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Multiplication and persistence of Spiroplasma melliferum strain A56 in experimentally infected suckling mice
C Chastel1, F Le Goff, I Humphery-Smith
1Faculté de Médecine, Université de Brest, France.
Abstract:
Strain A56 of the bee pathogen Spiroplasma melliferum was isolated from a honeybee (Apis mellifera) during ecological studies on mosquito spiroplasmas in Savoie (France). When inoculated intracerebrally (i.c.) into 48-h old suckling mice, this strain was found to replicate to very high titres and to persist in brain for up to 9 months in one individual. We attempted to increase the "neurotropism" of A56 by sequential i.c. passages. During the first two passages, multiplication of the organisms was observed at very high titres in suckling mouse brain (10(7) to 10(11) CCU/ml) generally without the appearance of antibody, thus mimicking the so-called "immunological tolerance" phenomenon. Intracerebral multiplication of A56 decreased during the third passage (10(2) to 10(4) CCU/ml) and ceased during the fourth passage. Spiroplasma multiplication in brain was apparently well tolerated, since brain lesions were minimal and clinical symptoms were limited to a clear, but only rarely significant, delay in growth curves of inoculated versus non-inoculated mice. Progressive spongiform encephalopathy was never observed. Strain A56 S. melliferum appears as the second spiroplasma, after the tick-derived Spiroplasma mirum capable of multiplying in both invertebrate and vertebrate hosts.
Insights
Spiroplasma melliferum strain A56 replicates in mouse brains, persisting for months. Sequential passages showed initial high replication, mimicking immunological tolerance, but later decreased, indicating limited neurotropism.
Area of Science:
- Microbiology
- Pathogen Research
- Veterinary Entomology
Background:
- Spiroplasma melliferum is a bee pathogen.
- Ecological studies investigated mosquito spiroplasmas in France.
- Spiroplasma mirum is known to infect both invertebrate and vertebrate hosts.
Purpose of the Study:
- To investigate the neurotropism of Spiroplasma melliferum strain A56.
- To assess the replication and persistence of A56 in the vertebrate central nervous system.
- To explore potential host-pathogen interactions and immune responses.
Main Methods:
- Isolation of Spiroplasma melliferum strain A56 from honeybees.
- Intracerebral inoculation of strain A56 into suckling mice.
- Sequential passage of the strain in mouse brains.
- Quantification of spiroplasma titres and assessment of host immune response (antibody detection).
- Monitoring of clinical symptoms and brain lesions in inoculated mice.
Main Results:
- Strain A56 replicated to high titres (10^7 to 10^11 CCU/ml) in suckling mouse brains during initial passages.
- High replication occurred without significant antibody appearance, suggesting immunological tolerance.
- Spiroplasma multiplication decreased significantly by the third passage and ceased by the fourth.
- Minimal brain lesions and limited clinical signs (slight growth delay) were observed.
- No progressive spongiform encephalopathy was detected.
Conclusions:
- Spiroplasma melliferum strain A56 exhibits limited neurotropism in mice.
- The initial high replication and lack of immune response mimic phenomena seen in other spiroplasma infections.
- Strain A56 is the second spiroplasma identified with the capability to multiply in both invertebrate and vertebrate hosts.