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Nine swine slaughter plants and 19 swine production units were randomly selected for sampling from the six highest swine-producing states representing a total of 64% of the United States swine production. Three composites of 10 fresh swine fecal samples were obtained from each slaughter plant, representing three different farm sources of swine. Two composite fecal samples were collected from two different production pens from each production unit. Samples were analyzed for salmonellae. Isolated salmonellae were biochemically and serologically identified and tested for antibiotic susceptibility and resistance transfer ability. Salmonellae were recovered from swine at seven of the nine slaughter plants and 16 of the 27 composites of slaughter swine. Of the 19 production units, 3 had swine shedding salmonellae. Resistances found included streptomycin, tetracycline, and sulfadiazine. Of the 52 total isolates tested, 71% had some level of antibiotic resistance. Only 3 of 37 resistant isolated could transfer resistance under the conditions used.

A six-week trial was conducted to determine if therapeutic use of chlortetracycline (CTC) would be affected by previous use of the same antibiotics at subtherapeutic levels in the feed. Results indicated therapeutic effect of CTC on mortality was not compromised by the previous use of the low level antibiotic.

The potential of bambermycins (a growth-promoting antimicrobial approved for turkeys, broilers, and swine) to overcome or control plasmid-mediated antimicrobial resistance was determined in a series of in vitro experiments. Four possible modes of action of bambermycins were studied: synergistic effect with 12 other antimicrobials, elimination of resistance (R) plasmids from Escherichia coli, selective killing or inhibition of E coli carrying R plasmids, and inhibition of R plasmid transfer. Bambermycins had no synergistic activity with the other drugs tested and had little effect on eliminating plasmids from host bacteria. Dependent on plasmid type, bambermycins decreased or increased transfer frequency of R plasmids. Bambermycins also selectively inhibited growth of bacteria harboring certain R plasmids.

Twenty broiler chickens were fed bambermycins (Flavomycin; an antibiotic produced by Streptomyces) at the rate of 3 g/ton (US) for 63 days, and 20 control birds were fed nonmedicated feed. The birds were inoculated (dosed) on the 10th and 11th feeding day with Salmonella typhimurium. The study evaluated the effects of bambermycins on Salmonella incidence, shedding, and antimicrobial resistance. Bambermycins had no effect on body weights, duration of shedding of salmonellae, number of salmonellae shed on postdosing day 3, tissue recoverability of salmonellae, and total number of resistance patterns. Bambermycins resulted in the decrease of salmonellae to be more gradual; however, both treatments were comparable at the end of the study. The majority of S typhimurium from bambermycins-treated birds maintained the original antibiogram of streptomycin, sulfadiazine, and nalidixic acid. The salmonellae isolated from the control birds were more resistant to 2 drugs (varying antibiograms). Bambermycins as a feed additive in broiler diets given at the dose level of 3 g/ton had no detrimental effects based on salmonellae shedding and antimicrobial resistance.

Selenite brilliant-green sulfa enrichment broth containing Tween 80 was streaked to brilliant-green sulfa plates for use in comparing recoverability of 61 different salmonella serotypes from turkey tails artifically contaminated with very low levels of each serotype. Recoverability was 100% with 43 of the serotypes, 80% with eight, 60% with four, and 40% or less with six.

Twenty broiler chickens were fed 80 g/T salinomycin, an antibiotic produced by Streptomyces albus, and 20 birds were fed a control, unmedicated feed. The birds were experimentally infected with Salmonella typhimurium. The study evaluated the effects of salinomycin on Salmonella incidence, shedding, and antimicrobial resistance. Salinomycin had no effect on body weights, length of time salmonellae were shed, number of salmonellae shed on postdosing day 3, salmonellae tissue recoverability, or on the total number of resistance patterns. Salinomycin caused the decline of salmonellae to be more gradual; however, both treatments were comparable at the end of the study. The majority of isolated from birds receiving salinomycin maintained the original S. typhimurium antibiogram of streptomycin, sulfadiazine, and nalidixic acid. The salinomycin salmonellae were more susceptible to tetracycline, amikacin, carbenicillin, gentamicin, and cephalothin. The multiple resistance patterns of eight and nine drugs tended to be more prevalent among salmonellae from control birds than salinomycin treated birds. The antibiotic salinomycin appears to be an acceptable feed additive in broilers at the level of 80 g/T based on these results of its effects on salmonellae shedding and antimicrobial resistance.

