Within a sufficiently large bacterial population, some members will naturally adopt an alternate, metabolically-active state that favors small molecule synthesis over cell division. These isogenic “tolerant” subpopulations have variable responses during antibiotic exposure and can remain viable in the presence of typically bactericidal concentrations. In this study, we determine the ability of typical and atypical antistaphylococcal therapies to reduce the viability of mupirocin-induced tolerant Staphylococcus aureus bacteria. Overall, tolerance-induced staphylococci exhibited a markedly decreased rate and extent of killing following antibiotic exposure. However, oritavancin remained effective at maintaining a similar extent of killing. Further studies to investigate the role of oritavancin against recurrent or relapse staphylococcal infection are warranted.
Bacteria can adapt to a changing environment by adopting alternate metabolic states favoring small molecule synthesis and resilience over growth. In Staphylococcus aureus, these states are induced by factors present during infection, including nutritional limitations, host responses and competition with other bacteria. Isogenic “tolerant” populations have variable responses to antibiotics and can remain viable. In this study, we compared the capability of antibiotics to reduce the viability of S. aureus made tolerant by different mechanisms. Tolerance was induced with mupirocin, HQNO, peroxynitrite or human serum. Tolerant cultures were exposed to ceftaroline, daptomycin, gentamicin, levofloxacin, oritavancin or vancomycin at physiological concentrations, and the viability was assessed by dilution plating. The minimum duration for 3-log viability reduction and 24 h viability reduction were calculated independently for each of three biological replicates. Each tolerance mechanism rendered at least one antibiotic ineffective, and each antibiotic was rendered ineffective by at least one mechanism of tolerance. Further studies to evaluate additional antibiotics, combination therapy and different tolerance inducers are warranted.
Background Within a sufficiently large bacterial population, some members will naturally adopt an alternate, metabolically-active state that favors small molecule synthesis over cell division. In Staphylococcus aureus this process can be sharply accelerated by multiple factors present during infection including nutrient limitation, host cationic peptide exposure and polymorphonuclear neutrophil internalization. These isogenic “tolerant” subpopulations have variable responses during antibiotic exposure and can remain viable in the presence of typically bactericidal concentrations. Survivors of antibiotic exposure can restart cell division upon cessation of antibiotics and cause relapse or recurrent infection. In this study we determine the ability of typical and atypical antistaphylococcal therapies to reduce the viability of tolerant Staphylococcus aureus bacteria. Methods S. aureus strain ATCC29213 as well as four clinical isolates (two MSSA, two MRSA) were selected for analysis. Overnight cultures were diluted in pre-warmed broth (MHB50) to 1×106 cfu/mL. Tolerance was induced by exposure to mupirocin (low [0.032 µg/mL] or high [3.2 µg/mL]) for 30 min. Tolerant cultures were exposed to vancomycin (35 µg/mL), cefazolin (25 µg/mL), daptomycin (7 µg/mL), telavancin (10 µg/mL), dalbavancin (6 µg/mL) or oritavancin (14 µg/mL) and viability was assessed by dilution plating at pre-defined time points (0, 2, 6, 24, 48 h). The minimum duration for 3-log viability reduction from baseline (MDK99.9) and culture viability at 48h were calculated independently for each of three biological replicates. Results The rate of bacterial killing (MDK99.9) was reduced for all study antibiotics by the addition of mupirocin in a dose-dependent manner. In contrast to all other regimens, including lipoglycopeptide comparators, oritavancin was the only antimicrobial agent that maintained a similar extent of bacterial killing against tolerant staphylococci. Conclusion Antimicrobial tolerant staphylococci exhibit a decreased rate of killing by antistaphylococcal agents. However, oritavancin remained effective at maintaining a similar extent of killing. Further studies to investigate the role of otritavancin against recurrent or relapse staphylococcal infection is warranted. Disclosures All Authors: No reported disclosures
Background Bacteria can adopt an alternate metabolic state favoring small molecule synthesis over growth. In Staphylococcus aureus this is induced by factors present during infection including nutritional limitation and competition with other bacteria. Isogenic “tolerant” subpopulations have variable responses to antibiotics and can remain viable. Survivors resume growth upon cessation of antibiotics and cause relapse or recurrent infection. In this study we compare the capability of antibiotics to reduce viability of S. aureus made tolerant by different mechanisms. Methods Overnight cultures of S. aureus SH1000 were diluted to 106 cfu/mL. Tolerance was induced with mupirocin or 2-n-heptyl-4-hydroxypuinoline N-oxide (HQNO) simulating nutritional or competitive tolerance, respectively. Tolerant cultures were exposed to ceftaroline, daptomycin, gentamicin, levofloxacin, oritavancin or vancomycin at physiological concentrations and viability assessed by dilution plating. Minimum duration for 3-log viability reduction (“bactericidal activity”, MDK99.9) and 24h viability reduction were calculated independently for each of three biological replicates. Significance (P < 0.05) was determined using Student’s t-test. Results Time to bactericidal activity was prolonged for all antibiotics tested against nutritionally-tolerant S. aureus. Time to bactericidal activity was similarly prolonged against competitively-tolerant S. aureus, although the MDK99.9 of oritavancin was not affected. Viability reduction was mitigated for all antibiotics tested against nutritionally-tolerant S. aureus with the exception of oritavancin. In contrast, 24h viability reduction of competitively-tolerant S. aureus only occurred with ceftaroline, gentamicin and vancomycin while daptomycin, levofloxacin and oritavancin remained equally potent. Conclusion Tolerance can alter both the time to bactericidal effect and the extent of killing. Both the antibiotic and the mechanism of tolerance impact time to bacterial effect and extent of killing. Oritavancin was the only antibiotic that maintained the same extent of killing regardless of tolerance mechanism. Further studies to evaluate additional antistaphylococcal antibiotics and different inducers of tolerance are warranted. Disclosures All Authors: No reported disclosures.
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