Antimicrobial resistance of gram-negative enteric bacteria from pigs in a nonantimicrobial-exposed herd before and after transportation

Loading pigs onto trucks and transporting them for 30 min resulted in a significant increase in proportion of antimicrobial resistance of gram-negative enteric bacteria in fecal material. Similarly, the mean number of antimicrobial agents in the resistance patterns of these bacteria increased during loading and transportation. However, the increases were of a transient nature, as resistance values were similar to those of a nontransported control group 1 day after the pigs had been transported.

Cytolethal distending toxin genes in Campylobacter jejuni and Campylobacter coli isolates: detection and analysis by PCR

Campylobacter jejuni produces a toxin called cytolethal distending toxin (CDT). Knowledge of the prevalence and homogeneity of Campylobacter sp. cdt genes is incomplete. In this work, we identified four PCR primer pairs that collectively amplified cdt genes in all of the C. jejuni and Campylobacter coli strains tested. Restriction analyses of the cdt PCR products showed clear differences between the cdt genes of these two species, yet there were few heterogeneities noted between members of the same species. Consequently, it may be possible to speciate C. jejuni and C. coli isolates on the basis of restriction patterns within their cdt genes.

Detection of cytolethal distending toxin activity and cdt genes in Campylobacter spp. isolated from chicken carcasses

This study was designed to determine whether isolates from chicken carcasses, the primary source of Campylobacter jejuni and Campylobacter coli in human infections, commonly carry the cdt genes and also whether active cytolethal distending toxin (CDT) is produced by these isolates. Campylobacter spp. were isolated from all 91 fresh chicken carcasses purchased from local supermarkets. Campylobacter spp. were identified on the basis of both biochemical and PCR tests. Of the 105 isolates, 70 (67%) were identified as C. jejuni, and 35 (33%) were identified as C. coli. PCR tests amplified portions of the cdt genes from all 105 isolates. Restriction analysis of PCR products indicated that there appeared to be species-specific differences between the C. jejuni and C. coli cdt genes, but that the restriction patterns of the cdt genes within strains of the same species were almost invariant. Quantitation of active CDT levels produced by the isolates indicated that all C. jejuni strains except four (94%) had mean CDT titers greater than 100. Only one C. jejuni strain appeared to produce no active CDT. C. coli isolates produced little or no toxin. These results confirm the high rate of Campylobacter sp. contamination of fresh chicken carcasses and indicate that cdt genes may be universally present in C. jejuni and C. coli isolates from chicken carcasses.

Microbial populations of Botrytis cinerea-inoculated strawberry fruit exposed to four volatile compounds

Aerobic, microaerophilic, coliform, and mold populations of Botrytis cinerea-inoculated strawberry fruit not exposed (control) or exposed to low and high quantities of four volatile compounds during storage at 2 degrees C were determined after storage for 7 days and after removal of the volatile and transfer to 22 degrees C for 3 days. Fruit harvested at the ripe stage were inoculated with 10(6) conidia B. cinerea per ml and were placed in plastic containers containing no volatile compound (control) or two quantities of (E)-2-hexenal (10 or 100 microliters), (E)-2-hexenal diethyl acetal (30 or 300 microliters), benzaldehyde (30 or 300 microliters), or methyl benzoate (12 or 60 microliters). The fruit containers were overwrapped with a low-density polyethylene film, sealed, stored at 2 degrees C for 7 days, and then transferred to 22 degrees C for 3 days. Aerobic, microaerophilic, and coliform populations of fruit exposed to volatile compounds tended to be lower than the controls after storage at 2 degrees C for 7 days and, depending on the volatile compound, similar, lower, or higher than the controls after transfer and storage at 22 degrees C. However, due to variability in initial aerobic, microaerophilic, and coliform populations of the fruit used in the different trials (P < 0.05), none of the differences between control and treatment and between treatments within a sample time were significant (P > 0.05). Strawberry fruit exposed to 100 microliters of (E)-2-hexenal was the only treatment that did not show a significant increase in mold populations after transfer and storage at 22 degrees C for 3 days. Additional studies are needed to determine if (E)-2-hexenal can be used in combination with other postharvest storage conditions, such as low temperature and controlled/modified atmosphere, to delay mold spoilage and extend the shelf life of the strawberry.

Lecithinase reaction of Staphylococcus aureus strains of different origin on Baird-Parker medium

Staphylococcus aureus produces one or more enzymes with lipolytic activity, but differences between strains have been reported (Owens and John 1975; O'Toole 1987; Rollof et al. 1987). The biological and biochemical properties of these enzymes have been investigated and results were recently reviewed (Kötting et al. 1984). Baird-Parker medium (Baird-Parker 1962) is a selective medium commonly used for the isolation of Staph. aureus. The presence of egg yolk in this medium permits the detection of two reactions due to lipolytic activity of staphylococci: (1) Lecithinase reaction, a zone of precipitate in the medium surrounding the colonies; and (2) Lipase reaction or 'pearly layer', an iridescent film in and immediately surrounding colonies, visible by reflected light (iridescent sheen or 'oil in water'). In this study, human and bovine strains, previously biotyped according to the scheme of Devriese et al. (1984), were compared for production of a zone of precipitation, lecithinase reaction, on Baird-Parker medium. Bovine and human strains of Staph. aureus were compared for production of the egg yolk reaction (lecithinase reaction) on Baird-Parker medium and the results were related to their biotypes and site of origin of the sample. Human strains and strains biotyped as human biotypes had higher percentage of positive results than bovine isolates and/or biotypes. However, all strains isolated from body sites of heifers produced a positive reaction regardless of the biotype.

