Bacteriology is the branch of microbiology that focuses on bacteria. Bacteria are named according to the binomial Linnean system that uses genus and species. For example, regarding the name of the well-known bacteria Escherichia coli, Escherichia is the genus and coli is the species name.
Important rules regarding nomenclature of Bacteria
Family: Enterobacteriaceae Order: Enterobacterales
Generic plural name: streptococci, staphylococci, mycobacteria
Binary genus-species combinations are always used in the singular. Genus used alone (capitalized and italicized) is usually used in the singular, but it may be used in the plural (not italicized) if it refers to all species within that genus.
Salmonella enterica is…
Salmonellae are ubiquitous…
In a hospital laboratory, the bacteriology section identifies pathogenic bacteria in a clinical sample, isolates them in an appropriate culture media, identifies them using different biochemical or molecular tests, and also determines the antimicrobial susceptibility patterns (including MIC determination) of the isolates.
Total laboratory automation (TLA) is a system that automates culture-based testing in the clinical microbiology laboratory.
BioMérieux's API identification products are test kits for the identification of Gram-positive bacteria, Gram-negative bacteria, and yeast.
ESKAPE is the acronym for six nosocomial pathogens that can ‘escape’ commonly used antibiotics and can develop into MDR.
Live, attenuated vaccines and inactivated vaccines are two basic types of vaccines used to protect susceptible individuals from infectious diseases.
Relapsing fever is a bacterial infection characterized by recurrent episodes of fever and nonspecific symptoms following exposure to insect vector-carrying Borrelia species.
Infective dose is defined as a minimum number of microorganisms required for an infection to proceed.
Treponema pallidum is the causative agent of syphilis, an infectious venereal disease in humans. Primary, secondary, tertiary latent stages.
Probiotic microorganisms displace pathogens and enhance the development and stability of the microbial balance in the large intestine.
Scrub typhus also known as bush typhus, is an emerging infectious disease caused by a bacteria called Orientia tsutsugamushi
Archaea is a group of phylogenetically related prokaryotes distinct from Bacteria and known for tolerance to physiochemical extremes.
Spirochetes are long, thin, flexible, spirally coiled helical bacilli. Spirochetes cause syphilis, Lyme disease, relapsing fever, leptospirosis, yaws.
Human skin is home to billions of diverse bacteria, archaea, fungi, and viruses with bacteria making up the vast majority
Bacillus is a gram-positive rods. It produces two enterotoxins, emetic (vomiting) and diarrheal – causing two types of illness.
Moraxella catarrhalis is a small gram-negative diplococci that resembles Neisseria and causes otitis media in children.
ESBL are a group of enzymes produced by both Gram-negative and Gram-positive bacteria which can hydrolyze all β- lactam agents except
Lyme disease or Lyme borreliosis is a vector-borne zoonotic disease caused by Borrelia burgdorferi.
Enterococcus is gram-positive cocci in chains and is catalase negative. It causes infections of Urinary tract and biliary tract.
Enteric gram-negative rod, produces red-pigmented colonies. It causes hospital-acquired pneumonia, UTI and sepsis.
Phenotypic assays to detect carbapenemase-producing organisms are either growth-based assays (MHT or CIM) or hydrolysis methods.
Dark field microscopy is the most specific and sensitive technique to diagnose syphilis when an active chancre or condyloma lata is present.
Presence of bacteria in sterile body fluids, isolation of Mycobacterium tuberculosis or any other bio-terrorism agents should be reported immediately.
Clerical errors, inappropriate containers/conditions, inappropriate or inadequate specimens, delay in transit lead to sample rejection.
Agent of whooping cough (pertussis), Bordetella pertussis is a small gram-negative coccobacilli.
Quorum sensing (QS) is a bacterial cell-cell signaling mechanism that helps them to adjust gene expressions based on requirements.
AWaRe classifies antibiotics into three stewardship groups: Access, Watch and Reserve to emphasize their optimal use.
Bacteroides fragilis is a gram-negative, pleomorphic anaerobe responsible for variety of anaerobic infections including peritonitis.
Actinomyces is a heterogeneous group of gram-positive, pleomorphic bacilli responsible for the disease actinomycosis.
Carba NP test (CNPt) is a biochemical test for rapid detection of carbapenemase production on Gram-negative bacilli.
Francisella tularensis is a gram-negative coccobacillus and is the etiologic agent of tularemia. It is transmitted to humans from rodents and rabbits.
