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Biomedical subjects

M E Stiles

Publications and source records attributed to M E Stiles.

At least 55 records · Page 3Linked to original sources
PubMed1990

Antibacterial activity of lactic acid bacteria isolated from vacuum-packaged meats.

Lactic acid bacteria isolated from vacuum-packaged fresh meat stored at 4 degrees C were shown to produce antagonistic substances active against closely related bacteria. Growth medium, pH and growth temperature all affected the production of the inhibitory substances. Ten strains including aciduric Lactobacillus-type organisms, Carnobacterium spp. and Leuconostoc spp. were selected that produced protein-aceous substances that caused inhibition of indicator strains. These were considered to be bacteriocins or bacteriocin-like compounds based on their inactivation with protease, generally narrow spectra of antibacterial activity and bactericidal or bacteriostatic modes of action. Activity was not lost from supernatant fluids as a result of heat treatment at 62 degrees C for 30 min, except for the Leuconostoc strains. Inhibitory spectra of some strains included Enterococcus spp. and Listeria monocytogenes. Some strains were of interest because their inhibitory substances were detected in the supernatant fluid early in the growth cycle. The inhibitory substances differed in characteristics between strains and there is evidence that more than one bacteriocin-like substance may be produced by some strains.

Animals↗
PubMed1990

Plasmid-associated bacteriocin production by a strain of Carnobacterium piscicola from meat.

Carnobacterium piscicola LV17 isolated from vacuum-packed meat produces bacteriocin(s) that is active against closely related lactic acid bacteria, Enterococcus spp., and a strain of Listeria monocytogenes but not against gram-negative bacteria. The bacteriocin has a bactericidal mode of action, is heat resistant, and is stable over a wide range of pH but is inactivated by proteolytic enzymes. Sensitive and resistant cells were shown to adsorb the bacteriocin, but cell death depended on contact of the bacteriocin with the cell membrane. Bacteriocin production is detected early in the growth cycle of the organism in APT broth, but it is not produced in APT broth adjusted to pH 5.5. Bacteriocin production and resistance to the bacteriocin produced are associated with two plasmids of 40 and 49 megadaltons. The possibility that two bacteriocins are produced is indicated because the inhibitory substances of the mutant strains containing either the 40- or 49-megadalton plasmids have different antimicrobial spectra.

Bacteriocins↗
PubMed1988

Characterization of freshly isolated Campylobacter coli strains and suitability of selective media for their growth.

Typical and atypical Campylobacter strains were isolated from the colons of cattle and swine by techniques that enabled the selective pressures of antibiotics to be avoided. Some cephalothin-susceptible strains and a strain with an indeterminate hippurate reaction were classified as Campylobacter coli by DNA homology testing. Tetracycline-resistant isolates were obtained from animals with no recorded exposure to antibiotics. A selection of 12 C. coli and 6 C. jejuni strains was used to determine the ability of fresh isolates to grow on a range of selective media. C. coli isolates were inhibited more than C. jejuni on selective media containing antibiotics. The least inhibitory media were Skirrow medium (M. B. Skirrow, Br. Med. J. 2:9-11, 1977) and the charcoal-based media developed by Hutchinson and Bolton (D. N. Hutchinson and F. J. Bolton, J. Clin. Pathol. 37:956-957, 1984) and Karmali et al. (M. A. Karmali, A. E. Simon, M. Roscoe, P. C. Fleming, S. S. Smith, and J. Lane, J. Clin. Microbiol. 23:456-459, 1986). The plasmid contents of the isolates did not appear to be related to their sensitivity to growth on selective (antibiotic-containing) media. The study indicates that selective media used to detect Campylobacter spp. could select against the isolation of C. coli.

Animals↗
PubMed1987

Classification of Campylobacter strains using DNA probes.

DNA homology determinations were used to classify atypical strains of Campylobacter spp. and Campylobacter-like organisms. Using the slot-blot hybridization technique, atypical strains were classified as C. coli or C. jejuni. Some of the Campylobacter-like organisms isolated from animals were catalase-positive, but they did not hybridize with the DNA probes prepared from the total genomic DNA of C. coli, C. jejuni, C. laridis, C. fetus subsp. fetus and C. hyointestinalis. The taxonomic classification of these strains remains uncertain. The slot-blot hybridization technique was simplified by applying whole cells from a 24 h broth culture, instead of pure DNA to nitrocellulose membranes. The results of DNA homology from both methods were comparable, and the classification of these organisms using these methods was the same. Therefore, the dot-blot hybridization method is recommended as a more economical and time-saving method for use in the taxonomic classification of atypical Campylobacter spp.

