Therapeutic drug monitoring of once daily tobramycin in cystic fibrosis—caution with trough concentrations

BACKGROUND

: Once daily intravenous aminoglycoside dosing (ODD) is widely used to treat acute Pseudomonas aeruginosa exacerbations in patients with cystic fibrosis. Controversy exists as to what is the most appropriate method of therapeutic drug monitoring (TDM) of such therapy with recommendations including trough plasma concentrations of <1 mg/L or <2 mg/L, area under curve (AUC) and various nomograms. This study aimed to compare the exposures to ODD of tobramycin in adults and children with cystic fibrosis using the AUC and trough TDM approaches.

METHODS

: Using a mono-exponential software program to calculate AUC from 2 plasma concentrations, AUCs were determined in 22 adults with pre-dose tobramycin concentrations <1 mg/L. The exposure of 5 children with reduced tobramycin clearances was simulated at the usual recommended dose of 10 mg/kg/daily but retaining a trough <1 mg/L.

RESULTS

: A tobramycin dose of 10 mg/kg of tobramycin in these patients with normal serum creatinine and a trough concentration <1 mg/L resulted in exposures in excess of those associated with conventional 8-hourly dosing.

CONCLUSIONS

: The TDM approach of a trough <1 mg/L, as used with conventional 8-hourly tobramycin dosing, is not relevant to ODD.

Prevalence of antimicrobial resistances in common pathogenic Enterobacteriaceae in Australia, 2004: report from the Australian Group on Antimicrobial Resistance

Antibiotic resistance in 3 common pathogenic types of Enterobacteriaceae was examined in a pointprevalence study in 2004. Strains of Escherichia coli, Klebsiello and Enterobacter species were collected prospectively in 25 institutions in Australian capital cities and tested by broth microdilution to 12 13-lactams and 3 other antibiotics. Almost 22% of isolates tested were from blood cultures. In E. coli, acquired resistance to ampicillin and piperacillin was common (> 40%), and clinically significant percentages of intermediate susceptibility and resistance (> 8%) were observed to amoxycillin-clavulanate, cefazolin and trimethoprim. In Klebsiella species, clinically important acquired resistance (> 8%) was seen to piperacillin, cephalothin and trimethoprim, while in Enterobacter species, this was found with piperacillin, ceftriaxone, ceftazidime and trimethoprim. Blood culture isolates had similar rates of resistance to isolates from other specimen sources. New South Wales/Australian Capital Territory (combined) tended to have higher percentages of resistance than the other states, which were otherwise comparable across the agents and species tested. Multi-resistance, defined as more than 3 acquired resistances to antibiotic classes, was found in 6.5% of E. coli, 8.3% in Klebsiella species and 16.9% of Enterobacter species. Co-resistance to ciprofloxacin, gentamicin and/or trimethoprim was common in isolates presumptively harbouring extended-spectrum beta-lactamases. Strains with extended-spectrum beta-lactamases, although common in other countries, appear to be at fairly low levels in Australia; less than 4% in E. coli and less than 9% in Klebsiella species. Rates in Enterobacter species were not able to be determined. Presumptive plasmid-borne AmpC beta-lactamases were seen at low levels across the country and carbapenemases have now been found for the first time in Australia in Enterobacteriaceae. Both of these types of resistance represent a significant threat to major last-line antibiotics.

Australian Government attempts at regulatory and other control of antimicrobial resistance

Antimicrobial resistance has been on the government agenda in Australia since the early 1980s. At that time the National Health and Medical Research Council (NHMRC) established a working party composed of human and veterinary microbiologists to look at antibiotic use and, in particular, the risks of using them in stockfeed. This action was taken in response to continuing reports from overseas, particularly the United Kingdom, of resistant and multi-resistant Salmonella species being selected in food animals and spread to humans. The working party report made a number of regulatory recommendations in terms of resistance surveillance and scheduling. None of these recommendations were adopted directly, but the national regulators continued to call on NHMRC for advice and in various guises the NHMRC maintained a working group on antibiotics and resistance until 1997, when it was decided that antimicrobial resistance was no longer a priority issue. As the regulators still wished to receive advice, the Therapeutic Goods Administration (TGA) took temporary responsibility for maintaining the expertise or the working party.

