Palindrome : A nucleotide sequence on a DNA molecule in which the same sequence is found on each strand, but in the opposite direction.

p-aminobenzoic acid (PABA) : A factor in the vitamin B complex, a part of all folic acids and required for its formation; neutralizes the bacteriostatic effects of the sulfonamides since it furnishes an essential growth factor for bacteria, the utilization with which the sulfonimides interfere; used as an ultraviolet screen in lotions and creams.

Palpation : A technique used during physical examination that involves the use of the hands to feel for organs, abnormal masses, pulses, or vibrations in the chest.

Pancytpoenia : A significant reduction in the number of red blood cells, white blood cells, and platelets in the circulating blood.

Pandemic : Epidemic over a wide geographical area, or even worldwide.

Pantothenic acid : The beta-alanine amide of pantoic acid. A growth substance widely distributed in plant and animal tissues, and essential for growth of a number of organisms.

PAPR : Powered air-purifying respirators.

Papule : Small, solid elevation of the skin.

Paracentesis : Surgical transcutaneous puncture of the abdominal cavity to aspire peritoneal fluid.

Parasite : An organism that lives on or in a living animal or plant host and derives nourishment from it. (Contrast with saprophyte.)

Parasitemia : Presence of parasites in the blood.

Paravertebral : Beside a vertebra or the vertebral column.

Parenchyma : Cells of a gland or organ that are contained within ans supported by the surrounding connective tissue network.

Parenteral : Route of administration of a drug other than by mouth; includes intramuscular and intravenous administration.

Paresis : Slight paralysis (cysticercosis).

Paronychia : Purulent inflammation about margin of a nail.

Parotitis : Inflammation of the parotid gland, the largest of the salivary glands; mumps is the most common cause of this.

Paroxysm : Rapid onset (or return) of symptoms; term usually applies to cyclic recurrence of malaria symptoms, which are chills, fever, and sweating.

Parthenogenesis : Form of sexual reproduction in which the organism develops without fertilization by the male gamete (Strongyloides stercoralis, parasitic generation).

PAS : Periodic acid-Schiff.

Passive immunity : Immunity resulting from transfer of antibodies or immune cells from an immune to a nonimmune individual. Compare with active immunity.

Pasteurization : A process using mild heat to reduce the microbial level in heat-sensitive materials.

Pathogen : Any disease-producing microorganism.

Pathogenic : Capable of causing disease.

Pathogenicity : The propermpopulation, or the power of an organism to produce disease.

Pathognomic : Symptoms or lesions characteristic of a single disease process, on the basis of which a diagnosis can be determined.

Pathological : Caused by or involving a morbid condition, as a pathological state.

PBP : Penicillin-binding protein.

PCP : Pneumocystis carinii pneumonia.

PCR : Polymerase chain reaction.

Pectinate : Resembling a comb.

Pectinate Body : Hyphal branch with projections on one side like a comb.

PEG : Polyethylene glycol.

Pellicle : A firm or buttonlike mass formed on liquid medium by some fungi.

Penicillinase-(B-lactamase I) : Enzyme produced by some bacterial species that inactivates the antimicrobial activity of certain penicillins (e.g., percutaneous bladder aspiration).

PEP : Protein electrophoresis.

Peptide bond : A type of covalent bond joining amino acids in a polypeptide.

Peptidoglycan : The rigid layer of the cell walls of bacteria, a thin sheet composed of N-acetylglucosamine, N-acetylmuramic acid, and a few amino acids. Also called murein.

Percutaneous : Performed through the skin (e.g., penicillin G).

Perfect State (teleomorph state) : Sexual state of a fungus in which spores are formed after nuclear fusion.

Pericardial tamponade : Condition resulting from accumulation of excess fluid in the pericardium.

Pericarditis : Inflammation of the covering of the heart (pericardium).

Perineum : The portion of the body bound by the pubic bone anteriorly, the coccyx posteriorly, and the bony prominences (tuberosities) of the ileum on both sides.

Periodicity : Recurrence of an event at regular intervals (nocturnal periodicity of microfilariae of Wuchereria bancrofti; malarial symptoms).

Periorbital : Around the eye socket (orbit).

