In vitro susceptibility of Enterococcus faecium isolated from food to growth-promoting and therapeutic antibiotics.

A total of 76 E. faecium strains, isolated at retail level from raw poultry meat, cheese, raw pork, and preparations of cheese and raw pork, were tested for their susceptibility and resistance to growth-promoting antibacterials used in animals and antibiotics used therapeutically in humans. All strains were uniformly susceptible to the growth promoters bambermycin and avilamycin. Resistance against bacitracin, virginiamycin and narasin was high among strains from poultry meat. With tylosin, a macrolide antibiotic used therapeutically and for growth promotion, resistance was mainly detected in strains originating from poultry meat, though also in some strains from pork and from pork and cheese preparations. The therapeutic antibiotic dalfopristin/quinupristin did not show full cross-resistance with the growth-promoting antibiotic virginiamycin. With dalfopristin/quinupristin two different levels of resistance were found. Only one E. faecium strain isolated from poultry was resistant to the glycopeptides avoparcin and vancomycin. Only one poultry meat strain was highly resistant to ampicillin. However, nearly all poultry meat strains showed decreased sensitivity. Only 3 out of 24 poultry strains were susceptible to minocycline, while all strains from other origins were susceptible to this tetracycline antibiotic. High-level streptomycin resistance was seen in strains of all origins, though infrequently. High-level gentamicin resistance was not found.

Efficacy of inactivated whole-cell vaccines against streptococcosis in pigeons.

Two experimental vaccines were developed and evaluated for their efficacy against Streptococcus gallolyticus septicaemia in pigeons. Both vaccines contained whole-cell formaldehyde-inactivated S. gallolyticus serotype 1 bacteria and a mineral oil adjuvant. The supernatant of a S. gallolyticus broth culture was also added to one of the vaccines. Four groups of 10 pigeons were inoculated either once, or twice, with a 4-week interval, with one of the vaccines. Four weeks after the last vaccination, pigeons were challenged by intravenous inoculation with S. gallolyticus serotype 1. Morbidity after infection was not significantly different between groups of pigeons vaccinated with the two vaccines. In groups of pigeons vaccinated once, morbidity after infection ranged from 50 to 70%; in pigeons vaccinated twice, morbidity was 10 to 30%. In a non-vaccinated inoculated control group, the morbidity was 80%. It was concluded that double vaccination can result in some clinical protection against streptococcosis in pigeons.

In vivo activity of orally administered antibiotics and chemotherapeutics against acute septicaemic pasteurellosis in rabbits.

Different antibiotics and chemotherapeutics were tested for therapeutic efficacy in rabbits, in an experimental model using a Pasteurella multocida strain which causes hyperacute septicaemia in this animal species. Only enrofloxacin, administered in the drinking water at a concentration of 50-100 mg/l cured the rabbits, provided that a daily intake of 5 mg/kg body weight was achieved. The other drugs tested (tetracycline, spiramycin, erythromycin and a combination of sulfamerazine with trimethoprim), at doses recommended for rabbits, showed little or no activity at all, with the exception of chloramphenicol, which was only partially effective.

Failure of oil adjuvants to enhance immunity induced in mice by an inactivated rabbit Pasteurella multocida vaccine.

Mice were immunized with different preparations of a killed whole cell Pasteurella multocida vaccine and challenged with successive tenfold dilutions of the homologous strain. Vaccines adjuvanted with mineral oil did not confer better protection against death than non-adjuvanted suspensions, even when the mice were challenged at 3 months after vaccination. Very good protection was obtained when the non-adjuvanted suspension had been administered twice.