Survey of marbofloxacin susceptibility of bacteria isolated from cattle with respiratory disease and mastitis in Europe.

A monitoring programme conducted in Europe since 1994 to survey the marbofloxacin susceptibility of bacterial pathogens isolated from cattle has established the susceptibility of bacterial strains isolated before any antibiotic treatment from bovine mastitis and bovine respiratory disease (BRD) cases between 2002 and 2008. Minimum inhibitory concentration (MIC) was determined by a standardised microdilution technique. For respiratory pathogens, Pasteurella multocida and Mannheimia haemolytica isolates (751 and 514 strains, respectively) were highly susceptible to marbofloxacin (MIC≤0.03 µg/ml for 77.39 per cent of the strains) and only 1.75 per cent of M haemolytica strains were resistant (MIC≥4 µg/ml). Histophilus somni isolates (73 strains) were highly susceptible to marbofloxacin (0.008 to 0.06 µg/ml). Mycoplasma bovis MIC (171 strains) ranged from 0.5 to 4 µg/ml. For mastitis pathogens, the majority of Escherichia coli isolates were highly susceptible to marbofloxacin (95.8 per cent of 617 strains). Staphylococcus aureus and coagulase-negative staphylococci (568 and 280 strains) had a homogenous population with MIC centred on 0.25 µg/ml. Streptococcus uberis and Streptococcus dysgalactiae (660 and 217 strains) were moderately susceptible with MIC centred on 1 µg/ml. Marbofloxacin MIC for these various pathogens appeared stable over the seven years of the monitoring programme and was similar to previously published MIC results.

In vitro activity of 10 antimicrobial agents against bacteria isolated from cows with clinical mastitis.

The susceptibility of 495 strains of bacteria, recently isolated in France from cows with clinical mastitis, to 10 antimicrobial agents--penicillin G, cloxacillin, oxacillin, cephalexin, cefazolin, cephapirin, cefquinome, neomycin, ampicillin and colistin--was determined by measuring their minimum inhibitory concentrations (MICS). Overall, the levels of resistance were very low except for staphylococci and penicillin G. The 167 streptococcal strains were susceptible to all of the beta-lactams tested, but six (3-6 per cent) were highly resistant to neomycin. Of the 171 staphylococcal isolates, 36.2 per cent were resistant to penicillin G, one strain of Staphylococcus sciuri was classified as methicillin-resistant, but they were all susceptible to neomycin. None of the 122 strains of Escherichia coli was resistant to colistin, but 12 had high MIC values for one or more of the cephalosporins.

Optimal growth temperature of O157 and non-O157 Escherichia coli strains.

AIMS: There are several biological characteristics that differ between Escherichia coli O157:H7, a dangerous food-borne pathogen, and the other serotypes of E. coli. METHODS AND RESULTS: The optimal growth temperatures (T(opt)) were determined for 32 E. coli strains, whether each strain belonged to the O157 serotype or not. The mean values of T(opt) for the O157 and non-O157 groups were 40.2 and 41.2 degrees C, respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: This difference is statistically significant (P=0.0002) but has no biological implication.

Improvement of the identification of staphylococci isolated from bovine mammary infections using molecular methods.

Fifty-six Staphylococcus strains isolated from cases of bovine mammary infections were identified by using phenotypic and genotypic methods. Twenty-eight strains (50%) were identified at the species level according to their phenotypic characteristics, whereas the remaining 28 strains presented atypical or unreliable profiles. A combination of phenotypic and genotypic methods allowed the 56 strains studied to be classified. Internal transcribed spacer-polymerase chain reaction (ITS-PCR) based on the polymorphism of the 16S-23S rDNA spacer region appeared as a rapid and reliable method for the classification of bovine staphylococcal isolates at the species and subspecies levels.

Reappraisal of the effect of temperature on the growth kinetics of Aeromonas salmonicida.

The effect of temperature (1-34 degrees C) on the maximum specific growth rate of Aeromonas salmonicida could not be described by the classical growth models; for some strains, two optimal temperatures at 23 degrees C and 30 degrees C were observed, as well as an unexpected increase in the pseudolag time above 27 degrees C. This could be explained by the presence of two subsets, notably S-layer+ and S-layer- sub-populations. The A- cells had higher growth parameters (Topt and mu opt) than the A+ cells and were selected by subcultures above 30 degrees C. Yet the relative proportion of A+ cells did not explain all the variation of mu max versus temperature, and the growth kinetics of an Aer. salmonicida isolate remained unpredictable.

Application of a modified disc diffusion technique to antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida clinical isolates.

Two techniques for antimicrobial susceptibility testing of Vibrio anguillarum and Aeromonas salmonicida strains were compared. The first method was the reference test that determines Minimal Inhibitory Concentrations (MIC); the second was a modified diffusion test that measures the Inhibitory Concentrations in Diffusion (ICD) by carrying out the diffusion test with five discs of differing contents. ICD measurement was not applicable for the susceptibility testing of oxytetracycline and sulfadimethoxine. On the other hand, a good correlation between the MICs and the ICDs was observed for oxolinic acid, sarafloxacin, chloramphenicol and trimethoprim. Moreover, the ICD values were close to those obtained for the MIC values. A. salmonicida resistant strains were detected by ICD determination. Thus, ICD could be used instead of MIC for oxolinic acid, sarafloxacin, trimethoprim and chloramphenicol susceptibility testings. The ICD technique is easy to carry out and is not dependent on the growth characteristics of bacteria.

The effect of incubation temperature and sodium chloride concentration on the growth kinetics of Vibrio anguillarum and Vibrio anguillarum-related organisms.