Burkholderia pseudomallei is a water- and soil-borne gram-negative bacterium. Causative agent of melioidosis, it is regarded as a potential bioterror agent.
Leptospira interrogans is a tightly coiled fine spirochete responsible for the disease leptospirosis (weil's disease).
Meningococci are capsulated gram-negative diplococci. Commensal of nasopharyx they may cause meningitis in susceptible persons.
Macrolides (erythromycin, azithromycin, clarithromycin) inhibit bacterial protein synthesis by binding with the 50S subunit of the ribosome.
Nocardia species are gram-positive, variably acid-fast, filamentous, and strictly aerobic organisms belonging to the actinomycetes group.
Legionella is a gram-negative pleomorphic rod, responsible for a serious type of pneumonia called Legionnaires' disease.
Ziehl-Neelsen staining, culture in Lowenstein-Jensen medium and GeneXpert MTB/RIF assay are useful methods for the diagnosis of tuberculosis.
Fluorescence microscopy is widely used in diagnostic microbiology (diagnosis of tuberculosis, trichomoniasis) and in microbial ecology.
Gram positive club shaped (chinese letter form) bacteria responsible for diphtheria.
Commensal in the large intestine of humans and is responsible for the disease, gas gangrene.
Gram positive, obligate anaerobe, looks like drum-stick shaped and causes tetanus.
Gram positive, anaerobic rod which produces powerful neurotoxin "botulinum toxin".
Yersinia pestis is a short gram-negative rod, responsible for deadly zoonotic disease, plague.
Dark-field microscopy is used for the observation of living, unstained cells. The specimen is brightly illuminated while the background is dark.
A potential biological weapon which causes important zoonotic disease called anthrax.
Streptococcus agalactiae (GBS), is a beta-hemolytic, CAMP test positive, gram-positive cocci. It can cause severe infection in newborns.
Listeria monocytogenes is a facultative intracellular Gram-positive coccobacilli responsible for listeriosis, one of the serious food-borne infections.
Internalin, listeriolysin O, phospholipases, etc are major virulence factors of Listeria monocytogenes.
Alpha (α) toxin, Beta (β) toxin, Epsilon (ε) toxin, and Iota (ι) toxin are the major toxins of Clostridium perfringens.
Most microorganisms grow best around neutral pH values (6.5 - 7.0), but some thrive in extreme pH conditions (pH10).
Penicillins, cephalosporins, monobactams, and carbapenems are major beta-lactam antibiotics; active against both gram-positive and negative bacteria.
MIC test determines the antimicrobial activity of a test agent against a specific bacteria. It is done via E-test, tube/agar dilution method.
Simple to use, best for laboratories with less sample load and the most commonly used method for anaerobiosis.
Major virulence factors of H. pylori are flagella, urease enzyme, adhesins, VacA, CagA, OpiA, and DupA.
Pili, outer membrane proteins, IgA1 protease and lipo-oligosaccharide (LOS) are important virulence factors of Neisseria gonorrhoeae.
Bacterial species capable of producing H₂S release sulfide which combines with iron present in the medium forming black precipitate.
Characterization of an organism beyond its species level to determine relatedness. Useful for epidemiologist in outbreak investigations.
When a panel of lytic phages is inoculated on a lawn inoculum of the bacteria, phages which are able to set up a lytic infection produce a clear zone.
Some bacteria such as Bacillus sps can hydrolyze starch (amylose and amylopectin) using the enzymes α-amylase and oligo-1,6-glucosidase.
Anaerobic bacteria are part of the normal flora but can cause abscess formation and tissue necrosis when enter into sterile sites.
Serotyping is the classic tools for epidemiological study of organisms having multiple serotypes: E. coli, Salmonella, Vibrio, Shigella, S. pneumoniae.
Gram-positive bacilli are a diverse group of bacteria responsible for variety of infections such as gas-gangrene, tetanus, anthrax, etc.
Patterns of acid production from the carbohydrates – glucose, maltose, lactose, sucrose, (and fructose) – are used to identify Neisseria.
Furazolidone disk test is used to differentiate staphylococci (sensitive) from micrococci (resistant).
An engineering control to protect laboratory workers, laboratory environment, and work materials from exposure to infectious or biohazardous aerosols.
Lac operon is a well-known example of an inducible gene network that regulates the transport and metabolism of lactose in Escherichia coli.