Detection of tetracycline resistance determinants in pig isolates from three herds with different histories of antimicrobial agent exposure

A total of 114 gram-negative fecal isolates from domestic pigs in herds with different histories of antimicrobial agent exposure were screened for the presence of plasmid DNA and specific tetracycline resistance determinants. More than 84% of the isolates harbored plasmid DNA, which ranged in size from 2.1 to 186 kb. A total of 78 isolates (68.4%) were resistant to tetracycline at concentrations greater than 4 micrograms/ml. Plasmid DNAs from about 56% of the tetracycline-resistant isolates hybridized with DNA probes for class A, B, C, and D tetracycline resistance determinants. The class B determinant was the most common determinant (35% of the isolates), followed by the class C determinant (12%) and the class A determinant (1%). About 9% of the isolates contained two determinants on plasmids. None of the plasmids from isolates hybridized with the class D determinant probe. The class C determinant was the most prevalent determinant on plasmids in isolates from pigs not exposed to antimicrobial agents for more than 146 months, while the class B determinant was more prevalent on plasmids in isolates from pigs exposed to either subtherapeutic or therapeutic levels of antimicrobial agents. Most tetracycline resistance determinants were localized on plasmids which were more than 30 kb long. A great number of wild-type tetracycline-resistant Escherichia coli strains were found with the class E determinant on their chromosomes. This study revealed a high prevalence of tetracycline resistance determinants in the fecal flora of pig herds whether or not they were fed with antibiotics.

Beta-glucuronidase activities of fecal isolates from healthy swine

Research has shown that various percentages of fecal Escherichia coli isolates obtained from healthy subjects may be beta-glucuronidase negative. The ability to detect beta-glucuronidase activity among fecal E. coli isolates from healthy subjects may be affected by assay conditions. A study was conducted in which agar and broth media containing 4-methylumbelliferyl-beta-D-glucuronide (MUG) were used to examine beta-glucuronidase activities of fecal isolates from healthy swine. Rectal swabs were plated on MacConkey agar plus 100 mg of MUG per liter (MAC-MUG) and incubated at 35 degrees C for 24 h. Each of 986 isolates picked from MAC-MUG was inoculated into duplicate tubes of lauryl tryptose broth plus 50 mg of MUG per liter (LT-MUG). One set of tubes was incubated at 35 degrees C and the other set of tubes was incubated at 44.5 degrees C. Gas production and hydrolysis of MUG, indicated by fluorescence when observed with UV light with a wavelength of 360 nm, were determined after incubation for 24 and 48 h. A higher percentage (P less than 0.01) of isolates was MUG positive at 44.5 degrees C than at 35 degrees C after 24 h of incubation in LT-MUG. A higher percentage (P less than 0.01) of isolates was MUG positive after 48 h than after 24 h of incubation at both 35 and 44.5 degrees C. A lower percentage of isolates (P less than 0.05) was observed to be MUG positive on MAC-MUG agar compared with their MUG reactions in LT-MUG at 35 and 44.5 degrees C. Approximately 89% of the isolates identified were beta-glucuronidase-positive E. coli. The largest proportion of MUG-positive E. coli was detected with LT-MUG at 35 degrees C after 48 h of incubation.

Prevalence of Staphylococcus species during the periparturient period in primiparous and multiparous cows

During a 14-mo period, 77 multiparous and 36 primiparous cows were sampled to determine the prevalence of staphylococci during the periparturient period. Distal streak canal swabs were taken at 14 d prepartum, and foremilk was sampled the first 5 consecutive wk of lactation. Staphylococcus aureus was isolated from 7.6% of quarters of primiparous cows but from only .6% of quarters of multiparous cows at parturition. Prevalence in primiparous cows declined to 3.5% by the wk-1 sampling. Quarter prevalence of coagulase-negative Staphylococcus species prepartum, at parturition, and wk 1 to 5 in primiparous cows was 38.9, 27.8, 15.3, 14.6, 13.2, 15.3, and 14.6%, respectively. In multiparous cows, prevalence at these times was 50.3, 12.3, 6.2, 8.1, 10.7, 7.1, and 8.1%. Staphylococcus chromogenes was the predominant species isolated, accounting for over 50% of the staphylococci isolated at each sampling time. Results suggest that high prevalence of staphylococci isolated prepartum is a reflection of natural skin flora and that a higher postpartum prevalence of these organisms was observed in primiparous cows than in multiparous cows. These data suggest also that the peripartum heifer could be a source of Staphylococcus aureus in the lactating herd.

Effect of naturally occurring coagulase-negative staphylococci infections on new infections by mastitis pathogens in the bovine

Microbiological data from 1123 uninfected quarters and 216 quarters with preexisting coagulase-negative staphylococci infections were analyzed to determine the influence of infection status on subsequent new infection rate. Overall, prevalence of new infections in uninfected quarters was approximately two times that in quarters already harboring a coagulase-negative Staphylococcus infection. New infections by coagulase-negative staphylococci were greater in uninfected quarters than in quarters with preexisting coagulase-negative staphylococci infections. However, no differences were observed between uninfected and infected quarters in number of new infections by major pathogens (Staphylococcus aureus, streptococci, and coliforms). No differences were observed in uninfected or coagulase-negative Staphylococcus-infected quarters in infections with minor pathogens compared with major pathogens. The influence of individual coagulase-negative Staphylococcus species on new infections was also analyzed. However, numbers of existing infections by Staphylococcus species other than Staphylococcus chromogenes were limited. Therefore, the protective capacity of each coagulase-negative Staphylococcus species was difficult to assess. Overall, a significant restriction of bacterial invasion was observed in quarters with a preexisting infection. These results suggest that quarters harboring a coagulase-negative Staphylococcus infection suppress colonization of the mammary gland by mastitis-causing pathogens.

Isolation of Staphylococcus aureus from sites other than the lactating mammary gland

The body sites of 163 heifers, bedding and feedstuff samples, flies, and hands and nares of the research personnel were sampled in order to determine the sources of Staphylococcus aureus in a dairy herd other than the lactating mammary gland. Lesions on the udder of lactating animals and the air in the milking parlor were also sampled. Staphylococci isolated from bedding samples were identified as to species. Staphylococcus aureus was isolated from all sources examined except flies. An enrichment procedure was necessary for isolating S. aureus from two bedding samples although other Staphylococcus species were present in high numbers. The designation "environmental staphylococci" is proposed for Staphylococcus species that were apparently free-living in the environment.

Effect of BiTek agar on lysostaphin susceptibility of staphylococci

Staphylococci which were considered to be lysostaphin susceptible on P agar containing Bacto-Agar showed different degrees of resistance to lysostaphin when tested on P agar made with BiTek agar. As a result, lysostaphin-susceptible strains were misidentified as lysostaphin-resistant strains.