The effect of temperature and NaCl concentration on the growth kinetics of Vibrio anguillarum and V. anguillarum-related (VAR) strains was studied. For one wild VAR strain, NaCl concentration interfered with growth temperature parameters, in particular, with the maximum growth temperature but also with the optimum temperature (defined as the temperature at which mumax equals its maximal value muopt), and with muopt itself. For the same strain, optimal growth required the adding of NaCl to the medium to a final concentration of 1.5%. These results were not confirmed by tests on a V. anguillarum collection strain. When the NaCl concentration in the culture media was 1.5%, the optimum temperature for the nine strains studied ranged from 29.7 degrees C to 34 degrees C whereas the maximum temperature ranged between 35.3 degrees C and 38.5 degrees C. Hence, antibiotic susceptibility testing as well as biochemical identification might be carried out at 30 degrees C in the presence of 1.5% NaCl, which corresponded to a suboptimal growth.

rRNA gene restriction patterns as possible taxonomic tools for the genus actinomyces.

Species delineation in the genus Actinomyces remains unclear, particularly regarding the two taxa, A. naeslundii and A. viscosus. The ribotyping patterns of 64 strains of Actinomyces, representing 8 species and comprising different serotypes, were studied as possible taxonomic tools, using an acetyl-aminofluorene (AAF)-labelled E. coli 16S + 23S rRNA probe. Similarities between patterns were assessed using Jaccard's coefficient and clustering achieved using the unweighted pair-group method with average linkage (UPGMA) on a Macintosh II (Apple, Cupertino, USA) computer. The dendrogram obtained from the ribotypes gave results which were in reasonable agreement with many previous reports: A. bovis, A. gerensceriae, A. israelii, A. meyerii, A. odontolyticus and A. pyogenes were found to be distinct species but the two taxa A. naeslundii and A. viscosus remained unclear. Further investigations, using a larger number of A. naeslundii and A. viscosus strains and other endonucleases, need to be carried out to provide more information concerning the relatedness of these two taxa. Nevertheless, these preliminary results suggested that the Actinomyces chromosome contains multiple rRNA operons which may be used as an epidemiological and taxonomical tool.

Molecular typing of Actinomyces pyogenes isolates.

The molecular characterization of 28 clinical Actinomyces pyogenes strains was attempted. SDS-PAGE protein profiles did not allow to distinguish isolates. Restriction endonuclease analysis of total DNA gave the finest differentiation between strains but the profiles were difficult to read. Ribotypes after DNA digestion by Bst EII or Sma I have a high discriminatory power and are more helpful epidemiological markers. No relationship could be demonstrated between molecular types and clinical sources.

Antimicrobial susceptibility testing of Actinomyces pyogenes: comparison of disk diffusion test and Api ATB Strep system with the agar dilution method.

The use of the disk diffusion and the Api ATB Strep system or a related technique for a few antibiotics was compared with the agar dilution method for antimicrobial susceptibility testing of 103 clinical isolates of Actinomyces pyogenes. There was complete agreement between disk diffusion and MIC in 98.8%, with minor errors, in 0.7% and with very large errors, in 0.5% of cases. The common criteria for the interpretation of zones could be kept for penicillin G, amoxicillin, methicillin, cephalothin, erythromycin, lincomycin, pristinamycin, vancomycin, rifampin, streptomycin, kanamycin, gentamicin and chloramphenicol. The proposed breakpoints for a tetracycline 30 IU disk were > or = 22 mm for susceptibility and < 22 mm for resistance. There was complete agreement between the ATB strip system and MIC in 98.3% of cases, with minor errors in 0.9% and with very large errors, in 0.8% of cases. All the dissimilarities were due to streptomycin and tetracycline and results could not be reported for these 2 antibiotics when using this system. Wells with kanamycin and gentamicin at low concentrations as well as chloramphenicol should be included by the manufacturer.

Actinomyces pyogenes: susceptibility of 103 clinical animal isolates to 22 antimicrobial agents.

Actinomyces pyogenes induces suppurative diseases in ruminants and many other animal species. Most of the earlier antimicrobial susceptibility data has been obtained by disk diffusion techniques. Minimal inhibitory concentrations (MIC) of 22 antibiotics for 103 strains of A pyogenes of animal origin were determined by agar dilution test (Mueller-Hinton agar supplemented with 5% sheep blood). All the strains were susceptible to penicillin G, amoxicillin, methicillin, cephalothin, cefoperazone, pristinamycin, kanamycin, gentamicin, spectinomycin, chloramphenicol, vancomycin, novobiocin and rifampin. Fifty-nine percent were resistant to streptomycin, 67% to tetracycline, doxycycline and minocycline, 12% to erythromycin, spiramycin and lincomycin. Most of the strains resistant to macrolides and lincosamides exhibited a constitutive MLS(B)-like phenotype. In the cultural conditions used, it was not possible to determine accurate MIC of fucidic acid and pefloxacin.

[Actinomyces pyogenes: conventional and Api system bacteriologic study of 103 strains isolated from ruminants]. / Actinomyces pyogenes: étude bactériologique conventionnelle et sur galeries Api de 103 souches isolées chez les ruminants.

One hundred and three strains of Actinomyces pyogenes isolated from ruminants were examined for morphological, cultural and biochemical properties by standard tests and by the Api 50 CH and Api Coryne methods. No biotype could be demonstrated, but a few atypical non- or practically non-proteolytic strains were detected which should be differentiated from Arcanobacterium haemolyticum. Criteria for laboratory identification of A pyogenes were established: Gram stain; culture on blood agar; deep agar and Loeffler's medium; catalase, nitrate reduction, acid formation from xylose; Hugh and Leifson test. The Api Coryne system correctly identified only 58 of 103 A pyogenes cultures, which implies that it should be re-evaluated before use in veterinary diagnosis laboratories.