Opportunistic Pathogens

PATHOGEN“A pathogen is a microbe or

microorganism such as a virus (such as HIV), bacterium (such as staph), prion, or fungus (such as yeast) that causes disease in its animal or plant host”.

First devised in 1880.

MAJOR HUMAN PATHOGENS

Bacillus anthracis Clostridium botulinumBartonella spp.Spanish influenza virusYersinia pestisMycobacterium leprae

PATHOGENESIS

“The pathogenesis of a disease is the mechanism by which the disease is caused. The term can also be used to describe the origin and development of the disease and whether it is acute, chronic or recurrent”.

OPPORTUNISTIC PATHOGEN “An infectious microorganism that is

normally a commensal or does not harm its host but can cause disease when the host’s resistance is low”.

OPPORTUNISTIC INFECTION “An opportunistic infection is an

infection caused by pathogens, particularly opportunistic pathogens”.

OPPORTUNISTIC CONDITIONS When the immune system isn’t working

properly, normal flora can overpopulate or move into areas of the body where they do not normally occur.

When the balance of normal microbes is disrupted, for example when a person takes broad spectrum antibiotics.

Disease can result when normal flora are traumatically introduced to an area of the body that is axenic or that they do not normally occur in.

Causes of Immunodeficiency Malnutrition Chemotherapy for cancer Skin damage Medical procedures Pregnancy Immunosuppressing agents for organ transplant

recipients The concomitant presence of certain underlying

diseases such as cancer, diabetes, cystic fibrosis Side effects of certain medical therapies and drugs

such as corticosteroids Infection with immunity-destroying microorganisms Age, both old and young

Candida albicans

Staphylococcus aureus

Pseudomonas aeruginosa

OPPORTUNISTIC BACTERIA

Campylobacter Flavobacterium Haemophilus Mycobacterium Nocardia Pseudomonas Rhodococcus Salmonella Shigella Staphylococcus Streptococcus Treponema Yersinia

REFERENCES TO STUDY OPPORTUNISTIC BACTERIA

There are two main references to study opportunistic bacteria:

1. Opportunistic bacteria with reference to the site change.

Example E.coli2. Opportunistic bacteria with reference to

the immunocompromised condition. ExampleAIDS and its related opportunistic bacteria.

Pseudomonas aeruginosa as an opportunistic pathogen

member of the Gamma Proteobacteria

Gram-negative, aerobic rod Belongs to family

Pseudomonadaceae. Oxidase-positive

Infections by Pseudomonas aeroginosa

urinary tract infections,

respiratory system infections,

dermatitis, bacteremia, bone and joint

infections, gastrointestinal

infections

Infections are caused particularly in :

Patients with severe burns cystic fibrosis cancer AIDS

Pseudomonas aeruginosa is primarily a nosocomial pathogen.

Characteristics contributing to its success as opportunistic pathogenNatural habitat

Ubiquitous in soil and water, and on surfaces in contact with soil or water

Actively swimming by means of its flagellum.Metabolism Respiratory and never fermentative Can grow in the absence of O2 if NO3 is

available as a respiratory electron acceptor

Nutritional requirements

Minimal nutritional requirements

Simplest medium for growth consists of acetate as a source of carbon and ammonium sulfate as a source of nitrogen.

Optimum temperature for growth 37 degrees Able to grow at temp as high as 42

degrees

Tolerance to physical conditions Resistant to high conc. of salt, dyes,

weak antiseptics and antibiotics

Resistance to antibiotics and phagocytes

Naturally resistant to antibiotics due to the permeabiliity barrier afforded by its Gram-negative outer membrane.

Living in association with the bacilli, actinomycetes and molds; resistant to their naturally-occuring antibiotics.

Slime layer; anti-phagocytic effect

Pathogenesis of Pseudomonas aeruginosa

Composed of three distinct stages

bacterial attachment and colonization;

local invasion; disseminated systemic disease.

Attachment and colonizationIt uses Flagella Pilli Exopolysaccharide (alginate or slime)

InvasionProduce extracellular enzymes and toxins that Break down physical barriers Damage host cells and immune defence.

Two exocellular proteases involved are: Elastase Alkaline protease

Some more proteins are; hemolysins and cytotoxins

Dissemination

Involves spread of infection to other parts

Mediated by same extracellular products that produce localized infection

E.coli

Escherichia coli  (E. coli ) is a Gram-negative, rod-shaped andfacultative anaerobic bacteriumCommonly found in the

lower intestine of warm-blooded organisms (endotherms)

Help in food digestion.

E.coli as an opportunistic bacteria:- Although it lives in a healthy

micro flora of a human body, but only in specific situation, when it arrive from intestine to other organs and tissues, unfortunately, it can cause a very serious infection and illnesses. The most frequent are urinary tract and sexual organs infections. 

