Eight hundred and eighty-three strains of Campylobacter spp. isolated between 1982 and 1989 from human stools and poultry products were screened for quinolone resistance. In this period the prevalence of resistant strains isolated from poultry products increased from 0% to 14%. During the same period the prevalence in man increased from 0% to 11%. The emergence of quinolone resistance has implications for the identification of campylobacter up to species level: the susceptibility for nalidixic acid can no longer be used as a criterion for identification in the laboratory. The rapid emergence of resistant campylobacter may also have important implications for the treatment and prophylaxis of diarrhoeal disease. The increase of quinolone resistance coincides with the increasing use of fluoroquinolones in human and veterinary medicine. Extensive use of enrofloxacin in poultry and the almost exclusive transmission route of campylobacter from chicken to man, in The Netherlands, suggests that the resistance observed is mainly due to the use of enrofloxacin in the poultry industry.
Accurate drug susceptibility testing (DST) for Mycobacterium tuberculosis is highly important for both therapy guidance and surveillance of drug resistance. Although liquid medium DST methods are used increasingly and seem most efficient and fast, the high costs hamper widespread implementation. In addition, an inability to check the colony morphology of the growing bacteria is a disadvantage of these methods. Moreover, these methods discriminate only between susceptibility and resistance and do not determine the MIC. In this paper, we describe a low-cost, reproducible, high-throughput, proportional absolute concentration DST method. The method uses a concentration series of antituberculosis drugs, including pyrazinamide in 7H10 medium, distributed semiautomatically in 25-well plates. The performance of this 25-well DST method was evaluated by the World Health Organization and the International Union against Tuberculosis and Lung Disease in 10 rounds of proficiency testing regarding sensitivity, specificity, efficiency, reproducibility, and predictive value for resistance and susceptibility. The performance of the method for these characteristics was 100% for isoniazid and from 96 to 100% for rifampin, 91 to 100% for streptomycin, and 85 to 100% for ethambutol. The method was 100% reproducible for all four drugs. The levels of drug resistance and the MIC distributions for the first-line antituberculosis drugs were determined for all 7,956 M. tuberculosis strains isolated in The Netherlands from 1998 to 2005 and amounted to 7.5% for isoniazid, 1.4% for rifampin, 8.5% for streptomycin, and 1.0% for ethambutol. Pyrazinamide testing was successful for 7,026 (88.3%) of the isolates and showed a resistance level of 0.8%.
Summary Minimum inhibitory concentrations (MICs) of 30 antimicrobial agents (including the hitherto unreported antimicrobial agents doxycycline, minocycline, vanomycin, 3 quinolones and 3 combinations of antimicrobial agents) for isolates of Salmonella spp. (20), Escherichia coli (17), Klebsiella spp. (8), Proteus spp. (7), Pseudomonas aeruginosa (7), Actinobacillus equuli (5), Rhodococcus equi (4), Streptococcus zooepidemicus (23), Streptococcus equisimilis (6), Streptococcus equi (4), coagulase‐positive Staphylococcus spp. (20) and Taylorella equigenitalis (19) were determined using the agar dilution method. All isolates were of equine origin. MICs were compared with recommended MIC breakpoints. The results indicate that, for some of the pathogenic bacteria evaluated, susceptibility testing of isolates from the individual patient is essential to determine an appropriate antimicrobial treatment.
The minimum inhibiting concentrations (MIC) of delta9-tetrahydrocannabinol (THC) and cannabidiol (CBD) for staphylococci and streptococci in broth are in the range of 1-5 mug/ml. In the same range, both compounds are also bactericidal. In media containing 4% serum or 5% blood the antibacterial activity is strongly reduced (MIC 50 mug/ml). Gram-negative bacteria are resistant to THC and CBD.
The molecular epidemiologic characteristics of penicillin-resistant pneumococci in the Netherlands were investigated in 1995. Dutch electronic surveillance data showed that 0.7% of all pneumococci were intermediately resistant and 0.4% were highly resistant to penicillin. From March 1995 to March 1996, 89 penicillin-resistant isolates were collected by 39 medical microbiology laboratories. Thirty different genotypes were observed by restriction fragment end labeling. Twenty-one DNA types were unique, whereas 9 distinct genotypes were shared by > or = 2 isolates. Different serogroups were found within 6 of the 9 genetically identical clusters of penicillin-resistant isolates, suggesting that horizontal transfer of capsular genes is common. Finally, nosocomial transmission of penicillin-resistant pneumococci was observed among 21 elderly adults with chronic obstructive pulmonary disease. This study demonstrates that multiple clones of penicillin-resistant pneumococci have been introduced in the Netherlands, a country with a low prevalence of pneumococcal infection. Some clones spread among the population in and outside hospitals.
