Gram negative bacteria (Facultative Anaerobic Gram-Negative Rods) 2nd part + Family Vibrionaceae

Serratia marcescens

Gram-negative, rod-shaped, facultative anaerobe.

Serratia marcescens

Motile: Uses peritrichous flagella for movement.

Serratia marcescens

Produces a distinctive red pigment called prodigiosin, especially when cultured at room temperature.

Serratia marcescens

Belongs to the Enterobacteriaceae family.

Opportunistic Pathogen

Causes disease mainly in immunocompromised individuals or those with underlying medical conditions.

Respiratory tract, Urinary tract, May also infect wounds, bloodstream and eye

Common Infection Sites of Serratia marcescens

Respiratory tract

Can cause pneumonia, particularly ventilator-associated pneumonia (VAP).

Urinary tract

Frequently causes catheter-associated urinary tract infections (CAUTIs).

Red Pigment

o Gives colonies a red or pink appearance.

o Useful for identification in the laboratory.

o Pigment production may be inhibited at higher incubation temperatures (e.g., 37°C).

Nosocomial Infections:

o Often associated with outbreaks in intensive care units (ICUs) and among patients with invasive

devices (e.g., catheters, ventilators).

o Found in moist environments, including respiratory equipment, intravenous fluids, and

disinfectants.

Many strains show resistance to multiple antibiotics, including:

o Beta-lactams (via beta-lactamase production)

o Aminoglycosides

o Some fluoroquinolones

Antibiotic susceptibility testing is essential for guiding effective therapy.

Antibiotic Resistance of Serratia marcescens

Due to its ability to survive in hospital environments, resist disinfectants, and form biofilms, Serratia

marcescens is considered a significant cause of nosocomial infections; Infection control practices (e.g., hand hygiene, sterilization) are critical in preventing outbreaks.

Clinical importance of Serratia marcescens:

Yersinia pestis

Gram-negative, non-motile, bipolar-staining bacillus

Yersinia pestis

High Virulence: Responsible for the plague,

Yersinia pestis

Non-enteric pathogen

• Primary reservoir: Rodents (e.g., rats)

• Vector: Flea bites (especially Xenopsylla cheopis)

• Direct contact with infected animals or tissues

• Inhalation of infectious respiratory droplets

transmission of Yersinia pestis:

Bubonic Plague, Pneumonic Plague, Septicemic Plague

Clinical Forms of Plague:

o Bite from an infected flea

o Direct contact with infected animals or tissues

Portal of Entry of Bubonic Plague

Buboes

Painful, swollen lymph nodes

o Buboes: Painful, swollen lymph nodes

o Fever, chills, malaise

o May progress to:

▪ Bacteremia

▪ Septicemia

symptoms of Bubonic Plague:

50–60% if untreated

Mortality Rate of Bubonic Plague

o Early antibiotic therapy significantly improves outcomes

o Effective antibiotics:

▪ Streptomycin

▪ Tetracycline (TCN)

▪ Chloramphenicol

▪ Gentamicin

Treatment for Bubonic Plague:

Streptomycin, Tetracycline (TCN), Chloramphenicol, Gentamicin

antibiotics for Bubonic Plague:

o Inhalation of respiratory droplets from an infected person

o Secondary complication from untreated bubonic or septicemic plague

portal of entry of Pneumonic Plague:

o High fever

o Severe cough with bloody sputum

o Dyspnea (shortness of breath), chest pain

o Rapid deterioration and potential for respiratory failure

symptoms of pneumonic plague:

Prodigiosin

red pigment produced by Serratia marcescens

Black death

other name for Bubonic plague

Yersinia pestis

safety pin looking

hemoptisis

bloody sputum

o Person-to-person via respiratory droplets

o Highly contagious and the most fatal form if left untreated

transmission of pneumonic plague

Near 100% if untreated within 24 hours of symptom onset

mortality rate of pneumonic plague

o Immediate administration of antibiotics is critical

o Effective antibiotics:

▪ Streptomycin

▪ Gentamicin

▪ Doxycycline

▪ Chloramphenicol

treatment for pneumonic plague:

▪ Streptomycin

▪ Gentamicin

▪ Doxycycline

▪ Chloramphenicol

antibiotics for pneumonic plague:

Septicemic Plague

Occurs when the bacteria multiply in the bloodstream without forming buboes

Septicemic Plague

May arise primarily or as a complication of the other two forms

Septicemic Plague

Symptoms include disseminated intravascular coagulation (DIC), necrosis, shock

• Vector control: Flea and rodent management

• Personal protective measures in endemic areas

• Post-exposure prophylaxis for close contacts (e.g., doxycycline)

• Isolation of pneumonic plague cases

• No widely available vaccine for general use, but some exist for high-risk groups

Prevention and Control of Septicemic plague

Proteus mirabilis

Gram-negative, facultative anaerobe, rod-shaped

Proteus mirabilis

Opportunistic pathogen that causes various human infections, especially in compromised hosts

Proteus mirabilis

Highly motile due to peritrichous flagella

swarming motility

a rapid, coordinated movement across solid surfaces

Actively Motile

o Exhibits "swarming motility" — a rapid, coordinated movement across solid surfaces

o Characteristic "waves" or concentric rings on agar media

Urease-positive

Converts urea to ammonia → raises urine pH → promotes struvite stone formation

Lactose-negative

Does not ferment lactose (colonies appear colorless on MacConkey agar)

Actively Motile, Urease-positive, Lactose-negative

Key Characteristics of Proteus mirabilis:

Urinary Tract Infections (UTIs)

• Especially in patients with catheters or structural urinary tract abnormalities

• Can lead to complicated UTIs, pyelonephritis, or urolithiasis

Wound Infections

• Occur in postsurgical sites or traumatic wounds

• More common in patients with weakened immune systems or poor wound care

Diarrhea

• May be associated with gastrointestinal disturbances, though less commonly than with E. coli or Shigella

• Infections can be nosocomial in origin

Urinary Tract Infections (UTIs), Wound Infections, Diarrhea

Pathogenic Capabilities of Proteus mirabilis

Proteus mirabilis

has innate and acquired resistance to several classes of antibiotics.

o Beta-lactam resistance (via beta-lactamase production)

o Resistance to tetracyclines and fluoroquinolones in some strains

Common resistance patterns of Proteus mirabilis:

• Empiric antibiotic therapy should be guided by local resistance trends

• Common antibiotics (if susceptible):

o Ciprofloxacin

o Trimethoprim-sulfamethoxazole (TMP-SMX)

o Third-generation cephalosporins (e.g., ceftriaxone)

o Aminoglycosides (e.g., gentamicin)

treatment of Proteus mirabilis

• Ciprofloxacin

• Trimethoprim-sulfamethoxazole (TMP-SMX)

• Third-generation cephalosporins (e.g., ceftriaxone)

• Aminoglycosides (e.g., gentamicin)

antibiotics for proteus mirabilis:

• Proper catheter care and wound hygiene

• Infection control practices in healthcare settings

• Judicious use of antibiotics to prevent emergence of resistant strains

Prevention and Control of Proteus mirabilis:

Genus Erwinia

Gram-negative, facultatively anaerobic, rod-shaped bacteria

Genus Erwinia

Primarily known as plant pathogens rather than human pathogens

Erwinia species

are significant phytopathogens

Plant Pathogenicity

o Erwinia species are significant phytopathogens

o They invade plant tissues and cause a range of destructive symptoms, especially in soft plant parts.

Host Specificity

o Species often have specific plant hosts they infect.

o Spread can occur through insects, mechanical wounds, rain splash, or contaminated tools.

