Bactericidal activity of three β-lactams alone or in combination with a β-lactamase inhibitor and two aminoglycosides against Klebsiella pneumoniae harboring extended-spectrum β-lactamases

Objective: To study the bactericidal activity of β-lactam antibiotics (imipenem, cefepime, cefpirome) alone or in combination with a β-lactamase inhibitor (sulbactam) in the presence or absence of aminoglycoside (amikacin or isepamicin) against Klebsiella pneumoniae strains producing extended-spectrum β-lactamases (ESBLs).
Methods: We characterized 10 strains by means of analytic isoelectric focusing and pulsed-field gel electrophoresis. The ESBLs produced by these strains were derived from either TEM (TEM-1, TEM-2) or SHV-1. The killing-curve method was used for this bacterial investigation. Bacteria (final inoculum 5×10 ⁵ CFU/mL) were incubated with antibiotics at clinical concentrations obtained in vivo.
Results: All the combinations with cefepime or cefpirome + sulbactam were bactericidal, with a 4 log₁₀ decrease being obtained within 6 h without regrowth at 24 h, whereas imipenem alone, and combinations, gave a bactericidal effect within 6 h. The two cephalosporins alone decreased the inoculum of 4 log₁₀ at 6 h but regrowth was observed at 24 h. When the aminoglycoside was added, this bactericidal effect was obtained within 3 h with amikacin and within 1 h with isepamicin.
Conclusions: Cefepime + sulbactam or cefpirome + sulbactarn may be an alternative to imipenem for the treatment of patients with ESBL-producing K. pneumoniae. Aminoglycosides are often associated in nosocomial infections due to ESBL-producing K. pneumoniae: isepamicin acted faster than amikacin, but both worked well. To conclude, it may be prudent to avoid extended-spectrum cephalosporins as single agent when treating serious infections due to ESBL-producing K. pneumoniae. Addition of a β-lactamase inhibitor such as sulbactam ± aminoglycoside is advisable to avoid failure of treatment.     

Transferable plasmid mediating resistance to multiple antimicrobial agents in Klebsiella pneumoniae isolates in Greece

Objective   To investigate the underlying resistance mechanisms in 10 Klebsiella pneumoniae isolates.
Methods   Ten K. pneumoniae strains according to distinct bacteriocin typing and REP-PCR, were examined for their plasmid content, their ability to transfer their resistance to aminoglycosides and third-generation cephalosporins, and their production of aminoglycoside-modifying enzymes and β -lactamases.
Results   Transfer of resistance to the above-mentioned antibiotics as well as to co-trimoxazole and tetracycline in Escherichia coli strain RC 85 at a frequency of 5–10⁶ was achieved for all strains by conjugation. Similar strains harbor a self-transferable multiresistant plasmid (80 kb) with similar Eco RI and Hind III restriction patterns. This plasmid encodes an extended-spectrum β -lactamase which confers high-level resistance to third-generation cephalosporins and aztreonam. It produces SHV-5 β -lactamase, as demonstrated by isoelectric focusing and DNA sequencing. Aminoglycoside resistance was co-transferred, and AAC(6')-I, mediating resistance to gentamicin, tobramycin, netilmicin and amikacin, and AAC(3)-I, mediating resistance to gentamicin and sisomycin, were encoded in all isolates and their transconjugants, while APH(3')-I, mediating resistance to kanamycin and neomycin, was encoded in seven strains.
Conclusions   It appears that a multiresistant transferable plasmid encoding the SHV-5 β -lactamase, causing unusually high resistance to ceftazidime and aztreonam, and the combination AAC(6')-I + AAC(3)-I of acetylating enzymes causing, also resistance to all clinically available aminoglycosides, is established in K. pneumoniae in Greece.     

