Enterococcus cecorum, a normal intestinal inhabitant, is increasingly responsible for outbreaks of arthritis and osteomyelitis in chickens worldwide. Enterococcal spondylitis (ES) is a specific manifestation of E. cecorum-associated disease in which increased flock morbidity and mortality result from chronic infection involving the free thoracic vertebra. In this study the genetic relatedness and antimicrobial resistance of isolates recovered from ES-affected flocks in the southeastern United States were determined. ES outbreaks from 2007 to 2011 were investigated in North Carolina (15 flocks, 13 farms, four integrators), South Carolina (one flock, one farm, one integrator) and Alabama (six flocks, six farms, one integrator). From these 22 epidemiologically distinct outbreaks, 326 isolates of E. cecorum were recovered. Isolates from spinal lesions and caeca of affected birds (cases) and caeca of unaffected birds (controls) were genotyped using pulsed-field gel electrophoresis; phenotyped using both GenIII MicroPlate TM (Biolog; Hayward, CA, USA) microbial identification plates and antimicrobial sensitivity testing; and compared with each other. Isolates from spinal lesions were incapable of mannitol metabolism and the majority of these isolates were genetically clonal. In contrast, caecal isolates from control birds varied in their ability to metabolize mannitol and were genetically diverse. Isolates from both case and control birds had high levels of antimicrobial resistance. These findings indicate that the increase in E. cecorum-associated disease in the southeast United States is due to the emergence of new clones with increased pathogenicity and multidrug resistance.

Enterococcus cecorum was isolated from spondylitis lesions in broilers from two flocks in North Carolina that were experiencing increased mortality. Affected birds showed paresis and paralysis, clinical signs characteristic of enterococcal spondylitis (ES). Affected birds rested on their hocks and caudal abdomens with legs extended forward and were unable to stand or walk. Necropsy examination of affected birds revealed firm to hard inflammatory masses involving the vertebral bodies at the level of the free thoracic vertebra that bulged dorsally and compressed the spinal cord. When opened, lesions contained pale, tan to yellow caseonecrotic material. Microscopically, necrosis and fibrinoheterophilic spondylitis with intralesional gram-positive bacteria were seen. Heavy growth of E. cecorum recovered from vertebral lesions confirmed the diagnosis of ES. To investigate possible sources of the organism for one of the flocks bacterial cultures were made from the environment, water lines, mice trapped on the farm, cecal/cloacal swabs from one of the parent broiler breeder flocks, egg residue, hatching eggs, and the hatchery environment. Except for cecal/cloacal swabs from the breeders, E. cecorum was not isolated from any of these samples. When compared phenotypically and genotypically, cecal/cloacal isolates of E. cecorum from the breeders differed from isolates from spondylitis lesions in the broilers. The source of E. cecorum for the broiler flocks was not determined, but vertical transmission appears unlikely.

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in both human and veterinary medicine. The importance of companion animals as reservoirs of human infections is currently unknown. The companion animals of 49 MRSA-infected outpatients (cases) were screened for MRSA carriage, and their bacterial isolates were compared with those of the infected patients using Pulsed-Field Gel Electrophoresis (PFGE). Rates of MRSA among the companion animals of MRSA-infected patients were compared to rates of MRSA among companion animals of pet guardians attending a “veterinary wellness clinic” (controls). MRSA was isolated from at least one companion animal in 4/49 (8.2%) households of MRSA-infected outpatients vs. none of the pets of the 50 uninfected human controls. Using PFGE, patient-pets MRSA isolates were identical for three pairs and discordant for one pair (suggested MRSA inter-specie transmission p-value = 0.1175). These results suggest that companion animals of MRSA-infected patients can be culture-positive for MRSA, representing a potential source of infection or re-infection for humans. Further studies are required to better understand the epidemiology of MRSA human-animal inter-specie transmission.

