Noise-induced hearing loss alters potassium-chloride cotransporter KCC2 and GABA inhibition in the auditory centers.

Homeostatic plasticity, the ability of neurons to maintain their averaged activity constant around a set point value, is thought to account for the central hyperactivity after hearing loss. Here, we investigated the putative role of GABAergic neurotransmission in this mechanism after a noise-induced hearing loss larger than 50 dB in high frequencies in guinea pigs. The effect of GABAergic inhibition is linked to the normal functioning of K + -Cl- co-transporter isoform 2 (KCC2) which maintains a low intracellular concentration of chloride. The expression of membrane KCC2 were investigated before and after noise trauma in the ventral and dorsal cochlear nucleus (VCN and DCN, respectively) and in the inferior colliculus (IC). Moreover, the effect of gabazine (GBZ), a GABA antagonist, was also studied on the neural activity in IC. We show that KCC2 is downregulated in VCN, DCN and IC 3 days after noise trauma, and in DCN and IC 30 days after the trauma. As expected, GBZ application in the IC of control animals resulted in an increase of spontaneous and stimulus-evoked activity. In the noise exposed animals, on the other hand, GBZ application decreased the stimulus-evoked activity in IC neurons. The functional implications of these central changes are discussed.

Increasing conception rate by addition of a second prostaglandin injection in an Ovsynch and progesterone treatment programme for dairy cows not detected in oestrus before the start of the seasonal mating period.

AIMS: To assess the effect on conception rate to first service, 3- and 6-week in-calf rates, final pregnancy rate and the hazard of pregnancy, of addition of a second prostaglandin (PG) injection 24 hours after the first, in a synchrony programme combining Ovsynch and progesterone in pasture-based dairy cows that had not been detected in oestrus before the start of the seasonal mating period. METHODS: This prospective, negative-controlled study was conducted using anoestrous cows (n = 1,411) from nine spring-calving dairy herds in the Waikato region of New Zealand. Ovaries of cows not detected in oestrus were examined by transrectal ultrasonography and the presence of a corpus luteum determined. All cows were then treated with an intravaginal progesterone-releasing device and injected I/M with gonadorelin (Day -9). Cows were injected I/M with cloprostenol at device removal (Day -2) and on Day -1 were injected with either water (single PG; n = 720), or cloprostenol (double PG; n = 692). On Day 0 cows were injected again with gonadorelin, unless previously detected in oestrus, and were inseminated on Day 1. Based on dated pregnancy diagnosis by transrectal ultrasonography, cows were categorised as conceiving to first insemination, becoming pregnant in the first 3 or 6 weeks, or becoming pregnant by the end of the mating period. RESULTS: Cows in the double PG group had increased conception rate to first service (45.3 (95% CI = 45.1-45.4)% vs. 41.1 (95% CI = 41.0-41.3)%; p < 0.001), 3-week in-calf rate (53.4 (95% CI = 53.6-54.0)% vs. 49.2 (95% CI = 49.0-49.4)%; p < 0.001), and 6-week in-calf rate (67.2 (95% CI = 65.7-68.8)% vs. 63.5 (95% CI = 62.0-65.0)%; p = 0.014) compared to cows in the single PG group. Final pregnancy rate and hazard of pregnancy did not differ between treatment groups (p >0.2). CONCLUSIONS: Addition of a second PG injection 24 hours after the first, increased conception rate to first service and the proportion of cows pregnant by 3 and 6 weeks after commencement of the mating period. CLINICAL RELEVANCE: Improved outcomes can be achieved when treating those cows not detected in oestrus by the start of the seasonal mating period by addition of a second PG injection to the currently recommended treatment protocol for these animals.

Characterisation of extended-spectrum ß-lactamase and AmpC ß-lactamase-producing Enterobacteriaceae isolated from companion animals in New Zealand.

