Transferrin and Staphylococcus aureus in kwashiorkor

Iron availability and infection

BACKGROUND

To successfully sustain an infection, nearly all bacteria, fungi and protozoa require a continuous supply of host iron.

METHODS

Literature review.

RESULTS

Mechanisms of microbial iron acquisition are determinants for the kinds of cells, tissues and hosts in which pathogens can flourish. As a corollary, hosts possess an array of iron withholding devices whereby they can suppress or abort microbial invasions.

GENERAL SIGNIFICANCE

Awareness of environmental and behavioral methods that can prevent iron loading plus development of pharmaceutical agents that can block microbial access to iron may help to reduce our dependence on antibiotics.

Serum C-reactive protein and C3 complement protein levels in severely malnourished Nigerian children with and without bacterial infections

Bacterial infections are the major determinants of fatality in severe protein-energy malnutrition (PEM). Unfortunately, these infections are difficult to diagnose clinically. C-reactive protein (CRP) levels were determined in 17 infected and 10 non-infected Nigerian children with severe PEM and compared with age/sex-matched apparently healthy controls. The aim was to study the response of this acute phase protein to bacterial infections as well as to assess its value in the diagnosis of infections in severe PEM. C3 complement protein levels were also determined in the same group of subjects. The major organisms isolated in samples from these subjects were S. aureus and the coliforms. Mean CRP level in the non-infected children with severe PEM was 13.8 +/- 6.21 mg/l and rose to 159.83 +/- 124.07 mg/l in the presence of infection. The mean value in healthy non-infected controls was 2.01 +/- 0.96 mg/l. The difference in the mean CRP levels between the infected and non-infected PEM children was statistically significant at p < 0.01. The mean difference between the non-infected and the control subjects was not significant. Using a diagnostic level of 20.00 mg/l of CRP gave a sensitivity of 85.0% and a specificity of 80.0%. This CRP level is a useful index of bacterial infections in severe PEM. C3 complement protein was low in the non-infected malnourished group, but rose significantly in the presence of infection to values similar to that of the healthy controls. C3 protein thus behaves as an acute phase reactant in the presence of infection in severe PEM, and does not appear to be consumed, probably due to a deficiency in the early components of the complement cascade. This suggests a role for C3 measurement in the monitoring of bacterial infections in severe PEM.

Iron, anemia, and infection

The data on the relationship between iron deficiency and infection are conflicting. Some researchers conclude that mild iron deficiency is beneficial for immunity, whereas others contend that any deficit is not good for immunity. Additionally, infection or inflammation generate anemia and profound changes in iron metabolism mediated by cytokines. These changes are important confounders to consider in assessments of iron status.

Iron and virulence in the family Enterobacteriaceae

The ability of bacterial pathogens to acquire iron in the host is an essential component of the disease process. Pathogenic Enterobacteriaceae spp. may either scavenge host iron sources such as heme or induce high-affinity iron-transport systems to remove iron from host proteins. The ease with which iron is acquired from the host will be at least partially determined by the iron status of the host at the time of infection. In response to infection, mammalian hosts reduce serum iron levels and withhold iron from the invading microorganisms. Thus the competition for iron is an active process which influences the outcome of a host-bacterial interaction.

Resistance to pesticin, storage of iron, and invasion of HeLa cells by Yersiniae

The independent abilities of Yersinia pestis to absorb exogenous pigments including hemin and Congo red (Pgm+) and to produce the bacteriocin pesticin with genetically linked invasive enzymes (Pst+) are established virulence factors of the species. Pst- Pgm+ strains of Y. pestis are sensitive to pesticin (Psts), and mutation of these isolates to pesticin resistance (Pstr) is known to result in concomitant conversion to Pgm-. Wild-type cells of Yersinia pseudotuberculosis and Yersinia enterocolitica are Pgm- but may be Psts; mutation of the latter to Pstr also results in avirulence. In this study, typical Pgm- mutants of Y. pestis exhibited a dramatic nutritional requirement at 37 degrees C but not 26 degrees C for iron which could be fulfilled by either Fe3+ or hemin. Iron privation of Pgm- yersiniae resulted in formation of osmotically stable spheroplasts similar to those previously observed after exposure of Psts bacteria to pesticin. At 37 degrees C, Pgm+ organisms rapidly overgrew initially predominant Pgm- populations in iron-deficient medium. However, Pgm-isolates could undergo a second mutation that permitted successful competition with Pgm+ cells in this environment. The mutation to Pstr in Y. pseudotuberculosis and Y. enterocolitica did not promote a similar requirement for iron but rather prevented these organisms from penetrating HeLa cells. The ability to invade these nonprofessional phagocytes was not shared by Pgm+ or Pgm- cells of Y. pestis.

Segregation distortion at the transferrin locus in Macaca mulatta

The transferrin phenotypes of 256 rhesus monkeys and their parents were identified by polyacrylamide gel electrophoresis. The segregation ratio for phenotypes involving only alleles of high electrophoretic mobility was statistically significantly higher than expected and suggests that selection favors these more negatively charged transferrins. Electrostatic-dependent processes associated with the binding and transportation of iron might be responsible for this outcome.

An other look at iron: role in host pathogen interaction

Iron, as participant of many biological processes is a prerequisite for life. Uptake, internal transport and storage by organisms is handled by highly specialized chemical systems endowed with strong metal binding affinities. Apart from the homeostatic function of iron-binding compounds they appear of significance for inter-species interactions. Thus, by tight binding transferrin withholds the iron from invading microorganisms required for their optimal growth. This bacteriostatic property of the iron transport protein is however partially overcome by small molecular substances synthesized by bacteria and successfully competing for the metal. The balance of such interaction is a complex one. Yet, strong evidence points to the crucial importance of the amount of iron offered by a host to infecting agents for determining the fate of bacterial disease.

Fatal infections in protein-calorie malnourished children with thymolymphatic atrophy

The clinicopathological features of 25 children who died with protein-calorie malnutrition were studied. All but four subjects were found at necropsy to have nutritional thymectomy and all but 3 died of infectious diseases. The infectious agents were chiefly intracellular micro-organisms including miliary tuberculosis, Herpes simplex, varicella, measles, Pneumocystis carinii, and Plasmodium falciparum. Staphylococcal infections, salmonellosis, shigellosis, strongyloidiasis, and hookworm were other significant infectious agents. Nutritionally acquired defective immunity, especially cell-mediated immunity, probably permitted these infectious agents to multiply and to disseminate widely.