user567: By first precept I shouldn't kill even a mosquito it bite me but when as by 7th precept I can listen music for therapy If things fall into such circumstances like this mosquito biting can lead me to malaria or dengue. Also I've to ask if I can consume yogurt when it's made with help of bacterias they are also living being. I don't mean I'm trying to find breaking precepts,but I stopped killing them really.       

user471: From Bhikkhu Bodhi's discussion on the first precept, we find some comments on the varying gravity of the kamma of killing:

The first distinction given is that between killing beings with moral
  qualities (guna) and killing beings without moral qualities. For all
  practical purposes the former are human beings, the latter animals,
  and it is held that to kill a fellow human being is a more serious
  matter ethically than to kill an animal. Then within each category
  further distinctions are drawn. In the case of animals the degree of
  moral gravity is said to be proportional to the animal, to kill a
  larger animal being more blameworthy than to kill a smaller one. Other
  factors relevant to determining moral weight are whether the animal
  has an owner or is ownerless, whether it is domestic or wild, and
  whether it has a gentle or a vicious temperament. The moral gravity
  would be greater in the former three alternatives, less in the latter
  three. In the killing of human beings the degree of moral blame
  depends on the personal qualities of the victim, to kill a person of
  superior spiritual stature or one's personal benefactors being more
  blameworthy than to kill a less developed person or one unrelated to
  oneself. The three cases of killing selected as the most culpable are
  matricide, parricide, and the murder of an arahant, a fully purified
  saint.

The five precepts are training rules and not strong prohibitions.
Furthermore, even for monks, based on the Patimokkha rules, intentionally bringing about the death of a human being is a parajika offense, while taking the life of an animal is a pacittiya offense. A parajika offense is the gravest offense causing immediate expulsion, but a pacittiya offense is milder, requiring only a confession.

Parajika Rule 3. Should any bhikkhu intentionally deprive a human
  being of life, or search for an assassin for him, or praise the
  advantages of death, or incite him to die (saying,): "My good man,
  what use is this evil, miserable life to you? Death would be better
  for you than life," or with such an idea in mind, such a purpose in
  mind, should in various ways praise the advantages of death or incite
  him to die, he also is defeated and no longer in affiliation.
Pacittiya Rule 61. Should any bhikkhu intentionally deprive an animal
  of life, it is to be confessed.

And also on the motivation for killing (from here):

Another factor determinative of moral weight is the motivation of the
  act. This leads to a distinction between premeditated murder and
  impulsive killing. The former is murder in cold blood, intended and
  planned in advance, driven either by strong greed or strong hatred.
  The latter is killing which is not planned in advance, as when one
  person kills another in a fit of rage or in self-defense. Generally,
  premeditated murder is regarded as a graver transgression than
  impulsive killing, and the motivation of hatred as more blameworthy
  than the motivation of greed. The presence of cruelty and the
  obtaining of sadistic pleasure from the act further increase its moral
  weight.

In my opinion, if rulers, government officials, neighbourhood resident associations and even individuals decide to kill mosquitoes and mosquito larvae due to a proven rising dengue or malaria epidemic, it would be a reasonably justifiable motivation for killing. After all, isn't it wrong to endanger fellow humans knowingly?
From the Lonaphala Sutta:

"Now, a trifling evil deed done by what sort of individual takes him
  to hell? There is the case where a certain individual is undeveloped
  in [contemplating] the body, undeveloped in virtue, undeveloped in
  mind, undeveloped in discernment: restricted, small-hearted, dwelling
  with suffering. A trifling evil deed done by this sort of individual
  takes him to hell.
"Now, a trifling evil deed done by what sort of individual is
  experienced in the here & now, and for the most part barely appears
  for a moment? There is the case where a certain individual is
  developed in [contemplating] the body, developed in virtue, developed
  in mind, developed in discernment: unrestricted, large-hearted,
  dwelling with the immeasurable. A trifling evil deed done by this
  sort of individual is experienced in the here & now, and for the most
  part barely appears for a moment.

