Methicillin‐resistant Staphylococcus aureus (MRSA) is resistant to most β‐lactams due to the expression of an extra penicillin‐binding protein, PBP2a, with low β‐lactam affinity. It has long been known that heterologous expression of the PBP2a‐encoding mecA gene in methicillin‐sensitive S. aureus (MSSA) provides protection towards β‐lactams, however, some reports suggest that the degree of protection can vary between different β‐lactams. To test this more systematically, we introduced an IPTG‐inducible mecA into the MSSA laboratory strain RN4220. We confirm, by growth assays as well as single‐cell microfluidics time‐lapse microscopy experiments, that PBP2a expression protects against β‐lactams in S. aureus RN4220. By testing a panel of ten different β‐lactams, we conclude that there is also a great variation in the level of protection conferred by PBP2a. Expression of PBP2a resulted in an only fourfold increase in minimum inhibitory concentration (MIC) for imipenem, while a 32‐fold increase in MIC was observed for cefaclor and cephalexin. Interestingly, in our experimental setup, PBP2a confers the highest protection against cefaclor and cephalexin—two β‐lactams that are known to have a high specific affinity toward the transpeptidase PBP3 of S. aureus . Notably, using a single‐cell microfluidics setup we demonstrate a considerable phenotypic variation between cells upon β‐lactam exposure and show that mecA ‐expressing S. aureus can survive β‐lactam concentrations much higher than the minimal inhibitory concentrations. We discuss possible explanations and implications of these results including important aspects regarding treatment of infection.

BackgroundHigh incidences of gastritis and gastric ulceration are observed in sled dogs participating in endurance races. Exercise-induced increases in hormones like gastrin and cortisol have been suggested as possible contributing factors. An increase in C-reactive protein (CRP) has also been observed in canines during physical exercise. The aim of this study was to evaluate the effect of long distance racing on the serum concentration of gastrin, cortisol and CRP in a group of sled dogs, by comparing the results achieved early in the training season and after participating in a long distance race; “Femundløpet”. Dogs that only trained to the race, but did not compete in the race, were used as control dogs. Sixty-five sled dogs participated in the study; 46 competing dogs (25 completing and 21 non-completing the race) and 19 non-racing dogs (control dogs). The blood samples were collected in October 2012 and February 2013.ResultsThe post-race serum concentration of gastrin, cortisol and CRP was significantly elevated in sled dogs participating in the race (both completing and non-completing dogs) when compared to the results from training. However, no significant differences were observed between the two sampling dates in the control dogs. Post-race results for completing and non-completing dogs were also compared. This demonstrated a significant elevation in gastrin in non-completing versus completing dogs, and a significant elevation in cortisol in completing compared to non-completing dogs.ConclusionsParticipation in a long distance race was associated with a significant increase in serum gastrin, cortisol and CRP in sled dogs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13028-016-0204-9) contains supplementary material, which is available to authorized users.

Background Long-distance racing is known to cause alterations in haematological and serum biochemical parameters in sled dogs. Given that finishing status reflects the physical condition in dogs completing a race, such variations will mainly be the result of physiological adaption achieved during endurance exercise. However, changes observed in withdrawn dogs may indicate pathological conditions. The aim of this study was to reveal changes in haematological and serum biochemical values in sled dogs participating in a long-distance race, with emphasis on the withdrawn dogs. Sixty-five sled dogs participated in a clinical prospective cohort study: 46 dogs competed in the 600 km race (25 finishing and 21 withdrawn dogs), and 19 dogs served as controls. Blood sampling was performed early in the training season and after the race. Results When compared to control dogs, both withdrawn and finishing dogs showed significant increases in neutrophil count, C-reactive protein, blood urea nitrogen and sodium/potassium ratio. Significant decreases were found in erythrocytes and eosinophil cell count, and in haematocrit, haemoglobin, total protein, albumin, globulin, creatinine, potassium and calcium levels. Finishing dogs presented significant increases in white blood cells, large unstained cells, monocyte count and cortisol level compared to control dogs. In contrast, withdrawn dogs had significant elevations in alanine aminotransferase and alkaline phosphatase activity, as well as parameters associated with muscle metabolism, such as aspartate aminotransferase, creatine kinase and phosphorus concentration. Conclusions Competing sled dogs experienced minor changes in blood parameters in general, mainly revealing the same pattern among withdrawals and finishers. This might indicate that numerous changes simply reflect physiological adaption due to endurance exercise. However, the serum concentration of muscle enzymes was significantly increased only in the withdrawals, and were well above reference ranges. This reflects muscle degradation, which could be the main cause of performance failure in some of the withdrawals. Electronic supplementary material The online version of this article (10.1186/s13028-019-0453-5) contains supplementary material, which is available to authorized users.