In vitro susceptibility of Staphylococcus aureus strains isolated from cows with subclinical mastitis to different antimicrobial agents

Sensitivity to commercial teat dips (nonoxinol-9 iodine complex and chlorhexidine digluconate) of 56 Staphylococcus (S.) aureus strains isolated from quarter milk samples of various German dairy herds treated with different teat dipping schemes was investigated in this study. The minimum inhibitory concentration was determined using a broth macrodilution method according to the German Veterinary Association guidelines. The main objective of the current study was to induce in vitro resistance induction of S. aureus to chemical disinfectants. Ten different strains were repeatedly passed ten times in growth media with sub-lethal concentrations of disinfectants. Nine strains showed a significant reduction in susceptibility to the nonoxinol-9 iodine complex but only one strain developed resistance to chlorhexidine digluconate. Stability of the acquired resistance was observed in all S. aureus strains adapted to the nonoxinol-9 iodine complex and chlorhexidine digluconate. In contrast, simultaneous resistance to different antibiotics was not observed in any of the ten investigated S. aureus strains. However, the isolates exhibited a high degree of resistance to penicillin G. Based on these results, resistance of S. aureus to chemical disinfectants may be more likely to develop if the chemicals are used at concentrations lower than that required for an optimal biocidal effect.

Spermicidal effect of Jieze No. 1 in combination with nonoxynol-9 in vitro / 华中科技大学学报（医学）（英德文版）

Spermicidal effect of Jieze No. 1 (JZ1) in combination with nonoxynol-9 (N-9) was examined in vitro. The minimum spermicidal concentration of JZ1 decoction, N-9 and their mixture solution in 20 s and 3 min were examined by improved spermicidal test of Sander-cramer in vitro. The percentages of progressively moving spermatozoa, moving spermatozoa and viable spermatozoa were also observed 20 s, 3 min and 30 min after the addition of the liquid medicine. Our results showed that sperms did not recover their activities in a revival test when the minimum spermicidal concentration of either JZ1 decoction, or N-9, or the mixed solution of the two agents, was used. N-9 (JZ1 in the mixed group) showed significant differences in the percentages of progressively moving spermatozoa, moving spermatozoa, and visible spermatozoa in 20 s, 3 min, and 30 min, when compared with N-9 alone (P < 0.01). We are led to conclude that JZ1 decoction can improve N-9 spermicidal action in vitro, and when used in combination with N-9, it has synergic effect.