Iycee Charles de Gaulle Summary Identifying Bacteria In Medical Microbiology Biology Essay

Identifying Bacteria In Medical Microbiology Biology Essay

Speed and cost are 2 vitally of import factors in clinical microbiology. Patients progressively expect trial consequences returned in the shortest possible clip, and hospital support cuts dictate that low-cost trials are of major significance. Biochemical trials are hence more normally used than new molecular and familial techniques in microbic taxonomy, as they have been found to be more time-consuming and expensive than standard biochemical trials.

The Gram ‘s discoloration is the empirical method of distinguishing bacterial species into two big groups ( Gram-positive and Gram-negative ) based on the chemical and physical belongingss of their cell walls. The Gram ‘s discoloration is about ever the first measure in the designation of a bacterial being. From placing whether the bacterial species is Gram-positive or Gram-negative, subsequent biochemical trials can be carried out to achieve farther designation.

One of the trials that can so be carried out is the Analytical Profile Index ( API ) . This is a trial that consists of a series of microtubules incorporating different dehydrated substances. A suspension of bacterial cells is so inoculated into the API home base, and is hence rehydrated. Following a period of incubation, the substrate will respond with the bacteriums and if the bacterium is capable of metabolizing the substrate, so a coloring material alteration will happen. There are different types of API home bases that may be used for specific designations. The API home base used in this probe is the 20E API which is used for aerophilic Gram-negative rods.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!

order now

This is a tabular array of the consequences found from the biochemical trials carried out on both bacterial civilizations. Catalase and coagulase trials were merely carried out on the Gram-positive bacteriums, and the oxidase trial was merely carried out on the Gram-negative bacteriums.

This is an image of the API home base innoculated, and the positive and negative consequences for each subdivision.

This API consequence was fed into the computing machine system and the designation returned is Citrobacter freundii ( 99.8 % ID )


1 ) Coagulase negative staphylcocci are considered as microorganissms with small virulency and are normally found as contaminations. The first bacteriums isolated in this experiment fits into this catergory. Coagulase negative coccus are usally found in bunchs, as I observed microscopically.

The major pathogen associated with coagulase negative coccus is Staphylcoccus cuticle, which has settlements which are typically little, white ecru and about 1-2 nanometer in diameter. S. cuticle is besides catalase positive, so tantrums with the consequences from this probe. This bacterial species is considered to be non-pathogenic but patients, in infirmaries for illustration, with comprimised immune systems, are frequently at hazard of developing infection. Most infection from S. epidermis are nosocomial or community acquired. Hospitals frequently carry more deadly strains of the bacteriums due to uninterrupted usage of germicides and antibiotics.

S. cuticle is a bacterium that grows biofilms on plastic and metal surfaces. This can cuase important infection if these biofilms grow on medical devices such as hip articulations or bosom valves. These biofilms produce thick surfaces with many beds of the bacteriums, which makes it difficult for antibiotics to be effectual when infection nowadayss as they can non efficaciously make all bacteriums.

S. epidermis, as a nosocomial pathogen, can do sepsis in premature infantiles, urinary piece of land infections, oculus infections, endocarditis, and infections associated with intravascular catheters.

The isolation of S. epidermis from clinical samples is of major significance. As S. epidermis effects chiefly those with diminished immune systems in a infirmary environment, this bacteriums must rapidly be isolated and idenntified so that the right method of intervention can be given. If the bacterium is non identified, patients could endure really important infections without the capableness in themselves to make an immune response.

Besides, nosocomial infections are easy spread in the clinical environment. Once an isolation of S. epidermis is made in the research lab, this suggests that there has been contamnation of infirmary equipment, and it is so brought to the attending of clinical staff in that country. All equipment must be kept unfertile to avoid farther infection of patients.

Since antibiotics are mostly uneffective in uncluttering biofilms, the most common intervention for these infections is to take or replace the implant. In all instances bar is ideal. Disease may be prevented by taking catheters and septic shunts. The drug of pick in handling S. epidermis infections is frequently vancomycin, to which Rifadin or aminoglycoside can be added. If the bacterium is non isolated from sample, unit of ammunitions of ineffiective intervention may ab initio be given to a patient, in which clip the wellness of the pateint could deteriorate. Without an designation of the bacteruim, clinicians would non cognize to take the deep-rooted device which is doing the disease, and the job would go on.

