Gram positive and gram negative cocci
Gram + Staphylococci, Streptococci and Enterococci
Gram -
Gonococci and Meningococci
Jawetz-Medical microbiology
Chapter 13,14,20
Domain:
Phylum:
Class:
Order:
Family:
Genus:
Bacteria
Firmicutes
Cocci
Coccus
Staphylococcaceae
Staphylococcus
The staphylococci are gram-positive spherical cells, Common inhabitant of the skin and mucous
membranes, usually arranged in grapelike irregular clusters. They fermenting carbohydrates
and producing pigments that vary from white to deep yellow. Staphylococci are nonmotile and
do not form spores.
The genus Staphylococcus has at least 40 species. The four most frequently
encountered species of clinical importance are
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Staphylococcus aureus- S. aureus produces a carotenoid pigment called
staphyloxanthin, which imparts a golden color to its colonies
Staphylococcus epidermidis
Staphylococcus lugdunensis
Staphylococcus saprophyticus
Staphylococci produce catalase, which converts hydrogen peroxide into water and
oxygen.
The catalase test differentiates the staphylococci, which are positive, from the
streptococci, which are negative.
Two species are commonly associated with staphylococcal diseases in humans
• Staphylococcus aureus-The more virulent strain that can produce a variety
of conditions depending on the site of infection
• S. aureus is distinguished from the others primarily by coagulase
production. Coagulase is an enzyme that causes plasma to clot by activating
prothrombin to form thrombin
• Staphylococcus epidermidis-Normal microbiota of human skin that can
cause opportunistic infections in immunocompromised patients or when
introduced into the body
Pathogenicity of Staphylococcus
infections result of produced
enzymes and toxins.
Virulence factors of Staphylococcus aureus
Staphylococcus diseases
• Furuncles (boils) are skin
abscesses, which involve a
hair follicle and surrounding
tissue.
• Carbuncles are clusters of
furuncles connected
subcutaneously, causing
deeper suppuration and
scarring.
• folliculitis – superficial
inflammation of hair follicle;
usually resolved with no
complications but can progress
• impetigo – bubble-like swellings
that can break and peel away;
most common in newborns
Toxin mediated disease
• Staphylococcal food poisoning-is a gastrointestinal illness caused by eating
foods contaminated with toxins produced by the bacterium.
✔ can contaminate food by people who carry it
✔ can also be found in unpasteurized milk and cheese products
✔ Because Staph is salt tolerant, it can grow in salty foods like ham
Symptoms:
• vomiting
• nausea
• stomach cramps
• Diarrhea
The illness cannot be passed to other people and typically lasts for only 1 day.
Severe illness is rare.
Staphylococcal Food Poisoning syndrome
gastrointestinal illness caused by eating foods contaminated with toxins
produced by Staph. Diagnosis based on
• Clinical evaluation- group of cases and symptoms characteristic to GI
infections
• Laboratory evaluation-Toxin-producing Staph can be identified in stool or
vomit The toxins can also be detected in foods.
Toxic shock Syndrome (TSS)- was first described in children but came to public
attention during the early 1980s, when hundreds of cases were reported in young
women using intravaginal tampons.
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high fever
vomiting
Diarrhea
Sore throat
muscle pain.
Treatment
• Aggressive Therapy -antibiotics
• Blood Transfusions
• Corticosteroids
• Electrolyte replacements
• Ventilator if lungs are damaged
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Scalded Skin Syndrome (SSS) also known as Ritter von Ritterschein disease- results from
the production of toxin exfoliatin , SSS characterized by red blistering skin that looks like
a burn or scald The disease is most common in neonates and children less than 5 years of
age.