Statistical characterisation of bacterial wild-type MIC value distributions and the determination of epidemiological cut-off values

MIC distribution data were obtained from a variety of international sources, and pooled after selection by a defined criterion. Sixty-seven of these datasets were subjected to a range of statistical goodness-of-fit tests. The log-normal distribution was selected for subsequent modelling. Cumulative counts of MIC distribution data were fitted to the cumulative log-normal distribution using non-linear least squares regression for a range of data subsets from each antibiotic-bacterium combination. Estimated parameters in the regression were the number of isolates in the subset, and (the log(2) values of) the mean and standard deviation. Optimum fits for the cumulative log-normal curve were then used to determine the wild-type MIC range, determined by calculating the MICs associated with the lower and upper 0.1% of the distribution, rounding to the nearest two-fold dilution, and calculating the probabilities of values higher and lower than these values. When plotted logarithmically, histograms of MIC frequencies appeared normal (Gaussian), but standard goodness-of-fit tests showed that the two-fold dilution grouping of MICs fits poorly to a log-normal distribution, whereas non-linear regression gave good fits to population (histogram) log-normal distributions of log(2) MIC frequencies, and even better fits to log-normal cumulative distributions. Optimum fits were found when the difference between the estimated and true number of isolates in the fitted subset was minimal. Sixteen antibiotic-bacterium datasets were fitted using this technique, and the log(2) values of the means and standard deviations were used to determine the 0.1% and 99.9% wild-type cut-off values. When rounded to the nearest two-fold dilution, > or = 98.5% of MIC values fall within the cut-off value range. Non-linear regression fitting to a cumulative log-normal distribution is a novel and effective method for modelling MIC distributions and quantifying wild-type MIC ranges.

Have South Australian isolates of Neisseria meningitidis become less susceptible to penicillin, rifampicin and other drugs? A study of strains isolated over three decades, 1971-1999

AIMS

To ascertain whether isolates of Neisseria meningitidis in South Australia (SA) have become less susceptible to antimicrobial agents. The patients studied were children and adults in SA with either meningococcal bacteraemia or meningitis or both.

METHODS

The susceptibility of meningococci to 11 antimicrobial agents, including sulphonamides, penicillin and rifampicin, was tested by agar dilution, and in the case of six of the drugs, by E test also.

RESULTS

Resistance to folate antagonists emerged in 1979 and became very common. Resistance peaked in 1995 at 76% of strains. Relative insusceptibility to penicillin was first encountered amongst strains isolated in 1985, and, while the incidence of such strains increased slightly, the overall incidence was low at 10 (5.2%) of 190 strains tested. Meningococci relatively insusceptible to rifampicin were encountered as early at 1971 and did not become more common. The incidence of such strains at 26 (13.7%) of 189 strains tested was higher than that for penicillin. For the 11-year period 1989-1999 of > or= 84 strains tested all were susceptible to ceftriaxone, chloramphenicol and ciprofloxacin; 98% were susceptible to azithromycin and 97% were susceptible to minocycline. Shifts in MIC values for these drugs were not detected.

CONCLUSIONS

Resistance was common to sulphonamides and co-trimoxazole, however >or=95% meningococci tested were susceptible to drugs commonly used in the treatment of meningococcal disease, including penicillin and ceftriaxone. Relative insusceptibility to rifampicin was more common but did not increase during the 29-year period. For all drugs tested, except rifampicin, there was good agreement between agar dilution and E test results.

Lower respiratory tract infections and community acquired pneumonia in adults

BACKGROUND

Lower respiratory tract infections--acute bronchitis and community acquired pneumonia (CAP)--are important causes of morbidity in Australia. Acute bronchitis is often treated with antibiotics, although the cause is usually viral. Community acquired pneumonia may be fatal, particularly in the elderly, therefore appropriate assessment and management is essential.

OBJECTIVE

This article describes the aetiology, clinical assessment, investigations and management of acute bronchitis and CAP in the community.

DISCUSSION

Clinical assessment is important for acute bronchitis and CAP, with investigations such as C reactive protein, serology, and chest X-ray informing diagnosis and management of the latter. Causative organisms are usually not identified, but are presumed to be viral for acute bronchitis, and Streptococcus pneumoniae for CAP; although 'atypicals' are also important. Antibiotics should generally not be prescribed for acute bronchitis, however, there is some evidence they may provide limited benefits in patients who have chest signs, are very unwell, are older, have comorbidities, or smoke. In patients with CAP, treated outside of hospital, the combination of amoxycillin and doxycycline/roxithromycin is the treatment of choice.