I take the killing of mosquitoes and mosquito larvae with the motivation of dengue or malaria eradication, to be a trifling evil deed, and if we do it with the correct motivation and the correct state of mind, then it is acceptable although not ideal. The same applies to rats and diseases spread by rats like leptospirosis and hantavirus.
Hitting a mosquito that bit you is also considered impulsive killing, rather than premeditated killing, and according to Bhikkhu Bodhi's description above, impulsive killing is less grave than premeditated killing.
Despite this, it is clear that not killing any sentient being for any reason, would be the higher dhammic decision.

user10967: Killing a mosquito should not be the first and initiative step. If you are honest and really struggle to maintain first precept better to make preventive measures. Just adhere to precepts will not create effective results. you have to adhere to precepts with wisdom in your capacity. 
As preventive measures
1.you can use mosquito repellent.
2.Use mosquito nets
3.Close windows and doors early in evening before enter mosquitoes to your house
4.close small spaces and ventilation holes with fine nets in your houses
5.remove mosquito breeding places.(keep clean your surrounding) 
above will protect your family effectively diseases spread by mosquitoes.Simply kill mosquitoes one by one is not effective and useless way.Above protective measures are more effective than killing them.In other hand you can protect first precept. "The protector of Dhamma will protect by Dhamma. May all being in peace and harmony. Thanks.

user11428: No, you should not even kill mosquitoes that bite you, according to the First Noble Precept.

user-1: Questions about killing insects have appeared a few times here, I suggest reading them:

Is killing vermin and insects justifiable?
What does Buddhism say about intentionally killing dangerous insects and beings?

While some may dispute whether or not the precept apply to insects or whether they are sentient beings, in general, deliberately killing a mosquito is considered akusala (unwholesome) action, rooted in dosa (aversion, ill will, hatred) / moha (ignorance).
As for traditions, I've heard Zen, Theravada and Tibetan monks teaching to regard insects to be living beings and they may consider intentionally killing them to be breaking the precept. 
In one answer from the questions linked above, Bhikkhu yuttadhammo writes:

Even if killing a single mosquito would end all cases of malaria in the world for ever, the (Theravada) Buddhist philosophy would be to abstain from killing the mosquito.

For more information from the Theravada point of view, check this text by Bhikkhu Bodhi on the precepts, The first precept: abstinence from taking life.
Now, on your question, killing a mosquito because it may threaten you may be justified if you regard it as a living being. Is killing it the only way to preserve oneself? Sometimes one can simply stay away, isolate oneself from it, os just go somewhere else. That's, I think, the general teaching to avoid breaking the precept to save oneself from harm: try to get away from danger without causing you and others harm, with a mind inclined to non-harm.
As for bacterias, I'm not so sure one is killing them by eating yogurt. Eating yogurt with the intention to kill them, however, would likely be worrisome. 
But in general, I think buddhism is silent regarding micro-organisms and most traditions seem to consider an act of killing by the intention to kill (thus, deaths caused accidentally are not considered such acts).

user7548: I think the formula is actually I will restrain from the killing of sentient beeings. Keep in mind that the 5 precepts are not obligations, but rather rules you take up voluntarily. Nobody forces you to keep them, but they are an absolute minimum of Buddhist morality. The mind that has the intention of killing, stealing... is not able to have a clear perception of reality, at all. 

user8157: The 1st precept is a training rule to refrain from killing 'breathing' things.
The Pali is: "Panatipata veramani sikkhapadam samadiyami", where the word "pana" means "life" or 'breath", such as in the term "ana-pana-sati".
The 1st precept does not apply to bacteria because they do not breathe.

