In vitro activities of RWJ-54428 (MC-02,479) against multiresistant gram-positive bacteria

RWJ-54428 (MC-02,479) is a new cephalosporin with a high level of activity against gram-positive bacteria. In a broth microdilution susceptibility test against methicillin-resistant Staphylococcus aureus (MRSA), RWJ-54428 was as active as vancomycin, with an MIC at which 90% of isolates are inhibited (MIC(90)) of 2 microg/ml. For coagulase-negative staphylococci, RWJ-54428 was 32 times more active than imipenem, with an MIC(90) of 2 microg/ml. RWJ-54428 was active against S. aureus, Staphylococcus epidermidis, and Staphylococcus haemolyticus isolates with reduced susceptibility to glycopeptides (RWJ-54428 MIC range, < or = 0.0625 to 1 microg/ml). RWJ-54428 was eight times more potent than methicillin and cefotaxime against methicillin-susceptible S. aureus (MIC(90), 0.5 microg/ml). For ampicillin-susceptible Enterococcus faecalis (including vancomycin-resistant and high-level aminoglycoside-resistant strains), RWJ-54428 had an MIC(90) of 0.125 microg/ml. RWJ-54428 was also active against Enterococcus faecium, including vancomycin-, gentamicin-, and ciprofloxacin-resistant strains. The potency against enterococci correlated with ampicillin susceptibility; RWJ-54428 MICs ranged between < or = 0.0625 and 1 microg/ml for ampicillin-susceptible strains and 0.125 and 8 microg/ml for ampicillin-resistant strains. RWJ-54428 was more active than penicillin G and cefotaxime against penicillin-resistant, -intermediate, and -susceptible strains of Streptococcus pneumoniae (MIC(90)s, 0.25, 0.125, and < or = 0.0625 microg/ml, respectively). RWJ-54428 was only marginally active against most gram-negative bacteria; however, significant activity was observed against Haemophilus influenzae and Moraxella catarrhalis (MIC(90)s, 0.25 and 0.5 microg/ml, respectively). This survey of the susceptibilities of more than 1,000 multidrug-resistant gram-positive isolates to RWJ-54428 indicates that this new cephalosporin has the potential to be useful in the treatment of infections due to gram-positive bacteria, including strains resistant to currently available antimicrobials.     

In Vitro Activities of a New Ketolide, ABT-773, against Multidrug-Resistant Gram-Positive Cocci

The in vitro activities of ABT-773 were evaluated against 324 strains of gram-positive bacteria, including multidrug-resistant Staphylococcus spp. and Enterococcus spp. ABT-773 had lower MIC ranges, MICs at which 50% of isolates are inhibited (MIC(50)s), and MIC(90)s than erythromycin or clindamycin for almost all isolates tested. The MICs of ABT-773 were also lower than those of quinupristin-dalfopristin (Q-D) for methicillin-susceptible Staphylococcus aureus, Rhodococcus spp., and Streptococcus spp., while the MICs of Q-D were lower than those of ABT-773 for methicillin-resistant S. aureus and Enterococcus faecium, including vancomycin-resistant isolates.     

In Vitro Activity of Josamycin Against Aerobic Gram-Positive Cocci and Anaerobes

Josamycin, a new macrolide antibiotic, was compared with ampicillin, erythromycin, and clindamycin in vitro against 25 isolates each of pneumococci, enterococci, Staphylococcus aureus, S. epidermidis, and nonenterococcal hemolytic streptococci and against 25 anaerobes including 10 Bacteroides fragilis. Minimal inhibitory concentration and minimal bactericidal concentration data were obtained for the aerobic organisms, using serial twofold tube dilutions in Mueller-Hinton broth. Minimal inhibitory concentrations were determined for the anaerobes by the agar dilution technique. Josamycin was comparable to erythromycin and clindamycin in activity against the pneumococci, streptococci, and staphylococci and was more active than clindamycin against enterococci. It was somewhat less active than ampicillin against enterococci and S. epidermidis and showed its greatest in vitro activity against anaerobes, being comparable to clindamycin.     

In Vitro Activity of Ozenoxacin against Quinolone-Susceptible and Quinolone-Resistant Gram-Positive Bacteria

In vitro activity of ozenoxacin, a novel nonfluorinated topical (L. D. Saravolatz and J. Leggett, Clin. Infect. Dis. 37:1210–1215, 2003) quinolone, was compared with the activities of other quinolones against well-characterized quinolone-susceptible and quinolone-resistant Gram-positive bacteria. Ozenoxacin was 3-fold to 321-fold more active than other quinolones. Ozenoxacin could represent a first-in-class nonfluorinated quinolone for the topical treatment of a broad range of dermatological infections.     

