Key Definitions - Microbiological Terms Flashcards
What is the definition of aetiology?
the cause of a disease
What is the definition of agar?
the solidifying agent in culture media
What is the definition of agglutination?
clumping of cells or particles visible to the naked eye
this is usually the end point in a test which depends upon some agent (e.g. antibody) recognising and cross-linking its target cells or bacteria
What is the definition of anaerobic?
without the presence of oxygen, as in culture of organisms
(obligate anaerobes - e.g. bacteroides
facultative anaerobes - e.g. E. coli
obligate aerobes - e.g. M. tuberculosis)
What is meant by obligate anaerobes, facultative anaerobes and obligate aerobes?
obligate anaerobes:
- an organism that only lives in an environment without oxygen
- will die in the presence of oxygen
facultative anaerobes:
- an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation / anaerobic respiration if oxygen is absent
obligate aerobes:
- cannot make ATP in the absence of oxygen
What is the definition of antiseptic?
chemicals which are used to inactivate vegetative bacteria, but will not kill spores
antiseptics are the least toxic disinfectants, so are used in skin and wound disinfection
What is the definition of autoclave?
pressure cooker for the sterilisation of instruments, clothing & culture media
killing is caused by high pressure and temperature steam which coagulates proteins
What is the definition of bacteriophage?
a virus that infects a bacterium and may carry virulence genes
e.g. in Corynebacterium diphtheriae
What is the definition of blood agar?
nutrient agar to which is added a small amount of blood to provide growth factors required by certain bacteria
What is the definition of a capsule?
the outermost layer of many micro-organisms
it is usually a polysaccharide, often inhibits phagocytosis and often antigenic
e.g. Streptococcus pneumonia, Cryptococcus neoformans
What is the definition of cell wall?
How is it different in Gram positive and negative bacteria?
rigidity comes from peptidoglycan which is much thicker in Gram-positive bacteria
In Gram-negative bacteria, the cell wall is surrounded by an outer membrane of lipopolysaccharide and proteins
these cell wall differences are reflected in the results of Gram staining
What is the definition of chocolate agar?
blood agar that has been partially heated to release more growth factors from the blood for the growth of certain fastidious organisms
(e.g. H. influenzae)
What is the definition of chromosome?
a DNA molecule that encodes the genetic material
one in prokaryotes and many in eukaryotes
What is the definition of coagulase?
an enzyme which clots plasma
it distinguishes S. aureus (which is coagulase positive) from other (“coagulase-negative”) staphylococci
What is the definition of commensal?
a symbiotic relationship in which neither organism is harmed or benefitted as a result of the relationship
applies to most members of the normal microbial flora of humans for most of the time
(e.g. Haemophilus spp., coagulase-negative staphylococci, E. coli)
What is the definition of complement fixation test (CFT)?
a test which detects antibody by virtue of its ability to fix complement
the CFT estimates the total amount of complement fixing antibody present in serum and does not differentiate between immunoglobulin classes
What is the definition of cytotopathic effect?
the effect which some viruses have on the appearance of tissue culture cells, thus allowing their presence to be detected
What is the definition of cytotoxic?
having the ability to lyse or kill other cells
What is the definition of dermatophytes?
fungi which grow on the skin surface
What is the definition of disc diffusion test?
a test for the susceptibility of bacteria to an antibiotic (s) by inhibition of growth of colonies on agar surface around a paper disc containing the antibiotic
What is the definition of disinfectant?
chemicals which are used to inactivate vegetative bacteria, but which will not kill spores
What is the definition of ELISA?
an acronym for enzyme linked immunosorbent assay
sometimes shortened to EIA - enzyme immunoassay
this is an immunological technique which can be adapted to measure either antibody or antigen
antibody may be measured in one immunoglobulin class (e.g. IgG or IgM)
the detection step employs an antibody which has an enzyme “label” and this enzyme can be detected by addition of the appropriate substrate
What is the definition of endotoxin?