Strictly speaking, bacteria do not “breathe” as humans and other animals do, but they must still engage in the act of cellular
respiration. Cellular respiration is the method by which cells convert
chemicals into energy that the cell needs to stay alive.
Bacteria

As for mosquitoes, the probability of contracting malaria or dengue fever is very low. I lived in Thailand for 9 years and had dengue fever only once. I can contract dengue fever where I have lived for the last 10 years & have never got it (although one friend did). When I lived in Thailand, there was a period of a few years when hundreds of mosquitoes would bite my feet when I was meditating at sunset. I never got dengue fever or malaria during this period. I felt very free when my mind became accustomed to not worrying about & fearing mosquitoes.
Not killing mosquitoes is beneficial for cultivating metta (loving-kindness), fearlessness & freedom. However, that said, killing mosquitoes is not particularly bad karma. When I first visited Thailand & learned meditation, I did not care about killing mosquitoes & killing a mosquito never affected my samatha (calmness; concentration) meditation. This is because killing a mosquito is kammically a natural act. The mosquito wants to steal our blood & can (possibly) kill us. This is why the kammic results (vipaka) of killing a mosquito are trifling (insignificant).
Most people have killed many mosquitoes & remain mentally normal. Their minds do not become deranged (crazy). Where as the majority of soldiers that kill in war are often mentally affected for life in a negative way. Some ex-soldiers become mentally deranged & even commit suicide. (Here, an ex-soldier must learn to forgive themselves!) This shows the difference between killing many mosquitoes & killing just one or even many human being/s. Kammic consequences (vipaka) follow the law of nature.
The Buddha taught "kamma is intention" (AN 6.63). A mosquito killed with the intention of avoiding malaria or dengue fever is not an unwholesome intention. However, it is still an intention rooted in fear, attachment & a lack of liberation.
For example, to kill a mosquito so it does not bite a small baby or child is probably good karma. If it was known you let mosquitoes bite your small baby, many people would criticize you. You would be blamed & censured for being a bad parent. The government may take your child away from you.
Personally, I would not worry too much about it since not killing mosquitoes is a higher level of dhamma practise. The Buddha did not make strict rules for monks about killing mosquitoes or even about killing animals (for food) for laypeople.

And which is intolerant practice? There is the case where a certain individual doesn't tolerate cold, heat, hunger, & thirst; the touch of
flies, mosquitoes, wind, sun & reptiles; ill-spoken, unwelcome words;
& bodily feelings that, when they arise, are painful, racking, sharp,
piercing, disagreeable, displeasing & menacing to life. This is called
intolerant practice.
And which is tolerant practice? There is the case where a certain individual tolerates cold, heat, hunger, & thirst; the touch of flies,
mosquitoes, wind, sun & reptiles; ill-spoken, unwelcome words; &
bodily feelings that, when they arise, are painful, racking, sharp,
piercing, disagreeable, displeasing & menacing to life. This is called
tolerant practice.
Khama Sutta


567: <p>By first precept I shouldn't kill even a mosquito it bite me but when as by 7th precept I can listen music for therapy If things fall into such circumstances like this mosquito biting can lead me to malaria or dengue. Also I've to ask if I can consume yogurt when it's made with help of bacterias they are also living being. I don't mean I'm trying to find breaking precepts,but I stopped killing them really.       </p>
 471: <p>From <a href="https://www.accesstoinsight.org/lib/authors/bodhi/wheel282.html#prec2" rel="nofollow noreferrer">Bhikkhu Bodhi's discussion</a> on the first precept, we find some comments on the varying gravity of the kamma of killing:</p>

<blockquote>
  <p>The first distinction given is that between killing beings with moral
  qualities (guna) and killing beings without moral qualities. For all
  practical purposes the former are human beings, the latter animals,
  and it is held that to kill a fellow human being is a more serious
  matter ethically than to kill an animal. Then within each category
  further distinctions are drawn. In the case of animals the degree of
  moral gravity is said to be proportional to the animal, to kill a
  larger animal being more blameworthy than to kill a smaller one. Other
  factors relevant to determining moral weight are whether the animal
  has an owner or is ownerless, whether it is domestic or wild, and
  whether it has a gentle or a vicious temperament. The moral gravity
  would be greater in the former three alternatives, less in the latter
  three. In the killing of human beings the degree of moral blame
  depends on the personal qualities of the victim, to kill a person of
  superior spiritual stature or one's personal benefactors being more
  blameworthy than to kill a less developed person or one unrelated to
  oneself. The three cases of killing selected as the most culpable are
  matricide, parricide, and the murder of an arahant, a fully purified
  saint.</p>
</blockquote>