2 ) In this probe, I used API 20E to place my Gram-positive bacteria. These are the trials done, and the consequences they give:

Test Substrate Reaction Tested Results ( positive ) Results ( negative )

ONPG ONPG Beta-galactosidase colorless yellow

ADH arginine arginine dihydrolase xanthous red/orange

LDC lysine lysine decarboxylase xanthous red/orange

ODC ortnithine ornithint decarboxylase xanthous red/orange

CIT citrate citrate use pale green/yellow blue-green/blue

H2S Na thiosulfate H2S production colorless/grey black sedimentation

URE urea urea hydrolysis xanthous red/orange

TDA tryptophan deaminase xanthous brown-red

IND tryptophan indole production yellow red ( min 2 mins )

VP Na pyruvate acetoin production colorless pink/red ( 10 mins )

GEL wood coal gelatin gelatinase no diffusion of black black diffuse

GLU glucose fermentation/oxidation blue/blue-green yellow

MAN mannitol fermentation/oxidation blue/blue-green yellow

INO inositol fermentation/oxidation blue/blue-green yellow

SOR sorbitol fermentation/oxidation blue/blue-green yellow

RHA rhamnose fermentation/oxidation blue/blue-green yellow

SAC sucrose fermentation/oxidation blue/blue-green yellow

MEL melibose fermentation/oxidation blue/blue-green yellow

AMY amygdalin fermentation/oxidation blue/blue-green yellow

ARA arabinose fermentation/oxidation blue/blue-green yellow

OX oxidase oxidase colorless-yellow violet

In placing Citrobacter freuindii the undermentioned trials were positive:












These positive consequences are of import in the designation of this species, as it shows us what substrates can be fermented/oxidised, or reacted with. These ractions differ for all bacteriums.

The oxidase trial is a cardinal trial in the designation of this bacteria. Because it is negative, it means that the bacterium does non incorporate cytochrome hundred oxidase and hence can non use O for energy production. Typically enteriobacteriaceae are OX- , which we have found.

The normal pattern of observing S. epidermidis is by utilizing the Baird-Parker Agar with egg yolk addendum. Colonies appear little and black. They can be confirmed utilizing the coagulase trial. Increasingly, techniques such as real-time PCR and quantitative PCR are being employed for the rapid sensing and designation of Staphylococcus strains. Normally sensitiveness to desferrioxamine can besides be used to separate it from most other staphylococcus, except in the instance of Staphylococcus hominis, which is besides sensitive. In this instance the production of acid from trehalose, by Staphylococcus hominis, can be used to state the two species apart.

3 )

a ) The oxidase trial is used in microbiology to detemine if a bacteria produces certain cytochrome degree Celsius oxidases. It uses discs impregnated with a reagent such as N tetramethyl-p-phenylenediamine ( TMPD ) or N, N-dimethyl-p-phenylenediamine ( DMPD ) which is besides a redox index. The index is a dark blue to strand colour when oxidised and colorless when reduced.

Oxidases catalyse electron conveyance between substrates moving as negatron givers in the bacteria and tetramethyl-p-phenylenediamine or dimethyl-p-phenylenediamine – a redox dye nowadays as the hydrochloride or oxalate salt ( the latter has a longer shelf-life ) . The dye is reduced to a deep lilac-blue coloring material in the presence of oxidase enzymes.

Oxidase positive bacteria may use O for energy production in the negatron conveyance concatenation. Oxidase negative bacteria can non use O in this manner.

B ) Bacterial species may be differentiated on the footing of their ability to cut down nitrate to nitrite or nitrogen-bearing gases. This is the biochemical tract im which nitrate is reduced to nitrite, which can so farther be reduced to azotic oxide, azotic oxide, or N.

The nitrate decrease trial is based on the sensing of nitrite in the medium after incubation with an being. If present in the medium, nitrite will respond with sulfanilic acid ( Nitrate reagent A ) to organize a colorless composite ( nitrite-sulfanilic acid ) . This composite will so give a ruddy precipitate ( prontosil ) when nitrate reagent B ( alpha-naphthylamine ) is so added to the trial, as shown below.

