Associations between memory performance and Bifidobacterium pseudolongum abundance in the canine gut microbiome

Memory has been identified as the least heritable cognitive trait in canines, suggesting a significant influence of non-genetic factors. We observed a trend that overall memory scores (OMS) improve with age in a cohort of 27 young dogs, but considerable plasticity exists. Employing linear discriminant analysis of gut microbiome data from dogs exhibiting low and high OMS, a single bacterial species, Bifidobacterium pseudolongum, was identified and confirmed to be correlated with elevated OMS. Subsequent analysis using a random forest regression model revealed that sex, litter, and breed identity had minimal predictive importance. Age had some predictive value but failed to achieve statistical significance in this dataset. In sharp contrast, the abundance of 17 bacterial taxa in the microbiome showed a stronger predictive capacity for memory performance. Our findings provide insights into microbiome underpinnings of mammalian cognitive functions and suggest avenues for developing psychobiotics to enhance canine memory and learning.

Application of pressurized steam and forced hot air for cleaning broiler transport container flooring

In the United States, cleaning poultry transport containers prior to arrival at the broiler grow-out farm is not currently a widely adopted practice in the industry. However, previous studies have shown that transport containers have an important role in cross-contamination before the broilers arrive at the processing plant. The objective of this study was to evaluate the efficacy of pressurized steam followed by forced hot air to clean transport container flooring and compare it to conventional cleaning procedures. Fiberglass and plastic flooring were cut into even pieces and inoculated with chicken intestinal contents containing Salmonella Infantis or Campylobacter jejuni. The cleaning treatments were pressurized steam, forced hot air, pressurized steam followed by forced hot air, water pressure washing, water pressure washing before and after disinfectant, and no cleaning. Counts for Salmonella, Campylobacter, Escherichia coli, coliforms, and aerobic bacteria were assessed. All reductions were made in comparison to noncleaned samples. Forced hot air applied by itself was not efficient in reducing Campylobacter, coliforms, and E. coli; and limited reductions (less than 1 log10 CFU/cm2) were observed for Salmonella and aerobic bacteria. Then, for all bacteria types evaluated, pressurized steam by itself showed reductions of 2.4 to 3.5 log10 CFU/cm2. Samples that were cleaned with a single-pressure water wash showed reductions of 4.0 to 4.6 log10 CFU/cm2 for all bacteria types. For Salmonella, Campylobacter, and E. coli, the greatest reductions were observed when samples were cleaned with pressurized steam followed by forced hot air (4.3-6.1 log10 CFU/cm2) or water washed before and after disinfectant (4.5-6.2 log10 CFU/cm2), and these treatments did not differ from each other. Pressurized steam followed by forced hot air was shown to be an efficient cleaning procedure to reduce poultry-associated pathogens on transport cage flooring, with the benefit of using less water than conventional water cleaning. Processors may be able to adapt this process to reduce potential cross-contamination and lessen the level of pathogens entering the processing plant.

Quantification of Salmonella Infantis transfer from transport drawer flooring to broiler chickens during holding

Transportation is a potential point of cross-contamination before broiler chickens arrive at the processing plant for slaughter. Previous studies have associated the use of uncleaned transport containers with the introduction of pathogenic bacteria onto uncontaminated broilers. The objective of this study was to quantify the transfer of Salmonella from transport drawer perforated flooring to broiler chickens during different holding times. For traceability, the flooring of each drawer was inoculated with fecal content slurry containing a marker strain of Salmonella Infantis. Three drawers per treatment were used, and each drawer was subjected to one of the following treatments: pressure wash, disinfectant, and pressure wash (A), pressurized steam followed by forced hot air (B), or no cleaning (C). Drawers were classified as top, middle, or bottom based on their relative position with each other. After treatment, broilers were introduced to each drawer and held for 2, 4, or 6 h. At each timepoint, broilers were removed from drawers, euthanized, and carcasses rinsed to obtain Salmonella counts. Samples under the limit of direct plating detection were enriched, plated, and later confirmed positive or negative. Differences were observed per treatment, holding time, and drawer relative position (P < 0.0001). Broilers placed in transport containers that underwent a cleaning procedure (A or B) had lower levels of Salmonella when compared to broilers placed in noncleaned containers (C). However, most of the samples below the limit of detection were positive after enrichment, indicating that both procedures evaluated need improvement for efficient pathogen inactivation. A decrease in Salmonella transfer was observed after 6 h in rinsates obtained from broilers placed in noncleaned containers (C). Rinsates obtained from top drawers had less Salmonella than the middle or bottom drawers when broilers were placed in transport containers that underwent a cleaning procedure (A and B). The application of pressurized steam and forced hot air was comparable to the use of water washes and disinfectant indicating a potential role in cleaning poultry transport containers.