TSN Database Australia, a new tool to monitor antimicrobial resistance in Australia

An electronic network of Australian microbiology laboratories was established to monitor the emergence and occurrence of antimicrobial resistance among clinically relevant bacteria. It is believed that the data network collected approximately 42 per cent of all antibacterial susceptibility test results generated by Australian laboratories. The network comprised 94 hospitals and 9 private commercial laboratories. Selected data elements were extracted and electronically transmitted to a central location. Upon receipt, all data were first normalised and thereafter examined for errors. Duplicate results for the same patient were identified to prevent skewing of the data toward resistance. All data passing quality assessment was staged for release of a new database release that occurred monthly. Unusual test results were first validated prior to their inclusion into the database. Using an Internet-based query tool, individual institutions could query their own data, but could only query aggregated data for other regional or national analyses. Individual patient results could be examined nor could the results of any individual institution other than their own. As of March 2002, TSN Database Australia contained 14,648,752 test results, from 2,000,394 strains (453 different taxa) and 1,213,605 patients. Since the same database concept has been established in 10 other countries (United States of America, Europe, and Canada), observations made in Australia may be compared to those observed elsewhere in the world. This article will describe TSN in greater detail, describe the query tool and some of the analyses that are possible.

SENTRY Antimicrobial Surveillance Program Asia-Pacific region and South Africa

The SENTRY Antimicrobial Surveillance Program was initiated in January 1997 and was designed to monitor the predominant pathogens and antimicrobial resistance for both nosocomial and community-acquired infections globally by using validated, reference-quality identification and susceptibility testing methods performed in a central laboratory. Consecutive bacterial or fungal isolates, deemed clinically significant by local criteria, are forwarded to the local reference laboratory from various study objectives. The major objectives include blood stream infections, community-acquired respiratory tract infections (Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis), pneumonias in hospitalised patients, skin and soft tissue infections, and urinary tract isolates from hospitalised patients. In 2001, special objectives were introduced to examine gastroenteritis pathogens and beta-haemolytic streptococcal isolates. Over 22 nations participate in SENTRY surveillance globally. The Women's and Children's Hospital, Adelaide has been the reference centre for the Asia-Pacific region and South Africa since 1998, and three other Australian institutions, from Brisbane, Perth, and Adelaide, are part of the global network. All isolates received from our region are tested against up to 29 antimicrobial agents using custom-made broth microdilution panels. The data generated from SENTRY allows Australia to compare our antimicrobial resistance patterns and trends with our regional neighbours.

Low levels of fluoroquinolone resistance in Escherichia coli. A five-year trend in Australia measured through the use of TSN Database Australia

In many countries, fluoroquinolones are among the most commonly used antibacterial drugs. Concerns about bacterial resistance to these and other frequently used drugs have been raised by the medical and scientific communities. While fluoroquinolone resistance has not yet developed among many bacteria, emergence of resistance in Escherichia coli would be a problem as multiple resistances to other antibiotics is now a common problem. This paper examines trends in resistance to fluoroquinolones in Escherichia coli through analysis of data collected from Australian institutions between 1997 and 2001. During the study period, norfloxacin and ciprofloxacin were the most frequently tested fluoroquinolones in Australian laboratories. An examination of results for strains tested simultaneously against both drugs indicated that testing against either drug accurately predicted resistance or susceptibility for the other (99.7% agreement). Over 400,000 tests were performed to determine the fluoroquinolone susceptibility of E. coil. Data were analysed by the test method used (Calibrated Dichotomous Sensitivity (CDS) or National Committee for Clinical Laboratory Standards (NCCLS)). The data indicate that fluoroquinolone resistance in E. coli has not yet emerged as a significant problem in Australia, but there are some indications of low level increases in resistance rates. Norfloxacin results are likely to be a better guide to fluoroquinolone resistance in this species using this method of surveillance.

