Activity of chequerboard combinations of ceftaroline and NXL104 versus beta-lactamase-producing Enterobacteriaceae.

BACKGROUND: Ceftaroline is a novel oxyimino-cephalosporin, strongly active against methicillin-resistant staphylococci and pneumococci. It is active against Enterobacteriaceae too, but is labile to common beta-lactamases, including AmpC and extended-spectrum types. To counteract these enzymes, ceftaroline is also being developed combined with NXL104, a beta-lactamase inhibitor. METHODS: Chequerboard MIC titrations were performed to determine the NXL104 concentrations needed to protect ceftaroline against beta-lactamase-producing Enterobacteriaceae, most of them with ceftaroline MICs >16 mg/L. RESULTS: All of 60 extended-spectrum beta-lactamase (ESBL) producers were susceptible to ceftaroline + NXL104, 1 + 1 mg/L, as were 5/5 Klebsiella oxytoca with high-level K1 enzyme. Among 30 Enterobacteriaceae with high-level chromosomal AmpC, 18 were susceptible at 1 + 1 mg/L, 28 at 1 + 4 mg/L and all at 4 + 4 mg/L; among 10 with plasmid AmpC enzymes, nine were susceptible at 1 + 1 mg/L and all at 1 + 4 mg/L. None of 10 isolates with combinations of AmpC or ESBL and impermeability was susceptible at 1 + 1 mg/L, but nine were susceptible at 1 + 4 mg/L and all at 4 + 4 mg/L. Among 12 with KPC carbapenemases, only two were susceptible at 1 + 1 mg/L, compared with 10 at 1 + 4 mg/L and 11 at 4 + 4 mg/L; 8/8 with OXA-48 carbapenemase were susceptible at 1 + 1 mg/L whilst 0/5 with metallo-beta-lactamases were inhibited by ceftaroline + NXL104, even at 8 + 4 mg/L. NXL104 potentiated the activity of ceftaroline against many ESBL- and AmpC-negative isolates for which ceftaroline MICs were 1-4 mg/L but not those for which MICs were < or = 0.5 mg/L, probably reflecting the slight lability of this cephalosporin to classical penicillinases, which were present in the former group but not the latter. CONCLUSIONS: At concentrations of < or = 4 mg/L, NXL104 protected ceftaroline against all relevant beta-lactamases except metalloenzymes.

Development of a standardized susceptibility test for campylobacter with quality-control ranges for ciprofloxacin, doxycycline, erythromycin, gentamicin, and meropenem.

A standardized agar dilution susceptibility testing method was developed for Campylobacter that consisted of testing on Mueller-Hinton medium supplemented with 5% defibrinated sheep blood in an atmosphere of 10% CO2, 5% O2, and 85% N2. Campylobacter jejuni ATCC 33560 was identified as a quality-control (QC) strain. Minimal inhibitory concentration (MIC) QC ranges were determined for two incubation time/temperature combinations: 36 degrees C for 48 hr and 42 degrees C for 24 hr. Quality-control ranges were determined for ciprofloxacin, doxycycline, erythromycin, gentamicin, and meropenem. For all antimicrobial agents tested at both temperatures, 95-100% of the QC MIC results fell within recommended QC ranges. Twenty-one Campylobacter clinical isolates, encompassing five species of Campylobacter (C. jejuni, C. coli, C. jejuni, subsp. doylei, C. fetus, and C. lari) were tested in conjunction with the C. jejuni QC strain. While C. jejuni and C. coli could be reliably tested under both test conditions, growth of C. jejuni subsp. doylei, C. fetus, and C. lari isolates was inconsistent when incubated at 42 degrees C. Therefore, it is recommended that these species only be tested at 36 degrees C.

Optimal use of antibiotic resistance surveillance systems.