Antimicrobial resistance patterns among aerobic Gram-negative bacilli isolated from patients in intensive care units: results of a multicenter study in Russia

Objective: To determine the antimicrobial resistance patterns among aerobic Gram-negative bacilli isolated from patients in intensive care units (ICUs) in different parts of Russia.
Methods: During 1995–96, 10 Russian hospitals from different geographic areas were asked to submit 100 consecutive Gram-negative isolates from patients with ICU-acquired infections. Minimal inhibitory concentrations (MICs) of 12 antimicrobials were determined by Etest and results were interpreted according to National Committee for Clinical Laboratory Standards (NCCLS) guidelines.
Results: In total, 1005 non-duplicate strains were obtained from 863 patients. The most common species were Pseudomonas aeruginosa (28.8%), Escherichia coli (21.4%), Klebsiella pneumoniae (16.7%), Proteus mirabilis (9.7%), Enterobacter spp. (8.2%) and Acinetobacter spp. (7.7%). High levels of resistance were seen to second- and third-generation cephalosporins, ureidopenicillins, β-lactam/β-lactamase inhibitor combinations and gentamicin. The most active agents were imipenem (no resistance in Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterobacter spp. and Acinetobacter spp., 7% resistance in Pseudomonas aeruginosa ), amikacin (7% resistance in Pseudomonas aeruginosa and Acinetobacter spp., 4% in Enterobacter spp., 1% in Escherichia coli and Proteus mirabilis, no resistance in Klebsiella pneumoniae ) and ciprofloxacin (15% resistance in Pseudomonas aeruginosa, 5% in Enterobacter spp. and Proteus mirabilis, 2% in Klebsiella pneumoniae, 1% in Escherichia coli ).
Conclusions: Second- and third-generation cephalosporins, ureidopenicillins, β-lactam/β-lactamase inhibitor combinations and gentamicin cannot be considered as reliable drugs for empirical monotherapy for aerobic Gram-negative infections in ICUs in Russia.     

P594 Intracellular killing of drug-resistant Staphylococcus aureus by different antibiotics

Objectives:  The aim of this study was to assess the carbapenem susceptibility of four nosocomial pathogens and to evaluate the reliability of the susceptibility results determined by E-test and disc diffusion (DD) methods.
Methods:  Escherichia coli ( n  = 73), Klebsiella pneumoniae ( n  = 60), Pseudomonas aeruginosa ( n  = 70) and Acinetobacter spp. ( n  = 70) isolated from nosocomial infections in 2002–2003 were included in the study. Thirty-five per cent of the strains were isolated from intensive care units. After determining antimicrobial susceptibility against imipenem and meropenem by DD (10  μ g; Oxoid, UK) and Etest (AB Biodisk, Solna, Sweden) methods, the results were categorised as susceptible (S), intermediate (I) and resistant (R) according to the NCCLS criteria. For statistical analyses, the intermediate group was included in the resistant category because of the low numbers of bacteria in the former group.
Results:  None of E. coli or K. pneumoniae strains were resistant to carbapenems, whereas, resistance reached up to 59.0% in Acinetobacter spp. and P. aeruginosa isolates. By either method, the pattern of the susceptibility of the four bacteria was not statistically significantly different for imipenem vs. meropenem. Total agreement of DD and E-test methods for susceptibility to imipenem was 95.7%, and 90.0% in Acinetobacter spp. and P. aeruginosa , respectively; and susceptibility to meropenem was 90.0% for both bacteria. However, the difference of the results obtained by either method was statistically significant for Acinetobacter spp.
Conclusion:  Study results suggest a high resistance rate for Acinetobacter spp. and P. aeruginosa strains against carbapenem antibiotics in our hospital. Further studies are needed to clarify whether E-test should be used to confirm meropenem resistance of Acinetobacter spp. determined by DD method.     

