Publikationsdatenbank

Susceptibility of staphylococcus aureus strains isolated from cows with subclinical mastitis to different types of disinfectants and antibiotics (2011)

Art

Hochschulschrift

Autor

El Behiry, Ayman Rabei Abd El Halim (WE 10)

Quelle

Berlin: Mensch und Buch Verlag, 2011 — XI, 97 S. Seiten

ISBN: 978-3-86664-988-0

Sprache

Englisch

Verweise

URL (Volltext): https://refubium.fu-berlin.de/handle/fub188/3197

Kontakt

Institut für Tier- und Umwelthygiene

Robert-von-Ostertag-Str. 7-13
14169 Berlin
+49 30 838 51845
tierhygiene@vetmed.fu-berlin.de

Abstract / Zusammenfassung

The primary objective of the current study was to determine in vitro the efficacy of two teat dips, Ujosan® dip and Eimü Chlorhexidin® dip against 56 Staphylococcus (S.) aureus strains isolated from subclinical cases of bovine mastitis. A further main objective was an attempt of resistance induction of selected strains of S. aureus against the same two types of teat disinfectants. Another objective was to test the antibiotic resistance patterns of bovine mastitis isolates of S. aureus and coagulase negative staphylococci (CNS). The last objective was to check the possibility of cross- resistance between reduced susceptibility to disinfectants and different types of antibiotics that are commercially available for the treatment of bovine S. aureus mastitis. Quarter milk samples were collected from six dairy herds with high prevalences of S. aureus in the federal state of Brandenburg, Germany. Of each herd, 32 cows in different stages of lactation and different age groups were chosen for sampling. Cows were divided according to the udder teat dipping scheme into three groups. Teats of the first group were dipped in the postmilking teat disinfectant Ujosan® dip; the second group was dipped in Eimü Chlorhexidin® dip, while the third group was kept without dipping (a negative control group). A total of seventy isolates of S. aureus and CNS were identified phenotypically by the tube coagulase test and the Staph ID 32 API system; genotypically by using the polymerase chain reaction (PCR) and the mass spectrally by matrix assisted laser desorption/ionisation- time of flight-mass spectrometry (MALDI-TOFMS), which was used as a confirmatory method for PCR. After identification of all strains, the minimum inhibitory concentration (MIC) of Ujosan® dip and Eimü Chlorhexidin® dip against S. aureus strains was determined, using the broth macrodilution method which is indicative of the guideline for examination of chemical disinfectants in the German Veterinary Association (Deutsche Veterinärmedizinische Gesellschaft, DVG). All strains were inoculated in a liquid medium (tryptose soya broth, TSB), serially diluted with the two teat dips. The mean MIC values of Ujosan® dip and Eimü Chlorhexidin® dip for dipped and control groups were 45.70 ± 2.54%; 42.6 ± 1.64% and 97.51 ± 0.98%; 96.8 ± 0.78%, respectively. This study showed that there was no significant difference (p<0.05) between dipped and negative control groups for both Ujosan® dip and Eimü Chlorhexidin® dip. The main objective was to induce in vitro sensitivity reduction (resistance) of the same two commercial teat dips with sub-lethal concentrations against ten different strains of S. aureus. For each disinfectant, 10 strains were repeatedly passed 10 times in growth media with sub lethal concentrations of Ujosan® dip and Eimü Chlorhexidin® dip. The MIC values of the teat dip after passages were determined and compared with the original MIC values before passages. According to the results, 9 strains (90%) became nonsusceptible to Ujosan® dip and only one strain (10%) became nonsusceptible to Eimü Chlorhexidin® dip. All isolates with a significant increase (p>0.001) of MICs were passed every day for 10 days in tryptose soya broth (TSB) without disinfectant (active substance), to check whether the acquired resistance was stable or not. Stability of acquired resistance was noticed in all Ujosan® dip and Eimü Chlorhexidin® dip adapted S. aureus strains. Furthermore, the sensitivity of 6 selected antimicrobial agents against 70 coagulase positive S. aureus and CNS strains was checked using the agar disk diffusion test. 85.71% of S. aureus strains and 28.57% of CNS were resistant to Penicillin G, 7.14% of S. aureus and CNS were resistant to tetracycline and only 10.71% of S. aureus and 7.14% of CNS were resistant to gentamycin. The percentages of resistant S. aureus and CNS to chloramphinicol were 1.78% and 7.14%, respectively. No resistance was detected for the other tested antimicrobial agents (oxacillin and erythromycin). Finally the current study investigated whether Ujosan® dip-and Eimü Chlorhexidin® dipadapted S. aureus strains were also resistant to antibiotics commercially available for the treatment of bovine S. aureus mastitis. According to the results obtained from the Federal Institute for Risk Assessment (Berlin, Germany), all Ujosan® dip and Eimü Chlorhexidin® dipadapted S. aureus strains showed in vitro the highest susceptibility to all types of antibiotics. Therefore, prolonged exposure of sub-inhibitory concentrations of Ujosan® dip or Eimü Chlorhexidin® dip did not increase emerging antibiotic resistance in S. aureus. The current results and published data indicate that more detailed investigations on the cross- resistance between reduced susceptibility of chemical disinfectants and antibiotics are needed.