Susceptibility of Enterobacteriaceae to β-lactam agents and fluoroquinolones: a 3-year survey in France

Objective   To assess trends in the susceptibility to β -lactam agents and to fluoroquinolones of clinically relevant Enterobacteriaceae isolated over a 3-year period in 14 French hospital laboratories.
Methods   During the second quarter of 1996, 1997 and 1998, 180 consecutive non-duplicate isolates of Enterobacteriaceae were collected in each center. Sixteen β -lactams and four quinolones were tested by the disk diffusion method. In addition, the double-disk synergy test was used to screen for the production of extended-spectrum β -lactamase (ESBL).
Results   Totals of 2507, 2312 and 2506 clinical isolates were obtained in each period, respectively. The distribution of Enterobacteriaceae species according to clinical specimens and wards was similar in each study period. No significant variation in the susceptibility rates to β -lactams and fluoroquinolones was observed, except in Klebsiella pneumoniae and Enterobacter aerogenes. The prevalence of ESBL-producing isolates decreased from 18% to 9% in the former, while it increased from 32% to 54% in the latter. At the same time, the susceptibility to ofloxacin and pefloxacin increased for K. pneumoniae ( P  < 0.003) and cephalosporinase-producing species ( P  < 0.05), except Enterobacter spp.
Conclusion   Over the 3-year study period β -lactams and fluoroquinolones remained highly active against Enterobacteriaceae clinical isolates, with the exception of E. aerogenes , probably as a result of the dissemination of multiresistant clones in French hospitals.     

Antimicrobial susceptibility of 136 Escherichia coli isolates from cases of neonatal meningitis and relationship with virulence

The susceptibility of 136 Escherichia coli isolates from cases of neonatal meningitis to amoxycillin, ceftriaxone, nalidixic acid, ciprofloxacin and gentamicin was determined in relation to the carriage of virulence factors and phylogenetic group. Only amoxycillin and nalidixic acid resistance was observed (40% and 3%, respectively). Nalidixic acid resistance alone was associated with non-virulent phylogenetic group A (50% vs. 6% of susceptible isolates; p 0.03). No difference in virulence was observed between two representative nalidixic acid-susceptible virulent group B2 isolates and their nalidixic acid-resistant derivatives in a rat model of neonatal meningitis, suggesting that nalidixic acid resistance does not affect the virulence of E. coli strains causing meningitis.     

Evaluation of several fluoroquinolones and beta-lactams in terms of their capability to restrict the selection of fluoroquinolone-resistant Salmonella: in vitro models

With a view to understanding the interaction between Salmonella and the drugs used to treat it, our aim was to compare the different capacities of various antibiotics to generate mutants resistant to fluoroquinolones following repeated exposure of the microorganisms to subinhibitory concentrations of these drugs. Mutants were generated by repeated exposure to fluoroquinolones and beta-lactams. In order to compare the different capacity to generate resistant mutants, we studied the minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) of the wild-type strains and of the mutants generated. These data were compared with pharmacokinetic parameters. Mutants generated following repeated exposure to fluoroquinolones exhibit an increased MPC as compared to the wild-type strains, both in strains that are nalidixic acid susceptible and in those that are nalidixic acid resistant, with repeated exposure to ciprofloxacin leading to the smallest increases. This increase in MPC is gradual and depends on the number of exposures the bacteria are subjected to. It results in a decrease in the AUC/MPC ratio, although the absolute values vary. Ciprofloxacin is the most active drug, both against nalidixic acid-susceptible and nalidixic acid-resistant strains, although in late mutants of originally nalidixic acid-resistant strains, the AUC/MPC values are low. Repeated exposure to amoxicillin and cefotaxime also produces an increase in the MPC of fluoroquinolones, with ciprofloxacin being the least affected. Exposure to amoxicillin leads to the greatest increase in the MPC of fluoroquinolones. When the AUC/MPC ratios of these mutants are compared, the values are still seen to be high (between 25 and 75). When we compare the MPC data with the antibiotic levels in humans following administration of the usual doses, it can be seen that ciprofloxacin exhibits the highest AUC/MPC and therefore the lowest risk of therapeutic failures. In addition, administration of subinhibitory concentrations of beta-lactams produces a decrease in fluoroquinolone susceptibility, which may lead to an increase in the risk of therapeutic failure if these compounds are subsequently used.     

