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Item Subclinical mastitis in New Zealand grazing dairy ewes 2: Relationships among somatic cell count, California Mastitis Test, and milk culture, and risk factors for elevated aerobic plate count(Elsevier Inc on behalf of the American Dairy Science Association, 2026-01-01) Chambers G; Lawrence K; Grinberg A; Velathanthiri N; Ridler A; Laven ROur objectives were, in grazing dairy ewes, (1) to describe SCC, California Mastitis Test (CMT) score, and ewe-level milk aerobic plate count (APC), (2) to explore the relationship between CMT and SCC, (3) to identify risk factors for elevated APC, and (4) to find the optimal SCC threshold for diagnosis of IMI. Gland-level milk samples were collected from ∼15 randomly selected ewes on each of 20 New Zealand dairy sheep farms at early, mid, and late lactation in a repeated cross-sectional study. Aerobic bacterial culture and CMT (measured on a scale of 0, trace, 1, 2, or 3) were performed at the gland level, and SCC and APC at the ewe level using composite milk samples. Milk samples were collected from 893 ewes, 870 of which had complete SCC and culture data. Geometric mean SCC was 169,039 (95% CI: 153,921–185,641) cells/mL, varying between farms and decreasing across visits. A CMT score ≥1 in one or both glands occurred in 21.2% of ewes. Mean log10 SCC increased linearly with CMT score, but the correlation between the ewe's highest gland-level CMT score and SCC was moderate (Kendall's tau = 0.47, 95% CI 0.43–0.52). Bacteria were isolated from 86 (9.9%) ewes, with the most common bacteria being NAS (7.0% of glands) and Staphylococcus aureus (0.6% of glands). A SCC threshold of ∼400,000 cells/mL had the greatest Youden's index for diagnosing IMI using a single SCC measurement. The APC was below the limit of quantification (1 × 103 cfu/mL) in 78.0% of ewes, and <100 × 103 cfu/mL in 96.9% of ewes, and varied between visits and farms. Using a mixed Bayesian ordinal regression model, elevated CMT score and SCC, positive milk culture, and subclinical mastitis, but not udder asymmetry, were confirmed as risk factors for elevated APC. These findings provide baseline milk quality data for New Zealand grazing dairy ewes, confirm that udder health should be considered when investigating elevated bulk milk APC, and can be used to help producers manage SCC, subclinical mastitis, and APC, as well as informing further research. Findings specific to New Zealand's emerging sheep dairy industry offer a benchmark for pastoral systems internationally and highlight the importance of udder health to bulk milk quality.Item Subclinical mastitis in New Zealand grazing dairy ewes 1: Prevalence and risk factors(Elsevier Inc on behalf of the American Dairy Science Association, 2026-01-01) Chambers G; Lawrence K; Grinberg A; Velathanthiri N; Ridler A; Laven ROur objectives were to describe subclinical mastitis and identify its risk factors among grazing dairy ewes in New Zealand. Gland-level milk samples were collected from ∼15 randomly selected ewes on each of 20 dairy sheep farms at early, mid, and late lactation in a repeated cross-sectional study. California Mastitis Tests (CMT; measured on a scale of 0, trace, 1, 2, or 3) and aerobic bacterial culture were performed at the gland level, and SCC at the ewe level using composite milk samples. Subclinical mastitis was defined at the ewe level as having 1 or 2 bacteriologically positive glands and SCC >500 × 103 cells/mL or a CMT score ≥1 (or both). Milk samples were collected from 893 ewes, and complete subclinical mastitis data were available for 856 ewes. Median (range) SCC was 128,000 (2,000–34,953,000) cells/mL. A CMT score ≥1 in one or both glands was found in 21.2% of ewes. Bacteria were isolated from 5.5% of glands, with the most common species being non-aureus staphylococci (4.0% of glands) and Staphylococcus aureus (0.6% of glands). The prevalence of subclinical mastitis was 6.4% (95% CI = 4.6%–8.7%) and was not strongly clustered within farms (intraclass correlation coefficient = 0.04). Ewes with moderate or severe teat end hyperkeratosis had 6.4 times higher odds of subclinical mastitis than ewes with no or mild