Research-Article| Volume 72, ISSUE 10, P2444-2451, October 1989

Growth Kinetics of Streptococcus thermophilus at Subbacteriostatic Penicillin G Concentrations

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      Streptococcus thermophilus may be subjected to the effects of penicillin G in contaminated milk used for yogurt production. Sensitivity of this microorganism to penicillin G has been conventionally determined by the help of penicillin G-impregnated disks placed on solid media. It was observed that the bacteriostatic penicillin G concentration was much greater in liquid media than in solid media. The conventional disk method may not be appropriate for antibiotic sensitivity determinations if the microorganisms will be used in liquid culture.
      A simple mathematical model simulated the growth of S. thermophilus in liquid culture. Numerical values of this model's parameters were regarded as the measure of the antibiotic effect on the culture. In penicillin G containing fresh medium, small concentrations of antibiotic decreased the specific growth rate considerably. Increasing the antibiotic concentration caused only slight additional decline. Antibiotic shock, i.e., rapidly introducing penicillin G into an actively growing antibiotic-free culture, stopped growth of the penicillin G-resistant microorganisms, and no death was observed, but a fraction of the microorganisms were killed in the wild culture. Both the wild and the resistant cultures recovered from the shock in a few hours. Addition of penicillin G-resistant microorganisms together with the antibiotic dosage into the wild culture prevented death.


        • Abraham E.P.
        The beta-lactam antibiotics.
        Sci. Am. 1981; 244: 64
        • Burden R.
        • Faircs D.J.
        • Reynolds A.C.
        Numerical analysis.
        2nd ed. PWS Publ., Boston, MA1981 (Pages 185–191)
        • Carpenter P.
        4th ed. Saunders Co., Philadelphia, PA1977 (Pages 200–201)
        • Egorov N.S.
        Mir Publ., Moscow, USSR1981 (Pages 367–371)
        • Klimek J.
        • Ollis D.F.
        Extracellular microbial polysaccharides: kinetics of Pseudomonas sp., Azotobacter vinelandii, and Aureobasidium pullulans batch fermentations.
        Biotechnol. Bioeng. 1980; 22: 2321
        • Lam J.C.
        • Ollis D.F.
        Kinetics of multiproduct fermentations.
        Biotechnol. Bioeng. 1981; 23: 1517
        • Marth E.H.
        • Ellickson B.E.
        Antibiotic residues in milk and milk products.
        J. Milk Food Technol. 1959; 22: 241
        • Özilgen M.
        Kinetics of amino acid production by over-producer mutant microorganisms.
        Enzyme Microb. Technol. 1988; 10: 110
        • Reinboid G.W.
        • Reddy M.R.
        Sensitive or resistant dairy starter and associated microorganisms to selected antibiotics.
        J. Milk Food Technol. 1974; 37: 517
        • Sanders C.C.
        • Sanders Jr., W.E.
        Clinical importance of inducible beta-lactamases in gram-negative bacteria.
        Eur. J. Clin. Microbiol. 1987; 6: 435
        • Sozzi T.
        • Smiley M.B.
        Antibiotic resistances of yogurt starter cultures Streptococcus thermophilus and Lactobacillus bulgaricus.
        Appl. Environ. Microbiol. 1980; 40: 862
        • Weiss R.M.
        • Ollis D.F.
        Extracellular microbial polysaccharides. I. Substrate, biomass and product kinetic equations for batch xanthan gum fermentations.
        Biotechnol. Bioeng. 1980; 22: 859
      1. Yöndem, F. 1987. Kinetics of antibiotic resistance development by S. thermophilus. M.S. Thesis, Middle East Tech. Univ., Ankara, Turkey.