Periosteum : The tough tissue surrounding the surface of any bone.

Periostitis : Inflammation of the periosteum (the thick fibrous membrane that covers the surface of the bone, except for the articular cartilage).

Periplasmic : Refers to the periplasmic space, the space between the cytoplasmic membrane and the outer membrane of Gram-negative bacteria.

Peristalsis : Movement of food through the intestine by contractions of the intestinal musculature.

Perithecium (pl. perithecia) : A large, round or pear-shaped structure usually having a small rounded opening (which differentiates it from a cleistothecium; the opening is called an ostiole) and containing asci and ascospores.

Peritoneal cavity : Space between the visceral and parietal layers of the peritoneum; the serous membrane lining the abdominal cavity and surrounding the contained viscera.

Peritonitis : Inflammation of the peritoneal cavity, most often caused by bacterial infection.

Peritrichous flagellation : Having flagella attached to many places on the cell surface.

Periumbilical : Pertaining to the area surrounding the navel (umbilicus).

Peroxidase : An enzyme which catalyzes the transfer of oxygen from the hydrogen peroxide to a suitable substrate and thus brings about oxidation of the substrate.

Person to person epidemic : An epidemic resulting from person to person contact, characterized by a gradual rise and fall in number of cases.

Personal hygiene : In the field of infectious control, those protective measures, primarily within the responsibility of the individual, that promote health and limit the spread of infectious diseases, chiefly those transmitted by direct contact.

Petechiae : Tiny hemorrhagic spots in the skin or mucous membranes.

Petechial rash : Small, pinpoint, and flat lesions of the skin and mucous membranes associated with hemorrhage beneath the tissue; similar to purpura, except the lesions seen with purpura tend to be larger.

Peyer's patches : Lymphatic tissues in the walls of the large intestine.

PFU : Stands for plaque-forming unit.

Phage : See bacteriophage.

Phagemid : A cloning vector that can replicate either as a plasmid or as a bacteriophage.

Phagocyte : A body cell able to ingest and digest foreign particles.

Phagocytosis : Ingestion of particulate material such as bacteria by protozoa and phagocytic cells of higher organisms.

Pharyngitis : Inflammation of the pharnyx, the muscular tube connecting the nose and mouth to the esophagus and larynx; sore throat.

Phase-contrast microscopy : Technique for direct observation of unstrained material in which light beams pass through the object to be visualized and are partially deflected by the different densities of the object. These light beams are deflected again when they impinge on a special objective lens, increasing in brightness when aligned in phase.

Phaeo : A prefix meaning dark (brownish or blackish).

Phaeohyphomycosis : A subcutaneous or systematic disease caused by a variety of black fungi that develop in tissue as dark, hyphae and/or yeastlike cells.

Phenotype : The observable properties of an organism. Compare with genotype.

Phenylethyl alcohol agar (PEA) : The primary purpose of this medium is to inhibit the Enterobacteriaceae. Most obligate anaerobes and gram-positive facultative anaerobes will grow on this medium.

Phialide : A conidiogenous cell that produces a succession of blastic conidia (phialoconidia) with no increase in length of the phialide.

Phialoconidium (pl. phialoconidia) : A conidium produced by a phialides.

Phosphodiester bond : A type of covalent bond linking nucleotides together in a polynucleotide.

Phospholipid : Lipids containing a substituted phosphate group and two fatty acid chains on a glycerol backbone.

Photoautotroph : An organism able to use light as its sole source of energy and carbon dioxide as sole carbon source.

Photochromogens : Mycobacteria that produce pigment after exposure to light but whose colonies remain buff-colored in the dark.

Photohetrotroph : An organism using light as a source of energy and organic materials as carbon source.

Photophobia : Abnormal sensitivity to light.

Photophosphorylation : Synthesis of high-energy phosphate bonds as ATP, using light energy.

Photosynthesis : The process of using the light energy to synthesize carbohydrates from carbon dioxide (CO2). In general, photosynthesis can be summarized by the equation: CO2 + 2 H2O --> [CH2O] + H2O + O2. See also anoxygenic photosynthesis and oxygenic photosynthesis.

Phototaxis : Movement toward light.