hyperkeratosis, and ewes with asymmetric udders had 2.3 times higher odds. The odds declined across the 3 visits. The prevalence was low compared with studies of more intensively farmed ewes in the northern hemisphere, but the bacterial causes were consistent. Subclinical mastitis management should be focused at the ewe level before the farm level, given the weak clustering within farms. When addressing or preventing a subclinical mastitis challenge, producers should consider teat end hyperkeratosis and udder asymmetry as simple visual screening tools but not rely on them alone to identify ewes at risk of subclinical mastitis. We present new information for New Zealand grazing dairy ewes, examine udder asymmetry as a diagnostic tool for subclinical mastitis, and show that, although prevalence was lower in New Zealand, the dominant pathogens are consistent, supporting the broader relevance of these findings to international mastitis control, albeit with adaptations for pasture-based systems.Item 20 years later: unravelling the genomic success of New Zealand’s home-grown AK3 community-associated methicillin-resistant Staphylococcus aureus(Microbiology Society, 2025-07-25) White RT; Bakker S; Bloomfield M; Burton M; Elvy J; Eustace A; French NP; Grant J; Greening SS; Grinberg A; Harland C; Hutton S; Karkaba A; Martin J; Matthews B; Miller H; Straub C; Tarring C; Taylor WT; Ussher J; Velasco C; Voss EM; Dyet KMethicillin-resistant Staphylococcus aureus (MRSA) represents a significant public health challenge. In New Zealand, the community-associated MRSA sequence type (ST)5, carrying the staphylococcal cassette chromosome mec (SCCmec) type IV genetic element (which confers methicillin resistance), has been predominant since its detection in 2005. Known informally as the AK3 strain, it also exhibits resistance to fusidic acid. Here, we investigated the genomic evolution of the AK3 strain by analysing 397 genomes, comprising 361 MRSA and 36 closely related methicillin-susceptible S. aureus (MSSA) genomes, including 285 recently sequenced isolates from New Zealand spanning 2020 (n=30), 2021 (n=77), 2022 (n=88), 2023 (n=73) and 2024 (n=17). Phylogenetic analysis revealed that the AK3 strain evolved through stepwise acquisition of mobile genetic elements, with an MSSA ancestor likely introduced to New Zealand in the late 1970s. The lineage first acquired a SaPITokyo12571-like pathogenicity island, which contains the staphylococcal enterotoxin C bovine variant (sec-bov) and an enterotoxin-like protein (sel), between 1984 and 1991. This was followed by the integration of SCCmec type IV and adjacent fusidic acid resistance operon between 1997 and 2000. This timing coincides with increased community fusidic acid use in New Zealand. The AK3 strain then diversified into three major clades, spreading throughout New Zealand and Australia, with sporadic detection in European countries and Samoa. Our findings demonstrate how the sequential acquisition of mobile genetic elements, combined with antibiotic selection pressure, likely contributed to the successful emergence of AK3 and its spread in the South Pacific region.Item The Host Adaptation of Staphylococcus aureus to Farmed Ruminants in New Zealand, With Special Reference to Clonal Complex 1(John Wiley and Sons Ltd, 2025-06) Nesaraj J; Grinberg A; Laven R; Chanyi R; Altermann E; Bandi C; Biggs PJGenetic features of host adaptation of S. aureus to ruminants have been extensively studied, but the extent to which this adaptation occurs in nature remains unknown. In New Zealand, clonal complex 1 (CC1) is among the most common lineages in humans and the dominant lineage in cattle, enabling between-, and within-CC genomic comparisons of epidemiologically cohesive samples of isolates. We assessed the following genomic benchmarks of host adaptation to ruminants in 277 S. aureus from cattle, small ruminants, humans, and pets: 1, phylogenetic clustering of ruminant strains; 2, abundance of homo-specific ruminant-adaptive factors, and 3, scarcity of heterospecific factors. The genomic comparisons were complemented by comparative analyses of the metabolism of carbon sources that abound in ruminant milk. We identified features