Meropenem-Clavulanic Acid Has High In Vitro Activity against Multidrug-Resistant Mycobacterium tuberculosis

We investigated the activity of meropenem-clavulanic acid (MEM-CLA) against 68 Mycobacterium tuberculosis isolates. We included predominantly multi- and extensively drug-resistant tuberculosis (MDR/XDR-TB) isolates, since the activity of MEM-CLA for resistant isolates has previously not been studied extensively. Using Middlebrook 7H10 medium, all but four isolates showed an MIC distribution of 0.125 to 2 mg/liter for MEM-CLA, below the non-species-related breakpoint for MEM of 2 mg/liter defined by EUCAST. MEM-CLA is a potential treatment option for MDR/XDR-TB.     

Comparative In Vitro Activity Profile of Oritavancin against Recent Gram-Positive Clinical Isolates

Oritavancin activity was tested against 15,764 gram-positive isolates collected from 246 hospital centers in 25 countries between 2005 and 2008. Organisms were Staphylococcus aureus (n = 9,075), coagulase-negative staphylococci (n = 1,664), Enterococcus faecalis (n = 1,738), Enterococcus faecium (n = 819), Streptococcus pyogenes (n = 959), Streptococcus agalactiae (n = 415), group C, G, and F streptococci (n = 84), and Streptococcus pneumoniae (n = 1,010). Among the evaluated staphylococci, 56.7% were resistant to oxacillin. The vancomycin resistance rate among enterococci was 21.2%. Penicillin-resistant and -intermediate rates were 14.7% and 21.4%, respectively, among S. pneumoniae isolates. Among nonpneumococcal streptococci, 18.5% were nonsusceptible to erythromycin. Oritavancin showed substantial in vitro activity against all organisms tested, regardless of resistance profile. The maximum oritavancin MIC against all staphylococci tested (n = 10,739) was 4 μg/ml; the MIC₉₀ against S. aureus was 0.12 μg/ml. Against E. faecalis and E. faecium, oritavancin MIC₉₀s were 0.06 and 0.12, respectively. Oritavancin was active against glycopeptide-resistant enterococci, including VanA strains (n = 486), with MIC₉₀s of 0.25 and 1 μg/ml against VanA E. faecium and E. faecalis, respectively. Oritavancin showed potent activity against streptococci (n = 2,468); MIC₉₀s for the different streptococcal species were between 0.008 and 1 μg/ml. These data are consistent with previous studies with respect to resistance rates of gram-positive isolates and demonstrate the spectrum and in vitro activity of oritavancin against a wide variety of contemporary gram-positive pathogens, regardless of resistance to currently used drugs. The data provide a foundation for interpreting oritavancin activity and potential changes in susceptibility over time once oritavancin enters into clinical use.Gram-positive infections remain a clinical challenge due to increasing rates of resistance to currently available antimicrobial agents (37). Among Staphylococcus aureus strains, the prevalence of methicillin (meticillin) resistance in both hospital and community settings is increasing (19). Reports of increased numbers of S. aureus isolates with decreased susceptibility to glycopeptides have also emerged (2). Similar increases in vancomycin-resistant enterococci, penicillin-nonsusceptible pneumococci, and erythromycin-nonsusceptible streptococci have been reported (13, 27, 28, 31). Against this backdrop, the need to develop new agents is clear, with special attention to agents that can overcome existing mechanisms of resistance.Oritavancin is a semisynthetic bactericidal lipoglycopeptide under clinical development for the treatment of serious infections caused by a variety of gram-positive species, including drug-resistant enterococci, staphylococci, and streptococci (30). Like the glycopeptides vancomycin and teicoplanin, oritavancin inhibits cell wall synthesis (1, 4, 25). Additionally, oritavancin differs from vancomycin and teicoplanin by partially inhibiting RNA synthesis (4) and collapsing transmembrane electrochemical potential and increasing membrane permeability (6). These additional activities help to explain the rapid concentration-dependent bactericidal activity of oritavancin in vitro, even against isolates with reduced susceptibility to vancomycin and teicoplanin (12, 26, 30). Oritavancin''s multiple mechanisms of action are hypothesized to forestall the development of high-level resistance to this agent.The recent development of methods for oritavancin susceptibility testing indicates that oritavancin MICs reported prior to 2006 underestimate the potency of the drug because of the physicochemical property of the drug to bind to laboratory plasticware (3). A revised broth microdilution method for oritavancin, one that includes polysorbate 80 to minimize binding to labware, has been approved by the Clinical Laboratory Standards Institute (10). This method was used in the present surveillance study, and our study represents the first report of an oritavancin surveillance program using polysorbate 80 methodology.Current and ongoing surveillance initiatives seek to establish an in vitro activity profile of oritavancin against contemporary gram-positive bacterial populations, including those resistant to currently available agents that may be used to treat gram-positive infections. The goals of the present study were to research the potential utility of oritavancin against clinical pathogens and to establish baseline MIC susceptibility data prior to the availability of oritavancin in clinical settings, against which further susceptibility studies could be compared. To these ends, we collected 15,764 recent gram-positive clinical isolates between 2005 and 2008 from 246 geographically dispersed hospital centers and tested their susceptibility to oritavancin as well as to antimicrobial agents currently used in the clinical setting.(Parts of this study have been presented previously in abstract form [15, 16, 18, 34].)     