Fluorogenic assay for differentiating Staphylococcus warneri and Staphylococcus hominis strains of bovine origin

A fluorogenic assay for the detection of beta-glucosidase was developed as part of a simplified conventional method to distinguish Staphylococcus warneri and Staphylococcus hominis isolated from bovine body sites. The assay is based on the fact that strains of S. warneri produce beta-glucosidase, while strains of S. hominis do not.

Antibiotic resistance of gram-negative enteric bacteria from pigs in three herds with different histories of antibiotic exposure

The antibiotic resistance patterns of gram-negative fecal bacteria from pigs in three herds with different histories of antibiotic exposure were examined. In general, smaller proportions of antibiotic-resistant or multiply resistant fecal isolates (P less than 0.05) were obtained from pigs in a herd not exposed to antimicrobial agents for 154 months than from pigs in a herd continuously exposed to antimicrobial agents at subtherapeutic doses or from pigs in a herd exposed only to therapeutic doses of antimicrobial agents. The proportions of antibiotic-resistant and multiply resistant strains were greater among isolates from pigs in the therapeutic herd than in the non-antibiotic-exposed herd (P less than 0.05). The proportion of antibiotic-resistant isolates in the non-lactose-fermenting population was greater than that in the lactose-fermenting population, regardless of herd. The results suggest that any form of antimicrobial exposure will increase the prevalence of antimicrobial resistance and multiple resistance of fecal bacteria.

Isolation and identification of coagulase-negative Staphylococcus species from bovine body sites and streak canals of nulliparous heifers

Heifers (n = 103) ranging in age from 1d to 2 yr were sampled to determine the coagulase-negative staphylococcal flora of haircoat, nares, vagina, teat skin, and streak canal. A total of 2706 staphylococal strains were identified from 3612 bacterial isolates. Other genera or groups identified included Bacillus, Micrococcus, Corynebacterium, and coliforms. Staphylococci were identified utilizing a simplified biochemical scheme. Staphylococcus xylosus, S. chromogenes, and S. warneri were the predominant species recovered from anatomic sites and streak canal. Staphylococcal strains identified from specific body sites (expressed as percentage of heifers harboring these species) were: nares 74% S. xylosus and 48% S. warneri; haircoat, 70% S. xylosus and 57% S. chromogenes; vagina, 60% S. chromogenes and 54% S. xylosus; teat skin 62% S. chromogenes and 61% S. warneri; streak canal 53% S. chromogenes, and 43% S. warneri. The prevalent staphylococcal strains identified differed from heifers in confined housing compared with heifers on pasture. Differences observed in distribution of Staphylococcus species among body sites, particularly those between teat skin and streak canal, suggest that establishment of staphylococcal microflora depends on the ability of a species to adapt to and colonize anatomic sites as well as on environmental conditions present.

Comparison of methods for determining DNase and phosphatase activities of staphylococci

A greater percentage of DNase-positive strains was detected with DNase test agar than with DNase test agar containing 0.005% methyl green or 0.005% toluidine blue (P less than 0.01). No significant differences were obtained in the percentage of phosphatase-positive strains with the four methods compared. On the basis of ease of use, P agar containing para-nitrophenylphosphate disodium (0.495 mg/ml) would be the preferred method for determining phosphatase activity of staphylococci.

Antimicrobial resistance of fecal coliforms from pigs in a herd not exposed to antimicrobial agents for 126 months

Patterns of antimicrobial resistance were determined for lactose-fermenting fecal coliforms obtained during a 20-month period from pigs in a herd without exposure to antimicrobial drugs for 126 months. Mean percent resistance to cephalothin, chloramphenicol, kanamycin, naladixic acid, streptomycin and tetracycline was lower (P less than 0.01) for isolates obtained during the 20-month period (Group 2) than for isolates obtained during the first 13 months (Group 1) after the withdrawal of antibiotics. Mean tetracycline resistance was 40.5% for Group 2 isolates. Approximately 44% of the Group 2 isolates were resistant to the 10 antimicrobial agents compared with 74.9% for the Group 1 isolates (P less than 0.01). Multiple resistance was lower (P less than 0.01) in the Group 2 isolates than in the Group 1 isolates. Four resistance patterns (tetracycline, tetracycline-streptomycin, tetracycline-sulfisoxazole, tetracycline-streptomycin-sulfisoxazole) accounted for 74% of the resistant isolates.

A Comparison of Six Selective Media for the Enumeration and Isolation of Staphylococci 1

The efficacy of Baird-Parker agar, Baird-Parker agar with bacitracin (0.8 μg/ml), Baird-Parker agar supplemented with acriflavin (7 μg/ml), polymyxin (20 units/ml) and sulphonamides (55 μg/ml), KRANEP agar, mannitol salt agar, and Staphylococcus medium 110 agar for the isolation and enumeration of Staphylococcus species was investigated. Bovine blood agar was used as the control medium. Thirty-seven staphylococci strains representing 23 species and 19 non- Staphylococcus species were tested. None of the six selective media supported the growth of all 37 Staphylococcus strains. The number of Staphylococcus species that grew on a specific medium ranged from only the S. aureus strains on Baird-Parker agar supplemented with acriflavin, polymyxin, and sulphonamides, to all but S. warneri BG 647 on Staphylococcus medium 110 agar. Strains of Bacillus , Corynebacterium , and Micrococcus grew on all six selective media.

Use of latex teat dip with germicide during the prepartum period

The efficacy of an acrylic latex barrier teat dip with germicide on new infections at parturition was tested on 113 cows and heifers during the prepartum period. A split udder design was used in which right quarters were undipped controls and left quarters were dipped with latex dip once daily for approximately 14 d prior to parturition. Distal streak canal swabs were taken from all quarters prior to the beginning of dipping, and all cows were quarter sampled in duplicate at drying off, parturition, and the first 5 consecutive wk of lactation. All quarters received antibiotic therapy at drying off. Excluding infections detected by distal streak canal swabs, the number of new infections at parturition in control and dipped quarters was 32 and 36. New infections at parturition in control and dipped quarters were Staphylococcus aureus, 2 and 2; coagulase-negative staphylococci, 8 and 9; stretptococci, 10 and 12; coliforms, 8 and 8; and others, 4 and 5. Differences were not significant. These results suggest no benefit to use of prepartum latex teat dip with germicide on new infections at parturition.