Base Composition↗
PubMed1987

DNA probes for identification of tetracycline resistance genes in Campylobacter species isolated from swine and cattle.

Tetracycline-resistant strains of Campylobacter jejuni and Campylobacter coli from swine and cattle colons were isolated and characterized by hybridization with DNA probes. A probe consisting of the 1.8-kilobase (kb) HincII fragment from pUA466 was highly specific for the detection of tetracycline resistance (Tcr) in C. jejuni and C. coli. The 5-kb tetM DNA probe from Streptococcus agalactiae plasmid pJI3 which has homology with the 1.8-kb HincII fragment from pUA466 could also be used to detect Tcr Campylobacter strains. However, the tetM probe had a much lower sensitivity and required a lower stringency of hybridization. Therefore, the 1.8-kb HincII fragment appeared to be more appropriate for the classification of Tcr in Campylobacter spp. No homology was detected between the Tcr determinant from Campylobacter spp. and the tetL and tetN probes from Streptococcus spp. DNA homology was demonstrated between pUA649, a derivative of plasmid pUA466 which had lost most of the Tcr region, and Tcr plasmids from C. jejuni and C. coli isolated from animal and human sources. There was also homology between pUA649 and the chromosomes of C. jejuni and C. coli strains. In this study, all but one of the tetracycline-resistant C. coli and C. jejuni strains contained plasmids of approximately 50 kb which hybridized with the 1.8-kb HincII probe. In one C. coli strain (UA703), Tcr appeared to be chromosomally mediated.

Animals↗
PubMed1987

Recovery of a marker strain of Escherichia coli from ozonated water by membrane filtration.

Selective and nonselective growth media were evaluated at two incubation temperatures, 35 and 44.5 degrees C, for the recovery of a nalidixic acid-resistant marker strain of Escherichia coli ATCC 11775 by membrane filtration from ozonated 0.05 M phosphate buffer (pH 6.9). There were significantly fewer bacteria recovered with the standard m-FC agar when compared with the same growth medium prepared without bile salts and rosolic acid. This effect was particularly noticeable at the elevated incubation temperature of 44.5 degrees C. These findings are contrary to previous work which concluded that the standard American Public Health Association membrane filtration procedure is suitable for recovery of fecal coliform indicator bacteria from ozonated wastewater.

Analysis of Variance↗
PubMed1985

Efficacy of low-concentration iodophors for germicidal hand washing.

The efficacy of iodophor germicides containing different concentrations of available iodine against transient (inoculated) bacteria and the natural hand microflora was compared with chlorhexidine gluconate (2 and 4%) liquid detergent (Hibitane), non-germicidal soap and a tap water rinse. The tap water rinse was ineffective compared with all other treatments. Only 4% chlorhexidine gluconate liquid detergent and iodophor containing 0.75% available iodine were significantly better than the non-germicidal soap for reduction of transient bacteria, Escherichia coli and Pseudomonas fluorescens, that had been inoculated onto hands. These agents also caused a significant reduction in the number of 'natural' microorganisms released from hands after a standard 15 s hand wash. The low-concentration iodophor products and the product containing 2% chlorhexidine gluconate failed to give results significantly better than the non-germicidal control soap. Baird-Parker medium and standard aerobic plate counts were highly correlated (r = 0.82), so that for studies of Gram-negative bacteria inoculated onto hands as a transient microflora, counts on Baird-Parker medium give a reasonable indication of the natural (residual) hand microflora.

Chlorhexidine↗
PubMed1985

Estimation of Campylobacter spp. in broth culture by bioluminescence assay of ATP.

The luciferin-luciferase bioluminescence reaction was used to estimate cell numbers of Campylobacter jejuni and Campylobacter coli in broth cultures based on a linear relationship between cell numbers (in excess of 10(4) to 10(5] and ATP levels. The sensitivity was lower than that obtained with Escherichia coli. The calculated amount of intracellular ATP per cell of C. jejuni and C. coli ranged from 1.7 to 2.1 fg.