<p>The five precepts are training rules and not strong prohibitions.</p>

<p>Furthermore, even for monks, based on <a href="https://www.accesstoinsight.org/tipitaka/vin/sv/bhikkhu-pati.html" rel="nofollow noreferrer">the Patimokkha rules</a>, intentionally bringing about the death of a human being is a parajika offense, while taking the life of an animal is a pacittiya offense. A parajika offense is the gravest offense causing immediate expulsion, but a pacittiya offense is milder, requiring only a confession.</p>

<blockquote>
  <p><strong>Parajika Rule 3</strong>. Should any bhikkhu intentionally deprive a human
  being of life, or search for an assassin for him, or praise the
  advantages of death, or incite him to die (saying,): "My good man,
  what use is this evil, miserable life to you? Death would be better
  for you than life," or with such an idea in mind, such a purpose in
  mind, should in various ways praise the advantages of death or incite
  him to die, he also is defeated and no longer in affiliation.</p>
  
  <p><strong>Pacittiya Rule 61</strong>. Should any bhikkhu intentionally deprive an animal
  of life, it is to be confessed.</p>
</blockquote>

<p>And also on the motivation for killing (from <a href="https://www.accesstoinsight.org/lib/authors/bodhi/wheel282.html#prec2" rel="nofollow noreferrer">here</a>):</p>

<blockquote>
  <p>Another factor determinative of moral weight is the motivation of the
  act. This leads to a distinction between premeditated murder and
  impulsive killing. The former is murder in cold blood, intended and
  planned in advance, driven either by strong greed or strong hatred.
  The latter is killing which is not planned in advance, as when one
  person kills another in a fit of rage or in self-defense. Generally,
  premeditated murder is regarded as a graver transgression than
  impulsive killing, and the motivation of hatred as more blameworthy
  than the motivation of greed. The presence of cruelty and the
  obtaining of sadistic pleasure from the act further increase its moral
  weight.</p>
</blockquote>

<p>In my opinion, if rulers, government officials, neighbourhood resident associations and even individuals decide to kill mosquitoes and mosquito larvae due to a proven rising dengue or malaria epidemic, it would be a reasonably justifiable motivation for killing. After all, isn't it wrong to endanger fellow humans knowingly?</p>

<p>From the <a href="https://www.accesstoinsight.org/tipitaka/an/an03/an03.099.than.html" rel="nofollow noreferrer">Lonaphala Sutta</a>:</p>

<blockquote>
  <p>"Now, a trifling evil deed done by what sort of individual takes him
  to hell? There is the case where a certain individual is undeveloped
  in [contemplating] the body, undeveloped in virtue, undeveloped in
  mind, undeveloped in discernment: restricted, small-hearted, dwelling
  with suffering. A trifling evil deed done by this sort of individual
  takes him to hell.</p>
  
  <p>"Now, a trifling evil deed done by what sort of individual is
  experienced in the here &amp; now, and for the most part barely appears
  for a moment? There is the case where a certain individual is
  developed in [contemplating] the body, developed in virtue, developed
  in mind, developed in discernment: unrestricted, large-hearted,
  dwelling with the immeasurable. A trifling evil deed done by this
  sort of individual is experienced in the here &amp; now, and for the most
  part barely appears for a moment.</p>
</blockquote>

<p>I take the killing of mosquitoes and mosquito larvae with the motivation of dengue or malaria eradication, to be a trifling evil deed, and if we do it with the correct motivation and the correct state of mind, then it is acceptable although not ideal. The same applies to rats and diseases spread by rats like leptospirosis and hantavirus.</p>