Characterization of multiple-antimicrobial-resistant Escherichia coli isolates from diseased chickens and swine in China

Escherichia coli isolates from diseased piglets (n = 89) and chickens (n = 71) in China were characterized for O serogroups, virulence genes, antimicrobial susceptibility, class 1 integrons, and mechanisms of fluoroquinolone resistance. O78 was the most common serogroup identified (63%) among the chicken E. coli isolates. Most isolates were PCR positive for the increased serum survival gene (iss; 97%) and the temperature-sensitive hemagglutinin gene (tsh; 93%). The O serogroups of swine E. coli were not those typically associated with pathogenic strains, nor did they posses common characteristic virulence factors. Twenty-three serogroups were identified among the swine isolates; however, 38% were O nontypeable. Overall, isolates displayed resistance to nalidixic acid (100%), tetracycline (98%), sulfamethoxazole (84%), ampicillin (79%), streptomycin (77%), and trimethoprim-sulfamethoxazole (76%). Among the fluoroquinolones, resistance ranged between 64% to levofloxacin, 79% to ciprofloxacin, and 95% to difloxacin. DNA sequencing of gyrA, gyrB, parC, and parE quinolone resistance-determining regions of 39 nalidixic acid-resistant E. coli isolates revealed that a single gyrA mutation was found in all of the isolates; mutations in parC together with double gyrA mutations conferred high-level resistance to fluoroquinolones (ciprofloxacin MIC, >/=8 microg/ml). Class 1 integrons were identified in 17 (19%) isolates from swine and 42 (47%) from chickens. The majority of integrons possessed genes conferring resistance to streptomycin and trimethoprim. These findings suggest that multiple-antimicrobial-resistant E. coli isolates, including fluoroquinolone-resistant variants, are commonly present among diseased swine and chickens in China, and they also suggest the need for the introduction of surveillance programs in China to monitor antimicrobial resistance in pathogenic bacteria that can be potentially transmitted to humans from food animals.     

Detection of decreased fluoroquinolone susceptibility in Salmonellas and validation of nalidixic acid screening test.

We evaluated 1,010 Salmonella isolates classified as fluoroquinolone susceptible according to the National Committee for Clinical Laboratory Standards guidelines for susceptibility to nalidixic acid and three fluoroquinolones. These isolates were divided into two distinct subpopulations, with the great majority (n = 960) being fully ciprofloxacin susceptible and a minority (n = 50) exhibiting reduced ciprofloxacin susceptibility (MICs ranging between 0.125 and 0.5 microg/ml). The less ciprofloxacin-susceptible isolates were uniformly resistant to nalidixic acid, while only 12 (1.3%) of the fully susceptible isolates were nalidixic acid resistant. A similar association was observed between resistance to nalidixic acid and decreased susceptibility to ofloxacin or norfloxacin. A mutation of the gyrA gene could be demonstrated in all isolates for which the ciprofloxacin MICs were >/= 0.125 microg/ml and in 94% of the nalidixic acid-resistant isolates but in none of the nalidixic acid-susceptible isolates analyzed. Identification of nalidixic acid resistance by the disk diffusion method provided a sensitivity of 100% and a specificity of 87.3% as tools to screen for isolates for which the MICs of ciprofloxacin were >/= 0.125 microg/ml. We regard it as important that microbiology laboratories endeavor to recognize these less susceptible Salmonella strains, in order to reveal their clinical importance and to survey their epidemic spread.     

Evolution of susceptibility of aerobic gram-negative aerobic bacilli to quinolones and fluoroquinolones in a university hospital (1992-2000)

Susceptibility to quinolones of aerobic gram-negative bacilli was assessed in a 2000-bed university hospital from 1992 to 2000. There was a significant downward trend in the rate of susceptibility to nalidixic acid (Nal) for Enterobacteriaceae as a whole from 1992 to 2000 (86% vs 82%), and E. coli (92% vs 84%), and an upward trend for K. pneumoniae (74% vs 82%), the latter being related to the control of the spread of epidemic ESBL producing strains. The overall susceptibility of Enterobacteriaceae to ciprofloxacin (Cip) paralleled the susceptibility to Nal: decreased susceptibility for Enterobacteriaceae as a whole (96% vs 89%) and E. coli (99% vs 91%). A clear decrease in the level of susceptibility to Cip occurred during the study period among the Nal-resistant strains as demonstrated by the decrease in the median zone diameter (D) observed among the Nal-resistant strains of E. coli (26 mm in 1992 vs 19 mm in 1998-2000). The zone diameter distribution pattern changed from an unimodal distribution in 1992 to a trimodal distribution in 2000 secondary to the occurrence of a population of resistant strains (D = 13 mm) and of a highly resistant population (D = 6 mm). Finally, the susceptibility to Cip of P. aeruginosa strains remained stable around 62% throughout the study period.     

