Affinity of ceftaroline and other beta-lactams for penicillin-binding proteins from Staphylococcus aureus and Streptococcus pneumoniae.

We compared the affinities of ceftaroline for all penicillin-binding proteins (PBPs) with those of ceftriaxone and cefotaxime in 6 Staphylococcus aureus and 7 Streptococcus pneumoniae isolates with various resistance phenotypes. Ceftaroline MICs were PBP1A, -1B, and -2A > PBP2B, and ceftaroline had >or=4-fold higher 50% inhibitory concentrations (IC(50)s) (0.1 to 4 microg/ml) for PBP2X, -2A, -2B, and -3 than those for the other cephalosporins tested. Among 3 penicillin-resistant S. pneumoniae strains, ceftaroline had a high affinity for PBP2X (IC(50), 0.1 to 1 microg/ml), a primary target for cephalosporin PBP binding activity, and high affinities for PBP2B (IC(50), 0.5 to 4 microg/ml) and PBP1A (IC(50), 0.125 to 0.25 microg/ml) as well, both of which are also known as major targets for PBP binding activity of cephalosporins. Ceftaroline PBP affinities in methicillin-susceptible S. aureus strains were greater than or equal to those of the 3 other beta-lactams tested. Ceftaroline bound to PBP2a in methicillin-resistant S. aureus (IC(50), 0.01 to 1 microg/ml) with up to 256-fold-higher affinity than those of other agents. Ceftaroline demonstrated very good PBP affinity against all S. aureus and S. pneumoniae strains tested, including resistant isolates.

Postantibiotic effect of ceftaroline against gram-positive organisms.

The postantibiotic effects (PAEs), postantibiotic sub-MIC effects (PA-SMEs), and sub-MIC effects (SMEs) of ceftaroline, a novel injectable cephalosporin, were determined for 15 gram-positive organisms. The pneumococcal, staphylococcal, and enterococcal PAEs were 0.8 to 1.8 h, 0.7 to 2.2 h, and 0.2 to 1.1 h, respectively. The corresponding PA-SMEs (0.4 times the MIC) were 2.5 to 6.7 h, 2.9 to >0.0 h, and 7.9 to >10.3 h, respectively. The PA-SMEs were longer than the PAEs, suggesting that sub-MIC levels extend the PAE of ceftaroline against gram-positive cocci.

Postantibiotic effects of telavancin against 16 gram-positive organisms.

The in vitro postantibiotic effects (PAEs), postantibiotic sub-MIC effects (PA-SMEs), and sub-MIC effects of telavancin were determined for 16 gram-positive organisms. Telavancin staphylococcal, streptococcal, and enterococcal PAE ranges were 0.9 to 3.9 h, 0.4 to 6.7 h, and 0.3 to 2.2 h, respectively. The PA-SME ranges (0.4 times the MIC) for staphylococci, streptococci, and enterococci were 6.7 to >10.7 h, >10.7 to >11.0 h, and >10 to >10.8 h, respectively. The extended PAE of telavancin, together with its long elimination half-life in humans, supports once-daily dosing for this investigational drug.

Postantibiotic effect of tigecycline against 14 gram-positive organisms.

The in vitro postantibiotic effects (PAEs), postantibiotic sub-MIC effects (PA-SMEs), and sub-MIC effects of tigecycline were determined for 14 gram-positive and gram-negative organisms. The pneumococcal, staphylococcal, and enterococcal PAEs were 1.9 to 5.1, 2.9 to 5.7, and 3.9 to 6.1 h, respectively, and those for Haemophilus influenzae, Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, and Acinetobacter baumannii were 1.1 to 5.0, 1.9 to 2.1, 1.7 to 1.8, 1.0 to 1.7, and 0.7 to 3 h, respectively. The PA-SMEs (four times the MIC) ranged from 6.7 to >11 h for gram-positive organisms and from 2.3 to >11.3 h for gram-negative organisms.

Activities of antistaphylococcal antibiotics towards the extracellular and intraphagocytic forms of Staphylococcus aureus isolates from a patient with persistent bacteraemia and endocarditis.