lipopolysaccharides of the Gram-negative cell wall which are released on lysis of the bacteria and may cause shock
Lipid A is the component which causes endotoxic shock by means of complex interactions with macrophages, the clotting cascade and the complement system
the polysaccharide component is antigenically variable and is responsible for the O group specificity of E. coli (e.g. E. coli O157)
What is the definition of enterotoxin?
an exotoxin with its site of action in the intestine
(e.g. from Vibrio cholerae)
What is the definition of epidemic?
an outbreak covering a wide geographical area
it is a pandemic if it is global
What is the definition of epitope?
a small portion of a macromolecule recognised by an antibody
What is the definition of eukaryote?
complex cells with nuclei and multiple chromosomes, mitochondria (e.g. fungi, parasites)
What is the definition of exotoxin?
proteinaceous toxins released by intact bacteria which can act either locally at the site of infection
(e.g. enterohaemorrhagic E. coli)
or remotely, if spread haematogenously
(e.g. tetanus, diphtheria)
What is the definition of fastidious?
description applied to micro-organisms with complex growth requirements
(e.g. media, atmosphere)
What is the definition of fimbriae?
short, proteinaceous filaments which allow attachment and adhesion of bacteria
What is the definition of flagella?
long, extracellular, proteinaceous filaments which confer motility to cells by rotating
What is the definition of gamma irradiation?
radiation used commercially to sterilise equipment
What is the definition of Gram stain?
extensively used double stain to broadly characterise bacteria and make them more easily seen in microscopy
Gram-positive bacteria are purple in colour
Gram-negative bacteria are pink
(the latter colour depends to some extent on the counterstain used in the staining technique)
What is the definition of haemagglutination?
agglutination of red cells, usually with a specific antigen pre-coated on their surface
What is the definition of haemolysin?
a toxin which lyses erythrocytes
What is the definition of haemolysis?
lysis of erythrocytes
may be used to differentiate, e.g. streptococcal, species on blood agar
What is the definition of immunofluorescence?
a technique in which an antibody with a fluorescent dye attached is used to detect either an antigen or another antibody
the antibody binds to its target and the fluorescent label is visible under an ultraviolet microscope
What is the definition of Koch’s postulates?
historical rules (often quoted but now outdated) to decide whether a particular organism is responsible for a particular disease:
- the organism is found in all cases of the disease
- the organism can be cultured in vitro in pure culture
- the organism can cause the disease in other susceptible hosts
What is the definition of lipopolysaccharide?
an endotoxin
lipopolysaccharides of the Gram-negative cell wall which are released on lysis of the bacteria and may cause shock
What is the definition of monoclonal?
a single antibody produced from an in vitro cell culture
a monoclonal antibody will only recognise its own particular epitope
commonly used in diagnostic tests because of their specificity
What is the definition of nucleic acid amplification test (NAAT)?
a test that detects micro-organism nucleic acid (DNA or RNA) by nucleic amplification
the most commonly used NAAT is the polymerase chain reaction (PCR)
What is the definition of nosocomial?
hospital acquired (e.g. infection)
What is the definition of nutrient agar?
minimal agar with the addition of amino acids, nucleotides and some cofactors
used for the growth of non-fastidious organisms
What is the definition of outbreak?
clusters of cases of the infection caused by the same organism, apparently related in time and/or geographically
What is the definition of pasteurization?
process of heating (e.g. milk) to 65oC for 30 minutes to kill spoiling organisms, and some pathogens
What is the definition of pathogenesis?
the ways in which micro-organisms produce disease
What is the definition of PCR?
polymerase chain reaction
an in vitro DNA amplification method for the selective amplification of a sequence of DNA from a specimen or sample
used to identify the presence or type of a particular genetic sequence
What is the definition of penicillin binding proteins (PBP)?
enzymes in the cell wall which help synthesise peptidoglycan and are inhibited by proteins (penicillins which bind directly to PBPs)
What is the definition of peptidoglycan?
