Microbiology Culture Media and Bacterial Growth

Comprehensive vocabulary flashcards covering microbial growth conditions, growth kinetics, classification of culture media, hemolysis reactions, selective/differential media, and microbiological laboratory techniques.

Microaerophiles

Organisms that grow under reduced $\text{O}_2$ ($5\%-10\%$) and increased $\text{CO}_2$ ($8\%-10\%$), such as Campylobacter and Helicobacter.

Capnophiles

Organisms requiring increased concentrations of $\text{CO}_2$ ($5\%$ to $10\%$) and approximately $15\%\,\text{O}_2$, such as pathogenic Neisseria and HACEK organisms.

Psychrophilic (Cryophilic)

Bacteria that grow at temperatures $<10\,^\circ\text{C}$ and can be isolated using cold enrichment medium, such as Listeria monocytogenes and Yersinia enterocolitica.

Mesophilic

Bacteria that grow in moderate temperatures from $20\,^\circ\text{C}$ to $40\,^\circ\text{C}$ (optimally $30\,^\circ\text{C}$ to $37\,^\circ\text{C}$); includes most pathogenic bacteria.

Thermophilic

Bacteria that grow at elevated temperatures from $50\,^\circ\text{C}$ to $55\,^\circ\text{C}$, with some species growing up to $47\,^\circ\text{C}$ (Campylobacter jejuni) or up to $65\,^\circ\text{C}$ (Legionella).

Acidophile

An organism that grows in acidic conditions around a pH of $3$, such as Lactobacillus acidophilus grown on Tomato Juice Agar.

Alkaliphile

An organism that grows in alkaline environments within a pH range of $8$ to $10$, such as Vibrio cultured in Alkaline Peptone Water.

Bacterial Growth Curve

A graphical representation showing the distinct phases of bacterial population change over time: lag phase, log phase, stationary phase, and death phase.

Lag Phase

The initial period in the bacterial growth cycle characterized by little to no multiplication, serving as an adjustment period.

Log Phase (Exponential Phase)

The growth cycle stage where organisms divide at their maximum rate; bacteria in this phase are most metabolically active and most sensitive to antimicrobials.

Stationary Phase (Plateau Phase)

The growth phase where replication ceases due to nutrient depletion or accumulation of toxic metabolic products; the number of living organisms equals the number of dead organisms.

Decline Phase (Death Phase)

The final stage of the growth curve where viable counts drop because the number of dead organisms exceeds the number of living organisms.

Semisolid Media

Media containing $0.5\%-1\%$ agar (derived from red algae genus Gelidium) used for assessing motility or as transport media when processing is delayed beyond $30\,\text{mins}$.

Liquefiable Solid Media

Agar-based solid media containing $2\%-3\%$ agar that melts into a liquid state when heated to $\ge 95\,^\circ\text{C}$ and solidifies below $50\,^\circ\text{C}$.

Biphasic Media

Culture media containing both a liquid phase and a solid phase; an example is Castañeda medium used for Brucella blood cultures.

Simple (Nutritive/Supportive) Media

Media that support the growth of most non-fastidious bacteria without conferring a growth advantage to any particular species; examples include nutrient agar/broth and trypticase soy agar.

Enriched Media

Nutritive media supplemented with specific nutrients to support fastidious bacteria; examples include Blood Agar Plate, Chocolate Agar Plate, and Buffered Charcoal Yeast Extract (BCYE).

Enrichment Media

Media designed to enhance the recovery of pathogens present in low numbers or mixed with heavy flora (e.g., stool) by shortening the pathogen's lag phase while delaying that of contaminants.

Alpha Hemolysis

Partial lysis of red blood cells around a colony on blood agar, producing a greenish or brownish discoloration due to methemoglobin.

Beta Hemolysis

Complete lysis of red blood cells around a bacterial colony, resulting in a distinct, completely clear zone in the agar.

Gamma Hemolysis

Absence of red blood cell lysis surrounding a bacterial colony, resulting in no color or transparency change in the agar.

Alpha-prime Hemolysis

A hemolytic pattern featuring a small inner zone of intact red blood cells immediately surrounding the colony, encompassed by an outer zone of beta hemolysis (observed in Viridans Streptococci).

Double Hemolysis

A hemolytic pattern consisting of an inner zone of beta hemolysis surrounded by an outer zone of alpha hemolysis, typically produced by Clostridium perfringens.

