Tatiana Bogdanovich

Antistaphylococcal Activity of Ceftobiprole, a New Broad-Spectrum Cephalosporin

ABSTRACT Ceftobiprole (formerly BAL9141), the active component of the prodrug BAL5788 (ceftobiprole medocaril), is a novel cephalosporin with expanded activity against gram-positive bacteria. Among 152 Staphylococcus aureus isolates, including 5 vancomycin-intermediate and 2 vancomycin-resistant strains, MIC50 and MIC90 values for ceftobiprole were each 0.5 μg/ml against methicillin-susceptible strains and 2 μg/ml against methicillin-resistant strains. Against 151 coagulase-negative staphylococci (including 4 vancomycin-intermediate strains), MIC50 and MIC90 values were, respectively, 0.125 μg/ml and 1 μg/ml against methicillin-susceptible and 1 μg/ml and 2 μg/ml against methicillin-resistant strains. Teicoplanin was less active than vancomycin against coagulase-negative strains. Linezolid, quinupristin-dalfopristin, and daptomycin were active against all strains, whereas increased MICs for amoxicillin-clavulanate, cefazolin, minocycline, gentamicin, trimethoprim-sulfamethoxazole, levofloxacin, rifampin, mupirocin, fusidic acid, and fosfomycin were sometimes observed. At 2× MIC, ceftobiprole was bactericidal against 11 of 12 test strains by 24 h. Prolonged serial passage in the presence of subinhibitory concentrations of ceftobiprole failed to select for clones with MICs >4 times those of the parents; the maximum MIC achieved for ceftobiprole after 50 passages (in 1 of 10 strains) was 8 μg/ml. Single-passage selections showed very low frequencies of resistance to ceftobiprole irrespective of genotype or phenotype; the maximal ceftobiprole MIC of recovered clones was 8 μg/ml.

Characterization of a Daptomycin-Nonsusceptible Vancomycin-Intermediate Staphylococcus aureus Strain in a Patient with Endocarditis

ABSTRACT We analyzed the emergence of daptomycin nonsusceptibility in a patient with persistent vancomycin-intermediate Staphylococcus aureus (VISA) bacteremia. The daptomycin-nonsusceptible VISAs cell wall demonstrated a reduction in muramic acid O-acetylation, a phenotypic parameter not previously reported for VISA; some isolates also contained a single point mutation in the mprF gene.

Colistin-Resistant, Klebsiella pneumoniae Carbapenemase (KPC)–Producing Klebsiella pneumoniae Belonging to the International Epidemic Clone ST258

Five cases of infection due to colistin-resistant, Klebsiella pneumoniae carbapenemase-producing K. pneumoniae belonging to the international epidemic clone ST258 occurred over a 4-month period. These cases likely represented both emergence of resistance and transmission of resistant organism. The colistin-resistant isolates were able to persist in the absence of selective pressure in vitro.

Molecular Epidemiology of Carbapenem-Nonsusceptible Acinetobacter baumannii in the United States

ABSTRACT Acinetobacter baumannii is emerging as an important nosocomial pathogen worldwide. We report molecular epidemiology of 65 carbapenem-nonsusceptible A. baumannii isolates identified from hospitals in New York, Pennsylvania, Florida, Missouri, Nevada, and California between 2008 and 2009. All isolates were subjected to pulsed-field gel electrophoresis (PFGE). Select isolates then underwent multilocus sequence typing (MLST). While the PFGE patterns tended to cluster within each hospital, sequence types (STs) belonging to the clonal complex 92 (CC92) and the pan-European clonal lineage II (EUII; worldwide clonal lineage 2) were predominant in all hospitals. Of them, ST122 and ST208 were the most common and were found in four of the six hospitals. Isolates belonging to the pan-European clonal lineages I and III were identified in one hospital each. Carbapenemase-encoding genes bla OXA-23 and/or ISAba1-bla OXA-51-like were present among the majority of isolates. These findings suggest that carbapenem-nonsusceptible A. baumannii isolates found in U.S. hospitals constitute part of the global epidemic driven by CC92, but have unique STs other than ST92, which may be spreading by means of patient transfer between health care facilities within the United States.

Use of O-Antigen Gene Cluster-Specific PCRs for the Identification and O-Genotyping of Yersinia pseudotuberculosis and Yersinia pestis.