Increasing concern about the emergence of resistance in clinically important pathogens has led to the establishment of a number of surveillance programmes to monitor the true extent of resistance at the local, regional and national levels. Although some programmes have been operating for several years, their true usefulness is only now being realised. This review describes some of the major surveillance initiatives and the way in which the data have been used in a number of different settings. In the hospital, surveillance data have been used to monitor local antibiograms and determine infection control strategies and antibiotic usage policies. In the community, surveillance data have been used to monitor public health threats, such as infectious disease outbreaks involving resistant pathogens and the effects of bioterrorism countermeasures, by following the effects of prophylactic use of different antibiotics on resistance. Initially, the pharmaceutical industry sponsored surveillance programmes to monitor the susceptibility of clinical isolates to marketed products. However, in the era of burgeoning resistance, many developers of antimicrobial agents find surveillance data useful for defining new drug discovery and development strategies, in that they assist with the identification of new medical needs, allow modelling of future resistance trends, and identify high-profile isolates for screening the activity of new agents. Many companies now conduct pre-launch surveillance of new products to benchmark activity so that changes in resistance can be monitored following clinical use. Surveillance data also represent an integral component of regulatory submissions for new agents and, together with clinical trial data, are used to determine breakpoints. It is clear that antibiotic resistance surveillance systems will continue to provide valuable data to health care providers, university researchers, pharmaceutical companies, and government and regulatory agencies.

Antibiotic susceptibility of isolates of Bacillus anthracis, a bacterial pathogen with the potential to be used in biowarfare.

Bacillus anthracis is a bacterial species that could be used in a bioterrorist attack. We tested a collection of isolates with a range of relevant antimicrobial compounds. All isolates tested were susceptible to ciprofloxacin and doxycycline. Penicillin and amoxicillin, with or without clavulanate, showed in vitro activity against all B. anthracis isolates. Ceftriaxone demonstrated lower-level in vitro activity compared to penicillin-related compounds against B. anthracis. In vitro data from this study are in keeping with available guidelines.

In vitro susceptibility of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis: a European multicenter study during 2000-2001.

OBJECTIVE: To assess the current (2001) activity of respiratory fluoroquinolones and comparator agents against respiratory pathogens isolated in European countries. METHODS: During 2000-2001, we prospectively collected 1995 isolates of Haemophilus influenzae, 1870 isolates of Streptococcus pneumoniae and 649 isolates of Moraxella catarrhalis from hospital laboratories in France, Germany, Greece, Italy, Spain and the UK. National Committee for Clinical Laboratory Standards (NCCLS)-approved broth microdilution antimicrobial susceptibility testing methods and interpretive criteria were used throughout. RESULTS: Of the S. pneumoniae isolates, 99.6% were susceptible to moxifloxacin, gatifloxacin and levofloxacin; the corresponding figure for H. influenzae was 100%. All M. catarrhalis isolates had moxifloxacin MICs

Antimicrobial susceptibility of 840 clinical isolates of Haemophilus influenzae collected in four European countries in 2000-2001.

In 2000-2001, 840 clinical isolates of Haemophilus influenzae were collected from laboratories in France, Germany, Italy and Spain (210 isolates/country). Beta-Lactamase production among the isolates varied considerably by country, ranging from 8.1% in Germany to 34.8% in France. H. influenzae from patients or=18 years (16.5%). All isolates were susceptible to amoxicillin-clavulanate, ciprofloxacin and levofloxacin; 99.6% and 98.9% of isolates were susceptible to azithromycin and cefuroxime, respectively. Among the macrolides tested, azithromycin (MIC90, 2 mg/L) was eight-fold more potent than clarithromycin (MIC90, 16 mg/L) and roxithromycin (MIC90, 16 mg/L). Despite variations in beta-lactamase production between different countries, > 99% of all isolates were susceptible to amoxicillin-clavulanate, ciprofloxacin, levofloxacin, and azithromycin.

In vitro activity of levofloxacin against contemporary clinical isolates of Legionella pneumophila, Mycoplasma pneumoniae and Chlamydia pneumoniae from North America and Europe.

OBJECTIVE: To assess the activities of levofloxacin and the comparator agents erythromycin, clarithromycin, azithromycin and doxycycline against atypical respiratory pathogens. METHODS: One hundred and forty-six Legionella pneumophila, 41 Mycoplasma pneumoniae and nine Chlamydia pneumoniae isolates were procured from various culture collections in North America and Europe and tested for susceptibility to the above agents by broth microdilution. The isolates came primarily from clinical sources and were collected from patients between 1995 and 1999. RESULTS: Against L. pneumophila, levofloxacin was the most active agent, with an MIC(90) of 0.03 mg/L, twofold more active than clarithromycin (0.06 mg/L), 16-fold more active than erythromycin and azithromycin (0.5 mg/L) and 64-fold more active than doxycycline. Against M. pneumoniae, azithromycin (MIC(90) < or = 0.0005 mg/L) was the most active agent. However, two isolates of M. pneumoniae, one from the USA and one from Finland, were macrolide resistant (MIC > or = 4 mg/L), but levofloxacin susceptible (MIC 0.25 mg/L). The geographic origin of L. pneumophila and M. pneumoniae did not affect the MIC range for any antimicrobial agent tested. Against C. pneumoniae, clarithromycin was the most active agent, with an MIC range of < or =0.008-0.03 mg/L. CONCLUSIONS: Levofloxacin had comparable activity to the other agents tested against the atypical respiratory pathogens, confirming its potential as an alternative for empirical therapy of community-acquired pneumonia.