Laboratory surveillance of invasive pneumococcal disease in Australia, 2003 predicting the future impact of the universal childhood conjugate vaccine program

A comprehensive invasive pneumococcal disease (IPD) laboratory surveillance program was carried out in Australia in 2003. This program provided data on the prevalence of pneumococcal serotypes and antimicrobial resistance. There were 1,995 isolates tested with 34 per cent (683) from children aged less than five years and 27 per cent (535) from the elderly aged more than 65 years. One thousand eight hundred and sixty were isolates from blood, 79 from CSF and 56 from other sterile sites. In young children, 84 per cent of isolates were a serotype and 92 per cent a serogroup in the 7-valent pneumococcal conjugate vaccine (7vPCV). Of penicillin resistant isolates in children less than five years of age 85 per cent and 98 per cent were a serotype and serogroup in the 7vPCV respectively. When the universal 7vPCV vaccine program in young children is introduced in 2005, a proportion of cases of IPD should also be prevented in young adults (estimated reduction of 54 cases annually) and elderly Australians (an estimated reduction of 110 cases annually) as a result of improved herd immunity. Pneumococcal serotypes with higher rates of penicillin resistance (19F, 14 and 6B) were more prevalent in the elderly than in young children. In contrast, erythromycin resistance was more common in children less than five years of age (24%) compared to the elderly (15%). The predominant serotype with erythromycin resistance in Australia was serotype 14 and thus there is likely to be a major reduction in erythromycin resistance as a result of 7vPCV vaccination. Continued surveillance of pneumococcal serotype distribution and antibiotic susceptibility will be essential in order to identify serotype replacement by non-vaccine serotypes and to monitor the overall impact of current and future vaccine programs on invasive pneumococcal disease in Australia, not only in young children but also in other age groups.

Impact of antibiotic resistance on the treatment of sepsis

Antibiotics are essential to the treatment of bacterial sepsis as they reduce the bacterial burden. The impact of bacterial resistance has recently been studied and found to be important in a range of conditions. Resistance to antibiotics can be defined genotypically, phenotypically and clinically through pharmacokinetic/pharmacodynamic studies and their correlations with clinical outcomes. Although the kinetics of antibiotics has been shown to be favourably altered in sepsis, a range of studies in sepsis has revealed that for most pathogens resistance contributes to significant increases in mortality. This has been clearly demonstrated in bacteraemia, including community- and hospital-acquired infection, and with bacteraemia caused by vancomycin-resistant enterococci, methicillin-resistant staphylococci and extended-spectrum producing Gram-negative bacteria. Significant mortality increases have also been seen with ventilator-associated pneumonia and serious infections requiring admission to intensive care. Gentotypic and phenotypic resistance in coagulase-negative staphylococci causing bacteraemia, and in invasive pneumococcal disease has not shown differences in mortality. In the latter case, dosage regimens have to date been adequate to overcome laboratory-defined resistance. Early indications are that de-escalating therapy from broad-spectrum initial coverage after results of cultures and susceptibility tests become available does not jeopardize outcomes, and further prospective studies are warranted. There is now convincing evidence that broad-spectrum initial therapy to cover the likely pathogens and their resistances pending culture results is mandatory in sepsis to minimize adverse outcomes.

Antibiotic use in animals--prejudices, perceptions and realities

Regulatory authorities have suspended the use of some antibiotics as growth promoters in animal feed. The subject remains a hotly debated topic around the world. Controversy surrounds whether such use in animals presents a real risk of increasing resistance in human pathogens, and hence a human health problem. Views tend to be polarized. Proponents of the bans point to falling rates of resistance in animal and human isolates as a direct result; detractors question whether evidence exists for a link between growth promoter use and resistance in human pathogens and cite a decline in animal health among the undesirable effects. The article by Phillips et al. in this issue puts one view, this article aims to consider the merits of the arguments put forward by both sides and looks to a way forward.

Steady-state pharmacokinetics of intravenous colistin methanesulphonate in patients with cystic fibrosis

OBJECTIVES

To define the steady-state pharmacokinetics of colistin methanesulphonate and colistin in patients with cystic fibrosis (CF) following intravenous administration of the former.

MATERIALS AND METHODS

The study was conducted in 12 patients with CF following intravenous administration of colistin methanesulphonate (1.63-3.11 mg/kg) every 8 h for at least 2 days. On the day of study, four blood samples were collected from each patient at 60, 120, 240 and 360 min after the end of the infusion. Concentrations of colistin methanesulphonate and colistin in plasma were measured separately by HPLC.

RESULTS

At steady-state, colistin methanesulphonate had a mean (+/- S.D.) total body clearance, volume of distribution and half-life of 2.01 +/- 0.46 mL/min per kg, 340 +/- 95 mL/kg and 124 +/- 52 min, respectively. Colistin had a significantly longer mean half-life of 251 +/- 79 min (P<0.001). With the regimen used, colistin methanesulphonate was well tolerated. This is the first report on the pharmacokinetics of colistin methanesulphonate in CF patients determined using concentrations of colistin methanesulphonate and colistin in plasma.