Use of Lysostaphin and Bacitracin Susceptibility for Routine Presumptive Identification of Staphylococci of Bovine Origin 1

A simple agar plate system based on susceptibility to lysostaphin and bacitracin to differentiate between staphylococci and micrococci is described. The system also uses susceptibility to novobiocin to aid in identification to species level of staphylococci. Growth from the agar plate can be used to prepare inocula for inoculation of rapid identification systems.

Quality of Dry-Cured Hams Produced from Pre-Frozen Hams as Affected by Mechanical Tenderization and Vacuum Packaging 1

Fifty frozen hams were thawed for 3 d at 2-3°C, skinned and partially defatted. Half the hams were passed twice through a Ross Industries needle tenderizer and half were not tenderized. All hams were dry-cured for 16 d with a mixture of salt, sugar, sodium nitrate and sodium nitrite. Cores of 2.54-cm diameter were obtained from the cushion of 5 hams from each group weekly for 5 weeks. Outer, middle and inner portions of the cores were analyzed for salt and nitrite. After curing, all hams were held at 13°C for 14 or 15 d for salt equalization. The intact hams were smoked and aged at 24°C until a yield of 82% or less was achieved. Half the hams in each group were then placed in vacuum bags and half were left uncovered. All were aged 4 additional weeks at 24°C. Hams were cut and examined visually, by a palatability panel, by shearing and by analyzing a center slice for moisture, salt and nitrite. Tenderization allowed faster salt and nitrite absorption but resulted in slightly lower flavor and overall satisfaction scores. Tenderized hams achieved the required 18% weight loss (82%) approximately 10 d sonner than non-tenderized hams. Vacuum packaged hams had higher final yields and contained a higher level of moisture and lower level of salt than non-vacuum packaged hams. Shear values in semitendinosus muscles were greater for tenderized than for nontenderized hams while shear values in biceps femoris muscles were higher in non-vacuum packaged than in the vacuum packaged hams. Aerobic and yeast and mold counts were higher while lactobacillus counts were lower in non-tenderized than in tenderized hams. Aerobic and lactobacillus counts were higher in vacuum packaged than in non-vacuum packaged hams. In general, tenderization allowed faster curing and aging while final aging in vacuum bags allowed higher yields.

Prevalence of minor udder pathogens after intramammary dry treatment

A total of 156 dairy cows was randomly assigned to one of four groups at drying off over an 18-mo period: untreated control or intramammary treatment of each mammary quarter with either 400 mg novobiocin, 300 mg cephapirin, or 1 g dihydrostreptomycin with 1 million units penicillin. Quarter foremilk samples were aseptically collected from each cow within 1 mo of drying off and within 1 mo after parturition for bacteriological analysis. Prior to drying off, 28.7% of quarters were positive of which 46.7% were Corynebacterium bovis and 45.5% were coagulase-negative staphylococci. Reductions in infection prevalence from drying off to postpartum samplings for control, novobiocin, cephapirin, and streptomycin-penicillin groups were 13.6, 60.5, 74.4, and 35.3% of quarters. Recovery rates for C. bovis infections were 47.6, 100, 100, and 94.1%; for coagulase-negative staphylococci infections they were 72.7, 86.4, 80.0, and 100%. The cephapirin group showed the lowest new infection rate (1.3%) with coagulase-negative staphylococci compared with control (6.9%). There were no significant differences in lactation milk production among groups following dry period therapy. Results suggest that dry treatment reduces the prevalence of infections by the minor mastitis pathogens.

Efficacy of an iodine backflush for preventing new intramammary infections

Efficacy of an iodine backflush system for reducing new intramammary infection was tested in two 11-wk trials. Forty cows in each trial were paired by breed, age, stage of lactation, and intramammary infection status. Each pair was assigned randomly either to a group milked with clusters that were reverse flushed with water, 25 ppm iodine, water and air or to a group milked with clusters receiving no backflush treatment between cows. Backflushing clusters reduced infections caused by Corynebacterium bovis and coagulase-positive staphylococci in both trials. However, backflushing clusters produced no clear advantage for reducing new infections with coagulase-negative staphylococci, Gram-negative bacilli, or streptococci (species other than Streptococcus agalactiae). No differences in somatic cell counts between experimental groups were observed. Teat cup liners and teat ends were swabbed after 120 and 1200 milkings/liner. Total microbial counts were significantly greater for liners that were not backflushed than from backflushed liners at each swabbing. However, no differences were significant between groups for mean teat end microbial counts in either trial.

Identification of Staphylococcus species of bovine origin with the DMS Staph-Trac system

The DMS Staph-Trac system was evaluated as a means for identifying the species of bovine strains of staphylococci routinely isolated from quarter-milk samples. The species identity of 83 of 91 (91.2%) isolates of staphylococci was correctly determined by this method. One isolate could not be identified by this system. The Staph-Trac system was able to distinguish between Staphylococcus hyicus and Staphylococcus epidermidis. We obtained a higher percentage of correct identifications with the DMS Staph-Trac system (91.2%) than we did in a previous study with the API Staph-Ident system (45.1%), using the same isolates (Langlois et al., J. Clin. Microbiol. 18:1212-1219, 1983).

Antibiotic resistance of fecal coliforms from swine fed subtherapeutic and therapeutic levels of chlortetracycline