Symptoms:
• Fussiness (irritability)
• Tiredness
• Fever
• Redness of the skin
• Fluid-filled blisters that break easily and leave an
area of moist skin that soon becomes tender and
painful
• Large sheets of the top layer of skin may peel away
Treatment may include:
Intravenous antibiotic therapy
Fluids to prevent dehydration
Nasogastric feeding
Use of skin creams or ointments and bandages
Pain medicines
Principles of Microbiology Diagnosis
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Culture Test
Catalase Test
Coagulase Test- To detect Coagulase –positive Staphylococci as it is considered
pathogenic for humans;
Susceptibility Testing-Broth
Serologic and Typing Test
Treatment
⮚ Bacteremia, endocarditis, pneumonia, and other severe
infections caused by S aureus require prolonged intravenous
therapy with a β-lactamase-resistant penicillin.
⮚ Vancomycin is often reserved for use with nafcillin-resistant
staphylococci.
⮚ Novobiocin: S. epidermidis is sensitive, whereas S. saprophyticus
is resistant.
⮚ Because of the frequency of drug-resistant strains, meaningful
staphylococcal isolates should be tested for antimicrobial
susceptibility to help in the choice of systemic drugs.
Domein: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Lactobacillales
Family: Streptococcaceae
Genus: Streptococcus
Streptococci are Gram-positive, nonmotile,
catalase-negative, facultatively anaerobic cocci that
occur in chains or pairs. They are widely distributed
in nature. Some are members of the normal human
microbiota; others are associated with important
human diseases.
The genus Streptococcus includes three of the most important pathogens of
humans.
• S. pyogenes- β-hemolytic group A streptococci the cause of “strep throat,”
which can lead to rheumatic fever and heart disease;
• S. agalactiae, the most frequent cause of sepsis in newborns.
• S. pneumoniae, a leading cause of pneumonia and meningitis in persons of all
ages.
Streptococcus diagnostic laboratory test
Specimen
• A throat swab
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pus
for culture identification
• blood test
• Serum for antibody determinations.
Smears
Culture
Antigen Detection Tests
Serologic Tests
• Determination of ASO,anti-ASO titer
• anti-DNase B and antihyaluronidase test
• Antistreptokinase test
• anti-M type-specific antibodies test
Streptococcus pyogenes-Group A streptococci
Erysipelas—It is an infection
of the upper dermis and
superficial lymphatics.
symptoms typically include:
Cellulitis—is an acute,
rapidly spreading infection
of the skin and
subcutaneous tissues.
Necrotizing fasciitis (streptococcal gangrene)- is very rare but serious
infection, It can destroy skin, fat, and the tissue covering the muscles within
a very short time. The disease sometimes is called flesh-eating bacteria.
Scarlet Fever
Scarlet fever or scarlatina – is a bacterial infection caused by group A
Streptococcus. It is usually a mild illness, but people with scarlet fever need treatment
to prevent rare but serious health problems.
Common Symptoms of Scarlet Fever:
• very red, sore throat
• fever (101° F or above)
• red rash with a sandpaper feel
• Bright red skin in underarm, elbow
• whitish coating on the tongue
• “strawberry” (red and bumpy) tongue
• Headache or body aches
• Nausea, vomiting, or abdominal pain
• Swollen glands
Long-term Health Problems from Scarlet Fever
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Rheumatic fever (an inflammatory disease that can affect the heart, joints, skin, and
brain)
Kidney disease (inflammation of the kidneys, called post-streptococcal
glomerulonephritis)
Otitis media (ear infections)
Skin infections
Abscesses (pockets of pus) of the throat
Pneumonia (lung infection)
Arthritis (joint inflammation)
Diagnosis:
Diagnosis is very easy, but sometimes milder forms can be confused with Rubella, Roseola,
Kawasaki disease, drug eruption.
• Swab test
• Blood test
• Blood test for bacterial identification
Treatment:
Group A strep is sensitive to penicillin. penicilin is drug of choice except in patient
allergic to penicillin(narrow-spectrum cephalosporin). Treatment with oral antibiotic for
10 days is recommended
Glomerulonephritis
Post streptococcal Glomerulonephritis is an immune mediated disease is characterized by the
sudden appearance of
• Hematuria
• proteinuria
• red blood cell casts in the urine
• Edema
• hypertension with or without oliguria.
