is a Gram positive, thermophilic spore forming soil bacterium closely related to B. subtilis
. It is widely used in the fermentation industry for production of enzymes, antibiotics and other chemicals and is generally regarded as a non-pathogen
]. However, there are several reports of B. licheniformis-
associated human infections such as bacteremia and enocarditis, bovine abortions and food borne diseases which raise the question of its pathogenic potential
]. More commonly, representatives of this species have caused spoilage of milk, bread and canned foods leading to severe economic losses to the food industry
is ubiquitous in the environment and able to grow under a wide range of temperatures (15–55°C) in both anaerobic and aerobic conditions making this species a highly potent food contaminant
]. During starvation, the cells may form thermo-stabile endospores in a process known as sporulation
]. These spores are resistant against many decontamination and preservation steps applied by the food industry such as pasteurization, pressure, freezing, extreme pH, radiation and desiccation
]. In the presence of nutrients (germinants) spores may germinate and grow out into vegetative cells which can multiply in the absence of competing microflora
]. Germination can be further accelerated by external stress such as a short, sublethal heat step (usually at 65–95°C)
]. This phenomenon, known as “activation”, is utilized in the “double heat treatment” (a modified tyndallisation), a decontamination strategy where spores that are activated in the primary heat step can be inactivated or killed as germs in the secondary heat treatment
]. Recent publications have provided new insight into the complexity of spore germination
]. The observed diversity in germination between and within populations makes spore behavior prediction challenging
] and might explain why spore decontamination strategies sometimes fail. Detecting strains with increased potential of causing food spoilage would therefore be of great value to the food industry.
Several molecular typing methods have been applied in order to characterize the population structure within B. licheniformis
]. Multi-locus sequence typing (MLST) has the advantage to other molecular typing methods of being unambiguous and easily portable between laboratories
]. It has been applied to numerous species including members of the B. cereus
family and Clostridium
] and has been used for epidemiological purposes identifying strains that could cause human infections
]. Basically, it relies on the sequence of several (usually six to eight) conserved house-keeping genes which are independently distributed in the genome. The method is therefore considered to be robust, discriminatory and capable of revealing the deeper evolutionary relation of populations that are studied
]. No MLST scheme has so far been developed for B. licheniformis.
The purpose of this study was to establish a MLST scheme for B. licheniformis in order to reveal the evolutionary relationship of 53 strains of this species and to see whether food-contaminating strains were restricted to certain lineages.