Karen Bush

Carbapenemases: the versatile beta-lactamases.

SUMMARY Carbapenemases are β-lactamases with versatile hydrolytic capacities. They have the ability to hydrolyze penicillins, cephalosporins, monobactams, and carbapenems. Bacteria producing these β-lactamases may cause serious infections in which the carbapenemase activity renders many β-lactams ineffective. Carbapenemases are members of the molecular class A, B, and D β-lactamases. Class A and D enzymes have a serine-based hydrolytic mechanism, while class B enzymes are metallo-β-lactamases that contain zinc in the active site. The class A carbapenemase group includes members of the SME, IMI, NMC, GES, and KPC families. Of these, the KPC carbapenemases are the most prevalent, found mostly on plasmids in Klebsiella pneumoniae. The class D carbapenemases consist of OXA-type β-lactamases frequently detected in Acinetobacter baumannii. The metallo-β-lactamases belong to the IMP, VIM, SPM, GIM, and SIM families and have been detected primarily in Pseudomonas aeruginosa; however, there are increasing numbers of reports worldwide of this group of β-lactamases in the Enterobacteriaceae. This review updates the characteristics, epidemiology, and detection of the carbapenemases found in pathogenic bacteria.

A Randomized, Double-Blind Trial Comparing Ceftobiprole Medocaril with Vancomycin plus Ceftazidime for the Treatment of Patients with Complicated Skin and Skin-Structure Infections

BACKGROUNDnA randomized, double-blind, multicenter trial involving patients with a broad range of complicated skin and skin-structure infections due to either gram-positive or gram-negative bacteria was conducted to compare ceftobiprole monotherapy with treatment with vancomycin plus ceftazidime.nnnMETHODSnPatients were randomized 2:1 to receive ceftobiprole or to receive vancomycin plus ceftazidime. Outcomes were determined at a test-of-cure visit (7-14 days after completion of therapy) and were analyzed for all patients with complicated skin and skin-structure infections, as well as for subgroups, on the basis of major types of infections and severity of disease.nnnRESULTSnAmong the clinically evaluable and the intent-to-treat populations, clinical cure rates at the test-of-cure visit were similar in the ceftobiprole and comparator treatment arms (clinical cure rate, 90.5% [439 of 485 patients] and 90.2% [220 of 244 patients] in the clinically evaluable population, respectively; 81.9% [448 of 547 patients] and 80.8% [227 of 281 patients] in the intent-to-treat population, respectively). Clinical cure rates in ceftobiprole-treated patients ranged from 86.2% (125 of 145 patients) among those with diabetes who had foot infections to 93.0% (80 of 86 patients) among those with cellulitis. Among patients treated with ceftobiprole, clinical cure rates were similar among patients from whom gram-negative bacteria were isolated (87.9% [109 of 124 patients]) and among patients from whom gram-positive bacteria were isolated (91.8% [292 of 318 patients]) and were not statistically different from the clinical cure rates among comparator-treated patients (89.7% [61 of 68 patients] and 90.3% [149 of 165 patients], respectively). Rates of adverse events and serious adverse events in the 2 treatment groups were similar.nnnCONCLUSIONSnCeftobiprole monotherapy is as effective as vancomycin plus ceftazidime for treating patients with a broad range of complicated skin and skin-structure infections and infections due to gram-positive and gram-negative bacteria.

Novel plasmid-mediated beta-lactamase (TEM-10) conferring selective resistance to ceftazidime and aztreonam in clinical isolates of Klebsiella pneumoniae.

Two clinical isolates of Klebsiella pneumoniae from seriously ill patients in Chicago, Ill., have been identified as resistant to ceftazidime and aztreonam but susceptible to other cephalosporins. This unusual antibiogram was shown to be due to a novel plasmid-mediated beta-lactamase which readily hydrolyzed ceftazidime and aztreonam in addition to penicillins such as piperacillin and carbenicillin. This enzyme and its attendant resistance were transferred to Escherichia coli by conjugation on a 50-kilobase plasmid. Isoelectric focusing revealed a single beta-lactamase band with a molecular weight of 29,000 and an isoelectric point of 5.57 in the resistant isolates and transconjugants. The beta-lactamase inhibitors clavulanic acid and sulbactam restored beta-lactam susceptibility in the resistant isolates. Fifty percent inhibitory concentrations of clavulanic acid and sulbactam were 4.4 and 940 nM, respectively. DNA hybridization studies indicated that this enzyme, designated TEM-10, is related to well-established TEM-type beta-lactamases. However, the TEM-10 enzyme was inhibited by p-chloromercuribenzoate, in contrast to TEM-2 beta-lactamase. On the basis of substrate and inhibition profiles, the TEM-10 enzyme could be easily discriminated from TEM-5 and RHH-I beta-lactamases. Images