Psychrophiles can grow at 0°C, mesophiles have optimum temperature near 37°C, and thermophiles grow best at 50-60°C.
Major virulence factors of S. aureus are capsule, teichoic acid, protein A, enterotoxin, TSST-1, coagulase, hyaluronidase, etc.
Glycopeptide antibiotics act by inhibiting cell wall synthesis of bacteria. Vancomycin, a glycopeptide drug is used to treat MRSA infections.
BACTEC by BD diagnostics utilizes fluorescent technology and detects the growth of organisms in the blood culture bottles.
Developed by Bruce Ames, this test is used to identify environmental carcinogens.
Detection of specific antigens present in the sample (blood, urine, or CSF) using specific antibodies is the mainstay for the rapid diagnosis of infections.
Plasmids are extra-chromosomal genetic elements that replicate independently of the host chromosome. The codes for drug resistance, virulence
Membrane Filtration Technique used for the presence of fecal contamination (fecal coliforms) is discussed here.
Kligler Iron Agar is used for the differentiation of microorganisms on the basis of glucose and lactose fermentation and H₂S production.
Leptospirosis is diagnosed using dark-field microscopy, microscopic agglutination test (MAT) or using IgM ELISA.
This smallest free-living bacteria does not have cell wall (so pleomorphic in shape) causes walking pneumonia.
This gram-negative capsulated rod-shaped bacteria causes hospital acquired pnuemonia, UTI and blood stream infection.
Known for its swarming motility, Proteus is a gram negative rod of Enterobacteriaceae family and causing urinary tract infections.
Reagents are primary stain (crystal violet), mordant (iodine), decolorizer (ethanol or acid-alcohol), and counterstain (safranin or dilute carbol-fuchsin).
For short-term storage (<2 weeks) of fastidious organism enriched chocolate or blood agar is used and stored at 2-8°C.
Capsule, adhesion proteins, lipooligosaccharides, pili, IgA protease, and phase variations of H.influenzae play major roles in pathogenesis.
S. pneumoniae virulence factors include capsular polysaccharide, C carbohydrate antigen, pneumolysin, autolysin.
Pus aspirate is the preferred sample. S. aureus, Strep pyogenes, and members of Enterobacteriaceae are major pathogens.
MRSA (methicillin-resistant Staphylococcus aureus) is resistant to all ß-lactam agents, including cephalosporins and carbapenems.
MALDI-TOF MS offers species-level identifications in minutes at low costs with accuracy that matches or even exceeds the conventional system.
The overall volume of blood cultured is more critical in increasing organism yield. More the blood volume cultured greater the chance of isolating pathogen.
SEM provides detailed images of the surfaces of cells whereas TEM provides details about internal composition, morphology, crystallization.
Individuals who travel to areas of poor sanitation and limited access to clean water are at greater risk of developing travelers’ diarrhea.
Acinetobacter are gram-negative coccobacilli, among them Acinetobacter baumannii accounts for most infections in humans in hospital settings.
Physicians may prefer blood culture in a number of suspected disease conditions such as enteric fever, infective endocarditis, meningitis, pneumonia, etc.
Bacterial culture method for estimating the viable bacterial count after serial dilutions (when required).
The most probable number (MPN) is a statistical serial dilution method for estimating viable numbers of bacteria present in a food or water sample.
Decreased permeability, efflux pump, altered target, and inactivation of antibiotics are major mechanisms of drug resistance.
There are innumerable species of bacteria which are innately resistant to particular drugs. For example, penicillin resistance of Mycoplasma.
Antibiotic-resistant "priority pathogens" is a catalogue of 12 families of bacteria that pose the greatest threat to human health. Organisms are divided as Critical Priority, High Priority and Medium Priority.
Pneumococcal urinary antigen testing is a rapid assay that detects Streptococcus pneumoniae antigen (C-polysaccharide) in the urine of patients.
It tests for the presence of acid and/or gas produced from carbohydrate fermentation. and is useful in differentiating among bacterial groups or species.
The most widely used anaerobic culture medium containing chopped meat particles and used for maintenance of stock cultures.
Some organism such as Proteus oxidatively deaminate phenylalanine to phenyl-pyruvic acid.
Odor of colonies of bacteria may help in their identification but sniffing culture plates is not a good idea and you may contract a disease.
One of the best methods to determine the number of bacteria present per mL of liquid broth/specimen.
The best way to visualize capsule is to stain the background using an acidic stain and to stain the cell itself using a basic stain.