Decreased susceptibility of Staphylococcus aureus to antistaphylococcal agents may be associated with inability to eradicate intracellular forms, which could explain therapeutic failures. This hypothesis was tested using clinical isolates obtained from a patient with persistent staphylococcal bacteraemia under therapy. Four isogenic isolates (three from tissue, one from blood) with increased MICs for vancomycin (1-4 mg/L) and for daptomycin (1-4 mg/L) were collected after an initial 16-day treatment with vancomycin-rifampicin-gentamicin, followed by 13-20 days of treatment with daptomycin-rifampicin-gentamicin. Isolates were tested for MICs and for: (i) vancomycin (BODIPY-FL-vancomycin) and daptomycin binding; (ii) cell wall turnover (loss of N-acetyl-d-[1-(14)C]glucosamine in 30 min after 1 h of labelling); and (iii) Triton X-100-induced autolysis. Extracellular (broth) and intracellular (THP-1 macrophages) activities of rifampicin, linezolid and fusidic acid at C(max), and of vancomycin, daptomycin, quinupristin-dalfopristin and oritavancin over a wide range of extracellular concentrations (with pharmacological modelling to determine E(max)), were measured at 24 h. Increases in vancomycin MICs correlated with increased drug binding, and decreased cell wall turnover and detergent-induced autolysis. Increases in daptomycin MICs correlated with decreased daptomycin binding. Intracellular activity was weak (E(max) <1 log(10) CFU decrease) for vancomycin against all isolates, and for daptomycin against isolates with MICs >1 mg/L. Among all antibiotics tested, only quinupristin-dalfopristin and oritavancin provided close to bactericidal intracellular activities (1.6-2.5 log(10) CFU decreases at C(max)). Determination of the intracellular susceptibility of S. aureus, combined with improved methods of diagnosis, could be useful when dealing with persistent staphylococcal infections and could improve therapy.

Postantibiotic effect of ceftobiprole against 12 Gram-positive organisms.

The in vitro postantibiotic effects (PAEs), postantibiotic sub-MIC effects (PA-SMEs), and sub-MIC effects of ceftobiprole were determined for 12 gram-positive organisms. Pneumococcal, staphylococcal, and enterococcal PAEs were 1.4 to 3.1 h, 0 to 1.8 h, and 0 to 0.9 h, respectively. The PA-SMEs (0.4 times the MIC) for pneumococci, staphylococci, and enterococci were 4.8 to >10.3 h, 1.5 to 9.6 h, and 3.8 to >10.7 h, respectively.

Antimicrobial resistance of nasopharyngeal pneumococci from children from day-care centres and orphanages in Russia: results of a unique prospective multicentre study.

This study assessed the antimicrobial resistance of nasopharyngeal pneumococci isolated from children aged < 5 years in day-care centres and orphanages throughout Russia during 2001-2002. Swabs were collected from 2484 children in 43 day-care centres and eight orphanages in 11 cities of European Russia, and from 1669 children in 37 day-care centres and three orphanages in eight cities of Asian Russia, with a total of 1144 and 912 Streptococcus pneumoniae isolates being recovered in European and Asian Russia, respectively. All macrolide-non-susceptible (MICs 0.5-128 mg/L) and fluoroquinolone-non-susceptible (ciprofloxacin MICs > or = 4 mg/L) isolates were tested for resistance mechanisms and clonal relatedness. Non-susceptibility rates, by CLSI criteria, were 19.3%, 0.9% and 0.4% for penicillin G, cefotaxime and amoxycillin-clavulanate, respectively. Resistance to macrolides and lincosamides was also relatively low, i.e., < 7% for clindamycin and 14- and 15-membered macrolides. The highest rates of non-susceptibility were for tetracycline and co-trimoxazole (52.0% and 64.5%, respectively). No clones resistant to ciprofloxacin (MICs > or = 8 mg/L) were found, but 1.7% of isolates were non-susceptible (MIC 4 mg/L). No resistance was found to levofloxacin, gemifloxacin, telithromycin or vancomycin. Pulsed-field gel electrophoresis analysis showed no relationship between ciprofloxacin- and macrolide-non-susceptible isolates in European and Asian Russia. Resistance among macrolide-resistant isolates resulted mostly from the presence of erm(B) and mef(A), and from changes in L4; additionally, L22 mutations were common in isolates from Asian Russia. Non-susceptibility to quinolones was associated with mutations in parC and parE among European isolates. Asian Russian isolates had mutations in parC and gyrA, and alterations in parE were more common. There were substantial differences in non-susceptibility and mechanisms of resistance between pneumococci from Asian and European Russia, with orphanages appearing to be 'hot-spots' of resistance.

MRSA--the tip of the iceberg.