Binding of Ceftobiprole and Comparators to the Penicillin-Binding Proteins of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus pneumoniae

ABSTRACT Ceftobiprole exhibited tight binding to PBP2a in methicillin-resistant Staphylococcus aureus, PBP2x in penicillin-resistant Streptococcus pneumoniae, and PBP3 and other essential penicillin-binding proteins in methicillin-susceptible S. aureus, Escherichia coli, and Pseudomonas aeruginosa. Ceftobiprole also bound well to PBP2 in the latter organisms, contributing to the broad-spectrum antibacterial activity against gram-negative and gram-positive bacteria.

Interactions of Ceftobiprole with β-Lactamases from Molecular Classes A to D

ABSTRACT The interactions of ceftobiprole with purified β-lactamases from molecular classes A, B, C, and D were determined and compared with those of benzylpenicillin, cephaloridine, cefepime, and ceftazidime. Enzymes were selected from functional groups 1, 2a, 2b, 2be, 2d, 2e, and 3 to represent β-lactamases from organisms within the antibacterial spectrum of ceftobiprole. Ceftobiprole was refractory to hydrolysis by the common staphylococcal PC1 β-lactamase, the class A TEM-1 β-lactamase, and the class C AmpC β-lactamase but was labile to hydrolysis by class B, class D, and class A extended-spectrum β-lactamases. Cefepime and ceftazidime followed similar patterns. In most cases, the hydrolytic stability of a substrate correlated with the MIC for the producing organism. Ceftobiprole and cefepime generally had lower MICs than ceftazidime for AmpC-producing organisms, particularly AmpC-overexpressing Enterobacter cloacae organisms. However, all three cephalosporins were hydrolyzed very slowly by AmpC cephalosporinases, suggesting that factors other than β-lactamase stability contribute to lower ceftobiprole and cefepime MICs against many members of the family Enterobacteriaceae.

Anti-MRSA β-lactams in development, with a focus on ceftobiprole: the first anti-MRSA β-lactam to demonstrate clinical efficacy

Ceftobiprole is the first of the investigational β-lactam antibiotics with in vitro activity against methicillin-resistant staphylococci to reach and complete Phase III therapeutic trials. Its antibacterial spectrum includes methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecalis, penicillin-resistant streptococci and many Gram-negative pathogens. It has demonstrated in vivo activity against many experimental infections caused by these pathogens. Ceftobiprole has completed Phase III clinical trials for complicated skin and skin structure infections, is being studied in Phase III pneumonia trials and has demonstrated non-inferiority compared with vancomycin in a Phase III complicated skin and skin structure infections trial, resulting in > 90% clinical cures of infections caused by MRSA. Other anti-MRSA β-lactams in therapeutic clinical trials include the carbapenem CS-023/RO-4908463 and the cephalosporin ceftaroline (PPI-0903). The future of all of these agents will depend on their clinical efficacy, safety and their ability to be accepted as β-lactams for the reliable treatment of a broad spectrum of infections, including those caused by MRSA.

In Vitro Antibacterial Activities of JNJ-Q2, a New Broad-Spectrum Fluoroquinolone