Thioglycollate broth supports the growth of anaerobes, aerobes, microaerophilic, and fastidious microorganisms.
Patients swallow 14C-urea capsule. Test urea will be broken down, if infected, and a lot of 14CO2 produced which is detected in the breathe.
Cary-Blair transport medium is used to transport clinical specimens suspected to contain enteric pathogens, including Shigella, Salmonella, Vibrio.
McIntosh and Fildes' anaerobic jar works on the principle of evacuation and replacement, where the air inside the chamber is evacuated and replaced with mixture of gases
Routine method for the isolation of bacteria from clinical specimen or for obtaining individual isolated colonies from a mixed culture.
For performing AST using Kirby Bauer disc diffusion method, a cell suspension of organisms equivalent to a 0.5 McFarland standard is used.
Haemophilus species require accessory growth factors such as X (hemin), V (NAD) or a combination of both.
M. tuberculosis gives rough, raised, dry, non-pigmented (cream/buff colored) colonies on Lowenstein Jensen (LJ) medium.
Red pigment of Serratia, golden yellow of S. aureus and green (pyoverdin) and blue (pyocyanin) of Pseudomonas help in their identification.
Gram-negative cocci of medical importance belong to the family Neisseriaceae which includes the genera Neisseria, Moraxella, Kingella, Acinetobacter.
TPHA is a treponemal test for the serologic diagnosis of syphilis, based on the principle of passive hemagglutination. It detects IgG and IgM.
The oxidative-fermentative (OF) test is used to differentiate oxidative bacteria from fermentative bacteria based on acid production.
Major virulence factors of S.pyogenes are adhesions, M protein, hemolysins, pyrogenic exotoxins and spreading factors.
To diagnose H. pylori infections, urea breathe test, fecal antigen test and rapid urease test are most widely used.
GeneXpert MTB/RIF assay is a NAAT that simultaneously detects DNA of M.tuberculosis complex and resistance to rifampin (i.e. mutation of the rpoB gene).
Quellung reaction is the gold standard technique for serotyping S. pneumoniae. Capsule get “swollen” and is more visible.
Fecal microbiota transplantation (FMT) also known as fecal bacteriotherapy is a novel approach used to treat Clostridioides difficile infections.
Widal test is one of the oldest and most widely used serological tests for the diagnosis of enteric fever.
Gram positive obligate anaerobe responsible for a unique colonic disease, pseudomembranous colitis.
Micrococcus is lysostaphin and furazolidone resistant, bacitracin sensitive and microdase positive. Find the results of Staphylococcus.
Neisseria meningitidis is capsulated and ferment maltose (MM), whereas Neisseria gonorrhoeae is non-capsulated and do not ferment maltose.
Elek test is an in vitro immunoprecipitation test to determine whether or not a strain of Corynebacterium diphtheriae is toxigenic.
Eukaryotic cells contain a nucleus with a nuclear membrane enclosing multiple chromosomes, while prokaryotic cells have a single chromosome.
This group A beta-hemolytic streptococci is bacitracin sensitive and causes strep sore throat, rheumatic fever, and PSGN.
Staphylococci are catalase positive, gram positive cocci in clusters but Streptococci are catalase negative and may appear in pairs or chains.
Microdase test is a rapid method to differentiate Staphylococcus aureus (negative) from Micrococcus luteus (positive).
These tests determine if an organism is motile (possesses flagella).
Lecithinase test is a biochemical test used to identify organisms that liberate phospholipases (lecithinases) e.g. Clostridium perfringens.
Tuberculin skin test is the standard method of determining whether a person is infected with M.tuberculosis or has exposure to tubercle bacilli.
Albert stain is a type of differential stain used for staining metachromatic granules or volutin granules found in Corynebacterium diphtheriae.
Acetate utilization test determines if an organism can use acetate as the sole source of carbon.
Rapid test for identifying Moraxella (Branhamella) catarrhalis which produce butyrate esterase enzyme.
Cetrimide agar test the ability of an organism to grow in the presence of cetrimide.
In Schaeffer-Fulton`s method, primary stain-malachite green is forced into the spore by steaming the smear, safranin is counterstain.
API-20E test strip (from bioMerieux, Inc.) is used to identify the enteric gram negative rods.
In the presence of specific Abs to an infectious agent, any complement in the system is bound, leaving no residual complement for rxn with Abs to the RBCs.