a complex carbohydrate polymer cross-linked with amino acids
it is an important constituent of cell walls
B-lactam and glycopeptide antibiotics, acting at different sites, inhibit its synthesis
What is the definition of plasmids?
supplementary DNA molecules of bacteria which often encode antibiotic resistances and allow their transfer to other cells
What is the definition of prokaryote?
simple cells without a nucleus and typically a single chromosome (e.g. bacteria)
What is the definition of rising titre?
a single high antibody level can represent previous exposure or immunisation
to diagnose infection reliably, the antibody level should increase significantly between the acute sample, collected when the patient first presents, and the convalescent sample, collected 10-14 days later
a fourfold difference between specimens tested simultaneously is generally accepted as a significant rising titre
What is the definition of serology?
general term for tests which infer the presence of infection by measuring the patient’s antibody response to likely pathogens
the presence of antibody does not always mean active infection, however, and informed interpretation of the results is vital
What is the definition of spore?
a thick-walled bacterial, or fungal, resting stage
may be useful in bacterial identification (e.g. terminal spores in Clostridium tetani)
in most cases they are highly resistant (e.g. anthrax spores on Gruinard Island)
What is the definition of synergy?
enhanced effect when certain antibiotics are used in combination
(e.g. gentamicin and penicillin)
What is the definition of titre?
many older serological tests (e.g. complement fixation test) involve the testing of a range of doubling dilutions of serum
the highest dilution at which the test is positive gives the titire
(technically the inverse of the dilution)
What is the definition of virulence?
degree of pathogenicity of an organism through its possession of virulence factors
What is the definition of Ziehl Neelsen stain (ZN)?
special stain required to identify mycobacteria on microscopy
once such organisms are stained, the stain is resistant to washing with concentrated acid and alcohol
these organisms are called acid-alcohol fast bacilli (AAFB)
What is the definition of adenoviruses?
What diseases are they associated with?
a family of over 40 viruses which are common causes of respiratory infections, conjunctivitis and gastroenteritis in children
agents of spongiform encephalopathy
abnormal proteins that accumulate in the brain to cause spongiform encephalopathy
e.g. Creutzfeld-Jacob disease (CJD), new variant CJD (ncCJD), Gerstmann Sträussler Scheinker syndrome (GSS), kuru and fatal familial insomnia
What is the definition of Ascaris lumbricoides?
What diseases are they associated with?
a large nematode that causes intestinal infection and (very rarely) obstruction
this worm is easily visible macroscopically, being 15-30 cm (approx) in length
infection is by ingestion of embryonated eggs
What is the definition of Aspergillus spp.?
What diseases are they associated with?
fungi which cause
- aspergilloma (fungal ball) in lung cavities
- otitis externa
- allergic bronchopulmonary aspergillosis
- invasive aspergillosis in immunocompromised individuals
the most common species encountered is A. fumigatus
What is the definition of atypical mycobacteria?
What diseases are they associated with?
there are a large number of Mycobacterium spp. which are present in the environment
some of these can cause disease in immunocompromised patients (Mycobacterium avium complex)
these can sometimes cause diagnostic problems by giving false positive Ziehl-Neelsen smears
e.g. in samples collected via bronchoscopes that have been washed with contaminated tap water
What is the definition of Bacillus spp.?
What diseases are they associated with?
large brick-shaped aerobic Gram-positive bacilli that produce spores
unidentified Bacillus spp. may be isolated from environmental sources (e.g. dust / clothing), but are rarely of clinical significance
Bacillus anthracis is the cause of the potentially fatal disease anthrax
Bacillus cereus causes an enterotoxin-mediated food poisoning, clasically as a result of germination of spores in food that has been kept warm for a prolonged period (e.g. rice)
What is the definition of Bacteroides fragilis group?
