In Vitro Susceptibilities of 27 Rickettsiae to 13 Antimicrobials

Abstract

The MICs of 13 antibiotics (doxycycline, thiamphenicol, rifampin, amoxicillin, gentamicin, co-trimoxazole, ciprofloxacin, pefloxacin, ofloxacin, erythromycin, josamycin, clarithromycin, and pristinamycin) were determined for 27 available rickettsial species or strains. We used two in vitro cell culture methods described previously: the plaque assay and the microplaque colorimetric assay. Our results confirm the susceptibilities of rickettsiae to doxycycline, thiamphenicol, and fluoroquinolones. Beta-lactams, aminoglycosides, and co-trimoxazole were not active. Typhus group rickettsiae were susceptible to all macrolides tested, whereas the spotted fever group rickettsiae,R. bellii, and R. canada were more resistant, with josamycin, a safe alternative for the treatment of Mediterranean spotted fever, being the most effective compound. Strain Bar 29,R. massiliae, R. montana, R. aeschlimannii, and R. rhipicephali, which are members of the same phylogenetic subgroup, were more resistant to rifampin than the other rickettsiae tested. Heterogeneity in susceptibility to rifampin, which we report for the first time, may explain in vivo discrepancies in the effectiveness of this antibiotic for the treatment of rickettsial diseases. We hypothesize that rifampin resistance and erythromycin susceptibility may reflect a divergence during the evolution of rickettsiae.

A bioinformatic approach to understanding antibiotic resistance in intracellular bacteria through whole genome analysis

“…Rickettsia are naturally resistant to ␤-lactams, aminoglycosides and co-trimoxazole. The typhus group is susceptible to erythromycin, whereas the spotted fever group is not [19,20] (Table 1). …”

“…In the majority of rifampicin-resistant isolates, mutations occurred within an 81-bp hotspot region (the rifampicin resistance-determining region (RRDR), codons 507-533 according to E. coli numbering) in the rpoB gene [4,107]. Previously, Rolain et al [19] found that susceptibility to rifampicin varied, with R. prowazekii, R. typhi, Rickettsia canada, Rickettsia bellii and most SFG rickettsiae being susceptible to rifampicin, whilst the Rickettsia massiliae subgroup (R. massiliae, Rickettsia montana, Rickettsia rhipicephalus and Rickettsia aeschlimannii) were more resistant to rifampicin. Drancourt and Raoult [108] investigated the genetic basis for natural rifampicin resistance in representatives of the TG and the two SFG subgroups of rickettsiae by sequence analysis of the rpoB gene.…”

“…holarctica, with biovar I being erythromycin sensitive and biovar II being erythromycin resistant [19]. The molecular mechanisms of resistance to erythromycin are not known, but alignment of domain V of the 23S rRNA using in silico methods showed an A → C transition at position 2059 (E. coli numbering) in one F. tularensis genome (F. tularensis subsp.…”

Statins limit Rickettsia conorii infection in cells

“…Lovastatin and pravastatin were purchased from Sigma-Aldrich (Saint-Quentin Fallavier, France) [7]. Lovastatin was hydrolysed as described elsewhere [8] and a stock solution (1 g/L) was stored at −20 • C until use.…”

Durch Zecken übertragene humanpathogene und bisher als apathogen geltende Mikroorganismen in Europa

“…Auch Fluoroquinolone und Makrolide (insbesondere Josamycin) haben nach verschiedenen Studien eine gute Wirksamkeit [83]. Eine Eindosistherapie mit 200 mg Doxycyclin hat sich für die Therapie des epidemischen Fleckfiebers in Afrika bewährt [74].…”