Anderson Technical, Inc. has developed rapid, semiautomated equipment for antimicrobial susceptibility testing. A total of 310 fresh clinical bacterial isolates (226 gram-negative and 75 gram-positive) were tested with the Anderson Technical system and compared with those of Micro-Media Systems, Inc. For the gram-positive organisms, 74.3% of the test pairs had identical minimum inhibitory concentration values, whereas 99.1 and 0.9% of the test pairs had minimal inhibitory concentration values differing by less than or equal to 1 and greater than 1 dilution level, respectively. Identical minimum inhibitory concentration values were obtained for 67.2% of the gram-negative test pairs, whereas 97.6 and 2.4% differed by less than or equal to 1 and greater than 1 dilution level, respectively. For all organisms tested, 98.0% differed by less than or equal to 1 dilution level. The Anderson Technical equipment proved to be a rapid and flexible system for microdilution testing.

Fecal coliforms, fecal streptococci, and antimicrobial resistance (AMR) associated with various pig transit and holding times were investigated at slaughter plants. Changes in the relative abundance of two biotypes of Streptococcus faecium were associated with transit and holding of pigs, although approximately 20% of the isolates were unidentified. The greatest variety of coliforms was isolated from porcine feces after short transit (2 h) or holding (3 h) times and was qualitatively similar to those from pigs on farms. Isolates from pigs with longer average transit or holding times were almost all Escherichia coli (four biotypes). Streptococcal resistance to most antimicrobial agents was significantly greater (P less than 0.05) in isolates from live pigs at slaughter plants than in those from pigs at farms and was apparent after a short transit time (2 h). Streptococci from pigs held an average of 15 h were less resistant to most antimicrobial agents than those from pigs held 3 or 43 h. When compared with short transit times, moderate transit times (6 h) were associated with significantly decreased (P less than 0.05) coliform resistance and decreased resistance transfer but a greater diversity of AMR patterns. Holding pigs overnight (14 h) was associated with lowered coliform resistance to several antimicrobial agents, compared with the resistance of isolates from pigs held 3 or 39 h. A substantial increase (18 to 48%) in the ability to transfer streptomycin resistance was demonstrated in coliforms from pigs held 39 h, when compared with those from pigs held 3 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Duplicate trials were conducted with male broiler chickens to evaluate virginiamycin as treatment against experimentally induced necrotic enteritis infection. Each trial consisted of seven treatments, each replicated four times, with 10 birds per replicate. Two treatments were fed control ration (noninfected control and infected control) and the five remaining treatments were fed virginiamycin at 5, 10, 15, 20, or 40 g/ton. Birds were orally dosed with 10 ml of Clostridium perfringens culture at 14 days of age. At 5 weeks of age, surviving birds were killed and necropsied to obtain lesion scores. Birds fed virginiamycin had significantly less mortality and lower intestinal lesion scores than nonmedicated birds when experimentally infected with necrotic enteritis.

Enteric bacteria isolated from feedlot heifers treated with tetracyclines (TET) were examined for resistance to TET and ampicillin. The effects of feeding (45 days) therapeutic and subtherapeutic quantities of chlortetracycline (CTC) and the injection of therapeutic doses of oxytetracycline (3 daily doses) were compared. Performance data from the 45-day trial did not identify an antibiotic effect on average daily gain, although cattle fed subtherapeutic quantities of CTC showed improved feed efficiency. Bacterial resistance to TET was increased in the heifers given the therapeutic and subtherapeutic quantities of CTC in the ration. However, an increase in resistance to ampicillin did not occur. Oxytetracycline injections had a short-term effect, increasing the number of resistant organisms only during the week of drug administration.

An experimental chick hatcher designed to filter recycled ventilation air was tested for its effectiveness in reducing the number of viable airborne microorganisms. Chicks in a filtered hatcher and a control hatcher (no filter) were artificially contaminated with Serratia marcescens as ventilation air was recycled in the hatchers for twelve hours. The number of viable S. marcescens particles in the filtered air of the conditioning chamber was less than detectable. The number of viable airborne S. marcescens particles in the hatching chamber of the filtered hatcher indicated a reduction of greater than 90 percent over the number in the unfiltered hatcher. The filter was effective in reducing the number of airborne particles carrying viable S. marcescens organisms in the hatcher.

