B. abortus ahpC mutants exhibit increased levels of endogenous peroxides. The levels of endogenous peroxides present in B. abortus 2308, KH16 (2308 ahpCD), KH2 (2308 katE), KK21 (2308 ahpCD katE), KH16 (pMWV77), and KH16 (pMEK21) cell suspensions following aerobic cultivation were determined using a xylenol orange/ferrous iron-based hydrogen peroxide assay (73). The data presented are means and standard deviations for triplicate determinations for a single strain in a single experiment. The data presented here are representative of multiple (≥6) experiments performed from which equivalent results and statistical trends were obtained. Statistical significance (P ≤ 0.05) as determined by the Student two-tailed t test for the comparison of 2308 versus the other strains is represented by an asterisk (*).