enterbacterales
identify members of the enterbacterales group and describe what members of this group have in common
General characteristics
gram-negative bacilli and coccobacilli
non-spore forming
facultative anaerobes
capable of fermenting glucose
oxidase negative
with the exception of plesiomonas spp.
reduce nitrates to nitrites
inhabit a wide variety of niches
including the GI tract of humans and animals and other environmental sites
Opportunistic pathogens
Citrobacter spp
inhabitants of the intestinal tract
most common infection site is the urinary tract
transmission is usually person-to-person
common pathogens include:
C. braakii
C. farmeri
C. freundii
C. koseri
Edwardsiella tarda
would infections related to aquatic incidents
causes gastroenteritis and typhoidal illness
associated with liver abscesses
Enterobacter spp.
one of the genera listed in the top 10 most commonly isolated healthcare associated infections
contaminated medical devices - respirators and other medical instruments
contaminated food and water
motile, lactose fermenter, mucoid colony appearance
common pathogens include:
E. cloacae
E. hormaechei
E. asburiae
E. cancerogenus
Hafnia alvei
resides in the GI tract of humans and many animals
gastrointestinal infections
contaminated food - meat and dairy
often isolated alongside other pathogens or opportunistic pathogens or in patients with severe underlying disease (after surgery or trauma)
motile and non-lactose fermenter
Klebsiella spp.
reside in nasopharynx and gastrointestinal tract
have a capsule, causing colonies to be very mucoid
associated with many different types of infections
liver abscesses
pneumonia
septicemia
UTIs
common pathogens include:
K. pneumoniae
indole negative
K. oxytoca
indole positive
K. ozaenae
Morganella spp
found throughout the environment and are normal flora of the GI tract
commonly found in wound, urinary tract, and GI tract infections
common pathogens include:
M. morganii subsp. morganii
M. morganii subsp. sibonii
Plesiomonas shigelloides
found in fresh water
cause gastroenteritis after ingestion of contaminated water
causes infection if open skin/mucosal surfaces are exposed
clinically similar to Aeromonas spp but are DNase negative
Proteus spp.
normal inhabitant of GI tract
often associated with UTIs, wound infections, and ear infections
also sometimes causes diarrhea and sepsis
motile, non-lactose fermenter
swarm on culture media
smells like chocolate cake or burnt chocolate
common pathogens
P. mirabilis
P. vulgaris
P. penneri
Providencia spp.
normal inhabitant of GI tract
associated with UTIs and pediatric diarrhea
motile and non-lactose fermenter
common pathogens include:
P. rettgeri
P. stuartii
P. alcalifaciens
Serratia spp.
known for colonization and the cause of pathogenic infections in health care settings
infections associated with contaminated medical devices
capable of survival under very harsh conditions
resistant to many disinfectants
common pathogens
S. marcescens (red pigment)
S. liquefaciens
S. odoriferous (smells like potatoes)
Escherichia spp.
5 species: E. albertii, E. blattae, E. fergusonii, E. vulneris, and E. coli
all species except E. blattae have been isolated from human clinical samples
Escherichia coli
normal bowel inhabitant
leading cause of Enterbacterales infections
divided into two groups:
intestinal
STEC - causes HUS
E. coli 0157:H7
ETEC - causes traveler’s diarrhea
EPEC - causes colon lesions, does not produce toxins
EAEC - causes pediatric diarrhea
extraintestinal
UPEC - causes UTIs
MNEC - causes meningitis and sepsis
Intestinal Pathogens
Salmonella spp.
intestinal pathogen
2 primary species
S. bongori (animal pathogen)
S. enterica (human pathogen)
divided into 6 subspecies - enterica most important
enterica divided further into serotypes based on different antigens or proteins produced
S. enterica subsp. enterica serotype typhi - typhoid fever
S. enterica subsp. enterica serotype enteritidis - contaminated eggs or chickens
Shigella spp.
intestinal pathogen
four subgroups
S. dysenteriae (group A)
S. flexneri (group B)
S. boydii (group C)
S. sonnei (group D)
each subgroup has several different serotypes
difficult to distinguish from E. coli
Shigellosis
watery diarrhea, fever, and abdominal cramps
dysentery with stools that contain blood or mucus
shigella dysenteriae 1 - leads to HUS
Yersinia spp.
intestinal pathogen
three species
Y. pestis
transmitted by bite of infected flea (Bubonic plague)
handling infected animals, inhaling infectious droplets, ingestion of undercooked meat
transmitted huma-to-human (Pneumonic plague)
Y. enterocolitica
found in GI tract of swine, rodents, and dogs
transmitted by ingestion of contaminated food or water
Y. pseudotuberculosis
found in rodents, birds, and rabbits
transmitted by contact with infected animals or ingestion of contaminated food and water
Rare human pathogens - all opportunistic
Budvicia spp.
Cedecea spp.
Leminorella spp.
Photohabdus spp.
Differentiate pathogens from common normal flora of the GI tract
Normal flora of GI tract includes
citrobacter spp
enterobacter spp
hafnia alvei
klebsiella spp
morganella spp
proteus spp
providencia spp
Pathogens
salmonella spp
shigella spp
yersinia spp
Inhabitants of other environments not including GI tract microflora
edwardsiella tarda - aquatic environment
hafnia alvei - also in animals
plesiomonas shigelloides - fresh water
serratia spp - human poop
escherichia spp. - bowel inhabitants
Identify common diseases caused by the organisms in this group
UTIs
citrobacter spp
klebsiella spp
morganella spp
proteus spp
providencia spp
escherichia spp
Wound infections
edwardsiella tarda
morganella spp
plesiomonas shigelloides
proteus spp
Contaminated medical devices
enterbacter spp
serratia spp
GI infections
hafnia alvei
morganella spp
plesiomonas shigelloides
Diarrhea
proteus spp
providencia spp
escherichia spp
shigella
Recognize virulence factors and how they help organisms cause disease
Klebsiella spp - have a capsule that makes them appear mucoid on plate cultures, makes them resistant to phagocytosis
Serratia spp - capable of survival under very harsh conditions, resistant to many disinfectants
Escherichia spp - toxin production
Identify and interpret common biochemical tests used to differentiate these organisms
Cultivation in the laboratory
media
routine agar - 5% SBA, chocolate, and MAC
other selective agar - HE, XLD, CHROMagar used specifically for cultivation of enteric pathogens from GI
broths - thioglycolate or BHI
growth within 24 hours
incubation conditions
5% CO2 or anaerobic
35C
exception: yersinia pestis (25-30C)
colonial appearance
chocolate and SBA - large, gray smooth
mucoid - klebsiella and enterbacter
non-hemolytic
exceptions: E. coli can be beta hemolytic
swarming - proteus
Identified using more than 50 biochemical tests - includes:
IMViC
TSI
LIA
oxidase negative
except plesiomonas spp
Describe how these organisms enter the body to cause disease
Epidemiology
patient’s own bacterial strains establish infection in a normally sterile body site
ingestion of contaminated food or water
animals
yersinia pestis
Pathogenesis
clinically relevant members can be divided into two groups:
intestinal pathogens
always identified as clinically significant
produce various potent virulence factors and can cause life-threatening infections
includes Salmonella typhi and Shigella spp.
opportunistic pathogens
can also produce significant virulence factors
generally, do not initiate disease in healthy, uncompromised human hosts
citrobacter, enterbacter, klebsiella