PFGE Typing Protocol Recommended by ARPAC for Acinetobacter baumannii

A genus of strictly aerobic, oxidase −ve, catalase+ve,Gram-type-negative bacteria of the family MORAXELLACEAE (within the
gamma subdivision of PROTEOBACTERIA); the organisms occur e.g. in soil and water and may act as opportunist pathogens in man.

Cells: short rods, 0.9–1.6 × 1.5–2.5 micron,or coccobacilli (coccoid in stationary-phase cultures);cells often in pairs. Nonmotile, but may exhibit TWITCHING MOTILITY. Non-pigmented.
Metabolism is respiratory (oxidative), with oxygen as terminal electron acceptor; no growth occurs anaerobically, with or without nitrate.
Most strains can grow on a mineral salts medium containing an organic carbon source such as acetate,ethanol or lactate as the sole source of carbon andenergy; some can use amino acids (e.g. L-leucine,ornithine) and/or pentoses (e.g. Larabinose,D-xylose), and some are able to degrade e.g. benzoate,n-hexadecane and alicyclic compounds.

Acinetobacters appear to contain all the enzymes of the TCA CYCLE and the glyoxylate cycle. Many carbohydrates can be used. Most strains in the A. calcoaceticus–A. baumannii complex (and in certain other groups) can form acid from glucose (oxidatively), but many (e.g. most strains designated A. lwoffii ) cannot. The optimal growth temperature is typically 33–35°C.

GC%: ∼38–47. Type species: A. calcoaceticus.

The taxonomy of Acinetobacter is confused and unsatisfactory.Emended descriptions of the two species A. calcoaceticus and A. lwoffii, and proposals for four new species (A. baumannii, A. haemolyticus, A. johnsonii and A. junii ), were published in 1986 [IJSB (1986) 36 228–240]. Since then, a number of adjustments have been made to the taxonomic structure of the genus.

Acinetobacters have been isolated in a number of hospitalassociated (and other) outbreaks of disease, often as part of a mixed infection; in most cases such infections involve glucolytic strains of the A. calcoaceticus–A. baumannii complex– particularly A. baumannii
(also called group 2, or genospecies 2).

The most common manifestations of disease include septicaemia and infections of the urinary tract, lower respiratory tract and central nervous system. Transmission may occur by direct contact or may involve the airborne route.

Acinetobacters have been reported to survive on dry surfaces for at least as long as e.g. Staphylococcus aureus.

One problem associated with the pathogenic role of Acinetobacter is that these organisms appear easily to acquire resistance to antibiotics – so that they have the potential to develop as multiresistant pathogens.

Protocol ARPAC

PFGE method

Organism--------Acinetobacter baumannii

Recommended lysis enzyme:proteinase K

Restriction enzyme---------SmaI, ApaI

Approximate no. of---------20–40 , 20–30
restriction Fragments

Fragments size------------5–300,10–300
range (kb)


A.baumannii ACICU:

Acinetobacter baumannii (MDR),second part

Multidrug-resistant (MDR) Acinetobacter baumannii has been reported worldwide and is now recognized to be among the most difficult antimicrobial-resistant Gram-negative bacilli (GNB) to control and treat.

The organism is a rapidly emerging pathogen in the healthcare setting, where it causes healthcare-associated infections including bacteremia, pneumonia, meningitis, urinary tract infections,
and wound infections.

Properties of A. baumannii, such as its ability to survive under a wide range of environmental conditions and to persist for extended periods of time on environmental surfaces, make it a frequent cause of outbreaks as well as an endemic pathogen in the healthcare setting.
Risk factors for colonization or infection with A. baumannii include prolonged length of hospital stay,exposure to intensive care units (ICUs) and mechanical ventilation, antimicrobial use, recent surgery, invasive procedures, and underlying severity of illness.