In Vitro Activity of Pyronaridine against Multidrug-Resistant Plasmodium falciparum and Plasmodium vivax

Pyronaridine, a Mannich base antimalarial, has demonstrated high in vivo and in vitro efficacy against chloroquine-resistant Plasmodium falciparum. Although this drug has the potential to become a prominent artemisinin combination therapy, little is known about its efficacy against drug-resistant Plasmodium vivax. The in vitro antimalarial susceptibility of pyronaridine was assessed in multidrug-resistant P. vivax (n = 99) and P. falciparum (n = 90) isolates from Papua, Indonesia, using a schizont maturation assay. The median 50% inhibitory concentration (IC₅₀) of pyronaridine was 1.92 nM (range, 0.24 to 13.8 nM) against P. falciparum and 2.58 nM (range, 0.13 to 43.6 nM) against P. vivax, with in vitro susceptibility correlating significantly with chloroquine, amodiaquine, and piperaquine (r_s [Spearman''s rank correlation coefficient] = 0.45 to 0.62; P < 0.001). P. falciparum parasites initially at trophozoite stage had higher IC₅₀s of pyronaridine than those exposed at the ring stage (8.9 nM [range, 0.6 to 8.9 nM] versus 1.6 nM [range, 0.6 to 8.9 nM], respectively; P = 0.015), although this did not reach significance for P. vivax (4.7 nM [range, 1.4 to 18.7 nM] versus 2.5 nM [range, 1.4 to 15.6 nM], respectively; P = 0.085). The excellent in vitro efficacy of pyronaridine against both chloroquine-resistant P. vivax and P. falciparum highlights the suitability of the drug as a novel partner for artemisinin-based combination therapy in regions where the two species are coendemic.Almost 40% of the world''s population is at risk for infection by Plasmodium vivax, with an estimated 132 to 391 million clinical infections each year (19). Although chloroquine (CQ) remains the treatment of choice in most of the P. vivax-endemic world, this status is now being undermined by the emergence and spread of chloroquine-resistant (CQR) P. vivax. First reported in the 1980s on the island of New Guinea (2, 23), CQR P. vivax has since spread to other parts of Asia and recently to South America (1). In Papua, Indonesia, CQ resistance in P. vivax has reached levels precluding the use of CQ in most of the province (22, 30). There is an urgency to assess the efficacies of alternative antimalarial agents against drug-resistant P. vivax and to develop new strategies to combat the parasite.Pyronaridine (Pyr), a Mannich base synthesized in China in the 1970s (3, 16), is being developed as a novel antimalarial for multidrug-resistant malaria. It demonstrates potent in vitro activity against erythrocytic stages of Plasmodium falciparum (8, 24, 26, 36), retaining efficacy against CQR isolates (12, 17, 18). Clinical trials have shown excellent efficacy of monotherapy against multidrug-resistant falciparum malaria (14, 24, 25), with the early therapeutic response faster when combined with artesunate (20). Phase III studies with a coformulation of Pyramax (Shin Poong Pharmaceuticals) containing artesunate plus pyronaridine have recently been completed (34).Less is known of the antimalarial properties of pyronaridine against P. vivax, although early clinical studies in China demonstrated a rapid therapeutic response (3). To investigate the activity of pyronaridine against CQR P. vivax, we applied a modified schizont maturation assay on fresh field isolates from Papua, Indonesia, where CQR P. vivax is highly prevalent.     

Comparison of the In Vitro Activity of Several Cephalosporin Antibiotics Against Gram-Negative and Gram-Positive Bacteria Resistant to Cephaloridine

The in vitro activity of each of two oral [cefatrizine (BL-S640), cephalexin] and three parenteral (cefamandole, cefazolin, cephapirin) cephalosporin antibiotics was compared with that of cephalothin against 168 clinical isolates of gram-negative and gram-positive bacteria selected as resistant to 20 μg of cephaloridine per ml on the basis of agar dilution susceptibility test data. Each of the five other cephalosporins inhibited a greater percentage of gram-negative bacillary isolates than did cephalothin or cephaloridine, with minimal inhibitory concentration values ranging 2- to 50-fold lower. Significant differences between minimal inhibitory concentrations of the compounds tested were also observed in tests against strains of Streptococcus faecalis and of methicillin-resistant Staphylococcus aureus. Potential advantages of including more than a single cephalosporin antibiotic in the panel of antibiotics used for routine susceptibility testing, suggested by these observations, are discussed.     