Bacterial and epidemiologic study of the resistance to oxyiminocephalosporins in Escherichia coli in a French hospital

Objective: To understand the mechanisms and epidemiology of resistance to oxyiminocephalosporins in Escherichia coli over a 2-year period in a French hospital.
Methods: Forty-four strains, resistant or intermediately resistant to one of the oxyiminocephalosporins or aztreonam, were collected from 35 patients. MIC determinations were carried out for the 44 isolates using a panel of β-lactam antibiotics, and characterization of the β-lactamases they produced by isoelectric focusing and catalytic activity measurement. Extended-spectrum β-lactamase production was studied by use of the double disk diffusion test. Conjugation experiments were used to search for plasmidic cephalosporinase. An epidemiologic study was then performed, by use of molecular typing of the strains with an ERIC-PCR method and a case-control analysis.
Results: Less than 1% of all the E. coli isolates at our hospital showed decreased susceptibility to oxyiminocephalosporins. Only three of the 44 isolates showed synergy between clavulanate and a third-generation cephalosporin and produced an extended-spectrum β-lactamase. For the other strains, a β-lactamase with a highly basic isoelectric point was detected. Spectrophotometric measures confirmed that most of these isolates were AmpC hyper-producers. No plasmidic cephalosporinase could be detected by conjugation experiments. Molecular typing showed all isolates to be different, except for two strains isolated in two patients of the same hospital unit, and for the repeated isolates of some patients. When 20 case patients were compared to 40 randomly selected control patients, prior receipt of an antimicrobial and more specifically of a β-lactam agent was significantly associated with case patients.
Conclusions: Although it appears to be very rare, the resistance to broad-spectrum cephalosporins needs our attention, because of the high frequency of E. coli infections and β-lactam use in their treatment.     

Recommendation for treatment of severe infections caused by Enterobacteriaceae producing extended-spectrum β-lactamases (ESBLs)

Extended-spectrum β-lactamase (ESBL)-producing organisms are a global problem. No randomized controlled trials have ever been performed to guide optimal treatment. However, in vitro studies and observational studies strongly suggest that carbapenems (imipenem or meropenem) should be regarded as drugs of choice for serious infections due to ESBL-producing organisms. Other β-lactam antibiotics (cefepime, β-lactam/β-lactamase inhibitor combinations) are not suitable as first-line therapy. The increasing frequency of the association between quinolone resistance and ESBL production have greatly limited the role of this class of antibiotic against ESBL producers.     

Resistance to second- and third-generation cephalosporins among Escherichia coli and Klebsiella species is rare in Finland

Objective: To investigate the antimicrobial resistance of Escherichia coli and Klebsiella spp. from pus, urine and respiratory specimens, with particular emphasis on the detection of third-generation cephalosporin resistance.
Methods: E. coli (698) and Klebsiella sp. (476) strains from pus, respiratory and urinary specimens from hospital patients were collected from 19 laboratories. Data about consumption of third-generation cephalosporins and cefuroxime were collected from 24 hospitals. Antimicrobial susceptibility was tested with disk diffusion in primary laboratories and by an agar dilution method. Extended-spectrum β-lactamase (ESBL) production was studied with a double disk synergy test and an ESBL Etest. The β-lactamase classes were characterized with polymerase chain reaction probes of the TEM and SHV β-lactamase families and isoelectric focusing.
Results: Only 0.6% of E. coli and 2.3% of Klebsiella spp. strains were resistant or intermediately resistant to cefotaxime, ceftriaxone and/or ceftazidime. The ESBL producers detected comprised one E. coli harboring TEM-like genes and five Klebsiella pneumoniae strains, two of which harbored SHV-like genes, two TEM-like genes and one both. Although consumption of cefuroxime has increased in the years 1990–1994, from 3.48 to 5.84 defined daily doses/100 bed-days, and the consumption of third-generation cephalosporins from 1.25 to 1.94 defined daily doses/100 bed-days, cefuroxime resistance of E. coli was only 3%.
Conclusion: Although the use of broad-spectrum cephalosporins has increased, resistance to second- and thirdgeneration cephalosporins is still rare in Finland.     

