A survey of mastitis pathogens including antimicrobial susceptibility in southeastern Australian dairy herds.

The objectives for this study were to (1) describe the pathogen profile in quarters from cows with clinical mastitis and in cows with subclinical mastitis in southeastern Australia; and (2) describe antimicrobial susceptibility among isolated pathogens. As a secondary objective, we aimed to compare antimicrobial resistance prevalence in pathogens isolated from clinical and subclinical mastitis samples. A convenience sample of dairy herds (n = 65) from 4 regions in southeastern Australia (Gippsland, Northern Victoria, Tasmania, Western Victoria) were invited to submit milk samples from cows with clinical and subclinical mastitis over a 14-mo period (January 2011 to March 2012). Farmers were instructed to collect aseptic quarter milk samples from the first 10 cases of clinical mastitis for each month of the study. In addition, farmers submitted composite milk samples from cows with subclinical mastitis at 1 or 2 sampling occasions during the study period. Aerobic culture and biochemical tests were used to identify isolates. Isolates were classified as susceptible, intermediate, or resistant to a panel of antimicrobial agents based on the zone of growth inhibition around antimicrobial-impregnated disks, with antimicrobial resistance (AMR) classified as nonsusceptibility by combining intermediate and resistant groups into a single category. Generalized linear mixed models were used to compare the prevalence of AMR between clinical and subclinical mastitis isolates. For clinical mastitis samples (n = 3,044), 472 samples (15.5%) were excluded for contamination. Of the remaining samples (n = 2,572), the most common results were Streptococcus uberis (39.2%), no growth (27.5%), Staphylococcus aureus (10.6%), Escherichia coli (8.4%), and Streptococcus dysgalactiae (6.4%). For subclinical mastitis samples (n = 1,072), 425 (39.6%) were excluded due to contamination. Of the remaining samples (n = 647), the most common results were no growth (29.1%), Staph. aureus (29.1%), and Strep. uberis (21.6%). The prevalence of AMR among common isolates was low for the majority of antimicrobial agents. Exploratory analysis found that the probability of Staph. aureus demonstrating resistance to penicillin was 5.16 times higher (95% confidence interval: 1.68, 15.88) in subclinical isolates relative to clinical Staph. aureus isolates. A similar association was observed for amoxicillin with subclinical Staph. aureus isolates being 4.70 times (95% confidence interval: 1.49, 14.75) more likely to be resistant than clinical Staph. aureus isolates. We concluded that the most common bacteria causing clinical mastitis in dairy herds in Australia is likely to be Strep. uberis, whereas Staph. aureus is likely to be the most common cause of subclinical mastitis. Despite decades of antimicrobial use to control these organisms, AMR appears to be uncommon.

Detection of brucellosis and leptospirosis in feral pigs in New South Wales.

OBJECTIVE: To determine the presence and estimate the prevalence of Brucella suis, Leptospira interrogans serovar Pomona (hereafter L. pomona) and Leptospira borgpetersenii serovar Hardjo (hereafter L. hardjo) in feral pigs culled in New South Wales (NSW), Australia. METHODS: During 2012 and 2013, 239 serum samples were collected from feral pigs killed as pests or game in NSW. All sera were subjected to the rose-bengal test for B. suis, with positives subjected to the complement fixation test (CFT). Attempts were made to detect B. suis by culture and PCR on CFT-positive samples. All sera were tested separately for the presence of L. pomona and L. hardjo antibodies using the microscopic agglutination test. RESULTS: Of 238 samples tested, 7 were positive (4 with CFT titres ≥ 32) for B. suis antibodies (3% seroprevalence). However, B. suis was not cultured or detected by PCR. Of 239 sera tested for L. pomona antibodies, 126 samples were positive (53%) and 9 (4%) were positive for L. hardjo. CONCLUSIONS: The findings are the first tangible evidence that feral pigs in northern NSW harbour B. suis, providing a plausible explanation for recent human and canine cases of brucellosis related to pig hunting. The increased seroprevalence of L. pomona occurred in years preceded by flooding and rodent plagues, suggesting a potential for zoonotic infection much greater than previously realised. Advice to the community should focus on encouraging the adoption of improved hygiene practices during pig hunting and consideration of vaccinating livestock against leptospirosis.

Incidence of calf scours and associated risk factors in southern New South Wales beef herds.

OBJECTIVE: The aim of this study was to identify the incidence of morbidity and mortality associated with calf scours in beef calves between birth and 14 days of age. Farm characteristics, animal factors and management practices were also assessed for any association with calf scours being present on the farm. METHODS: A questionnaire and return address envelope were distributed to 721 farms with at least 50 head of beef cattle in the Hume area of New South Wales, Australia. RESULTS: In total, 147 (20.4%) farmers responded to the survey, of which 76 (51.7%) indicated calf scours did occur on their farm. On average, farmers estimated the morbidity of calf scours was 4.5%, but only 0.2% of all calves died as a result of scours. Affected herds were more likely to have multiple breeds and a higher proportion of cows with mismothering problems or weak calves compared with unaffected herds. These differences were confirmed with regression analysis. A large proportion of farmers with affected herds reported the loss of many calves from 'unexplained' or 'sudden' death within the first 14 days of life. CONCLUSIONS: The incidence of calf morbidity was lower and mortality was within the same range compared with other studies on beef farms around the world. The high percentage of farms reporting losses from 'unexplained' or 'sudden' death of calves requires further monitoring and diagnostic and economic investigations.

Effects of 5-chloro-2-methyl-4-isothiazolin-3-one and other candidate biodiesel biocides on rat alveolar macrophages and NR8383 cells.

Biocides are added to biodiesels to inhibit and remove microbial growth. The effects of 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), a candidate biodiesel biocide, were studied using freshly isolated rat alveolar macrophages (AM) and NR8383 cell line. CMIT markedly inhibited phagocytic oxidative burst as measured by zymosan-induced chemiluminescence, and cellular cytokine secretion as measured by zymosan-induced TNF-α secretion. The 50% inhibition concentration (LC(50)) for CMIT was 0.002-0.004 mM for both cellular functions. AM exposed to CMIT for as little as 2 min showed markedly inhibited functions that persisted for at least 5 h. Sodium metabisulfite was able to partially neutralize the inhibitory activity of CMIT. Cysteine and glutathione, when present at a molar ratio of 2-1 or higher against CMIT, were effective neutralizers, while serine, histidine, alanine, and albumin were without effect. When the AM testing system was used to compare the toxicity of CMIT against three other candidate biodiesel biocides, methylene dithiocyanate (MDC) was found to be of comparable toxicity to CMIT, 2-methyl-4-isothiazolin-3-one (MIT) was much less toxic, and dimethyl acetylenedicarboxylate (DMAD) was non-toxic. Because AM is among the first cell-type exposed to inhaled biodiesel aerosols, the result suggested that CMIT present in biodiesel may produce respiratory effects, and further investigations including animal studies are warranted.

Generation of third-order spherical and coma aberrations by use of radically symmetrical fourth-order lenses.

We have extended the method of Alvarez [J. Am. Optom. Assoc. 49, 24 (1978)] to generate a variable magnitude of third-order spherical and/or coma aberration by using a combination of fourth-order plates with a magnification system. The technique, based on the crossed-cylinder aberroscope, is used to measure the wave-front aberration generated by the plates. The method has been applied to correct the third-order spherical aberration generated by an artificial eye as well as the coma produced by a progressive addition ophthalmic lens. The simplicity of the method and its relatively low cost make it attractive for partial correction of the aberrations of the eye.