In vivo antibacterial activity of RWJ-54428, a new cephalosporin with activity against gram-positive bacteria

RWJ-54428 (MC-02,479) is a new cephalosporin with activity against resistant gram-positive organisms, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and penicillin-resistant Streptococcus pneumoniae. The in vivo efficacy of RWJ-54428 was evaluated against gram-positive bacteria in four mouse models of infection. RWJ-54428 was effective in vivo against methicillin-susceptible and -resistant S. aureus in a mouse model of sepsis, with 50% effective doses being similar to those of vancomycin. In a single-dose neutropenic mouse thigh model of infection, RWJ-54428 at 30 mg/kg of body weight showed activity similar to that of vancomycin at 30 mg/kg against a strain of methicillin-resistant S. aureus. RWJ-54428 also showed a prolonged in vivo postantibiotic effect in this model. In a mouse model of pneumonia due to a penicillin-susceptible strain of Streptococcus pneumoniae, RWJ-54428 displayed efficacy and potency superior to those of penicillin G and cefotaxime. In a mouse model of pyelonephritis due to Enterococcus faecalis, RWJ-54428 had bactericidal effects similar to those of vancomycin and ampicillin, but at two- to threefold lower total daily doses. These studies show that RWJ-54428 is active in experimental mouse models of infection against gram-positive organisms, including strains resistant to earlier cephalosporins and penicillin G.     

In Vitro Activities of Tedizolid and Linezolid against Gram-Positive Cocci Associated with Acute Bacterial Skin and Skin Structure Infections and Pneumonia

Tedizolid is a novel, expanded-spectrum oxazolidinone with potent activity against a wide range of Gram-positive pathogens. A total of 425 isolates of Gram-positive bacteria were obtained consecutively from patients with acute bacterial skin and skin structure infections (ABSSSIs) or pneumonia. These isolates included methicillin-susceptible Staphylococcus aureus (MSSA) (n = 100), methicillin-resistant Staphylococcus aureus (MRSA) (n = 100), Streptococcus pyogenes (n = 50), Streptococcus agalactiae (n = 50), Streptococcus anginosus group (n = 75), Enterococcus faecalis (n = 50), and vancomycin-resistant enterococci (VRE) (Enterococcus faecium) (n = 50). The MICs of tedizolid and linezolid were determined by the agar dilution method. Tedizolid exhibited better in vitro activities than linezolid against MSSA (MIC₉₀s, 0.5 versus 2 μg/ml), MRSA (MIC₉₀s, 0.5 versus 2 μg/ml), S. pyogenes (MIC₉₀s, 0.5 versus 2 μg/ml), S. agalactiae (MIC₉₀s, 0.5 versus 2 μg/ml), Streptococcus anginosus group (MIC₉₀s, 0.5 versus 2 μg/ml), E. faecalis (MIC₉₀s, 0.5 versus 2 μg/ml), and VRE (MIC₉₀s, 0.5 versus 2 μg/ml). The tedizolid MICs against E. faecalis (n = 3) and VRE (n = 2) intermediate to linezolid (MICs, 4 μg/ml) were 1 μg/ml and 0.5 μg/ml, respectively. The tedizolid MIC₉₀s against S. anginosus, S. constellatus, and S. intermedius were 0.5, 1, and 0.5 μg/ml, respectively, and the rates of susceptibility based on the U.S. FDA MIC interpretive breakpoints to the isolates were 16%, 28%, and 72%, respectively. Tedizolid exhibited 2- to 4-fold better in vitro activities than linezolid against a variety of Gram-positive cocci associated with ABSSSIs and pneumonia. The lower susceptibilities of tedizolid against isolates of S. anginosus and S. constellatus than against those of S. intermedius in Taiwan were noted.     