The nitrocefin test is a sensitive technique for detecting beta-lactamase-producing strains of N. gonorrhoeae, H. influenzae, Enterococcus spp.
Auramine-rhodamine fluorochrome staining also known as "Truant method of staining", is used to visualize Acid-fast bacilli (AFB).
Certain bacteria produce acetoin as the chief end product of glucose fermentation. Acetoin gets oxidized to diacetyl giving red color.
The presence of lysine, ornithine, and arginine decarboxylase enzyme is routinely tested in the identification of Enterobacteriaceae.
Hippurate test is used in the identification of Campylobacter jejuni, Listeria monocytogenes, Gardnerella vaginalis, and Streptococcus agalactiae.
Beta hemolytic streptococci are arranged into twenty (20) groups A-U without I and J (i.e. A through H and K through V).
Mycobacterium species possess an enzyme-lipase, that splits Tween-80 and releases oleic acid and polyoxyethylated sorbitol.
Teixobactin is an extract of β-proteobacteria named Eleftheria terrae. It has shown excellent activity against Gram-positive bacteria.
Organism producing β-galactosidase hydrolyzes the ONPG producing visible yellow product (orthonitrophenol).
Gram-positive, catalase negative cocci which produce the enzyme leucine aminopeptidase gives positive LAP test results.
Gram-positive bacteria retain the crystal violet-iodine complex and stain purple, whereas gram-negative bacteria stain pink.
Nitrate reduction test is used to determine the ability of an organism to reduce nitrate.
Common culture media are bismuth sulfite agar, MacConkey agar, deoxycholate citrate agar, xylose lysine deoxycholate agar, salmonella-shigella agar, etc.
V. cholerae emulsified in sodium deoxycholate, it lyses the cell wall and releases DNA giving a mucoid “string” when a loop is drawn away.
Quantative method for detecting MIC by using the principles of both dilution and diffusion of antibiotics into the medium.
Modified Hodge test (MHT) is a simple phenotypic test for the detection of the presence of carbapenemase enzyme in bacteria.
Stokes’ disc diffusion method allows each individual isolate to be compared with a sensitive control of the same or similar species.
DNase test determines the ability of an organism to hydrolyze DNA.
Atypical mycobacteria include species such as M. avium, M. intracellularae, M. kansasii, M. xenopi, and M. fortuitum.
The drop hangs from the coverslip, and the petroleum jelly forms a seal that prevents evaporation. This preparation gives good views of microbial motility.
Bacteria are easier to detect in broth culture if the preparation is stained using toluidine blue rather than stained by the Gram staining technique.
Virulence factors of UPEC are adhesins (P fimbriae), K antigen, hemolysin and aerobactin system.
Clean-catch midstream urine, suprapubic aspiration and straight catheter techniques are common method of urine sample collection.
Majority of community-acquired UTIs in elderly women are caused by E coli. Preferred drugs are nitrofurantoin, trimethoprim-sulfamethoxazole, etc.
New York City medium is primarily designed for the isolation of pathogenic Neisseria. It also supports the growth of genital mycoplasmas.
Certain bacteria ferment glucose to produce stronger acids that take the media pH below 4.4 in which Methyl Red indicator turns red.
Gelatin hydrolysis test determines the ability of an organism to produce gelatinases that liquefy gelatin.
Safety in a microbiology laboratory is important in the prevention of infection because virulent and/or potentially pathogenic microorganisms are cultured (grown) there.
Bile-esculin test is widely used to differentiate Enterococci and Non-enterococcus group D streptococci from non-group D viridans group streptococci.
Salt tolerance test determines the ability of an organism to grow in high concentrations of salt (6.5%).
Ziehl-Neelsen acid fast stain is designed to stain bacterial cells containing long chain fatty (mycolid acids) such as Mycobacterium.
Sodium hypochlorite centrifugation technique is used to concentrate the AFB present in the sputum, as it increases the chances of detecting AFB.
MIC can be determined by broth dilution or agar dilution methods. Broth dilution testing allows the option of providing both quantitative MIC and qualitative results.
Some gram-positive cocci such as Enterococcus produces enzyme L-pyrroglutamylaminopeptidase that hydrolyze PYR substrate.
Group B Streptococci produce CAMP factor that acts synergistically with beta-lysin of S. aureus.
Tran-isolate medium is used to inoculate and transport CSF sample, If the CSF cannot be transported to a microbiology laboratory immediately.
Proper Hand-washing technique. Learn when and how you should wash your hands to stay healthy.