Two experimental chick hatchers in which ventilation air within the hatcher was partially recirculated in a positive pressure system, one with an air filter in the system and the other without a filter, were simultaneously tested to determine effect of the filter on quantitative reduction of viable airborne microorganisms. Chicks were artificially contaminated with either Escherichia coli or Staphylococcus aureus (coagulase-positive). Air was sampled for total test bacteria per cubic foot of hatcher air. The filter effectively reduced the number of viable airborne particles contaminated with E. coli and S. aureus contributed by chicks in the hatcher.

Human clinical streptococcal isolates can be identified rapidly by means of commercially available miniaturized biochemical systems, in contrast to animal and environmental isolates which may require extensive characterization using conventional methods. Streptococcal isolates (n=548) from fresh animal feces of cattle, swine, and broiler chickens were tested by means of conventional biochemical and physiological techniques, and also with a miniaturized technique in which conventional formulations were dispensed in 0.1 ml volume into microtiter plates. Agreement of the positive feature frequencies of the two methods were compared. Results from the tolerance tests in the two methods were generally in good agreement. However, the miniaturized method tended to give false negative results in some carbohydrate fermentation tests. Agreement between the 2 methods ranged from 100% for bile esculin tests to 71% for raffinose fermentation. Cluster analysis of the conventional method data indicated that there were 11 biochemically related groups of isolates, 2 of which were identified asStreptococcus faecalis, andS. morbillorum. Half of the isolates biochemically resembledS. faecium. Errors of miniaturized tests occurred mainly in certain tests and in certain biochemically related clusters of isolates. The data indicate that further investigation of experimental conditions such as medium formulation and inoculum size could lead to a successful miniaturized technique for testing animal streptococcal isolates.

A comparison between initial inseminations of Large White turkey hens prior to or after onset of egg production was undertaken to determine the effect on fertility. Semen from Bronze toms was utilized for the initial inseminations whereas all subsequent inseminations utilized White sires. After 10 weeks there were no significant differences between treatments for percent egg production or hatchability. Inseminating prior to the onset of egg production resulted in a significantly different (P less than or equal to .05) 8-week average of 97.5% fertility in the early insemination (EI) group as compared to an average of 90.4% in the late insemination (LI) group. Differences between the EI and the LI groups were greatest during the last 2 weeks of the experiment during which the EI hens maintained higher levels of fertility. Bronze poults were observed in the EI progeny following three subsequent inseminations with semen from White sires, whereas no Bronze poults were obtained from the LI hens following the third subsequent insemination with White semen.

Eighty broiler chickens were randomly assigned to each of 12 chambers in a controlled environment poultry facility. Ammonia gas was injected at 0, 50, or 100 ppm from 28 to 53 days of age. All chicks, except the control pens, were innoculated with coccidia at 36 days of age. No significant differences were found in mortality, but weight gains were significantly reduced in chambers that received ammonia gas. This was probably due to the increase in severity of air sac and intestinal lesions in the ammonia pens.

Bambermycins and bambermycins plus roxarsone were fed to broilers in ten consecutive experiments to determine if response (measured by body weight and feed efficiency) was continuous over a long term. Bambermycins was added at 1.1 ppm (1 to 44 days) and 2.2 ppm (45 to 51 days) to both test rations. In addition, one test ration contained roxarsone (3-nitro-4-hydroxyphenylarsonic acid) at 50 ppm (1 to 44 days). Each experiment was conducted with 1,080 commercial broiler cross-run chickens. Broilers fed bambermycins and bambermycins plus roxarsone were heavier (P less than .05) than controls in every experiment. Bambermycins plus roxarsone treated broilers were heavier (P less than .05) than bambermycins treated broilers in 2 out of 10 experiments. Broilers fed bambermycins converted feed more efficiently (P less than .05) than controls in 6 of 10 experiments and were more efficient (P less than .05) than bambermycins plus roxarsone fed broilers in 1 of 10 experiments. Bambermycins plus roxarsone treated broilers were more efficient (P less than .05) than controls in 5 of 10 experiments. These findings indicate that over a long term bambermycins and bambermycins plus roxarsone consistently and significantly (P less than .05) increased broiler body weights over controls, although the addition of roxarsone was not always effective in increasing body weights or improving feed efficiency over bambermycins fed alone.

