Two-dimensional gel electrophoretic analysis of cell lysates from Brucella abortus 2308 and the isogenic hfq mutant Hfq3 revealed that the RNA binding protein Hfq (also known as host factor I or HF-I) is required for the optimal stationary phase production of the periplasmic Cu,Zn superoxide dismutase SodC. An isogenic sodC mutant, designated MEK2, was constructed from B. abortus 2308 by gene replacement, and the sodC mutant exhibited much greater susceptibility to killing by O 2 ؊ generated by pyrogallol and the xanthine oxidase reaction than the parental 2308 strain supporting a role for SodC in protecting this bacterium from O 2 ؊ of exogenous origin. The B. abortus sodC mutant was also found to be much more sensitive to killing by cultured resident peritoneal macrophages from C57BL6J mice than 2308, and the attenuation displayed by MEK2 in cultured murine macrophages was enhanced when these phagocytes were treated with gamma interferon (IFN-␥). The attenuation displayed by the B. abortus sodC mutant in both resting and IFN-␥-activated macrophages was alleviated, however, when these host cells were treated with the NADPH oxidase inhibitor apocynin. Consistent with its increased susceptibility to killing by cultured murine macrophages, the B. abortus sodC mutant also displayed significant attenuation in experimentally infected C57BL6J mice compared to the parental strain. These experimental findings indicate that SodC protects B. abortus 2308 from the respiratory burst of host macrophages. They also suggest that reduced SodC levels may contribute to the attenuation displayed by the B. abortus hfq mutant Hfq3 in the mouse model.The Brucella spp. are gram-negative facultative intracellular pathogens capable of infecting a wide variety of mammalian hosts. Brucella abortus is the etiological agent of bovine brucellosis, an infection that leads to spontaneous abortion and infertility (10). Human brucellosis presents as a debilitating febrile illness commonly referred to as Malta Fever or undulant fever (59), and an active infection is characterized by fever, malaise, chills, night sweats, and anorexia. Human brucellosis is a zoonotic disease; therefore, the incidence of disease in humans is directly related to its occurrence in animals (43). Although considered mainly an occupational hazard in many countries, human brucellosis remains a significant problem where the disease is endemic in food animals and raw milk or other unpasteurized dairy products are still consumed.Brucella spp. are not found free living, nor are they commensal organisms (23). The preferred ecological niche for the brucellae is within the phagosomal compartment of host macrophages, and the capacity of this organism to establish and maintain chronic infections is dependent upon its ability to survive and replicate within these phagocytic cells (48). Experimental evidence indicates that the production of reactive oxygen intermediates (ROIs) represents one of the primary mechanisms utilized by host macrophages for limiting the intracellular replic...

SummaryMembers of the bacterial genus Brucella are facultative intracellular pathogens that reside predominantly within membrane-bound compartments within two host cell types, macrophages and placental trophoblasts. Within macrophages, the brucellae route themselves to an intracellular compartment that is favourable for survival and replication, and they also appear to be well-adapted from a physiological standpoint to withstand the environmental conditions encountered during prolonged residence in this intracellular niche. Much less is known about the interactions of the Brucella with placental trophoblasts, but experimental evidence suggests that these bacteria use an iron acquisition system to support extensive intracellular replication within these host cells that is not required for survival and replication in host macrophages. Thus, it appears that the brucellae rely upon the products of distinct subsets of genes to adapt successfully to the environmental conditions encountered within the two cell types within which they reside in their mammalian hosts.

A gene encoding superoxide dismutase (SOD), sodM, from S. aureus was cloned and characterized. The deduced amino acid sequence specifies a 187-amino-acid protein with 75% identity to the S. aureus SodA protein. Amino acid sequence comparisons with known SODs and relative insensitivity to hydrogen peroxide and potassium cyanide indicate that SodM most likely uses manganese (Mn) as a cofactor. The sodM gene expressed from a plasmid rescued an Escherichia coli double mutant (sodA sodB) under conditions that are otherwise lethal. SOD activity gels of S. aureus RN6390 whole-cell lysates revealed three closely migrating bands of activity. The two upper bands were absent in a sodM mutant, while the two lower bands were absent in a sodA mutant. Thus, the middle band of activity most likely represents a SodM-SodA hybrid protein. All three bands of activity increased as highly aerated cultures entered the late exponential phase of growth, SodM more so than SodA. Viability of the sodA and sodM sodA mutants but not the sodM mutant was drastically reduced under oxidative stress conditions generated by methyl viologen (MV) added during the early exponential phase of growth. However, only the viability of the sodM sodA mutant was reduced when MV was added during the late exponential and stationary phases of growth. These data indicate that while SodA may be the major SOD activity in S. aureus throughout all stages of growth, SodM, under oxidative stress, becomes a major source of activity during the late exponential and stationary phases of growth such that viability and growth of an S. aureus sodA mutant are maintained.Staphylococcus aureus is a gram-positive facultative anaerobe that typically resides on the skin and mucous membranes of approximately 30% of healthy individuals and up to 90% of health care workers (42). Therefore, it is not surprising that of the estimated 2 million hospitalizations each year that result in a nosocomial infection, S. aureus is one of the most common causative agents (5, 15). S. aureus has the capacity to produce more than 30 secreted proteins in the form of enzymes, immunotoxins, and cytotoxins and numerous cell surface-associated factors that promote adherence to various tissues and prevent attack by the host's defenses (17, 36). Consequently, S. aureus causes numerous different kinds of infections, ranging from skin abscesses to life-threatening endocarditis, meningitis, and pneumonia as well as toxemias such as scalded skin and toxic shock syndromes (42).The skin and mucous membranes serve as the primary line of defense against infection by S. aureus (41). However, when this organism is introduced into the underlying tissues, the primary defense mechanism is the professional phagocyte (41). Polymorphonuclear leukocytes and macrophages use toxic reactive oxygen intermediates such as superoxide and hydrogen peroxide to aid in the killing of phagocytized bacteria (11,22,35). In addition, these same oxygen species are produced during aerobic respiration and have the potential to damage DNA, p...

