Salmonella Typhimurium infections in pigs: a closer look at the pathogenesis

Salmonellose bij de mens wordt vaak veroorzaakt door Salmonella enterica subspecies enterica serovar Typhimurium (Salmonella Typhimurium). De ziekte veroorzaakt door deze bacterie is voornamelijk geassocieerd met het eten van varkensvlees. Varkens die geïnfecteerd zijn met Salmonella Typhimurium zijn meestal symptoomloze dragers. De mechanismen die Salmonella Typhimurium gebruikt om deze dragerdieren blijvend te infecteren zijn niet gekend. Het doel van deze thesis was om inzicht te verkrijgen in de mechanismen die Salmonella Typhimurium gebruikt om varkens te kolonizeren en er in te persisteren. In het eerste hoofdstuk van deze thesis werd een Salmonella Typhimurium stam geselecteerd die een persisterende infectie bij varkens kan veroorzaken. Hiervoor werd een veldstam, geïsoleerd uit een persistent geïnfecteerd varken, vergeleken met een standaard laboratorium stam die vaak wordt gebruikt voor onderzoek in muizen. De laboratorium stam was virulenter in muizen, maar de varkensstam was efficiënter in het veroorzaken van een persisterende infectie bij varkens. Deze varkensstam werd gekozen om te gebruiken in verdere experimenten. In het tweede hoofdstuk werden verschillende in vitro en in vivo modellen op punt gesteld om de pathogenese van Salmonella Typhimurium infecties bij varkens te onderzoeken. In het derde hoofdstuk werd de rol van verschillende virulentiegenen van Salmonella in de pathogenese van Salmonella Typhimurium infecties bij het varken onderzocht. In een eerste reeks experimenten werd de rol nagegaan van de genen die gelegen zijn op het Salmonella Pathogeniciteitseiland 1 (SPI-1). Deze genen waren essentieel voor Salmonella Typhimurium om varkensdarmcellen en macrofagen te kunnen binnen dringen. Alle SPI-1 mutanten waren sterk verzwakt in hun vermogen om diarree te veroorzaken. Zowel vroege als late celdood werd gezien in de macrofagen, maar enkel de vroege celdood bleek SPI-1 afhankelijk. Wanneer varkens peroraal geïnfecteerd werden met een combinatie van de Salmonella Typhimurium veldstam enerzijds en een SPI-1 deletiemutant anderzijds, bleek dat de mutant stam sterk verzwakt was in het invaderen en kolonizeren van de darmen, maar niet in het kolonizeren van de tonsillen. In een tweede reeks experimenten werd de rol nagegaan van de genen die gelegen zijn op het Salmonella Pathogeniciteitseiland 2 (SPI-2). Hierbij werd gebruik gemaakt van een mutant in het ssrA gen. Deze mutant was minder goed in staat om in vitro in macrofagen te vermeerderen en om de organen te kolonizeren van varkens die intraveneus geïnfecteerd werden. Bij biggen die oraal geïnoculeerd werden met de ssrA mutant stam verliep de infectie evenwel gelijkaardig in vergelijking met biggen die geïnoculeerd waren met de wild type stam. In een derde reeks experimenten, werd het belang van het fibronectine bindend eiwit ShdA in het ontstaan van een persisterende infectie onderzocht. Alhoewel dit gen bij muizen recent geïdentificeerd is als een belangrijke factor in de intestinale kolonizatie en persistentie in muizen, kon dit in deze experimenten niet worden bevestigd voor Salmonella Typhimurium infecties bij varkens. De resultaten van deze thesis tonen aan dat zowel de gastheermodellen als de Salmonella stammen met zorg gekozen moeten worden om relevant onderzoek te kunnen doen naar de pathogenese van Salmonella infecties. Tevens kan geconcludeerd worden dat SPI-1 afhankelijke invasie cruciaal is voor de kolonizatie van de darmen, maar niet van de tonsillen. De bijdrage van SPI-2 en shdA tot de persistentie van Salmonella Typhimurium in varkens is veel kleiner dan beschreven voor muizen

Bacterial blood culture isolates and their antimicrobial susceptibility obtained from 42 critically ill neonatal foals presented at Ghent University between 2011 and 2017

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Thermic dehorning and ear tagging as atypical portals of entry of Clostridium tetani in ruminants

This paper describes two infections with Clostridium tetani (C. tetani). One outbreak occurred after dehorning of calves, the second infection happened after ear tagging of a goat. In the first case 3 young Holstein Friesian calves showed generalized stiffness, severe lock-jaw and bloat two weeks after dehorning. The thermal dehorning wounds were identified as the infection sites of C. tetani by bacterial culture and PCR. The second case was a three-year old male castrated goat, with generalized stiffness. The animal had been ear tagged one week prior to the onset of the symptoms. C. tetani could be cultured from pus on the ear tag. Treatment was attempted in two calves and the goat. Wounds were debrided and disinfected, penicillin and anti-tetanus serum were administered and polyionic perfusions provided. In addition, the goat was vaccinated against tetanus. The goat and one calf fully recovered after 36 and 8 days respectively. To the authors' knowledge a tetanus outbreak in association with thermal dehorning has not been described previously. Also ear tagging as a possible cause for C. tetani infection has not been described in goats