(Gram-negative bacillus ; anaerobe)
What diseases are they associated with?
group of anaerobes which are the most predominant organisms in normal large bowel flora and faeces
often present in mixed intra-abdominal infections
RESISTANT to penicillin but SENSITIVE to metronidazole
What is the definition of Bordetella pertussis?
What diseases are they associated with?
fastidious Gram-negative bacilli
strictly aerobic and a little difficult to grow - a special perinasal swab is used to collect the sample
causes whooping cough (pertussis)
most children are immunised in their first year
What is the definition of Borrelia burgdorferi?
What diseases are they associated with?
the spirochaete that causes Lyme disease
the organism is transmitted from rodent and ruminant hosts to man by the Ixodes tick, a zoonosis
it characteristically presents with a skin rash (erythema chronicum migrans) and an arthritis
as the organism is difficult to grow, diagnosis is by serology
What is the definition of Brucella spp.?
What diseases are they associated with?
fastidious Gram-negative bacilli
strictly aerobic and difficult to culture so diagnosis is largely achieved by antibody detection (serology)
transmitted from farm animals (zoonosis)
cause of brucellosis
What is the definition of Campylobacter spp.?
What diseases are they associated with?
curved Gram-negative bacilli
microaerophilic and grows at 42oC
commonest bacterial cause of gastroenteritis in the UK
What is the definition of Candida spp.?
What diseases are they associated with?
yeasts that cause superficial infections in the normal host
(oral and genital thrush , nappy rash)
and deep infection in the immunocompromised host
(e.g. oesophageal candidiasis, disseminated candidiasis)
the commonest species encountered is C. albicans
What is the definition of Chlamydia pneumoniae?
What diseases are they associated with?
the most recently recognised species of Chlamydia
it is a cause of community acquired pneumonia
diagnosis is unsatisfactory at present
culture is difficult and serology for antibody is the best option, though specific tests are not widely available
What is the definition of Chlamydia psittaci?
What diseases are they associated with?
the cause of psittacosis and ornithosis
a zoonosis contracted by contact with birds (especially parrots), lambs and other mammals
in humans, the disease presents as a pneumonia
pregnant women are at risk of abortion and should avoud contact with sheep during lambing
diagnosis is usually serological
What is the definition of Chlamydia trachomatis?
What diseases are they associated with?
a cause of genital and opthalmic infections including:
- nonspecific (non-gonococcal) urethritis
- cervicitis
- pelvic inflammatory disease (PID)
- lymphogranuloma venereum
- neonatal conjunctivitis and trachome
- pneumonia in neonates & immunocompromised
different serotypes are responsible for the different diseases
C. trachomatis is the commonest cause of sub- and in-fertility in the developed world
culture is laborious and time-consuming and infection is usually diagnosed by detecting chlamydia DNA by a NAAT (e.g. PCR)
What is the definition of chlamydiae?
What diseases are they associated with?
small obligately intracellular bacteria which, like viruses, can only be grown in cell culture
What is the definition of Clostridium botulinum?
( Gram-positive bacillus ; spore forming anaerobe)
What diseases are they associated with?
cause of botulism following ingestion of contaminated food
most potent neurotoxin known to man
rare in the UK
What is the definition of Clostridium difficile?
(Gram-positive bacillus ; spore forming anaerobe)
What diseases are they associated with?
cause of pseudomembranous colitis and antibiotic-associated diarrhoea
produces toxins and spreads easily in hospital due to spore formation
treated with oral metronidazole or vancomycin
What is the definition of Clostridium perfringens?
(Gram-positive bacillus ; spore forming anaerobe)
What diseases are they associated with?
formerly called C. welchii
present in normal faeces, but toxigenic strains can cause food poisoning
it is also the main cause of “gas gangrene”, but this is now rare and most isolates from wounds represent faecal contamination
serious infection is treated with penicillin and/or metronidazole
What is the definition of Clostridium tetani?