Antimicrobial resistance among respiratory pathogens collected in Thailand during 1999-2000.

A multi-center surveillance study was conducted in Thailand during 1999-2000 to determine antimicrobial susceptibilities among the respiratory pathogens Streptococcus pneumoniae (n = 206), Haemophilus influenzae (n = 305), and Moraxella catarrhalis (n = 39). Of the S. pneumoniae isolates collected, 33.5% were penicillin-susceptible, 27.2% intermediate and 39.3% resistant. Expectedly, resistance rates to beta-lactams were higher among penicillin-resistant (ceftriaxone, 14.8%; amoxicillin-clavulanate, 42.0%; cefuroxime, 100%) than penicillin-susceptible (ceftriaxone, 0%; amoxicillin-clavulanate, 0%; cefuroxime, 0%) isolates. Likewise, azithromycin and clarithromycin resistances were 4.3% and 5.8% among penicillin-susceptible isolates, and 77.8% and 95.1% among penicillin-resistant isolates. All S. pneumoniae remained susceptible to vancomycin and 99.5% were susceptible to levofloxacin. Multidrug resistance (resistance to >3 antimicrobial classes) was present in 25.2% of pneumococcal isolates (n = 52), with resistance to azithromycin, penicillin and trimethoprim-sulfamethoxazole the most common phenotype (40/52 isolates; 77.0%). Among the isolates of H. influenzae, the prevalence of beta-lactamase production was 45.2%. All isolates of H. influenzae were susceptible to amoxicillin-clavulanate, azithromycin, ceftriaxone, cefuroxime and levofloxacin while 49.5% were resistant to trimethoprim-sulfamethoxazole. All 39 isolates of M. catarrhalis produced beta-lactamase. Azithromycin (MIC90, < or = 0.03 microg/ml) and levofloxacin (MIC90, 0.03 microg/ml) were the most active agents tested against M. catarrhalis. The results of this study may serve as a baseline for future studies to monitor antimicrobial susceptibilities among respiratory pathogens in Thailand.

Proficiency of Italian clinical laboratories in detecting reduced glycopeptide susceptibility in Enterococcus and Staphylococcus spp. using routine laboratory methodologies.

OBJECTIVE: To assess the ability of 59 clinical microbiology laboratories distributed throughout Italy to correctly identify and detect reduced susceptibility to glycopeptides in staphylococci and VanA-, VanB- or VanC-mediated glycopeptide resistance in enterococci. METHODS: Eight test strains comprising three staphylococci (S. aureus ATCC 29212 and two vancomycin-intermediate S. haemolyticus [11105301, 10030683Y]) and five enterococci (E. faecalis ATCC 29212, E. faecalis ATCC 51299 VanB, E. faecium AIB40 VanA, E. faecalis V583 VanB and E. gallinarum AIB39 VanC1) were distributed to 59 Italian clinical microbiology laboratories. Each isolate was blind-coded, and laboratories were instructed to identify the strains and test isolates for susceptibility to teicoplanin and vancomycin using their standard methods. Results were assessed against consensus test results obtained by a reference laboratory. In addition, to complement data interpretation, laboratories were asked to provide retrospective routine test results from their respective hospitals. RESULTS: All 59 laboratories participating in the study completed the susceptibility testing and provided data for analysis. A total of 53 laboratories provided retrospective routine data. Overall, laboratories were able to identify isolates to the genus level successfully. E. gallinarum and S. haemolyticus posed problems for species identification, with only 40.6 and 71.2%, respectively, of results reported correctly; most incorrect results were reported as 'other species'. For enterococcal test strains, VanA phenotypes were detected correctly by 96.6% of laboratories; VanB by 30.5% (E. faecalis ATCC 51299) and 88.1% (E. faecalis V583); and VanC1 by 67.8%. For staphylococcal test strains, 28.8% (S. haemolyticus 11105301) and 23.7% (S. haemolyticus 10030683Y) of the laboratories were able to detect reduced susceptibility to vancomycin. Errors in detecting vancomycin resistance in VanB and VanC1 enterococci were made with all methods, most noticeably by disk diffusion users. For staphylococci, most errors in reporting vancomycin-intermediate resistance occurred with disk diffusion and Vitek (software version 5.04) users. Overall, considerably fewer errors occurred with the detection of teicoplanin resistance, especially for staphylococci. For 1999, routine results show that 41/1749 (2.4%) of E. faecium, 220/11 180 (2.0%) of E. faecalis, 29/24 927 (0.12%) of S. aureus and 54/22 102 (0.24%) of coagulase-negative staphylococci were reported as resistant to vancomycin. CONCLUSION: Italian laboratories are able to identify staphylococci and enterococci adequately, although all methodologies used have problems in identifying E. gallinarum and coagulase-negative staphylococci to the species level. While VanA phenotypes were efficiently detected, problems were experienced in detecting VanB and VanC phenotypes. The majority of laboratories were unable to detect reduced vancomycin susceptibility in staphylococci adequately, especially with disk diffusion and older Vitek systems. Teicoplanin appeared useful as a marker for detecting vancomycin resistance, particularly with disk diffusion. Should enterococcal VanB or staphylococcal glycopeptide-intermediate phenotypes become prevalent in Italy, it is likely that they would be under-detected. New systems under development, such as Vitek2, should improve this situation.

