Resistance to Antibiotics in Strains of Staphylococcus spp., Enterococcus spp. and Escherichia coli Isolated from Rectal Swabs of Pigs

The study aimed at determining the level of resistance of selected bacterial species (Staphylococcus spp., Enterococcus spp., Escherichia coli) isolated from rectal swabs of pigs to antimicrobial agents. The tested strains were isolated from piglets aged 7 to 30 days. Bacterial species were identified by standard microbiological techniques and susceptibility to antibiotics was determined quantitatively by the standard microdilution method. Resistance of the Staphylococcus aureus strain to oxacillin was confirmed by detection of the mecA gene and PBP2a. A total of 115 Staphylococcus spp. isolates were collected. In the case of Staphylococcus aureus, the methicillin-resistant strain (MRSA) was identified. Moreover, higher frequency of coagulase-negative staphylococci with minimum inhibitory concentration of oxacillin ≥ 0.5 mg/l was noticed. Inducible resistance to clindamycin in the Staphylococcus hominis strain was also detected. The strains of Enterococcus spp. (61 isolates) exhibited high resistance to tetracycline (98.5%), erythromycin (86.8%) and chloramphenicol (54.4%). Vancomycin-resistant enterococci were not isolated. In the case of Escherichia coli strains (111 isolates), higher frequency of resistant strains to tetracycline (81.1%) and ampicillin (62.2%) was documented. Resistance to fluoroquinolones and production of broad-spectrum β-lactamases was not noticed. The presented study may be considered as a pilot project assessing the prevalence of resistant bacteria in piglets kept on a single farm. It demonstrated the presence of resistant strains of Staphylococcus spp., including one MRSA strain, Enterococcus spp. and Escherichia coli. These strains may be present as a result of postnatal colonization with both bacterial microflora of dams and environmental microflora

Evolution and distribution of virulence characteristics of Belgian Bremia lactucae populations between 2008 and 2013

Downy mildew, caused by the oomycete Bremia lactucae, is a devastating disease of lettuce, which is controlled by applying fungicides and/or planting resistant lettuce cultivars. As resistance of lettuce cultivars is based on gene-for-gene interaction and offers mostly short-term protection, a lot of effort is put in breeding new resistant lettuce cultivars. For efficient breeding, it is important to know the virulence characteristics of B. lactucae populations in order to select for lettuce cultivars carrying the most effective resistance genes for production. In this study, 55 isolates of B. lactucae were collected from Belgian lettuce culture and their virulence characteristics were analysed. Results showed that the resistance genes with the highest resistance efficacy to the B. lactucae isolates are Dm 15, Dm 17 and the resistance factors of Balesta, Bedford and Bellissimo, while Dm 1, Dm 4, Dm 5/8, Dm 10 and Dm 12 were least effective. There was a lot of variability in virulence within the B. lactucae populations, with 41 of the 55 characterized isolates having a unique virulence-phenotype. This virulence variability may result from sexual reproduction or asexual genetic variation. Sexual reproduction, however, does not seem to be an important cue for B. lactucae variation in Belgium since oospore formation did not occur frequently and attempts for oospore germination were not successful. In addition, mating type B1 was predominant in the B. lactucae population. Our results provide important information for selection and future breeding of resistant lettuce cultivars, especially for Belgian lettuce producers