The survival of the bacteria is affect by temperature and the surface


A group in the Department of Immunology, Microbiology and Parasitology at the UPV/EHU has conducted an in-depth study into the survival of the Acinetobacter baumannii bacterium, as well as the strategies it uses to survive.

This bacterium is responsible for many outbreaks of hospital or nosocomial infections that arise in intensive care units.

It is capable of surviving long periods of time in liquid media as well as on solid surfaces, even when up against the action of disinfectants.

Acinetobacter baumannii causes all kinds of infections, ranging from pneumonia to blood infections in people admitted to hospital, especially those in intensive care units.

“We studied the capacity of this bacterium to persist in various conditions that may be similar to those found in the hospital environment, the survival strategies it uses and its capacity to resist disinfectants,” explained Maite Orruño-Beltrán, Ph.D. in Biology and one of the lead authors of this study.

The results of the study have been published in the Journal of Hospital Infection.

For their research, they used four strains of A. baumannii obtained from standard culture collection as well as from clinical isolates from the Hospital de Valdecilla.

“To conduct the survival studies, we incubated the strains for 30 days without nutrients at various temperatures (20 and 37 degrees) and in various media (in liquid and on different solid surfaces).

We also checked the effect exerted by various disinfectants routinely used in hospitals.

From time to time we gathered samples to determine how many remained cultivable and/or viable,” said Orruño.

Surviving for periods of up to 90 days

Factoring out disinfectants, the researchers found that the survival of the bacteria was affected by temperature and the surface on which they were placed.

Orruño says, “Above all, we found that those kept at 20 degrees on solid surfaces resisted 30 days in a cultivable state without any apparent changes.

We even extended some experiments to 90 days, and the population still remained cultivable.”

The bacteria that remained at 37 degrees displayed reduced survival.

“That temperature is the optimum one for growth, but not for survival when they are deprived of nutrients. In these conditions, bacteria in general withstand lower temperatures better,” explained Dr. Orruño.

As they were able to confirm in the research, at 37 degrees, the surviving bacteria adopted two survival strategies: “Some moved to a state known as viable but nonculturable.

In that state, although the bacteria are unable to grow, they remain in a dormant state from which they could recover if conditions become favourable again.

This state could be of considerable importance, because many techniques for detecting microorganisms are based on their cultivability, and therefore do not detect the presence of these bacteria, which can however retain their pathogenicity,” said the researcher.

The second strategy that some strains developed was that many of the cells lose viability.

They may be mostly dead cells, but a more or less significant fraction of the population remains cultivable by using the nutrients from the cells that have died off.

With respect to the effect of disinfectants, they found that even though the vast majority of the cells became non-cultivable, Acinetobacter baumannii was not eliminated from the surfaces studied, and a considerable fraction retained viability.

This phenomenon could entail risks since hospital workers could regard the disinfection procedure as having been sufficient, although some bacteria remain on surfaces as potential spreaders of diseases.

Microbial standards in hygiene are necessary for a healthy life. People often believe that microbes are only present in research labs or in hospitals and clinics and thus they have a misleading feeling of security in other places.

Lack of knowledge about where germs occur could be the cause of health problems. In fact, 80% of infections are spread through hand contact with hands or other objects [1].

Bacteria are found almost everywhere in air, water, soil, food, and in plants and animals organisms, including humans.

It is generally acknowledged that inanimate objects can also carry microorganisms originating from the surrounding environment. Predominantly Gram-positive cocci (Staphylococcus spp., Micrococcus spp.), but also spore-forming rods (Bacillus spp.) or Gram-negative bacteria, can be transmitted through devices like mobile phones or computer keyboards [2].

These attached microorganisms have a potential to be transferred to food or human body, where the growth of bacteria may continue.

Furthermore, formation of biofilm by one bacterial agent can affect the survival of other pathogens on the same surface [3].

Once deposited on surfaces, many infectious agents can survive for extended periods unless they are eliminated by disinfection or sterilisation procedures [4]. Depending on environmental conditions, pathogens may remain infectious on surfaces for weeks after being contaminated [5].

Mobile phone usage has a personal character, being attached to the close proximity of parts of the body such as the face, ears, nose, lips, and hands, which are the most common infection gateways. Transferred microorganisms can, especially in people with suppressed immune system, cause opportunistic infections and mild to chronic disease.

Computer keyboards are among the most commonly used user interfaces. The majority of keyboards have over 101 individual keys, which makes it difficult and time consuming to clean. This is often the reason why most owners do not clean and disinfect the keyboard.

Today, mobile phones have become one of the most indispensable accessories for professional and social life.

In addition to the standard voice function of a telephone, mobile phones can support many additional services such as SMS (Short Message Service) for text messaging, email, pocket switching for access to the Internet, and MMS (Multimedia Messaging Service) for sending and receiving photos and video [3].

Although mobile phones are usually stored in bags or pockets, they are handled frequently and held close to the face [6]. Mobile phones can spread infectious diseases by their frequent contact with hands [7] and they have also been reported to be a reservoir for microorganisms [8].

Mobile phones are also in close relationship to nosocomial infections, they may act as a mobile reservoir for microbial pathogens [9].

The use of cell phones often occurs in hospitals, by patients, visitors, and health care workers, and this is one environment where hospital-associated (nosocomial) infections are most prevalent [10]. One study came to a result that pathogenic bacteria are present on approximately 40% of mobile phones belonging to patients in a hospital and on approximately 20% of mobile phones belonging to hospital staff [3].

As well as mobile phones, computer keyboards have been also implicated as a potential reservoir for infectious agents [11].

Given that computers are not routinely disinfected, the opportunity for the transmission of contaminating microorganisms is potentially great.

he computerߣs keyboard and also mouse have a very dynamic environment. In general, the bacteria that live on our skin, fingernails, hands, and anywhere the hands have been are likely to transfer new bacteria over to the keyboard.

Especially, in a place where there is a lot of people moving in and out, such as a hospital, school or office, there is likely to be a good number of people that are sick, and through them come the new bacteria that will eventually settle on the keyboard through the air or from physical contact.

Inadequately performed hand hygiene and not disinfected surfaces are two reasons why the computer keys could be the sources of microbial contamination, consequently resulting in indirect transmission of potential pathogens [12].

Eating above computer keyboards is also one of the causes of bacterial contamination. Spills can wind up on and between the keys, and the food deposits encourage the growth of millions of bacteria. Dust can trap moisture and enable any bacteria that are already on the keyboard to flourish [13].

Studies dealing with cell phone or keyboard contamination are mainly focused on HAI (hospital-acquired infections) and transmission of nosocomial pathogens [14,15].

The present study was undertaken to evaluate the bacteriological contamination of mobile phones and computer keyboards and their susceptibility patterns to commonly used disinfectant wipes with active ingredients chlorhexidine digluconate and triclosan.

This work was not conducted in a hospital, rather the samples were taken from devices of people working in microbiology lab and teachers.

The aim of this study was to show that mobile devices present potential risk of infection not only in hospitals.

Mobile devices and electronic keyboards can carry pathogens that can be harmful to human beings.

While many believe pathogen transmission is only harmful in healthcare settings, many people lack knowledge that the transmission of these harmful bacteria can occur in everyday life activities and underrate the disinfection of these devices.

Using disinfectant wipes once daily for mobile phones and keyboards can decrease the probability of contamination and spreading of bacterial pathogens through these devices.

More information: Z. Bravo et al. Analysis of Acinetobacter baumannii survival in liquid media and on solid matrices as well as effect of disinfectants, Journal of Hospital Infection (2019). DOI: 10.1016/j.jhin.2019.04.009


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