Phototroph : An organism that uses light energy for metabolism. (Contrast with chemotroph.)

Phototroph : In reference to energy source - an organism which uses light as the energy source to drive the electron flow from the electron donors (e.g. water, hydrogen sulfide). Compare with autotroph, lithotroph, heterotroph, organotroph.

Phycobilin : Also phycobiliprotein or biliprotein. A water-soluble pigment which occurs in cyanobacteria and functions as the light-harvesting pigments for phytosystem II.

Phycobiliproteins : Water-soluble red or blue proteins, the colored portion of which is a linear tetrapyrrole. Found in cyanobacteria.

Phycomycosis : Serious infection involving fungi of the zygomycete group, often beginning with necrotic lesions in the nasal mucous or palate but rapidly spreading to involve other tissues. See in immunocompromised patients.

Phylogeny : The ordering of species into higher taxa and the construction of evolutionary trees based on evolutionary (natural) relationships.

Phytanyl : A branched-chain hydrocarbon containing 20 carbon atoms, commonly found in the lipids of Archaea.

Pica : A craving for substances not fit for food, such as starch, clay, ashes, or plaster; ingestion of clay or soil can be associated with exposure to Ascaris, Trichuris, hookworm, Strongyloides, Toxocara, Toxoplasma organisms.

PID : Pelvic inflammatory disease.

Pili : Structures in bacteria similar to fimbrae that participate in bacterial conjugation and transfer of genetic material.

Pilonidal cyst : Hair-containing cyst in the skin or subcutaneous tissue, often with a sinus tract, commonly in the sacrococcygeal area.

Pilus (plural pili) : A fimbria-like structure that is present on fertile cells, both Hfr and F+, and is involved in DNA transfer during conjugation. Sometimes called sex pilus. See also fimbria.

Pinocytosis : In eukaryotes, phagocytosis of soluble molecules.

Pinworm : Human roundworm parasite of the colon and rectum; extremely common in children; diagnostic approach is Scotch tape preparation (Enterobius vermicularis).

Pipe-stem fibrosis : Granulomatous reaction around schistosome eggs in periportal tissues; fibrous tissue is white and hard (Schistosoma japonicum, S. mansoni).

Plaque : A localized area of clearing in a bacterial lawn on an agar plate. The clearing is due to lysis or inhibited growth of cells which is caused by virus or bacteriophage infection.

Plaque-forming unit : Abbreviated as pfu. Refer to any entity which can give rise to a plaque. For example, if a phage stock solution has 1010 pfu/ml, it means that every ml of this stock has 1010 phage particles which can form plaques. This (pfu/ml) is the conventional way to refer to the concentration of a phage preparation. Compare with CFU.

Plasma : Fluid portion of blood; obtained by centrifuging anticoagulated blood.

Plasma cell : A large differentiated and short-lived B lymphocyte specializing in abundant (but short term) anitbody production.

Plasma membrane : See cytoplasmic membrane.

Plasmids : Extrachromosomal DNA elements of bacteria carrying a variety of determinants that may permit survival in an adverse environment or successful competition with other microorganisms of the same or different species.

Platelet : A noncellular disc-shaped structure containing protoplasm found in large numbers in blood and functioning in the blood clotting process.

Pleocytosis : The presence of abnormally large numbers of an organism's genes and the environment on its physical appearance, biochemistry, and physiology.

Pleomorphic : Having various shapes.

Pleomorphism : The occurrence of two or more forms in the life cycle of an organism . Also refers to the occurrence of a form of dermatophyte that ceases to produce conidia (becomes sterile).

Plerocercoid : A tapeworm larva of the genera Diphyllobothrium and Spirometra; also known as a sparganum larva.

Pleura : The serous membrane enveloping the lung and lining the internal surface of the thoracic cavity.

Pleuritic : Referring to inflammation of the pleura (pleurisy).

Pleurodynia : Episodic pain to to transient intercostal muscle (muscles between the ribs which assist in respiration) spasms, caused by irritation of the pleura.

Pleuropulmonary : Pertaining to the lungs and pleura.

Plus-strand nucleic acid : An RNA or DNA strand which has the same sense as the mRNA of a virus.

PM : Postmortem; evening.