The gene designated BAB1_1460 in the Brucella abortus 2308 genome sequence is predicted to encode the manganese transporter MntH. Phenotypic analysis of an isogenic mntH mutant indicates that MntH is the sole high-affinity manganese transporter in this bacterium but that MntH does not play a detectable role in the transport of Fe 2؉ , Zn 2؉ , Co 2؉ , or Ni 2؉ . Consistent with the apparent selectivity of the corresponding gene product, the expression of the mntH gene in B. abortus 2308 is repressed by Mn 2؉ , but not Fe 2؉ , and this Mn-responsive expression is mediated by a Mur-like repressor. The B. abortus mntH mutant MWV15 exhibits increased susceptibility to oxidative killing in vitro compared to strain 2308, and a comparative analysis of the superoxide dismutase activities present in these two strains indicates that the parental strain requires MntH in order to make wild-type levels of its manganese superoxide dismutase SodA. The B. abortus mntH mutant also exhibits extreme attenuation in both cultured murine macrophages and experimentally infected C57BL/6 mice. These experimental findings indicate that Mn 2؉ transport mediated by MntH plays an important role in the physiology of B. abortus 2308, particularly during its intracellular survival and replication in the host.Brucella abortus is a gram-negative bacterium that is responsible for the zoonotic disease brucellosis. Brucellosis causes spontaneous abortion and sterility in ruminants (27) and a debilitating febrile illness in humans known as undulant fever (17). The ability of brucellae to cause disease is directly related to their capacity to establish and maintain intracellular infection in host macrophages (63). Within the phagosomal compartment in these host cells, brucellae must cope with oxidative stress, low pH, and nutrient deprivation. The availability of metal ions is restricted within this environment due in part to the activity of the host natural resistance-associated macrophage protein (NRAMP-1), which transports divalent cations out of the phagosome (40). Mn 2ϩ serves as an important cofactor for a variety of bacterial enzymes, including those involved in carbon metabolism, induction of the stringent response, and detoxification of reactive oxygen species (ROS) (55). Consequently, the inability of brucellae to acquire sufficient levels of this divalent cation may compromise their ability to successfully adapt to the environmental conditions encountered during residence in their intracellular niche.Manganese uptake by bacteria is typically accomplished through the activity of either ABC-type transporters such as the SitABC complex (4, 42, 59, 65) or H ϩ -dependent manganese transporters such as MntH (37, 41, 52, 60). Many bacteria possess both types of Mn 2ϩ transporters (55), but a survey of the publicly available Brucella genome sequences (14,20,36,57) suggests that these bacteria do not produce a SitABC-type transporter and rely solely on an MntH homolog for the highaffinity transport of Mn 2ϩ . Escherichia coli MntH was originally des...

Brucella abortus 2308 derivatives with mini-Tn5 insertions in purE, purL, and purD display significant attenuation in the BALB/c mouse model, while isogenic mutants with mini-Tn5 insertions in pheA, trpB, and dagA display little or no attenuation in cultured murine macrophages or mice. These experimental findings confirm the importance of the purine biosynthesis pathways for the survival and replication of the brucellae in host macrophages. In contrast to previous reports, however, these results indicate that exogenous tryptophan and phenylalanine are available for use by the brucellae in the phagosomal compartment.Brucella abortus is a facultative, gram-negative pathogen of humans and animals that inhabits macrophages (2). The capacity to withstand nutritional deprivation would be expected to be particularly important for the survival of B. abortus, since this organism does not escape from the phagosome into the nutrient-rich environment of the host cell cytoplasm (2). Indeed, previous studies suggest that the brucellae encounter a considerable degree of nutritional deprivation during their long-term residence in host macrophages. Brucella melitensis purE (5) and Brucella suis aroC (12) mutants, for example, are unable to maintain chronic infection in experimentally infected mice, and the attenuation of the B. melitensis purE mutant purE201 extends to the natural ruminant host (4) and nonhuman primates (M. Nikolich, personal communication). These observations are also consistent with those seen with auxotrophic mutants of Salmonella and Mycobacterium and indicate that the availability of certain nutrients is severely restricted in the phagosomal compartment of host macrophages (3,11,22).In an effort to gain a better understanding of the metabolic versatility required for sustained intracellular residence by the brucellae in host macrophages, transposon mutagenesis and an in vitro screen were employed to identify B. abortus 2308 derivatives with mini-Tn5 insertions in genes required for resistance to nutrient deprivation. Transposon mutagenesis of this strain was performed by conjugative transfer of the mini-Tn5 derivative Km1 by employing pUT as the delivery vector and Escherichia coli S17-1pir as the conjugal donor strain (6,14,28). Approximately 1,000 B. abortus mini-Tn5 mutants were patched with sterile toothpicks onto Schaedler agar supplemented with 5% defibrinated bovine blood (SBA), SBA supplemented with 45 g of kanamycin/ml (SBAk), and Gerhardt's minimal medium (13) supplemented with 1.5% agar (GMMA). Plates were incubated at 37°C with 5% CO 2 and examined for growth after 4, 7, and 10 days of incubation. Schaedler agar, the basal medium for SBA, is a complex culture medium containing enzymatic digests of casein, animal and plant tissues, yeast extract, glucose, cystine, and hemin (Difco manual, 10th ed., Difco Laboratories, Detroit, Mich.). In contrast, GMM, the base for GMMA, is a defined medium formulated during a study aimed at defining the minimal in vitro growth requirements of Brucella strains (1...