Biomedical subjects

M Raccach

Publications and source records attributed to M Raccach.

3 recordsLinked to original sources

PubMed1989

Antibiosis of some lactic acid bacteria including Lactobacillus acidophilus toward Listeria monocytogenes.

Eleven strains of lactic acid bacteria were tested by the 'spot' on the 'lawn' method for their antagonistic activity against four strains of Listeria monocytogenes. Four out of the five strains of lactic acid bacteria most antagonistic toward the pathogen were those cultures known to produce bacteriocins. Four other strains of lactic acid bacteria were not antagonistic against Listeria by this method. Seventeen inhibition zones of the pathogen were obtained at 25 degrees C as compared to 10 at 32 degrees C. Lactobacillus acidophilus strains NU-A and 88, growing in the presence of L. monocytogenes in milk prevented the latter from attaining populations it would have in pure culture (P less than 0.01). 10(1.4)-10(3.5) lower numbers were noted. L. acidophilus in most cases exhibited a bacteriostatic effect toward the pathogen except for strain 88 which appeared to have a bactericidal effect (P less than 0.01) against Listeria strain OH. The lactobacilli reduced the pH of the milk to 4.7 over a 24 h period, showing that acid played a role in the observed antibiosis.

Animals↗

PubMed1987

Pediococci and biotechnology.

Nomenclature changes of pediococci postdate the publication of Bergey's Manual. Pediococci possess both a "group" and a "type" antigen. They are gram positive, asporogenous, nonmotile, generally catalase negative, but may possess catalase-like activity. The pediococci may have either a cytochrome or a flavoprotein enzyme system. Anaerobically they are homofermentative using the PEP:PTS and the EMP pathway. Catalase positive strains utilize glucose aerobically and anaerobically while lactose and glycerol are only used aerobically. Some pentoses are fermented to lactate and acetate. Absolute requirement for folinic acid and nearly all amino acids is observed. Pediococci grow luxuriously in All Purpose Tween (APT) broth and are isolated on Rogosa SL agar. Detection can be done by electrical impedance and fluorescent antibody techniques. The Arrhenius concept was utilized in selecting metabolically efficient strains. Antibiotics, antioxidants, some chloride salts and some spices are detrimental to the pediococci. On the other hand, some chloride salts, manganese, and some spices are stimulant. Dialysis-fermentation and immobilization of pediococcal cells were recorded. Some strains decarboxylate histidine to histamine. The resting cell metabolism and the production of bacteriocin have been utilized in antibiosis. An intra and intergeneric genetic transfer system of plasmids from pediococci was by a conjugation-like mechanism. Formation of bacteriocin and fermentation of carbohydrates were linked to plasmids. Lytic bacteriophages to pediococci have not yet been identified. Industrial cultures are mainly frozen concentrates. Linear equations were developed to model the fermentative activity of pediococci and the effects of environmental factors.

Antibiosis↗

PubMed1975

Survival of frozen mycoplasmas.

Cooling to -70 C killed a higher percentage of Acholeplasma laidlawii and Mycoplasma mycoides var. capri cells than cooling to -20 C. However, to preserve cell viability for prolonged periods storage at -70 C was much more preferable. The percentage of cells surviving freezing could be increased by increasing the initial cell concentration or by the addition of dimethyl sulfoxide or glycerol as cryoprotective agents. In the presence of 1.5 M of any one of these agents survival rates of up to 100% could be obtained. The optimal cooling rates for maximal survival of A. laidlawii under the experimental conditions tested were 11 C/min for cooling to -20 C and about 15 C/min for cooling to -70 C. Increasing the warming rate during thawing from 0.6 to 67 C/min increased survival by 3 log. Oleic acid enrichment of A. laidlawii membrane lipids, or reduction in the cholesterol content of M. mycoides var. capri membranes, increased the percentage of organisms surviving freezing. Hence, the composition of membrane lipids appears to have a marked influence on the susceptibility of mycoplasmas to freezing injury.

Acholeplasma laidlawii↗