The specific purpose was to investigate the possible interrelationships of genotypes of Staphylococcus aureus found in mammary glands, horn flies, and extramammary sites on 3 southeastern US dairies. A total of 1,228 samples were obtained from various sources on the 3 dairy herds, each of which had a history of Staph. aureus mastitis. Dairy herds studied had access to pasture, and samples were collected during the summer when horn flies (Haematobia irritans) were active. Samples collected included milk samples from all lactating herd cows, colostrum samples from heifers calving during the study period, heifer body sites (mouth, nostrils, and teats), the heifer environment (water, feed, and soil/vegetation/pasture), horn flies, and humans (hands and nostrils). Isolation of Staph. aureus was attempted from all samples, with isolates subjected to genotypic analysis using pulsed-field gel electrophoresis. A total of 244/1228 (or 19.9%) of all samples were positive for Staph. aureus. For milk samples, 52/383 (or 13.6%) of samples were Staph. aureus positive, and 70/411 (or 17.0%) of heifer quarter colostrum samples were positive. Horn fly samples were frequently positive, with over one-half (29/52, or 55.8%) of samples positive for Staph. aureus. Staphylococcus aureus obtained during the study comprised isolates from 12 different genotype groups as defined in this study. Identical genotypes were obtained from horn flies, heifer colostrum samples, and cow milk samples. Group B genotypes were shared among flies, heifer colostrum samples, body sites, and cow milk samples, whereas group A genotypes were common to the same sample locations and body sites but rarely (once) found in horn flies. We conclude, based upon the finding of identical pulsed-field gel electrophoresis genotypes in flies, heifer body sites, and heifer colostrum samples, that flies and heifer body sites could be important sources of Staph. aureus for heifer intramammary infections.

The organic dairy industry is growing rapidly across the United States and has recently expanded into the southeastern states. To date, no published comparisons of milk quality exist between organic and conventional dairies in the Southeastern United States. Maintaining high milk quality is challenging in this region due to the longer periods of high heat and humidity. The objective of this observational study was to compare milk quality on organic and conventional dairies in North Carolina during the warm summer months of the year. Data were compared from 7 organically and 7 conventionally managed herds in North Carolina. To assess milk quality, milk samples were aseptically collected from each functional quarter of each cow in the milking herds at the time of sampling and linear somatic cell scores (SCS) were obtained for individual cows. A total of 4,793 quarter milk samples (2,526 conventional and 2,267 organic) were collected from 1,247 cows (652 conventional and 595 organic). Milk samples were cultured and bacterial growth was identified using protocols consistent with those of the National Mastitis Council (Verona, WI). Subclinical mastitis was defined as the presence of SCS ≥ 4 and also a microbiological infection in at least 1 quarter. The proportion of cows with subclinical mastitis did not differ between conventional (20.8%) and organic (23.3%) herds. No significant difference was observed between herd management types in the proportion of cows without microbiological growth in milk samples. Also, no significant differences were observed between organic and conventional herds for cow-level prevalence of Staphylococcus aureus, coagulase-negative Staphylococcus spp., Streptococcus spp., or Corynebacterium spp. Two of the organic herds had a notably higher prevalence of Corynebacterium spp. and higher SCS. Coliforms were found in 5 of 7 conventional herds and in only 1 of 7 organic herds. Mean SCS did not differ between conventional (3.3±0.2) and organic (3.5±0.2) herds. Despite differences in herd management, milk quality was remarkably similar between the organic and conventional dairies compared for this study.

Antimicrobial resistance was uncommon among the mastitis-causing S aureus isolates identified in the milk samples. A limited number of genotypes were associated with mastitis in these herds. Antimicrobial resistance phenotypes were associated with particular S aureus PFGE types; this association may have implications for future treatment and control of S aureus-associated mastitis in cattle.

Staphylococcus aureus is a gram-positive organism that is frequently associated with clinical or subclinical mastitis. The use of germicidal teat dips is one of the measures taken by the dairy industry to control mastitis. Iodine and chlorhexidine compounds are commonly used disinfectants in teat dips. We determined the minimum inhibitory concentrations (MIC) of iodine for 37 isolates of Staph. aureus and observed variations in MIC. Seven of these Staph. aureus isolates were selected as genotype group representatives based on their pulsed-field gel electrophoresis patterns. Dose responses against iodine and chlorhexidine were determined for the 7 genotype group representatives. The response of these isolates to iodine varied significantly, whereas all isolates were susceptible to chlorhexidine, even at concentrations as low as 0.0002%. We also evaluated whether exposure of Staph. aureus to sublethal levels of iodine influenced subsequent antibiotic susceptibility. No differences in antibiotic susceptibility of Staph. aureus were observed among cultures grown in brain heart infusion broth with and without supplemental iodine. The observed variation in iodine dose responses of Staph. aureus may have implications for the occurrence of Staph. aureus mastitis on dairy farms.

Results indicate that a combination of vaccination and antimicrobial treatment can be successful in eliminating some cases of chronic intramammary S aureus infections in dairy cattle. However, it is important to consider extended treatment protocols carefully because many cows are likely to remain infected with S aureus despite treatment and vaccination.