Emmett B. Shotts

A medium for the selective isolation of Edwardsiella ictaluri.

A selective medium, called Edwardsiella ictaluri medium (EIM), has been formulated for the isolation of Edwardsiella ictaluri. The medium inhibits the growth of most gram-negative bacteria, except Proteus sp., Serratia marcescens and some isolates of Aeromonas hydrophila and Yersinia ruckeri. The bacteria that grow on the EIM are easily differentiated from E. ictaluri based on colony morphology. The EIM inhibits gram-positive bacteria with the exception of enterococci. The addition of fungizone to EIM suppressed the growth of most fungi. The EIM allows the evaluation of environmental reservoirs, levels of contamination and carrier states of E. ictaluri.

Effect of short-chain fatty acids on the growth of Salmonella typhimurium in an in vitro system.

Previous studies have revealed a reduction of cecal Salmonella carriage from feeding either carbohydrate or short-chain fatty acids (SCFAs). This in vitro study presents a profile of the relative SCFA content of the ceca when chicks are fed an unmedicated diet with 2.5% carbohydrate. Subsequent incorporation of these acids into culture medium was used to demonstrate their antagonistic activity toward in vitro growth of Salmonella typhimurium. Commonly found concentrations of SCFAs based upon the above findings reduced in vitro Salmonella growth by at least 50%, and 10 x concentrations inhibited growth more than 80%. An explanation of the mechanism(s) involved in growth reduction is offered.

Effect of Feeding Selected Short-chain Fatty Acids on the in vivo Attachment of Salmonella typhimurium in Chick Ceca

Two groups of 20 chicks each were fed 1% fatty acid continuously starting at 1 day of age, while a control group of 20 chicks received unsupplemented feed. At 2 days of age, chicks were inoculated orally with 1 ml of Salmonella typhimurium (1 x 10(6) colony-forming units/ml). Ceca were obtained from six chicks of each group at 7, 14, and 21 days of age. At 14 days of age, formic and propionic acids had statistically reduced Salmonella recovery by 2.56 logs and 3.09 logs, respectively, compared with controls. At 21 days of age, both test groups showed significant reductions of approximately 3.6 logs compared with controls. There were no statistical differences in body weights among the groups at 21 days of age.

Inhibition of Salmonella typhimurium in the Chicken Intestinal Tract by a Transformed Avirulent Avian Escherichia coli

An avirulent, wild-type avian Escherichia coli (E. coli Av) was electrotransformed with a plasmid coding for the production of microcin 24 (pGOB18) and was designated E. coli AvGOB18. The transformant inhibited the growth of seven serotypes of Salmonella commonly associated with colonization and contamination of poultry products and seven strains of E. coli O157:H7 in the in vitro colicin/microcin assay. The transformant did not inhibit the replication of multiple isolates of Listeria monocytogenes or Campylobacter jejuni in similar assays. The transformant is nonconjugative, indicating that the plasmid would not be transmitted to other intestinal microflora in the environment. The transformant also survived in sterile tap and deionized water incubated at 25 C and 37 C in the laboratory for 30 days and was recovered from drinkers and birds in in vivo floor pen studies. In in vivo studies, E. coli AvGOB18 did not colonize the intestinal tract of broiler chicks when given as a single or multiple dose and did not reduce the Salmonella load in the broilers. But Salmonella typhimurium was reduced significantly in the intestinal tracts of broiler chickens when E. coli AvGOB18 was administered continually in the water supply.

Antimicrobial susceptibility of Edwardsiella tarda from the United States and Taiwan

Edwardsiella tarda isolates from the United States and Taiwan were screened against 37 antimicrobial agents. These isolates were highly susceptible to the amino-glycosides, second and third generation cephalosporins, newer penicillins, nitrofurantoin, sulfamethoxazole/trimethoprim, and the quinolones. Source-related resistance was found for penicillin G, sulfadiazine, colistin, novobiocin, spectinomycin, ampicillin, tetracycline, and chloramphenicol. Generally, the Taiwan isolates were more resistant than the United States isolates.