Diagnosis
Laboratory studies in acute poststreptococcal
glomerulonephritis (APSGN) include tests to provide
evidence of preceding streptococcal infection,
renal function studies, and serologic studies.
• Antibody titer in blood
• Urine Analysis
• Imagine studies (Chest radiographs may show findings of congestive heart failure.Renal
ultrasound images usually reveal normal-sized kidneys bilaterally)
• Histologic tests
• Renal biopsy
Treatment
• Anti-infection treatment, antibiotic therapy
• Immunosupresant
Group B Streptococcus
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Growth on Granada/columbia sheep blood agar
Growth characteristics
 Microaerophilic/ aerobic
condition
 β-hemolysis
 Small grey or white
colonies 2-4 mm in
diameter
Group B Streptococcus
S. Agalactiae Group B Streptococcus
GBS is cause of postpartum infection and as the most common cause of neonatal sepsis.
Diagnosis: staining, culturing on selective medium, latex agglutination, biochemical
test, molecular test (PCR)
Treatment: mainly with beta-lactams, which includes penicillin and ampicillin.
Streptococcus pneumonia
 Growth characteristics
 Facultative anaerobic
 α-hemolysis
 Small grey mucoidal
colonies
Streptococcus pneumonia Virulence factors
Pneumococcal Disease
Symptoms of pneumococcal disease depend on the part of the body that is infected.
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Fever
Cough
shortness of breath
chest pain
stiff neck
confusion and disorientation
sensitivity to light
joint pain, chills, ear pain
hearing loss
brain damage, and death.
Diagnosis
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Blood test
Cerebrospinal fluid test
Treatment
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The pneumococcal vaccine can protect you from pneumococcal disease.
Antibiotic therapy with broad spectrum antibiotic
Levofloxacin is rapidly becoming a popular choice in pneumonia; this agent is a
fluoroquinolone used to treat CAP caused by, S pneumoniae (including penicillinresistant strains)
Symptoms:
Nausea
Vomiting
Photophobia
Altered mental status (confusion)
Diagnosis:
Identification of causative agent
from blood or cerebrospinal fluid
It is important to start treatment as
soon as possible.
The most effective way to protect
against certain types of bacterial
meningitis is VACTINATION.
There are vaccines for three types
of bacteria that can cause
meningitis:
Neisseria meningitidis
Streptococcus pneumoniae
Hib
Streptococcus mutans
 Gram-positive coccus that
is a major inhabitant of the
oral cavity
 is considered a significant
contributor of tooth decay
and cavities.
 Facultative anaerobic
 α-hemolytic or nonhemolytic
 0.5–1.0 mm in diameter
colonies
Streptococcus in oral cavity
DIAGNOSIS
•Lab diagnosis of Streptococcus mutans is based on the identification of the organism by its microscopic,
cultural, and biochemical characteristics. Dental plaque and swabs from the cavities and taken as samples
for laboratory identification.
TREATMENT
•Chlorhexidine, ofloxacin, doxycycline, tetracycline, chlortetracycline, erythromycin, vancomycin,
clindamycin, methicillin, and gentamycin
Enterococcus
⮚ Facultative anaerobic, catalase-negative Gram- positive cocci
⮚ Arranged individually, in pairs, or short chains.
⮚ Optimal temperature for growth 23-30 C
⮚ They are normal inhabitants of the intestinal tract, female genital
tract, and (less commonly) oral cavity.
⮚ There are at least 47 species of enterococci, but associated with
disease in humans are Enterococcus faecalis and Enterococcus
faecium.
Gram negative Cocci
Neisseria
Domain: Bacteria
Phylum: Proteobacteria
Class: Cocci
“kidney bean” appearance
Order: Coccus
Family:Neiseriaceae
Genus: Neiseria, Kingella,
Eikenella, Simonsiella, and
Alysiella
NEISSERIA GONORRHEA
Pathogenesis
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Gonococci exhibit several morphologic
types of colonies but only piliated
bacteria appear to be virulent.
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Gonococci are not normal inhabitants
of the respiratory or genital flora.