PMC : Pseudomembranous colitis.

PML : Polymorphonuclear leukocyte.

PMN : Polymorphonuclear neutrophil.

Pneumonia : Inflammation of the lungs, primarily caused by infectious agents.

Pneumonia, aspiration : Pneumonia caused by aspiration of oropharyngeal or gastric contents.

Pneumonitis : Inflammation of the pulmonary tissue (Ascaris, Strongyloides, and Pneumocystis infections).

Pneumothorax : Introduction of air (usually inadvertently) into the pleural space, leading to collapse of the lung on that side.

PO, p.o. : By mouth, orally (per os).

Polar : Possessing hydrophilic characteristics and generally water soluble.

Polar filaments : Filaments arising from opposite poles of the oncosphere membrane of Hymenolepis nana; they lie between the egg shell and the oncosphere.

Polar flagellation : Condition of having flagella attached at one end or both ends of the cell.

Polar plugs : Mucoid plugs present at both ends of the egg (Trichuris trichiura).

Polyarticular : Occurring in more than one joint.

Poly-beta-hydroxybutyrate (PHB) : A common storage material of prokaryotic cells consisting of a polymer of beta-hydroxybutyrate (PHB) or other beta-alkanoic acids. (PHA).

Polyclonal antiserum : A mixture of antibodies to a variety of antigens or to a variety of determinants on a single antigen.

Polymer : A large molecule formed by polymerization of monomeric units.

Polymerase Chain Reaction (PCR) , is a highly efficient method to amplify low levels of specific DNA sequences in a sample to reach the threshold of detection. Two short DNA "primers", oligonucleotides (small portions of a single DNA strand) specific for the pathogenic DNA sought whose sequence flanks that section of DNA to be amplified, are used. Repeated cycles of DNA denaturation (separation of the double DNA strands), primer annealing (recombination of the double-stranded structure) and extension of the primed DNA sequence (by the enzyme DNA polymerase in the presence of added purine and pyrimidine bases) are performed. Each cycle doubles the amount of specific DNA sequence present and results in an exponential accumulation of the DNA fragment being amplified. The reaction products are hybridized to a radioactiviely labeled DNA segment complementary to a short sequence of the amplified DNA. Following electrophoresis, the radiolabeled product of specific size is detected by autoradiography.

Polymorphonuclear leukocyte (PMN) : Small, actively motile white blood cells containing many lysosomes and specializing in phagocytosis.

Polynucleotide : A polymer of nucleotides bonded to one another by phosphodiester bonds.

Polypeptide : Several amino acids linked together by peptide bonds.

Polysaccharide : A long chain of monosaccharides (sugars) linked by glycosidic bonds.

Porin : A protein channel in the lipopolysaccharide layer of gram-negative bacteria.

Porphin : A cyclic tetrapyrrole in which the four pyrrole groups are linked by their alpha-carbon atoms via methene (-CH=) bridges; porphin is the partial compound of porphyrins.

Porphyrin : A porphin derivative in which the pyrrole beta-carbons are variously substituted. Porphyrin can readily chelate various metals, the metalloporphyrins being components of several important biological pigments, e.g. chlorophylls, cytochromes, heme.

Portal circulation : The circulation of blood to the liver from the small intestine, the right half of the colon, and the spleen via the portal vein.

Porter : A membrane protein that functions to transport substances into and out of the cell.

Post ictal : Referring to a patient's condition following a seizure. Many people are less alert, and transient neurologic findings may be observed.

PPD : Purified protein derivative (skin test antigen for tuberculosis).

PPNG : Penicillinase-producing (i.e., penicillin-resistant) Neisseria gonorrhoeae.

PRAS : Prereduced, anaerobically sterilized.

Precipitation : A reaction between antibody and soluble antigen resulting in a visible mass of antibody-antigen complexes.

Precipitin test : Detection of antigen by allowing specific antibody to diffuse through liquid or gel until an antigen-antibody complex forms, which can be viewed as a line of precipitated material.

Preeclampsia : A condition of the late stages of pregnancy caused by accumulation of toxins in the blood; characterized by high blood pressure,s welling of the hands and feet, and the presence of proteins in the urine. If seizures are present, it becomes known as eclampsia.

