Antimicrobial susceptibility and genetic relatedness of respiratory tract pathogens in weaner pigs over a 12-month period.

The collaboration project VASIB aims at reducing the antibiotic consumption in pig production by integrating information from consulting expertise in clinical inspection, hygiene, epidemiology, microbiology and pharmacology. In this VASIB subproject, we investigated the antimicrobial susceptibility and relatedness of porcine respiratory tract pathogens. Bordetella bronchiseptica (n = 47), Pasteurella multocida (n = 18) and Streptococcus suis (n = 58) were obtained from weaner pigs at two farms. Antimicrobial susceptibility testing was performed by broth microdilution according to CLSI standards. Resistance genes were detected via specific PCR assays. Macrorestriction analysis was conducted to determine the relatedness of the isolates and to identify clones. The B. bronchiseptica isolates showed indistinguishable (farm 1) or two closely related XbaI-patterns (farm 2). Different SmaI-PFGE patterns of P. multocida isolates were obtained at three different time points. In contrast, PFGE analysis of S. suis indicated more than one fragment pattern per pig and time point. Isolates exhibiting indistinguishable PFGE patterns were considered to represent the same clone. This study showed that only two closely related B. bronchiseptica clones were present in both farms, which had low MICs to all antimicrobials, except to ß-lactams. Different P. multocida clones were present at the three time points. They showed overall low MIC values, with two clones being resistant and one intermediate to tetracycline. S. suis clones were resistant to tetracycline (n = 19) and/or erythromycin/clindamycin (n = 16). They harboured the tetracycline resistance genes tet(O), tet(M) or tet(L) and/or the macrolide/lincosamide/streptogramin B resistance gene erm(B). Five penicillin-resistant S. suis clones were also detected.

The sensor kinase KdpD of Escherichia coli senses external K+.

The Kdp system of Escherichia coli is composed of the high-affinity K(+) transporter KdpFABC and the two regulatory proteins KdpD (sensor kinase) and KdpE (response regulator), which constitute a typical two-component system. The kdpFABC operon is induced under K(+) -limiting conditions and, to a lesser extent, under high osmolality in the medium. In search for the stimulus sensed by KdpD, we studied the inhibitory effect of extracellular K(+) on the Kdp system at pH 6.0, which is masked by unspecific K(+) transport at higher pH values. Based on KdpD derivatives carrying single aspartate replacements in the periplasmic loops which are part of the input domain, we concluded that the inhibition of the Kdp system at extracellular K(+) concentrations above 5 mM is mediated via KdpD/KdpE and not due to inhibition of the K(+) -transporting KdpFABC complex. Furthermore, time-course analyses of kdpFABC expression revealed that a decline in the extracellular K(+) concentration efficiently stimulates KdpD/KdpE-mediated signal transduction. In this report we provide evidence that the extracellular K(+) concentration serves as one of the stimuli sensed by KdpD.