Pervasive genotype-by-environment interactions shape the fitness effects of antibiotic resistance mutations

The fitness effects of antibiotic resistance mutations are a major driver of resistance evolution. While the nutrient environment affects bacterial fitness, experimental studies of resistance typically measure fitness of mutants in a single environment only. We explored how the nutrient environment affected the fitness effects of rifampicin-resistant rpoB mutations in Escherichia coli under several conditions critical for the emergence and spread of resistance-the presence of primary or secondary antibiotic, or the absence of any antibiotic. Pervasive genotype-by-environment (GxE) interactions determined fitness in all experimental conditions, with rank order of fitness in the presence and absence of antibiotics being strongly dependent on the nutrient environment. GxE interactions also affected the magnitude and direction of collateral effects of secondary antibiotics, in some cases so drastically that a mutant that was highly sensitive in one nutrient environment exhibited cross-resistance to the same antibiotic in another. It is likely that the mutant-specific impact of rpoB mutations on the global transcriptome underpins the observed GxE interactions. The pervasive, mutant-specific GxE interactions highlight the importance of doing what is rarely done when studying the evolution and spread of resistance in experimental and clinical work: assessing fitness of antibiotic-resistant mutants across a range of relevant environments.

Repeated use of the GnRH analogue deslorelin to down-regulate reproduction in male cheetahs (Acinonyx jubatus)

The GnRH analogue deslorelin, as a subcutaneous implant, was initially developed in Australia as an ovulation-inducing agent in mares. Its uses, for the suppression of reproduction in the domestic dog and cat and in other species, including humans, have been developed subsequently. Such implants have been used as a contraceptive modality in a variety of wild carnivores, both males and females. This paper describes the use of deslorelin implants as a contraceptive agent for cheetah males maintained in a semi-captive environment and housed in various camps together with females. Annually, male cheetahs were treated for 1 (n = 2), 2 (n = 7), 3 (n = 9), 4 (n = 3) or 5 (n = 1) consecutive years with an implant containing 4.7, 5.0 or 6.0 mg of deslorelin. On the first day of treatment and then on an annual basis, blood testosterone concentrations were analysed, testicular measurements were taken, appearance of penile spikes was determined, and semen was collected and evaluated. Pregnancy rates of mated or inseminated females were determined. A dose of 6 mg of deslorelin suppressed reproduction for at least 1 year, whereas with 4.7 and 5 mg of deslorelin, 3 of 17 males had a few non-motile spermatozoa in their ejaculates. All testosterone concentrations were basal at 1 year post-implant and no side effects were observed. We concluded that deslorelin implantation, at a dose of 6 mg, was a safe and reliable method of annual contraception in male cheetahs.

Cardiopulmonary effects of medetomidine or midazolam in combination with ketamine or tiletamine / zolazepam for the immobilisation of captive cheetahs (Acinonyx jubatus)

Captive cheetah (Acinonyx jubatus) scheduled for either general health examination or dental surgery were immobilised with combinations of medetomidine-ketamine (K/DET, n = 19), midazolam-ketamine (K/MID, n = 4) or medetomidine-tiletamine-zolazepam (Z/DET, n=5). Induction time and arterial blood pressure was not statistically significantly (P 0.05) different between treatment groups. Transient seizures were observed in the K/DET treated animals during induction. Hypertension was present in all groups during anaesthesia with mean(+SD) systolic pressure of 30.7+5.0 kPa for the K/DET group, 27.7+ 2.7 kPa for the K/MID group, and 33.1+4.6 kPa for the Z/DET group. Heart rate was statistically significantly (P 0.05) lower in the K/DET group (69 + 13.2 beats/min) compared to the K/MID group (97 + 22.6 beats/min), and ventilation rate was statistically significantly (P 0.05) lower in the K/MID group (15 + 0.0 breaths/min) compared with the K/DET group (21+4.6). A metabolic acidosis and hypoxia were observed during anaesthesia when breathing air. Oxygen (O2) administration resulted in a statistically significant (P 0.05) increase in the arterial partial pressure of carbon dioxide (hypercapnoea), arterial partial pressure of O2, and % oxyhaemoglobin saturation.

Antibodies to some pathogenic agents in free-living wild species in Tanzania

A total of 535 sera from eight species of wildlife were collected from different game areas in Tanzania between 1987 and 1989. These sera were tested for antibodies against foot-and-mouth disease, bovine herpes virus types 1 and 2, lumpy skin disease, bovine viral diarrhoea, Akabane, bovine ephemeral fever, bluetongue, enzootic bovine leucosis, African horse sickness and African swine fever viruses and Brucella abortus based on the expected species susceptibility. Sera from buffalo Syncerus caffer, wildebeest Connochaetes taurinus and topi Damaliscus korrigum contained antibodies against the majority of the pathogens tested. Antibodies to fewer pathogens were detected in sera from the other species. No antibodies to lumpy skin disease virus were detected in any of the sera examined. African horse sickness antibodies were detected in sera from Zebra and African swine fever antibodies were detected in wart hog. The occurrence of antibodies to these agents suggests that wild species act as reservoirs of infection for some of these pathogens. However, until the susceptibility of individual species is proven by isolation of the aetiological agents their role must remain speculative.

A serological survey of rinderpest antibody in wildlife and sheep and goats in northern Tanzania

An extensive serological survey for rinderpest antibody in wildlife, principally buffalo (Syncerus caffer), and sheep and goats has been undertaken in the previously endemic region of Northern Tanzania to determine whether or not the virus has continued to cycle in susceptible species since the last occurrence of overt disease in 1982. The results show that infection but not disease has occurred at least until 1987 in buffalo in parts of the Serengeti National Park but not in the other game areas of Tanzania where samples were taken. Sero-positive sheep and goats were widely distributed and have been found in 10 of the 14 districts sampled but there have been no reports of disease. These findings bring into question the possibility of eradicating the disease from Africa and continuous annual monitoring of this and other similar ecological zones will be required.

Cephalosporinase and penicillinase activities of a beta-lactamase from Pseudomonas pyocyanea

1. Pseudomonas pyocyanea N.C.T.C. 8203 produces a beta-lactamase that is inducible by high concentrations of benzylpenicillin or cephalosporin C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. 2. No evidence was obtained that the crude enzyme preparation consisted of more than one beta-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. 3. The maximum rate of hydrolysis of cephalosporin C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolysable substrates. 4. Cephalosporin C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin C yielded 1 equiv./mole. Evidence was obtained that the opening of the beta-lactam ring of cephalosporin C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. 5. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolysable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a beta-lactamase contributed to the factors responsible for the very high resistance of Ps. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.