ABSTRACT
Transition of bacteria to cell wall deficient L-forms in response to stress factors has been assumed as a potential mechanism for survival of microbes under unfavorable conditions. In this article, we provide evidence of paradoxal survival through L-form conversion of E. coli high cell density population after lethal treatments (boiling or autoclaving). Light and transmission electron microscopy demonstrated conversion from classical rod to polymorphic L-form shape morphology and atypical growths of E. coli. Microcrystal formations observed at this stage were interpreted as being closely linked to the processes of L-form conversion and probably involved in the general phenomenon of protection against lethal environment. Identity of the morphologically modified L-forms as E. coli was verified by species specific DNA-based test. Our study might contribute to a better understanding of the L-form phenomenon and its importance for bacterial survival, as well as provoke reexamination of the traditional view of killing strategies against bacteria.
Subject(s)
Escherichia coli/physiology , Escherichia coli/ultrastructure , Hot Temperature , Stress, Physiological , Microscopy , Microscopy, Electron, TransmissionABSTRACT
Clinical strains of Staphylococcus aureus with different phenotypic methicillin susceptibility characteristics, bearing or lacking the mecA gene, were tested for their ability to transform into a cell wall-deficient state under special conditions of cultivation. Conversion to L-form growth with formation of typical L-form 'fried egg' colonies and expression of oxacillin resistance was observed in sensitive (mecA-negative) and heteroresistant (mecA-positive) strains. Transmission electron microscopy observation of these strains revealed pleomorphic populations of cell wall-deficient cells with ultrastructure morphology similar to that of a control stable L-form strain of S. aureus. The results demonstrate that expression of phenotypic methicillin resistance could be associated with cell wall deficiency in S. aureus strains and could underlie the phenomenon of heteroresistance.