CONCLUSIONS

Based on the in vitro pharmacodynamics against Pseudomonas aeruginosa previously published by our group and these pharmacokinetic findings, dose escalating trials may be warranted to maximize efficacy.

Pharmacodynamics and dosing of aminoglycosides

Aminoglycosides are concentration-dependent killing agents whose pharmacodynamic predictors of efficacy are the area-under-the-curve to minimum inhibitory concentration ratio and the peak to minimum inhibitory concentration ratio. Prospective studies have shown that these agents can be given once-daily or less frequently in most clinical settings, with equal efficacy and possible reduced toxicity. Dosages for different clinical settings have been studied and methods are available to monitor once-daily dosing.

Laboratory surveillance of invasive pneumococcal disease in Australia in 2001 to 2002--implications for vaccine serotype coverage

This paper reports the results of comprehensive laboratory surveillance of invasive pneumococcal disease (IPD) in Australia during 2001 and 2002. The 7-valent conjugate pneumococcal vaccine was introduced for high risk paediatric groups, including Indigenous children, in late 2001. Of 1,355 isolates from non-Indigenous children, 86 per cent belonged to serotypes and 93 per cent to serogroups represented in the 7-valent pneumococcal conjugate vaccine. Thirteen per cent and 24 per cent of isolates had reduced susceptibility to penicillin and erythromycin, respectively and of these, more than 99 per cent belonged to serogroups represented in the 7-valent vaccine. Of the 1,504 isolates from non-Indigenous adults, 96 per cent belonged to serotypes included in the 23-valent polysaccharide vaccine; 14 per cent and 15 per cent had reduced susceptibility to penicillin and erythromycin, respectively and more than 95 per cent of these belonged to serotypes included in the 7-valent conjugate vaccine. In Western Australia and the Northern Territory (the only states for which Indigenous status was consistently available), there were 29 cases of IPD in Indigenous children, of which 21 were due to 7-valent vaccine serotypes in 2001, compared with 24 cases, including 10 due to vaccine serotypes, in 2002. This represents a statistically significant increase in the proportion of total isolates due to non-vaccine serotypes (chi2 = 3.93, p = 0.048) following the introduction of the 7-valent conjugate vaccine, principally due to serotypes 7F and 12F. The number of episodes due to penicillin resistant isolates decreased from nine in 2001 to two in 2002. Ninety per cent of isolates from Indigenous adults were included in the 23-valent polysaccharide vaccine and six per cent and five per cent had reduced susceptibility to penicillin and erythromycin, respectively. Conjugate pneumococcal vaccines can be expected to reduce the incidence of IPD due to vaccine serotypes in vaccinated children and potentially, their adult contacts. It may also impact favourably on the incidence of IPD due to penicillin and erythromycin resistant strains. Continued surveillance of both serotype distribution and antibiotic susceptibility are required to identify serotype replacement by non-vaccine serotypes and to monitor the overall impact of current and future vaccine programs on invasive pneumococcal disease in Australia.

A risk analysis framework for the long-term management of antibiotic resistance in food-producing animals

In recent years, there has been increasing concern that the use of antibiotics in food-producing animals, particularly their long-term use for growth promotion, contributes to the emergence of antibiotic-resistant bacteria in animals. These resistant bacteria may spread from animals to humans via the food chain. They may also transfer their antibiotic-resistance genes into human pathogenic bacteria, leading to failure of antibiotic treatment for some, possibly life-threatening, human conditions. To assist regulatory decision making, the actual risk to human health from antibiotic use in animals needs to be determined (risk assessment) and the requirements for risk minimisation (risk management and risk communication) determined. We propose a novel method of risk analysis involving risk assessment for three interrelated hazards: the antibiotic (chemical agent), the antibiotic-resistant bacterium (microbiological agent) and the antibiotic-resistance gene (genetic agent). Risk minimisation may then include control of antibiotic use and/or the reduction of the spread of bacterial infection and/or prevention of transfer of resistance determinants between bacterial populations.