The effect of feeding subtherapeutic (27.5 micrograms/g of diet for 85 d) and therapeutic (220 micrograms/g of diet for 14 d, followed by an antibiotic-free diet for 71 d) levels of chlortetracycline (CTC) on the antibiotic resistance of fecal coliforms of pigs from two herds (36 pigs/herd) with different histories of antibiotic exposure when housed in a newly constructed confinement facility was determined. The CTC-resistant coliforms were higher (65 vs 51%) for antibiotic (AB) pigs than for nonantibiotic (NAB) pigs after they had been fed an antibiotic-free diet for 21 d. Percentages of isolates resistant to ampicillin, kanamycin, neomycin and tetracycline and multiple antibiotic resistance were greater (P less than .05) in AB pigs after 21 d. Feeding subtherapeutic CTC resulted in a linear increase in CTC-resistant coliforms with time on experiment (P less than .03, NAB; P less than .06, AB). The CTC-resistant coliforms increased during the 14 d that therapeutic CTC was fed, then they decreased during the 71 d that the antibiotic-free diet was fed, resulting in a quadratic response with time (P less than .03, AB). Feeding subtherapeutic CTC resulted in a greater increase in CTC-resistant coliforms in AB (47%) than in NAB (23%) pigs. The CTC-resistant coliforms decreased after the therapeutic group had been returned to the antibiotic-free diet (P less than .05, NAB). Feeding CTC caused greater changes in the precentages of isolates from NAB pigs that were resistant to selected antibiotics and in multiple antibiotic resistance than in isolates from AB pigs.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of chlortetracycline on the spread of R-100 plasmid-containing Escherichia coli BEL15R from experimentally infected pigs to uninfected pigs and chicks

Swine from two herds with different histories of antibiotic exposure were fed diets containing 0 or 55 mg of chlortetracycline (CTC)/kg. One of five pigs in each herd-diet treatment group was infected orally with Escherichia coli strain BEL15R that was resistant to nalidixic acid (NA), chloramphenicol (C), streptomycin (S), sulfamethizole (TH) and tetracycline (TE). Effects of CTC on the quantity and duration of fecal shedding of E. coli BEL15R and on the transmission of strain BEL15R and its R-100 plasmid from infected pigs to uninfected pigs and chicks were determined. Quantity and duration of shedding were greater in infected antibiotic-herd pigs than in infected nonantibiotic-herd pigs. Feeding on CTC increased the duration of shedding in infected pigs from both herds. Strain BEL15R colonized and was shed in one uninfected antibiotic pig in each treatment group, but it did not colonize in any of the uninfected nonantibiotic-herd pigs or in the uninfected chicks. In vivo transfer of resistance to C, S, TH and TE occurred in the infected antibiotic-herd pigs but not in the infected nonantibiotic-herd pigs. Transfer of the R-100 plasmid occurred from the infected to the uninfected antibiotic-herd pigs and to the uninfected chicks housed near the antibiotic-herd pigs fed CTC, but not to the chicks housed with the antibiotic-herd pigs fed the control diet. No transfer of resistance occurred from the infected nonantibiotic-herd pigs fed either CTC or control diet.

Effect of Time and Method of Aging on the Composition of the Microflora of Beef Loins and Corresponding Steaks 1

Twenty-four cattle were slaughtered at a commercial packing plant. Carcasses were chilled for 72 h at 4°C, and then fabricated into wholesale cuts. Right loins were vacuum packaged and aged for 1, 3 and 5 weeks at 4°C while the left loins were aged conventionally for 1, 2 and 3 weeks at the same temperature. Core samples were removed from both ends of the conventionally and vacuum-aged loins and analyzed using standard microbiological procedures. Isolates from aerobic plates incubated at 35 and 20°C, and from gram-negative enteric plates were used to determine the composition of the aerobic (35 and 20°C) and gram-negative enteric microflora. Loins were cut into 2.54-cm thick steaks, wrapped in oxygen permeable fresh meat wrap and placed at 4°C in a simulated retail meat case. After 1, 3, 6 and 7 d, steaks were evaluated using the same microbiological techniques used for loins. Vacuum packaged loins had lower percentages of pseudomonads than conventionally aged loins after 1 and 3 w of aging. The lactobacilli were higher in vacuum packaged loins than in conventionally aged loins after 3 weeks. The aerobic (35 and 20°C) microflora of the retail cuts generally reflected the flora of the loins from which they were prepared. Enterobacteriaceae tended to be higher in vacuum packaged loins and corresponding steaks, and constituted 34% of the flora of the vacuum packaged loins after 5 weeks of aging.

Effect of Time and Method of Aging on the Microbiological Quality of Beef Loins and Corresponding Steaks 1

Twenty-four cattle were slaughtered at a commercial packing plant. Carcasses were chilled for 72 h at 4°C, and then fabricated into wholesale cuts. Right loins were vacuum packaged and aged for 1, 3 and 5 weeks at 4°C while the left loins were aged conventionally for 1, 2 and 3 weeks at the same temperature. Core samples were removed from both ends of the loins and were analyzed using standard microbiological procedures. Loins were cut into 2.54-cm thick steaks, wrapped in oxygen-permeable fresh meat wrap and placed at 4°C in a simulated meat case. On days 1, 3, 6 and 7 steaks were evaluated using the same microbial technique used for loins. Counts generally were similar for conventionally and vacuum-aged loins after aging 1 week. After 3 weeks of aging, the vacuum-aged loins had higher (P<.05) coliform, anaerobic, streptococcus and lactobacillus counts. In addition to these counts, the aerobic (20°C and 35°C) of vacuum-aged loins increased (P<.05) after an additional 2 weeks of aging. Counts of steaks from 1-week old loins generally were not different as a result of method of loin aging. Lactobacillus counts of steaks from 3-week old loins differed as a result of method of aging. Except for higher lactobacillus counts, counts of steaks from 5-week old vacuum aged loins were similar to the counts of steaks from loins which were vacuum-aged for 3 weeks.

Antibiotic resistance in anaerobic and coliform bacteria from the intestinal tract of swine fed therapeutic and subtherapeutic concentrations of chlortetracycline

Chlortetracycline (CTC) resistance in anaerobic and coliform bacteria was examined in the large intestines of two groups of growing pigs that had received antibiotic-free diets since weaning. One group of pigs was from a low resistance herd (LR) that had not received antibiotics for 8 yr, while the other group of pigs was from a high resistance herd (HR) that routinely received antibiotics. After a 20-d adjustment period in a common production facility, LR pigs on an antibiotic-free diet had lower proportions of anaerobes (27%) and coliforms (22%) that were resistant to 25 micrograms CTC/ml than did similarly fed HR pigs (81 and 48%, respectively). Continued maintenance of LR and HR pigs on the antibiotic-free diet in a common production facility tended to increase resistance in anaerobes and coliforms from LR pigs to levels comparable with those in HR pigs at the end of an 85-d feeding trial, but not after 14 d. Administration of CTC in the feed at therapeutic (220 micrograms/g for 14 d) and growth-promoting (27.5 micrograms/g for 85 d) levels markedly increased percentages of resistant anaerobes and coliforms in LR pigs, but not in HR pigs after 14 d. Similar antibiotic effects were not seen at the end of the 85-d trial. These data demonstrate that, while exposure to antibiotics in feed may increase resistance in intestinal populations, other factors such as environment, cross-contamination and herd history can also influence the observed level of antibiotic resistance in swine.