Rose Bengal test is a simple, rapid slide-type agglutination assay performed with a stained B. abortus to diagnose brucellosis.
Brucellosis, also known as “Undulant fever”, “Mediterranean fever” or “Malta fever” or “Bang’s disease” is a zoonosis caused by Brucella melitensis.
Q fever is caused by the intracellular bacterium Coxiella burnetii and is endemic in nearly every country in the world.
Catalase test is used to distinguish among Gram-positive cocci. Staphylococci are catalase-positive but Streptococci are catalase-negative.
Sexually transmitted diseases (STDs) or infections (STIs), are passed from one person to another through sexual activity including vaginal, oral, and anal sex.
Enterobacteriaceae is a family of gram-negative rods which are catalase positive and oxidase negative.
Weil-Felix is a nonspecific agglutination test that detects anti-rickettsial antibodies in patient serum using OX strains of Proteus vulgaris.
Process of random uptake of free DNA fragments by the competent bacteria from the surrounding environment.
A colony is defined as a visible mass of microorganisms. Colony characteristics of microorganisms help in their identification.
Modified Kirby-Bauer disc diffusion test method is a reference method to test the susceptibility of a bacterial isolate in a clinical laboratory.
Susceptible organism is likely to respond to treatment with this drug, at the recommended dosage but resistant wont respond.
Haemophilus spp may grow on sheep blood agar very close to the colonies of Staphylococcus aureus.
RPR test is a macroscopic, nontreponemal flocculation card test used to screen for syphilis. RPR test measures IgM and IgG antibodies to lipoidal material.
Gram positive bacteria appear purple and gram-negative bacteria appear pink when stained by Gram-staining methods.
Rapid latex agglutination test for the qualitative and semi-quantitative determination of anti-streptolysin-O antibodies (ASO) in serum.
Common etiologic agents of acute meningitis are enteroviruses and bacteria (S. pneumoniae, Neisseria meningitidis, Haemophilus influenzae).
Inducible clindamycin resistance should be checked in all staphylococci that are erythromycin-resistant and clindamycin susceptible or intermediate.
Gram-negative, oxidase-positive, coccobacilli, which requires X and V factors for the growth.
Gram positive diplococci (lanceolate shaped), alpha hemolysis, optochin sensitive and bile soluble isolates are S.pneumoniae.
Tests are; Tween-80 hydrolysis test, niacin test, nitrate reduction test, tellurite reduction test, urea hydrolysis test and citrate utilization test.
Novobiocin test is used to differentiate CONS and presumptively identify the isolate as Staphylococcus saprophyticus (novobiocin resistant).
IMViC is an acronym that stands for four different tests; indole test, methyl red test, Voges-Proskauer test, and citrate utilization test.
Escherichia coli produces the enzyme beta-D-glucuronidase, which hydrolyzes a substrate giving blue fluorescence.
Most common cause are E. coli, S. aureus, Salmonella, Klebsiella pneumoniae, S. pnuemoniae and H. influenzae.
TSI test determines whether a gram-negative rod utilizes glucose, and lactose or sucrose fermentatively and forms hydrogen sulfide.
Gram negative rods, catalase positive and oxidase positive. It produces pigments (pyocyanin and pyoverdin).
Neisseria gonorrhoeae is a gram-negative kidney-shaped diplococci. It causes gonorrhea, a sexually transmissted infection.
Major virulence factors of Neisseria meningitidis are capsular polysaccharide, outer membrane proteins, endotoxin and IgA protease.
Syphilis is diagnosed by using dark field microscopy, non-treponemal tests (VDRL, RPR) or treponemal tests (TPHA, FTA-ABS).
FTA-ABS is an indirect fluorescent antibody technique used as a confirmatory test for syphilis. FTA-ABS is the first serological test to become positive following infection.
Venereal disease research laboratory (VDRL) test is a nonspecific flocculation test for the screening of syphilis.
Sample from sites known to have anaerobes as part of the normal flora (eg mouth) is unacceptable for anaerobic culture.
Positive gram stain with negative culture report gives information regarding the adequacy of sample collection, transport, and also of culture methods used.
Commonly used anaerobic culture media are; Robertson's cooked meat broth, anaerobic blood agar, egg-yolk agar, bacteroides bile esculin agar.
Obligate intracellular bacteria cannot be grown in artificial media (agar plates/broths) in laboratories but requires viable eukaryotic host cells.