Comparative In Vitro Activity Profiles of Novel Bis-Indole Antibacterials against Gram-Positive and Gram-Negative Clinical Isolates

Antimicrobial susceptibilities of 233 Gram-positive and 180 Gram-negative strains to two novel bis-indoles were evaluated. Both compounds were potent inhibitors of Gram-positive bacteria, with MIC₉₀ values of 0.004 to 0.5 μg/ml. One bis-indole, MBX 1162, exhibited potent activity against all Gram-negative strains, with MIC₉₀ values of 0.12 to 4 μg/ml, even against high-level-resistant pathogens, and compared favorably to all comparator antibiotics. The bis-indole compounds show promise for the treatment of multidrug-resistant clinical pathogens.Antibiotic resistance is reaching a crisis level because few options remain to treat certain pathogenic bacteria—mainly those causing hospital-acquired infection, but with the potential to occur in the community (8) and on the battlefield (2). Of special note are the following particularly problematic pathogens: multidrug-resistant (MDR) Acinetobacter baumannii, extended-spectrum β-lactamase (ESBL)-producing Escherichia coli and Klebsiella species, Pseudomonas aeruginosa, vancomycin-resistant enterococci (VRE [Enterococcus faecium]), methicillin-resistant Staphylococcus aureus (MRSA), and coagulase-negative staphylococci such as methicillin-resistant Staphylococcus epidermidis (MRSE).The continuing erosion of the efficacy of current antibiotics requires the discovery and development of new antibacterials that are not subject to existing mechanisms of target-based resistance. This can be accomplished by building derivatives of existing antibiotics which escape resistance mechanisms or by the development of entirely new chemical classes of antibiotics. The latter approach is preferred because preexisting target-based resistance mechanisms are unlikely to be present in the bacterial population. Here, we report MIC₉₀ values versus several problematic bacterial pathogens for a recently described series of bis-indole compounds (6, 7). MBX 1066 (Fig. ​(Fig.1),1), along with MBX 1090, 1113 and 1128 (7) were identified in a screen of the NCI repository for compounds active against Bacillus anthracis. The indole groups of MBX 1066 and MBX 1090 face each other in a symmetrical fashion (“head-to-head”), while they are positioned in a tandem arrangement (“head-to-tail”) in MBX 1113 and 1128. The head-to-head compounds were found to be more potent than the head-to-tail compounds against Gram-negative species while being nearly equipotent against Gram-positive species. MBX 1066 exhibited low cytotoxicity against HeLa cells (50% cytotoxic concentration [CC₅₀], 33 μg/ml) upon 3-day exposure, while the other compounds were slightly more cytotoxic (7). MBX 1066 displayed rapid bactericidal activity against both Gram-positive (Bacillus anthracis and B. subtilis) and Gram-negative (Yersinia pestis) bacteria (7) and demonstrated efficacy in murine models of Gram-positive (B. anthracis and S. aureus) and Gram-negative (Y. pestis) infections (7). MBX 1066 and related compounds bound serum proteins less than 25% (M. Butler, unpublished observation). Finally, experiments to isolate MBX 1066-resistant mutants by serial passage and spontaneous mutation selection were unsuccessful against both S. aureus and E. coli, although mutants resistant to a closely related compound, MBX 1090, were isolated (6, 7).Open in a separate windowFIG. 1.Structures of bis-indole compounds MBX 1066 and MBX 1162.We have conducted a structure activity relationship (SAR) program around the head-to-head compounds, typified by MBX 1066. While the molecular target(s) of these compounds is not known, the fact that they share some structural features with compounds that bind in the minor groove of duplex DNA (1) suggests that these compounds may inhibit DNA synthesis by binding to DNA. In fact, we have shown that they are potent inhibitors of DNA synthesis (7). However, their efficacy in murine models of infection, together with favorable in vitro selectivity indices, indicates that these compounds discriminate to some degree between bacterial and mammalian targets (7).Analogs of MBX 1066, particularly MBX 1162 (Fig. ​(Fig.1),1), exhibit improved Gram-negative activity while maintaining the Gram-positive potencies displayed by the parent compound. MBX 1162 is remarkably potent against antibiotic-resistant bacterial strains such as MDR A. baumannii, ESBL-producing Klebsiella pneumoniae, VRE, and MRSA, making it a promising new antibacterial agent. While MBX 1162 appeared somewhat more cytotoxic than MBX 1066 against HeLa cells (CC₅₀, 4 μg/ml) upon 3-day exposure, it retained the favorable features of MBX 1066, including bactericidal activity against both Gram-positive and Gram-negative pathogens, low serum binding (M. Butler, unpublished), and absence of susceptibility to resistance development (T. Opperman, unpublished observation), and its enhanced antibacterial activity provided selectivity index values (CC₅₀/MIC) comparable to those of MBX 1066 for Gram-negative species. In addition, MBX 1162 exhibited potent inhibition of DNA synthesis (T. Opperman and M. Butler, unpublished), suggesting its mechanism of action is similar to that of MBX 1066. Although we have observed an exceptionally broad antimicrobial profile for MBX 1066 and 1162 against single isolates of a variety of species, it is important to determine efficacy against larger groups of single species isolates, obtained from several clinical sources, looking specifically at populations of antibiotic-resistant clinical pathogens. To this end, we analyzed potencies against multiple strains of eight Gram-positive and eight Gram-negative species.Two hundred thirty-three Gram-positive strains and 180 Gram-negative aerobic strains were tested by the broth microdilution method (4) against MBX 1066 and 1162 as well as four comparator antibiotics. The comparator antibiotics were selected to be the most appropriate for each family as well as for verifying particular resistances and were thus different for Gram-positive versus Gram-negative isolates. These included linezolid (ChemPacifica), daptomycin (Cubist), vancomycin (Sigma-Aldrich), and imipenem (United States Pharmacopeia) for the Gram-positive aerobic bacteria and imipenem, tigecycline (Wyeth), gentamicin (Sigma-Aldrich), and ciprofloxacin (United States Pharmacopeia) for the Gram-negative aerobic bacteria. In addition, 18 isolates of the Gram-positive anaerobe Clostridium difficile were analyzed (3) using clindamycin (Sigma-Aldrich), imipenem, and metronidazole (Sigma-Aldrich) as comparators. The growth medium used in these studies was the CLSI-recommended Mueller-Hinton broth II (MHB II), with the exception of the streptococci (MHB II plus 2% lysed horse blood), Haemophilus influenza (HTM medium), and C. difficile (supplemented brucella broth). The quality control reference strains, S. aureus ATCC 29213, E. faecalis ATCC 29212, Streptococcus pneumoniae ATCC 49619, E. coli ATCC 25922, P. aeruginosa ATCC 27853, and Bacteroides fragilis ATCC 25285, were tested in accordance with CLSI methodology, and the results were within published ranges (5). The locations of the sources of the clinical isolates are listed in Table ​Table11.