fulfilling the three benchmarks in virtually all ruminant isolates, including CC1. Data suggest the virulomes adapt to the ruminant niche sensu lato accross CCs. CC1 forms a ruminant-adapted clade that appears better equipped to utilise milk carbon sources than human CC1. Strain flow across the human–ruminant interface appears to only occur occasionally. Taken together, the results suggest a specialisation, rather than mere adaptation, clarifying why zoonotic and zoo-anthroponotic S. aureus transmission between ruminants and humans has hardly ever been reported.Item An observational study of farmer-reported clinical mastitis in New Zealand dairy ewes.(Taylor and Francis Group, 2024-07-01) Chambers G; Laven R; Grinberg A; Ridler A; Velathanthiri NAIMS: To describe the incidence, aetiology, treatment, and outcomes of farmer-reported clinical mastitis on New Zealand dairy sheep farms. METHODS: A prospective cohort study was conducted on 20 spring-lambing New Zealand sheep milking farms over the 2022-2023 season. Clinical mastitis was defined as a change in the appearance of milk and/or signs of inflammation in the gland. Farmers were required to report all cases of clinical mastitis and collect information on affected ewes' demographics, clinical features, treatments (where applicable), and outcomes. Milk samples from mastitic glands were submitted for microbiological culture and identification by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF). RESULTS: Partial or complete clinical mastitis data were available for 236 cases from 221 ewes on 18/20 study farms. Clinical mastitis was diagnosed in 0-6% of ewes at the farm level, with an overall incidence of 1.8 (95% CI = 1.0-3.2)% using the study data, or 2.3 (95% CI = 1.6-3.3)% using the study data and farmer estimates that included unreported cases. Cases occurred mostly in early lactation, with 59% detected during the lambing period (August-October), at a median of 7 (IQR 3, 40) days in milk. The majority of cases featured clots in the milk (59%), swelling (55%), and unevenness (71%) of the glands. Pyrexia (rectal temperature ≥ 40.0°C) was diagnosed in 25% of cases and depression (lethargy, inappetence, or inability to stand) in 26% of cases. Treatment was given to 46% of cases, with tylosin being the most commonly used treatment (50% of treated cases). The most common outcome was immediate drying off to be culled without treatment (32%), followed by still milking and recovered but with lasting problems (25%). Nearly half of all the milk samples submitted were culture negative. Streptococcus uberis (14%), non-aureus staphylococci (12%), and Staphylococcus aureus (11%) were the most common isolates, found on 12, 8 and 8 of the 16 farms with microbiological data, respectively. CONCLUSIONS: Clinical mastitis affected up to 6% of ewes at the farm level. Systemic signs were observed in one quarter of affected ewes, suggesting a role for supportive treatment. Clinical mastitis can be severe and challenging to fully resolve in New Zealand dairy sheep. CLINICAL RELEVANCE: This is the first systematic study of clinical mastitis in New Zealand dairy ewes. It provides baseline information specific to New Zealand conditions for farmers, veterinarians, and other advisors to guide the management of mastitis for the relatively new dairy sheep industry in New Zealand.Item Staphylococcus microti Strains Isolated from an Italian Mediterranean Buffalo Herd(MDPI (Basel, Switzerland), 2023-01-03) Ambrosio M; Nocera FP; Garofalo F; De Luca P; Grinberg A; De Martino L; Nielsen SS. microti is a new species among non-aureus staphylococci (NAS) frequently found in bovine milk samples and associated with subclinical mastitis (SCM). The aim of this study was to analyze the presence of S. microti in 200 composite milk samples and 104 milking parlor surface swabs collected at a buffalo farm in Southern Italy to define its presence in milk and a milking parlor environment. The samples were inoculated onto different agar plates, and the isolates were identified by MALDI-TOF MS. The strains identified as S. microti (54/304 samples, 17.8%) were collected, and their purified genomic DNA was subjected to PCR amplification and whole 