Typhoid fever due to a Salmonella typhi strain of reduced susceptibility to fluoroquinolones

Objective: To report a case of typhoid fever contracted in Portugal in 1994 due to a Salmonella typhi isolate which had reduced susceptibility to fluoroquinolone (MIC 1 mg/L of ciprofloxacin) and high level resistance to nalidixic acid (MIC ≥56 mg/L).
Methods: Molecular studies of reduced susceptibility to fluoroquinolones comprised complementation tests with a wild-type allele and sequencing directly from PCR products of the gyrA gene.
Results: Complementation tests and DNA sequencing showed that a mutation occurred in the gyrA gene of this clinical isolate, resulting in a substitution of phenylalanine for serine at position 83 of GyrA.
Conclusions: Because quinolones may be regarded as a treatment of choice in typhoid fever, it seems important now to recommend cautious use of these drugs as first-line therapy and possibly use of nalidixic acid resistance as a marker for detection of 'first-step' resistance to fluoroquinolones in S. typhi.     

Activity of 5 fluoroquinolones on hospital Gram-negative bacilli with different sensitivities to pefloxacin

The minimum inhibitory concentrations (MIC) of 5 fluoroquinolones, fleroxacin (FLE), ciprofloxacin (CIP), ofloxacin (OFL), enoxacin (ENO) and norfloxacin (NOR) have been determined by the agar dilution method towards 140 strains of Pseudomonas aeruginosa (Pa) and 146 Enterobacteriaceae showing different sensitivities to pefloxacin (PEF). The strains were isolated in 1988 at the Bellevue Hospital. The modal MIC is 0.12 for CIP, 0.25 for NOR, 0.5 for OFL, and 1 for FLE and ENO when used on Pa strains which are sensitive to PEF (n = 35) (MIC less than or equal to 1mg/1). The modal MIC is 0.25 - 0.5 for CIP, 0.5 for NOR, 1 for OFL and ENO, and 2 for FLE when used on Pa strains which are of intermediate sensitivity to PEF (n = 70) (1 less than MIC less than or equal to 4). The modal MIC is 2 for CIP, 8 for NOR and OFL, 8 - 16 for ENO, and 32 for FLE when used on Pa strains which are resistant to PEF (n = 35) (MIC greater than 4). The modal MIC is 0.015 for CIP, 0.06 for OFL, 0.12 for FLE, NOR and ENO when used on Escherichia coli strains which are sensitive to PEF (n = 47). The modal MIC is 0.5 for CIP, 1 for OFL and NOR, and 2 FLE and ENO, when used on Escherichia coli strains which are of intermediate sensitivity to PEF (n = 38). The modal MIC is 1 for CIP, 4 for OFL and NOR, 16 for FLE, and 32 for ENO when used on E coli strains which are resistant to PEF (n = 15). The 26 Serratia marcescens and 20 Citrobacter with MIC greater than or equal to 8 for PEF all have MICs greater than 1 and modal MICs greater than or equal to 4 for all the fluoroquinolones studied. CIP always showed greater activity than the other quinolones whatever the sensitivity shown towards PEF.     