Genotyping and antimicrobial resistance patterns of Escherichia coli O157 originating from cattle farms

During a Escherichia coli O157 prevalence study on cattle farms, 324 E. coli O157 isolates were collected from 68 out of 180 cattle farms. All isolates harbored the eaeA gene and the enterohemolysin (ehxA) gene. The majority of the strains only contained vtx2 (245 isolates), the combination of vtx1 and vtx2 was detected in 50 isolates, and in 29 isolates none of the vtx genes was present. Pulsed-field gel electrophoresis (PFGE) revealed that at a similarity level of 98% the isolates grouped into 83 different genotypes, 76 of which were only detected on one farm. Twenty-two out of the 68 positive farms harbored isolates belonging to more than one PFGE type, with a maximum of four different PFGE types. Minimal inhibitory concentrations of 10 antimicrobial agents were determined on a subset of 116 isolates, that is, one isolate per positive age category per farm. Acquired resistance to at least one antimicrobial agent was detected in 18 isolates and within a farm, only one resistance pattern was observed. All these 18 isolates were resistant toward streptomycin, and 16 of them also showed resistance toward sulfisoxazole. Six isolates were resistant to three or more antimicrobial agents

Clinical resistance and decreased susceptibility in Streptococcus suis isolates from clinically healthy fattening pigs

Streptococcus suis (S. suis) has often been reported as an important swine pathogen and is considered as a new emerging zoonotic agent. Consequently, it is important to be informed on its susceptibility to antimicrobial agents. In the current study, the Minimum Inhibitory Concentration (MIC) population distribution of nine antimicrobial agents has been determined for nasal S. suis strains, isolated from healthy pigs at the end of the fattening period from 50 closed or semiclosed pig herds. The aim of the study was to report resistance based on both clinical breakpoints (clinical resistance percentage) and epidemiological cutoff values (non-wild-type percentage). Non-wild-type percentages were high for tetracycline (98%), lincomycin (92%), tilmicosin (72%), erythromycin (70%), tylosin (66%), and low for florfenicol (0%) and enrofloxacin (0.3%). Clinical resistance percentages were high for tetracycline (95%), erythromycin (66%), tylosin (66%), and low for florfenicol (0.3%) and enrofloxacin (0.3%). For tiamulin, for which no clinical breakpoint is available, 57% of the isolates did not belong to the wild-type population. Clinical resistance and non-wild-type percentages differed substantially for penicillin. Only 1% of the tested S. suis strains was considered as clinically resistant, whereas 47% of the strains showed acquired resistance when epidemiological cutoff values were used. In conclusion, MIC values for penicillin are gradually increasing, compared to previous reports, although pigs infected with strains showing higher MICs may still respond to treatment with penicillin. The high rate of acquired resistance against tiamulin has not been reported before. Results from this study clearly demonstrate that the use of different interpretive criteria contributes to the extent of differences in reported antimicrobial resistance results. The early detection of small changes in the MIC population distribution of isolates, while clinical failure may not yet be observed, provides the opportunity to implement appropriate risk management steps

Mycoplasma bovis peritonitis and omental bursitis after C-section in two Belgian Blue cows

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Rapid identification of respiratory bacterial pathogens from bronchoalveolar lavage fluid in cattle by MALDI-TOF MS

Respiratory tract infections are a major health problem and indication for antimicrobial use in cattle and in humans. Currently, most antimicrobial treatments are initiated without microbiological results, holding the risk of inappropriate first intention treatment. The main reason for this empirical treatment is the long turnaround time between sampling and availability of identification and susceptibility results. Therefore the objective of the present study was to develop a rapid identification procedure for pathogenic respiratory bacteria in bronchoalveolar lavage fluid (BALf) samples from cattle by MALDI-TOF MS, omitting the cultivation step on agar plates to reduce the turnaround time between sampling and identification of pathogens. The effects of two different liquid growth media and various concentrations of bacitracin were determined to allow optimal growth of Pasteurellaceae and minimise contamination. The best procedure was validated on 100 clinical BALf samples from cattle with conventional bacterial culture as reference test. A correct identification was obtained in 73% of the samples, with 59.1% sensitivity (Se) (47.2-71.0%) and 100% specificity (Sp) (100-100%) after only 6 hours of incubation. For pure and dominant culture samples, the procedure was able to correctly identify 79.2% of the pathogens, with a sensitivity (Se) of 60.5% (45.0-76.1%) and specificity (Sp) of 100% (100-100%). In mixed culture samples, containing >= 2 clinically relevant pathogens, one pathogen could be correctly identified in 57% of the samples with 57.1%Se (38.8-75.5%) and 100% Sp (100-100%). In conclusion, MALDI-TOF MS is a promising tool for rapid pathogen identification in BALf. This new technique drastically reduces turnaround time and may be a valuable decision support tool to rationalize antimicrobial use

An update on pathogenesis and control of Salmonella infections in pigs

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