Erwinia amylovora, Erwinia carotovora (now as Pectobacterium), Erwinia chrysanthemi (also reclassified)

Common Species and Associated Diseases of genus erwinia:

Fire blight

disease of Erwinia amylovora

Soft rot, blackleg

disease of Erwinia carotovora (now as Pectobacterium)

Soft rot

Erwinia chrysanthemi (also reclassified)

Apple, pear, and other rosaceae

host plants of Erwinia amylovora:

Potatoes, carrots, and many vegetables

host plants of Erwinia carotovora (now as Pectobacterium)

Ornamentals and vegetables

host plants of Erwinia chrysanthemi (also reclassified)

• Wilting

• Soft Rot

• Leaf Spots

• Cankers or Oozing Lesions

Symptoms of Erwinia Infections in Plants:

Wilting

Caused by blockage or destruction of xylem vessels

Soft Rot

Tissue degradation and foul odor due to enzyme secretion (e.g., pectinases)

Leaf Spots

Necrotic lesions or discolorations

Cankers or Oozing Lesions

Bacterial ooze from stems or fruits

• Can cause major crop losses and economic damage

• Common in temperate climates, especially in humid and warm conditions

• Control and prevention involve:

o Crop rotation

o Sanitation of tools and equipment

o Use of resistant cultivars

o Application of bactericides (e.g., copper-based sprays)

agricultural importance of genus erwinia:

Genus Enterobacter

Gram-negative, facultatively anaerobic, motile (with peritrichous flagella)

Genus Enterobacter

Widely distributed in soil, water, sewage, and intestinal tracts of animals and humans

Genus Enterobacter

Includes species that are opportunistic pathogens in humans

Enterobacter species

are part of the normal flora, especially in the gastrointestinal tract, they can

cause disease under certain conditions, particularly in immunocompromised individuals or those in

healthcare settings.

Urinary Tract Infections (UTIs), Nosocomial Infections (Healthcare-associated infections)

Common Infections Caused by Enterobacter:

Urinary Tract Infections (UTIs)

Enterobacter cloacae and Enterobacter aerogenes (now reclassified as Klebsiella aerogenes) are

frequent culprits.

Urinary Tract Infections (UTIs)

Can occur in both community-acquired and hospital-acquired settings.

Urinary Tract Infections (UTIs)

Catheter-associated UTIs (CAUTIs) are common in hospitalized patients.

Enterobacter cloacae and Enterobacter aerogenes (now Klebsiella aerogenes)

are frequent culprits of UTI

Nosocomial Infections (Healthcare-associated infections)

Wound infections

Nosocomial Infections (Healthcare-associated infections)

Bloodstream infections (sepsis)

Nosocomial Infections (Healthcare-associated infections)

Lower respiratory tract infections (e.g., ventilator-associated pneumonia)

Nosocomial Infections (Healthcare-associated infections)

Common in ICU settings and among patients with invasive devices or prolonged hospital stays.

Enterobacter species (SOME)

possess inducible AmpC beta-lactamases, which confer resistance to:

o Penicillins

o First- to third-generation cephalosporins

Penicillins, First- to third-generation cephalosporins

Some Enterobacter species possess inducible AmpC beta-lactamases, which confer resistance to:

Enterobacter species

May also acquire extended-spectrum beta-lactamases (ESBLs) or carbapenemases, making them multi-drug resistant (MDR).

Carbapenems, Fluoroquinolones, Aminoglycosides

Common treatments of Enterobacter species (if susceptible) may include:

• Strict adherence to hand hygiene, disinfection protocols, and device management in hospitals can help prevent spread.

• Surveillance and antibiotic stewardship are essential to combat resistance.

Infection Control of Enterobacter species:

Family Vibrionaceae

Gram-negative, facultatively anaerobic, curved rods (comma-shaped)

Family Vibrionaceae

Motile with polar flagella

Family Vibrionaceae

Oxidase-positive (distinguishing them from Enterobacteriaceae)

Family Vibrionaceae

Halophilic or salt-tolerant – commonly found in marine or estuarine environments

Family Vibrionaceae

Includes several genera, but most notably:

• Vibrio (e.g., V. cholerae, V. parahaemolyticus, V. vulnificus)

Vibrio cholerae, Vibrio parahaemolyticus, Vibrio vulnificus

family Vibrionaceae Includes several genera, but most notably:

Vibrio cholerae

Gram-negative, comma-shaped (curved rod), facultative anaerobe

Vibrio cholerae

Motile with a single polar flagellum