TABLE 1.

Activities of MBX 1066 and MBX 1162 and selected comparators against Gram-positive and Gram-negative isolates

In Vitro Activity of the New Glycopeptide LY333328 against Multiply Resistant Gram-Positive Clinical Isolates

The in vitro activity of LY333328 was compared with those of vancomycin and teicoplanin against 425 gram-positive clinical isolates, including a variety of multiply resistant strains. LY333328 at ≤4 μg/ml inhibited all microorganisms tested, including methicillin- and teicoplanin-resistant staphylococci, glycopeptide-resistant enterococci, penicillin- and multiply resistant pneumococci, and viridans and beta-hemolytic streptococci.     

Cefamandole: Antimicrobial Activity In Vitro of a New Cephalosporin

Cefamandole, a new cephalosporin derivative, was found to have a broad spectrum of activity against a cross-section of both gram-positive and gram-negative bacteria isolated from clinical material. Gram-positive cocci, except for Streptococcus faecalis, were very susceptible. Penicillin G-resistant Staphylococcus aureus also was susceptible to cefamandole. Minimal bactericidal concentrations for gram-positive cocci approximated the minimal inhibitory concentrations. Strains of Haemophilus influenzae were very susceptible to the drug. Most strains of Escherichia coli, Klebsiella sp., and Proteus sp. were inhibited by low concentrations. Increasing resistance occurred with larger inocula. Strains of Pseudomonas sp. were resistant to cefamandole.     

Comparative In Vitro Activity of Five Cephalosporin Antibiotics Against Salmonellae

The in vitro activities of five cephalosporin antibiotics against 121 strains of salmonellae were compared. Cefamandole and cefaclor were more potent than cefazolin, and these three drugs were more active than cephalothin and cephalexin.     

ACHN-490, a Neoglycoside with Potent In Vitro Activity against Multidrug-Resistant Klebsiella pneumoniae Isolates

