Antimicrobial susceptibility of equine and environmental isolates of Clostridium difficile.

This research article discusses the susceptibility of bacteria Clostridium difficile found in horse feces and environmental sites to various antimicrobial agents like vancomycin, erythromycin, spiramycin etc. The study shows that all the isolates tested were susceptible to vancomycin, while some showed higher resistance to erythromycin, oxytetracycline, spiramycin, and virginiamycin, especially those isolated from horses at animal hospitals and farms.

Research Objectives and Methodology

• The major objective of this research was to determine the susceptibility of 50 Clostridium difficile isolates to several antimicrobial agents. Out of these, 36 isolates were taken from horse feces and another 14 were sourced from environmental sites.
• The researchers carried out their investigations using a technique called broth microdilution. This method is commonly used in medical microbiology to examine the effect of various antimicrobial agents on bacteria.

Antimicrobials Tested and Results

• A number of antimicrobial agents were tested in the study. These included avilamycin, cephalothin, chloramphenicol, clindamycin, erythromycin, gentamicin, neomycin, oxacillin, oxytetracycline, penicillin, spiramycin, streptomycin, trimethoprim/sulfamethoxazole, vancomycin, and virginiamycin.
• It was found that all the tested isolates were susceptible to vancomycin. This means that this specific drug was effective against all strains of Clostridium difficile under study.
• The results also revealed a bimodal distribution in the minimum inhibitory concentrations (MICs) of four antimicrobials erythromycin, oxytetracycline, spiramycin, and virginiamycin. A bimodal distribution indicates that the sample had two different groups or modes.
• For 18 isolates, mostly from horses at animal hospitals and stud farms, the resistance to antimicrobials was higher compared with majority of the isolates.

Differences in Antimicrobial Susceptibility

• A distinguishing point observed in the study was that all isolates, except one, taken from healthy foals had low MICs of erythromycin, spiramycin, virginiamycin, and oxytetracycline. This suggests that bacteria isolated from healthy foals were more susceptible to these four antimicrobials.
• Similarly, the Clostridium difficile bacteria isolated from the soil in public parks were also more susceptible to the aforementioned antimicrobials.

Reliability of the Method

• The authors reported that the broth microdilution method provided reliable and reproducible results for susceptibility testing of C. difficile.
• They also noted that the method was easy to perform and the endpoints for minimum inhibitory concentrations (MICs) were straightforward to read.