Whereas prior to the 1990s Acinetobacter baumannii were almost universally susceptible to broad spectrum antibiotics, during
this decade they became increasingly resistant to penicillins, cephalosporins, fluoroquinolones and aminoglycosides (Bergogne-Berezin and Towner, 1996). Thus in recent years, many of these antimicrobials are no longer reliable for treatment of infections caused by this organism. Most notable is the increase in resistance to the carbapenems which are caused by a variety of Beta- lactamases and changes in penicillin-binding proteins (PBPs) (Nordmann and Poirel, 2002). There are now reports of multidrug resistant A. baumannii strains that are susceptible only to polymixin B and colistin (Levin et al., 1998).

U.S. Military Experience

An increased number of A. baumannii infections have been noted in U.S. military personnel wounded during the conflicts in Iraq and Afghanistan. These infections are generally extremely resistant to a variety of antimicrobial agents, are commonly associated with traumatic injuries, and include deep wound infections, osteomyelitis, respiratory infections, and bacteremia.

There are three main hypotheses for how wounded soldiers acquire Acinetobacter

-The first is that soldiers are previously colonized with the organism, perhaps on their skin or in their nares, and are auto-inoculated during a penetrating traumatic injury. However, cultures taken prior to deployment from healthy soldiers' skin and nares found no Acinetobacter in the nares, and though skin colonization was common,strain types did not match the strains that infect returning wounded soldiers. Therefore, it is less likely that prior colonization explains Acinetobacter infected war wounds.

-The second hypothesis is that Acinetobacter from the local environment (soil or water) is introduced during traumatic injury. Two studies showed that cultures of war wounds taken in Iraq soon after injuries grew primarily low virulence Gram-positive organisms. The few Gram-negative organisms recovered were susceptible to many antimicrobial agents, which does not support the hypothesis of environmental contamination at the time of injury.

-The third hypothesis is that Acinetobacter is healthcare-associated, acquired by soldiers in medical facilities during the process of stabilization, emergency treatment,and evacuation through the military medical system.

Acinetobacter baumannii Infections Among Patients at Military Medical Facilities Treating Injured U.S. Service Members, 2002--2004

Definitions of MDR Acinetobacter

Vary in the medical literature,referring to a wide array of genotypes and phenotypes that can be confusing to both researchers and clinicians.

Two of the most common criteria for MDR are:

-carbapenem resistance

-resistance to three or more antimicrobial classes

Carbapenem-resistant Acinetobacter has been reported by tertiary-care hospitals, usually in the setting of nosocomial outbreaks. Some strains of MDR Acinetobacter are susceptible only to
colistin or polymyxin B, peptide antibiotics not routinely used due to earlier reports of toxicities (sometimes these isolates are referred to as polymyxin-only-susceptible or POS Acinetobacter).

Strains that demonstrate resistance to all antimicrobial agents including polymyxin (sometimes referred to as pan-drug-resistant, or PDR, Acinetobacter) have also been reported making treatment of these infections extremely difficult and in some cases impossible to treat.

Mechanisms of resistance

The mechanisms of resistance generally fall into three categories:

(i) antimicrobial inactivating enzymes

(ii) reduced access to bacterial targets

(iii) mutations that change targets or cellular functions

Given the lack of good therapeutic options, the development or discovery of new therapies and greater emphasis on the prevention of healthcareassociated transmission of MDR Acinetobacter are essential.

Acinetobacter baumannii (MDR), first part

Colonies are 1 to 2 mm, nonpigmented, domed, and mucoid, with smooth to pitted surfaces.





Acinetobacter baumannii: An Emerging Multidrug-resistant Threat


Wikipedia:Acinetobacter baumannii







Acinetobacter spp.


Acinetobacter

Example of trend in Phage Therapy research

OBJECTIVE: Develop an antibiotic solution or substance consisting of least three different lytic bacteriophages that kill Acinetobacter baumannii for eventual use in human wound infections.

Development of Bacteriophage Therapy for Treatment of A. baumannii Infected Wounds