title: Loss of Multicellular Behavior in Epidemic African Nontyphoidal Salmonella enterica Serovar Typhimurium ST313 Strain D23580.
abstract: Nontyphoidal Salmonella enterica serovar Typhimurium is a frequent cause of bloodstream infections in children and HIV-infected adults in sub-Saharan Africa. Most isolates from African patients with bacteremia belong to a single sequence type, ST313, which is genetically distinct from gastroenteritis-associated ST19 strains, such as 14028s and SL1344. Some studies suggest that the rapid spread of ST313 across sub-Saharan Africa has been facilitated by anthroponotic (person-to-person) transmission, eliminating the need for Salmonella survival outside the host. While these studies have not ruled out zoonotic or other means of transmission, the anthroponotic hypothesis is supported by evidence of extensive genomic decay, a hallmark of host adaptation, in the sequenced ST313 strain D23580. We have identified and demonstrated 2 loss-of-function mutations in D23580, not present in the ST19 strain 14028s, that impair multicellular stress resistance associated with survival outside the host. These mutations result in inactivation of the KatE stationary-phase catalase that protects high-density bacterial communities from oxidative stress and the BcsG cellulose biosynthetic enzyme required for the RDAR (red, dry, and rough) colonial phenotype. However, we found that like 14028s, D23580 is able to elicit an acute inflammatory response and cause enteritis in mice and rhesus macaque monkeys. Collectively, these observations suggest that African S. Typhimurium ST313 strain D23580 is becoming adapted to an anthroponotic mode of transmission while retaining the ability to infect and cause enteritis in multiple host species.
  
  
  OBJECTIVE
  The last 3 decades have witnessed an epidemic of invasive nontyphoidal Salmonella infections in sub-Saharan Africa. Genomic analysis and clinical observations suggest that the Salmonella strains responsible for these infections are evolving to become more typhoid-like with regard to patterns of transmission and virulence. This study shows that a prototypical African nontyphoidal Salmonella strain has lost traits required for environmental stress resistance, consistent with an adaptation to a human-to-human mode of transmission. However, in contrast to predictions, the strain remains capable of causing acute inflammation in the mammalian intestine. This suggests that the systemic clinical presentation of invasive nontyphoidal Salmonella infections in Africa reflects the immune status of infected hosts rather than intrinsic differences in the virulence of African Salmonella strains. Our study provides important new insights into the evolution of host adaptation in bacterial pathogens.
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle, Washington, USA.
authors.forename: Larissa A
authors.initials: LA
authors.lastname: Singletary
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle, Washington, USA.
authors.forename: Joyce E
authors.initials: JE
authors.lastname: Karlinsey
authors.affiliation: Department of Laboratory Medicine, School of Medicine, University of Washington, Seattle, Washington, USA.
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Libby
authors.affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, Davis, California, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Mooney
authors.affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, Davis, California, USA.
authors.forename: Kristen L
authors.initials: KL
authors.lastname: Lokken
authors.affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, Davis, California, USA.
authors.forename: Renée M
authors.initials: RM
authors.lastname: Tsolis
authors.affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, Davis, California, USA.
authors.forename: Mariana X
authors.initials: MX
authors.lastname: Byndloss
authors.affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, Davis, California, USA.
authors.forename: Lauren A
authors.initials: LA
authors.lastname: Hirao
authors.affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, Davis, California, USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Gaulke
authors.affiliation: Department of Biological Sciences, California State University Sacramento, Sacramento, California, USA.
authors.forename: Robert W
authors.initials: RW
authors.lastname: Crawford
authors.affiliation: Department of Medical Microbiology and Immunology, School of Medicine, University of California at Davis, Davis, California, USA.
authors.forename: Satya
authors.initials: S
authors.lastname: Dandekar
authors.affiliation: Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, United Kingdom Institute of Food Research, Norwich Research Park, Norwich, Norfolk, United Kingdom.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kingsley
authors.affiliation: Malawi-Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi.
authors.forename: Chisomo L
authors.initials: CL
authors.lastname: Msefula
authors.affiliation: Malawi-Liverpool Wellcome Trust Clinical Research Programme, College of Medicine, University of Malawi, Blantyre, Malawi Division of Infection and Immunity, University College London, London, United Kingdom.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Heyderman
authors.affiliation: Department of Microbiology, School of Medicine, University of Washington, Seattle, Washington, USA Department of Laboratory Medicine, School of Medicine, University of Washington, Seattle, Washington, USA fcfang@uw.edu.
authors.forename: Ferric C
authors.initials: FC
authors.lastname: Fang
mesh_terms: D000220:Adaptation, Biological; D017954:Africa South of the Sahara / Q000453:epidemiology; D000818:Animals; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D004195:Disease Models, Animal; D058872:Epidemics; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008253:Macaca mulatta; D051379:Mice; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D012480:Salmonella Infections / Q000453:epidemiology / Q000382:microbiology*; D012486:Salmonella typhimurium / Q000201:enzymology* / Q000235:genetics / Q000302:isolation & purification / Q000502:physiology*; D013312:Stress, Physiological
chemical_list: D050505:Mutant Proteins; D002374:Catalase; D005964:Glucosyltransferases; C478648:cellulose synthase