Some characteristics and antibiotic resistance of anaerobic bacteria from the ceca and colons of pigs fed chlortetracycline-containing and unmedicated diets

Morphology and end product patterns were used to group 112 bacterial isolates from the ceca and colons of pigs fed unmedicated and chlortetracycline-containing diets. Most of the isolates (68%) were resistant to chlortetracycline (greater than 4 micrograms/ml). Chlortetracycline resistance was associated with all groups of anaerobic and facultative bacteria.

Antibiotic resistance of fecal coliforms after long-term withdrawal of therapeutic and subtherapeutic antibiotic use in a swine herd

Tetracycline resistance of fecal coliforms isolated from swine decreased from 82 to 42%, a decrease of less than 50%, after the use of all forms of antimicrobial agents were discontinued in the herd for 126 months.

Identification of Staphylococcus species of bovine origin with the API Staph-Ident system

The API Staph-Ident system was evaluated as a means for identifying the species of bovine strains of staphylococci routinely isolated from quarter-milk samples. The species identity of 314 of 581 (54%) isolates of staphylococci was correctly determined by this method. The API Staph-Ident system was more accurate in correctly identifying Staphylococcus aureus (93.9%) than in correctly identifying non-S. aureus species (41.8%). False identifications of Staphylococcus epidermidis and Staphylococcus hominis were the main reasons for the incorrect identifications of the non-S. aureus species.

Multiple antibiotic resistance in fecal, cecal and colonic coliforms from pigs fed therapeutic and subtherapeutic concentrations of chlortetracycline

Multiple resistance and antibiotic resistance were examined in coliforms isolated at slaughter from the large intestines of two groups of growing pigs that had received antibiotic-free diets since weaning. One group of pigs was from an antibiotic-fed (AB) herd that routinely received chlortetracycline (CTC) in feed, while the other group was from a nonantibiotic-fed (NAB) herd that had not received antibiotics for 8 yr. After a 20-d adjustment period in a common production facility, the mean number of antibiotics in the resistant pattern of isolates from NAB pigs was found to be lower (P less than .05) than that in isolates from AB pigs. The proportions of isolates resistant to ampicillin, kanamycin, neomycin, penicillin, streptomycin and sulfamethizole were lower (P less than .05) in NAB pigs than in AB pigs. Similar herd differences were not observed after pigs from both herds were maintained in a common production facility on an antibiotic-free diet for 105 d. Oral administration of CTC at therapeutic (220 micrograms/g of diet) and at subtherapeutic (27.5 micrograms/g) levels for 14 d increased (P less than .05) the mean numbers of antibiotics in the resistance patterns of isolates from NAB pigs, but did not alter multiple resistance in isolates from AB pigs. After 14 d, subtherapeutic CTC increased the percentage of isolates resistant to ampicillin, kanamycin, penicillin, streptomycin, tetracycline and sulfamethizole, while therapeutic CTC only increased the percentage of isolates from NAB pigs resistant to penicillin, tetracycline and sulfamethizole. Similar antibiotic effects were not seen in isolates from AB pigs after 14 d and were not seen in isolates from either group of pigs at the end of an 85-d feeding trial.

Effect of feeding chlortetracycline or virginiamycin on shedding of salmonellae from experimentally-infected swine

Swine from a herd routinely fed subtherapeutic levels of chlortetracycline (CTC) were fed a diet containing 55 mg of CTC/kg, a diet containing 55 mg of virginiamycin/kg, or a control diet. All animals were inoculated with Salmonella typhimurium that was susceptible to tetracycline. The quantity, duration and prevalence of shedding of S. typhimurium were determined. The infecting organism was first recovered from the animals fed CTC or the control diet on d 2, from animals fed virginiamycin on d 7 and from animals in a second control group on d 10. The infecting organism was recovered in fewer samples obtained during the initial 7 d postinfection than in those obtained during the last 24 d of the study. Little transfer of resistance to the infecting organism seemed to have occurred from the resident microflora because only two isolates (1%) had resistant patterns that differed from that of the infecting organism. Feeding CTC or virginiamycin to swine did not significantly increase or prolong shedding of an experimentally infected tetracycline-susceptible strain of S. typhimurium. Neither antibiotic affected the drug resistance of the infecting organism.

Milking frequency as related to udder health and milk production

Twenty-four cows each in two trials were paired on age, stage of lactation, and projected milk production to compare the incidence of mastitis with milking two or three times per day over 12 wk. Teats of all cows were dipped daily in a suspension of Streptococcus agalactiae (one of two strains). Average daily milk production for the combined trials was 24.0 kg for the thrice daily group and 22.0 kg for the twice daily group. Quarter foremilk samples were taken every 2 wk for somatic cell counts and bacterial isolations. Somatic cell counts of cows milked twice per day averaged 31 x 10(3) per milliliter compared to 26 x 10(3) for three milkings. There were no significant differences in numbers of new bacterial infections between groups. Cows milked twice per day had 41 new infections and 7 clinical infections and the three-time group had 39 new infections and 2 clinical infections. The many corynebacteria infections were related to the experimental design in which no disinfectant teat dip was used. Three milkings per day did not affect udder health.

Influence of bilateral nephrectomy on selected gastrointestinal bacteria in the rat

A series of experiments was designed to investigate the influence of acute renal failure on selected gastrointestinal bacteria. Sprague-Dawley male rats were bilaterally nephrectomized to induce acute renal failure, with sham-operated animals serving as controls. After 48 h animals were sacrificed and the stomachs, upper and lower small intestines, ceca, and colons were excised and subjected to microbial analyses. Lactobacilli and streptococci including enterococci, were 1-2 log counts higher in the stomachs of anephric rats than those of sham-operated controls; lactobacilli were increased similarly in the upper small intestines of these animals. Coliforms including Escherichia coli, and Proteus were 1-2 log counts higher in the lower small intestine of anephric rats than those of sham-operated rats. The decreased gastric pH, increased cecal pH, hypothermia, and delayed gastric emptying observed in nephrectomized rats could partly explain the different microfloras in these animals.