(Gram-positive bacillus ; spore forming anaerobe)
What diseases are they associated with?
cause of tetanus due to toxin acting on the central nervous system
infected wound is often insignificant and the organism may not be cultured
toxoid (modified toxin) is used for immunisation
What is the definition of coronaviruses?
What diseases are they associated with?
a cause of the common cold
a new form of coronavirus is responsible for the new described infection SARS (severe acute respiratory syndrome)
What is the definition of Corynebacterium diphtheriae?
What diseases are they associated with?
an aerobic Gram-positive bacillus that is the cause of the toxin-mediated disease, diphtheria
only strains of the bacterium that are infected with a bacteriophage produce toxin
the usual site of infection is the throat, and the target organs for the diphteria toxin are the heart and CNS
if fatal, death is caused by respiratory obstruction, heart failure and/or respiratory paralysis
diphtheria is treated with antibiotics and antitoxin
most strains of C. diphtheriae that are isolated are non-toxigenic, and therefore not capable of causing diphtheria
What is the definition of Coxsackie viruses (enteroviruses)?
What diseases are they associated with?
cause a wide range of infections
coxsackie A viruses (1-24) associated especially with herpangina (mouth blisters) and hand foot & mouth disease
and coxsackie B viruses (1-6) associated with Bornholm disease (pleurodynia)
What is the definition of Cryptococcus neoformans?
What diseases are they associated with?
a yeast that causes meningitis in immunosuppressed patients, predominantly those with AIDS
this organism is easily cultured and there is a good antigen detection test which works on serum or CSF
the polysaccharide capsule gives a characteristic halo when examined microscopically in a suspension of India Ink
What is the definition of Cryptosporidium spp.?
What diseases are they associated with?
a protozoan first recognised as a cause of severe diarrhoea in AIDS patients
it is now known to be a common cause of self-limiting diarrhoea in children
cysts are frequently found in water supplies and lead to outbreaks
diagnosis is by microscopy for cysts in stools and there is no available treatment
What is the definition of cytomegalovirus (CMV)?
What diseases are they associated with?
a herpesvirus
primary post-natal infection in 0.3% of births though only a minority are affected
in adults subclinical infection is common but CMV may cause glandular fever
retinitis and colitis are common in AIDS patients
What is the definition of dengue?
What diseases are they associated with?
caused by four mosquito-borne viruses
cause rash, fever and viral haemorrhagic fever (VHF)
recent change in epidemiology with new areas affected (e.g. Carribbean)
no anti-viral treatment or prophylaxis is available
What is the definition of dermatophytes?
What diseases are they associated with?
filamentous fungi that cause infections of the skin (ringworm, tinea pedis) and nails (onychomycosis)
the commonest are Tricophyton spp. and Microsporum canis
What is the definition of ebola?
What diseases are they associated with?
a viral haemorrhagic fever with high mortality , restricted to central and western africa
What is the definition of Echinococcus spp.?
What diseases are they associated with?
a genus of helminth that causes hydatid disease
the commonest species is E. granulosus, a tapeworm of dogs, whose life cycle includes the small intestine of dogs (foxes, wolves, etc.) and the internal organs of ruminants (e.g. sheep, goats)
if humans ingest the tapeworm ova, the worms hatch out and migrate to distant tissues (most commonly lungs / liver) and form large fluid-filled cysts
because the lifecycle does not progress in human infection, the human is considered to be an “accidental” or “dead-end” host
What is the definition of Echoviruses (enteroviruses)?
What diseases are they associated with?
viruses which cause a wide range of infections
(e.g. fever, non-vesicular rashes, meningitis)
What is the definition of Entamoeba histolytica?
What diseases are they associated with?
an amoeba that causes severe diarrhoea (amoebic dysentery)and, occasionally, fluid-filled lesions in the liver (“amoebic abscess”)
infection is by the faecal-oral route, and is acquired in areas of poor sanitation
diagnosis is by direct detection of amoebic cysts (and more rarely motile trophozoites) in stool samples
amoebic abscesses may be diagnosed by serology
What is the definition of enterobacteriaceae?