Investigation of the potential of aerosolized Salmonella Enteritidis on colonization and persistence in broilers from day 3 to 21

The presence of Salmonella in air of poultry houses has been previously confirmed. Therefore, it is important to investigate the entry of Salmonella into broilers through air. The present study aimed to evaluate different levels of Salmonella Enteritidis aerosol inoculations in broiler chicks for colonization of ceca, trachea, and liver/spleen and persistence over time. In 3 independent trials, 112 one-day-old birds were randomly divided into 4 groups (n = 28/group). On d 1 of age, one group was exposed to an aerosol of sterile saline and the remaining three groups were exposed to an aerosol generated from one of 3 doses (10³, 10⁶, or 10⁹ CFU/mL) of S. Enteritidis inoculum. Aerosol exposure time was 30 min/group and was performed using a nebulizer. On d 3, 7, 14, and 21 of age, ceca, trachea, and liver/spleen were aseptically removed. Ceca were cultured for Salmonella counts (log₁₀ CFU/g) and all tissues were cultured for Salmonella prevalence. All tissues from the control group were Salmonella negative for all sampling days. On sampling d 3 and 7, ceca Salmonella counts were highest (5.14 and 5.11, respectively) when challenged with 10⁹Salmonella (P ≤ 0.0281). Ceca Salmonella counts increased from d 3 (2.43) to d 7 (4.43), then remained constant when challenged at 10³Salmonella, and counts decreased over time for all other groups. Tissue Salmonella prevalence increased with increasing challenge levels at all sampling timepoints (P ≤ 0.0213). Salmonella prevalence was low (0/18 to 4/18) and did not change over time following 10³Salmonella challenge (P ≥ 0.2394). Prevalence decreased over time in ceca and trachea following 10⁶ and 10⁹Salmonella challenge (P ≤ 0.0483). Liver/spleen Salmonella prevalence increased from d 3 (13/18) to d 14 (18/18) and then decreased at d 21 (10/18) in birds exposed to an aerosol of 10⁹Salmonella but remained constant over time for rest of the Salmonella inoculated groups. Overall, this study demonstrated the Salmonella colonization and persistence in different tissues in broilers following exposure to aerosolized Salmonella.

Impact of poultry litter Salmonella levels and moisture on transfer of Salmonella through associated in vitro generated dust

Dust present in poultry houses can contain high concentrations of microorganisms and has the potential to include pathogens from the litter. The objective of this study was to examine in vitro the potential for litter to dust transfer of aerobic bacteria, Salmonella, E. coli, and coliforms, and the role of the litter moisture on this process. Poultry litter was inoculated with 10² to 10⁹ CFU/mL of Salmonella Typhimurium to evaluate litter to dust transfer of bacteria (Experiment 1). To evaluate the effect of litter moisture on litter to dust microbial transfer (Experiment 2), litter was inoculated with 10⁹S. Typhimurium with increasing amounts of sterilized water added for moisture adjustment. Dust was generated by blowing air in a direct stream onto inoculated litter while simultaneously collecting dust through impingement. Following litter and dust sample collection, microbial analyses for aerobic plate counts (APC),Salmonella, E. coli, and coliforms were conducted. Both experiments were repeated 5 times and their data analyzed by one-way ANOVA and simple logistic regression. In Experiment 1, APC of litter (log₁₀ CFU/g) and dust samples (log₁₀ CFU/L) were 10.55 and 4.92, respectively. Salmonella ranged from 1.70 to 6.16 log₁₀ CFU/g in litter and only one dust sample had 1.10 log₁₀ CFU/L of Salmonella. As Salmonella levels in litter increased, the probability of obtaining a dust Salmonella positive result also increased. In Experiment 2, attained moisture percentages were 13.0, 18.2, 23.0, 28.2, and 33.3%. Litter recovery for APC, Salmonella, E. coli, and coliforms counts did not differ (P > 0.05) with increasing moisture levels. Dust sample bacterial counts significantly decreased with increasing moisture levels (P < 0.0001). Results from this in vitro study indicate that there is potential for Salmonella to be present in generated dust and the higher levels of Salmonella in litter increase the likelihood of detecting Salmonella in dust. Additionally, with higher litter moisture percentage, prevalence of Salmonella in generated dust was decreased.