Risk factors for antimicrobial resistance and influence of resistance on mortality in patients with bloodstream infection caused by Pseudomonas aeruginosa

This study was conducted to evaluate risk factors for antimicrobial resistance and influence of resistance on mortality in Pseudomonas aeruginosa bacteremia. Data on 190 patients with P. aeruginosa bacteremia were analyzed retrospectively. Antimicrobial resistance to antipseudomonal antibiotics was evaluated. The main outcome measure was 30-day mortality. In P. aeruginosa bacteremia, resistance rates to piperacillin (PIP), ceftazidime (CAZ), ciprofloxacin (CIP), and imipenem (IPM) were 29 (56/190), 19 (36/190), 17 (32/190) and 15% (28/190), respectively. Prior uses of fluoroquinolones or carbapenems were independent risk factors for resistance to CIP and IPM, and prior use of extended-spectrum cephalosporins was a risk factor for PIP-R. An indwelling urinary catheter was a risk factor for PIP-R, CAZ-R, and CIP-R. An invasive procedure was a risk factor for CIP-R and IPM-R. The 30-day mortality rate was 44% (33/75) in patients infected by strains resistant to any of the antipseudomonal antibiotics, but 33.9% (39/115) in those by strains susceptible to all antipseudomonal antibiotics (p = 0.161). Among patients with bloodstream infection due to antimicrobial-resistant P. aeruginosa, those infected by IPM-R strains had the highest mortality (IPM-R, 53.6% vs. CAZ-R, 47.2% vs. CIP-R 46.9%, PIP-R, 39.3%). In this study regarding P. aeruginosa bacteremia, prior uses of fluoroquinolones, carbapenems, or extended-spectrum cephalosporins, a prior invasive procedure, and an indwelling urinary catheter were found to be associated with antimicrobial resistance. The patients with bloodstream infection caused by antimicrobial-resistant P. aeruginosa, especially to imipenem, had a tendency toward higher mortality than those infected by susceptible strains.     

Antibiotic susceptibility and genotypic characterization of Haemophilus influenzae strains isolated from nasopharyngeal specimens from children in day-care centers in eastern France

Objective   To determine the overall carriage rate for Haemophilus influenzae in young children in day-care centers, the frequency of resistance to various classes of antibiotic, and the clonal relationship between isolates of the various resistant phenotypes.
Methods   Nasopharyngeal (NP) specimens were obtained and cultured on chocolate agar with bacitracin. Antibiotic susceptibility testing and serotyping were performed for all isolates. The genetic polymorphism of ampicillin-susceptible and β-lactamase-producing isolates was studied by pulsed-field gel electrophoresis using Sma I.
Results   Of the 596 NP secretion cultures, 152 (25.5%) were positive for H. influenzae . Sixty-four (42.1%) isolates produced β-lactamase and two (1.3%) were ampicillin resistant but did not produce β-lactamase. We were unable to serotype 150 isolates; one isolate belonged to capsular serotype e and one to serotype f. Forty-six major DNA patterns were identified among 76 randomized isolates. β-lactamase producing isolates more frequently showed EP than ampicillin-susceptible isolates P  < 10⁻⁴. The frequency of isolates with EP was significantly lower in day-care centers attended by less than 20 children than in those attended by more than 20 children ( P  = 0.020).
Conclusions   Resistance due to β-lactamase production has disseminated in some day-care centers, mostly by person-to-person spread but also via the possible conjugal transfer of large plasmids between strains. The size of day-care centers may affect the risk of transmission.     

Development of resistance in Pseudomonas aeruginosa obtained from patients with cystic fibrosis at different times

Objective  Determination of the extent of changes in quantitative resistance in Pseudomonas aeruginosa isolates from patients with cystic fibrosis over a period of approximately 2 years.
Methods  Three hundred and ninety nine isolates of P. aeruginosa collected from 34 pediatric patients in the period between April 1994 and April 1996 were investigated. During the 2 years the children were treated with a combination of a betalactam and an aminoglycoside, approximately every 3 months. In between they received ciprofloxacin orally, when required. The minimal inhibitory concentrations (MICs) of 38 clones of P. aeruginosa defined by different patterns in macrorestriction analysis (pulse field gel electrophoresis, PFGE) were established for 12 antibiotics: gentamicin, amikacin, tobramycin, ciprofloxacin, levofloxacin, moxifloxacin, trovafloxacin, imipenem, meropenem, ceftazidime, cefepime, and piperacillin by means of broth microdilution tests according to DIN 58940.
Results  Twenty-four of the 38 clones developed increased MIC values during the time of observation especially for aminoglycosides and quinolones. Comparatively less affected were ceftazidime, imipenem and meropenem. An association between the number of the intravenous treatment courses and the increase of the MIC values could not be verified.
Conclusions  A trend towards an increase of the MICs against antipseudomonal agents was observed over a limited period of time. It is necessary to prevent this development possibly by employing suitable combinations of antibiotics and the introduction of new substances.     