Molecular characterization of vancomycin-resistant Enterococci repopulating the gastrointestinal tract following treatment with a novel glycolipodepsipeptide, ramoplanin.

We characterized baseline and repopulating stool isolates recovered during a phase II trial of ramoplanin for the treatment of patients with stool carriage of vancomycin-resistant enterococci (VRE). Repopulation with a strain with a related genotype was found in 74, 60, and 53% of individuals in groups treated with placebo, 100 mg of ramoplanin, and 400 mg of ramoplanin, respectively. All ramoplanin-treated patients with a culture positive for VRE at day 7 had a relapse caused by a genotypically related isolate. In ramoplanin-treated patients, antibiotics with activities against anaerobic organisms were associated with positive cultures on day 7 (relative risk [RR] = 8.8; P = 0.004), and the avoidance of such antibiotics was significantly associated with culture negativity through day 21 (RR = 0.16; P = 0.02).

Comparative activity of cefditoren and other oral beta-lactams against nonpneumococcal streptococci.

BACKGROUND: In vitro studies of cefditoren activity have focused primarily on Streptococcus pneumoniae and other bacterial species isolated from patients with respiratory infections, but relatively few reports have been published describing the activity of cefditoren against clinical isolates of nonpneumococcal streptococci. METHODS: Cefditoren activity was determined by broth microdilution (M7-A5, NCCLS, 2000) for 450 viridans group streptococci, 917 Streptococcus pyogenes and 800 other beta-hemolytic streptococci collected throughout the US during 1999-2000. RESULTS: Against viridans group streptococci, cefditoren (MIC(90), 0.5 microg/ml) was 4- to 32-fold more active than the other beta-lactams tested (penicillin ampicillin, amoxicillin-clavulanate, cefprozil and cefuroxime). The difference in activity between cefditoren and the other beta-lactams was greater for penicillin-nonsusceptible isolates (MIC(90s), 1 microg/ml versus 8-32 microg/ml) than among penicillin-susceptible isolates (MIC(90s), 0.12 versus 0.25- 1 microg/ml). Cefditoren also demonstrated potent activity against S. pyogenes (MIC(90), 0.015 microg/ml) and other beta-hemolytic streptococci (MIC(90), 0.06 microg/ml), comparable to that of the other beta-lactams. CONCLUSIONS: The activity demonstrated by cefditoren against nonpneumococcal streptococci, including beta-lactam- and macrolide-resistant isolates, suggests that this agent holds promise as therapy for infections caused by all clinically significant species of streptococci.

Prevalence of antimicrobial resistance among urinary tract pathogens isolated from female outpatients across the US in 1999.