Antimicrobial susceptibility patterns of clinical Escherichia coli isolates from dogs and cats in the United States: January 2008 through January 2013

Escherichia coli is among the most common bacterial pathogens in dogs and cats. The lack of a national monitoring program limits evidence-based empirical antimicrobial choices in the United States. This study describes antimicrobial susceptibility patterns for presumed clinical E. coli isolates from dogs (n=2392) or cats (n=780) collected from six geographic regions in the United States between May 2008 and January 2013. Minimum inhibitory concentrations (MIC) were determined for 17 drugs representing 6 drug classes. Urinary tract isolates were most common (71%). Population MIC distributions were generally bimodal with the second mode above the resistant breakpoint for all drugs except gentamicin, amikacin, and meropenem. The MIC90 exceeded the susceptible breakpoint for ampicillin, amoxicillin-clavulanic acid, cephalothin (surrogate drug for cephalexin), and doxycycline but was below the susceptible breakpoint for all others. None of isolates was susceptible or resistant to all drug tested; 46% were resistant to 1 or 2 antimicrobial categories, and 52% to more than three categories. The resistance percentages were as follows: doxycycline (100%), cephalothin (98%)>ampicillin (48%)>amoxicillin-clavulanic acid (40%)>ticarcillin-clavulanic acid (18%)>cefpodoxime (13%), cefotaxime (12%), cefoxitin (11%), cefazolin (11%), enrofloxacin (10%), chloramphenicol (9.6%)>ciprofloxacin (9.2%), ceftazidime (8.7%), trimethoprim-sulfamethoxazole (7.9%), gentamicin (7.9%)>meropenem (1.5%), amikacin (0.7%) (P<0.05). Resistance to ampicillin and amoxicillin-clavulanic acid was greatest in the South-Central region (P<0.05). E. coli resistance may preclude empirical treatment with doxycycline, cephalexin, ampicillin, or amoxicillin-clavulanic acid. Based on susceptibility patterns, trimethoprim-sulfonamides may be the preferred empirical oral treatment.

Mechanisms of infertility associated with clinical and subclinical endometritis in high producing dairy cattle

Clinical and subclinical endometritis are common causes of infertility and subfertility in high producing dairy cattle, delaying the onset of ovarian cyclic activity after parturition, extending luteal phases and reducing conception rates. Escherichia coli and Arcanobacterium pyogenes cause endometrial damage and inflammation. Components of microbes, such as lipopolysaccharide (LPS), are detected by Toll-like receptors on endometrial cells, leading to secretion of cytokines, chemokines and antimicrobial peptides. Long luteal phases associated with endometritis are probably caused by a switch in endometrial prostaglandin production from prostaglandin F2a (PGF) to prostaglandin E2. In addition, LPS impairs the function of the hypothalamus and pituitary, and directly perturbs ovarian granulosa cells steroidogenesis, providing mechanisms to explain the association between uterine disease and anovulatory anoestrus. Cows with uterine disease that ovulate have lower peripheral plasma progesterone concentrations that may further reduce the chance of conception associated with endometritis.

