Characterization of VCC-1, a Novel Ambler Class A Carbapenemase from Vibrio cholerae Isolated from Imported Retail Shrimp Sold in Canada

One of the core goals of the Canadian Integrated Program for Antimicrobial Resistance Surveillance (CIPARS) is to monitor major meat commodities for antimicrobial resistance. Targeted studies with methodologies based on core surveillance protocols are used to examine other foods, e.g., seafood, for antimicrobial resistance to detect resistances of concern to public health. Here we report the discovery of a novel Ambler class A carbapenemase that was identified in a nontoxigenic strain of Vibrio cholerae (N14-02106) isolated from shrimp that was sold for human consumption in Canada. V. cholerae N14-02106 was resistant to penicillins, carbapenems, and monobactam antibiotics; however, PCR did not detect common β-lactamases. Bioinformatic analysis of the whole-genome sequence of V. cholerae N14-02106 revealed on the large chromosome a novel carbapenemase (referred to here as VCC-1, for Vibrio cholerae carbapenemase 1) with sequence similarity to class A enzymes. Two copies of bla_VCC-1 separated and flanked by ISVch9 (i.e., 3 copies of ISVch9) were found in an acquired 8.5-kb region inserted into a VrgG family protein gene. Cloned bla_VCC-1 conferred a β-lactam resistance profile similar to that in V. cholerae N14-02106 when it was transformed into a susceptible laboratory strain of Escherichia coli. Purified VCC-1 was found to hydrolyze penicillins, 1st-generation cephalosporins, aztreonam, and carbapenems, whereas 2nd- and 3rd-generation cephalosporins were poor substrates. Using nitrocefin as a reporter substrate, VCC-1 was moderately inhibited by clavulanic acid and tazobactam but not EDTA. In this report, we present the discovery of a novel class A carbapenemase from the food supply.     

Effect of Repeated Freezing and Thawing on 18 Clinical Chemistry Analytes in Rat Serum

In a preclinical research laboratory, using serum samples that have been frozen and thawed repeatedly is sometimes unavoidable when needing to confirm previous results or perform additional analysis. Here we determined the effects of multiple cycles of refrigeration or freezing and thawing of rat serum at 3 temperature conditions for different storage times on clinical chemistry analytes. Serum samples obtained from adult Wistar rats were stored at 2 to 8 °C and −10 to −20 °C for as long as 72 h and at −70 °C for as long as 30 d. At different time points (24, 48, and 72 h for samples stored at 2 to 8 °C or −10 to −20 °C and 1, 7, and 30 d for samples stored at −70 °C), the samples were brought to room temperature, analyzed, and then stored again at the designated temperature. The results obtained after each storage cycle were compared with those obtained from the initial analysis of fresh samples. Of the 18 serum analytes evaluated, 14 were stable without significant changes, even after 3 freeze–thaw cycles at the tested temperature ranges. Results from this study will help researchers working with rat serum to interpret the biochemical data obtained from serum samples that have been frozen and thawed repeatedly.Repeated cooling or freezing and thawing has long been assumed to affect the biochemical analytes of serum samples. However sometimes the use of such samples is unavoidable, as when needing to confirm the previous results or analyze additional analytes or at the time of instrument failure. The stability of biochemical analytes in human,^1,7 canine,¹⁰ and rat serum³ that has been stored and thawed only once for analysis has been addressed. In addition, the effect of repeated freezing and thawing on selected analytes in the serum and plasma of humans,^2,4 baboons,⁵ and canines⁹ has been reported previously. However similar information is unavailable for rats (Rattus norvegicus), a common laboratory animal used in various in vivo pharmacology and toxicity studies of drugs and pesticides.Typically serum is used to assess the effects of drugs on clinical chemistry analytes in these studies. Often, researchers need to reanalyze a few or all of the serum analytes to confirm conclusions or previous results. In addition, in the case of instrument failure, serum samples may need to be stored for future analysis. Under such circumstances, serum samples may need to be frozen and thawed repeatedly. Generally, serum samples for clinical chemistry analysis are refrigerated (2 to 8 °C) or frozen (−10 to −20 °C) for short-term durations and stored at −70 °C for long periods. In view of these practical situations, we investigated the effect of 3 freeze–thaw cycles on 18 serum clinical chemistry analytes that are evaluated routinely during nonclinical studies of drugs or chemicals in rodents.¹¹     

Hypocalcaemia mimicking long QT syndrome: case report

We describe a teenage girl who presented with syncope on exertion and prolonged QT on electrocardiogram (ECG). She was found to be hypocalcaemic due to hypoparathyroidism. Following oral calcium and vitamin D supplementation, there were no further episodes of syncope with normalization of the QT segment. This case highlights the need to consider all causes of a long QT segment.