The intestinal microflora of a group of broilers fed a diet containing .04% sorbic acid from Days 1 through 49 of their lives was compared with broilers given a diet without the fungistat. Four broilers from each group were killed at 7, 21, 35, and 49 days, and intestinal sections of the duodenum, the lower small intestine, and both ceca were removed aseptically. Samples of the contents of the intestinal sections were analyzed microbiologically. Groups of microorganisms analyzed included total aerobes, total anaerobes, coliforms, streptococci, lactobacilli, clostridia, Bacteroides, Bifidobacterium, yeasts, and molds. Generally, there was a large variation in viable counts of microorganisms for birds of the same treatment. Of the nine groups of microorganisms analyzed the highest counts obtained (greater than 10(6)/g) were for total aerobes, total anaerobes, lactobacilli, and Bifidobacterium. Coliforms, streptococci, and clostridia showed intermediate counts (greater than 10(3)/g), while yeasts and molds and Bacteroides showed the lowest counts (greater than 10(2)/g). Total microbial numbers, in most cases and irrespective of sorbic acid treatment, were highest in the ceca, lower in the small intestine, and still lower in the duodenum. There were no major trends of microbial population changes observed in a given treatment, intestinal location, or group of organisms with age and time on feed. Inclusion of sorbic acid in the feed did not influence total aerobes, total anaerobes, lactobacilli, streptococci, Bifidobacterium, and clostridia. However, broilers on sorbic acid-containing feed had, at 49 days of age, lower coliform counts in the duodenum, lower yeast and mold counts in the ceca, and higher Bacteroides counts in the ceca.

An experiment was conducted to evaluate antimicrobial resistance of coliforms and streptococci isolated from feces of chickens fed salinomycin. Two groups of 20 chickens were fed either a control feed or feed supplemented with 80 g/ton salinomycin. Chicken fecal coliforms and streptococci were isolated at 5, 15, 19, 22, 26, 33, 40, and 47 days of age and their resistance to 11 or 12 antibacterial agents (coliforms and streptococci, respectively) were determined in both groups of chickens. Salinomycin significantly reduced the number of coliforms resistant to sulfadiazine and reduced the number of streptococci resistant to erythromycin and lincomycin. Streptococci from birds fed salinomycin had lower minimum inhibitory concentrations for streptomycin. No streptococci isolates developed resistance to salinomycin. Coliforms from birds fed salinomycin had more (P less than .05) resistance patterns involving two, five, and six drugs. Numbers of coliforms resistant to streptomycin, ampicillin, carbenicillin, and cephalothin were greater (P less than .05) from birds fed salinomycin.

A comparison between fogged and nonfogged hatcher air was undertaken in 4 trials to determine effects on hatcher airborne bacteria, hatch statistics, and broiler performance. Eighteen day incubated eggs were artificially contaminated with a mixed Eschericia coli and Staphylococcus aureus culture when eggs were transferred to hatchers. Fogging with a disinfectant at 12-hr intervals during the hatching period caused significant reductions in total airborne bacteria and S. aureus counts. Counts of E. coli were not significantly affected. Growth data from 150 chicks from each hatcher from each trial showed 50-day feed efficiency and 50-day male body weights were significantly improved in chicks hatched in the fogged hatcher.

Five different transport media (buffered glycerol saline, Amies, Cary and Blair, Stuart, and modified Stuart) were tested to determine if antimicrobial resistance transfer could occur among bacteria in the media. Transfer of resistance occurred in all of the media, except buffered glycerol saline, within 2 h of holding both at room temperature and 4 degrees C.