Use of Bacteriophages in Combination with Competitive Exclusion to Reduce Salmonella from Infected Chickens

Salmonella-spedfic bacteriophages (BP) and competitive exclusion (CE) were used to reduce Salmonella colonization in experimentally infected chickens. A "cocktail" of distinct phage (i.e., phage showing different host ranges and inducing different types of plaques on Salmonella Typhimurium [ST] cultures) was developed. The killing activity of the selected BPs on ST cultures differed significantly, as determined in in vitro killing assays. BPs were administered orally to the chickens several days prior and after ST challenge but not simultaneously. BPs were readily isolated from the feces of the BP-treated chickens approximately 48 hr after administration. A CE product consisting of a defined culture of seven different microbial species was used either alone or in combination with BP treatment. CE was administered orally at hatch. Salmonella counts in intestine, ceca, and a pool of liver/spleen were evaluated in Salmonella-challenged chickens treated with BP or with BP and CE. In both trials 1 and 2, a beneficial effect of the phage treatment on weight gain performance was evident. A reduction in Salmonella counts was detected in cecum and ileum of BP-, CE-, and BP+CE-treated chickens as compared with nontreated birds. In trial 1, BP treatment reduced ST counts to marginal levels in the ileum and reduced counts sixfold in the ceca. A reduction of Salmonella counts with BP, CE, and BP+CE treatments was evident in chickens from trial 2. Both CE and BP treatments showed differences in the reduction of Salmonella counts after challenge between spedmens obtained at days 4 and 14 postchallenge in ceca, liver/spleen, and ileum. The preliminary data presented in this report show that isolation and characterization of Salmonella-specific BP is uncomplicated and feasible on a larger scale. Results indicate a protective effect of both Salmonella-specific BPs and a defined competitive exclusion product against Salmonella colonization of experimentally infected chickens. These results are encouraging for further work on the use of BP as an effective alternative to antibiotics to reduce Salmonella infections in poultry.

Acid resistance systems required for survival of Escherichia coli O157:H7 in the bovine gastrointestinal tract and in apple cider are different

Escherichia coli O157:H7 is a highly acid-resistant food-borne pathogen that survives in the bovine and human gastrointestinal tracts and in acidic foods such as apple cider. This property is thought to contribute to the low infectious dose of the organism. Three acid resistance (AR) systems are expressed in stationary-phase cells. AR system 1 is sigma(S) dependent, while AR systems 2 and 3 are glutamate and arginine dependent, respectively. In this study, we sought to determine which AR systems are important for survival in acidic foods and which are required for survival in the bovine intestinal tract. Wild-type and mutant E. coli O157:H7 strains deficient in AR system 1, 2, or 3 were challenged with apple cider and inoculated into calves. Wild-type cells, adapted at pH 5.5 in the absence of glucose (AR system 1 induced), survived well in apple cider. Conversely, the mutant deficient in AR system 1, shown previously to survive poorly in calves, was susceptible to apple cider (pH 3.5), and this sensitivity was shown to be caused by low pH. Interestingly, the AR system 2-deficient mutant survived in apple cider at high levels, but its shedding from calves was significantly decreased compared to that of wild-type cells. AR system 3-deficient cells survived well in both apple cider and calves. Taken together, these results indicate that E. coli O157:H7 utilizes different acid resistance systems based on the type of acidic environment encountered.

Role of rpoS in acid resistance and fecal shedding of Escherichia coli O157:H7

Acid resistance (AR) is important to survival of Escherichia coli O157:H7 in acidic foods and may play a role during passage through the bovine host. In this study, we examined the role in AR of the rpoS-encoded global stress response regulator sigma(S) and its effect on shedding of E. coli O157:H7 in mice and calves. When assayed for each of the three AR systems identified in E. coli, an rpoS mutant (rpoS::pRR10) of E. coli O157:H7 lacked the glucose-repressed system and possessed reduced levels of both the arginine- and glutamate-dependent AR systems. After administration of the rpoS mutant and the wild-type strain (ATCC 43895) to ICR mice at doses ranging from 10(1) to 10(4) CFU, we found the wild-type strain in feces of mice given lower doses (10(2) versus 10(3) CFU) and at a greater frequency (80% versus 13%) than the mutant strain. The reduction in passage of the rpoS mutant was due to decreased AR, as administration of the mutant in 0.05 M phosphate buffer facilitated passage and increased the frequency of recovery in feces from 27 to 67% at a dose of 10(4) CFU. Enumeration of E. coli O157:H7 in feces from calves inoculated with an equal mixture of the wild-type strain and the rpoS mutant demonstrated shedding of the mutant to be 10- to 100-fold lower than wild-type numbers. This difference in shedding between the wild-type strain and the rpoS mutant was statistically significant (P </= 0.05). Thus, sigma(S) appears to play a role in E. coli O157:H7 passage in mice and shedding from calves, possibly by inducing expression of the glucose-repressed RpoS-dependent AR determinant and thus increasing resistance to gastrointestinal stress. These findings may provide clues for future efforts aimed at reducing or eliminating this pathogen from cattle herds.