Infections:-Virulent strains of E. coli can

cause  Gastroenteritis

(inflammation of stomach and small intestine)

 Urinary tract infections and  Neonatal meningitis

(colonisation of new born’s intestine)

In rarer cases, virulent strains are also responsible for 

Hemolytic-uremic syndrome Peritonitis (inflammation of

peritoneum)  Mastitis (inflammation of breast

tissues) Septicemia (inflammation of

whole body)  and Gram-negative pneumonia.

Classification of E.coli:- Enterotoxigenic E. coli  (ETEC) diarrhea (without fever) in humans, pigs,

sheep, goats, cattle, dogs, and horses Enteropathogenic E.coli (EPEC) diarrhea in humans, rabbits, dogs, cats

and horses Enteroinvasive E. coli  (EIEC) found only in humans Enterohemorrhagic E.coli (EHEC) found in humans, cattle, and goats Enteroaggregative E.coli  (EAEC) found only in humans

Serotypes

Pathogenic E.coli strains can be categorised as follows:-

O antigen: part of lipopolysaccharide layer

K antigen: capsule H antigen: flagellin F antigen: MR fimbriae (rare) For example E.coli strain

EDL933 is of the O157:H7 group.

Symptoms:- Bad stomach cramps Belly pain Vomiting Diarrhea, sometimes with

blood in it Painful urination Children are more likely than

adults to have symptoms. 3 or 4 days

Causes of infection:-

E. coli in food During meat processing. Meat is not cooked to 160°F

(71°C). Food come in contact with

raw meat E. coli from person-to-person

contact

When an infected person does

not wash his hands well after a

bowel movement. 

E. coli in water Human or animal feces infected

with E. coli sometimes get into lakes, pools, and water supplies. People can become infected when a contaminated city or town water supply has not been properly treated with chlorine or when people accidentally swallow contaminated water.

Precautions:-

Cook all types of beef to at least 160°F (71°C).

Wash any tools or kitchen surfaces that have touched raw meat.

Wash your hands properly after using washroom.

Use only pasteurized milk, dairy, and juice products.

Use only treated, or chlorinated, drinking water.

Summary

In summary, E. coli is an opportunistic pathogen that can produce a variety of symptoms in its host. However, if precautionary measures are taken, E. coli infections can be limited or eliminated.

GENERAL INTRODUCTION OF AIDS

Acquired immunodeficiency syndrome (AIDS)

Human immunodeficiency virus (HIV) Retrovirus CD4 T cells, macrophages and

dendrite cells. Cellular immunity is lost. leaves individuals susceptible to

various opportunistic infections

Opportunistic infections association with HIV and AIDS

HIV does not kill anybody directly. People with HIV can get many infections

called opportunistic infections. Many of these illnesses are very serious,

and they need to be treated and some can be prevented.

People with advanced HIV infections are vulnerable to infections and malignancies.

Opportunistic Infections are caused by various pathogenic microorganisms such as bacteria, fungi, virus and parasites.

OPPORTUNISTIC BACTERIAL PATHOGENS

Bacterial pathogens are associated with the significant proportion of morbidity and mortality. The following genera of pathogens are most common in person infected with HIV.

Campylobacter Flavobacterium Haemophilus Mycobacterium Nocardia Pseudomonas Rhodococcus

Salmonella Shigella Staphylococcus Streptococcus Treponema Yersinia

Campylobacterr Campylobacter Campylobacter is a genus that belongs

to Family Campylobacteraceae of Kingdom Bacteria.

Twisted bacteria with spiral or corkscrew appearance.

These are motile with either unipolar or bipolar flagella

Gram-negative. Microaerophilic Oxidase positive test.

Campylobacter &AIDS

Campylobacter infections are among the most common bacterial infections in humans.

Diarrhoea Bacteremia C. jejuni is usually the most common

cause of community-acquired inflammatory enteritis.

Symptoms Includes abdominal pain, cramping, dehydration and fever.

Flavobacterium

Flavobacterium is a genus that belongs to Family Flavobacteriaceae. Gram-negative bacteria. Rod shaped bacteria They maybe motile or non-motile Found in soil and fresh water

Flavobacterium & AIDS

Flavobacterium spp. may play a pathogenic role in patients with advanced HIV disease

Endocarditis Pneumonia Bacteremia F. meningosepticum is the most imp

example of this genus.