16S rRNA gene sequencing. Furthermore, their phenotypic resistance profiles were evaluated by a disk diffusion method, and the genotypic characterization of the tetracycline resistance was performed for the tetM and tetK genes by multiplex PCR. Four and forty-seven S. microti isolates from milk samples of lactating animals with subclinical mastitis (SCM) and intramammary infection (IMI), respectively, and three isolates from milking parlor surfaces were recovered. The genomic DNA was purified from the bacterial isolates, and the amplification and sequencing of the 16S gene further supported the proteomic identification as S. microti. No clinical mastitis was detected in the herd during the study period. The antimicrobial susceptibility testing revealed a worrisome 100% resistance to tetracyclines, genotypically mediated by the tetM gene for all strains. This study highlights that S. microti may be commonly isolated from dairy buffalo milk and milking parlor equipment. Its association with SCM or IMI remains to be established.Item Epidemiological and molecular evidence of a monophyletic infection with Staphylococcus aureus causing a purulent dermatitis in a dairy farmer and multiple cases of mastitis in his cows(Cambridge University Press, 2004) Grinberg A; Hittman A; Leyland M; Rogers L; LeQuesne BAn epidemiological and molecular investigation of a cutaneous suppurative infection with Staphylococcus aureus in a dairy farmer, occurring concurrently with an outbreak of clinical mastitis in his herd, was carried out. A common aetiology for the diseases in the farmer and his cows was established by combining clinical evidence with a molecular genomic analysis of the bacterial isolates using pulsed field gel electrophoresis of DNA macro-restriction fragments. This case indicates the possibility of the emergence and circulation of anthropozoonotic clones of S. aureus in dairy herds. It also provides further evidence of the severe impact of infection with highly virulent clones on dairy lactating cattle.Item Molecular epidemiology of C. coli isolated from different sources in New Zealand between 2005 and 2014(2/11/2015) Nohra A; Grinberg A; French N; Midwinter AC; Collins-Emerson J© 2016, American Society for Microbiology. Campylobacteriosis is one of the most important foodborne diseases worldwide and a significant health burden in New Zealand. Campylobacter jejuni is the predominant species worldwide, accounting for approximately 90% of human cases, followed by Campylobacter coli. Most studies in New Zealand have focused on C. jejuni; hence, the impact of C. coli strains on human health is not well understood. The aim of this study was t o genotype C. coli isolates collected in the Manawatu region of New Zealand from clinical cases, fresh poultry meat, ruminant feces, and environmental water sources, between 2005 and 2014, to study their population structure and estimate the contribution of each source to the burden of human disease. Campylobacter isolates were identified by PCR and typed by multilocus sequence typing. C. coli accounted for 2.9% (n = 47/1,601) of Campylobacter isolates from human clinical cases, 9.6% (n = 108/1,123) from poultry, 13.4% (n = 49/364) from ruminants, and 6.4% (n = 11/171) from water. Molecular subtyping revealed 27 different sequence types (STs), of which 18 belonged to clonal complex ST-828. ST-1581 was the most prevalent C. coli sequence type isolated from both human cases (n = 12/47) and poultry (n = 44/110). When classified using cladistics, all sequence types belonged to clade 1 except ST-7774, which belonged to clade 2. ST-854, ST- 1590, and ST-4009 were isolated only from human cases and fresh poultry, while ST-3232 was isolated only from human cases and ruminant sources. Modeling indicated ruminants and poultry as the main sources of C. coli human infection. Importance: We performed a molecular epidemiological study of Campylobacter coli infection in New Zealand, one of few such studies globally. This study analyzed the population genetic structure of the bacterium and included a probabilistic source attribution model covering different animal and water sources. The results are discussed in a global context.