Transcriptional analysis of the Yersinia pestis pH 6 antigen gene

The pH 6 antigen of Yersinia pestis is a virulence protein whose gene, psaA, is positively regulated at the transcriptional level by low pH, mammalian temperature, and an upstream locus, psaE. Low pH appears to be required for initial psaA transcription, although increased temperature is necessary for full expression of the gene. In addition, psaA is monocistronic and its transcript has a relatively long 5' nontranslated region.

Molecular analysis of a cryptic plasmid isolated from avian strains of Pasteurella multocida

Twelve small plasmids isolated from avian strains of Pasteurella multocida were examined by restriction enzyme mapping, cross-hybridization, and minicell analysis. These plasmids contained sites for several commonly used restriction enzymes and ranged in size from 3.4 to 3.8 kilobases. Restriction enzyme maps of the 12 plasmids were similar and divided the plasmids into 3 families, designated pFS1, pFS2, and pFS4. Restriction fragments of pFS1 DNA isolated from strain X-73 were used to probe AvaI/HindIII/EcoRV digests of pFS2 and pFS4 DNA. The results of these hybridization experiments demonstrated that the plasmids found in all three families shared extensive regions of homology and may have originated from a common ancestor. Escherichia coli minicells containing recombinant plasmid constructs bearing fragments of pFS1 expressed two pFS1-specific peptides, 12.5 and 28 kilodaltons in size, suggesting that some P. multocida plasmid-encoded proteins can be expressed in E. coli. These results indicate that pFS may be useful as a genetic tool for moving DNA into and out of P. multocida, since it is small, contains common restriction sites, and encodes at least two genes that are recognized and expressed in E. coli.

The Yersinia pestis V antigen is a regulatory protein necessary for Ca2(+)-dependent growth and maximal expression of low-Ca2+ response virulence genes

The low-Ca2+ response is a multicomponent virulence regulon of the human-pathogenic yersiniae in which 12 known virulence genes are coordinately regulated in response to environmental cues of temperature, Ca2+, and nucleotides such as ATP. Yersinial growth also is regulated, with full growth yield being permitted at 37 degrees C only if Ca2+ or a nucleotide is present. In this study, we constructed and characterized a mutant Yersinia pestis specifically defective in the gene encoding the V antigen, one of the virulence genes of the low-Ca2+ response. An in-frame internal deletion-insertion mutation was made by removing bases 51 through 645 of lcrV and inserting 61 new bases. The altered lcrV was introduced into the low-Ca2+ response plasmid in Y. pestis by allelic exchange, and the resulting mutant was characterized for its two-dimensional protein profiles, growth, expression of an operon fusion to another low-Ca2+ response virulence operon, and virulence in mice. The mutant had lost its Ca2+ and nucleotide requirement for growth, showed diminished expression of Ca2(+)-and nucleotide-regulated virulence genes, and was avirulent in mice. The mutation could be complemented with respect to the growth property by supplying native V antigen operon sequences in trans in high copy number (on pBR322). Partial complementation of the growth defect and almost complete complementation of the virulence defect were seen with a lower-copy-number complementing replicon (a pACYC184 derivative). The data are consistent with the interpretation that V antigen is bifunctional, with a role in regulating growth and expression of low-Ca2+ response virulence genes in addition to its putative role as a secreted virulence protein.

