Susceptibility Of Pig Respiratory And Systemic Bacteria Against HydroTrim®
Ulrich Klein
Successful treatment of bacterial infections is only achieved when bacterial pathogens are highly susceptible to corresponding antibiotic and antibiotic combinations. Swine respiratory disease complex (SRD) is a common problem in the field worldwide caused by pathogens including Pasteurella multocida, Streptococcus suis, Actinobacillus pleuropneumoniae, and Glaeserella parasuis.
Sulfonamides and trimethoprim are classified by the European Medicines Agency (EMA) as Category D which promotes their use by veterinarians as first-line treatment compared to other antibiotics.
HydroTrim® (500 mg sulfadiazine + 100 mg trimethoprim/g) is registered for the treatment and metaphylaxis of respiratory infections caused by Actinobacillus pleuropneumoniae, Pasteurella multocida and infections caused by Streptococcus suis and Escherichia coli.
Sulfadiazine and trimethoprim (HydroTrim®) were tested for their minimum inhibitory concentration (MIC) to investigate the susceptibility of respiratory and systemic pathogens to sulfadiazine and trimethoprim alone and in combination (5:1 ratio; Tables 1 and 2).
Table 1. Minimum inhibitory concentration (MIC) of sulfadiazine (SDZ) and trimethoprim (TMP) alone and in combination against respiratory and systemic bacterial pathogens
Table 2. Combination efficacy (ratio 5:1) between sulfadiazine and trimethoprim against four bacteria species
The MIC data indicate that the combined use of sulfadiazine and trimethoprim leads to modifications and reductions in MIC90 values and MIC ranges. The combination of sulfadiazine and trimethoprim enhances sulfadiazine and trimethoprim activity against P. multocida, S. suis, A. pleuropneumoniae and G. parasuis.
A synergistic effect of the combination sulfadiazine/trimethoprim in a ratio of 5:1 was found for three tested pathogens (S. suis, A. pleuropneumoniae, and G. parasuis).
The use of HydroTrim® in the case of PRDC-based infections is useful as it:
- takes advantage of the broad-spectrum activity of the sulfadiazine and trimethoprim combination
- increases the efficacy of sulfonamides from bacteriostatic to bactericidal drugs
- uses the synergistic effect for treatment of low susceptible and resistant bacteria
- reduces the incidence of resistance
- considers no cross-resistance with antibiotics used in human medicine (EMA classification Category D)
In the context of the EU guidelines on prudent use and the EMA categorisation of antibiotics, HydroTrim® is an appropriate option for the treatment of PRDC.