Antimicrobial susceptibility of mastitis pathogens isolated from North American dairy cattle, 2011-2022.

A total of 10,890 bacterial isolates of Streptococcus dysgalactiae, Streptococcus uberis, Staphylococcus aureus and Escherichia coli isolated as etiological agents from dairy cows with mastitis by 29 veterinary laboratories across North America between 2011 and 2022 were tested for in vitro antimicrobial susceptibility by broth microdilution to ampicillin, cefoperazone, ceftiofur, cephalothin, erythromycin, oxacillin, penicillin-novobiocin and pirlimycin according to CLSI standards. Using available clinical breakpoints, antimicrobial resistance among S. dysgalactiae (n = 2406) was low for penicillin-novobiocin (0% resistance), ceftiofur (0.1%), erythromycin (3.2%) and pirlimycin (4.6%). Among S. uberis (n = 2398), resistance was low for ampicillin (0%) and ceftiofur (0.2%) and moderate for erythromycin (11.9%) and pirlimycin (18.4%). For S. aureus (n = 3194), resistance was low for penicillin-novobiocin (0%), ceftiofur (0.1%), oxacillin (0.2%), erythromycin (0.7%), cefoperazone (1.2%) and pirlimycin (2.8%). For E. coli (n = 2892), resistance was low for ceftiofur (2.8%) and cefoperazone (3.4%) and moderate for ampicillin (9.2%). Overall, the results indicate that mastitis pathogens in the United States and Canada have not shown any substantial changes in the in vitro susceptibility to antimicrobial drugs over the 12 years of the study, or among that of the proceeding survey from 2002-2010. The data support the conclusion that resistance to common antimicrobial drugs among mastitis pathogens, even to drugs that have been used in dairies for mastitis management for many years, continues to remain low.

Effects of food restriction on steroidogenesis in dispersed adrenocortical cells from Yarrow's Spiny Lizard (Sceloporus jarrovii).

Changes in energy balance can lead to functional alterations at all levels of the hypothalamic-pituitary-adrenal (HPA) axis. However, relatively little is known about how energy balance affects functional properties of adrenocortical cells themselves. We investigated effects of restricted food intake on sensitivity to ACTH and rates of steroidogenesis in adrenocortical cells isolated from growing female and male Yarrow's Spiny Lizards (Sceloporus jarrovii). At the end of the feeding regimen, we assayed acute (3h) progesterone (P(4)), corticosterone (B), and aldosterone (ALDO) production in response to ACTH in dispersed adrenocortical cells. Food restriction depressed growth rate by about 50% in both males and females but did not alter baseline plasma B measured at 10 weeks in either sex. At the cellular level, food restriction had the following effects: (1) increased basal B production in both sexes and basal ALDO production in males, (2) increased net maximal rates of production of P(4), B, and ALDO in response to ACTH, and (3) no overall effect on adrenocortical cellular sensitivity to ACTH. There were modest sex differences: overall rates of P(4) production were 46% greater in cells from females than from males, and in response to food restriction, the net maximal rate of ALDO production was 50% greater in cells from males than from females. Our results demonstrate that food restriction in S. jarrovii increases adrenocortical cellular rates of steroid production without affecting overall cellular sensitivity to ACTH.

Gonadal modulation of in vitro steroidogenic properties of dispersed adrenocortical cells from Sceloporus lizards.

Effects of adrenal corticosteroids on reproductive and endocrine functions of the gonads are well known, but reciprocal effects of gonadal hormones on the hypothalamo-pituitary-adrenal (HPA) axis and on adrenocortical steroidogenesis in particular have received much less attention. We investigated effects of gonadectomy and testosterone (T) replacement on adrenocortical cell function in a year-long field study of male Sceloporus undulatus (Eastern Fence Lizard) and in a shorter term laboratory study with male Sceloporus jarrovii (Yarrow's Spiny Lizard). We also compared females to males in Sceloporus virgatus (Striped Plateau Lizard) and investigated effects of gonadectomy in short-term laboratory experiment on females of this species. As measured by in vitro production of progesterone (P(4)), corticosterone (B), and aldosterone (ALDO), sensitivity of adrenocortical cells to corticotrophin (ACTH) was lower in control males than females of S. virgatus. In S. jarrovii males, cellular sensitivity to ACTH was reduced by orchiectomy but was not restored to levels of intact controls by T replacement. By contrast, in S. undulatus, cellular sensitivity to ACTH was not affected by orchiectomy alone but was reduced by T replacement in orchiectomized males. Maximal rates of steroid production were less consistently affected by experimental treatments, but were lower in males than in females of S. virgatus and were dramatically reduced by T replacement in orchiectomized S. undulatus males. Overall, our experiments clearly demonstrate two distinct sources of variation in functional capacities of dispersed adrenocortical cells isolated from Sceloporus lizards: (1) naturally occurring differences between males and females (Carsia and John-Alder, 2003), and (2) species-dependent changes in response to surgical gonadectomy with or without exogenous testosterone. Sex differences and functional lability in adrenocortical cells are probably widespread among vertebrates and may be an important component of variation in output of the HPA.