Isolates, antimicrobial susceptibility profiles and multidrug resistance of bacteria cultured from samples collected from sheep in New Zealand (2003-2016)

Aim:To describe the common species, antimicrobial susceptibility and multidrug resistance (MDR) of bacteria cultured from samples submitted to veterinary diagnostic laboratories from sheep in New Zealand between 2003 and 2016. Methods:Bacterial culture and antimicrobial susceptibility test data from June 2003 to March 2016 for animals identified as sheep were obtained from two commercial veterinary diagnostic laboratories in New Zealand. Submission information included animal signalment, geographic origin, specimen description, the organisms cultured, and where available, antimicrobial susceptibilities of the isolates. MDR was defined as any isolate with resistance to >= 3 antimicrobial classes. Results:There were 1,971 unique laboratory submissions, yielding 2,188 isolates. Of the 1,971 submissions, the most commonly represented breeds were Romney (933; 47.3%), Romney cross (264; 13.4%), and Coopworth (197; 10.0%), and there were more submissions from females (1,006; 51.0%) than males (184; 9.3%). Most submissions were from Canterbury (549; 27.9%), Southland (471; 23.9%), and Manawatu-Wanganui (272; 13.8%) regions. Other signalment data were inconsistently described. Submitted samples most commonly originated from the gastrointestinal tract (852; 43.2%), faeces (378; 12.1%), or liver (146; 7.4%). Of the 2,188 isolates, 1,771 (80.9%) were identified by species and 247 (11.4%) by genus, with the most common isolates beingSalmonellaspp. (880; 40.2%),Campylobacterspp. (408; 18.6%),Listeriaspp. (140; 6.4%) andYersiniaspp. (113; 5.2%). Susceptibility results were available for 117/2,188 (5.3%) isolates from 51/1,971 (2.6%) submissions. No antimicrobial susceptibility data were available forSalmonellaspp.,Campylobacterspp.,Listeriaspp. orYersiniaspp. Overall for the isolates tested, susceptibility to the fluoroquinolones and tetracyclines was greatest, and MDR was found in 24/117 (20.5%) isolates. MDR was a more frequent finding forEnterococcusspp.,Bacillusspp., andProteus mirabilis, but was infrequent in isolates ofStaphylococcus aureus, alpha-haemolytic streptococci,Escherichia coliorEnterobacterspp.

Automated summary

This study described the bacterial species, antimicrobial susceptibility, and multidrug resistance in sheep samples submitted to veterinary diagnostic labs in New Zealand between 2003 and 2016. The most commonly isolated bacteria were Salmonella, Campylobacter, Listeria, and Yersinia, with varying levels of susceptibility to fluoroquinolones and tetracyclines. Multidrug resistance was found in a subset of isolates, with differences between bacterial species.