(enteric Gram-negative bacilli)
What diseases are they associated with?
often colloquially called “coliforms”
they are inhabitants of the human gut
Gram-negative rods that ferment glucose and are oxidase negative
includes:
- Escherichia coli
- Klebsiella spp.
- Proteus spp.
- Salmonella spp.
- Shigella spp.
- Yersinia spp.
What is the definition of Enterobius vermicularis?
What diseases are they associated with?
pin worm, threadworm
a very common helminth infection, transmitted by ingestion of ova from the faeces of infected individuals
diagnosis is by detection of ova in stool or from anal samples
when diagnosed, this infection is usually treated with an anti-helminthic agent but many cases remain undiagnosed
What is the definition of Enterococcus spp.?
What diseases are they associated with?
inhabitants of the human gut
Gram-positive cocci that were formerly classified as Streptococci
What is the definition of Enterococcus faecalis?
(Gram positive coccus)
What diseases are they associated with?
a gut commensal, which can cause a urinary tract infection
vancomicin resistant enterococci (VRE) are an increasing problem in some hospitals
What is the definition of enterovirus 70?
What diseases are they associated with?
a major cause of outbreaks of acute haemorrhagic conjunctivitis
while enterovirus 71 causes outbreaks of hand, foot & mouth disease, meningitis and encephalitis
What is the definition of enteroviruses?
What diseases are they associated with?
this group includes:
- polio
- coxsackie
- echo and entero viruses
all can cause non-specific febrile illnesses, and aseptic meningitis
despite the name, enteroviruses generally DO NOT cause gastrointestinal disease
What is the definition of Epstein-Barr virus?
What diseases are they associated with?
this herpesvirus is a cause of glandular fever (infectious mononucleosis)
EBV is associated with several tumours: particularly Burkitt’s lymphoma and nasopharyngeal carcinoma
What is the definition of Escherichia coli?
(Gram negative bacilli)
What diseases are they associated with?
a lactose fermenting coliform and commensal of the GI tract
most common cause of urinary tract infection
also causes neonatal meningitis and some strains cause diarrhoea
different serotypes tend to cause different diseases, with E. coli 0157 the best known as a cause of bloody diarrhoea & haemolytic-uraemic syndrome
What is the definition of Giardia intestinalis?
What diseases are they associated with?
a protozoan found as trophozoites in the upper small intestine or as cysts in faeces
it is a major cause of diarrhoea worldwide and can cause failure to thrive due to malabsorption in children
diagnosis is by microscopy of stools for cysts or of duodenal aspirates or duodenal biopsies for trophozoites
treatment is with metronidazole
What is the definition of Haemophilus influenzae?
What diseases are they associated with?
fastidious Gram-negative coccobacilli
capsulated strains type b (Hib) cause childhood meningitis and epiglottitis, but all children are now offered immunisation
non-capsulated strains cause exacerbations of CGAD, sinusitis and otitis media
What is the definition of Helicobacter pylori?
What diseases are they associated with?
curved Gram-negative bacilli
it is microaerophilic and strongly urease positive
it causes gastritis and peptic ulceration
What is the definition of helminths?
What diseases are they associated with?
term for parasitic worms
these are further divided into:
- nematodes (roundworms)
- cestodes (tapeworms)
- trematodes (flukes)
parasitic worms have life cycles which include, but are not restricted to, the human host
the host in which sexual reproduction takes place is known as the definitive host
What is the definition of hepatitis A?
What diseases are they associated with?
spread by the faecal-oral route, hepatitis due to HAV is often subclinical in children
in adults, although symptoms may be prolonged, fulminant infection and death are very rare and a carrier state does not develop
active and passive immunisation are available
What is the definition of Hepatitis B?
