Actinobacillus pleuropneumoniae Eradication with Enrofloxacin May Lead to Dissemination and Long-Term Persistence of Quinolone Resistant Escherichia coli in Pig Herds.

Norway has a favourable situation with regard to health status and antimicrobial usage in the pig production sector. However, one of the major disease-causing agents in the commercial pig population is Actinobacillus pleuropneumoniae (APP). In some herds, APP eradication has been performed by using enrofloxacin in combination with a partial herd depopulation. The aim of this study was to investigate the long-term effects of a single treatment event with enrofloxacin on the occurrence of quinolone resistant Escherichia coli (QREC). The study was designed as a retrospective case/control study, where the herds were selected based on treatment history. Faecal samples were taken from sows, gilts, fattening pigs and weaners for all herds where available. A semi-quantitative culturing method was used to identify the relative quantity of QREC in the faecal samples. A significant difference in overall occurrence and relative quantity of QREC was identified between the case and control herds, as well as between each animal age group within the case/control groups. The results indicate that a single treatment event with enrofloxacin significantly increased the occurrence of QREC in the herd, even years after treatment and with no subsequent exposure to quinolones.

Experimental infection of cattle with ovine Dichelobacter nodosus isolates.

BACKGROUND: Dichelobacter nodosus is the main causative agent of ovine footrot, and there are strong indications that the bacterium can be transferred to cattle grazing on the same pasture as sheep. The aim of this study was to investigate if benign and virulent D. nodosus strains isolated from sheep can be transferred to the interdigital skin of cattle under experimental conditions. Further, we wanted to observe the impact of such infection on bovine foot health, and test the effect of topical chlortetracycline (Cyclo spray(®): Eurovet) on the infection. FINDINGS: Six heifers were included in the study. After an initial 18-day maceration period, three heifers were inoculated on one single foot with a benign strain and three with a virulent strain by adding bacterial suspension in a bandage. The bandages were left on for 17 days, and when removed, D. nodosus was isolated from all six heifers. All six heifers developed interdigital dermatitis. In five of the heifers D. nodosus organisms were demonstrated within the epidermis. Twenty-four days after treatment with chlortetracycline all heifers were negative by cultivation, but tested positive for D. nodosus by polymerase chain reaction (PCR). Two of the six heifers still tested positive for D. nodosus by PCR 49 days after treatment. After 70 days, all heifers tested negative for D. nodosus. CONCLUSIONS: This study shows that both virulent and benign D. nodosus strains originating from sheep can be transferred to naïve heifers under experimental conditions. Further, the study supports the hypothesis that infections with virulent D. nodosus in cattle are associated with interdigital dermatitis. No conclusion regarding the treatment of D. nodosus infection with chlortetracycline was possible.

Characterisation of Dichelobacter nodosus isolates from Norway.

An outbreak of ovine footrot in Norway in 2008, the first reported since 1948, prompted action to investigate Norwegian isolates of Dichelobacter nodosus. A total of 579 isolates from 124 different farms were characterised. These included 519 isolates from sheep, 52 isolates from cattle and 8 isolates from goats. The potential virulence of the isolates was assessed by the gelatin gel test (GG-test) and the elastin agar test, that test the heat stability and elastase activity of bacterial proteases, respectively. The isolates were also tested for the presence of intA by PCR, and allocated to serogroups by differentiation of fimA variants using multiplex PCR or sequencing. Thirty of the isolates were also serogrouped by slide agglutination. Three hundred and five isolates were defined as virulent by the GG-test. All these were from sheep from 52 farms located in the county of Rogaland in the south west of Norway. All isolates from cattle and goats were defined as benign by the GG-test. IntA was only detected in 6 (2.0%) of the virulent isolates. All serogroups except D and F were detected. Three hundred and seventy-two (64.3%) of the isolates belonged to serogroup A, and 96% of the virulent isolates belonged to this serogroup. On the grounds that virulent isolates were only found in one county, and that the majority belonged to the same serogroup (A), it is believed that a virulent D. nodosus strain was introduced to Norway relatively recently and that so far it has only spread locally.