MIC determination of fusidic acid and of ciprofloxacin using multidisk diffusion tests

Objective   To investigate the possibility of estimating the MICs of fusidic acid and ciprofloxacin for bacterial isolates using series of antibiotic disk concentrations in diffusion tests, so-called M-tests.
Methods   Thirty Staphylococcus aureus and S. epidermidis strains were tested for fusidic acid susceptibility. Sixty-one clinical isolates of eight bacterial species were tested for ciprofloxacin susceptibility. Disk diffusion was standardized according to the Swedish reference group for antibiotics (SRGA). For fusidic acid, a series of disks (1.5, 5.0, 15, 50 and 150 µg) was used. Ciprofloxacin was applied in four different diffusion sources (1, 3, 10 and 30 µg) on a single strip, the M-strip, and used. True MIC values were determined using the standardized agar dilution method according to the SRGA. Single-strain regression analysis (SRA) was employed to calculate critical concentration equivalents ( Q _zero).
Results   Fusidic acid and ciprofloxacin critical concentrations were determined for the bacterial isolates. The mean conversion factors for Q _zero to yield the true MIC were 2.06 (range 0.34–8.9) for fusidic acid and 2.05 (range 0.37–8.1) for ciprofloxacin. There was a correlation between true MIC values (all MICs expressed as 2 log + 9) and the calculated MIC values ( Q _zero× conversion factor) for both fusidic acid ( R  = 0.9822) and ciprofloxacin ( R  = 0.9696).
Conclusions   MIC values of clinical isolates can be estimated using SRA calculations on zone measurements in disk tests with several concentrations of the antibiotic in diffusion sources.     

Isolation of fluoroquinolone-resistantEscherichia coli andKlebsiella pneumoniae from an infected hickman catheter

Escherichia coli andKlebsiella pneumoniae resistant to fluoroquinolones were isolated from an infected Hickman catheter in a 43-year-old diabetic patient who had previously been treated with a 24-day course of ciprofloxacin (200 mg/12 h i.v.). MICs and MBCs of nalidixic acid, norfloxacin, ciprofloxacin, ofloxacin, pefloxacin and fleroxacin were determined for the strains using the methodology recommended by the NCCLS. Both strains were resistant to all the quinolones tested. Since long-term treatment with quinolones might favour the emergence of quinolone resistance or colonization with quinolone-resistant organisms, it is important to monitor for the development of bacterial resistance during therapy with the new fluoroquinolones.     

Six-year susceptibility trends and effect of revised Clinical Laboratory Standards Institute breakpoints on ciprofloxacin susceptibility reporting in typhoidal Salmonellae in a tertiary care paediatric hospital in Northern India

The antimicrobial trends over 6 years were studied, and the effect of revised Clinical Laboratory Standards Institute (CLSI) breakpoints (2012) for ciprofloxacin susceptibility reporting in typhoidal Salmonellae was determined. A total of 874 (95.4%) isolates were nalidixic acid-resistant (NAR). Using the CLSI 2011 guidelines (M100-S21), 585 (66.9%) isolates were ciprofloxacin susceptible. The susceptibility reduced to 11 (1.25%) isolates when interpreted using 2012 guidelines (M100-S22). Among the forty nalidixic acid susceptible (NAS) Salmonellae, susceptibility to ciprofloxacin decreased from 37 isolates (M100-S21) to 12 isolates (M100-S22). The 25 cases which appeared resistant with newer guidelines had a minimum inhibitory concentration (MIC) range between 0.125 and 0.5 μg/ml. MIC50 for the third generation cephalosporins varied between 0.125 and 0.5 μg/ml over 6 years whereas MIC90 varied with a broader range of 0.19–1 μg/ml. The gap between NAR and ciprofloxacin-resistant strains identified using 2011 guidelines has been reduced; however, it remains to be seen whether additional NAS, ciprofloxacin-resistant isolates are truly resistant to ciprofloxacin by other mechanisms of resistance.     

Drug resistance in Campylobacter jejuni, C coli, and C lari isolated from humans in north west England and Wales, 1997

AIMS: To test the sensitivity of strains of Campylobacter species isolated from humans in England and Wales against a range of antimicrobial agents for the purpose of monitoring therapeutic efficacy and as an epidemiological marker. METHODS: An agar dilution breakpoint technique was used to screen isolates against ampicillin, chloramphenicol, gentamicin, kanamycin, neomycin, tetracycline, nalidixic acid, ciprofloxacin, and erythromycin. Minimal inhibitory concentrations (MIC) were also determined for a sample of quinolone resistant strains. RESULTS: Approximately 50% of strains tested were resistant to at least one drug. Strains which were resistant to four or more of the drugs tested were classified as multiresistant; this occurred in 11.3% of C jejuni, 19.9% of C coli, and 63.6% of C lari. Resistance to erythromycin occurred in 1.0% of C jejuni and 12.8% of C coli. Resistance to quinolones occurred in 12% of strains, with a ciprofloxacin MIC of > 8 mg/l and a nalidixic acid MIC of > 256 mg/l; a further 4% of strains had intermediate resistance with a ciprofloxacin MIC of between 0.5 and 2 mg/l (fully sensitive strains, 0.25 mg/l or less) and a nalidixic acid MIC of between 32 and 64 mg/l (fully sensitive strains, 8 mg/l or less). CONCLUSIONS: Resistance to quinolones in campylobacters from human infection may relate to clinical overuse or use of fluoroquinolones in animal husbandry. Both veterinary and clinical use should be reconsidered and fluoroquinolone drugs used only as a treatment for serious infections requiring hospital admission. Erythromycin resistance is still rare in C jejuni but much more common in C coli.     