In the United States, trimethoprim-sulphamethoxazole (TMP-SMX) is the recommended first-line treatment for uncomplicated urinary tract infections (UTIs) in females, in regions with resistance rates of <10-20%. Unfortunately, current data on regional resistance is often not readily available to physicians and regional variability in resistance remains largely unknown. This report presents antimicrobial susceptibility data for TMP-SMX and three other commonly tested antimicrobials organized by state and region to demonstrate current regional variability in resistance in the US. In the last quarter of 1999, 5739 fresh clinical isolates of Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Staphylococcus saprophyticus were collected from 202 laboratories throughout the US. Susceptibility testing was performed against TMP-SMX, cephalothin, nitrofurantoin and ciprofloxacin using broth microdilution. Data were analyzed by patient age and specimen source, and by state and region. In the US as a whole, resistance to TMP-SMX was 16.8% for E. coli, 7.8% for K. pneumoniae, 12.1% for P. mirabilis and 3.0% for S. saprophyticus, but these rates showed considerable regional variation. By state, E. coli resistance ranged from 7.4% in Pennsylvania to 33.3% in Iowa (among states with > or =50 isolates tested). Regionally, resistance for all uropathogens taken together ranged from 8.5% in East South-Central to 22.8% in West South-Central. Ciprofloxacin demonstrated the broadest activity of the antimicrobials tested and was more active than TMP-SMX against all pathogens. Resistance to TMP-SMX among E. coli now approaches or exceeds 20% in some areas. As resistance among uropathogens reaches clinically significant levels in many areas, continued regional surveillance is essential to ensure the provision of effective empiric therapy for urinary tract infections.

Need for annual surveillance of antimicrobial resistance in Streptococcus pneumoniae in the United States: 2-year longitudinal analysis.

Although changing patterns in antimicrobial resistance in Streptococcus pneumoniae have prompted several surveillance initiatives in recent years, the frequency with which these studies are needed has not been addressed. To approach this issue, the extent to which resistance patterns change over a 1-year period was examined. In this study we analyzed S. pneumoniae antimicrobial susceptibility results produced in our laboratory with isolates obtained over 2 consecutive years (1997-1998 and 1998-1999) from the same 96 institutions distributed throughout the United States. Comparison of results revealed increases in resistant percentages for all antimicrobial agents studied except vancomycin. For four of the agents tested (penicillin, cefuroxime, trimethoprim-sulfamethoxazole, and levofloxacin), the increases were statistically significant (P < 0.05). Resistance to the fluoroquinolone remained low in both years (0.1 and 0.6%, respectively); in contrast, resistance to macrolides was consistently greater than 20%, and resistance to trimethoprim-sulfamethoxazole increased from 13.3 to 27.3%. Multidrug resistance, concurrent resistance to three or more antimicrobials of different chemical classes, also increased significantly between years, from 5.9 to 11%. The most prevalent phenotype was resistance to penicillin, azithromycin (representative macrolide), and trimethoprim-sulfamethoxazole. Multidrug-resistant phenotypes that included fluoroquinolone resistance were uncommon; however, two phenotypes that included fluoroquinolone resistance not found in 1997-1998 were encountered in 1998-1999. This longitudinal surveillance study of resistance in S. pneumoniae revealed that significant changes do occur in just a single year and supports the need for surveillance at least on an annual basis, if not continuously.

Antimicrobial resistance in respiratory pathogens isolated in Brazil during 1999-2000.

The in vitro antimicrobial susceptibility of the respiratory pathogens Streptococcus Pneumoniae, Hemophilus influenzae, and Moraxella catarrhalis to commonly tested and prescribed agents was investigated during 1999-2000 and compared with results obtained during a previous 1997-1998 study. Of 448 isolates of S. Pneumoniae collected and tested in 1999-2000, 77.2% were susceptible, 19.9% were intermediate, and 2.9% were resistant to penicillin, demonstrating that there were no major changes in susceptibility to penicillin from 1997-1998 (77.1% susceptible, 18.7% intermediate, 4.2% resistant). All S. Pneumoniae isolates from 1999-2000 were susceptible to levofloxacin and vancomycin and >90% were susceptible to the B-lactams (amoxicillin-clavulanate, ceftriaxone, and cefuroxime) and macrolides (axithyromycin and clarithromycin), showing that susceptibility to these agents also remained unchanged since 1997-1998. The most notable increase in resistance between the two studies was demonstrated by trimethoprim-sulfamethoxazole, which increased from 23.4% to 38.6%. Penicillin resistance correlated with resistance to B-lactams, macrolides, and trimethoprim-sulfamethoxazole in both studies. In H. influenzae, the prevalence of B-lactamase-producing isolates remained unchanged (10.6% in 1999-2000; 11.0% in 1997-1998). All H. influenzae isolates were susceptible to levofloxacine, ceftriaxone, cefuroxime, and azithromycin, and showed no change between the two studies. Trimethoprim-sulfamethoxazole resistance was present in 40.1% of isolates in 1999-2000, and in 45.2% in 1997-1998. In M. catarrhalis, the prevalence of B-lactamase-producing isolates was unchanged (97.9% in 1999-2000;98.0% in 1997-1998). The most active agents against M. catarrhalis were azithromycin (MIC(90),< or = 0.03 microg/ml) and levofloxacin (MIC(90),< or = 0.03 microg/ml). Overall, these results suggest that, in Brazil, between 1999-2000 and 1997-1998, there have been no significant changes in the susceptibility of respiratory pathogens to any of the commonly tested and prescribed agents with the exception of trimethoprim-sulfamethoxazole for S. Pneumoniae.