Procedures are described for determining the effects of low level antibiotic feed additives in broiler chick rations when chicks are artificially infected with Salmonella typhimurium var. copenhagen and the effectiveness of the same antibiotics used therapeutically for salmonellosis. These procedures also permit study of development of antibiotic resistant enteric flora related to antibiotic feeding and the transferability of the resistance. Measures should be taken to monitor and assure minimal extraneous bacterial contamination of eggs, chicks, feed and facilities and minimize baseline antibiotics resistance. Facilities and equipment should be fumigated extensively, chicks should be from primary breeder flocks off antibiotics for two generations, handled minimally, and fed all-vegetable protein rations. Optimum procedures for oral induction of salmonellosis with a chick-virulent strain of Salmonella typhimurium var. copenhagen are reported. Effects of low level antibiotic feeding and subsequent therapeutic level feeding of infected and control birds are measured by mortality, feed efficiency and weight gain, and microbiological analyses of fecal samples, intestinal samples and necropsied dead chicks. Gathering all data possible from all facets of the trials is imperative for ascertaining antibiotic effects.

Breeding pigs and one-half of their progeny were fed antimicrobial-free rations; the other half of the progeny received rations supplemented with 100 g of chlortetracycline (Ctc)/ton. Effects of dietary Ctc with respect to the distribution of species and biotypes of faecal Gram-positive cocci and their relative resistance to 12 antimicrobial agents were studied. Diversity of antimicrobial resistance (AMR) patterns and modal AMR patterns were determined for bacterial species common to all three groups. Numerical taxonomic analysis placed 1140 of 1150 isolates (99%) into 10 groups. Three of these were biotypes of Streptococcus faecium and contained the largest number of isolates (n = 934, 81%). Streptococcus faecalis, Strep. morbillorum, Pediococcus halophilus and Gemella haemolysans also were isolated. Generally, the proportion of tetracycline-resistant strains for a species or biotype was greater from pigs fed Ctc, although differences were not significant (P greater than 0.05). There was a significant difference (P less than 0.05) among all the groups for the percentage of penicillin-resistant strains in a biotype of Strep. faecium. Overall, 57 and 43 different AMR patterns, including 2 to 11 and 1 to 11 resistance determinants, were demonstrated in isolates from control pigs and pigs fed Ctc, respectively. Modal AMR patterns in species and biotypes were the same from both progeny groups, except for Strep. faecium. AMR pattern diversity was decreased for strains from pigs fed Ctc. Similar proportions of resistant strains from each group of progeny pigs were accompanied by decreased AMR pattern diversity in strains from pigs fed Ctc. These results indicated a change in distribution of AMR phenotypical patterns, rather than a change in overall frequency of individual resistant phenotypes.

Three replicate trials were conducted with broiler male chicks to test the therapeutic efficacy of doxycycline, chlortetracycline and lincomycin-spectinomycin in water against an artifically induced Escherichia coli infection. Mortality, lesion scores (heart, liver and air sac), and performance data were the criteria in evaluating therapeutic efficacy of these drugs. Results indicated the therapeutic efficacy of doxycycline was greater than chlortetracycline and lincomycin-spectinomycin.

A breeder flock and a control group of progeny birds were fed antimicrobial-free rations; a second group of progeny received rations supplemented with 50 g chlortetracycline (Ctc)/ton. Effects of dietary Ctc on the distribution of species and biotypes of faecal Gram-positive cocci and their relative resistance to 12 antimicrobial agents were studied. Antimicrobial resistance (AMR) pattern diversity and modal AMR patterns were determined for bacterial species common to all three groups. Numerical taxonomic analysis placed 1321 (97%) of 1360 isolates into eight species or biotypes. The largest cluster (n = 659, 48%) was a biotype of Streptococcus faecalis. Three clusters were biotypes of Streptococcus faecium and contained 580 isolates (42%). The isolates were susceptible to ampicillin and almost uniformly resistant to methicillin, neomycin, streptomycin, sulfadiazine and tetracycline. There were 54 and 47 different AMR patterns, including 0 to 11 and 1 to 11 resistance determinants, in isolates from control and Ctc-fed birds, respectively. Modal AMR patterns for Strep. faecalis and one biotype of Strep. faecium were very similar for all three groups of birds. However, modal patterns in a second biotype of Strep. faecium varied considerably for all three groups. Interpretation of AMR pattern diversities were equivocal among biotypes from both progeny groups. The variable distribution of isolates, proportions of resistant strains, modal patterns and diversity indices among the progeny were probably due to their exposure to different environmental sources of bacteria.