aeruginosa (including multidrug-resistant strains) in mouth-washing and gargling samples even after 60 s. The above-mentioned results show that the in vitro killing activity of the standard concentration of PVP-I was hardly affected by the oral organic matter and that a mouth-washing or gargling solution containing PVP-I has a stronger bactericidal activity than BEC and CHG. Although mouth-washing and gargling samples were obtained from healthy individuals in this study, PVP-I may be used for protection against infections in patients with various diseases, if proper concentrations and usage are encouraged.

Optimization of dose and dose regimen of biapenem based on pharmacokinetic and pharmacodynamic analysis.

Pharmacokinetic and pharmacodynamic (PK/PD) parameters, which are important indices of the therapeutic efficacy of antimicrobials, and the minimum inhibitory concentration (MIC) predictive of clinical efficacy at common clinical doses, were examined for biapenem (BIPM; 300 mg b.i.d.), imipenem/cilastatin (IPM/CS; 500 mg/500 mg b.i.d.), meropenem (MEPM; 500 mg b.i.d.), and ceftazidime (CAZ; 1000 mg b.i.d.), using a mouse model of thigh infection caused by Pseudomonas aeruginosa. The PK/PD parameter that most closely correlated with the therapeutic efficacy of all these antimicrobials was time above MIC (T > MIC). The values of T > MIC predictive of clinical efficacy against P. aeruginosa infection varied among antimicrobials and were >/=17%, >/=17%, >/=23%, and >/=33% for BIPM, IPM/CS, MEPM, and CAZ, respectively. From these values and the known plasma concentrations of the antimicrobials in humans after administration at the common clinical doses, the MIC for bacterial strains at which clinical efficacy can be expected was estimated to be