Imipenem resistance inEnterobacter

Blood cultures obtained on two separate occasions from a 37-year-old male who received multiple antibiotics (including imipenem) for treatment of repeated episodes of intraabdominal abscesses and bacteremia yielded two isolates ofEnterobacter with reduced susceptibility to imipenem, extended-spectrum cephalosporins, penicillins and aztreonam. Both isolates were unstable, giving rise to different colony types, each of which produced a single, non-inducible Bush group 1 -lactamase (pI=9.6) that hydrolyzed imipenem. Outer membrane proteins were analyzed but no differences were detected between strains with different levels of imipenem resistance. Three-dimensional tests performed in conjunction with disk diffusion susceptibility tests provided a rapid and convenient means of detecting the production of imipenem-hydrolyzing enzymes by theEnterobacter strains. These isolates provided additional evidence that overproduction of the group 1 cephalosporinase ofEnterobacter can contribute to resistance to imipenem.     

Multicenter study of the in vitro activity of cefepime in comparison with five other broad-spectrum antibiotics against clinical isolates of Gram-positive and Gram-negative bacteria from hospitalized patients in Switzerland

Objective: To assess the in vitro susceptibility of clinical isolates to cefepime and five other antimicrobial agents with broad-spectrum activity.
Methods: The minimal inhibitory concentrations of 1521 Gram-positive cocci and 3170 Gram-negative rods were determined by the Etest procedure.
Results: The susceptibilities were as follows. Gram-positive bacteria: cefepime, 92.7%; ceftazidime, 60.5%; ceftriaxone, 87.8%; imipenem, 92.6%; amikacin, 56.5%; ciprofloxacin, 72.5%. Gram-negative bacteria: cefepime, 97.8%; ceftazidime, 94.3%; ceftriaxone, 83.1%; imipenem, 95.7%; amikacin, 96.6%; ciprofloxacin, 95.8%.
Conclusions: Cefepime had the best activity when compared with the other broad-spectrum β-lactams ceftazidime, ceftriaxone, imipenem, and the non-β-lactams amikacin and ciprofloxacin.     

Natural antibiotic susceptibility of Enterobacter amnigenus, Enterobacter cancerogenus, Enterobacter gergoviae and Enterobacter sakazakii strains

Objective   To investigate the natural susceptibility to 69 antimicrobial agents of 107 Enterobacter strains comprising E. amnigenus ( n  = 18), E. cancerogenus ( n  = 26), E. gergoviae ( n  = 28) and E. sakazakii ( n  = 35).
Methods   Minimal inhibitory concentrations (MICs) were determined with a microdilution procedure in Isosensitest broth and cation-adjusted Mueller–Hinton broth.
Results   All the species were naturally sensitive or intermediate to tetracyclines, amino-glycosides, numerous β -lactams (acylureidopenicillins, ticarcillin, ampicillin/sulbactam, several cephalosporins, carbapenems, aztreonam), quinolones, antifolates, chloramphenicol and nitrofurantoin. Natural resistance was found to penicillin G, oxacillin, several macrolides, lincosamides, streptogramins, glycopeptides, rifampicin and fusidic acid. Species-related differences in natural susceptibility were found to some β -lactams, azithromycin and fosfomycin. Whereas E. gergoviae was the most susceptible species to azithromycin, E. cancerogenus was most susceptible to fosfomycin and was the only species showing natural resistance to amoxicillin, amoxicillin/clavulanic acid, cefaclor, cefazoline, loracarbef and cefoxitin. There were only minor medium-dependent differences in susceptibility to most antibiotics.
Conclusions   The present study establishes a database concerning the natural susceptibility of recently established Enterobacter species to a wide range of antibiotics, which can be applied for the validation of routine susceptibility test results. β -Lactam susceptibility patterns indicate the expression of species-specific β -lactamases expressed at high or low levels in all the species except E. sakazakii .     