Prepatent period : Time from entry of a parasite into the body until the infection is manifested clinically or can be detected by routine diagnostic methods.

PreReduced Anaerobically Sterilized (PRAS) : Media that is sterilized, dispensed, and packaged under anaerobic conditions.

Presumptive identification : An identification of a microorganism based upon simple colony and Gram stain observation and the results of relatively simple and inexpensive tests. Although a presumptive identification is believed to be valid, it may not be.

Prevalence : The proportion of individuals in a population having a disease.

Prevalence rate : The total number of persons sick or portraying a certain condition in a stated population at a particular time (point prevalence), or during a stated period of time (period prevalence), regardless of when that illness or condition began, divided by the population at risk of having the disease or condition at the point in time or midway through the period in which they occurred.

Pribnow box : The consensus sequence TATAAT located approximately 10 base pairs upstream from the transcriptional start site.

Primary antibody response : Antibodies made upon first exposure to antigen; mostly of the class IgM.

Primary metabolite : A metabolite excreted during the growth phase.

Primary producer : An organism that uses light to synthesize new organic material from carbon dioxide.

Primary structure : In an informational macromolecule, such as a polypeptide or a nucleic acid, the precise sequence of monomeric units.

Primary transcript : An unprocessed RNA molecule which is the direct product of transcription.

Primer : A molecule (usually a polynucleotide) to which DNA polymerase can attach the first nucleotide during DNA replication.

Prion : Proteinaceous infectious agent associated with Creutzfeldt-Jakob disease and perhaps other chronic, debilitating central nervous system diseases.

PRN, p.r.n. : As required (pro re nata).

Probe : See nucleic acid probe.

Prochlorophyte : A prokaryotic oxygenic phototroph that contains chlorophylls a and b but which lack phycobilins.

Proctitis : Inflammation of the rectum.

Proctocolitis : Inflammation of the colon (large intestine) and rectum.

Prodromal : Early manifestations of a disease before specific symptoms become evident.

Proglottid : Segments of the tapeworm containing male and female reproductive systems; may be immature, mature or gravid.

Prognosis : Forecast as to the possible outcome of a disease.

Progressive bacterial synergistic gangrene : Serious polymicrobial infection of skin and soft tissue, often a postoperative complication, involving a mixture of microaerobic streptococci and Staphylococcus aureus classically. At times the streptococci are anaerobic or gram-negative bacilli are seen in lieu of the staphylococci.

Prokaryote : A cell or organism lacking a unit membrane-bound (true) nucleus and other organelles, usually having its DNA in a single circular molecule.

Prokaryotic : Organisms without a true nucleus.

Promastigote : Development stage of the family Trypanosomatidae; the base of the flagellum is anterior to the nucleus, and the free flagellar portion is short; there is no undulating membrane present.

Promoter : The site on DNA where the RNA polymerase binds and begins transcription.

Propagule : A unit that can give rise to another organism.

Prophage : The state of the genome of a temperate virus when it is replicating in synchrony with that of the host, typically integrated into the host genome.

Prophylactic : Treatment, usually immunologic or chemotherapeutic, designed to protect an individual from a future attack by a pathogen.

Prophylaxis : Preventive treatment (e.g., the use of drugs to prevent infection).

Prostatisis : Inflammation of the prostate gland, usually caused by infection, characterized by fever, low back or perineal pain, and at times urinary frequency and urgency; a common background factor for recurrent cystitis in males.

Prostheca : A semi-rigid extension of the cell wall, cytoplasmic membrane and cytoplasm and which has a diameter less than that of the cell. (Contrast with stalk).

Prosthesis : An artificial part such as a hip joint or eye.

Prosthetic group : The tightly bound, nonprotein portion of an enzyme; not the same as coenzyme.

Protein : A polymeric molecule consisting of one or more polypeptides.

Protein A : A protein on the cell wall of strains of Staphylococcus aureus (Cowan strain) that binds the Fc portion of antibiotics.

Protenuria : Protein in the urine (Taenia and Hymenolepis spp.).

Protist : A member of the Protista.

