Micorbiology SOLO 4

Cytochrome oxidase

• blue coloration is positive

• all Enterobacteriales are negative

Voges-Proskaur (acetoin production)

• determine abilities to produce and maintain stable acid end products from glucose fermentation

• detects ability to convert acid products to acetoin and 2,3-butanediol

Nitrate reductase

• nitrate is reduced to nitrite

• majority of Enterobacteriales can reduce nitrate to nitrite

Phenylalanine Deaminase

important ID of the Protease tribe

Hydrogen sulfide

Sodium thiosulfate is reduced to H2S which reacts with lead acetate to produce a black lead sulfide precipitate

Indole production substrate

tryptophane

Ornithine decarboxylase

decarboxylated to putrescine

Lysine decarboxylase

decarboxylated to cadaverine

Urease

urea and water are hydrolyzed to ammonia and CO2

ONPG

determines whether an organism can utilize lactose

Citrate utilization

growth without a color change or a color change from green to blue is considered positive

DNase

test used for the genus Serratia

Triple Sugar Iron Agar (TSIA)

contains glucose, lactose, and sucrose

Iron Agar (KIA)

contains glucose and lactose

What happens with an H2S producer on TSIA or KIA?

it will mask the results by turning the agar black

What media should be used with H2S producers?

O-F media

What does a reaction on TSIA or KIA look like?

• yellow coloration for positive

• red coloration for negative

Citrobacter, Morganella, Proteus, Providencia, Salmonella, Serratia, Shigella tube TSIA reaction

• K/A

• glucose fermenter, lactose neagtive

Enterobacter, Escherichia, Klebsiella TSIA tube reaction

• A/A

• Glucose and lactose fermenter

Enterobacteriales general characteristics

• capable of fermenting glucose

• oxidase negative

  • except Plesiomonas

• reduce nitrates into nitrites

• catalase positive

  • except Shigella dysenteriae

Enterobacteriales antigens

• O antigen

  • heat stable, somatic antigens, react with biochemicals

• K antigen

  • heat labile, capsular antigens

• H antigen

  • heat labile, flagellar antigens

For negative reactions that should be positive for a particular organsism:

• heat the substance then retest

• takes away the K and H antigens

Escherichia coli virulence factors

• endotoxins

• capsule production

• pili

spectrum of disease for Escherichia coli

most common cause of health-care associated infections

Pathogenic strains of E.coli are grouped into what two groups?

• intestinal (diarrheagenic)

• extraintestinal

Two categories of extraintestinal Escherichia coli?

• uropathogenic E. coli (UPEC)

• Meningitis/sepsis associated E.coli (MNEC)

  • causes neonatal meningitis

Intestinal Escherichia coli strains

• STEC

• ETEC

• EIEC

• EPEC

• EAEC

Serotoxigenic E. coli

• cause of hemolytic uremic syndrome

• no WBC in stool (unlike dysentery)

• most common strain is O157:H7

• toxin similar to shiga toxin

• transmitted by undercooked ground beef or raw milk

Enterotoxigenic E. coli

• produces a heat-labile enterotoxin (LT) and a heat-stable enterotoxin

• associated with traveler’s diarrhea

Enteroinvasive E. coli

• may produce a watery/bloody diarrhea as a result of direct invasion of the epithelial cells

• can cause dysentery

Enteropathogenic E. coli

• does not produce toxins

• associated with attachment and effacement

Enteroaggregative E. coli

virulence genes associated with a global aggregative regulator gene AggR is responsible for cellular adherence

Shigella species habitat

not part of normal microbiota

Shigella groups

• S. dysenteriae

• S. flexneri

• S. boydii

• S. sonnei (most common)

Shigella sp. main virulence factor

Shiga toxin

Shigellosis

• watery diarrhea with fever and ab cramps

• progressive infection then leads to dysentery with bloody, mucoid stools

All Shigella species can cause?