Susceptibility patterns of enteroaggregative Escherichia coli associated with traveller's diarrhoea: emergence of quinolone resistance.

Enteroaggregative Escherichia coli (EAggEC) isolates were identified as a cause of traveller's diarrhoea in 50 (9%) of 517 patients and their antimicrobial susceptibility was determined. Molecular epidemiological characterisation and investigation of the mechanisms of acquisition of quinolone resistance among nalidixic acid-resistant EAggEC strains was performed. Seventeen (34%) of 50 patients needed antimicrobial therapy, because of persistence of symptoms in nine cases and the severity of symptoms in eight cases. Ampicillin and tetracycline resistance was high, whereas chloramphenicol and co-trimoxazole showed moderate activity and amoxicillin plus clavulanic acid, nalidixic acid and ciprofloxacin showed very good activity. Resistance to nalidixic acid was demonstrated in three isolates, two from patients who had travelled to India. In all three strains the resistance was linked to mutations in the gyrA gene alone or in both gyrA and parC genes. Although ciprofloxacin shows excellent in-vitro activity and could be useful in the treatment of traveller's diarrhoea in patients travelling abroad, it may not be useful in patients who have journeyed to India or to Mexico.     

Comparative in vitro activities of five quinolone antibiotics, including gemifloxacin, against clinical isolates

The in vitro activities of ciprofloxacin, ofloxacin, norfloxacin, levofloxacin and gemifloxacin against 343 clinical isolates were compared. Gemifloxacin showed the greatest activity, with MIC₉₀ values as low as 0.03–0.25 mg/L against Streptococcus pneumoniae , Haemophilus influenzae , Moraxella catarrhalis , methicillin-susceptible Staphylococcus aureus and Klebsiella pneumoniae , while methicillin-resistant Staphylococcus aureus , Enterococcus spp., Pseudomonas spp., Acinetobacter spp., Escherichia coli and Enterobacter spp. strains exhibited low rates of susceptibility to all five fluoroquinolones.     

Antimicrobial susceptibility of bacteria causing urinary tract infections in Latin American hospitals: results from the SENTRY Antimicrobial Surveillance Program (1997)

Objectives: To evaluate the antimicrobial susceptibility patterns among 469 pathogens isolated as a significant cause of urinary tract infections in 10 Latin American medical centers.
Methods: Consecutively collected isolates were susceptibility tested by broth microdilution methods, and selected isolates were characterized by molecular typing methods.
Results: Escherichia coli and Klebsiella spp. isolates revealed high rates of resistance to broad-spectrum penicillins and to fluoroquinolones. Ceftazidime MICs of ≥2 mg/L, suggesting the production of extended-spectrum β-lactamases (ESBLs), were observed in 37.7% of K. pneumoniae and 8.3% of Escherichia coli isolates. Enterobacter spp. isolates were characterized by high resistance rates to ciprofloxacin (35%) and to ceftazidime (45%), but they generally remained susceptible to cefepime (95% susceptible). Pseudomonas aeruginosa and Acinetobacter spp. were highly resistant to ciprofloxacin and ceftazidime. Imipenem was active against 80% of P. aeruginosa and 93% of Acinetobacter spp. isolates.
Conclusions: Our results demonstrate a high level of resistance to various classes of antimicrobial agents among isolates causing nosocomial urinary tract infections in Latin American hospitals. Clonal dissemination of ESBL-producing K. pneumoniae strains was infrequent.     

