aerobic gram-positive cocci and rods

Aerobic gram-positive cocci

• Staphylococcus spp

  • found on skin and mucous membranes

  • gram stain: gram-positive cocci in pairs, tetrads, and grape-like clusters

  • catalase positive

  • hemolysis varies

  • facultative anaerobe

  • Coagulase negative Staphylococcus (CNS)

    • includes: S. epidermidis, S. saprophyticus, S. lugdunensis, S. hominis, and S. intermedias

      • usually do not need to speciate

    • all have potential to cause infections but are also normal skin flora

    • usually white/gray, non-hemolytic colonies

    • catalase positive

    • staph latex negative

    • S. saprophyticus is resistant to novobiocin

  • Staphylococcus aureus

    • large white/yellow beta hemolytic colonies

    • catalase positive

    • staph latex positive

    • most are resistant to penicillin

    • causes: skin lesions, abscesses, pneumonia, septicemias, wound infections, UTIs, TSS, and impetigo

      • MRSA= Methicillin resistant staph aureus

        • infection control concern

• Rothia (Stomatococcus)

  • normal oral flora

  • looks like CNS

  • has a capsule that makes colonies stick to agar

    • known as “sticky-staph”

  • catalase negative/ weak positive

  • no growth in 5% NaCl

• Micrococcus

  • very yellow colonies, takes up to 48 hours for good growth

  • catalase positive

  • bacitracin sensitive

  • can sometimes be pathogenic in a susceptible host

  • less virulent than staph

• Streptococcus spp

  • gram stain: gram-positive cocci in chains

  • facultative anaerobe

  • catalase negative

  • Lancefield serotyping

  • Viridans Strep

    • lab tests:

      • alpha hemolytic

      • catalase negative

      • optochin disk resistant

      • PYR negative

    • usually do not need to speciate, normal flora of oral cavity and respiratory tract, opportunistic pathogens

    • includes Streptococcus anginosus

  • Streptococcus pneumoniae

    • gram stain: gram-positive lancet shaped cocci

    • alpha hemolytic, gray colonies that look like an upside-down bottle cap

    • lab tests:

      • optochin sensitive

      • bile soluble

      • 6.5% NaCl

      • SF and PYR negative

      • quelling reaction

        • antibody-antigen reaction seen by swelling of capsule

    • causes septicemia, ear infections, and pneumonia

  • Streptococcus pyogenes (Type A)

    • small translucent colonies, large zone of beta hemolysis

    • lab tests:

      • catalase negative

      • bacitracin sensitive

      • 6.5% NaCl negative

      • CAMP negative

      • SF negative

      • grows on SXT

    • most are susceptible to penicillin

    • causes pharyngitis, scarlet fever, cellulitis, and impetigo

    • if left untreated, causes rheumatic fever and glomerulonephritis

  • Streptococcus agalactiae (Type B)

    • larger translucent colonies with a small zone of hemolysis

    • lab tests:

      • catalase negative

      • bile esculin

      • PYR and SF negative

      • CAMP positive

      • bacitracin resistant

    • Most common cause of neonatal sepsis

      • does not cross placenta

  • Other Beta Streptococcus (not A or B)

    • small colonies: usually A, C, G, F

    • large colonies: usually C or G

    • S. anginosus is most common

    • lab tests:

      • catalase negative

      • bacitracin resistant

      • bile esculin

      • PYR, Hippurate, and SF negative

  • Enterococcus spp (Type D)

    • opaque, gray colonies, can have any kind of hemolysis

    • lab tests:

      • catalase can be variable, should be negative

      • PYR positive, bile esculin and SF positive

    • motile strains are resistant to vancomycin

    • normal fecal flora

      • E. faecalis, E. faecium, E. avium, and E. durans

    • causes UTIs, wound infections, septicemia, and nosocomial infections

    • resistant to many antibiotics

      • VRE= super infections

  • Group D Streptococcus

    • white/gray alpha or gamma hemolytic colonies

    • lab tests:

      • catalase negative

      • bile esculin positive

      • PYR and SF negative

      • cannot grow in high salt concentrations

    • normal fecal flora

    • causes UTIs, wound infections, endocarditis, sepsis

      • S. bovis/galactoliticus septicemia can indicate loss of GI mucosal integrity

  • Nutritionally deficient/variant Strep

    • “Satelliting strep”

      • does not grow on sheep blood agar, but can satellite with staph streak

      • some can grow on chocolate

      • can grow in liquid media

    • requires vitamin B6 and pyridoxine

• Aerococcus spp - A. urinae and A. viridans

  • strep like organism found in the environment

  • causes opportunistic infections

  • gram stain: gram-positive cocci in tetrads

    • can be confused with viridans strep or enterococcus spp

  • A. urinae = LAP positive, PYR negative

  • A. viridans = LAP negative, PYR positive

• Gamella spp - G. haemolysans and G. morbillorum

  • gram stain: gram-positive cocci that can look like diplococci

    • similar appearance to viridans strep

  • normal flora of mouth and respiratory tract

  • can cause endocarditis, meningitis, and wound infections

• Leuconostoc spp

  • gram stain: gram-positive cocci/coccobacillus

  • associated with the spoilage of meat and meat products

  • normal flora of the digestive tract

  • opportunistic infection

  • intrinsically resistant to vancomycin

Aerobic gram-positive rods

• Bacillus spp

  • gram stain: large gram-positive rod, spore forming

  • catalase positive, grows on most media

  • usually, beta hemolytic and motile

  • often a lab contaminant, most species are of no concern

  • Bacillus anthracis

    • major pathogen (bioterrorism)

