Transcript Bacterial Classification

Nature of Disease
Introduction - Definitions
Normal Bacteria & Host
Koch’s Postulates
Patterns of Disease
Spread of Infection
Nosocomial Infections
Disease - Introduction
Pathogens - disease causing with
special properties that permit host
invasion
 Disease - when microorganism
overcomes host defenses; an abnormal
physiological state
 Pathology - the study of disease

Disease - Introduction
Infection - invasion & growth of
pathogen in host; systemic vs. localized
 Pathogenesis – the study of the
development of disease
 Etiology – the study of the cause of
disease

Disease - Normal Bacteria
Animals - germ free in utero but are
colonized almost immediately after
birth
 Different bacteria are normally
associated with different parts of body
 Transients - microorganisms that may
occasionally be found associated with
the host

Disease - Normal Bacteria

Skin
– S. epidermidis/S. aureus

Gastrointestinal Tract
– Gram negative bacteria (large intestine)
– Streptococcus. mutans (mouth)

Genito-Urinary Tract
– Lactobacillus
Disease - Normal Bacteria
Antagonism - normal bacteria prevent growth
of others
 Bacteria and host have symbiotic relationship
(living together)
 Three types of symbiosis

– Commensalism (one benefits)
– Mutalism (both benefit)
– Parasitism (one benefits & other harmed)

Opportunistic - do not cause disease normally
Disease - Koch’s Postulates

Etiology or cause established using
Koch’s postulates
– same pathogen present in every instance of
disease
– pathogen isolated in pure culture
– isolated pathogen causes disease when
reintroduced into a healthy host
– pathogen re-isolated from the now
diseased host
Disease - Patterns

Predisposing factors make hosts more
susceptible & include:
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age
gender
climate
level of fatigue
nutrition
Disease - Patterns - Development
Incubation period - time between
infection & first signs
 Prodromal period - first mild signs
 Illness period - period when all
symptoms are present
 Decline period
 Convalescence period

Disease - Spread of Infection

Reservoirs of Infection
– a continuing source of infection

Reservoirs include:
– Human - people who have disease or are
carriers (infected but no symptoms)
– Zoonoses - wild or domestic animals that
transmit disease to humans
– Nonliving - soil & water
Disease - Spread of Infection

Transmission
– Direct contact
– Fomites - inanimate objects
– Droplet - saliva, mucus coughing or
sneezing
– Medium - food, water air
– Airborne - carried > 1 meter
– Arthropod - insect vectors
Disease - Nosocomial Infection
Acquired during hospitalization or a
stay in other health care facilities
 Occurs at 5-15%
 Can be normal organisms introduced
into wrong part of body during
invasive procedures
 Opportunitic drug resistant G-, e.g.
Pseudomonas

Disease - Nosocomial Infection

Compromised host
– burns
– wounds
– immune suppressed (disease or drugs)

Chain of Transmission
– Direct contact
– Fomites
Disease - Nosocomial Infection

Control
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Aseptic techniques
Proper cleaning storage
Maintenance
Properly trained staff
Problems
– Multiple drug resistance
– Nonuse of effective cleaning agents
– Training of staff