Other Chemical and Physical Aspects of Culture
Antimicrobials such as malachite green, cycloheximide, amphotericin B, vancomycin, nalidixic acid, chloramphenicol, penicillin G, polymyxin B, trimethoprim, azlocillin and ampicillin have been included in various media but thorough evaluation of their potential to inhibit growth of MAP is mostly lacking (Shin, 1989; Whitlock and Rosenberger, 1990; Stabel, 199 7; Kalis et al., 1999; Whittington et al., 1999; Gumber and Whittington, 2007).
Dyes may be added to solid media to improve visibility of colonies. Brilliant green was effective (Minett, 1942). Methylene blue becomes concentrated in the colonies as they develop (Fig. 18.1) (Whittington et al., 1999). Dye uptake by colonies can vary between strains and variant colonies may be observed within a culture (Parrish et al., 2004). Colonies are readily observed on media containing malachite green, particularly LJ medium, which has a smooth surface. The surface of HEYM slopes is often finely pitted, which can make recognition of small colonies quite challenging despite the inclusion of the dye. Small colonies are relatively difficult to see on modified Middlebrook 7H10 and 7H11 agars, which are pale yellow due to their egg yolk content.
Polyoxyethylene sorbates (Tweens) and polyoxyethylene stearates (POES) influence the in vitro growth of mycobacteria, leading to alterations in replication rate, intracellular storage vacuoles, cell surface properties and colony morphology; they can be stimulatory or inhibitory depending on concentration (Stinson and Solotorovsky, 19 71; Cutler et al., 1987; van Boxtel et al., 1990; Realini et al., 1997). Tweens are a source of carbon and energy and are wetting agents, enabling dispersal of bacterial cells (Stinson and Solotorovsky, 1971). One per cent w/v Tween 80 was associated with optimal growth of MAP clinical isolates in Middlebrook 7H9 medium with mycobactin J (van Boxtel et al., 1990) but its inclusion in similar medium in another study had equivocal effects on growth of C and S strains of MAP (Whittington et al., 2013).
POES was present in BACTEC 12B medium through the antibiotic mixture PANTA-PLUS to which it may have been added to aid dissolution of antibiotics during media preparation, but it is not present in BACTEC MGIT Para TB medium (BD). It did not appear to be required for optimal growth of MAP-C and S strains in Middlebrook 7H9 medium with egg yolk (Whittington et al., 2013), probably because the egg yolk provides major carbon and energy sources in addition to those already included in the complex medium, and also provides the surfactant lecithin. Oleic acid, the hydrolysis product of Tween, is an additive in Middlebrook 7H11 agar and MGIT medium, but it is not required for growth of MAP in the presence of egg yolk because MAP grows equally well on Middlebrook 7H10 agar that does not contain added oleic acid (Whittington et al., 1999).Twort and Ingram, and later Merkal, investigated many fundamental properties of media and incubation conditions (Twort and Ingram, 1912; Merkal et al., 1982). Shaking a liquid culture reduced growth of MAP, a CO2 atmosphere was not required and pH 6 was beneficial to growth compared with a higher pH.
18.7
More on the topic Other Chemical and Physical Aspects of Culture:
- Physical and Chemical Defences
- In the previous section, we saw how nutrients undergo biological, chemical, and physical transformations as they are taken up by organisms and released through decomposition, ultimately returning to their original forms (or similar ones).
- CONCEPT 22.2 Chemical and biological transformations in ecosystems alter the chemical form and supply of nutrients.
- Werner Reiss, author of the most detailed recent discussion on the subject of violence in the Greek world, defined violence as ‘a physical act', stating further that it is a ‘process in which a human being inflicts harm on another human being via physical strength’.1
- Chemical and Photochemical Reactions in Atmosphere
- The Chemical Environment
- Microorganisms modify the chemical form of nutrients
- Physical Injury
- Physical Examination
- The generation of chemical energy by autotrophs, known as primary production, is derived from the uptake of carbon during photosynthesis and chemosynthesis (see Chapter 5).
- CONCEPT 2.6 Salinity, acidity, and oxygen concentrations are major determinants of the chemical environment.
- Other Aspects of Climate Change
- A Brief Overview of the Important Aspects