Thiosulfate Citrate Bile Salts Sucrose (TCBS) Agar

A selective and differential medium for Vibrio species containing bile salts to inhibit gram-positive organisms, bromthymol blue as a pH indicator, and sucrose as the differentiating carbohydrate.

Salmonella-Shigella (SS) Agar

A selective and differential medium containing bile salts as inhibitors and neutral red as a pH indicator, differentiating organisms based on lactose fermentation and $\text{H}_2\text{S}$ production.

Thayer-Martin Agar (TMA)

A selective enriched medium for pathogenic Neisseria containing vancomycin (inhibits gram-positives), colistin (inhibits gram-negatives), and nystatin (inhibits fungi).

Backup Broth

A liquid medium containing $0.075\%$ agar and thioglycollate as a reducing agent to maintain anaerobiosis; boiled to drive off dissolved oxygen.

Prokaryotic Oxygen Requirements

The physiological classification of prokaryotes according to their oxygen tolerance and detoxification enzymes (catalase and superoxide dismutase), including obligate aerobes, facultative anaerobes, obligate anaerobes, microaerophiles, and aerotolerant organisms.

Bile Esculin Agar (BEA)

A differential and selective medium used for the isolation and presumptive identification of group D Streptococci and Enterococci.

Bile Esculin Azide Agar with Vancomycin

A selective and differential medium formulated for the cultivation of vancomycin-resistant Enterococci (VRE) from clinical and surveillance specimens.

Bordet-Gengou Agar

A potato blood glycerol medium used for the primary isolation of Bordetella pertussis and Bordetella parapertussis.

Buffered Charcoal-Yeast Extract (BCYE) Agar

An enriched medium designed for the cultivation of Legionella spp. that also supports the growth of Francisella and Nocardia.

Burkholderia cepacia Selective Agar

A selective culture medium specifically designed for the recovery of Burkholderia cepacia from cystic fibrosis patients.

Cefsulodin-Irgasan-Novobiocin (CIN) Agar

A selective medium used for isolating Yersinia spp., which may also facilitate the recovery of Aeromonas spp.

Columbia Colistin-Nalidixic Acid (CNA) Agar

A selective medium containing colistin and nalidixic acid designed to inhibit gram-negative organisms while isolating gram-positive cocci.

Cystine-Tellurite Blood Agar (CTBA)

A selective and differential medium containing potassium tellurite used for the isolation of Corynebacterium diphtheriae.

MacConkey Sorbitol Agar

A selective and differential culture medium used for the detection and differentiation of Escherichia coli O157:H7 in stool specimens.

New York City (NYC) Agar

A selective medium that recovers Neisseria gonorrhoeae while also supporting the growth of Ureaplasma urealyticum and Mycoplasma spp.

Phenylethyl Alcohol (PEA) Agar

A selective medium that inhibits gram-negative bacilli to isolate gram-positive cocci, aerobic gram-positive bacilli, and anaerobic gram-negative bacilli.

Regan Lowe Agar

Charcoal-cephalexin agar formulated as an enrichment and selective medium for isolating Bordetella pertussis.

Xylose Lysine Desoxycholate (XLD) Agar

A selective and differential medium used to isolate and differentiate Salmonella and Shigella spp. from other gram-negative enteric bacilli.

Tap Water Agar

A medium made of Bacto agar added to $100\,\text{mL}$ of tap water, incubated at $30\,^\circ\text{C}$ for up to $7\,\text{days}$ to differentiate aerobic Actinomycetes by checking for aerial hyphae.

Autoclaving

A physical method of media sterilization performed at $121\,^\circ\text{C}$ for $15\,\text{mins}$.

Membrane Filtration

A sterilization method utilizing filter membranes with pore sizes from $0.2$ to $0.45\,\mu\text{m}$ to sterilize heat-labile components.

Quantitative Plating (Cross-Streaking)

An inoculation procedure employing a calibrated loop ($1:100$ or $1:1000$) across a central line and perpendicular cross-streaks, used for urine cultures and burn victim tissues to quantify CFU/mL.

Isolation Streaking (Semiquantitation)

A four-quadrant streak plating method used to dilute and isolate colonies, graded semiquantitatively from $1+$ (rare) to $4+$ (many, heavy growth).