Protista1 : A taxon (kingdom) which includes the algae, fungi and protozoa (collectively, the eukaryotic protists), and the prokaryotes.

Protista2 : A kingdom comprising the eukaryotic protists.

Protoheme : A cytochrome produced by Porphyromonas spp. that causes colonies of these anaerobic, gram-negative bacilli to become brown to black in color.

Proton motive force (PMF) : An energized state of a membrane created by expulsion of protons through action of an electron transport chain. See also chemiosmosis.

Protoplasm : The complete cellular contents, cytoplasmic membrane, cytoplasm, and nucleus; usually considered to be the living portion of the cell, thus excluding those layers peripheral to the cytoplasmic membrane.

Protoplast : A cell from which the wall has been removed.

Protoporphyrin : A cytochrome produced by pigmented Prevotella spp., resulting in the characteristic brown-black colonies of these anaerobic, gram-negative bacilli.

Prototroph : The parent from which an auxotrophic mutant has been derived. Contrast with auxotroph; Naturally occurring or wild strain..

Protozoa : Unicellular eukaryotic microorganisms that lack cell walls.

Provirus : See prophage.

Proximal phalanx : The part of a digit (fingers and toes) that is closest to its attachment to the body.

Pruritus : Severe itching (cutaneous larva migrans, infection with scabies or itch mite).

Pseudocyst : Usually refers to a large number of Toxoplasma gondii trophozoites enclosed in a macrophage or some other host cell; parasites bound by host cell tissue.

Pseudohypha : Chain of cells formed by budding which, when elongated, resembles a true hypha; differs from true hyphae by being constricted at the septa, forming branches that begin with a septation, and having terminal cells smaller than the other cells.

Pseudohypha (pl. pseudohyphae) : A series of elongated budding cells remaining attached, resembling hyphae.

Pseudomembrane : Necrosis of mucosal surface simulating a membrane.

Pseudomembranous colitis (PMC) : Syndrome in the large bowel characterized by a layer of necrotic tissue and dead inflammatory cells often caused by the toxin of Clostridium difficile.

Pseudomonad : Member of the genus Pseudomonas, a large group of gram-negative, obligately respiratory (never fermentative) Bacteria.

Pseudopodium (plural : pseudopodia: The protrusion of an amoeboid cell formed by the extrusion or streaming of the cytoplasm (but still enclosed in the membrane) for the purpose of movement or feeding.

Psychrophile : An organism able to grow at low temperatures and showing a growth temperature optimum of < 15 degrees C.

Psychrophilic : Cold-loving (e.g., microorganisms that grow best at low [4C] temperatures.

Psychrotolerant : An organism able to grow at low temperature but having a growth temperature optimum of > 15 degess C.

Ptosis : Dropping of the upper eyelid.

PTT : Partial thromboplastin time.

Public health : The health of the population as a whole.

Punctate : Pertaining to lesions or markings which look like points or dots.

Pure culture : A culture containing a single kind of microorganism.

Purple sulfur bacteria : A group of phototrophic prokaryotes containing bacteriochlorophylls a or b and characterized by the ability to oxidize hydrogen sulfide (H2S) and store elemental sulfur inside the cells.

Purpura : Purplish lesions of the skin and mucous membranes due to hemorrhage beneath the tissues; usually less than 1 cm in size, lesions may be flat or raised.

Purulent : Consisting of pus.

Pus : Product of inflammation, consisting of fluid and many white blood cells; often bacteria and cellular debris are also present.

Pustular : Pertaining to the skin rash with the presence of pus in the lesions.

Pycnidium (pl. pycnidia) : A large, round or flask-shaped fruiting body containing conidia. Pycnidia usually have an opening (an ostiole).

Pyelonephritis : Infection of the kidney and renal pelvis and the late effects of such infection.

Pyocin : Pigment produced by a bacterium that has antimicrobial properties against other strains or species of bacteria.

Pyoderma : Any of the pus-producing lesions of the skin such as boils or impetigo.

Pyogenic : Pus-producing.

Pyriform : Pear shaped.

Pyrite : A common iron ore FeS2.

Pyrogenic : Producing fever.

Pyuria : The presence of pus in the urine (bacteria, white blood cells).

PZA : pyrazinamide.