In search of a counter you can count on: relative efficacy of human visual and automated colony counting.

To evaluate comparative efficiency of traditional vs automated colony counting methods, cultures of Escherichia coli (ATCC 25945), Staphylococcus epidermidis (ATCC 12225), Streptococcus pyogenes (ATCC19615) and Streptococcus pneumoniae (ATCC49619) were prepared as pure cultures and mixed cultures at 0·5 McFarland standard and serial dilutions were performed. Plates were inoculated in triplicate with 50, 125, 250 and 500 colony forming units and counted by four researchers, visually and using each of the automated counters. Colony count and counting time were recorded. The pattern of efficiency for all bacterial species was similar: plates with low counts were accurate and quick to count for all methods, with an increase in time and a decrease in accuracy and precision as counts rose. Higher counts of single round colonies required less time and had greater precision with automated counters than human visual counting counts with no loss of accuracy; however, counts were reduced in accuracy and increased in time for species with less regular morphology or when plates had mixed species. Surprisingly, a free phone application was only slightly less precise and more time consuming than the high-end professional counter indicating that automation may be achievable at lower cost than expected. SIGNIFICANCE AND IMPACT OF THE STUDY: Colony quantification is essential in clinical and research settings as well as pedagogy at the college level. Human visual (HV) counting, the most common method, is time consuming and fraught with errors. The time, accuracy and precision of HV counting were compared to a high-end professional automated counter, an inexpensive phone application and a free phone application. Low cost benefits of increased speed and accuracy with automated counting are maximized when counting single round colonies; but much reduced if colonies have irregular morphology or demonstrate haemolysis.

Seasonal variations in oviductal activity, extensibility, and tensile strength in Chrysemys picta.

In vivo and in vitro myometrial activity, tissue extensibility, and tensile strength were measured during the annual cycle of the female turtle Chrysemys picta. Contractile rate, in vivo and in vitro, increased to a maximum in the periovulatory period, but contractile strength in vitro was inversely proportional to rate, being least in the periovulatory period. Initial oviductal circumference was highest in April and lowest in September. Although extensibility varied little, this parameter was inversely proportional to the initial circumference. Tensile strength was greatest in midwinter and least in postovulatory animals. The results are discussed in relationship to the known seasonal endocrine cycle and suggest important hormonal (estrogen, progesterone) effects upon egg retention and egg laying in this species.