Evaluation of current activities of fluoroquinolones against gram-negative bacilli using centralized in vitro testing and electronic surveillance.

Given the propensity for Enterobacteriaceae and clinically significant nonfermentative gram-negative bacilli to acquire antimicrobial resistance, consistent surveillance of the activities of agents commonly prescribed to treat infections arising from these organisms is imperative. This study determined the activities of two fluoroquinolones, levofloxacin and ciprofloxacin, and seven comparative agents against recent clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia using two surveillance strategies: 1) centralized in vitro susceptibility testing of isolates collected from 27 hospital laboratories across the United States and 2) analysis of data from The Surveillance Network Database-USA, an electronic surveillance network comprising more than 200 laboratories nationwide. Regardless of the surveillance method, Enterobacteriaceae, P. aeruginosa, and A. baumannii demonstrated similar rates of susceptibility to levofloxacin and ciprofloxacin. Susceptibilities to the fluoroquinolones approached or exceeded 90% for all Enterobacteriaceae except Providencia spp. (

Benchmarking the in vitro activities of moxifloxacin and comparator agents against recent respiratory isolates from 377 medical centers throughout the United States.

To benchmark the activity of moxifloxacin (a newer fluoroquinolone), a U.S. study comprising 16,141 contemporary isolates of Streptococcus pneumoniae (5,640), Haemophilus influenzae (6,583), and Moraxella catarrhalis (3,648) referred from 377 institutions during 1998 is described. For S. pneumoniae the modal MIC and MIC at which 90% of the isolates were inhibited (MIC(90)) for moxifloxacin were 0.12 and 0.25 microg/ml, respectively, independent of susceptibility to other drug classes, geography, or site of infection. Eleven isolates were intermediate or resistant to levofloxacin and grepafloxacin; of these isolates, 1 remained susceptible to sparfloxacin, 2 remained susceptible to moxifloxacin, and 4 remained susceptible to trovafloxacin. All 11 isolates possessed classic mutations in gyrA and/or parC known to confer reduced susceptibility to fluoroquinolones. Four isolates (originating from four separate states) belonging to a multidrug-resistant, fluoroquinolone-resistant clone were identified by pulsed-field gel electrophoresis. For moxifloxacin and trovafloxacin, at least 87% of isolates demonstrated MICs > or =3 twofold concentrations below the susceptibility breakpoints, in contrast to no more than 15% for levofloxacin, grepafloxacin, and sparfloxacin. Of the isolates that were multidrug resistant (7.4%), >98% remained susceptible to moxifloxacin. The modal MIC and MIC(90) for M. catarrhalis (both 0.06 microg/ml) and for H. influenzae (both 0.03 microg/ml) were independent of beta-lactamase production. These data demonstrate the in vitro activity of moxifloxacin and establish a baseline for future studies.

Analysis of ciprofloxacin activity against Streptococcus pneumoniae after 10 years of use in the United States.