When introduced onto a mucosal
surface adherence ligands such as pili
and Opa proteins allow initial
attachment of the bacteria to receptors
on epithelial cells.
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Gonococci attack mucous membranes
of the genitourinary tract, eye, rectum,
and throat, producing acute
suppuration that may lead to tissue
invasion;
Genital gonorrhea
Signs &
Symptoms
• Painful or burning sensation
when urinating;
• Vaginal bleeding.
• A burning sensation during
urination
• A white, yellow, or green
discharge from the penis
• Painful or swollen testicles
Gonococcal ophthalmia
neonatorum
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infection of the eye in newborns
Infected during passage through an
birth canal.
The initial conjunctivitis rapidly
progresses and, if untreated, result is
blindness.
To prevent
Gonococcal ophthalmia neonatorum, instillation of tetracycline, erythromycin, or silver nitrate into the
conjunctival sac of newborns is compulsory in the United States.
Laboratory Diagnosis
 Specimens- Pus and secretions are taken from the urethra, cervix, rectum,
conjunctiva, throat, or synovial fluid for culture and smear.
 Smear- Gram-stained smears of urethral or endocervical exudates reveal
many diplococci within pus cells. These give a presumptive diagnosis.
 Culture- after collection, pus or mucus is streaked on enriched selective
medium (modified Thayer-Martin medium [MTM]) and incubated in an
atmosphere containing 5% CO2 at 37°C.
 Nucleic Acid Amplification Tests- detect gonococci in genital and urine
specimens without culture. Important method for screening population.
Treatment
Because of the problems with antimicrobial resistance in
N. gonorrhea CDC recommended:
 ceftriaxone (250 mg) intramuscularly as a single dose or 400 mg
of oral cefixime as a single dose.
 Additional therapy with 1 g of azithromycin orally in a single
dose or with 100 mg of doxycycline orally twice a day for 7 days.
Patients who do not complete a course of treatment once they begin to feel better present a risk of
continued transmission and selection of resistant strains
NEISSERIA MENINGITIDIS
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Meningococci produce mediumsized smooth colonies on blood
agar plates after overnight
incubation.
Thirteen serogroups have been
defined on the basis of the
antigenic specificity of their
polysaccharide capsule.
The most important diseaseproducing serogroups are A, B, C,
W-135, and Y.
Antigenic structure
Pathogenesis
Clinical Manifestation
The meningococcus is spread horizontally
(person to person) by respiratory droplets or
direct contact.
Acute Purulent MeningitisThe most common form of
meningococcal infection
 Fulminant meningococcemia
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Common symptoms are:
• sudden fever
• Purplish rash
• Headache
• stiff neck
• Nausea
• Vomiting
• increased sensitivity to light
• confusion
Laboratory diagnosis
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Specimens- blood and spinal fluid for smear and culture
Smear - Gram-stained smears of the sediment of centrifuged
spinal fluid or of petechial aspirate often show typical neisseriae
within polymorphonuclear leukocytes or extracellularly.
Culture - Culture media without sodium polyanethol sulfonate
are helpful in culturing blood specimens. Cerebrospinal fluid
specimens are plated on chocolate agar and incubated at 37°C
in an atmosphere of 5% CO2.
Treatment
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Penicillin G is the drug of choice for treating patients with
meningococcal disease.
Either chloramphenicol or a third generation cephalosporin
such as cefotaxime or ceftriaxone is used in persons who are
allergic to penicillins.
Epidemiology, Prevention and Control
Meningococcal meningitis occurs in epidemic waves -called
“meningitis belt”
 military encampments
Meningococcal Conjugate
 religious pilgrims
Vaccine Quadravalent (MCV4) sub-Saharan Africa
stimulates T-cell–dependent
Recently, vaccine 4CMenB
(Bexsero®) was licensed in the
European Union.
Three vaccines against serogroups A,
C, Y, and W-135 and one that contains
only C and Y available in the United
States.
responses.
 Use is recommended beginning
at age 11 with boosters at 16
years.
 It is also recommended down to
the age of 9 months for anyone
at high risk for meningococcal
disease