Psychrotrophic Bacteria Reduce Cheese Yield 1

Psychrotrophic strains of Bacillus and Pseudomonas that demonstrated both proteolytic and lipolytic activity were incubated with Grade A milk. The yield of direct-acid cheese manufactured from inoculated milk decreased as psychrotrophic inoculation level increased. Yield reduction resulted from both lipid and protein degradation, and accounted for approximately 45 and 55% of the dry matter loss, respectively. Fat losses were observed from decreased milkfat tests and increased acid degree values. Protein losses were observed from increased non-protein nitrogen and whey nitrogen values. Therefore, cheese yield studies must involve assays of both protein and lipid on a dry matter basis. Acid degree values and fat disappearance in stored milk and total nitrogen in whey were the best indicators of reduction in yields. Although bacterial enumeration, titratable acidity and pH were not good indicators of yield, they may be important in determining when yield loss starts.

Effect of Pre-Cure Freezing and Thawing on the Microflora, Fat Characteristics and Palatability of Dry-Cured Ham 1

Hams were placed in cure after thawing by 3 methods: at 2C, at 16C, and in water at 37C. A fourth group was placed in cure while still frozen. Microbiological populations and fat rancidity tests were determined at various intervals during processing. Sensory scores and tenderness values were determined after 3 months of aging. Clostridium perfringens , Bacillus cereus , Escherichia coli , coliforms and enterococci were not detected after salt equalization. Hams cured without thawing had lower initial bacterial, yeast and mold counts but no differences among thaw groups were observed in counts during aging. Hams thawed in water had lower flavor and overall satisfaction scores than the other groups. Fat breakdown as noted by FFA, TBA and peroxide values increased with aging but were erratic although ham cured without thawing had lower peroxide values. Satisfactory dry-cured aged hams were produced regardless of method of thawing. However, since hams cured without thawing had less weight loss, lower peroxide numbers, lower initial microbial counts and similar final microbial counts and sensory scores, it appears that hams do not need to be thawed to produce dry-cured aged hams.

Effects of Pre-cure Storage and Smoking on the Microflora and Palatability of Aged Dry-cured Hams 1

Forty-two similar weight hams were held 3 and 6 days postmortem at 2 C, dry-cured, and held at 13 C for 4 weeks for salt equalization. Half were then smoked and half were not smoked. All hams were aged for 3 months at 24 C. Six hams from each group were selected for external microbial evaluation and three were selected for internal microbial evaluation before curing, after curing, after salt equalization or smoking, and after aging 1, 2 and 3 months. Aerobic counts were higher in hams held 6 days than in those held 3 days but the difference decreased as processing time progressed. Smoking decreased surface counts. Enterococci, Bacillus cereus and fluorescent pseudomonads counts were initially low and these organisms were virtually absent after aging 1 month. Coliforms were initially low and were not detected after salt equalization. Staphylococci increased through 3 months of aging with very few isolates being coagulase-positive. Yeasts and molds increased gradually through processing and aging. No Clostridium perfringens or Salmonella were detected in uncured hams. There were no significant differences in palatability traits due either to pre-cure holding time or smoking.

Milking vacuum influencing indicators of udder health

In 23 first-calf heifers we ascertained effects that milking vacuums of 34, 42.5, and 51 kPa had on udder health by percentage of quarter-samples positive for Staphylococcus aureus, total counts of bacteria on blood agar, teat end scores, California Mastitis Test, and direct microscopic somatic cell count. Measures were higher for 51 kPa than for 34 or 42.5 kPA. Samples from cows milked at 42.5 kPa had a lower percentage of samples positive for Staphylococcus aureus, lower total count, lower California Mastitis Test, and lower direct microscopic somatic cell count than samples from cows milked with 34 kPa. Test end scores increased with increase in milking vacuum. Approximately 49% of the samples from cows milked with 51 KPa were positive for Staphylococcus aureus compared with 19.9 and 16.7% for 34 and 42.5 kPa. Milking vacuum of 51 kPa resulted in the highest percentage of cows with three (44.5%) and four (24.1%) quarters positive for Staphylococcus aureus. A milking vacuum of 51 kPa could increase mastitis in a herd having Staphylococcus aureus as the prevalent microorganism causing mastitis.

Variation of Laboratory Cheesemaking Procedures

The variability of yield for Cheddar cheese manufactured in 7- and 390-kg-size vats and cottage and direct-acid-set cheese manufactured in 7-kg-size vats was compared. The direct-acid-set cheese had less variability than Cheddar or cottage cheese (% coefficient of variation was .91, 1.79 and 4.69, respectively) manufactured in 7-kg-size vats and Cheddar cheese manufactured in 360-kg-size vats (% coefficient of variation was .91 and 1.98, respectively). Cottage cheese had the largest variability between replications using small vats because of additional stirring and curd manipulation required in its manufacture. Therefore, when cheese variety is of no concern, the direct-acid-set cheese procedure would reduce variation between replication more than traditional Cheddar procedures when used in an experimental design. In addition, a greater number of vats of cheese could be manufactured per day using the small vat system.

Effect of Five Surface Area-to-Sample Volume Ratios During Preliminary Incubation on The Bacterial Count of Raw Milk 1, 2

Effects of ratio of surface area to volume of sample during preliminary incubation (PI) and of different plate incubation temperatures on bacterial counts of raw milk samples were studied. One hundred and twenty Grade A raw milk samples collected during a 10-month period were divided into five 100-ml aliquots and allotted to one of five surface area to volume ratios. The ratios during PI ranged from 0 cm²/100 ml to 149.74 cm²/100 ml. Following PI, pour plates of each treatment were incubated at 26, 30 and 32 C for 72 h. The Standard Plate Counts (SPC) ranged from 89 × 10¹ to 20 × 10⁸/ml, with the SPC of 73.6% of the samples being less than 1 × 10⁵/ml. Counts after PI tended to be higher as the plate incubation temperature decreased from 32 to 26 C and as the ratio of surface area to volume of sample increased. None of the differences between the counts for the 15 treatment-incubation temperatures was significant. Counts of 61 samples increased less than one log count during PI, while counts of 33 and 16 samples increased one to two log counts and over two log counts, respectively. The greater the SPC, the smaller the increase in count during PI. Of the 81 samples with SPC less than 1 × 10⁵/ml, 29 had counts after PI that exceeded 2 × 10⁵/ml.