Methicillin-resistant Staphylococcus aureus (MRSA) strains cause serious nosocomial infections all over the world. Overall, approximately 20% of S. aureus isolates in Europe are reported as methicillin-resistant, whereas in US hospitals the prevalence ranges from 33% to 55%. The past few years have also witnessed an increase in life-threatening community-acquired infections caused by Panton-Valentine leukocidin-producing MRSA in the USA. Increasing use of glycopeptides for treatment of community-acquired MRSA infections may result in higher rates of glycopeptide resistance. Since 1996, five vancomycin-intermediate S. aureus (VISA; vancomycin MIC = 8-16 mg/L) strains have been identified in Europe, Asia and the USA, and vancomycin-resistant S. aureus (VRSA) strains (vancomycin MIC > or = 32 mg/L) have also been reported in the USA between 2002 and 2005. Most infections with VISA and VRSA have occurred in a setting of heavy prior use of glycopeptides and other antimicrobial agents. Emergence of reduced vancomycin susceptibility in S. aureus increases the possibility that currently available antimicrobial agents may become ineffective for treating systemic infections, especially bacteraemia, endocarditis and osteomyelitis. Ceftobiprole is a novel broad-spectrum cephalosporin with expanded activity against Gram-positive bacteria, including MRSA. Ceftobiprole is refractory to the development of endogenous resistance both in vitro and in vivo. The additional activity of ceftobiprole against MRSA strains makes it a potentially important addition to currently available agents.

The emergence of vancomycin-intermediate and vancomycin-resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is well-recognised as a major cause of infection in the health care setting but, even more worryingly, is now emerging in the community. The glycopeptides-notably vancomycin-have traditionally been the mainstay of treatment of MRSA but overuse has led to the emergence of vancomycin-intermediate and vancomycin-resistant MRSA (VISA and VRSA, respectively). Although the mechanisms underlying vancomycin resistance are not yet fully understood, changes to the bacterial cell wall-the site of action of the glycopeptides-are believed to be key. Recent evidence also supports the transfer of genetic material among bacteria as contributing to the development of VRSA. Based on the cases identified to date, risk factors for the development of VRSA may include older age, compromised blood flow to the lower limbs, and the presence of chronic ulcers. The true extent of the problem, however, remains to be determined-it is likely that many cases of VISA and VRSA infection go undetected because of suboptimal screening programmes and possible limitations of automated and non-automated detection methods. Effective screening directed at those patients considered to be most at risk should therefore be a priority. Not surprisingly, the spread of MRSA from the hospital to the community setting, coupled with the emergence of VISA and VRSA, has become a major cause of concern among clinicians and microbiologists. The treatment options available for these infections are now severely compromised and thus new classes of antimicrobial agents effective against MRSA, VISA and VRSA are urgently required.

Activity of five quinolones, three macrolides and telithromycin against 12 Haemophilus influenzae strains with different resistance phenotypes.

Gemifloxacin MICs for 12 Haemophilus influenzae strains with different resistance phenotypes were 0.001-0.015 mg/L. Gemifloxacin was bactericidal against all 12 strains after 24 h at 2 x MIC. Ciprofloxacin, levofloxacin, gatifloxacin and moxifloxacin had MICs of 0.008-0.03 mg/L and similar kill kinetics. Macrolides and telithromycin had unimodal MICs (1.0-8.0 mg/L), except for two strains without efflux systems (0.0125-0.5 mg/L) and two with efflux systems and ribosomal protein mutations (> 64.0 mg/L), and were bactericidal against eight to ten strains tested at 2 x MIC after 24 h.

Postantibiotic effect of DX-619 against 16 gram-positive organisms.

The in vitro postantibiotic effects (PAEs), the postantibiotic sub-MIC effects (PA-SMEs), and the sub-MIC effects (SMEs) of DX-619 were determined for 16 gram-positive organisms. DX-619 pneumococcal, staphylococcal, and enterococcal PAE ranges were 1.7 to 5.0 h, 0.7 to 1.8 h, and 1.2 to 6.5 h, respectively. The PA-SME ranges (0.4x MIC) for pneumococci, staphylococci, and enterococci were 5.2 to >8.6 h, 2.1 to 8.3 h, and 4.9 to >10.0 h, respectively.

Activity of the new quinolone WCK 771 against pneumococci.