A ruddy colour will be produced in the medium merely when nitrite is present in the medium. Lack of a ruddy colour in the medium after the add-on of sulfanilic acid and alpha-naphthylamine agencies merely that nitrite is non present in the medium.

degree Celsius ) The ONPG trial uses the substrate 0-nitrophenyl-?-galactopyranoside to find the presence or obsence of the enzyme ?-galactosidase in an being. The trial is of import in distinguishing among the Enterobacteriaceae which are normally classified harmonizing to their ability to ferment lactose. It is besides used to distinguish Neisseria lactamica from other fastidious Neisseria species.

The presence of two enzymes, permease and ?-galactosidase, are required to show lactose agitation. True lactose non-fermenters do non possess either of these enzymes. Late lactose fermenting beings do non hold permease, but do possess ?-galactosidase which hydrolyses lactose to organize brain sugar and glucose. ONPG is similar in construction to lactose. If ?-galactosidase is present, the colourless ONPG is split in to galactose and o-nitrophenol, a xanthous compound.

If an being posses B-Galactosidase, the enzyme will divide the B-Galactosidase bond, let go ofing of o-nitrophenol xanthous colour compound. If being lacks the enzyme, the Galactoside bond remains integral and the medium remains colourless.

Positive: xanthous colour within 4 hours

Negative: colorless at 4 hours

vitamin D ) The indole trial is a biochemical trial performed on bacterial species to find the ability of the being to divide indole from the amino acid tryptophan. This division is performed by a concatenation of a figure of different intracellular enzymes, a system by and large referred to as “ tryptophanase. ”

Indole is generated by reductive deaminization from tryptophan via the intermediate molecule indolepyruvic acid. Tryptophanase catalyzes the deaminization reaction, during which the aminoalkane ( -NH2 ) group of the tryptophan molecule is removed. Concluding merchandises of the reaction are indole, pyruvic acid, ammonium hydroxide ( NH3 ) and energy. Pyridoxal phosphate is required as a coenzyme.

Pure bacterial civilization must be grown in unfertile tryptophan or peptone broth for 24-48 hours before executing the trial. Following incubation, add 5 beads of James’/Kovac ‘s reagent ( isoamyl intoxicant, p-Dimethylaminobenzaldehyde, concentrated hydrochloric acid ) to the civilization stock.

A positive consequence is shown by the presence of a ruddy or reddish-violet colour in the surface intoxicant bed of the stock. A negative consequence appears xanthous. A variable consequence can besides happen, demoing an orange colour as a consequence. This is due to the presence of skatole, besides known as methyl indole or methylated indole, another possible merchandise of tryptophan debasement.

5 ) 5 ) . PCR could be used to prove for bug, this is where the bacterium will be broken up into familial pieces and utilizing a figure of techniques to spread out the deoxyribonucleic acid by tempering and reheating to interrupt it will let for better proving strands of deoxyribonucleic acid that can be probed to happen specific ‘flagship ‘ deoxyribonucleic acid sequences for the bacteriums.

Agglutination trial stimulates the antigens of a bacterium, it is placed in saline and assorted with antisera that has been cultured agaisnt a known bacterium, the trial is positive if the bacteriums clump together ; Used to separate between different strains of the same bacterium.

Bacteriophage typewriting is another technique in which the bacterium is identified harmonizing to their response a viral phage, phages are specific to bacteriums, the phage will be placed with thebacteria turning on a home base, where the bacteriums do n’t turn you know it is non immune to that specific phage and therefore that bacterium.

Electrophoresis could besides be used to analyze the protein stimilarites between beings, the form branded at the terminal will be really similar for most bacteriums.