Antibiotic resistance of Escherichia coli from community-acquired urinary tract infections in relation to demographic and clinical data

This prospective study determined the antibiotic susceptibility of 164 isolates of Escherichia coli from the urine of 164 patients (112 female, 52 male; mean age of 54.12 years) with community-acquired urinary tract infection (UTI). Half of the isolates were from uncomplicated UTI and half from complicated UTI (52 males and 34 females). Overall, 57.3% of isolates were resistant to ampicillin, 25% to co-trimoxazole, 20.1% to nalidixic acid, 14% to norfloxacin and ciprofloxacin, and 0% to fosfomycin and nitrofurantoin. Of the 82 isolates from complicated UTI, 16 (19.5%) were resistant to norfloxacin and ciprofloxacin, compared with seven (8.5%) from uncomplicated UTI (p 0.043). Isolates from patients aged >50 years were significantly more resistant than those from patients aged <50 years for nalidixic acid (p 0.007) and the fluoroquinolones tested (p 0.015). Resistance to fluoroquinolones was 25% (13/52) in males and 9% (10/112) in females (p 0.006). For patients with and without previous antimicrobial therapy, there was a significant difference only for resistance to nalidixic acid (p < 0.001) and the fluoroquinolones (p 0.011). There were adequate susceptibility rates to fosfomycin, nitrofurantoin and the fluoroquinolones for empirical use in the treatment of acute uncomplicated UTI. In order to interpret cumulative susceptibility data from the primary healthcare setting, it is necessary to take into account the type of UTI (uncomplicated vs. complicated), previous antimicrobial therapy, and the sex and age of each patient.     

Virulence and antimicrobial resistance profiles among Escherichia coli strains isolated from human and animal wastewater

To gain insight into whether Escherichia coli isolated from humans and resistant to some common antimicrobial agents are derived from animals, 85 E. coli strains were selected by ERIC-PCR from human and animal wastewater samples. Phylogroup, pathogenicity islands (PAIs), resistance to quinolones, fluoroquinolones and presence of extended-spectrum beta-lactamases (ESBLs) were analyzed. Among the total, 55% were resistant to nalidixic acid and 38% to ciprofloxacin; 12% produced ESBLs. Chicken-derived strains were associated with quinolone and fluoroquinolone resistance and presence of ESBLs, while human strains were associated with susceptibility. Group B2 E. coli strains were associated with human origin, susceptibility to fluoroquinolones and presence of PAIs, whereas groups A, B1 and D showed a low virulence profile and a high level of antimicrobial resistance. In both human and animal wastewater, E. coli A, B1 and D were prevalent, and strains from both origins showed a similar virulence profile in each phylogroup. These findings led us to hypothesize that abusive antibiotic use in food animal production may promote the development of resistance among these intestinal E. coli phylogroups, which could later be transmitted to humans through the food supply. The low prevalence of E. coli group B2 in the animal gut may explain, at least in part, the absence of emergence of resistant B2 isolates.     

Development of a rapid assay for detecting gyrA mutations in Escherichia coli and determination of incidence of gyrA mutations in clinical strains isolated from patients with complicated urinary tract infections.

The MICs of ofloxacin for 743 strains of Escherichia coli isolated from 1988 to 1994 were determined by testing. The strains were from patients with urinary tract infections complicated by functional or anatomical disorders of the urinary tract. Those determined to be ofloxacin resistant (MIC, > or =12.5 microg/ml) comprised 3 of 395 strains (1.3%) from the 1988 to 1990 group, 2 of 166 strains (1.2%) from the 1991 to 1992 group, and 7 of 182 strains (3.8%) from the 1993 to 1994 group. The incidence of resistant strains increased significantly during this period. The percentage of isolates with moderately decreased susceptibilities to ofloxacin (MIC, 0.39 to 3.13 microg/ml) also rose during the same period. To determine the incidence of gyrA mutations in urinary-tract-derived strains of E. coli, we developed a simple and rapid assay based on PCR amplification of the region of the gyrA gene containing the mutation sites followed by digestion of the PCR product with a restriction enzyme. Using this assay, we examined all 182 strains isolated in 1993 and 1994 for the presence of mutations at Ser-83 and Asp-87 in the gyrA gene. Of these strains, 33 (18.1%) had mutations in the gyrA gene. The incidences of mutations at Ser-83, at Asp-87, and at both codons were 10.4 (19 strains), 4.4 (8 strains), and 3.3% (6 strains), respectively. To determine the correlation of the mutations in the gyrA gene with susceptibilities to quinolones (nalidixic acid, ofloxacin, norfloxacin, and ciprofloxacin), we further examined 116 strains for which the MICs of ofloxacin were > or =0.2 microg/ml that were chosen from the isolates in the 1988 to 1992 group. The MICs of nalidixic acid for the strains without mutations at either Ser-83 or Asp-87 were < or =25 microg/ml, whereas those for the strains with single mutations or double mutations were from 50 to >800 microg/ml. For the fluoroquinolones, significant differences in the distributions of the MICs were observed among the strains without mutations, with single mutations, and with double mutations. The accumulation of mutations in the gyrA gene was associated with an increase in fluoroquinolone resistance. Ofloxacin MICs for the majority of the strains with single and double mutations were 0.39 to 3.13 and 6.25 to 100 microg/ml, respectively. This study demonstrates a chronological increase in the percentage of not only highly fluoroquinolone-resistant strains, corresponding to those with double mutations in the gyrA gene, but also strains with moderately decreased susceptibilities to fluoroquinolones, corresponding to those with single mutations. This increase in the incidence of strains with a single mutation in the gyrA gene portends a further increase in the incidence of strains with clinically significant resistance to fluoroquinolones.     