Molecular characterization of the Clostridium difficile toxin A gene

The gene encoding the toxin A protein of Clostridium difficile (strain VPI 10463) was cloned and sequenced. The coding region of 8,133 base pairs had a mol% G + C of 26.9 and encodes 2,710 amino acids. The deduced polypeptide has a molecular mass of ca. 308 kilodaltons. Nearly a third of the gene, at the 3' end, consists of 38 repeating sequences. The repeating units were grouped into two classes, I and II, on the basis of length and the low levels of DNA sequence similarities between them. There were seven class I repeating units, each containing 90 nucleotides, and 31 class II units, which, with two exceptions, were either 60 or 63 nucleotides in length. On the basis of DNA sequence similarities, the class II repeating units were further segregated into subclasses: 7 class IIA, 13 class IIB, 5 class IIC, and 6 class IID. The dipeptide tyrosine-phenylalanine was found in all 38 repeating units, and other amino acid sequences were unique to a specific class or subclass. This region of the protein has epitopes for the monoclonal antibody PCG-4 and includes the binding region for the Gal alpha 1-3Gal beta 1-4GlcNAc carbohydrate receptor. Located 1,350 base pairs upstream from the toxin A translation start site is the 3' end of the toxin B gene. Between the two toxin genes is a small open reading frame, which encodes a deduced polypeptide of ca. 16 or 19 kilodaltons. The role of this open reading frame is unknown.

Molecular analysis of lcrGVH, the V antigen operon of Yersinia pestis

The lcrGVH operon of plasmid pCD1 in Yersinia pestis KIM encodes the virulence-associated V antigen, the regulatory protein LcrH, and LcrG, a protein of undefined function. In this study we sequenced lcrGVH and analyzed it for transcription initiation sites. There were three open reading frames within the sequence, 288, 981, and 507 bases in length, which could encode proteins with molecular weights and isoelectric points corresponding to those of LcrG, LcrV (V antigen), and LcrH, respectively. The predicted LcrV protein lacked an N-terminal signal sequence; however, an internal signallike sequence was present. An Escherichia coli-like promoter consensus sequence was detected upstream from lcrG. Primer extension analysis showed that (i) the transcriptional start site for lcrGVH was spaced only three bases upstream from the nearest ATG potential start site, raising the possibility that Y. pestis may use an alternate initiation codon for the V operon; (ii) there was much more primer-extended product in yersiniae grown in the absence of Ca2+ than in its presence, showing for the first time that lcrGVH is regulated at the transcriptional level by Ca2+; (iii) no separate lcrV initiation was detected, indicating that the V antigen is expressed from messages initiating at lcrG; and (iv) a non-Ca2+-regulated transcriptional start site was found upstream from lcrH, suggesting that the LcrH protein is expressed constitutively. However, two-dimensional gel analysis showed that net LcrH expression was regulated by Ca2+. We propose that lcrH lies within two differentially regulated operons, its own and lcrGVH.

lcrH, a gene necessary for virulence of Yersinia pestis and for the normal response of Y. pestis to ATP and calcium

We are investigating the functions of the three proteins encoded by the V operon (lcrGVH) of the low-calcium response virulence plasmid pCD1 of Yersinia pestis KIM5. The purpose of this study was to define the role of the 18-kilodalton protein encoded by lcrH, the third gene of the V operon. Using marker exchange mutagenesis, we constructed a Y. pestis mutant that failed to express the LcrH protein. This LcrH- mutant was "ATP blind" in that it failed to show altered growth and V-antigen expression at 37 degrees C when 18 mM ATP was present. It also showed only a partial response to 2.5 mM Ca2+. The parental Y. pestis strain showed full growth yield at 37 degrees C and depressed expression of V antigen and of yop (yersinial pCD1-encoded outer membrane protein) genes in response to ATP or Ca2+. In contrast, the LcrH- mutant failed to grow at 37 degrees C in the presence of ATP and showed only limited growth when Ca2+ was present. V-antigen expression in the mutant was not depressed by ATP and only partially depressed by Ca2+. These findings show that LcrH is necessary for the normal response of Y. pestis to ATP and that LcrH contributes to Ca2+ responsiveness. The mutant also showed abnormal yopJ expression, indicating that LcrH also is necessary for normal yop regulation. The LcrH- mutant was avirulent in mice, probably because of its compromised growth at 37 degrees C. These findings indicate that the responses of Y. pestis to ATP and Ca2+ are distinct and that lcrH encodes a protein that is an important mediator of Ca2+ and ATP regulation of pCD1-encoded virulence determinant(s) in Y. pestis.