ABSTRACT Yersinia pestis is a very recently evolved clone of Yersinia pseudotuberculosis serotype O:1b. This close relationship causes potential difficulties in DNA-based diagnostic methods. Analysis of the O-antigen gene clusters in these two organisms identified two regions that were used to specifically identify Y. pestis-Y. pseudotuberculosis as a group or Y. pestis alone. Both PCR assays were found to be 100% specific when tested on a large collection of Yersinia species and other Enterobacteriaceae. Furthermore, advantage was taken of the different setups of the O-antigen gene clusters of the 21 known Y. pseudotuberculosis serotypes to develop a multiplex PCR assay to replace the conventional serotyping method of Y. pseudotuberculosis by O-genotyping. The multiplex PCR assay contained nine sets of specific PCRs in a single tube and when used on Y. pseudotuberculosis reference strains allowed the distinction of 14 individual serotypes and two duplex serotypes (O:4a-O:8 and O:12-O:13). Serotype O:7, O:9, and O:10 strains required additional PCRs for O-genotyping. Once applied to Y. pseudotuberculosis strains of various origins, a very good correlation between classical serotypes and O-genotypes was observed, although some discrepancies were found. O-genotyping also proved useful to correct misidentification of some strains and to type Y. pseudotuberculosis isolates that had lost the expression of the O-antigen. The PCR-based O-genotyping can easily be applied in conventional laboratories, without the need for tedious preparation of a large set of specific antisera.

Single- and Multistep Resistance Selection Studies on the Activity of Retapamulin Compared to Other Agents against Staphylococcus aureus and Streptococcus pyogenes

ABSTRACT Retapamulin had the lowest rate of spontaneous mutations by single-step passaging and the lowest parent and selected mutant MICs by multistep passaging among all drugs tested for all Staphylococcus aureus strains and three Streptococcus pyogenes strains which yielded resistant clones. Retapamulin has a low potential for resistance selection in S. pyogenes, with a slow and gradual propensity for resistance development in S. aureus.

Epidemiology and Molecular Characterization of Bacteremia Due to Carbapenem-Resistant Klebsiella pneumoniae in Transplant Recipients

We conducted a retrospective study of 17 transplant recipients with carbapenem‐resistant Klebsiella pneumoniae bacteremia, and described epidemiology, clinical characteristics and strain genotypes. Eighty‐eight percent (15/17) of patients were liver or intestinal transplant recipients. Outcomes were death due to septic shock (18%), cure (24%) and persistent (>7 days) or recurrent bacteremia (29% each). Thirty‐ and 90‐day mortality was 18% and 47%, respectively. Patients who were cured received at least one active antimicrobial agent and underwent source control interventions. Forty‐one percent (7/17) of patients had intra‐abdominal infections; all except one developed persistent/recurrent bacteremia despite drainage. Two patients tolerated persistent bacteremia for >300 days. All patients except one were infected with sequence type 258 (ST258), K. pneumoniae carbapenemase (KPC)‐2‐producing strains harboring a mutant ompK35 porin gene; the exception was infected with an ST37, KPC‐3‐producing strain. Seventy‐one percent (12/17) of patients were infected with ST258 ompK36 mutant strains. In two patients, persistent bacteremia was caused by two strains with different ompK36 genotypes. Three ompK36 mutations were associated with significantly higher carbapenem minimum inhibitory concentrations than wild‐type ompK36. Pulse‐field gel electrophoresis identified a single ST258 lineage; serial strains from individual patients were indistinguishable. In conclusion, KPC‐K. pneumoniae bacteremia exhibited highly diverse clinical courses following transplantation, and was caused by clonal ST258 strains with different ompK36 genotypes.

Identification of Diverse OXA-40 Group Carbapenemases, Including a Novel Variant, OXA-160, from Acinetobacter baumannii in Pennsylvania

ABSTRACT Three Acinetobacter baumannii isolates that possess OXA-40 group carbapenemase genes were identified. They belonged to novel sequence types (ST122, ST123, and ST124) and harbored bla OXA-160, bla OXA-72, and bla OXA-40, respectively. OXA-160 is a novel variant of OXA-40 with a P227S substitution. An isogenic Escherichia coli clone producing OXA-160 was more susceptible to carbapenems than a clone producing OXA-40. The genetic environment of bla OXA-160 and bla OXA-40 beyond the putative XerC/XerD recombination sites was distinct from the scaffold reported previously.

Activities of ceftobiprole, a novel broad-spectrum cephalosporin, against Haemophilus influenzae and Moraxella catarrhalis.