Pathogen occurrence and antimicrobial resistance trends among urinary tract infection isolates in the Asia-Western Pacific Region: report from the SENTRY Antimicrobial Surveillance Program, 1998-1999

Worldwide surveillance of antimicrobial resistance among urinary tract pathogens is useful to determine important trends and geographical variation for common Gram-positive and -negative species. The most common causative uropathogens often have intrinsic or acquired resistance mechanisms which include ESBL production among enteric bacilli, multi-drug resistant staphylococci and non-fermentative Gram-negative bacilli such as Pseudomonas aeruginosa and Acinetobacter spp. and vancomycin-resistant Enterococcus spp. This study evaluates pathogen frequency and the resistance rates among urinary tract infection (UTI) pathogens in 14 medical centres in the Asia-Pacific region between 1998 and 1999. The isolates were referred to a central monitor for reference NCCLS broth microdilution testing, identification confirmation and patient demographic analysis. Over 50% of the 958 pathogens were Escherichia coli and Klebsiella spp. followed by P. aeruginosa, Enterococcus spp. and Enterobacter spp. Susceptibility for the three enteric bacilli was high for carbapenems (100%), 'fourth-generation' cephalosporins (cefepime 94.9-98.6%) and amikacin (> or = 93.0%). Beta-lactamase inhibitor compounds were more active against E. coli (piperacillin/tazobactam; > 90% susceptible) than the other two enteric species and all other tested agents had a narrower spectra of activity. The rank order of anti-pseudomonal agents was amikacin (91.5% susceptible)> imipenem > piperacillin/tazobactam > tobramycin > ceftazidime and cefepime (77.4 and 76.4% susceptible, respectively). Susceptibility to quinolones for the P. aeruginosa isolates was only 63.2-67.0%. Only one vancomycin-intermediate Enterococcus spp. (van C phenotype) was detected among the 103 strains tested. Newer fluoroquinolones (gatifloxacin; MIC(50), mg/l) were more potent against enterococci than ciprofloxacin (MIC(50), 2 mg/l) and high-level resistance to aminoglycosides was common (41.7%). The data presented are compared to studies of similar design from other areas which are part of the SENTRY surveillance network.

In vitro activities of ertapenem (MK-0826) against recent clinical bacteria collected in Europe and Australia

Ertapenem (MK-0826, L-749,345) is a 1-beta-methyl carbapenem with a long serum half-life. Its in vitro activity was determined by broth microdilution against 3,478 bacteria from 12 centers in Europe and Australia, with imipenem, cefepime, ceftriaxone, and piperacillin-tazobactam used as comparators. Ertapenem was the most active agent tested against members of the family Enterobacteriaceae, with MICs at which 90% of isolates are inhibited (MIC(90)s) of < or =1 microg/ml for all species. Ertapenem also was more active than imipenem against fastidious gram-negative bacteria and Moraxella spp.; on the other hand, ertapenem was slightly less active than imipenem against streptococci, methicillin-susceptible staphylococci, and anaerobes, but its MIC(90)s for these groups remained < or =0.5 microg/ml. Acinetobacter spp. and Pseudomonas aeruginosa were also much less susceptible to ertapenem than imipenem, and most Enterococcus faecalis strains were resistant. Ertapenem resistance, based on a provisional NCCLS MIC breakpoint of > or =16 microg/ml, was seen in only 3 of 1,611 strains of the family Enterobacteriaceae tested, all of them Enterobacter aerogenes. Resistance was also seen in 2 of 135 anaerobes, comprising 1 Bacteroides fragilis strain and 1 Clostridium difficile strain. Ertapenem breakpoints for streptococci have not been established, but an unofficial susceptibility breakpoint of < or =2 microg/ml was adopted for clinical trials to generate corresponding clinical response data for isolates for which MICs were as high as 2 microg/ml. Of 234 Streptococcus pneumoniae strains tested, 2 required ertapenem MICs of 2 microg/ml and one required an MIC of 4 microg/ml, among 67 non-Streptococcus pyogenes, non-Streptococcus pneumoniae streptococci, single isolates required ertapenem MICs of 2 and 16 microg/ml. These streptococci also had diminished susceptibilities to other beta-lactams, including imipenem as well as ertapenem. The Etest and disk diffusion gave susceptibility test results in good agreement with those of the broth microdilution method for ertapenem.