Using treatment plans for quality assurance monitoring in a residential center

Treatment plans for children in residential centers are required for accreditation and reimbursement, and they can provide important insights to the quality of care. One residential center has developed a system for reviewing treatment plans as part of its quality assurance (QA) monitoring. QA staff use checklists to review plans to assure that they are complete and technically correct and to evaluate the quality and appropriateness of care as revealed in the treatment strategy.

Studies on bacterial synergism in mice infected with Bacteroides intermedius and Fusobacterium necrophorum

This study was undertaken to characterize the kinetics of possible bacterial synergy using a mouse model of mixed intraabdominal infection with Bacteroides intermedius and Fusobacterium necrophorum. Female CD-1 mice were injected intraperitoneally with B. intermedius, F. necrophorum or mixtures of both organisms. Generalized septic peritonitis developed within 24 hr, with abscess formation occurring after one to two wk in survivors with the mixed infection. Involvement of the reticuloendothelial system was evidenced by dose-dependent hepatosplenomegaly, which appeared during the first wk postinfection and progressed throughout the course of the experiment. Indirect immunofluorescence confirmed the presence of both species of bacteria in frozen sections of liver tissue. The median lethal dose (LD50) was 2.11 x 10(9) for the mixture, 3.03 X 10(9) for B. intermedius alone, and 1.07 X 10(9) for F. necrophorum alone. The median abscess-producing dose (AD50), the dose required to produce abscesses in fifty percent of the surviving mice at two wk, was approx. 1/100 of the LD50 dose. The AD50 for intrahepatic abscesses was 2.8 x 10(8) for the mixture, whereas the AD50 for intraabdominal abscesses occurring in any site was 5.14 X 10(7). Both Bacteroides and Fusobacterium persisted in tissue for at least 22 wk following mixed infection. The persistence of the Bacteroides in tissue represents a synergistic result of mixed infection with Fusobacterium and contributed to the chronicity of intraabdominal abscess formation. Bacteroides, injected alone, did not produce abscesses at any of the doses tested. However, when passaged (isolated from mixed infection hepatic abscesses) B. intermedius was used, the bacteria did induce abscesses.

Enhancement of Bacteroides intermedius growth by Fusobacterium necrophorum

Previous work from this laboratory has demonstrated the persistence of Bacteroides intermedius in the livers of mice receiving an intraperitoneal inoculum of B. intermedius and Fusobacterium necrophorum. This study was undertaken to determine whether F. necrophorum enhanced the in vitro growth of B. intermedius. Tryptose phosphate broth did not support the growth of B. intermedius alone, but the bacterium did survive in a tryptose phosphate broth culture of F. necrophorum. B. intermedius cultured in F. necrophorum-conditioned tryptose phosphate broth grew impressively, reaching maximal absorbance at 24 h after inoculation. The growth of B. intermedius in F. necrophorum-conditioned tryptose phosphate broth was proportional to the amount of conditioned medium present. The B. intermedius growth-stimulating factor was detectable in conditioned medium 8 h after inoculation with F. necrophorum and could be detected throughout the 96-h incubation period. Growth-factor-active fractions eluted from a Sephadex G-100 column did not absorb at 280 nm and were retained on the column until 4 column volumes were eluted. The growth factor was nondialyzable and stable to boiling, lyophilization, extraction with hot aqueous phenol, and trypsin digestion. The factor was inactivated by exposure to pH 2.0 in the pepsin digestion protocol. Significant amounts of hexose, methyl pentose, and 2-keto-3-deoxyoctonate were detected in pooled growth-factor-active fractions eluted from the Sephadex column. This pool was also active in the Limulus lysate endotoxin assay. These results suggest that the B. intermedius growth-stimulating factor produced by F. necrophorum is a lipopolysaccharide.

Comparison of antimicrobial susceptibility patterns among coagulase-negative staphylococci

Coagulase-negative staphylococci, identified as S. epidermidis, S. saprophyticus, S. haemolyticus, S. hominis, and S. warneri, were tested for susceptibility to a number of antimicrobial agents by disk agar diffusion and broth microdilution methods, S. warneri and S. saprophyticus were found to be the most susceptible, and S. haemolyticus and S. epidermidis were found to be the least susceptible. Differences in antimicrobial susceptibility patterns are discussed, along with their epidemiological and therapeutic implications.