Dysentery

Edwardsiella tarda

• found in the GI tract of fish, animals, and humans

• immunocompromised individuals are more susceptible

Klebsiella species

• normal microbiota

• all resistant to ampicillin

• associated with liver abscesses

• wet or mucoid lactose fermenters

• K. pneumoniae

• K. ozaenae

• K. oxytoca

• K. aerogenes

Enterobacter species

• capsule layer

• common HAI

• can have plasmids that can encode multiple antibiotic resistant genes

Pantoea species

• associated with traumatic injury from objects contaminated with soil

• P. agglomerans

Serratia species

• resistant to ampicillin and first-gen cephalosporins

• resistance from AmpC beta-lactamase

• prodigiosin pigment

Plesiomonas shigelloides

• associated with food and water-borne illness

• acute watery diarrhea to dysentery like diarhea

• TSIA K/A

• Oxidase positive

Proteus species

• assocoaited with UTIs

• “swarming” morphology

• strong “chocolate” smell

Morganella morganii

• found throughout environment and normal GI microbiota

• typically Beta-hemolytic

Salmonella enterica serotypes are differentiated by…

O, H, and Vi antigen

Primary Salmonella species

• S. enterica (human)

• S. bongori (animal)

Salmonella typhi

• only found in humans but NOT part of normal microbiota

• fecal oral route transmission

• associated with typhoid fever

Salmonella enteritidis

• acquired from ingestion of eggs and chicken

• salmonella associated gastroenteritis

Salmonella species appear as what on XLD?

black colonies

Citrobacter freundii

• may show AmpC genes

  • encode resistance to ampicillin and first generation cephalosporins

• distinct terrible odor

Virulence factors for Citrobacter, Enterobacter, Klebsiella, Morganella, Proteus, Providencia, and Serratia species

• endotoxins

• capsules

• adhesion proteins

• resistance to mutliple antimicrobial agents

Extended spectrum beta-lactamases

able to hydrolyze penicillins and cephalosporins (1-4) due to AmpC

Carbapenem resistant enterobacteriales

Produce Carbapenemase and resistant to Carbapenems and Cephlosporins

therapeutic options for Enterobacteriales (except Yersinia)

• aminoglycosides

• beta-lactams

• quinolones

Yersinia enterocolitica

• not part of normal microbita

• transmitted from improperly cooked food, ESP PORK

• causes enterocolitis

  • can cause mesenteric lymphadenitis

  • pseudoappendicular syndrome

Identification of Yersinia enterocolitica

• Bull’s eye colony

• indole positive

• oxidase negative

• catalase positive

• urea positive

• non-lactose fermenting

• optimal temp 25C

Yersinia pestis

• transmitted by bite of a flea

• bubonic plague

  • buboes swelling

• pneumonic plague

identification of Yersinia pestis

• bipolar, safety pin, gram stain

• indole negative

• oxidase negative

• catalase positive

• urea negative

• non lactose fermenting

• optimal temp 25C

Antimicrobial therapy for Yersinia pestis

• Streptomycin (choice)

• tetracycline

• chloramphenicol

Antimicrobial therapy for other Yersinia species

• Fluoroquinolones (choice)

• cephalosporins NOT used

Acinetobacter species and Stenotrophomonas maltophilia are…

• non fermenting

• third and fourth most common GNR in clinical specimens

• able to survive on inanimate objects for weeks to months

• often multidrug resistant

• saccharolytic or asaccharolytic

• present in moist hospital environments

Acinetobacter species major virulence factor

lipopolysaccharide capsule production

identification of Acinetobacter baumanii

• non-glucose/lactose fermenter

• K/K

• glucose oxidizer (saccharolytic)

• oxidase negative

• does NOT oxidize MALTOSE

identification of Acinetobacter lwoffii

• non glucose/lactose fermenter

• K/K

• non-oxidizer (asaccharolytic)

• oxidase engative

• variable maltose

Stenotrophomonas maltophilia spectrum of disease

nosocomial infections

identification of Stenotrophomonas maltophilia

• kavender-green to light purple pigment

• non glucose/lactose fermenter

• K/K

• delayed oxidizer of glucose

• oxidase negative

• oxidizes maltose

• Lysine positive

Antimicrobial susceptibility for Acinetobacter species

• acquire antibiotic resistant enzymes such as beta-lactamase and metallo-beta-lactamases

  • metallo-beta-lactamases code for carbapenem resistance

• commonly referred to as Multi-Drug Resistant Organism (MDRO)

• Polymyxins, minocycline, or tigecycline main therapeutic options

Antimicrobial susceptibility for Stenotrophomonas maltophilia

• high intrinsic resistance

• trimethoprim-sulfamethoxazole (choice)

• minocycline and levofloxacin other choices