AIMS: To assess the occurrence of, and characterise, extended-spectrum ß-lactamase (ESBL) and AmpC ß-lactamase (AmpC)-producing Enterobacteriaceae isolated by veterinary diagnostic laboratories from infection sites in companion animals in New Zealand. METHODS: Selected Enterobacteriaceae isolates were submitted by seven New Zealand veterinary diagnostic laboratories. They were isolated from infection sites in companion animals between June 2012 and June 2013, and were resistant to amoxicillin-clavulanic acid, fluoroquinolones, or any combination of two or more antimicrobials. Based on disk diffusion test results, the isolates were phenotypically categorised according to production of ESBL and AmpC. Genes for ESBL and AmpC production were amplified by PCR and sequenced. Escherichia coli isolates were also typed by multilocus sequence typing. RESULTS: A total of 115 isolates matching the inclusion criteria were obtained from the participating laboratories, of which 74 (64%) originated from dogs and 29 (25%) from cats. Seven bacterial species were identified, of which E. coli was the most common (87/115, 76%). Of the 115 isolates, 10 (9%) expressed the ESBL phenotype, 43 (37%) the AmpC phenotype, and seven (6%) both ESBL and AmpC phenotypes. Of the 60 ESBL and AmpC-producing isolates, 36 (60%) were E. coli. Amongst these isolates, 27/60 (45%) were classified as multidrug resistant, compared with 15/55 (27%) non-ESBL or AmpC-producing isolates (p<0.01). Ninety five isolates were resistant to amoxicillin-clavulanic acid and 58 (61%) of these were ESBL or AmpC-producing. The predominant ESBL genes were blaCTX-M-14 and blaCTX-M-15, and the dominant plasmid-encoded AmpC gene was blaCMY-2. Thirty-eight E. coli multilocus sequence types (ST) were identified, and the most prevalent were ST12 (12/89, 13%), ST131 (6/89, 7%) and ST648 (6/89, 7%). ESBL and AmpC-producing isolates accounted for 35/1,082 (3.2%) of the Enterobacteriaceae isolated by one laboratory network over the study period. CONCLUSIONS AND CLINICAL RELEVANCE: ESBL and AmpC-producing Enterobacteriaceae were associated with clinical infections in companion animals in New Zealand, and were often multidrug resistant. In this study, these organisms accounted for <5% of all Enterobacteriaceae isolated from infection sites by one laboratory network, but their prevalence among isolates resistant to amoxicillin-clavulanic acid was 61%. Therefore routine secondary testing for ESBL and AmpC production by Enterobacteriaceae that are resistant to amoxicillin-clavulanic acid in primary testing could improve the accuracy of definitive antimicrobial therapy in companion animals in New Zealand.

Characterisation of methicillin-resistant Staphylococcus aureus clinical isolates from animals in New Zealand, 2012-2013, and subclinical colonisation in dogs and cats in Auckland.

AIMS: To characterise methicillin-resistant Staphylococcus aureus (MRSA) isolates from infection sites in animals in New Zealand and assess the prevalence of subclinical MRSA colonisation in dogs and cats attending veterinary clinics in Auckland. METHODS: MRSA isolates from clinical specimens obtained by the main New Zealand veterinary diagnostic laboratories between June 2012 and June 2013, were genotypically characterised by DNA microarray hybridisation analysis and spa typing. In addition, nasal or perineal skin swabs collected from a cross-sectional sample of dogs (n=361) and cats (n=225) attending 29 veterinary clinics in Auckland during the same period were analysed for MRSA by culture. RESULTS: Eight MRSA clinical isolates were submitted for characterisation by the participating laboratories. The isolates originated from five dogs, including two isolates from the same dog, one foal, and one isolate had no identification of the source. The strain-types identified were AK3 (ST-5 SCCmecIV t045; n=1), USA500 (ST8 SCCmecIV t064; n=1), WSPP (ST30 SCCmecIV t019; n=1), Rhine Hesse (ST5 SCCmecII t002; n=2), and EMRSA-15 (ST22 SCCmecIV t032; n=3). No MRSA were isolated from 586 cultured swabs. Methicillin-susceptible S. aureus were detected in 9/257 (3.5%) swabs and non-aureus staphylococci in 22/257 (8.5%) swabs. The estimated true MRSA subclinical colonisation prevalence was 0%, with an upper 95% CI boundary of 1.9% for cats and 1.4% for dogs. CONCLUSIONS: The modest number of MRSA isolates submitted for this study by the participating laboratories suggests clinical MRSA infection in animals in New Zealand continues to be sporadic. The wide variety of strain-types found mirrored the evolving strain-type diversity observed in humans. We cannot rule out bias due to the non-random sampling of dogs and cats, but the apparent colonisation prevalence of 0% was consistent with the low prevalence of subclinical colonisation in humans in New Zealand. These similarities indicate the epidemiology of animal and human MRSA infections are linked. CLINICAL RELEVANCE: In the last decade, the prevalence of human MRSA infections in New Zealand has steadily increased. This is the second published study of MRSA in animals in New Zealand. The results indicate clinical MRSA infection in animals remains sporadic, but the diversification of the strain-types may pose new therapeutic challenges to veterinarians, due to their diverse resistome.