Gram-Posiitve Cocci and Streptococcus and Enterococcus Objectives

Micrococcus Species

• Gram-Positive Coccii in Clusters

• Distinctive Yellow colonies

• Catalase Positive

• Oxidase Positive

• Suseptiple to Bacitracin

• Couagulase Negative

Staphylococcus Species

• Gram-Positive Cocci in grape-like clusters

• White/Yellowish Colonies

• Catalase Positive

• Oxidase Negative

• Resistant to Bacitracin

• Couagulase Positive

Staphylococcus Aureus (Potential Pathogen - MRSA and GISA)

• Habitat: Nasal passages

• Mode of transmission: Direct, Respiratory droplets, contaminated objects

• Colony Morphology: Large yellow colony on rich medium

• Biochemical reactions patterns: Catalase positive, Coagulase positive, and beta-hemolytic

• Diseases: Sepsis, Heart infections, toxic shock syndrome

MRSA

• S. Auerues resistant to methicilin

• Has MecC  and Mec A gene

• the acquisition of the mecA gene via a mobile genetic element called SCCmec, which encodes PBP2a. PBP2a is a modified penicillin-binding protein with low affinity for beta-lactam antibiotics, allowing it to continue cell wall synthesis in their presence, thus conferring resistance.

Chromagar

detects MRSA - shows up pink

GISA

less effective by the antibiotic vancomycin

Staphylococcus Epidermidis (opprotunistic infections)

• Habitat: The skin

• Mode of transmission: skin-to-skin contact, indirect contact(catheters, implants)

• Colony Morphology: Relatively small white colonies

• Biochemical Reaction Patterns: Catalase positive, Coagulase negative, Non-hemolytic, novobiocin suseptible

• Diseases: Catheter bloodstream infections, prosthetic joint infections, implanations of devices

Staphylococcus saprophyticus

• Habitat: Normal flora of perineum, rectum, urethra, cervix, and gastrointestinal tract

• Mode of transmission: Direct contact, contaminetated food, 

• Colony Morphology: small to medium, orund, sticky , cream, yellow, or white

• Biochemical Reaction Patterns: Catalase Positive, couagulase negative, novobiocin resisitant

• Diseases: STDs

Staphylococcus lugdunensis

• Habitat: Areas around the lower abdomen, groin, and perineal areas

• Mode of transmission: Direct and indirect

• Colony Morphology: rough, medium-sized, opaque, and non-pigmented, often with a glossy sheen and beta-hemolysis on blood agar

• Biochemical Reaction Patterns: Catalyse positive, Coagulase negative in tube test, PYR positive, Oxidase Negative

• Diseases: Endocardidtis

Micrococcus Spp.

• Habitat:Skin, dust, soil, and water

• Mode of transmission: Direct and indirect, Inhalatin through dust

• Colony Morphology:yellow or orange, slightly raised, 

• Biochemical Reaction Patterns: Catalase Positive

• Diseases: Only specific genes are pathogenic

General effect of the following virulence factors of S. Aureus

• Enterotoxin - Food Poisoning and superantigens

• Toxic Shock Syndrome Toxin: high fever, low blood pressure, diffuse rash, and multi-organ failure

• Exfoliative toxin: S. Scalded Skin Syndrome (Dsg1)

• Hemolysins: damage host cell membranes

• Coagulase: Abscess formation

• Hyaluronidase: breaks down connective tissue - promotes bacterium invasion

Phenylethyl alcohol agar (PEA)

• Allows growth of Gram-Posiitve Cocci

• Can isolate GPC from a mix of bacteria

Columbia colisitin-nalidixic acid agar (CNA)

• Allows growth of Gram-Positive organisms

Mannitol Salt Agar (MSA)

• Detects specifically S. Aureus from other bacteria

• Will turn yellow based on its ability to ferment mannitol

Why are MRSA and GISA are threats to public health

They are both resistant to antibiotics

General characteristics of Streptococcus

• Gram Reaction: Gram-Positive

• Microscopic Morphology: Clusters or chains

• Colony Morphology: small, circular, mucoid, hemolysis

• Catalase Reaction: Negative

General characteristics of Enterococcus

• Gram Reaction: Gram-positive

• Microscopic Morphology: Cocci in pairs

• Colony Morphology: Non-hemolytic, grayish or light pink

• Catalase Reaction: Negative

Streptococcus pyogenes

Habitat: Skin, nose, and throat

Mode of Transmission: Respiratory Droplets, Direct conta t

Colony morphology: small, white, mucoid, beta-hemolytic

Biochemical reactions: Caougulase negative, bacititracin suceptiple

Disease: Strep throat, scarlet fever

Streptococcus agalacticae

Habitat: gastrointestinal and genital tract

Mode of Transmission: Mother to child - Vertical transmission, person to person

Colony morphology: white, beta-hemolytic, mucoid

Biochemical reactions: Coaugulase negative, bacititracin resistant

Disease: pneumonia,sepsis, meningitis

Streptococcus pneumoniae

Habitat: upper respiratory tract - nasopharnyx

Mode of Transmission:direct, droplets

Colony morphology: slight yellow tint, mucoid, alpha hemolytic, depression

Biochemical reactions: catalyse negative, optochin suseptible

Disease: pnuemoina

Streptococcus (bovis)

Habitat: Gut

Mode of Transmission: directly or indirectly

Colony morphology: small, grey, non-hemolytic

Biochemical reactions: Catalyse negative, No growth in NaCl

Disease: Tumour growth, colorectal cancer

Viridans Strep Group

Habitat: human mouth, throat gastrointestinal tract

Mode of Transmission: Orally

Colony morphology:small, alpha-hemolytic

Biochemical reactions: Catalyst negative, Optochin resistant

Disease: sepsis and pnuemonia

Enterococcus faecalis

Habitat: gastrointestinal tract

Mode of Transmission: direct contact, fecal oral route

Colony morphology:convex, non-hemolytic smooth

Biochemical reactions: Catalyse negative, growth in NACL

Disease: UTIs

Enterococcus faecium

Habitat: gastro tract, oral cavity

Mode of Transmission:direct transmission

Colony morphology: Small to grey, gamma-hemolytic, smooth edges

Biochemical reactions: Catalyse Negative, growth in NaCl

Disease: UTIs, IE, meningitis

the principle, method, and expected results of the CAMP Test

• Test to identify group B β-hemolytic streptococci

• observing a synergistic lysis of red blood cells forming an arrowhead shape on a blood agar plate

• If the unknown is S. agalactiae, its CAMP factor protein will interact with the S. aureus hemolysin, creating an enhanced, arrowhead-shaped zone of clearing (lysis) between the two streaks

The clinical significance of Lansfield typing and the portion of the cell wall that characterizes the typing

• a serological method for classifying streptococci into one of 20 groups

• based on the carbohydrate composition of bacterial antigens found on their cell walls.

Three virulence factors produced by Streptococcus pyogenes

• M protein: bacteria attaches

• Hyaluronic Acid Capsule: mimics hosts connective tissue and prevents it from being recognized

• Cytolytic toxins: SLS and SLO< damage membranes of host cells

The sequelae that can occur if strep throat occurs

Acute Rheumatic fever and PSGN

Why Vancomycin-resistant Enterococci (VRE) is a threat to public health

• Limited treatment options

• Rapid spread of resistance

• Increased patient mortality.