The in vitro activity of ACHN-490, a novel aminoglycoside (“neoglycoside”), was evaluated against 102 multidrug-resistant (MDR) Klebsiella pneumoniae strains, including a subset of 25 strains producing the KPC carbapenemase. MIC₅₀ values for gentamicin, tobramycin, and amikacin were 8 μg/ml, 32 μg/ml, and 2 μg/ml, respectively; MIC₉₀ values for the same antimicrobials were ≥64 μg/ml, ≥64 μg/ml, and 32 μg/ml, respectively. ACHN-490 showed an MIC₅₀ of 0.5 μg/ml and an MIC₉₀ of 1 μg/ml, which are significantly lower than those of comparator aminoglycosides. ACHN-490 represents a promising aminoglycoside for the treatment of MDR K. pneumoniae isolates, including those producing KPC β-lactamase.The spread of Klebsiella pneumoniae isolates producing extended-spectrum β-lactamases (ESBLs) represents a serious threat to our therapeutic armamentarium (21). These isolates are also frequently resistant to other classes of antibiotics, such as β-lactam/β-lactamase inhibitor combinations, quinolones, and aminoglycosides (8, 9), thereby limiting our choice to carbapenems for the treatment of serious infections (21).Unfortunately, there is growing concern regarding the emergence of carbapenem-resistant K. pneumoniae isolates (20). In particular, K. pneumoniae isolates producing KPC carbapenemases (KPC-Kp) are spreading at an alarming rate in North and South America, the Caribbean, Europe, Israel, and Asia (6, 7, 15, 17, 18). Like ESBL producers, KPC-Kp are often resistant to quinolones and aminoglycosides (6). Therefore, our therapeutic options against KPC-Kp are limited to tigecycline and colistin. However, tigecycline may not reach desired serum levels to treat bloodstream infections (19), leaving colistin as the “last choice” against infections caused by KPC-Kp (13). Unfortunately, colistin-resistant KPC-Kp isolates are also reported in the United States (1, 12). As a result of this therapeutic dilemma, new antimicrobial agents with potent activity against multidrug-resistant (MDR) K. pneumoniae need to be developed.Recently, there has been an increased interest in developing novel aminoglycosides. This new attention is due to (i) the potent bactericidal activity of aminoglycosides against a wide spectrum of aerobic gram-positive and gram-negative pathogens, (ii) the more gradual decline in susceptibility to aminoglycosides among gram-negative bacteria than that in susceptibility to other antimicrobials, and (iii) the ability of novel aminoglycosides to bypass common mechanisms of resistance that have gradually decreased the susceptibility to clinically used aminoglycosides (e.g., gentamicin, tobramycin, and amikacin) (11, 14, 16).ACHN-490 (Achaogen, San Francisco, CA) is a “neoglycoside,” a next-generation aminoglycoside, currently in early clinical development (FDA, http://clinicaltrials.gov/), which has never been reported previously in the literature. The chemical structure of ACHN-490 is presented in Fig. ​Fig.11.Open in a separate windowFIG. 1.Chemical structure of ACHN-490 [6′-(hydroxylethyl)-1-(haba)-sisomicin].In the present work, we analyzed the in vitro activity of ACHN-490 against a collection of 102 K. pneumoniae clinical isolates collected from January 2006 to October 2007 at the University of Pittsburgh Medical Center, and three Cleveland institutions, including University Hospitals Case Medical Center, the Cleveland Clinic, and the Louis Stokes Department of Veterans Affairs Medical Center.The 102 K. pneumoniae isolates were selected based on an MDR phenotype (i.e., resistance to ≥3 antibiotic classes). Twenty-five isolates were KPC-Kp and were part of a previous study in which the β-lactamase background and clonality were characterized (6). The remaining 77 MDR K. pneumoniae isolates were ESBL producers, according to the phenotypic results (see below).MICs were determined by a microdilution method using cation-adjusted Mueller-Hinton broth, according to the Clinical and Laboratory Standards Institute (CLSI) criteria (2). Specific panels containing the following antibiotics were customized by Trek Diagnostics (Cleveland, OH): cefotaxime, cefotaxime-clavulanate (constant concentration of 4 mg/liter), ceftazidime, ceftazidime-clavulanate (constant concentration of 4 mg/liter), piperacillin-tazobactam, imipenem, ciprofloxacin, tigecycline, gentamicin, tobramycin, amikacin, arbekacin, neomycin, and ACHN-490. The following ATCC control strains were used: Escherichia coli 25922, Pseudomonas aeruginosa 27853, and K. pneumoniae 700603. Susceptibility results were interpreted according to the guidelines recommended by CLSI (3). Tigecycline MICs were interpreted according to the U.S. FDA criteria (i.e., susceptible at an MIC of ≤2 μg/ml). According to the CLSI criteria, isolates were defined as ESBL producers when they showed a ≥3 twofold concentration decrease in MICs for ceftazidime or cefotaxime when tested in combination with clavulanate versus their MICs when tested alone (3).The 25 KPC-Kp isolates were analyzed by PCR for the presence of 16S rRNA methylase genes (i.e., armA, rmtA, rmtB, rmtC, rmtD, and npmA), using primers and conditions previously reported (4, 23). In addition, these strains were examined by PCR and sequencing for the presence of the most common aminoglycoside-modifying enzymes (AMEs) in gram-negative pathogens (22). In particular, the following genes were analyzed: aac(6′)-Ib, aac(6′)-Ic, aac(6′)-Id, ant(3")-Ia, ant(2")-Ia, aac(3)-Ia, aac(3)-Ib, aac(3)-IIc, aph(3′)-VIa, and aph(3′)-VIb, using primers previously reported (5, 10).As shown in Table ​Table1,1, MDR K. pneumoniae isolates were highly resistant to ceftazidime and piperacillin-tazobactam (each MIC₉₀, >32 μg/ml). Two-thirds of the isolates were resistant to ciprofloxacin, whereas approximately 75% and 90% of strains were still susceptible to imipenem and tigecycline, respectively. Almost all KPC-Kp isolates were resistant to β-lactams and quinolones, whereas tigecycline frequently remained active in vitro (Table ​(Table1).1). All of these 25 isolates were colistin susceptible, as previously reported (6).