The activity of WCK 771, a new experimental quinolone being developed to overcome quinolone resistance in staphylococci, against quinolone-susceptible and -resistant pneumococci was determined. Comparative activities of ciprofloxacin, levofloxacin, gatifloxacin, moxifloxacin, clinafloxacin, vancomycin, linezolid, amoxycillin, cefuroxime, azithromycin and clarithromycin were determined with MIC and time-kill experiments. Animal experiments were also performed to test the in-vivo anti-pneumococcal activity of WCK 771 compared to levofloxacin. WCK 771 MIC50/90 values for 300 quinolone-susceptible Streptococcus pneumoniae isolates (108 penicillin-susceptible, 92 penicillin-intermediate and 100 penicillin-resistant) were 0.5/0.5 mg/L; the MICs of beta-lactams and macrolides rose with those of penicillin G, and all isolates were susceptible to vancomycin and linezolid. WCK 771 MIC50/90 values for 25 quinolone-resistant pneumococcal isolates were 4/8 mg/L, compared to 0.5/1 mg/L for clinafloxacin, 2/4 mg/L for gatifloxacin and moxifloxacin, 8/16 mg/L for levofloxacin, and 16/>32 mg/L for ciprofloxacin. Time-kill studies showed that WCK 771 was bactericidal against pneumococci after 24 h at 4 x MIC, as were the other quinolones tested. Animal model studies showed that WCK 771 had efficacy comparable to that of levofloxacin, by both the oral and subcutaneous routes, for systemic infection caused by three quinolone-susceptible isolates of pneumococci. Overall, WCK 771 was potent both in vivo and in vitro against quinolone-susceptible, but not quinolone-resistant, S. pneumoniae, regardless of penicillin susceptibility.

Alterations of penicillin-binding proteins 1A, 2X, and 2B in Streptococcus pneumoniae isolates for which amoxicillin MICs are higher than penicillin MICs.

Penicillin-binding proteins (PBPs) of 15 selected penicillin- and amoxicillin-resistant Streptococcus pneumoniae isolates (MICs of 2 to 8 and 8 to 16 microg/ml, respectively) were studied. In addition to typical changes in PBPs 1A and 2X, these strains had 10 unique changes in PBP 2B, including a (618)A-G substitution, which may be the key alteration associated with amoxicillin resistance.

Antimicrobial selection for community-acquired lower respiratory tract infections in the 21st century: a review of gemifloxacin.

Community-acquired lower respiratory tract infections (LRTIs) are more prevalent in the elderly than in children and younger adults and form a significant proportion of all consultations and hospital admissions in this older age group. Furthermore, in a world of increasing life expectancy the trend seems unlikely to be reversed. Antimicrobial treatment of community-acquired pneumonia (CAP) must cover Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis, and in many circumstances should also cover the intracellular (atypical) pathogens. In contrast, acute exacerbations of chronic bronchitis (AECB) are mainly associated with H. influenzae and S. pneumoniae and not with atypical bacteria: in severe cases, other Gram-negative bacteria may be involved. Frequently in LRTIs, the aetiology of the infection cannot be identified from the laboratory specimens and treatment has to be empirical. In such situations it is important to not only to use an antibiotic that covers all likely organisms, but also one that has good activity against these organisms given the local resistance patterns. Gemifloxacin is a new quinolone antibiotic that targets pneumococcal DNA gyrase and topoisomerase IV and is highly active against S. pneumoniae including penicillin-, macrolide- and many ciprofloxacin-resistant strains, as well as H. influenzae and the atypical pathogens. In clinical trials in CAP and AECB, gemifloxacin has been shown to be as effective a range of comparators and demonstrated an adverse event profile that was in line with the comparator agents. In one long-term study in AECB significantly more patients receiving gemifloxacin than clarithromycin remained free of recurrence after 26 weeks. The improved potency, broad spectrum of activity and proven clinical and bacteriological efficacy and safety profile should make it a useful agent in the 21st century battle against community-acquired LRTIs.

Development of macrolide resistance by ribosomal protein L4 mutation in Streptococcus pyogenes during miocamycin treatment of an eight-year-old Greek child with tonsillopharyngitis.

Streptococcus pyogenes isolates with the same pulsed-field patterns were recovered from the throat cultures of a child with tonsillopharyngitis before and after treatment with miocamycin, a 16-membered macrolide. The initial isolate was macrolide-susceptible, but the isolates after the treatment were resistant to 14 and 15-membered macrolides and had two amino acid (65WR66) deletions in ribosomal protein L4.

Postantibiotic effects of daptomycin against 14 staphylococcal and pneumococcal clinical isolates.

Daptomycin mean staphylococcal postantibiotic effects (PAEs) were 1.1 to 6.2 h, with a mean of 2.5 h. The mean pneumococcal PAEs were 1.7 h, ranging between 1.0 and 2.5 h. The staphylococcal and pneumococcal postantibiotic sub-MIC effects at 0.4 times the MIC ranged from 3.0 to >12.0 h and 1.9 to >12.0 h, respectively.