Antibacterial activity of enoxacin in vitro and in urine

Minimal inhibitory concentrations (MIC) of enoxacin (ENO) were evaluated by agar dilution, in comparison with MIC of nalidixic acid (NAL), pipemidic acid (PIP), oxolinic acid (OXO), pefloxacin (PEF), norfloxacin (NOR), ofloxacin (OFL) and ciprofloxacin (CIP), for eleven Enterobacteriaceae reference strains chosen as a function of sensitivity and level of resistance to NAL. In the four strains susceptible to NAL, MIC of ENO (0.06 to 0.25 micrograms/ml) were similar to those for PEF and NOR, 2 to 4 times inferior to those for OXO, 16 to those for PIP and 32 to those for NAL; this ratio of activity was also seen in the majority of strains resistant to NAL. Measurement of MIC of ENO for 397 recent clinical isolates confirmed efficacy of this substance against Enterobacteriaceae and showed its activity against Pseudomonas aeruginosa (mode MIC: 0.5-1 micrograms/ml), and Gram positive cocci, essentially Staphylococcus aureus (mode MIC: 0.5-1). Antibacterial activity in the urine was measured by the Heilman test in 5 male adults after two doses of 200 mg of ENO administered at 12 hours intervals, two doses of 400 mg of ENO and, in comparison two of 400 mg of PIP administered under the same conditions. Maximal inhibitory dilutions obtained with ENO reached (mean for 5 subjects): 1/64 to 1/128 after 200 mg and 1/128 to 1/512 after 400 mg for a sensitive Providencia strain (MIC ENO: 0.25); 1/32 to 1/128 and 1/64 to 1/256 for an E. coli strain of low level of resistance to NAL (MIC ENO: 2); activity was very low on a Serratia strain highly resistant to NAL (MIC ENO: 16).(ABSTRACT TRUNCATED AT 250 WORDS)     

In vitro activity of 4 fluoroquinolones against Klebsiella pneumoniae. Distribution according to phenotype resistance to aminoglycosides or beta-lactams

Minimal inhibitory concentrations (MIC) of pefloxacin (PEF), norfloxacin (NOR), ofloxacin (OFL) and ciprofloxacin (CIP) are evaluated by agar dilution against 100 Klebsiella pneumoniae strains isolated in hospital. MIC 50 and 90%, micrograms/ml, are respectively: CIP (0.25/8), OFL (1/16), NOR (1/32), PEF (2/64). We determined the phenotypes PEF/NOR/OFL/CIP by taking into account the critic concentrations of the French Committee for Antibiogram. The results are: SSSS = 45%, RI/RI/RI/RI = 20%, RI/SSS = 19%, RI/RI/RI/S = 8%, RI/RI/SS = 7%. When a strain is resistant to pefloxacin alone, the MICs of the other fluoroquinolones are higher than those of the sensitive strains. The resistance to fluoroquinolones is most frequent in strains that have acquired resistance to aminoglycosides or betalactams, but exists also in strains that have no acquired resistance to these antibiotics.