Gram negative Bacteria

Pathogenic features of Gram negatives:

Infections: Intraabdominal, UTI, pneumonia, cellulitis, osteomyelitis, meningitis

Endotoxin- lipopolysaccharide
Enterotoxins- E Coli, Shigella, infectious diarrhea

Enteric gram-negative bacilli

Enterobacterales

• Escherichia coli

• Klebsiella pneumoniae

• Klebsiella oxytoca

• Klebsiella aerogenes (formerly Enterobacter aerogenes)

• Proteus mirabilis and vulgaris

• Serratia marcescens

• Citrobacter spp.

• Morganella morganii

• Salmonella, Shigella, Campylobacter

Enterobacterales

→Enteric gram-negative bacilli
considered part of the normal flora of the gastrointestinal (GI) tract.
→Primary cause of clinically significant gram negative infections

Currently considered a Threat by the CDC

Enterobacterales- Food borne illness

Salmonella, Campylobacter, E Coli, Vibrio

What is the Most common shiga toxin producing E. Coli

Escherichia coli O157:H7

Resistant Enterbacterales Currently considered a Threat by the CDC

Drug resistant salmonella serotype typhi
Carbapenem resistant enterobacteriaceae
Drug resistant resistant campylobacter
Extended Spectrum Beta lactamase (ESBL) producing enterobacteriaceae
Drug resistant shigella 
Drug resistant non typhoidal salmonella

Antibiotic resistance in Gram negatives

• Mutation in lipopolysaccharide (e.g., polymyxin resistance)

• Hydrolysis by β-lactamase (plasmid-acquired or overexpressed chromosomal genes)

• Overexpression of efflux pumps (multidrug resistance)

• Modified drug target (e.g., quinolones)

• Antibiotic modification (e.g., aminoglycosides)

• Porin loss or mutation (reduces antibiotic entry

Non enterobacterales

Non-fermentative, Gram negative bacilli

Organisms

• Pseudomonas aeruginosa

• Acinetobacter baumannii

• Stenotrophomonas maltophilia

• Burkholderia cepacia

1. Not normal flora

2. Nosocomial infections

3. Multi-drug resistant organisms

Pseudomonas aeruginosa Pathogenesis

Acute→Invasive, hospital associated
Chronic→Decreased cytotoxicity, resistance, biofilm and adhesion

Pseudomonas aeruginosa infections

CNS infections, Ear and eye infections, bacteremia, skin burn wounds, localized infections, UTIs, Resp tract infections, musculoskeletal tissue, surgical wounds

Pseudomonas aeruginosa resistance

1)Intrinsic

2)Acquired

3)Adaptive

Acinetobacter baumannii

Very similar to Pseudomonas

Mostly found in hospitals- can last days to week on equipment, infection control is key

Infects immunocompromised host

High crude mortality

Infections: pneumonia, open wounds, lines

SUPER RESISTNAT! URGENT THREAT

Acinetobacter baumannii approved agent

Sulbactam-durlobactam (Xacduro)

When should you cover for pseudomonas

Suspected hospital infection until pathogen identified

Important clincial pear for non enterobacterales

INFECTION CONTROL AND PREVENTION

Gram negative Cocci

Haemophilus Influenzae

Nisseria meningitidis

Neisseria gonorrhoeae

Moraxella

Haemophilus Influenzae

Encapsulates facultative anaerobe 7 serotypes- type b more clinically important Infections → Mostly children: CAP, meningitis, sinusitis, otitis media , conjunctivitis

Nisseria meningitidis

Requires culture from sterile body fluids like blood, Cerebrospinal Fluid, synovial, pleural, or pericardial fluid for diagnosis Cause of meningitis  Outbreaks in semi closed populations ie childcare centers, colleges, military camps Treatment: B lactams Treatment required noth higher bacteridicdal antibiotics & high CSF penetration- CEFTRIAXONE

Neisseria gonorrhoeae

Transmission through sex or birth  Complications: Pelvic inflammatory disease, epididymitis, disseminated gonococcal disease  Very limited options to treat- Zoliflodacin & Gepotidacin (not yet approved)

Chlamydia trachomatis

Number 1 bacteria STD in the USA 75% women no sx, 50% men no sx

Gram negative anaerobes

Metronidazole susceptible  Bacteroides fragilis- Most common and pathogenic, Lower GI, abdominal ascesses