The first European survey of the prevalence of antibiotic resistance in Haemophilus influenzae was conducted between February and October 1986. Eighty laboratories in nine countries participated (Austria, Belgium, France, FRG, The Netherlands, Spain, Sweden, Switzerland and the UK). A total of 1,961 clinical isolates was examined for type b encapsulation, beta-lactamase production and susceptibility to ampicillin, chloramphenicol, cefaclor, erythromycin and tetracycline, using a unique microdilution method. The proportion of isolates resistant to these antibiotics varied considerably between individual countries. The highest prevalence of ampicillin resistance was found in Spain (30.6%), and the lowest in the FRG (1.6%), with a mean value of 10% for all countries. Chloramphenicol resistance was highest in Spain (24.9%) and Belgium (10.9%) and lowest in The Netherlands (0.6%) and Austria (0.5%), with a mean value of 4.7%. Resistance to erythromycin ranged from 27% of the isolates in The Netherlands to 1.1% in Austria. For tetracycline, values ranged from 1.5% in the UK to 17.8% in Belgium and 25.4% in Spain. The lowest mean prevalence of resistance was observed for cefaclor (breakpoint 8 mg/l): 5% or less in all countries. These inter-country differences could only partially be explained by variations in the proportion of type b strains, the source of the isolates and the mode of collection.
Group D streptococci isolated from clinical specimens and from sewage were investigated with regard to resistance to tetracycline (Tc), erythromycin (Em), and chloramphenicol (Cm). The median values of the percentages of resistant strains from sewage were: for Tc, 14%; for Em, 2.8%; and for Cm, 0.1%. For the recent isolates of clinical origin, resistance percentages found were 58% for Tc, 12% for Em, and 14% for Cm, and, in comparison to clinical isolates from 1964, the incidence of drug resistance slightly increased. In strains of both sources, the drug resistance was often found to be transferable to another group D streptococcus, probably by conjugation. Two strains were able to transfer their Em resistance to a streptococcus strain of group B. No transfer of drug resistance to a group A streptococcus and Escherichia coli was observed. All beta-hemolytic streptococci were also bacteriocinogenic, and frequently these properties were found to be transferable. The function, size, and base composition of the plasmids of two drug-resistant Streptococcus faecalis strains were investigated; strain M439 harbors at least two conjugative plasmids: pRI401, molecular weight 30 × 10 6 , coding for Tc resistance, and pRI402, molecular weight 41 × 10 6 , coding for Em resistance. Strain M403 carries one single conjugative plasmid species, coding for Tc resistance. The molecular weight of this plasmid, pRI404, was 37 × 10 6 . The guanine plus cytosine content of these plasmids was 35 to 36%.
The minimal inhibitory concentrations (MIC) of five tetracyclines and ten other antimicrobial agents were determined for four porcine bacterial respiratory tract pathogens by the agar dilution method. For the following oxytetracycline-susceptible strains, the MIC50 ranges of the tetracyclines were: P. multocida (n = 17) 0.25-0.5 micrograms/ml; B. bronchiseptica (n = 20) 0.25-1.0 micrograms/ml; H. pleuropneumoniae (n = 20) 0.25-0.5 micrograms/ml; S. suis Type 2 (n = 20) 0.06-0.25 micrograms/ml. For 19 oxytetracycline-resistant P. multocida strains the MIC50 of the tetracyclines varied from 64 micrograms/ml for oxytetracycline to 0.5 micrograms/ml for minocycline. Strikingly, minocycline showed no cross-resistance with oxytetracycline, tetracycline, chlortetracycline and doxycycline in P. multocida and in H. pleuropneumoniae. Moreover, in susceptible strains minocycline showed the highest in vitro activity followed by doxycycline. Low MIC50 values were observed for chloramphenicol, ampicillin, flumequine, ofloxacin and ciprofloxacin against P. multocida and H. pleuropneumoniae. B. bronchiseptica was moderately susceptible or resistant to these compounds. As expected tiamulin, lincomycin, tylosin and spiramycin were not active against H. pleuropneumoniae. Except for flumequine, the MIC50 values of nine antimicrobial agents were low for S. suis Type 2. Six strains of this species showed resistance to the macrolides and lincomycin.
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