Chlamydia trachomatis, is an obligate intracellular bacteria which causes pelvic inflammatory disease and other infections (e.g. eye).
The causative agent of Bacillary dysentery, Shigella is a member of family Enterobacteriaceae. It is non-motile, non-lactose fermenter.
The most common cause of gastroenteritis worldwide, Campylobacter is a curved, gram-negative rod. It is an oxidase-positive microaerophile.
Optochin (ethylhydrocupreine hydrochloride) lyses pneumococci (positive) but alpha-streptococci are resistant (negative).
Bile solubility test differentiates S. pneumoniae (positive) from alpha-hemolytic streptococci (negative).
Citrate test determines the ability of an organism to utilize sodium citrate as source source of carbon.
Bacitracin test differentiates S. pyogenes (inhibited) from other beta-hemolytic streptococci.
Pneumococcus is lanceolate shaped gram-positive cocci and causes pneumonia and meningitis. Its is optochin sensitive and bile soluble.
Typical growth curve of microorganisms in a closed system consists of distinct phases called lag phase, log phase, stationary phase, and death phase.
Microorganisms can be classified as obligate aerobes, facultative, microaerophilic, aerotolerant and obligate anaerobes based on their oxygen requirements.
Work with microbes at the K–12 level, informal education settings and in undergraduate non-microbiology laboratories would almost always be at BSL1.
Catalase test, oxidase test, MUG test, optochin sensitivity test, bacitracin sensitivity test, coagulase test, etc are some of the common biochemical tests.
Bacteria exist in four basic morphologies: cocci; rod-shaped cells, or bacilli; spiral-shaped cells, or spirilla; and comma-shaped cells, or vibrios.
E. coli is the preferred model organism for different experiments as it is easy to grow and work within the laboratory.
Characteristics pigmentation observed in the culture media is because of the changes in the pH of the medium.
Motility patterns of Gram-negative bacteria are also used for their identification. Most of the Gram-positive bacteria are non-motile.
Peptidoglycan consists of carbohydrate backbone composed of alternating units of NAG and NAM molecules attached through β-1,4-glycosidic bonds.
Transposons, also called 'jumping genes' are mobile genetic elements. Barbara McClintock got Nobel Prize for the study of transposons.
Concentrated deposits of certain substances which are presented/located in the cytoplasm of certain bacteria.
Teichoic acids are fibers of glycerol phosphate or ribitol phosphate and is located in the cell-wall of gram-positive bacteria.
Lipopolysaccharide (LPS) layer also called the outer membrane is the outermost layer present in the cell wall of gram-negative bacteria.
Pili or fimbriae are hair-like filaments that help pathogen in adherence to host cells. Sex pili play role in conjugation.
Bacterial toxins are broadly divided into two general categories: exotoxins (secreted outside the cell) and endotoxins (LPS).
Flagella are long, whiplike appendages that move the bacteria toward nutrients and other attractants
Bacterial spores are highly resistant, dormant structures formed in response to adverse environmental conditions
Capsule is a gelatinous layer covering the bacterium and is a major virulence factor of S. pneumoniae, H. influenzae, etc.
Frequent colonizer of skin, S. aureus is a major cause of surgical wound infection. This gram-positive cocci is catalase and coagulase +ve.
Normal flora of GI tract, E.coli is a major cause of urinary tract infections. It is lactose fermenting, gram negative bacilli.
PAIs are large genomic islands located in the chromosome which codes for numerous virulence factors such as toxins, invasions, iron uptake.
EHEC can cause severe foodborne diseases; diarrhea or hemorrhagic colitis. It can not ferment sorbitol. EHEC O157:H7 is a major strain.
This test determines the ability of an organism to produce the enzyme urease which hydrolyzes urea.
Organism having cytochrome oxidase oxidizes tetramethyl-p-phenylenediamine hydrochloride to indophenol (a dark purple-colored) compound.
We can not culture T. pallidum, M. leprae, Chlamydia trachomatis, Coxiella burnetti and Rickettsia in in-vitro culture media.
Also known as Hansen’s disease, leprosy is a chronic infectious disease caused by an acid-fast bacillus, Mycobacterium leprae.
Coagulase test detects clumping factors and bound coagulase and differentiates Staphylococcus aureus (positive) from CoNS (negative).
Indole test determines the ability of an organism to split tryptophan to form indole.
Membrane filter technique is an effective, accepted technique for testing fluid samples for microbiological contamination.