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Microbial Pathogenesis
Vol. 78, 2015, Pages: 103–113

Bacteroides fragilis response to subinhibitory concentrations of antimicrobials includes different morphological, physiological and virulence patterns after in vitro selection

Michele C.R. Freitas, Vânia Lúcia Silva, Jacy Gameiro, Alessandra Barbosa Ferreira-Machado, Cíntia Marques Coelho, Denise Carmona Cara, Cláudio Galuppo Diniz

Department of Parasitology, Microbiology and Immunology, Institute of Biological Sciences, Federal University of Juiz de Fora, 36036-900 Juiz de Fora, Minas Gerais, Brazil.


As antimicrobials are introduced into the environment, microorganisms may respond in different ways, sometimes displaying alterations in cellular physiology. Considering the clinical relevance of the Bacteroides fragilis, strains were selected to investigate bacterial response after exposure to subinhibitory concentrations (SIC) of ampicillin (AMP), ampicillin-sulbactam (AMS), clindamycin (CLI), chloramphenicol (CHL), and its relationship to a host model (BALB/c mice) after experimental challenge. Morphological alterations, and biochemical-physiological and genetic profiles were evaluated among drug-selected bacteria. Histopathological evaluation of the liver and spleen, and inflammatory cytokines were determined after bacterial infection in mice. AMP and AMS exposure were related to most significant cellular alterations. Decreased sensitivity to all antimicrobials was observed for all drug-selected bacteria. Down regulation in adherence properties were also observed. Spleen and liver alterations were observed in different patterns. Increased levels of TNF-α, IL-6 and IFN-γ were also observed. Our results show that SICs of AMP, AMS, CLI and CHL may be related to alterations in cell physiology in B. fragilis with implications to the host–bacteria relationship. The data emphasizes the risks of inappropriate chemotherapy, and the concerns regarding ecological consequences lead by SICs of antimicrobials in resident microbiota.

Keywords: Resident microbiota; Antimicrobial therapy; Host–bacteria relationship.

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