Integration of molecular characterization of microorganisms in a global antimicrobial resistance surveillance program

The SENTRY Antimicrobial Surveillance Program has incorporated molecular strain typing and resistance genotyping as a means of providing additional information that may be useful for understanding pathogenic microorganisms worldwide. Resistance phenotypes of interest include multidrug-resistant pathogens, extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci, and fluoroquinolone-resistant (FQR) strains of gram-negative bacilli and Streptococcus pneumoniae. Clusters of > or =2 isolates within a given resistance profile that are linked temporally and by hospital location are flagged for DNA fingerprinting. Further characterization of organisms with respect to resistance genotype is accomplished with use of polymerase chain reaction and DNA sequencing. This process has been highly successful in identifying clonal spread within clusters of multiresistant pathogens. Between 50% and 90% of MRSA clusters identified by phenotypic screening contained evidence of clonal spread. Among the Enterobacteriaceae, ESBL-producing strains of Escherichia coli and Klebsiella pneumoniae are the most common pathogens causing clusters of infection, and approximately 50% of recognized clusters demonstrate clonal spread. Clusters of Pseudomonas aeruginosa, Acinetobacter species, and Stenotrophomonas maltophilia have been noted with clonal spread among patients with urinary tract, respiratory, and bloodstream infections. Characterization of mutations in the FQR-determining region of phenotypically susceptible isolates of E. coli and S. pneumoniae has identified first-stage mutants among as many as 40% of isolates. The ability to characterize organisms phenotypically and genotypically is extremely powerful and provides unique information that is important in a global antimicrobial surveillance program.

Characterization of Pseudomonas aeruginosa isolates: occurrence rates, antimicrobial susceptibility patterns, and molecular typing in the global SENTRY Antimicrobial Surveillance Program, 1997-1999

During 1997-1999, a total of 70,067 isolates (6631 Pseudomonas aeruginosa isolates) were analyzed in the SENTRY program by geographic region and body site of infection. The respiratory tract was the most common source of P. aeruginosa. P. aeruginosa isolation rates increased during the study interval. Europe was the only region to show a significant decline in beta-lactam and aminoglycoside susceptibility rates. There was a reduction in the rates of susceptibility of Canadian isolates to imipenem and of Latin American isolates to meropenem. A total of 218 multidrug-resistant P. aeruginosa isolates (MDR-PSA; resistant to piperacillin, ceftazidime, imipenem, and gentamicin) were observed; MDR-PSA occurrence rates (percentages of all isolates) ranged from 8.2% (Latin America) to 0.9% (Canada). No antimicrobial inhibited >50% of MDR-PSA strains. Molecular characterization of selected, generally resistant strains was performed. Isolates showing unique ribogroups were found in Europe, Latin America, and the United States, but clonal spread was documented in several medical centers.

Genetic relatedness of multidrug-resistant, methicillin (oxacillin)-resistant Staphylococcus aureus bloodstream isolates from SENTRY Antimicrobial Resistance Surveillance Centers worldwide, 1998

We reviewed Staphylococcus aureus bloodstream infection isolates from SENTRY centers worldwide during 1998 to evaluate the molecular epidemiology of multiply drug-resistant methicillin (oxacillin)-resistant S. aureus (MDR-MRSA). MDR-MRSA was defined as a S. aureus isolate with a MIC for oxacillin at >2 microg/ml and with four or more additional resistances. A total of 325 unique patient isolates of MDR-MRSA from five continents were analyzed using ribotyping and pulsed-field gel electrophoresis (PFGE). The frequency of MDR-MRSA among all S. aureus BSI isolates ranged from only 2.2% in Canada to 35.6% in the Asia-Pacific region. Forty-eight ribotypes (RT) were distinguished, but over 80% of the isolates were contained within the 10 most prevalent RTs. The most common RT, RT 184.5, which included 30% of all MDR-MRSA, was found on four of five continents. PFGE provided superior discrimination and identified numerous clusters of possible clonal dissemination of MDR-MRSA within individual medical centers and between institutions that are in geographic proximity. In four instances, strains with indistinguishable PFGE patterns were found on more than one continent. The predominant PFGE subtype in South America (RT 893.5/Ia) was isolated from patients at centers in Brazil, Argentina, and Portugal, and closely related subtypes were isolated in Chile and Italy. There is great geographic variation in rates of methicillin- and multidrug-resistance among S. aureus bloodstream isolates worldwide. Although many MDR-MRSA strains group geographically, a few closely related epidemic strains have wide regional and even global range.