More than one variant of Listeria monocytogenes isolated from each of two human cases of invasive listeriosis

Growth, detection and virulence of Listeria monocytogenes in the presence of other microorganisms: microbial interactions from species to strain level

Like with all food microorganisms, many basic aspects of L. monocytogenes life are likely to be influenced by its interactions with bacteria living in close proximity. This pathogenic bacterium is a major concern both for the food industry and health organizations since it is ubiquitous and able to withstand harsh environmental conditions. Due to the ubiquity of Listeria monocytogenes, various strains may contaminate foods at different stages of the supply chain. Consequently, simultaneous exposure of consumers to multiple strains is also possible. In this context even strain-to-strain interactions of L. monocytogenes play a significant role in fundamental processes for the life of the pathogen, such as growth or virulence, and subsequently compromise food safety, affect the evolution of a potential infection, or even introduce bias in the detection by classical enrichment techniques. This article summarizes the impact of microbial interactions on the growth and detection of L. monocytogenes primarily in foods and food-associated environments. Furthermore it provides an overview of L. monocytogenes virulence in the presence of other microorganisms.

Occurrence of genetic variants of Listeria monocytogenes strains

Isolates of Listeria monocytogenes saved from outbreaks of listeriosis, cases of sporadic listeriosis, and similar events do not always belong to a solitary genetic variant. Variants of the same strain may have evolved from a unique clone, and plasmid loss or gain and phage-mediated genetic changes are suggested as the main mechanism. Some of these reports are summarized in this short communication.

Listeria monocytogenes-associated joint and bone infections: a study of 43 consecutive cases

BACKGROUND

Little is known about Listeria monocytogenes-associated bone and joint infections. Only case reports of this infection have been published.

METHODS

Retrospective study of culture-proven bone and joint cases reported to the French National Reference Center for Listeria from 1992 to 2010.

RESULTS

Forty-three patients were studied: 61% were men, and the median age was 72 (range, 16-89); 24 patients exhibited comorbidities (56%). Thirty-six patients (84%) had orthopedic implant devices: prosthetic joints (n = 34) or internal fixation (n = 2); the median time after insertion was 9 years (0.1-22). Subacute infection was more frequent (median, 4 weeks [range, 2-100], 74%) than acute infection (<7 days, 23%), with nonspecific clinical features; 45% of patients had no fever. Blood cultures were positive in 3 of 19 cases. Isolate polymerase chain reaction genogrouping revealed 4 patterns: IVb (21 of 42, 50%), IIa (17 of 42, 40%), IIb (2 of 42, 5%), and IIc (2 of 42, 5%). Five groups of strains with similar pulsotype patterns were identified without an epidemiological link. Antibiotics, primarily amoxicillin (80%) with aminoglycosides (48%), were prescribed for a median duration of 15 weeks (range, 2-88). Eighteen patients (50%) underwent prosthesis replacement; all were successful after median follow-up of 10 months (range, 1-75). Five of 13 patients for whom material was not removed had protracted infection despite prolonged antibiotherapy; 3 of these patients later underwent prosthesis replacement with sustained recovery.

CONCLUSIONS

Osteoarticular listeriosis primarily involves prosthetic joints and occurs in immunocompromised patients. It requires intensive treatment with antibiotherapy and usually requires implant removal or replacement for cure.