Haemophilus

Haemophilus is a genus that belongs to the Pasteurellaceae family

Gram-negative bacteria. Pleomorphic bacteria (wide range of

shapes they occasionally assume) Aerobic or facultatively anaerobic. The genus includes commensal

and pathogenic organisms

Haemophilus & AIDS

Meningitis is one of the most common bacterial infections occurring in persons infected with HIV caused by Haemophilus influenzae,

Pneumonia Upper respiratory tract infections, such as

otitis and sinusitis Genital infections. Recently HIV infection increases the risk of

acquiring invasive H. influenza infection.

OPPORTUNISTIC BACTERIAL PATHOGENS

Oppertunistic infections are also caused by abnormal immune system of host

Because of this reason such infections are most common in person infected with

HIV. We will discuss the effect of five

bacterial genera as oppertunistic pathogens due to weak immune system of the host

Nocardia

Nocardia is a gram positive actinomycete. Human infection is rare and contracted through inhalation. Infection is more common among immunocompromised patients, especially those with impaired cell mediated immunity. The patient may have other infections

e.g tuberculosis.

Rhodococcus

Pneumonia is the most common manifestation of Rhodococcus infection.

Very most of cases originally reported were in patients who were immunocompromised due to malignancies, immunosuppressive.

Pulmonary infection occurs by the inhalation of the Rhodococcus particularly Rhodococcus equi

Salmonella

Salmonella infection has an increased incidence in HIV infected populations.

Salmonellosis and bacteremia are occurring at an increased rate in person with HIV.

A characteristic feature of Salmonellosis in AIDS is the relapses that occur during appropriate antibiotic therapy.

S. typhimurium and S. enteridis are the two most common serotypes isolated from the blood of patients with AIDS in the United States

Yersinia

Yersinia is responsible for causing plague in peoples infected with AIDS

Y. pestis is a gram-negative, facultatively aerobic rod it is primarily a rodent pathogen.

The vactor for this bacterium is a rat flea , Xenopsylla cheopis.

Rat flea is actually an insect which transmits that bacterium between two hosts.

Mycobacterium

 Tuberculosis is an unquestionably, the most potent opportunistic bacterial infection complicating HIV infection caused by Mycobacerium tuberculosis.

It is responsible for more than 2 million deaths and 8 million new cases annually

In India, tuberculosis is the most common opportunistic infection.

About a third of the HIV positive population worldwide is coinfected with M. tuberculosis.

Shigella

Taxonomy Family

Enterobacteriaceae   Four species:

• Shigella dysenteriae:• Shigella flexneri:• Shigella sonnei:• Shigella boydii

Morphology

rod-shaped Gram-negative

General characteristics facultatively anaerobic Non-lactose fermenting non-motile

Infection spread from human to human via the

fecal-oral route major cause of diarrheal disease HIV-infected persons are at increased risk

for infection

StaphylococcusTaxonomy Genus Staphylococcus Family

Staphylococcaceae

Morphology spherical 1 µm in size thick cell wall

Gram-positive

General characteristics facultative anaerobe immobile Coagulase Positive

Are resistant to 122 °F temperatures high salt concentrations (<10%) drying

Infection common flora: skin, nasal cavity, pharynx,

gastrointestinal tract, genitourinary tract

A bacteremia may result in seeding other internal abscesses, other skin lesions, or infections in the lung, kidney, heart, skeletal muscle or meninges.

common cause of community-acquired (CA) or hospital-acquired (HA) bacterial skin and soft-tissue infections among patients with HIV infection.

Pseudomonas aeruginosa Taxonomy

genus Pseudomonas family

Pseudomonadaceae

Morphology rod-shape 1-5 µm long and 0.5-

1.0 µm wide monoflagellated

gram-negative

Infection it often colonizes immuno compromised

patients, like those with cystic fibrosis, cancer, or AIDS .

takes advantage of an individual's weakened immune system .

produces tissue-damaging toxins. causes urinary tract infections, respiratory

system infections, dermatitis, soft tissue infections, bone and joint infections, gastrointestinal infections .

Streptococcus pneumoniae Taxonomy Genus Streptococcus family

Streptococcaceae.

Morphology Cocci 0.5-1.2um often Arranged in Pairs or

Chains

Gram-positive

General characteristics Non motile Carbohydrates fermenters

Infection spontaneously cause disease in humans,

monkeys, rabbits, horses, mice and guinea pigs. Patients with HIV infection are at increased risk

for bacterial pneumonia

Treponema pallidum

Taxonomy genus Treponema family

Spirochaetaceae.

Morphology spiral-shaped 0.2 µm in diameter and 6-

15 µm in length

Gram negative

General characteristics mobile endoflagella Infection transmitted by direct contact Infection is initiated when T. pallidum penetrates

dermal micro abrasions or intact mucous membranes.

Neurosyphilis is most common in patients with HIV infection.

headache, meningeal irritation and nerve abnormalities.