Adenosine Triphosphate↗
PubMed1985

Morphological forms and viability of Campylobacter species studied by electron microscopy.

Electron microscopic studies of Campylobacter revealed that different morphological forms predominate at different parts of a colony. At the periphery, cells were almost all spirals, while in the center of the colony cells were mainly coccus shaped. Unusual ring-shaped cells, "donuts", were observed in the raised, peripheral region of the colony. Donut or ring forms have not previously been reported for Campylobacter organisms. Our data indicate that young or actively growing cells are mainly spiral shaped. Older cells undergo a degenerative change to coccoid forms. The donut shape appears to be an intermediate stage between spirals and cocci. Comparisons of plate counts of actively growing and inactive cells confirmed that coccoid cells are probably nonviable.

Campylobacter↗
PubMed1985

Comparison of basal media for culturing Campylobacter jejuni and Campylobacter coli.

Four strains of Campylobacter jejuni and four strains of Campylobacter coli were used to compare the quantitative growth of Campylobacter cells on blood agar base no. 2 (Oxoid), brucella agar (BBL Microbiology Systems and Difco Laboratories), campylobacter agar base (Difco), Columbia blood agar base (Difco and Oxoid), and Mueller-Hinton agar (Difco and Oxoid). Columbia blood agar base and blood agar base no. 2 were inhibitory to most of the strains tested, as evidenced by reduced (10- to 1,000-fold) colony counts compared with other basal media. One of the brucella agars was inhibitory to two of the C. coli strains. The inhibitory effect of these media could be eliminated by addition of FBP (0.05% each ferrous sulfate hydrate, sodium metabisulfite, and sodium pyruvate) or 7% defibrinated sheep blood. However, addition of FBP or blood to brucella agar, campylobacter agar base, or Mueller-Hinton agar did not significantly affect the count, indicating that supplements are not required in these media for growth of Campylobacter in pure culture.

Campylobacter↗
PubMed1985

Inhibition of Campylobacter coli and Campylobacter jejuni by antibiotics used in selective growth media.

The ability of Campylobacter coli and Campylobacter jejuni to grow in the presence of antibiotics used in selective growth media was compared. MIC data for C. coli indicated that some strains were more susceptible to the antibiotics than were the C. jejuni strains tested. A reduction of greater than 1 log cycle in the numbers of cells growing on plates containing antibiotics was considered to be a marked level of inhibition. Only one of nine of the antibiotic combinations studied did not markedly inhibit most of the C. coli strains tested. Although one C. coli strain was not inhibited by any of the antibiotic combinations, the other six strains were inhibited for up to 7 log cycles. The addition of blood or growth supplements reduced but did not eliminate the inhibitory effect. The inhibition of laboratory strains of C. coli on media developed for the isolation of Campylobacter spp. indicates that the incidence of C. coli may be underestimated.

Anti-Bacterial Agents↗
PubMed1984

Escherichia coli variants for gas and indole production at elevated incubation temperatures.

Two strains of Escherichia coli were subjected to heat and cold-storage treatments to determine the stability of the fecal E. coli characteristics of gas production from lactose and indole production at elevated incubation temperatures. No variants were detected with repeated sublethal heat treatment. A high incidence of variants was observed with extended cold storage of the organisms in liquid and semisolid media, especially with poor nutrient composition, and in the absence of cryoprotective agents. The indole characteristic at elevated temperature was more stable than the production of gas from lactose. The critical temperature at which both gas production from lactose and the indole characteristic were lost was 44.5 degrees C. It appeared that the variants resulted from increased temperature sensitivity of the formic hydrogen lyase and tryptophanase enzymes, respectively.

Culture Media↗
PubMed1981

Biochemical characteristics and identification of Enterobacteriaceae isolated from meats.