Fate of Selected Pathogens Inoculated into Foods Prepared in Slow Cookers 1, 2

Staphylococcus aureus , Clostridium perfringens . Salmonella choleraesuis , and Salmonella typhimurium were inoculated (10⁸ cells or spores) into two slow cookers containing green bean casserole, baked navy beans, chicken cacciatore, barbecued ribs or pork pot roast, and their fate determined after cooking. Heating patterns also were determined at three positions inside the two cookers. None of the foods cooked in either of the slow cookers contained detectable levels of S. aureus or salmonellae. The similarity between C. perfringens vegetative and spore counts indicate that only spores were present in the cooked foods. Except for the green bean casserole cooked using a low temperature setting, cooking resulted in a 0.44-1.67 and 0.36-1.54 log count reduction, respectively, of vegetative cells and spores of C. perfringens . Counts of vegetative cells and spores after cooking the green bean casserole were approximately .18 and .30 log counts higher than the uncooked counts. The mean times for the coldest areas in Cooker A to reach 50 C were 2.57 and 0.97 h, respectively, for the low (80 watts) and high (160 watts) temperature settings. The mean times for the coldest areas in Cooker B (removable liner) to reach 50 C were 2.35 and 0.52 h for the low (130 watts) and high (260 watts) temperature settings, respectively. Results suggest that when the recommended quantities of ingredients are used and the proper cooking procedure followed, foods prepared in the slow cookers studied do not present a health hazard.

Comparing Three Methods for Counting Raw-Milk Pour Plates 1

Six hundred Grade A raw milk samples were plated on Standard Methods agar and the pour-plate counts compared using three methods. Counts of each sample were determined after incubation at 26, 30 and 32 C for 72 h with an automatic colony counter (ACC). Quebec colony counter and hand tally (HT) and Quebec colony counter and electronic probe with digital register (DT). No significant differences were found between the counts obtained with the HT and the DT for any of the three incubation temperatures. The ACC counts were lower (P < .01) than the manual counts at each temperature. The ACC counts were .39, .35 and .31 log counts lower than the manual count at 26, 30 and 32 C, respectively. The ACC counts at 72 h were higher (P < .01) than the ACC counts at 48 h for all temperatures. The difference was about .41 log counts. The two manual counts were totally correlated, while the correlation between the ACC counts and the manual count; was 97. Regression equations were formulated for predicting the 72 h HT count from either the 48 or 72 h ACC count.

Effect of Heat Treatments on Survival and Growth of a Psychrotroph and on Nitrogen Fractions in Milk 1

Grade A raw milk which had initial psychrotrophic counts of less than 10³/ml was inoculated with an antibiotic-resistant Pseudomonas sp. to a final cell concentration of 10², 10⁴, or 10⁶/ml. The inoculated milk was held at 4 C for 14 h and then exposed to the following time-temperature treatments: 72 C for 15 sec, 79 C for 15 sec, 88 C for 10 sec, and 95 C for < 5 sec. An uninoculated raw milk control was handled and analyzed along with inoculated samples. Aliquots of milk were analyzed for marked Pseudomonas sp., total psychrotrophic counts, numbers of Pseudomonas , and for distribution of nitrogen before and after each heat treatment and after storage of non-heat-treated raw milk and heat-treated samples for 7 and 14 days at 7 C. Psychrotrophic counts were significantly affected by heat treatment, initial cell inoculum, days stored, and plating media. Non-casein N, non-casein protein, total albumin, β-lactoglobulin, proteose-peptone, and globulin N were significantly decreased by heat treatment. Non-casein N, non-casein protein, β-lactoglobulin, and proteose-peptone were significantly increased by days of storage.

Microflora of Retail Fluid Milk Products 1

Numbers and types of microorganisms in retail pasteurized fluid milk products were determined as well as the effect that type of product, brand, and season of the year had on counts of 13 different microbial types. Clostridium perfringens was the only pathogen detected and it averaged less than one organism per milliliter. Chocolate milk samples generally had the highest mean counts, followed by skim milk, low-fat (2%), and whole milk (3.25%). Most brands had means for the various microbial counts which were not significantly different from each other. Only three brands had counts which differed significantly from other brands. Psychrotrophic, coliform, staphylococcal, yeast and mold, and Standard Plate Counts were highest between May and October, while counts for spores, streptococci, and thermophiles were highest between December and March. No seasonal trends were detected for counts of anaerobes, C. perfringens , enterococci, or lactobacilli.

Effect of Various Combinations of Medium, Diluent and Incubation Conditions on Recovery of Bacteria from Manufacturing Grade and Grade A Raw Milk 1

Recovery of microorganisms from manufacturing grade and Grade A raw milk was determined using 18 plating combinations which consisted of three media, three diluents, and two incubation temperatures. Plating conditions specified in Standard Methods for doing the Standard Plate Count was one of the 18 combinations used. Combinations studied consisted of Standard Methods Agar, Schaedler Agar, and Eugonagar as plating medium; phosphate buffered distilled water, 0.1% peptone water, and Ringer solution as diluent; and 28 C for 72 h and 32 C for 48 h as incubation temperature. Forty manufacturing grade and 40 Grade A raw milk samples were plated using each of the 18 combinations. Highest mean counts were obtained for both grades of milk with the combination of Standard Methods Agar, phosphate buffered distilled water, and 28 C for 72 h. Samples, diluents, media, and samples × diluents interaction had a highly significant (P<.01) effect on counts of manufacturing grade milk samples; while samples, media, and temperatures had a highly significant (P<.01) effect on counts of the Grade A raw milk samples. Nonsignificant differences were obtained in counts of the manufacturing gradesamples with eight of 17 plating combinations when compared with counts obtained with Standard Methods. Counts for Grade A samples obtained with six of 17 combinations were similar to counts obtained with Standard Methods.