<p>Hitting a mosquito that bit you is also considered impulsive killing, rather than premeditated killing, and according to Bhikkhu Bodhi's description above, impulsive killing is less grave than premeditated killing.</p>

<p>Despite this, it is clear that not killing any sentient being for any reason, would be the higher dhammic decision.</p>
 10967: <p>Killing a mosquito should not be the first and initiative step. If you are honest and really struggle to maintain first precept better to make preventive measures. Just adhere to precepts will not create effective results. you have to adhere to precepts with wisdom in your capacity. 
As preventive measures
1.you can use mosquito repellent.
2.Use mosquito nets
3.Close windows and doors early in evening before enter mosquitoes to your house
4.close small spaces and ventilation holes with fine nets in your houses
5.remove mosquito breeding places.(keep clean your surrounding) 
above will protect your family effectively diseases spread by mosquitoes.Simply kill mosquitoes one by one is not effective and useless way.Above protective measures are more effective than killing them.In other hand you can protect first precept. "The protector of Dhamma will protect by Dhamma. May all being in peace and harmony. Thanks.</p>
 11428: <p>No, you should not even kill mosquitoes that bite you, according to the First Noble Precept.</p>
 -1: <p>Questions about killing insects have appeared a few times here, I suggest reading them:</p>

<ul>
<li><p><a href="https://buddhism.stackexchange.com/questions/87/is-killing-vermin-and-insects-justifiable">Is killing vermin and insects justifiable?</a></p></li>
<li><p><a href="https://buddhism.stackexchange.com/questions/7562/what-does-buddhism-say-about-intentionally-killing-dangerous-insects-and-beings">What does Buddhism say about intentionally killing dangerous insects and beings?</a></p></li>
</ul>

<p>While some may dispute whether or not the precept apply to insects or whether they are sentient beings, in general, deliberately killing a mosquito is considered <em>akusala</em> (unwholesome) action, rooted in <em>dosa</em> (aversion, ill will, hatred) / <em>moha</em> (ignorance).</p>

<p>As for traditions, I've heard Zen, Theravada and Tibetan monks teaching to regard insects to be living beings and they may consider intentionally killing them to be breaking the precept. </p>

<p>In one answer from the questions linked above, Bhikkhu yuttadhammo writes:</p>

<blockquote>
  <p>Even if killing a single mosquito would end all cases of malaria in the world for ever, the (Theravada) Buddhist philosophy would be to abstain from killing the mosquito.</p>
</blockquote>

<p>For more information from the Theravada point of view, check this text by Bhikkhu Bodhi on the precepts, <a href="http://www.accesstoinsight.org/lib/authors/bodhi/wheel282.html#prec2" rel="nofollow noreferrer">The first precept: abstinence from taking life</a>.</p>

<p>Now, on your question, killing a mosquito because it may threaten you may be justified if you regard it as a living being. Is killing it the only way to preserve oneself? Sometimes one can simply stay away, isolate oneself from it, os just go somewhere else. That's, I think, the general teaching to avoid breaking the precept to save oneself from harm: try to get away from danger without causing you and others harm, with a mind inclined to non-harm.</p>

<p>As for bacterias, I'm not so sure one is killing them by eating yogurt. Eating yogurt with the intention to kill them, however, would likely be worrisome. </p>