As the most commonly used fluoroquinolone in the United States since 1987, ciprofloxacin has exerted the greatest selective pressure on S. pneumoniae and provides a valuable marker to evaluate the actual and potential emergence of fluoroquinolone resistance in this species. Analysis of susceptibility results obtained with 5,640 strains collected from throughout the United States showed that only 16 (0.3%) of the isolates demonstrated MICs of > or =4 microg/ml. The prevalence of this phenotype was significantly higher (P < 0.05) among penicillin-resistant populations, among isolates from patients >64 years old, and among respiratory isolates. However, >99% of strains had MICs of <4 microg/ml regardless of the risk group examined, and the MIC population distributions were the same for each risk group. These findings demonstrate that the phenotype of a MIC of > or =4 microg/ml remains uncommon after 10 years of ciprofloxacin use; however, these findings are no reason to become complacent with regard to appropriate use of fluoroquinolones and the need to carefully track resistance trends. Equally important is careful analysis of data that result from surveillance in terms of risk factors and other associated trends so that resistance and susceptibility, and their consequences, are neither over- nor underestimated.

Benchmarking the in vitro activity of moxifloxacin against recent isolates of Streptococcus pneumoniae, Moraxella catarrhalis, and Haemophilus influenzae. A European multi-centre study.

To benchmark the activity of moxifloxacin, a European study comprising 900 Streptococcus pneumoniae, 1051 Haemophilus influenzae, and 226 Moraxella catarrhalis referred from 30 institutions during 1998 is described. For S. pneumoniae, moxifloxacin and trovafloxacin MIC(90) and modal MICs values were 0.12 microg/ml and independent of susceptibility to other drug classes, geography, or site of infection. MIC(90)/modal MICs were, respectively, 0.25/0.12 microg/ml for grepafloxacin, 0.25/0.25 microg/ml for sparfloxacin, and 1.0/0.5 microg/ml for levofloxacin. The moxifloxacin C(max):MIC ratio of 20.8-26.3 is higher than comparator fluoroquinolones. Five isolates were intermediate or resistant to grepafloxacin, sparfloxacin, or levofloxacin of which four and three remained susceptible to trovafloxacin and moxifloxacin, respectively. For moxifloxacin, > 90% of S. pneumoniae isolates demonstrated MICs > or =3 dilutions below the susceptibility breakpoint used. Modal MICs and MIC(90) for M. catarrhalis (both 0.03 microg/ml) and H. influenzae (0.03 microg/ml and 0.06 microg/ml) were independent of beta-lactamase production. These data demonstrate the in vitro activity of moxifloxacin and establish a baseline for future surveillance studies that will be important for detecting and tracking any trends in changing activity of this fluoroquinolone.

Antimicrobial susceptibility of Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis collected from five centers in Brazil, 1997-98.

OBJECTIVE: To assess the susceptibility of the key respiratory pathogens Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis to antimicrobial agents used to treat respiratory tract infections. METHODS: Isolates were collected from five centers in Brazil during 1997-98, and susceptibility testing was conducted at a central laboratory according to National Committee for Clinical Laboratory Standards criteria. RESULTS: Of the 359Streptococcus pneumoniae isolates tested, 77% were susceptible, 19% were intermediate and 4% were resistant to penicillin. The susceptibility of S. pneumoniae to other beta-lactams and macrolides was greater than 90%, but cotrimoxazole was active against only 48% of the isolates. The prevalence of susceptible isolates was 100.0% for vancomycin and 99.7% for levofloxacin. beta-Lactam, macrolide, and cotrimoxazole activities were negatively associated with penicillin resistance. Of the 219 isolates of Haemophilus influenzae tested, 11% produced beta-lactamase and 11% were not susceptible to ampicillin. Nearly all H. influenzae isolates were susceptible to all other drugs, except cotrimoxazole (47% susceptibility). Of the 52 Moraxella catarrhalis isolates, 98% produced beta-lactamase, and the MIC of all drugs was 8 mg/L. CONCLUSIONS: When these data are compared with previous reports, our findings suggest that the prevalence of pneumococci that are resistant to agents such as penicillin and cotrimoxazole may be increasing in Brazil, which highlights the need to continue surveillance programs.

Effect of antibiotics on non-growing planktonic cells and biofilms of Escherichia coli.

Several classes of antibiotics were assessed for activity against non-growing Escherichia coli and cells grown as a biofilm. Antibiotics which had activity against non-growing cells also showed some activity against biofilms. Cephamycins were more active than other cephalosporins, but the most effective antibiotics were imipenem and ciprofloxacin, which were also active against steady state biofilms. However, none of the antibiotics studied was capable of completely eradicating a biofilm. These results suggest that growth rate plays a role in mediating resistance of biofilms to antibiotics.