ABSTRACT Ceftobiprole, a broad-spectrum pyrrolidinone-3-ylidenemethyl cephem currently in phase III clinical trials, had MICs between 0.008 μg/ml and 8.0 μg/ml for 321 clinical isolates of Haemophilus influenzae and between ≤0.004 μg/ml and 1.0 μg/ml for 49 clinical isolates of Moraxella catarrhalis. Ceftobiprole MIC50 and MIC90 values for H. influenzae were 0.06 μg/ml and 0.25 μg/ml for β-lactamase-positive strains (n = 262), 0.03 μg/ml and 0.25 μg/ml for β-lactamase-negative strains (n = 40), and 0.5 μg/ml and 2.0 μg/ml for β-lactamase-negative ampicillin-resistant strains (n = 19), respectively. Ceftobiprole MIC50 and MIC90 values for β-lactamase-positive M. catarrhalis strains (n = 40) were 0.12 μg/ml and 0.5 μg/ml, respectively, whereas the ceftobiprole MIC range for β-lactamase-negative M. catarrhalis strains (n = 9) was ≤0.004 to 0.03 μg/ml. Ceftriaxone MICs usually were generally at least twofold lower than those of ceftobiprole, whereas amoxicillin-clavulanate MICs usually were higher than those of ceftobiprole. Azithromycin and telithromycin had unimodal MIC distributions against H. influenzae, with MIC90 values of azithromycin and telithromycin of 2 μg/ml and 4 μg/ml, respectively. Except for selected quinolone-nonsusceptible H. influenzae strains, moxifloxacin proved highly active, with MIC90 values of 0.12 μg/ml. Time-kill analyses showed that ceftobiprole, ceftriaxone, cefpodoxime, amoxicillin-clavulanate, azithromycin, telithromycin, and moxifloxacin were bactericidal at 2× MIC by 24 h against all 10 H. influenzae strains surveyed. Only modest increases in MICs were found for H. influenzae or M. catarrhalis clones after 50 serial passages in the presence of subinhibitory concentrations of ceftobiprole, and single-passage selection showed that the selection frequency of H. influenzae or M. catarrhalis clones with elevated ceftobiprole MICs is quite low.

Antistaphylococcal Activity of DX-619, a New Des-F(6)-Quinolone, Compared to Those of Other Agents

ABSTRACT The in vitro activity of DX-619, a new des-F(6)-quinolone, was tested against staphylococci and compared to those of other antimicrobials. DX-619 had the lowest MIC ranges/MIC50s/MIC90s (μg/ml) against 131 Staphylococcus aureus strains (≤0.002 to 2.0/0.06/0.5) and 128 coagulase-negative staphylococci (0.004 to 0.25/0.016/0.125). Among strains tested, 76 S. aureus strains and 51 coagulase-negative staphylococci were resistant to ciprofloxacin. DX-619 had the lowest MIC50/MIC90 values against 127 quinolone-resistant staphylococci (0.125/0.5), followed by sitafloxacin (0.5/4), moxifloxacin (2/8), gatifloxacin (4/16), levofloxacin (16/>32), and ciprofloxacin (>32/>32). Raised quinolone MICs were associated with mutations in GyrA (S84L) and single or double mutations in GrlA (S80F or Y; E84K, G, or V) in all S. aureus strains tested. A recent vancomycin-resistant S. aureus (VRSA) strain (Hershey) was resistant to available quinolones and was inhibited by DX-619 at 0.25 μg/ml and sitafloxacin at 1.0 μg/ml. Vancomycin (except VRSA), linezolid, ranbezolid, tigecycline, and quinupristin-dalfopristin were active against all strains, and teicoplanin was active against S. aureus but less active against coagulase-negative staphylococci. DX-619 produced resistant mutants with MICs of 1 to >32μ g/ml after <50 days of selection compared to 16 to> 32 μg/ml for ciprofloxacin, sitafloxacin, moxifloxacin, and gatifloxacin. DX-619 and sitafloxacin were also more active than other tested drugs against selected mutants and had the lowest mutation frequencies in single-step resistance selection. DX-619 and sitafloxacin were bactericidal against six quinolone-resistant (including the VRSA) and seven quinolone-susceptible strains tested, whereas gatifloxacin, moxifloxacin, levofloxacin, and ciprofloxacin were bactericidal against 11, 10, 7, and 5 strains at 4× MIC after 24 h, respectively. DX-619 was also bactericidal against one other VRSA strain, five vancomycin-intermediate S. aureus strains, and four vancomycin-intermediate coagulase-negative staphylococci. Linezolid, ranbezolid, and tigecycline were bacteriostatic and quinupristin-dalfopristin, teicoplanin, and vancomycin were bactericidal against two, eight, and nine strains, and daptomycin and oritavancin were rapidly bactericidal against all strains, including the VRSA. DX-619 has potent in vitro activity against staphylococci, including methicillin-, ciprofloxacin-, and vancomycin-resistant strains.