    • colonies with “medusa head” edges

    • nonhemolytic and nonmotile

    • can have a capsule

    • gram stain: square-ended gram-positive rod with elliptical spores

    • must be worked up under a hood

    • causes anthrax

      • cutaneous - enters through break in skin

      • pulmonary - inhaled (sheep wool0

      • gastrointestinal - ingested in infected meat

  • Bacillus cereus

    • can be small shiny colonies or large feathery colonies

    • catalase positive and motility positive

    • often causes infections in immunocompromised patients

    • found in soil, vegetation, and water

    • causes food poisoning (especially rice dishes), wound/eye/burn infections, and septicemia

  • Bacillus subtilis

    • large flat colony, ground glass appearance

    • motility positive

    • causes food poisoning and wound/eye infections

    • used to check proper function of autoclave

• Listeria spp

  • gram stain: small gram-positive rod/coccobacilli

  • narrow zone of hemolysis, look similar to group B strep

  • catalase positive and motility positive

    • tumbling motility

  • CAMP positive

    • rectangular zone

  • Listeria monocytogenes

    • found in dairy products, raw veggies, sausage/deli meats

    • cold enhancement

    • causes neonatal sepsis and meningitis

      • can cross placenta

• Erysipelothrix rhusiopathiae

  • gram stain: gram-positive rod, non-spore forming

  • motility, catalase, and oxidase negative

  • only gram-negative rod to produce H2S on TSI slant

  • found in soil, food, and water, common veterinary pathogen

  • causes cellulitis type skin lesion called erysipeloides

• Corynebacterium spp

  • gram stain: pleomorphic gram-positive rod/Chinese letter stacking formation

  • normal skin flora (many nonpathogenic spp)

  • catalase positive, nonmotile, ERIC testing

  • Corynebacterium jeikeium

    • causes septicemia, meningitis, peritonitis, and nosocomial infections

    • resistant to multiple antibiotics but sensitive to Vanco

  • Corynebacterium urealyticum

    • causes nosocomial bacteremia and pneumonia

      • most commonly causes cystitis, UTI, and pyelonephritis

    • urea positive

    • infection produces alkaline urine

      • promotes formation of kidney stones

  • Corynebacterium diphtheriae

    • causes diphtheria

      • acute febrile illness

      • produces endotoxin in throat that is carried to other organs

      • heart and CNS are most affected

      • can form pseudo-membrane

    • special media:

      • Loeffler’s agar

      • cysteine tellurite agar

• Lactobacillus spp

  • gram stain: pleomorphic gram-positive rods, can chain, non-spore forming

  • catalase negative and motility negative

  • pinpoint alpha hemolytic colonies on blood

  • normal flora of oral cavity, GI tract, and female genital tract

  • rarely causes serious infection

  • can be anaerobic or aerobic

• Aerobic Actinomycetes

  • gram stain: filamentous gram-positive rods that branch

  • slow growing

  • smells like a musty basement

  • Nocardia spp

    • suspect if long branding rods are seen in a direct smear

    • slow growing, dry, chalky colonies

    • partial acid-fast positive

    • inhabits soil and water

    • infects via inhalation or through breaks in the skin

      • often infects immunocompromised

  • Streptomyces spp

    • chalky colonies

    • pungent, musty basement odor

    • partial acid-fast negative

    • causes chronic granulomatous lesions of the skin and subcutaneous tissue

      • usually only found in immunocompromised patients

  • Rhodacoccus spp

    • branching filamentous rods that fragment into cocci and rods

    • colonies resemble K. pneumo but does not grow on MAC

    • partial acid-fast positive

    • found in environment, infect via inhalation

    • causes pulmonary, skin, and device infections

Biochemical tests used to differentiate gram-positive cocci

• Catalase

  • staph and strep

• Hemolysis

  • different species of staph or strep

• Bacitracin

  • micrococcus (S)

  • Strep pyogenes (S)

• Novobiacin

  • Staph saprophyticus (R)

• Optichin

  • Strep pneumo (S)

  • viridans strep (R)

• PYR

  • Strep pyogenes positive

• SF

  • Enterococcus positive

• Bile solubility

  • Strep bovis positive

  • Strep anginosus negative

• CAMP

  • Strep agalactiae positive

  • Strep anginosus negative

• LAP

  • Aerococcus urinae positive

  • Aerococcus viridans negative

Biochemical tests used to differentiate gram-positive rods

• Catalase

• Gram-stain

  • filamentous

  • beaded rods

  • spore forming

• Urea

  • Actinomyces negative

  • Corynebacterium jeikeium negative

• Motility

  • Bacillus cereus or subtilis positive

• hemolysis

  • Lactobacillus has alpha hemolysis

Distinguish organisms considered normal flora from those always considered pathogens

• Normal flora

  • Staphylococcus aureus

  • Coagulase negative Staphylococcus

  • Rothia

  • Micrococcus

  • Viridans Streptococcus

  • Streptococcus pneumoniae

  • Streptococcus agalactiae

  • Streptococcus anginosus

  • Enterococcus spp

  • Group D Streptococcus

  • Gemella spp

  • Leuconostoc spp

  • Corynebacterium spp

  • Lactobacillus spp

  • Streptomyces spp

• Pathogenic

  • Streptococcus pyogenes

  • Aerococcus spp

  • Bacillus spp

  • Listeria spp

  • Erysipelothrix rhusiopathiae

  • Corynebacterium diphtheriae

  • Nocardia spp

  • Rhodacoccus spp