Susceptibility of Channel Catfish to Infection with Edwardsiella ictaluri: Effect of Exposure Method

Abstract Three methods of infecting channel catfish Ictalurus punctatus with Edwardsiella ictaluri were compared. Groups of fish were exposed to the bacterium by intraperitoneal (IP) injection, bath immersion with stress, or bath immersion without stress. We determined infection rate by culturing tissues for the presence of E. ictaluri over a 3-week period. Fish in the IP-injected and bath-stressed groups had higher rates of infection than the bath-unstressed fish. Three weeks after exposure, the cumulative percentage of fish that cultured positive for E. ictaluri was 46.6% in the IP-exposed group, 52.7% in the bath-stressed group, and only 15.7% in the bath-unstressed group. Tissues from the IP-injected and the bath-stressed fish also cultured positive at an earlier time postexposure. Edwardsiella ictaluri were isolated from liver, head kidney, brain, spleen, and trunk kidney at some time during the 3-week sampling period. Anti-E. ictaluri antibody levels determined by agglutination and enzyme-linked imm...

Comparison of a Quantitative Microtiter Method, a Quantitative Automated Method, and the Plate-Count Method for Determining Microbial Complement Resistance

A quantitative microtiter method for determining the degree of complement resistance or sensitivity of microorganisms is described. The microtiter method is compared with a quantitative automated system and the standard plate-count technique. Data were accumulated from 30 avian Escherichia coli isolates incubated at 35 C with either chicken plasma or heat-inactivated chicken plasma. Analysis of data generated by the automated system and plate-count techniques resulted in a classification of the microorganisms into three groups: those sensitive to the action of complement; those of intermediate sensitivity to the action of complement; and those resistant to the action of complement. Although the three methods studied did not agree absolutely, there were statistically significant correlations among them.

Mutation Rate of Avian Intestinal Coliform Bacteria When Pressured with Fluoroquinolones

The purpose of this study was to determine the rate at which resistance developed in avian coliform bacteria when exposed to nalidixic acid, sarafloxacin, or enrofloxacin. In in vitro studies, the rates of mutation of avian isolates of Escherichia coli and Salmonella were determined following nalidixic acid, sarafloxacin, or enrofloxacin pressure. The rates of mutation were similar for nalidixic acid and sarafloxacin, whereas a lower rate of mutation was seen after enrofloxacin pressure. In in vivo studies, the quinolones were administered in the drinking water to broiler chickens at a concentration of 40 ppm for five consecutive days. Samples of feces were inoculated onto appropriate media and the frequency of resistance was determined. The frequency rates of resistance to nalidixic acid and sarafloxacin were similar. Enrofloxacin-medicated birds did not develop enrofloxacin-resistant coliform bacteria. The in vitro and in vivo data appear to correlate.

SHELL DISEASE IN RIVER COOTERS (PSEUDEMYS CONCINNA) AND YELLOW–BELLIED TURTLES (TRACHEMYS SCRIPTA) IN A GEORGIA (USA) LAKE

A disfiguring shell disease was detected in river cooters (Pseudemys concinna) and yellow-bellied turtles (Trachemys scripta) from Lake Blackshear, Georgia (USA). The turtles used were part of a mark-recapture study conducted from September 1991 to June 1993. Histologic changes on four turtles included acute segmental necrosis of the epidermis, followed by ulceration, necrosis of the underlying dermis and dermal bone, and exaggerated remodeling of bone. Additional findings included visceral inflammatory lesions and bacterial infection, sepsis, and marked trematode ova granulomatosis. The cause of the shell lesions was not determined.

Effect of EDTA-TRIS on an Escherichia coli isolate containing R plasmids

Solutions of ethylenediaminetetraacetate (EDTA)-tris combined with antibiotics have been shown to be effective in treating selected cases of persistent bacterial infections. Basic techniques in microbial genetics, including mating frequencies, chemical elimination of R plasmids, isolation of plasmid DNA and agarose gel electrophoresis, were used to determine if EDTA-tris has a curing effect on an R plasmid as part of its clinical action. Results of this study indicated that EDTA-tris by itself eliminated an antibiotic resistance marker from a clinical isolate of Escherichia coli and when combined with another chemical curing agent altered the isolates mating frequency.