Surveillance of Pseudomonas aeruginosa sensitivity to antibiotics in France and distribution of beta-lactam resistance mechanisms: 1998 GERPB study

In a prospective study carried out during a three-week period in October 1998 in 13 teaching hospitals, 735 non-repetitive isolates of Pseudomonas aeruginosa were collected. In patients presenting cystic fibrosis (70 strains), the main serotypes isolated were O:6 (14.3%) and O:1 (14.3%). Serotypes O:11 and O:12 were exceptional. In other patients (665 strains), the most frequent serotypes were O:6 (15.9%), O:11 (15.6%), O:1 (10.7%) and O:12 (9.2%). The antibiotic susceptibility rates were as follows (respectively, non-cystic fibrosis and cystic fibrosis strains): ticarcillin, 55 and 59%, piperacillin, 71 and 67%, ceftazidime, 75 and 67%, cefepime, 56 and 43%, cefpirome, 37 and 21%, aztreonam, 57 and 56%, imipenem, 83 and 70%, amikacin, 69 and 33%, ciprofloxacin, 56 and 61% and fosfomycin, 33 and 43%. Serotype O:12 was the least susceptible to antibiotics. Forty-five percent of the non-cystic fibrosis strains presented intermediate susceptibility or resistance to ticarcillin. The most frequent mechanisms of resistance were: non-enzymatic resistance (14.3%), overproduction of the constitutive cephalosporinase (13.8%), production of transferable beta-lactamase (8.6%) and a combination of these mechanisms (4.2%). Among cystic fibrosis strains, resistance to beta-lactam antibiotics was mainly due to overproduction of the constitutive cephalosporinase (18.6%), whereas production of a transferable beta-lactamase was rare (1.4%). Susceptibility to aminoglycosides and fluoroquinolones was less frequent in isolates producing transferable beta-lactamases and/or overproducing cephalosporinase. Decreased susceptibility to imipenem was more frequent in strains presenting a high level of cephalosporinase production. Among the cephalosporins, cefepime was the least affected by the overproduction of constitutive cephalosporinase. Ceftazidime remained the most efficient antibiotic against both susceptible isolates and strains presenting a non-enzymatic or PSE-1 penicillinase-producing mechanism.     

Comparative in vitro pharmacodynamics of BO-2727, meropenem and imipenem against Gram-positive and Gram-negative bacteria

Objective: To investigate and compare the in vitro pharmacodynamics of three carbapenems: imipenem, meropenem and BO-2727.
Method: The following studies were performed: (1) comparative studies of the rate of killing of the three carbapenems of reference strains of Gram-positive and Gram-negative bacteria at a concentration corresponding to the 1-h serum level following 500 mg intravenously in humans; (2) comparative studies of the rate of killing of BO-2727, meropenem and imipenem at different antibiotic concentrations of reference strains of Gram-positive and Gram-negative bacteria; (3) comparative studies of the rate of killing of BO-2727, meropenem and imipenem of bacteria which are phenotypically tolerant; (4) studies of the postantibiotic effect of BO-2727 using viable counts and optical density; (5) studies of the postantibiotic sub-MIC effect (PA SME) of BO-2727 using optical density.
Results: No difference in killing rate was noted between the three carbapenems, and there was no concentration-dependent killing of the Gram-negative strains after 6 h. A pronounced paradoxical effect was seen against Staphylococcus aureus. All three antibiotics were able to kill phenotypically tolerant bacteria. Only very short or no postantibiotic effect of BO-2727 was found against the investigated strains. Very long PA SMEs were noted for the Gram-negative strains, although there was a pronounced variation for the different strains of Pseudomonas aeruginosa.
Conclusions: There was no significant difference between the studied carbapenems in their pharmacodynamic properties. All three antibiotics acted similarly to other β-lactam antibiotics.     