The isolation and identification of 2,220 Enterobacteriaceae from meats indicated that Escherichia coli biotype I, Enterobacter agglomerans, and Serratia liquefaciens were the principal types to be differentiated in meats. Citrobacter freundii, Klebsiella pneumoniae, Enterobacter cloacae, and Enterobacter hafniae were also commonly identified. Identification of isolates by the Encise II (Roche Diagnostics Inc., Nutley, N.J.) and Minitek (BBL Microbiology Systems, Cockeysville, Md.) coding systems gave similar results with only 255 (11.5%) discrepancies in identity, but both systems required large numbers of supplementary tests for identification of the isolates. Not only the distribution of Enterobacteriaceae types isolated from meats but also some of the biochemical reactions of the isolates differed from those of clinical isolates. The Minitek technique is recommended because of its versatility. However, with the addition of cellobiose and salicin disks and the inclusion of methyl red to the Minitek test and the use of the Voges-Proskauer test and gas production in EC medium at elevated temperature as standard tests, the identification of these Enterobacteriaceae from meats would be greatly facilitated. The inclusion of the motility test, for example, using nitrate motility agar, would also be of value to Enterobacteriaceae identification.

Carbohydrate Metabolism↗
PubMed1981

Enterobacteriaceae associated with meats and meat handling.

The source of Enterobacteriaceae on meats was shown to be associated with the meat-handling work surfaces in two packing plants studies. A total of 2,343 Enterobacteriaceae were isolated and identified from meat samples and work surfaces at the packing plants and at the retail facilities. Escherichia coli biotype I and Serratia liquefaciens were detected at all stages of meat handling, indicating that they may be present in meats throughout the meat-handling system. Enterobacter agglomerans and S. liquefaciens were the predominant Enterobacteriaceae at the retail level, but they had limited indicator potential for sanitation and hygiene, Klebsiella pneumoniae was a frequent isolate among Enterobacteriaceae from meats and meat-handling surfaces in the packing plants but not at the retail level, indicating that this organism might signal unhygienic handling of meats at the retail level.

Animals↗
PubMed1980

Estimation of Escherichia coli in raw ground beef.

This study was undertaken to establish and evaluate more rapid methods of estimating Escherichia coli in ground beef than the standard most probable number (MPN) technique. Direct inoculation of and modifications to EC medium gave unreliable estimates of the presumptive E. coli count. Solid media incubated at an elevated temperature were compared to the MPN technique. Anderson and Baird-Parker's tryptone bile agar (TBA) method and prepoured plates of Endo, Levine eosin methylene blue (EMB), and violet red bile (VRBA) agars incubated at 44 degree C gave equivalent counts to the standard MPN method. Anderson and Baird-Parker TBA was the most selective solid medium for E. coli estimation, but all selective media incubated at elevated temperature reduced apparent E. coli counts by as much as 50%. Indole-producing and lactose-fermenting Enterobacteriaceae, capable of growth at elevated temperature, were tested for their growth on TBA, EMB, and VRBA at elevated temperature. TBA was selective for E. coli biotype I compared to other Enterobacteriaceae that predominate in meats. VRBA and EMB incubated at elevated temperature were not as selective as TBA, but differences in colonies could be observed between typical E. coli colonies and other Enterobacteriaceae on these media. Therefore, VRBA incubated at elevated temperature is proposed as a quality assurance screening test for presumptive E. coli in ground meat. Resuscitation techniques and prepoured plates with VRBA increased recovery levels of presumptive E. coli, but, under the conditions of this study, not to levels that represented a significant practical difference.

Animals↗
PubMed1978

Incidence and relationship of group D streptococci with other indicator organisms in meats.

Raw and processed meats were analyzed for presumptive group D streptococci using KF streptococcus agar. Counts were compared with coliform, presumptive Escherichia coli, and Enterobacteriaceae counts but no meaningful relationships were observed. Results indicated that group D streptococci and E. coli type I were principally contaminants from the packing plant, rather than at retail level. The predominating group D streptococcus in both beef and pork cuts was Streptococcus faecalis, while in processed meat (bologna), the predominating group D streptococci were Streptococcus faecium var. durans and Streptococcus faecium. Streptococcus bovis was not detected among the isolates from any meat samples. Marked differences were noted in numbers of group D streptococci in processed meat from different manufacturers. The results did not support the use of group D streptococci as alternative indicator organisms for meats. However, the association of group D streptococci with packing plant contamination may prove to be of value.

Animals↗