First description of two moderately halophilic and psychrotolerant Mycoplasma species isolated from cephalopods and proposal of Mycoplasma marinum sp. nov. and Mycoplasma todarodis sp. nov

Two moderately halophilic and psychrotolerant new Mycoplasma species were isolated from common cephalopods. Three strains were isolated in pure culture from two individual European flying squid (Todarodes sagittatus), and two individual octopuses (Octopus vulgaris). The strains showed optimal growth at 25 °C and a salinity of 3% (w/v) NaCl. Molecular analyses revealed that the isolates belonged to two new, but phylogenetically related species, divergent from all previously described Mollicutes, representing the first marine isolates of the class, and also the first Mycoplasma strains for which NaCl requirement has been demonstrated. A genome search against all available marine metagenomes and 16S rRNA gene databases indicated that these two species represent a novel non-free-living marine lineage of Mollicutes, specifically associated with marine animals. Morphology and physiology were compatible with other members of this group, and genomic and phenotypic analyses demonstrated that these organisms represent two novel species of the genus Mycoplasma, for which the names Mycoplasma marinum sp. nov. and Mycoplasma todarodis sp. nov. are proposed; the type strains are PE^T (DSM 105487^T, CIP 111404^T) and 5H^T (DSM 105,488^T, CIP 111405^T), respectively.

In vitro activity of tylvalosin against Spanish field strains of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae is involved in the porcine enzootic pneumonia and respiratory disease complex; therefore, the search for new treatment options that contribute to the control of this organism is relevant. The minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations of tylvalosin and 19 other antimicrobial agents against 20 Spanish field isolates of M. hyopneumoniae were determined using the broth microdilution method, with the type strain (J) as a control strain. Tylvalosin had MIC50 and MIC90 values of 0.016 and 0.06 µg/ml, respectively, and was the second-most effective of the assayed antibiotics, after valnemulin. Tiamulin, tylosin and lincomycin were also among the antibiotics with the lowest MIC50 and MIC90 values against the 20 field isolates (0.06-0.25 µg/ml). However, resistance to tylosin and spiramycin, which like tylvalosin, are 16-membered macrolides, was observed. The MIC50 and MIC90 values for ciprofloxacin and enrofloxacin ranged from 0.125 to 1 µg/ml; the corresponding values ranged from 2 to 4 µg/ml for oxytetracyline, which was the most active tetracycline. Furthermore, tylvalosin and valnemulin exhibited the highest bactericidal activities. In conclusion, the macrolide tylvalosin and the pleuromutilin valnemulin exhibited the highest in vitro antimicrobial activities against M. hyopneumoniae field isolates in comparison with the other tested antibiotics.

In vitro susceptibilities of field isolates of Mycoplasma agalactiae

In order to determine how widespread antibiotic resistance has become to standard treatments, the in vitro susceptibilities of 28 Mycoplasma agalactiae Spanish field isolates to 16 antimicrobial agents were determined using a broth microdilution method. The most effective antimicrobials based on minimum inhibitory concentration (MIC)(90) values were fluoroquinolones, tetracyclines and macrolides. Two strains were tetracycline resistant. Streptomycin, erythromycin and nalidixic acid resistance was observed in all strains.

In vitro susceptibilities of Mycoplasma putrefaciens field isolates

MICs were determined for 15 antimicrobial agents against 37 Mycoplasma putrefaciens isolates. The most effective antimicrobial drug classes were the fluoroquinolones, the tetracyclines, the lincosamide lincomycin, and the macrolides. The susceptibility profile of the isolates correlated with the geographic origin. This is the first report of decreased susceptibility to the macrolides, lincomycin, and the tetracyclines in M. putrefaciens strains.

In vitro susceptibilities of field isolates of Mycoplasma mycoides subsp. mycoides large colony type to 15 antimicrobials

In vitro susceptibilities of 16 Mycoplasma mycoides subsp. mycoides large colony type field isolates to 15 antimicrobial agents were determined using a broth microdilution method. The most effective antimicrobials were fluoroquinolones, tetracyclines and macrolides, with MIC values under 2 microg/ml. Resistance to nalidixic acid, gentamicin, streptomycin and spectinomycin was observed.

Decreased permeability and enhanced proton-dependent active efflux in the development of resistance to quinolones in Morganella morganii

Five quinolone-resistant strains were developed from a clinical Morganella morganii isolate (M1 strain) which was susceptible to nalidixic acid and fluoroquinolones. All five in vitro selected mutants showed diminished norfloxacin accumulation and two of them also decreased the expression of the AgO in the outer membrane lipopolysaccharide with respect to their parent strain and to the M. morganii NCTC-235 type strain. Likewise, the M1 strain did not express a 37-38 kDa protein and accumulated less norfloxacin than the M. morganii NCTC-235 strain. The decreased norfloxacin uptake in the five mutants compared with the M. morganii NCTC-235 strain was due to an enhanced proton-dependent active efflux plus a pre-existent decreased expression of a 37-38 kDa protein in the parent strain.

Resolution of high-molecular-weight components in lipopolysaccharides of Escherichia coli, Morganella morganii, Citrobacter freundii and Citrobacter diversus strains with sodium dodecyl sulfate polyacrylamide gels

The use of 0.5% sodium dodecyl sulfate in polyacrylamide separation gels allowed the resolution in several bands of high-molecular-mass components in smooth lipopolysaccharide of bacterial outer membrane from Escherichia coli, Morganella morganii, Citrobacter freundii and Citrobacter diversus. With or without 0.1% SDS, however, such a result was not possible.

Mechanisms involved in the development of resistance to fluoroquinolones in Escherichia coli isolates

Eighteen quinolone-resistant isolates of Escherichia coli were selected by exposing ten clinical isolates to increasing concentrations of norfloxacin and lomefloxacin. The mutant isolates showed a multiple-antibiotic-resistance phenotype. All of them contained single mutations in gyrA consisting of the substitution of Ser-83-->Leu (n = 14), Val (n = 1) or Ala (n = 1) and the substitution of Asp-87-->Asn (n = 2). Only one concomitant mutation in parC (Ser-80-->Arg) was detected. Four parent isolates exhibited a single mutation in gyrA which required < or = 12 mg/L of norfloxacin to be inhibited. Fluoroquinolone resistance, in the 18 quinolone-resistant mutants, was a result of mutations affecting DNA gyrase plus decreased fluoroquinolone uptake. This latter mechanism of resistance was a combined effect of an absence of OmpF and an increase in active efflux in eight isolates, or an increased active efflux alone in the remaining ten selected mutants.