Fifteen isolates of Escherichia coli obtained from the blood and tissues of septic foals had plasmid DNA of size ranging from 2.5 to 93 megadaltons. These isolates grew in normal equine serum (serum resistant), a trait previously documented to be expressed by isolates obtained from blood and tissues of septic foals, but not by isolates obtained from the feces of clinically normal horses. Of these isolates, 3 contained conjugal plasmids that encoded resistance to multiple antimicrobial agents linked to serum resistance and, in 1 isolate, to production of aerobactin as well. Serum resistance and production of aerobactin are related to virulence of septicemic E coli from non-equine sources.

Six calves with areas of pulmonary consolidation attributable to bronchopneumonia, and 6 calves with no areas of consolidation were given IV injections of danofloxacin. This injection was followed approximately 55 minutes later by injection of 15-micrometer radio-labeled microspheres to measure regional pulmonary blood flow. Calves were euthanatized exactly 1 hour after the danofloxacin injection. Six samples for determination of danofloxacin concentration, each surrounded by 4 samples for determination of gamma emission counts, were taken from each lung, Additional samples focusing on the line of demarcation between consolidated and nonconsolidated tissue were taken from calves with pulmonary consolidation. Data from calves with no areas of pulmonary consolidation indicated that blood flow was significantly reduced in the caudodorsal position of the left lung and the caudodorsal and cranioventral positions of the right lung, compared with that in other positions within the lungs. Danofloxacin concentrations in the cranioventral positions of the right and left lungs were significantly lower than those in the middle-dorsal positions. Differences in danofloxacin concentrations and blood flow were analyzed in consolidated and nonconsolidated cranioventral and middle-ventral positions of the lungs from calves with pulmonary consolidation. Decreases in blood flow in consolidated lung tissue ranged from 83.3 to 91.7%. Danofloxacin concentrations in consolidated lung tissue were significantly reduced by 41% in the middleventral position of the left lung. The line of demarcation step study revealed a significant reduction of blood flow at 2 and 4 cm into consolidated lung tissue, with reductions of 84 and 88%, respectively. Danofloxacin concentration did not significantly decrease in consolidated tissue.

An epidemiologic study of Pasteurella haemolytica serovar 1 (Ph1) in market-stressed feeder calves from 7 farms in eastern Tennessee was conducted. The nasal mucus of each calf was cultured sequentially at the farm of origin (day 0), at an auction market (day 133), and at a feedyard in Texas (days 141, 148, 155, and 169). Of the 103 calves tested, 77 were culture-positive, including 1 on day 0, 1 on day 133, 20 on day 141, 57 on day 148, 50 on day 155, and 14 on day 169. From the 143 Ph1 isolates, 20 enzyme profiles were determined by use of a commercial enzyme system that detects 19 enzymatic reactions; 4 antimicrobial susceptibility profiles were obtained, using the disk-diffusion method, which evaluated susceptibility to 11 antibacterial drugs. All isolates were positive for acid phosphatase and alkaline phosphatase, but were negative for alpha-galactosidase, alpha-mannosidase, beta-glucosidase, beta-glucuronidase, cystine aminopeptidase, N-acetyl-beta-glucosaminidase, and trypsin. Other positive enzyme reactions included: leucine aminopeptidase, 140 Ph1 isolates; phosphohydrolase, 90 isolates; alpha-fucosidase, 63 isolates; esterase (C4), 59 isolates; valine aminopeptidase, 30 isolates; esterase lipase (C8), 24 isolates; beta-galactosidase, 2 isolates; and alpha-glucosidase, chymotrypsin and lipase (C14), 1 isolate each. Thirty-four Ph1 profiles were identified, using combined enzyme and antimicrobial susceptibility profiles. The data indicate that the strains isolated during the feedyard period may have been determined more by farm of origin (P < 0.001) than by habitation with calves from other farms while in the feedyard. The combined enzyme and antimicrobial susceptibility profile method is a rapid and simple epidemiologic technique for tracking Ph1 strains in market-stressed feeder calves.

Plasma and lung tissue pharmacokinetics of danofloxacin calves with naturally induced acute pneumonia were determined in 2 separate studies. A maximal pneumonic tissue concentration of 1.17 microgram/g was achieved 1.8 hours after IM injection of 1.25 mg of danofloxacin/kg of body weight. Pneumonic tissue danofloxacin concentrations were 5.5 times greater than those in plasma at 1 and 2 hours after injection. Cranioventral pneumonic tissue had significantly decreased danofloxacin concentration, compared with that of grossly normal tissue from the caudodorsal part of the lungs at 2 of 6 sample times. After IV injection, the apparent steady-state volume of distribution was 3.44 +/- 1.13 L/kg, and the elimination half-life was 6.26 2.27 hours. Maximal plasma danofloxacin concentration of 0.25 microgram/ml was detected 0.80 hour after IM injection. Bioavailability was 91%. Our findings indicated that a large percentage of danofloxacin is rapidly absorbed after IM administration to calves with acute pneumonia. Extensive tissue penetration was suggested by a high steady-state volume of distribution and was indicated by high concentrations in pneumonic tissue.