<p>But in general, I think buddhism is silent regarding micro-organisms and most traditions seem to consider an act of killing by the intention to kill (thus, deaths caused accidentally are not considered such acts).</p>
 7548: <p>I think the formula is actually <em>I will restrain from the killing of sentient beeings</em>. Keep in mind that the 5 precepts are not obligations, but rather rules you take up voluntarily. Nobody forces you to keep them, but they are an absolute minimum of Buddhist morality. The mind that has the intention of killing, stealing... is not able to have a clear perception of reality, at all. </p>
 8157: <p>The 1st precept is a training rule to refrain from killing 'breathing' things.</p>
<p>The Pali is: &quot;<em>Panatipata veramani sikkhapadam samadiyami</em>&quot;, where the word &quot;pana&quot; means &quot;life&quot; or 'breath&quot;, such as in the term &quot;ana-pana-sati&quot;.</p>
<p>The 1st precept does not apply to bacteria because they do not breathe.</p>
<blockquote>
<p><em>Strictly speaking, bacteria do not “breathe” as humans and other animals do, but they must still engage in the act of cellular
respiration. Cellular respiration is the method by which cells convert
chemicals into energy that the cell needs to stay alive.</em></p>
<p><a href="https://www.reference.com/science/bacteria-breathe-27fb019917dae7bc" rel="noreferrer"><em>Bacteria</em></a></p>
</blockquote>
<p>As for mosquitoes, the probability of contracting malaria or dengue fever is very low. I lived in Thailand for 9 years and had dengue fever only once. I can contract dengue fever where I have lived for the last 10 years &amp; have never got it (although one friend did). When I lived in Thailand, there was a period of a few years when hundreds of mosquitoes would bite my feet when I was meditating at sunset. I never got dengue fever or malaria during this period. I felt very free when my mind became accustomed to not worrying about &amp; fearing mosquitoes.</p>
<p>Not killing mosquitoes is beneficial for cultivating metta (loving-kindness), fearlessness &amp; freedom. However, that said, killing mosquitoes is not particularly bad karma. When I first visited Thailand &amp; learned meditation, I did not care about killing mosquitoes &amp; killing a mosquito never affected my <em>samatha</em> (calmness; concentration) meditation. This is because killing a mosquito is kammically a natural act. The mosquito wants to steal our blood &amp; can (possibly) kill us. This is why the kammic results (<em>vipaka</em>) of killing a mosquito are trifling (insignificant).</p>
<p>Most people have killed many mosquitoes &amp; remain mentally normal. Their minds do not become deranged (crazy). Where as the majority of soldiers that kill in war are often mentally affected for life in a negative way. Some ex-soldiers become mentally deranged &amp; even commit suicide. (Here, an ex-soldier must learn to forgive themselves!) This shows the difference between killing many mosquitoes &amp; killing just one or even many human being/s. Kammic consequences (<em>vipaka</em>) follow the law of nature.</p>
<p>The Buddha taught &quot;kamma is intention&quot; (AN 6.63). A mosquito killed with the intention of avoiding malaria or dengue fever is not an unwholesome intention. However, it is still an intention rooted in fear, attachment &amp; a lack of liberation.</p>
<p>For example, to kill a mosquito so it does not bite a small baby or child is probably good karma. If it was known you let mosquitoes bite your small baby, many people would criticize you. You would be blamed &amp; censured for being a bad parent. The government may take your child away from you.</p>
<p>Personally, I would not worry too much about it since not killing mosquitoes is a higher level of dhamma practise. The Buddha did not make strict rules for monks about killing mosquitoes or even about killing animals (for food) for laypeople.</p>
<blockquote>
<p><em>And which is intolerant practice? There is the case where a certain individual doesn't tolerate cold, heat, hunger, &amp; thirst; the touch of
flies, mosquitoes, wind, sun &amp; reptiles; ill-spoken, unwelcome words;
&amp; bodily feelings that, when they arise, are painful, racking, sharp,
piercing, disagreeable, displeasing &amp; menacing to life. This is called
intolerant practice.</em></p>
<p><em>And which is tolerant practice? There is the case where a certain individual tolerates cold, heat, hunger, &amp; thirst; the touch of flies,
mosquitoes, wind, sun &amp; reptiles; ill-spoken, unwelcome words; &amp;
bodily feelings that, when they arise, are painful, racking, sharp,
piercing, disagreeable, displeasing &amp; menacing to life. This is called
tolerant practice.</em></p>
<p><a href="http://www.accesstoinsight.org/tipitaka/an/an04/an04.165.than.html" rel="noreferrer"><em>Khama Sutta</em></a></p>
</blockquote>
