Staphylococci

STAPHYLOCOCCI

STAPHYLOCOCCI Dr. Younis A. Al-Khafaji

• Staphyloccocci - derived from Greek “stapyle” (bunch of grapes)
• Gram positive cocci arranged in clusters
• Hardy organisms surviving many non physiologic conditions
• Include a major human pathogen and skin commensals



Grouping for Clinical Purposes
• 1. Coagulase positive Staphylococci
– Staphylococcus aureus

• 2. Coagulase negative Staphylococci
– Staphylococcus epidermidis
– Staphylococcus saprophyticus
A. Staphylococcus aureus
• Major human pathogen
• Habitat - part of normal flora in some humans and animals
• Source of organism - can be infected human host, carrier, fomite or environment
Natural history of disease
• Many neonates, children, adults -intermittently colonised by S. aureus
• Usual sites - skin, nasopharynx, perineum
• Breach in mucosal barriers - can enter underlying tissue
• Characteristic abscesses
• Disease due to toxin production

• DISEASES
• Due to direct effect of organism
– Local lesions of skin
– Deep abscesses
– Systemic infections
• Toxin mediated
– Food poisoning
– toxic shock syndrome
– Scalded skin syndrome
• Factors predisposing to S. aureus infections
• Host factors
– Breach in skin
– Chemotaxis defects
– Opsonisation defects
– Neutrophil functional defects
– Diabetes mellitus
– Presence of foreign bodies
• Pathogen Factors
– Catalase (counteracts host defenses)
– Coagulase
– Hyaluronidase
– Lipases (Imp. in disseminating infection)
– B lactasamase(associated with antibiotic resistance)
• SKIN LESIONS
• Boils
• Styes
• Furuncles(infection of hair follicle)
• Carbuncles (infection of several hair follicles)
• Wound infections(progressive appearance of swelling and pain in a surgical wound after about 2 days from the surgery)
• Impetigo(skin lesion with blisters that break and become covered with crusting exudate)



• DEEP ABSCESSSES
• Can be single or multiple
• Breast abscess can occur in 1-3% of nursing mothers in puerperiem
• Can produce mild to severe disease
• Other sites - kidney, brain from septic foci in blood
• Systemic Infections
• 1. With obvious focus
• Osteomyelitis, septic arthritis
• 2. No obvious focus
• heart (infective endocarditis)
• Brain(brain abscesses)
• 3. Associated with predisposing factors
• multiple abscesses, septicemia(IV drug users)
• Staphylococcal pneumonia (Post viral)
• B. TOXIN MEDIATED DISEASES
• 1. Staphylococcal food poisoning
• Due to production of entero toxins
• heat stable entero toxin acts on gut
• produces severe vomiting following a very short incubation period
• Resolves on its own within about 24 hours
• 2. Toxic shock syndrome
• High fever, diarrhoea, shock and erythematous skin rash which desquamate
• Mediated via ‘toxic shock syndrome toxin’
• 10% mortality rate
• Described in two groups of patients
• ass. With young women using tampones during menstruation
• Described in young children and men



• 3. Scalded skin syndrome
• Disease of young children
• Mediated through minor Staphylococcal infection by ‘epidermolytic toxin’ producing strains
• Mild erythema and blistering of skin followed by shedding of sheets of epidermis
• Children are otherwise healthy and most eventually recover
• Antibiotic sensitivity pattern
• 1.B lactamase production - plasmid mediated
• Has made S. aureus resistant to penicillin group of antibiotics - 90% of S. aureus (Gp A)
• B lactamase stable penicillins (cloxacillin, oxacillin, methicillin) used
• 2. Alteration of penicillin binding proteins
• (Chromosomal mediated)
• Has made S. aureus resistant to B lactamase stable penicillins
• 10-20% S. aureus Gp (B) GH Colombo/THP resistant to all Penicillins and Cephalasporins)
• Vancomycin is the drug of choice

• Tested in lab using methicillin
• Referred to as methicillin resistant S. aureus (MRSA)
• Emerging problem in the world
• In Iraq prevalence varies from 40-65% in hospitals
• Drug of choice - vancomycin
• In Japan emergence of VIRSA(vancomycin intermediate resistant S. aureus)
• Meropenem effective antibiotics discovered recently.

• DIAGNOSIS
• 1. In all pus forming lesions
– Gram stain and culture of pus
• 2. In all systemic infections
– Blood culture
• 3. In infections of other tissues
– Culture of relevant tissue or exudates
• 2. Staphylococcus epidermidis
• Skin commensal
• Has predilection for plastic material
• Ass. With infection of IV lines, prosthetic heart valves, shunts
• Causes urinary tract infection in cathetarised patients
• Has variable ABS pattern
• Treatment should be aided with ABST
• 3. Stapylococcus saprophyticus
• Skin commensal
• Important cause of UTI in sexually active young women
• Usually sensitive to wide range of antibiotics