Activity of telithromycin and seven other agents against 1034 pediatric Streptococcus pneumoniae isolates from ten central and eastern European centers.

OBJECTIVE: To test the activity of telithromycin against 1034 Streptococcus pneumoniae isolates from pediatric patients in ten centers from ten central and eastern European countries during 2000-2001, and to compare it with the activities of erythromycin A, azithromycin, clarithromycin, clindamycin, and quinupristin-dalfopristin. METHODS: The minimum inhibitory concentrations (MICs) of telithromycin, erythromycin A, azithromycin, clarithromycin, clindamycin, levofloxacin, quinupristin-dalfopristin and penicillin G were tested by the agar dilution method with incubation in air, and mechanisms of resistance to macrolides and quinolones were investigated. RESULTS: Strains were isolated from sputum, tracheal aspirates, ear, eye, blood, and cerebrospinal fluid. Among S. pneumoniae strains tested, 36% had raised penicillin G MICs (>/= 0.12 mg/L). Susceptibilities were as follows: telithromycin, quinupristin-dalfopristin and levofloxacin, >/= 99%; clindamycin, 83%; and erythromycin A, azithromycin and clarithromycin, 78%. Of 230 (22.3%) erythromycin A-resistant S. pneumoniae strains, 176 (79.6%) had erm(B), 38 (16.1%) had mef(A), and 10 (4.3%) had mutations in 23S ribosomal RNA or in ribosomal protein L4. The rates of drug-resistant S. pneumoniae are high in all centers except Kaunas, Riga, and Prague. CONCLUSION: Telithromycin had low MICs against all strains, irrespective of macrolide, azalide or clindamycin resistance. Ribosomal methylation was the most prevalent resistance mechanism among all resistant strains, except in Sofia, where the prevalence of the efflux mechanism was higher.

Activity of telithromycin compared with seven other agents against 1039 Streptococcus pyogenes pediatric isolates from ten centers in central and eastern Europe.

In total, 1039 pediatric Streptococcus pyogenes isolates from Bulgaria, Croatia, the Czech Republic, Hungary, Latvia, Lithuania, Poland, Romania, Slovakia and Slovenia were studied. All strains were susceptible to penicillin G, levofloxacin, and quinupristin-dalfopristin, 91-100% to telithromycin, and 82-100% to erythromycin, azithromycin, and clarithromycin, and 90-100% to clindamycin. Macrolide resistance occurred mainly in Slovakia (25%), the Czech Republic (17.3%), and Croatia (15.8%). Overall, 9.7% of S. pyogenes isolates were erythromycin resistant due to erm(B)- or erm(A)-encoded methylases (72.3%) or to a mef(A)-encoded efflux pump (25.7%). One strain had alterations of both 23S rRNA (A2058G Escherichia coli numbering) and ribosomal protein L22 (G95D).

Postantibiotic effects of garenoxacin (BMS-284756) against 12 gram-positive or -negative organisms.

Conventional in vitro methods were used to determine the postantibiotic effects (PAEs), sub-MIC effects (SMEs), and postantibiotic sub-MIC effects (PA-SMEs) of garenoxacin for a range of organisms. The mean PAEs of garenoxacin for pneumococci, staphylococci, and enterococci were 0.3 to 2.2 h. For Escherichia coli and Pseudomonas aeruginosa, the PAEs were 0.9 to 1.6 h. The mean PA-SMEs (0.4 times the MIC) for pneumococci, staphylococci, and enterococci were 3.0 to >10 h, 1.8 to >10.7 h, and 5.8 h, respectively, while those for E. coli and P. aeruginosa were 7.6 and 4.4 h, respectively.

Antianaerobe activity of RBX 7644 (ranbezolid), a new oxazolidinone, compared with those of eight other agents.

The activity of ranbezolid (RBX 7644), a new oxazolidinone, against 306 anaerobes was compared with those of 11 other agents. The MICs at which 50% of the isolates tested are inhibited and those at which 90% of the isolates tested are inhibited (in micrograms per milliliter) were as follows: ranbezolid, 0.03 and 0.5; linezolid, 2 and 4; vancomycin, >16 and >16; teicoplanin, 1 and >16; quinupristin-dalfopristin, 1 and >8; amoxicillin-clavulanate, 0.5 and 2; imipenem, 0.125 and 1; clindamycin, 0.25 and 8; metronidazole, 1 and 4; gatifloxacin, 0.5 and 4; and moxifloxacin, 0.5 and 2, respectively. Ranbezolid had very good in vitro activity against both gram-negative and -positive anaerobes.