What diseases are they associated with?
spread perinatally or by sexual contact, in blood or bodily fluids
symptoms and outcome of infection are related to age and immune competence
acute infection is subclinical in most neonates and the immunosuppressed and the risk of chronic infection is high
a person who is positive for hepatitis B surface antigen for more than 6 months is considered to have a chronic infection
chronic infection is associated with increased risk of cirrhosis and hepatoma (primary liver cancer, hepatocellular carcinoma) and of extra-hepatic manifestations (e.g. polyarteritis nodosa and glomerulonephritis)
active and passive immunisation are available
What is the definition of Hepatitis C?
What diseases are they associated with?
spread mainly in blood or bodily fluids
acute infection is often subclinical, but chronic infection (HCV RNA positive > 6 months) follows 80% of acute infections
chronic infection is associated with increased risk of cirrhosis and hepatoma
the success of antiviral treatment is genotype-dependent and there are neither active nor passive immunisations available
What is the definition of Hepatitis D?
What diseases are they associated with?
this defective virus, also known as delta agent, can only infect in the presence of hepatitis B
either by co-infection at the same time or by super-infection of a hepatitis B carrier
it is preventable by preventing hepatitis B
What is the definition of hepatitis E?
What diseases are they associated with?
a cause of enterically transmitted hepatitis in many developing countries
no carrier state develops
mortality is high in pregnant women
there is no active or passive immunisation availble
What is the definition of herpes B?
What diseases are they associated with?
a monkey herpes virus which is a rare cause of severe encephalitis in man
What is the definition of Herpes simplex virus?
What diseases are they associated with?
infections particularly important in the immunosuppressed
specific antivirals are available
Type 1 is the common cause of oropharyngeal disease (gingivostomatitis and recurrent cold sores)
Type 2 is the common cause of genital herpes simplex
Keratoconjunctivitis is a common and encephalitis is a rare HSV complication
What is the definition of herpes virus family?
What diseases are they associated with?
large family of viruses including:
- herpes simplex
- varicella zoster
- cytomegalovirus
- Epstein Barr virus
- human herpes viruses 6, 7 and 8
- herpes B
they remain latent in cells of the host after primary infection and may reactivate later
What is the definition of HIV?
What diseases are they associated with?
a retrovirus
human immunodeficiency virus type 1 is a global infection
type 2 is largely restricted to western africa or contacts with west africa
several subtypes of HIV1 recognised with differing epidemiology
both viruses cause AIDS
What is the definition of hookworms?
What diseases are they associated with?
two species of helminths - Ankylostoma duodenale and Necator americanus
hookworms live attached to the small intestine, from where they release ova into the gastrointestinal tract
on excretion, ova hatch into free-living larvae
the larvae penetrate the skin of the foot and migrate to the lungs, from which they make their way to the small intestine (the site of infection)
the volume of blood lost as a result of hookworm infection may result in an iron-deficiency anaemia
What is the definition of human T-cell leukaemia viruses (HTLV)?
What diseases are they associated with?
retroviruses
HTLV1 is the cause of adult T-cell leukaemia / lymphoma and tropical spastic paraparesis
no diseases are associated with HTLV2 yet
What is the definition of human herpesvirus 6?
What diseases are they associated with?
HHV6 is the cause of exanthem subitum (roseola infantum)
this is a common disease in babies and infants that causes a high fever followed by a rash
What is the definition of human herpesvirus 7?
What diseases are they associated with?
no disease associations yet
What is the definition of human herpesvirus 8?
What diseases are they associated with?
also known as Kaposi’s sarcoma associated herpesvirus (KSHV)
it has recently shown to be the cause of Kaposi’s sarcoma
What is the definition of influenza viruses?
What diseases are they associated with?
- Types A and B cause a wide range of respiratory illness, including influenza
- Type C causes mild respiratory infection
annual epidemics due to types A or B occur and pandemics due to type A occur at unpredictable frequency
infection is more severe in those with chronic heart and lung disease and the immunocompromised, for whom annual immunisation is recommended
chemoprophylaxis and antiviral therapy are available but little used in the UK
What is the definition of Klebsiella spp.?
