CHAO C, THOMPSON CM, MALLEY R, VILHELMSSON SE, KRISTINSSON K, LIPSITCH M; Interscience Conference on Antimicrobial Agents and Chemotherapy (41st : 2001 : Chicago, Ill.).
Abstr Intersci Conf Antimicrob Agents Chemother Intersci Conf Antimicrob Agents Chemother. 2001 Dec 16-19; 41: abstract no. C1-654.
Harvard Sch Publ Hlth, Boston, MA
BACKGROUND: Rates of decline of resistance following interventions (eg reduced antibiotic use) are expected to depend on the ``fitness burden of resistant bacteria relative to susceptible strains in untreated hosts. METHODS: 4 clinical isolates from the Icelandic 6B multiresistant clone (J Clin Micriobiol 38:1475, 2000) were used. 2 resistant (R) strains (I176 and I460) had, and 2 susceptible (S) strains (I210 and I434) lacked a 25 kbp tet-ery ct. Apart from the ct, these strains were identical by pulsed-field typing. Additional R strains were made by conjugative transfer of the ct into previously S pneumococcal strains. We measured the effect of the ery-tet ct on competitive ability (``fitness) by intranasally inoculating a 10:1 mix of otherwise isogenic (S:R) pneumococci into untreated infant rats and daily estimating the S:R ratio by selective plating of nasal washes. Virulence was measured as 50% bacteremic dose in intraperitoneally injected infant rats. RESULTS: I176 showed no decline or a slight increase in frequency relative to both S strains, while I460 declined relative to both S strains. R transconjugants of various pneumococcal strains showed fitness costs ranging from 0 to 1.8 log10/week compared to their S parents. Most S:R pairs did not differ measurably in virulence, and in one strain where the ct reduced virulence, intranasal fitness was unaffected. Ongoing work will determine ct integration sites to identify possible gene interruptions affecting fitness and virulence. CONCLUSION: Carriage of a tet-ery-R ct exacts a fitness cost in some but not all strains; natural selection will favor those strains with lowest fitness cost. Reductions in the prevalence of resistance at the population level may be difficult to achieve if fitness costs are low or zero.
Publication Types:
Keywords:
- Animals
- Anti-Bacterial Agents
- Erythromycin
- Humans
- Infant
- Pneumococcal Vaccines
- Rats
- Streptococcus pneumoniae
- Tetracycline
- Tetracycline Resistance
- Virulence
Other ID:
UI: 102270585
From Meeting Abstracts