TABLE 1.

Susceptibility results of MDR K. pneumoniae isolates, including those producing KPC enzymes

Cefuroxime, a New Cephalosporin Antibiotic: Activity In Vitro

Cefuroxime is a new broad-spectrum cephalosporin antibiotic with increased stability to beta-lactamases. This stability, although no absolute in all cases, has the effect of widening the antibacterial spectrum of the compound so that many organisms resistant to the established cephalosporins are susceptible to cefuroxime. It is active against gram-positive organisms, including penicillinase-producing staphylococci, but it is less active against methicillin-resistant strains. In addition to its high activity against non-beta-lactamase-producing gram-negative bacteria, cefuroxime effectively inhibits the growth of many beta-lactamase-producing strains, including Enterobacter, Klebsiella, and indole-positive Proteus spp. It is highly active against Neisseria gonorrhoeae, Neisseria meningitidis, and also Haemophilus influenzae, including ampicillin-resistant strains. Cefuroxime is rapidly bactericidal and induces the formation and subsequent lysis of filamentous forms over a small concentration range.     

In Vitro Activity of Gemifloxacin (SB 265805) against Anaerobes

Gemifloxacin mesylate (SB 265805), a new fluoronaphthyridone, was tested against 359 recent clinical anaerobic isolates by the National Committee for Clinical Laboratory Standards reference agar dilution method with supplemented brucella blood agar and an inoculum of 10(5) CFU/spot. Comparative antimicrobials tested included trovafloxacin, levofloxacin, grepafloxacin, sparfloxacin, sitafloxacin (DU-6859a), penicillin G, amoxicillin clavulanate, imipenem, cefoxitin, clindamycin, and metronidazole. The MIC(50) and MIC(90) (MICs at which 50 and 90% of the isolates were inhibited) of gemifloxacin against various organisms (with the number of strains tested in parentheses) were as follows (in micrograms per milliliter): for Bacteroides fragilis (28), 0.5 and 2; for Bacteroides thetaiotaomicron (24), 1 and 16; for Bacteroides caccae (12), 1 and 16; for Bacteroides distasonis (12), 8 and >16; for Bacteroides ovatus (12), 4 and >16; for Bacteroides stercoris (12), 0.5 and 0.5; for Bacteroides uniformis (12), 1 and 4; for Bacteroides vulgatus (11), 4 and 4; for Clostridium clostridioforme (15), 0.5 and 0.5; for Clostridium difficile (15), 1 and >16; for Clostridium innocuum (13), 0.125 and 2; for Clostridium perfringens (13), 0.06 and 0.06; for Clostridium ramosum (14), 0.25 and 8; for Fusobacterium nucleatum (12), 0.125 and 0.25; for Fusobacterium necrophorum (11), 0.25 and 0.5; for Fusobacterium varium (13), 0.5 and 1; for Fusobacterium spp. (12), 1 and 2; for Peptostreptococcus anaerobius (13), 0.06 and 0.06; for Peptostreptococcus asaccharolyticus (13), 0.125 and 0.125; for Peptostreptococcus magnus (14), 0.03 and 0.03; for Peptostreptococcus micros (12), 0.06 and 0.06; for Peptostreptococcus prevotii (14), 0.06 and 0.25; for Porphyromonas asaccharolytica (11), 0.125 and 0.125; for Prevotella bivia (10), 8 and 16; for Prevotella buccae (10), 2 and 2; for Prevotella intermedia (10), 0.5 and 0.5; and for Prevotella melaninogenica (11), 1 and 1. Gemifloxacin mesylate (SB 265805) was 1 to 4 dilutions more active than trovafloxacin against fusobacteria and peptostreptococci, and the two drugs were equivalent against clostridia and P. asaccharolytica. Gemifloxacin was equivalent to sitafloxacin (DU 6859a) against peptostreptococci, C. perfringens, and C. ramosum, and sitafloxacin was 2 to 3 dilutions more active against fusobacteria. Sparfloxacin, grepafloxacin, and levofloxacin were generally less active than gemifloxacin against all anaerobes.