What diseases are they associated with?
gram negative bacilli and a lactose fermenting coliform
cause urinary tract infections and hospital acquired infections (rarely pneumonia)
may become resistant to commonly used antibiotics
What is the definition of Lactobacillus spp.?
What diseases are they associated with?
a genus of Gram-positive cocci that constitutes the majority of the normal flora of the post-pubertal vagina
rarely implicated in disease
also forms a component of “probiotic” foods
(e.g. L. acidophilus)
What is the definition of lassa fever?
What diseases are they associated with?
a highly infectious viral haemorrhagic fever of Western Africa
What is the definition of Legionella pneumophilia?
What diseases are they associated with?
the cause of Legionnaire’s Disease and Pontiac Fever
lives in water supplies, cooling towers, etc. and infection usually results from exposure to a fine aerosolised spray
diagnosis by culture (extended incubation on specialised media) is possible, and the organism can be detected by direct immunofluorescence
in both cases, bronchial lavage gives a better yield than sputum
serology for Legionella antibody may be used, but the appearance of the antibody may be considerably delayed
more commonly the diagnosis is made by detection of Legionella antigen in urine samples
What is the definition of Leptospira interrogans?
What diseases are they associated with?
the spirochaete responsible for leptospirosis (Weil’s disease)
approximately 200 serovars of L. interrogans have been recognised, each associated with a specific mammilian host, including:
- canicola (dogs)
- icterohaemorrhagiae (rats)
- hardjo (cattle)
the organism is excreted in urine, hence the risk of contracting the disease through exposure to contaminated water (e.g. sewage, water sports)
although the organism can be cultured from blood, urine and CSF, this is difficult and diagnosis is made by serology for antibody
What is the definition of Listeria monocytogenes?
What diseases are they associated with?
gram-positive rod
found in animal (e.g. unpasterurised cheese) and vegetable (e.g. salads) products and may be ingested
causes meningitis in neonates and the elderly and bacteraemia in pregnancy
What is the definition of lice?
What diseases are they associated with?
small wingless blood-sucking insects
three species of lice infect humans:
- the body louse - Pediculus humanus
- the head louse - Pediculus capitis
- the pubic (crab) louse - Phthirus pubis
of these, only the body louse is a disease vector responsible for transmission of infections such as rickettsial diseases and relapsing fever
head and pubic lice spend their lives attached to hairs, predominantly in the regions suggested by their names
conversely, body lice tend to occupy clothing,to which they return after taking blood meals
the eggs of head lice are attached to scalp hairs, whereas body lice lay their eggs in clothing
What is the definition of Malassezia spp.?
What diseases are they associated with?
a group of dimorphic fungi that cause the skin conditions seborrhoeic dermatitis and pityriasis versicolor
What is the definition of measles?
What diseases are they associated with?
increased severity in those with impaired cell-mediated immunity who are at risk of life-threatening illness without any rash
incidence greatly reduced by active immunisation (MMR) of children
passive immunisation available for contacts at risk of severe disease
What is the definition of Microsporum canis?
What diseases are they associated with?
a form of dermatophyte
What is the definition of Milleri-group streptococci?
What diseases are they associated with?
formerly classified as Streptococcus milleri
a group of usually non-haemolytic streptococci that includes, among others, S. constellatus and S. anginosus
Milleri-group streptococci are normally found in the gastrointestinal tract
they are common causes of deep abscesses e.g. in the liver, brain or lung
What is the definition of Moraxella catarrhalis?
(Gram negative coccus)
In what diseases is it implicated?
has undergone successive name changes from Neisseria catarrhalis to Branhamella catarrhalis
it is a respiratory pathogen, causing exacerbations of chronic bronchitis
also causes otitis media in children
third commonest cause of both after Streptococcus pneumoniae and Haemophilus influenzae
80% or more strains contain beta-lactamase