Comparison of screening methods for TEM- and SHV-derived extended-spectrum β-lactamase detection

Objective   To compare common extended-spectrum β -lactamase (ESBL) screening methods and β -lactams for their ability to detect TEM- and SHV-related ESBL enzymes.
Methods   This study compared disk diffusion testing by NCCLS methodology, the Jarlier double disk test, a disk-on-disk test, a modified three-dimensional test and the E test method for their sensitivity and specificity in detecting TEM- and SHV-related ESBL producers. Three negative and 22 positive controls were studied. These were two Klebsiella pneumoniae and 23 Escherichia coli transconjugants. Seventeen β -lactam antibiotics were tested: cefamandole, cefotetan, cefoxitin, cefuroxime, cefixime, cefoperazone, cefotaxime, cefpodoxime, cefsulodin, ceftazidime, ceftibuten, ceftizoxime, ceftriaxone, moxalactam, cefepime, cefpirome and aztreonam.
Results   NCCLS disk diffusion was 14% sensitive with ceftriaxone, 36% with cefotaxime, 64% with aztreonam, 68% with cefpodoxime, and 73% with ceftazidime. Cefoperazone, cefamandole, cefpodoxime and cefpirome showed 91% sensitivity using the Jarlier test. Using the disk-on-disk test, cefsulodin showed 95% sensitivity, and cefoperazone, cefepime and cefamandole showed 91% sensitivity. With the modified three-dimensional test, cefoperazone, cefpodoxime and cefpirome showed 91% sensitivity.
Conclusions   For practical reasons, we would recommend use of either the Jarlier test or the commercial cephalosporin disks containing clavulanic acid to screen for ESBL producers. Cefoperazone, cefamandole, cefpodoxime and cefpirome showed good sensitivity across the methods tested.     

Clinical significance of beta-lactamase induction and stable derepression in gram-negative rods

Most strains of enterobacteria andPseudomonas aeruginosa produce chromosomally-determined Class I-lactamases. When synthesized copiously these enzymes cause resistance to almost all-lactams, except imipenem and, sometimes, carbenicillin and tenocillin. Elevated-lactamase production arises transiently, via induction, inPseudomonas aeruginosa andEnterobacter, Citrobacter, Morganella, indole-positiveProteus andSerratia spp. when these organisms are exposed to-lactams. Permanent high-level enzyme production arises via mutation, in the stably-derepressed mutants of these species. These mutants arise spontaneously at high frequency (10^–5–10^–8). Most early penicillins and first-generation cephalosporins are strong inducers of Class I enzymes at sub-inhibitory concentrations, as are cefoxitin and imipenem. Consequently their MICs reflect what lability these antibiotics have to inducibly-expressed-lactamase. Except with imipenem this lability usually is so great that the inducible enzyme causes clinical resistance. Although most other newer cephalosporins and ureidopenicillins are labile to the Class I enzymes they induce poorly below the MIC, and their lability is not reflected in resistance unless secondary inducers (e.g. cefoxitin or imipenem) are present. Although the weak inducer activity of these agents helps to maintain their activity against the inducible cells it renders the drugs highly selective for the pre-existing stably-derepressed mutants. Many cases have been reported where stably-derepressed mutants have overrun inducible populations of bacteria in patients undergoing therapy with-lactamase-labile weak inducers such as ureidopenicillin and third-generation cephalosporins.     