ABSTRACT JNJ-Q2, a novel fluorinated 4-quinolone, was evaluated for its antibacterial potency by broth and agar microdilution MIC methods in studies focused on skin and respiratory tract pathogens, including strains exhibiting contemporary fluoroquinolone resistance phenotypes. Against a set of 118 recent clinical isolates of Streptococcus pneumoniae, including fluoroquinolone-resistant variants bearing multiple DNA topoisomerase target mutations, an MIC90 value for JNJ-Q2 of 0.12 μg/ml was determined, indicating that it was 32-fold more potent than moxifloxacin. Against a collection of 345 recently collected methicillin-resistant Staphylococcus aureus (MRSA) isolates, including 256 ciprofloxacin-resistant strains, the JNJ-Q2 MIC90 value was 0.25 μg/ml, similarly indicating that it was 32-fold more potent than moxifloxacin. The activities of JNJ-Q2 against Gram-negative pathogens were generally comparable to those of moxifloxacin. In further studies, JNJ-Q2 exhibited bactericidal activities at 2× and 4× MIC levels against clinical isolates of S. pneumoniae and MRSA with various fluoroquinolone susceptibilities, and its activities were enhanced over those of moxifloxacin. In these studies, the activity exhibited against strains bearing gyrA, parC, or gyrA plus parC mutations was indicative of the relatively balanced (equipotent) activity of JNJ-Q2 against the DNA topoisomerase target enzymes. Finally, determination of the relative rates or frequencies of the spontaneous development of resistance to JNJ-Q2 at 2× and 4× MICs in S. pneumoniae, MRSA, and Escherichia coli were indicative of a lower potential for resistance development than that for current fluoroquinolones. In conclusion, JNJ-Q2 exhibits a range of antibacterial activities in vitro that is supportive of its further evaluation as a potential new agent for the treatment of skin and respiratory tract infections.

A point mutation in influenza B neuraminidase confers resistance to peramivir and loss of slow binding

The influenza neuraminidase (NA) inhibitors peramivir, oseltamivir, and zanamivir are potent inhibitors of NAs from both influenza A and B strains. In general, these inhibitors are slow, tight binders of NA, exhibiting time-dependent inhibition. A mutant of influenza virus B/Yamagata/16/88 which was resistant to peramivir was generated by passage of the virus in tissue culture, in the presence of increasing concentrations (0.1-120 microM over 15 passages) of the compound. Whereas the wild type (WT) virus was inhibited by peramivir with an EC(50) value of 0.10 microM, virus isolated at passages 3 and 15 displayed EC(50) values of 10 and >50 microM, respectively. Passage 3 virus contained 3 hemagglutinin (HA) mutations, but no NA mutation. Passage 15 (P15R) virus contained an additional 3 HA mutations, plus the NA mutation His273Tyr. The mechanism of inhibition of WT and P15R NA by peramivir was examined in enzyme assays. The WT and P15R NAs displayed IC(50) values of 8.4+/-0.4 and 127+/-16 nM, respectively, for peramivir. Peramivir inhibited the WT enzyme in a time-dependent fashion, with a K(i) value of 0.066+/-0.002nM. In contrast, the P15R enzyme did not display the property of slow binding and was inhibited competitively with a K(i) value of 4.69+/-0.44nM. Molecular modeling suggested that His273 was relatively distant from peramivir (>5A) in the NA active site, but that Tyr273 introduced a repulsive interaction between the enzyme and inhibitor, which may have been responsible for peramivir resistance.

New agents in development for the treatment of bacterial infections.

New antibacterial agents to treat infections caused by antibiotic-susceptible and antibiotic-resistant pathogens are in various stages of clinical development. In this review are compounds with demonstrated activity against methicillin-resistant staphylococci including investigational cephalosporins, carbapenems, and a new tetracycline, as well as glycopeptides effective against vancomycin-resistant enterococci (VRE), and fluoroquinolones with improved potency against respiratory pathogens and multidrug-resistant Gram-positive bacteria. Although most recent progress has occurred in the identification of agents for Gram-positive infections, broad-spectrum carbapenems are described for the treatment of multidrug-resistant Gram-negative pathogens. Also discussed are agents with mechanisms of action other than inhibition of protein synthesis, penicillin-binding proteins, and DNA topoisomerases; among these are inhibitors of bacterial fatty acid biosynthesis, peptidoglycan synthesis, and dihydrofolate reductase.

SME-3, a Novel Member of the Serratia marcescens SME Family of Carbapenem-Hydrolyzing β-Lactamases

ABSTRACT Imipenem-resistant Serratia marcescens isolates were cultured from a lung transplant patient given multiple antibiotics over several months. The strains expressed SME-3, a β-lactamase of the rare SME carbapenem-hydrolyzing family. SME-3 differed from SME-1 by a single amino acid substitution of tyrosine for histidine at position 105, but the two β-lactamases displayed similar hydrolytic profiles.