Finally a urease trial could be used to see secrete if the urease enzyme, which catalyzes the transition of urea to ammonia and bicarbonate will impact growing

Practical 2

1 ) . Based on the experiments carried out, I would reccomend intervention for infection caused by PS. aeruginosa with antibiotic Cipro. Cefuroxine has no consequence on the bacterium, as there is no zone cleared at all. Contrastingly, Cipro has the greatest diameter of bacteriums cleared, and is the most sensitive to the antibiotic. Piperacillin would besides be a suited antiobiotic for intervention of this bacterium, but non every bit effectual as Cipro. Administeration of this antiobiotic would be effectual on a higher proportion of bacteriums in the organic structure than any of the other antiobiotics tested.

2 ) . The mic for impipenem on E.coli was 0.19, which meant it was senstitive to the antibiotic used.

3a ) . The consequences of this probe demo me that the deepness of agar has an consequence on the size of agar diffusion by antiobiotics. In about all instances, the size of the zone environing each antibiotic phonograph record decreases as the deepness of agar incraeses. Agar ‘s construction is do up of a additive polymer made up of a mixture of agarose and agaropectin. Its ‘ construction dictates that antiobiotics will foremost spread downwards, and so across the agar home base. An agar deepness of 35ml agencies that the zone of diffusion is lower than that of the 25ml. This means that a batch of the antibiotic has diffused downwards, and the consequence we are given is non a clear indicant of whether the bacterium is immune or sensitive to the antibiotic. A swallow agar deepness means that the antibiotic does non spread downwards at all. This leaves the home base really hard to read, as zones merge into one another, and it is hard to construe where zones terminal. BSAC reccomended deepness agar is a changeless, and is effectual as all measurings will be changeless when the same deepness of agar is used. All zone measurings will non be affected by deepness.

3b ) . The dilution has affected the radius of the antibiotic opposition which greatly affects the intervention of a patient and that is why the 1.0×10 ( 5 ) cfu/ml is used, the weaker solution would do more strains seem that they are more sensitive to an antibiotic than they are which in contrast utilizing a heavier dilution would do the effectivity of the antibiotic to look less discernible. In about all instances the zone country additions as the dilution is less concentrated. This is due to the fact that there is less bacteriums in a set country, so antibiotics can distribute over a larger country. Changes in concentration of solution makes the difference between an antibiotic being classified as resistant or sensitive.

3c ) . Depth of agar and dilutions of specimen are non controlled, this could hold effects on the method of intervention for the patient. Variation in these 2 factors will give greatly changing consequences for the glade zone diameters. This could intend a patient could be traeted with a certain antibiotic because there was a big clear zone around the antibiotic disc. It could be considered that a bacterium is sensitive to a certain antibiotic, due to measuring of zone diameter. However, this big zone deepness could be attributed to a shallow agar deepness, or weak concentration of sample. This could ensue in a patient being treated with the incorrect antibiotic and holding no effectual consequence.

3 ) There was fluctuation in the consequences of these 2 experiments, even though there was the same agar deepness and the same innoculum concentration. This could be attributed to:

Mistake in innoculating the home bases by manus – may non acquire complete coverage of the home base – semi feeder growing.

The dilution factor was done between a scope of figures, so the figure we picked might non be accuartely repeated.

Bacterias may non be dispersed equally throughout the sample, so there could be a higher concentration of bacterial cells in one home base to another.

The placing of the antibiotic discs was done by manus so the zones could overlap more on one home base than on another, due to the discs being closer to each other.

The method of mensurating the diameter of the zones was inaccurate, as it was done by taking a swayer to the zones and measurement by oculus. This will of course do great fluctuation in measurings.

4 ) . Blood agar home bases are frequently used to prove for micro-organism of a infective nature. Blood agar usually hasa concentration for 10-15 % mammalian blood, frequently utilizing sheep or Equus caballus blood but for some instances require the usage of human blood. Blood agar trials for fastidious beings that require. Blood agar is utile in observing where settlements have grown every bit frequently the consequence of the pathogen is the cause of haemoglobin lysis utilizing I?-hemolytic enzyme.

5 ) .Synergistic activity is the activity in which two antibiotics will be taken and the consequence of one will greatly heighten the effectivity of the 2nd antibiotic. Linear activity is when two or more chemicals equal the amount of their single original effects. Anatagonistic is when two or more chemical substances on a biological system, the combined consequence is less than it should be due to them working against one another.

Hostility occurs between penicillin and Erythrocin.