TEM-24 extended-spectrum β-lactamase-producing Enterobacter aerogenes: long-term clonal dissemination in French hospitals

Objective To investigate interstrain relatedness of TEM-24-producing Enterobacter aerogenes clinical strains isolated between 1993 and 1998 in 10 French hospitals from nine areas by pulsed-field gel electrophoresis (PFGE) and plasmid patterns.
Methods Fifteen TEM-24 - producing strains and a set of 16 control strains having various other antibiotic resistance phenotypes were genotyped by PFGE. Plasmid DNA from TEM-24 - producing strains and transconjugants was analyzed .
Results Analysis of Xba I macrorestriction patterns revealed only minor variations, and showed that all 15 TEM-24 - producing strains were closely related. Some isolates originating from distant areas had indistinguishable patterns . According to their clustering correlation coefficients, they were also genomically distant from the control strains . Two plasmid patterns were observed in TEM-24-producing strains, one of them in 13 of the strains. Large plasmids of 85 kb encoding TEM-24 β-lactamase were present in all isolates and, in all except one strain, could be transferred with high frequency by conjugation .
Conclusions These results confirm that the spread of the TEM-24 extended-spectrum β-lactamase in France was essentially due to the dissemination of a single clone .     

Is antimicrobial resistance also subject to globalization?

In recent years one of the more alarming aspects of clinical microbiology has been the dramatic increase in the incidence of resistance to antibacterial agents among pathogens causing nosocomial as well as community-acquired infections. There are profound geographic differences in the incidence of resistance among pathogens of the respiratory tract, only some of which can be explained by the local use of antibiotics. A high percentage of Moraxella catarrhalis strains produce β -lactamase and are thus resistant to many β -lactam antibiotics. In contrast, β -lactamase production among strains of Haemophilus influenzae rarely reaches more than 30% around the world. Methicillin-resistance in Staphylococcus aureus is a common and increasing problem in hospitals but its extent varies both locally and nationally. Resistance is usually associated with the local spread of resistant strains. High standards of hygiene in hospitals can prevent the spread of such strains but once established they can be difficult to eradicate. Although Streptococcus pyogenes remains highly susceptible to penicillins, even after many decades of their use, resistance to macrolides has occurred. This resistance can rise and fall. Although the increase of macrolide resistance in S. pyogenes can often be associated with an increase in the use of these drugs, this is not always so. In some cases it has been shown to be caused by the spread of one or more resistant clones. Eradication of these clones can reduce the level of resistance markedly. Resistance to both macrolides and penicillins among strains of Streptococcus pneumoniae is seen world-wide but is highly variable from country to country. Local habits of drug usage may play a part. In Italy, for example, there is preference for the use of parenteral third-generation cephalosporins for some severe infections and there is a corresponding low level of penicillin-resistance among pneumococci.     

Detection of imipenem-resistant and metronidazole-resistant Bacteroides fragilis group strains in fecal samples

Objective: To investigate the imipenem and metronidazole resistance profiles of Bacteroides fragilis group strains in fecal samples and to detect the resistance genes ( ccrA and nim ) coding for imipenem and metronidazole resistance in B. fragilis group strains.
Methods: In total, 925 fecal samples, 729 from consecutive diarrhea patients and 196 from healthy controls, were collected at Huddinge University Hospital in 1997. A modified disk diffusion method was employed to screen for imipenem-resistant and metronidazole-resistant B. fragilis group strains. In strains considered resistant by the modified disk diffusion method, the minimum inhibitory concentrations (MICs) were further determined by the agar dilution method. PCR assays were used to detect the carbapenem-hydrolyzing metallo-β-lactamase gene ( ccrA ) and the 5-nitroimidazole resistance genes ( nim ) in pure cultures (purePCR), directly from fecal samples through direct broth enrichment (dirPCR) and by immunomagnetic separation (imsPCR).
Results: Two imipenem-resistant B. fragilis strains, one of which was simultaneously resistant to metronidazole, and two B. fragilis group strains with MICs near the breakpoint for metronidazole resistance, were isolated from the fecal samples of diarrhea patients. The ccrA gene was identified in all the imipenem-resistant B. fragilis strains by purePCR, dirPCR and imsPCR. The nim genes were also detectable by these PCR assays.
Conclusions: The incidences of imipenem-resistant and metronidazole-resistant B. fragilis group strains were low in the investigated diarrhea patients. Simultaneous resistance to imipenem and metronidazole is of great concern in clinical medicine, and the proposed PCR assays may be useful in epidemiologic studies of distribution of resistance genes in the fecal microflora.